I Ste Agricultural College | j Class J\^o. . .'O > s^o^l^i^S^a^HL ^tot*3' ^ultv\o^ iS«3U Digitized by the Internet Archive in 2009 with funding from . Boston Library Consortium IVIember Libraries http://www.archive.org/details/geologyofyellowsOOhagu r J DEPARTMENT OF THE INTERIOR MONOGRAPHS OF THE United States Geological Survey VOLUME XXXII F^RT II WASHINGTON GOVERNMENT PRINTING OFFICE 1899 UNITED STATES GEOLOGICAL SURVEY CHARLKS II. WALCOTT, DIRKCTOK GEOLOGY YELLOWSTONE NATIONAL PARK P^RT II DESCRIPTIVE GEOLOGY, PETROGRAPHY, AND PALEONTOLOGY ARNOLD HAGUE, J. P. IDDINGS, W. H. WEED C. D. WALCOTT, G. H. 6IRTY, T. W. STANTON, AND F. H. KNOWLTON V. WASHINGTON GOVERNMENT PRINTING OFFICE 1899 ^510 CONTENTS, Page. Letter of transmittal xiii OUTLINK XV Chapter I. — Descriptive geology of the Gallatin Mountains, by J. P. IcUlings and W. H. Weed 1 Introduction 1 The Crags and vicinity 3 The Crags 3 Crowfoot section 6 Mountains south of Panther Creek 9 South End Hills 10 Trilobite Point 11 The Dome 12 Indian Creek laccolith 13 Mount Holmes by sraallth 16 Antler Peak 20 Three River Peak 23 Bighorn Pass 24 Crowfoot Ridge and Gallatin Valley 27 Quadrant Mountain, Bannock Peak, and the valley of the Gallatin Eiver 31 Banuock Peak 31 Quadrant Mountain 33 Little Quadrant Mountain and Fawn Creek Valley 36 Little Quadrant Mountain 36 Fawn Creek Valley 39 Region north of Gallatin River 41 The Fan 45 Electric Peak 50 Western flanks of the Gallatin Range 56 Eastern flank of the Madison Range 57 Chapter II. — The intrlsive rocks of the Gallatin Mountains, Bunsen Peak, and Mount Everts, by J. P. Iddings 60 Indian Creek laccolith 60 Hornblende-mica-andesite-porphy ry 60 Mount Holmes bysmalith 64 Dacite-porphyry , 64 Bighorn Pass sheet 69 Kersantite 69 Gray Mountain mass and connected sheets 73 Hornblende-mica-andesito porphyry and andesite 73 Hornbleude-andesite-porphy ry and andesite 77 Hornblende-pyroxene-andesite-porphyries and andesites 80 Chemical composition 81 V VI CONTENTS. Chapter II — Continued. Page. Ditterentiated sheet southeast of Electric Peak 82 Gallatin River laccolith 84 Dacite-porphy ry 84 Intrusive sheets in Mount Everts 85 The Bunsen Peak mass 86 Daeite-porphy ry 86 Chapter III. — The igneous rocks of Electric Peak and Sepulchre Mountain, hy J. P. Iddings 89 Geological sketch of the region 89 The intrusive rocks in Electric Peak 92 The dike rock.s and certain contact forms of the stock 94 The stock rocks and apophyses 97 Varieties in which the dark-colored and light-colored minerals are nearly equal 99 Varieties in which the light-colored minerals are in excess, hut in which quartz is not excessive 102 Varieties with an excess of light-colored minerals, in which quartz is abundant 103 Quartz-mica-diorite-porphyry 103 General consideration of the mineral and chemical composition of the intrusive rocks in Electric Peak 105 Mineral composition 105 Chemical composition 115 The volcanic rocks of Sepulchre Mountain 121 The lower breccia 121 The upper breccia 122 The dike rooks 128 General consideration of the mineral and chemical composition of the eruptive rocks of Sepulchre Mountain 134 Miueral composition 134 Chemical composition 135 The extrusive igneous rocks west and southwest of the Gallatin Mountains 137 Comparison of the rocks from Electric Peak and Sepulchre Mountain 138 Correlation of the rocks on a chemical basis 142 Chapter IV. — Descriptive geology op the northern end of the Teton Range, by J. P. Iddings and W. H. Weed 149 Introduction 149 Topographic features 151 Crystalline axis aud region east 152 Region west of the crystalline axis 157 Chapter V. — Descriptive geology of Huckleberry Mountain and Big Game Ridge, by Arnold Hague 165 General features 165 Region of Wildcat Peak and Huckleberry Mountain 168 Region of Snake River gorge 173 Region between Red and Basin creeks 175 Snake River Hot Springs 177 Region of Coulter Creek and Bobcat Ridge 179 Region of Wolverine Creek 181 Region of Pinyon Peak 184 Big Game Ridge '. 188 Chicken Ridge 191 CONTENTS. VII ClUPTF.n V — Continued. Page. Outlet t'iiiiyoii 194 Clianui'l Miiuntaiii 196 Flat Mouutaiii 196 West Base of Two Ocean Plateau 197 Two Ocean Plateau 200 ChaI'TKR VI.— (JkoI.OGY of the 80UTHEHN END OF THE Snowy Range, by W. H. Weed 203 (ieueial description 203 Topography 201 Sedimentary rocks 20.5 Buffalo Plateau 206 Lamar Valley 207 Slough Creek 208 Soda Butte Creek 210 Pebble Creek 211 Soda Butte Valley 212 CiiArxER VII.— The dissected volcano of Crandall Basin, Wyoming, by J. P. Iddings.. 21,5 Introduction 215 Geological description 216 General features 216 Early acid breccia 219 Basic breccia and flows 220 Distinctly bedded breccia 221 Chaotic breccia 222 Dikes 224 Extent of erosion 232 Petrography of the rocks of the district 237 Early acid breccia 237 Basic breccia and lava flows 238 Basalt flows 239 Intrusive rocks 240 Outlyiug dikes 240 Granular core and intersecting dikes 246 Mineral and chemical variations of rocks 259 Crystallization 265 Development of pheuocrysts 266 Chapter VIII. — The igneous rocks of the Absaroka Range and Two Ocean Plateau and op outlying portions of the Yellowstone National Park, by J. P. Iddings 269 Introduction 269 Early acid breccia 270 Early basic breccia and associated basaltic flows 275 Late acid breccia 281 Late basic breccia 296 Dikes and surficial flows 304 Vicinity of Sylvan Pass 304 Dikes south and southeast of Sylvan Pass 311 Massive flows and intrusions of light-colored andesite 314 Trachy tic rhyolite 321 Chapter IX. — Absarokitk-shoshonite-banakite series, by J. P. Iddings 326 Introduction 326 Absarokite 328 VIII CONTENTS. Chapter IX— Continued. Page. Shoahonite 339 Banakite 347 Similar rocks in Montana 351 Chapter X.— The khyoi.ites, Ijy J. P. Iddings 356 Introduction 356 Megascopical cliaracters 357 Vicinity of the Mammotli Hot Springs 357 Obsidian Cliff 359 Canyons of Gibbon River and Madison River 366 Madison Plateau north of the Lower Geyser Basin 367 Vicinity of the Lovrer Geyser Basin 369 Upper Geyser Basin 372 Madison Plateau south of the Geyser basins 374 Bechler Canyon 375 Falls River Basin 377 Pitchstone Plateau 379 Red Mountains 381 Vicinity of Yellowstone Lake 382 Natural Bridge 386 North and east of Yello wstoue Lake 387 Vicinity of Yellowstone River 388 Vicinity of the Grand Cauyon of the Yellowstone 389 Northeastern corner of Yellowstone Park 391 Microscopical characters of the rhyolite 393 Phenocrysts 394 Quartz 395 Sanidiue 398 Plagioclase 399 Pyroxene 399 Magnetite and titaniferous iron oxide 400 Zircon ^01 Pseudobrookite *01 AUanite and apatite 402 Groundmass 4"2 Glasses free or almost free from microlites 403 Globulitic glass 406 Microlitic glass 408 Forms of growth of microscopic crystals 410 Lithophysie ^^° Microgr.anular structure - 4— Relations of the various microstructures to one another in the rock mass 423 Lamination and banding 41.4 Variations in composition among the rhyolites 427 Intermingled rhyolite and basalt 430 Chapter XL— Recent basalts, by J. P. Iddings 433 Ophitic basalt "136 Basalts related to those with ophitic structure 437 A'ery fiue-grained bas.alts with minute phenocryts - 439 Chapter XIL— Paleozoic fossils 440 Section I.— Cambrian fossils, by C. D. VValcott 440 Section II.— Devonian and Carboniferous fossils, by G. H. Girty 479 CONTENTS. IX Pago. Chaptku XIII. — Mksozoic Fds.siLS, by T. W. Stanton 600 Chai'Ter XIV. — Fossil, I'l.oitA, by F. H. Knowlton ''51 Historical sunimary *'51 Enumeration anil description of fossil plants from the Laramie 6.^5 Discussion of Laramie flora ''"3 Enumeration and duscription of fossil plants from the Tertiary 665 Plants, exclusive of fossil wood ''65 Fossil forests .- ^^5 Biological consideration of the Tertiary flora 773 Geological consideration of the Tertiary flora 783 Indkx *^83 ILLUSTRATIONS. Page. Plate I. Mountains north of Mount Holmes 4 II. Paleozoic section, Crowfoot Ridge 8 III. Geological cross sections of Gallatin Range 12 IV. Panoramic view of Gallatin Range from Norris Geyser Basin 18 V. Cross sections showing Mount Holmes bysmalith 18 VI. Antler Peak from valley 22 VII. Three River Peak from Gallatin Valley 24 VIII. Bannock Peak from Panther Creek Valley 32 IX . Geological cross sections 50 X. Geological map of Gallatin Range 56 XI. Photomicrographs of audesiteporphyry and. dacite-porphyry 62 XII. View of Echo Peak 68 XIII. Electric Peiik from Sepulchre Mountain 90 XIV. Head of East Gulch of Electric Peak 90 XV. Sepulchre Mountain from its northwest spur 96 XVI. Geological map of Electric Peak and Sepulchre Mountain 96 XVII. Diorites 100 XVIII. Granite and diorite-porphy ry 100 XIX. Photomicrographs of andesite-porphyry and diorite 104 XX. Photomicrographs of diorite and diorite-porphyry 104 XXI. Photomicrographs of diorite-porphyry and dacite 104 XXII. Photomicrographs of pyroxene-andesite and dacite 130 XXIII. Map of the northern end of the Teton Range 150 XXIV. Snake River Hot Springs 178 XXV. Outlet Canyon 194 XXVI. BarouettPeak 204 XXVII. Geological map showing dissected volcano of Crandall Basin, Wyoming 216 XXVIII. Index Peak 218 XXIX. The Thunderer and Mount Norris 222 XXX. Koodoos 222 XXXI. Hurricane Ridge 226 XXXIl. Geological cross sections 232 XXXIII. Photomicrographs of gabbro, diorite, and granitic aplite 250 XXXIV. Photomicrographs of monzouite, diorite, and basalt 250 XXXV. Eagle Peak 296 XXXVI. Photomicrographs of absarokite 332 XXXVII. Photomicrographs of shoshonite and diorite-porphyry 344 XXXVIII. Photomicrographs of banakite, quartz-banakite, and andesite 350 XXXIX. Obsidian Cliff columns 360 XL. Top of columns 360 XLI. Lithophysie 364 XI XII ILLUSTRATIONS. Page. Plate XLII. Fissile litboidal rhyolite, Obsidian Cliff 364 XLIII. Lithophys:^ 364 XLIV. Columnar rhyolite 364 XLV. Columnar Cliff, Madison Canyon 368 XLVI. Banded perlite 370 XLVII. Perlite with spherulites 370 XLVIII. Natural Bridge 386 XLIX. Natural Bridge, vertical plates 386 L. Photomicrographs of rhyolitiu glasses 406 LI. Photomicrographs of rhyolitio glasses 406 LII. Spherulites 410 LIU, Spherulites and feldspar needles 414 LIV. Photomicrographs of micrographic phenocrysts and spherulites 414 LV. Photomicrographs of spherulitic structures 414 LVI. Photomicrographs of spherulitic structures and feldspar microlites 422 LVII. Diagrams of lithophys;e 422 LVIII. Columnar structure 436 LIX. Photomicrographs of basalt '. 436 LX-LXV. Cambrian fossils 468-478 LXVI-LXXI. Devonian and Carboniferous fossils 580-598 LXXII-LXXVI. Mesozoic fossils 642-650 LXXVII-CXXI. Fossil flora 794-882 Fig. 1. Diagram showing variation in silica percentages of rocks from Electric Peak 117 2. Diagram showing molecular variation of the rocks at Electric Peak 119 3. Diagram showing molecular variation of the rocks of Sepulchre Mountain 136 4. Sections of spherulites with projecting prisms of orthoclase and a crescent-shaped belt free from granulation 413 LETTER OF TRANSMITTAL, Department of the Interior, United States Geological Survey, Washington, D. C, June 30, 1896. Sir: 1 have the honor to transmit herewith the manuscript of Part II of a monograph on the Geology of the Yellowstone National Park. It embraces chapters on the descriptive geology of the mountains surrounding the Park Plateau, by myself and colleagues; elaborate investigations of the petrography of the crystalline rocks, by Prof. J. P. Iddings; reports upon the invertebrate paleontology of the Park and the Absaroka Range, by Messrs. C. D. Walcott, George H. Girty, and T. W. Stanton; and an exhaustive study of the fossil flora of the region, by Mr. F. H. Knowlton Very respectfully, Arnold Hagie, Geologist in Charge. Hon. Charles D. Walcott, Director United States Geological Survey. XIII OUTLINM: OF THIS VOLUME. CiiArTEK I. The (iallatin Mountains, extending IK miles within the boundary of the Yellowstone National Talk, consist of sedimentary strata ranging from the Cambrian, through the Silurian, Devonian, Carboniferous, and Juratrias, to the Laramie of the Cretaceous. These sedimentary rocks have been uplifted by forces acting from the southwest. They dip northeast, and have been folded to a slight extent transverse to the strike. .Subseqnently they have been strongly faulted. The dis- location at the close of the Laramie was accompanied by intrusions of igneous magmas in several large lacoolithio bodies and in numerous sheets, and in the vicinity of Electric Peak by dikes. Erosion has uncovered crystalline schists at the southern and southwestern end of the range, and has laid baie exposures of all the sedimentary and igneons rocks. Finally, glaciation has modified the topography in a striking manner. The structural relations of the sedimentary and igneous rocks are illustrated by a number of geological sections. Chapter II. Thi.s chapter treats almost exclusively of the intrusive rocks of the Gallatin Moun- tains. They are mainly line-grained and aphanitic masses, in most occurrences porphyritic and andesitic in character. The large bodies differ from one another .somewhat in composition, and vary slightly in texture, in diH'erent parts of the rock bodies. In one intrusive sheet there has been a pro- nounced dlft'erentiation by the settling of phenocrysts of augite. Chapter III. Electric Peak aud Sepulchre Mountain are described as parts of a Tertiary volcano ■which were faulted across the conduit, the amount of vertical displacement having been more than 5,000 feet. The deeper i)ortion.s of the mountains, consisting of sedimentary strata intersected by dikes, sheets, and the stock or conduit of the volcano, have been brought to the surface, as shown in the mass of Electric Peak. The ejected breccias and lava flows, together with the upper portion of the conduit, constitute Sepulchre Mountain. Lavas which are andesites in the latter mass are diorites and porphyries in the former. Rocks with like chemical composition are found to have different mineral composition according as they are crystallized into phanerocrystalline diorites or into apha- nitic andesites. Chapter IV. The northern end of the Teton Range extends but a short distance within the Yellow- stone National Park. It consists of a nucleus of crystalline schists aud gneisses overlain by Paleozoic and Mesozoie strata flexed in an anticline witli northward-dipping axis and faulted to a slight extent. Birch Hills, a few miles to the north, are an outlier of the range. Upon greatly eroded strata basic breccias were thrown out, and after these had undergone fresh erosion vast flows of rhyolite covered the country and now form a part of the plateau of the Park, beneath which the northern extremity of the Teton Range is hidden. Chapter V. The country described in this chapter embraces a mountainous area irregular in outline and of great diversity of form. It is situated in the southern part of the Park and the Yel. lowstone Park Forest Reservation. It consists of a number of ridges trending northwesterly and southeasterly, formed for the most part of Mesozoie rocks. The older sedimentary rocks are exposed but the ridges are essentially made up of sandstones of Cretaceous age. The irregular outline of the mountains is due to the rhyolites of the Park Plateau that abut against the slopes of the upturned beds. The principal physical features of the region are Wildcat Peak and Huckleberry Mountain, Bobcat Ridge, Big Game Ridge, Chicken Ridge, Two Ocean Plateau, and the gorge of Snake River. West of Huckleberry Mountain occur several exposures of dacite surrounded by rhyolite. They are among the few outcrops of dacite known in the Park, and are apparently older than the rhyolite. In the gorge of Snake River the Madison limestones, Teton sandstones, and the Ellis limestones and XVI OUTLINE OF THIS VOLUME. shales are well shown. The Snake River hot springs are situated near the contact of the rhyolite with the Carboniferous limestone, the lime of the travertine being derived from the Madison lime- stones. The incrustations around the springs resemble the travertine deposits found at the Mammoth Hot Springs. The characteristic and limited Wolverine flora, of Laramie age, occurs near the base of Pinyon Peak. The conglomerate of Pinyon Peak, a striking physical feature of the region, is described as overlying unconformably the Laramie sandstones, and evidence is given showing that the conglomerate probably belongs to Eocene time, as it iinderlies the basic breccia of the Absaroka Range. The impressive gorge of Outlet Canyon cuts a deep passage completely through Chicken Ridge. The interesting feature of the canyon is that it at one time served as the discharge for the waters of Yellowstone Lake. This sheet of water, which now flows northward and drains to the Atlantic through Yellowstone Canyon, formerly discharged into Snake River and thence to the Pacific. Two Ocean Plateau shuts in the sedimentary ridges on the east. The plateau, which rises 10,000 feet above sea level, forms a part of the Absaroka range and Is made up of similar volcanic breccias and silts. Chaptbk VI. The extreme southern end of the Snowy Kange forms the northeast corner of the Park. The crystalline core of the range forms a broad, plateau-like summit, bordered by sedimentary rocks of Paleozoic age, which along the south slope dip gently away from it toward the Park. The highest peaks, together with extensive areas, are formed of andesitic breccias, but erosion has cut through them and exposed the underlying limestones, showing that the volcanic rocks rest upon a very uneven anil rugged surface. Detailed sections of the Paleozoic sedimentary rocks from the Flat- head formation to the Madison limestone are given, but the igneous rocks are described in other chapters. Chapter VII. The Miocene volcano of Crandall Basin built itself upon a ridge of eroded Pale- ozoic rocks which dip toward the southwest from the crystalline schists of the Beartooth Range. Beneath the volcano are remnants of Eocene breccias and lava flows. The volcano consisted of basic andesitic breccias topped by basalt flows and traversed by dikes that radiated from the stock or core which was the conduit beneath the crater. While bedded breccias characterize the outer portions of the volcano, chaotic unbedded breccias form the central portion. Comparison with modern active volcanoes indicates that the Crandall volcano rose to about 13,400 feet above its limestone floor. The phanerocrystalline rocks within the core are gabbros and diorites, approaching monzonites in part, and are chemically like the basalts and andesites of the breccias, dikes, and flows, but diifer from them in mineral composition. They also are parts of the volcano and are properly volcanic rocks. Chapter VIII. The Absaroka Range consists largely of volcanic breccias, with subordinate amounts of massive flows or intrusive bodies. This chapter presents a petrographic treatment of those io-neous rocks which lie withiu the limits of the Yellowstone Park, and their discussion is confined to an account of their field occurrence and distribution and a systematic description of their mineralogical characteristics and composition. The earliest accumulations occur at the northern end of the range and are made up of early acid breccias found in disconnected remnants beneath early basic breccias. They consist mainly of hornblende-andesite and hornblende-mica-andesite. The early basic breccias are pyroxene-andesite, passing upward into the massive basalt flows. Upon the latter were thrown the late acid breccias, similar in composition and appearance to the early acid breccia. This passes upward into late basic breccia, consisting of basic andesites with less basalt than is associated with the early basic breccia. The late basic breccia forms the southern portion of the range within the Yellowstone Park and also Two Ocean Plateau. At Sylvan Pass and in its vicinity it is traversed by dikes of andesite and a few of diorite. Remnants of surficial flows of massive andesite form the summits of Mount Stevenson, Mount Doane, Colter Peak, and several prominent mountains south of Sylvan Pass. OUTLINE OK THUS VOLUME. XVII t'llAPTEl! IX. Certain b.isultic Mini otluT rocks assiiriatfd with the andesitic hrecrias and basalt Hows have a considerable content of iiitlio(Mase in niicrnscci))!!' crystals, and a comparatively high percentage oC potash. They occnr as lava Hows and as dikes in v.ariiiiis localities within the I'ark. According to their ('honiical and niiiicral composition tliey have been classed as absarokites, shoshonitcs, and banakites. CllAl'TF.R X. The rbVoIites of the I'aiU are almost wholly extrnsivc Lavas of very niiiform compo- sition, bnt having a wide range of color, texture, and mog.ascopic habit. Tlic appcar.ancc of the rhy- olito ill the field, and tlio microscopical cliarnctcristics of pbcnocrysts, spheriilites, litliophys:c, and groniidmass, are dencrilied in detail. The dill'ciont modidcations of cryst.allization, besides the lami- nation and formation of pnniicc, are referable to lieteiogeiieity of the molten magma, especially with reference to the amonnt of vapor contained in it. Examples of intermingled b.asalt and rhyolite are de.scribed, in which the basalt appears to have been inclosed and partly melted by the rhyolite. CiiAPTEU XI. The recent biisalts overlie the rhyolite in most inst.anccs, but .are found beneath it, and also between older and younger sheets of rhyolite in several localities. These basalts arc distin- guished from those .associated with the early .and Kate basic breccias by being ophitic .and iionpor- pbyritic for the most p.art. Chapter XII. This chapter describes the Paleozoic fossils known to occur in the Yellowstone Niitional Park and the Absaroka Range. It is divided into two sections, the first treating of the Cam- brian species and the second of the Devonian .and Carboniferous species. Both Flathead and GalKatiu formaticms have yielded a sm.all but characteristic fauna. From the Cambrian 21 species in all have been obtained, several of which are new to science .and described here for the first time. No fossils of undoubted Silurian age have been obtained, altliongh the beds carry imperfect and partially oblit- erated organic forms. The Three Forks limestone has furnished a well-recognized Devonian fauna. From the Madison limestone a varied fauna has been collected, but belonging wholly to the Lower Carboniferous period. CllAPTKU XIII. The Mesozoic fossils obtained from the Yellowstone N.atioual Park were found in the G.all.atin Range near Electric Peak, Teton Range, in the neighborhood of Wildcat Peak .and Huckleberry Mountain, and from the Cret.accous ridges in the southern end of the Park and Yellow- stone Forest Reserve. The Mesozoic str.ata have yielded 78 species of invertebrates, of which one is from beds supposed to be of Triassic age, 4G are .Turassie, and 31 are Cretaceous. The fossils obtained were mainly from the Ellis form.atiou of the .Jura and the Colorado of the Cretaceous. The .Jnr.assic fossils form much the largest and most prominent part of this collection, and in number of species it compares favorably to the .Jur.assic of other parts of the Rocky Mount.ains. Chapter XIV. The Mesozoic fo.ssil llora of the Yellowstone National Park is confined to the Laramie sandstones of the Cretaceous .and is found on Mount Everts, near M.ammoth Hot Springs, and at the base of Pinyou Peak near the head of Wolverine Creek. The llora from this Latter locality has been designated the Wolverine Creek llora. The Tertiary llora is very v.aried and possesses great biological interest. It is a rich llora, and on comparing it with the living llora it becomes app.areut th.at great clim.atic ch.anges must have taken place since the do.se of Miocene time to have m.ade these changes in pl.ant life possible. It is found at numerous localities associated with the breccias and silts of the igneous rocks of the Absaroka Range. It is found in the early acid breccias, in the early basic breccias, in the late acid breccias, and in the l.ate basic lireccias, where the muds and silts furnish a soil favorable for a vegetable growth. The most interesting locality as reg.ards number of species and mode of occurrence is the well-known Fossil Forest of .Specimen Ridge. The Terti.ary fossil llora embraces about 150 forms th.at have been distrrbuted among .S3 natural orders. This fossil flora is illustrated by forty-five plates. . MON XXXII, PT II II GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, PART IL By ARNOLD HAGUE AND OTHERS. CHAPTER I. DESCRIPTIVE GEOLOGY OF THE GALLATIN MOUNTAINS. By Joseph Paxson Iddings aud Walter Harvey Weed. I^TTRODUCTION. The Gallatiu Mountains form a range of peaks and ridges extending southward for 63 miles from the vicinity of Bozeman, on the line of the Northern Pacific Railroad, about latitude 45° 40'. The range lies between the Yellowstone and Gallatin rivers and terminates in the neighborhood of Mount Holmes, at about latitude 44° 45'. The southernmost 18 miles of the range lies within the boundary of the Yellowstone National Park aud forms that portion of it described in the present chapter. The northern portion falls within the region described in folios 1 and 24 of the Geologic Atlas of the United States.^ Within the Park boundary the peaks of the main chain reach altitudes of from 10,000 to 10,500 feet, and at Electric Peak 11,100 feet, and stretch from Electric Peak, which is situated directly on the northern boundary line, southward to Mount Holmes. The country has been deeply cut by erosion, and is drained by tributaries of the Yellowstone, Gallatin, and I Geologic Atlas U. S., folio 1, Livingston, Mout., 1893 ; and folio 24, Three Forks, Mont., 1896. MON XXXII, PT II 1 1 2 GEOLOGY OF THE YELLOWSTOInE NATIONAL PARK. Madison rivers, the watersheds between which meet one another in Tln-ee River Peak. The special description of the physiographic features of the region, however, inchiding the glaciation, will be found in Part I of this report, where it is treated by Mr. Hague. Without entering into a topo- graphic description of the Gallatin Mountains, it will be in place here to call attention to the fact that the region in question, within the Park boundary, is a block of country delimited on the east and on the west by profound faults trending nearly north and south, the western fault line having a somewhat northeasterly trend. This block, about 7 miles wide, is bounded on the south by a capping of lavas, which borders it also to some extent on the east and on the west. The northern end of the block lies beyond the Park boundary, in the neighborhood of Cinnabar Mountain. The block is wider at the south, and narrows northward. It is a wedge- shaped mass cut diagonally across a synclinal trough, with one long and one very short limb. The latter appears for only a short distance at the northern end, in Cinnabar Mountain. Within the area of the Park the block has the structure of a monocline, dipping northeast across the longer diameter of the block. Minor faults and folds modify the structure some- what and introduce local complications, which will be described in detail. As a result of the dipping of the block to the northeast, the oldest formations are found at the southern and southwestern ends, and the youngest formations at the northern. The rocks are well exposed, the succession of the strata is clearly made out, and the form and character of the igneous material that has been forced through the sedimentary rocks are readily observed. The study of the igneous bodies and their relations to the geological structure of the block proves that the dynamic history of this particular area was complex, and extended over a long period after the deposition of the coal-bearing Laramie sandstones. In fact, a succession of dislocations must have followed one another through the greater part of the Tertiary period. This will aj^pear from the description which follows. Erosion has carved deeply the surface of this upturned, fractured, and distorted block, grooving it with valleys and gulches, the eastern system trending northeast and east and draining with the dip of the strata, the western system trending and draining northwest along the general line of the strike and being in all probability controlled by lines of fracture in this direction. The intervening elevations rise abruptly to sharp peaks THE CRAGS. 3 and ridges, attaining altitudes of from 10,000 to 11,000 feet above sea level, with occasional plateaus, 2,000 feet or more above the valley bottom. The bold escarpment and barren upper portions of these mountains permit their general structure to be made out with ease, even from a distance. Thus the general structure of the eastern face of the range may be seen from Bunsen Peak or Ten-ace Mountain. The open, park-like character of the valleys and lower slopes of the mountains, the abundance of grass and water, and the multitude of flowers that cover the whole country during the summer season render this one of the most picturesque and delightful of mountain regions, both for the geologist and for the artist. THE CRAGS AISTP VICINITY. A description of the geological features of the Gallatin Range naturally begins with an account of the region where the basal and lowest rocks of the series are exposed. These occur in the southern and southwestern part of the range, and a descrijDtion of the range from these peaks northward is, in general, also a description of successively later geological formations. The oldest rocks of the region are crystalline schists, which are mainly gneisses. These rocks form two prominent topographic features of the southern end of the range. The first of these is the group of rugged peaks called The Crags, together with their less elevated spurs to the south, and their prolongation in the ridge trending northwest, parallel to Grayling Creek. Crowfoot Ridge constitutes the second prominent mass of crystal- line schists, while the low rounded hills at the head of Grayling Creek are also formed of these rocks. A few inconspicuous outlying exposures of schist occur to the southwest, where erosion has removed the overlying sheet of rhyolitic lava. THE CRAGS. The rocky summits of The Crags and the ridges northwest are very rugged and difficult to traverse on account of the loose ddbris and thick- timbered slopes. But while the southern escarpment of Crowfoot Ridge is equally obstructed, its summit is comparatively open and level topped, showing little erosion since the removal of the sedimentary cover. The lower hills between Grayling and Maple creeks are rounded and smoothed, with every evidence of having been glaciated and considerably worn. Tlnroughout this area of crystalline schists, coarse and fine grained gneisses 4 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. alternate with one another, the coarser varieties being generally light- colored mica-gneisses rich in feldspar and quartz. The finer-grained, dark-colored varieties are for the most part mica-gneisses richer in biotite. Mica-schists, sometimes highly garnetiferous, occur in smaller quantities, and amphibolites are also found. The pronounced lamination or schistositv of the whole body of these rocks is quite uniform in its jiosition, the layers standing at high angles or nearly vertical, with a general north-south trend. The microscopical study of these rocks shows them to be normal crystalline schists, having the microstructure of highly metamorphosed rocks and exhibiting no traces of their previous character. Their study in the field was not thorough enough to throw any light on the question of their possible origin. South and west of The Crags the crystalline schists are directly overlain by volcanic breccia and tuffs of andesites, whose subaerial accumulation is beyond question. These rocks are generally dark colored, and occur in rugged outcrops and rough, angular talus blocks. In general, the easterly slopes are smooth, covered with soil, and less steep than the western sides of the hills. The andesites are variegated in color and are chiefly hornblende-andesite, carrying some pyroxene and a little biotite. The occurrence of these subaerial breccias shows that at the time of their eruption the crystalline schists were exposed sui-face rocks which had undergone extensive erosion, by which they had acquired a pronounced mountainous topography. On the west and south the schists pass under massive rhyolitic lava, which is part of the great plateau lavas farther south, and whose position with respect to the crystalline schists and andesitic breccias is such as to show that the rhyolitic lava flooded the lower levels of this gneissic region after the andesitic material had been accumulated and had been partly removed by erosion. That the rhyolite overlies the andesitic breccia is clearly shown in the walls of Maple Creek Canyon. The rhyolite also fills the valley bottom between two ridges of andesitic breccia in this vicinity, indicating- the extent to which the andesite had been previously eroded. There is marked contrast in the scenery and topography of the gneissic areas and of the country formed by the rhyolite, the former being essentially rugged and broken, while the latter is as yet comparatively little affected by erosion, the streams flowing in trenches and canyons cut THE CKAGS. 5 in the soft rock. Often the boundary between gneiss and rhyolite is defined by small drainage ways woni along the contact. Along the western side of the gneissic area the rhyolitic lava rises to altitudes of 8,000 to 8,200 feet, while at the head of Maple Creek it rises to 8,700 feet, the level of the divide between this creek and Grayling Creek. From this it seems highly probable that the lava flooded the valley of Grayling Creek at the time of its eruption, and has since been removed by erosion. The absence of au)^ remnant of rhyolite within this valley, as the map represents, is not based on a careful examination of the valley, but expresses our ignorance in respect to its occurrence there. The marked contrast between the topographic character of the southern side of Crowfoot Ridge and that of the northern side is note- worthy. The southern slopes are almost free from lateral spurs of any size and the ridge is approximately straight. On the north, spurs branch off at short intervals, increasing in size toward the west until they attain the proportions of mountain ridges. The tlu-ee most prominent of these spurs trend north. This contrast in topographic configuration is to be explained by the position of the former covering of sedimentary rocks, which were removed during the downcutting of the Grayling Creek Valley. This creek, following the well-known habit of streams, formerly cut its channel westward along the strike of the northward-dipping sedimentary rocks, gradually deepening its channel until, reaching the underlying crystalline schists, it was compelled to continue in the same course, deepening and widening the valley, whose straight northerly walls are due to the absence of lateral drainage channels consequent upon the northward dip of the strata. The same configuration is seen in the upper valley of the Gallatin River and the valley of Fawn Creek, where the mountain gorges are cut in sedimentary rocks. The topography of this vicinity is so closely dependent on the charac- ter and position of the strata immediately overlying the gneiss, and these strata have been tilted, curved, and faulted to such an extent, that it is advisable to postpone the description of this area until the less distributed rocks lying immediately east of the main body of crystalline schists have been described. The region just mentioned lies east of the main gneissic area, and is 6 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK, separated from it by a fault trending a little west of north. This fault crosses the southern end of Crowfoot Ridge, about a mile west of the summit of Three River Peak, and passes southward along the west base of the mountains, between Indian and Maple creeks, disappearing beneath the more recent rhyolitic lavas. The eastern area embraces the most joromi- nent peaks of the southern portion of the Gallatin Mountains, including Mount Holmes and the bare porphyry peaks around the head of Indian Creek, besides Trilobite Point, The Dome, Antler Peak, and Three River Peak, peaks that are directly connected with the mountains north of Panther Creek. CROWFOOT SECTION. Before taking up the description of these mountains, involving sedi- mentary rocks, it will be best to give an account of the stratigraphic series. A very carefully measured section was made of the Paleozoic strata exposed on a northern lateral spur of Crowfoot Ridge. This high mountain ridge shows the entire sequence of the Paleozoic sediments of the region, from the crystalline schists to the top of the Carboniferous, exposed in an unbroken succession of apparently conformable beds dipping at an angle of 30° N. The general form and profile of the ridge is shown in PL II, which gives a view of the ridge from the east. The illustration shows the bluffs formed by the harder beds of the series, rising above the slopes into which the shales and thinl)^ bedded strata have weathered down. Two lines of cliffs, formed by the mottled limestone. No. 14 of the section, and the Jefferson limestone. No. 19, are seen in the view. These horizons form characteristic cliffs throughout the range, and are an important aid in reading the structure of the mountains. The section of the sedimentary rocks made at this place has served as a basis of comparison for all the other sections of the Paleozoic rocks made in the Gallatin Range. The beds are well exposed, the crest of the ridge being bare of soil or vegetation and the trend of the ridge being very nearly at right angles to the strike of the strata. THE GALLATIN MOUNTAINS. Grotrfoot Ridge section. Nuinber. ^eet. 33 Quailiaiit qnartzite. Siindstono and ([uartzito, saccharoidal in texture, reddish near the base, with daik-gray and very calcareous layers; passes at top to a white sand- stone 200 d. Limestone, light gray, brecciat(Hl and broken; in places iron stained 100 c. Limestone, light gray, varied with brown baiidsor fiuestripes antl lines; contains chert, and is in ])lace8 breeciated, the fragments being cemented by calcite 400 b. Limestone; crystalline, very light gray, weathering creamy white; contains white chert in bands and nodules 30 a. Limestone, crystalline, dark brownish gray, intersected with calcite seams. Chert bands and nodules are abundant 125 655 Limestone, light gray and gray, weathering gray ; banded with brown ; banded appear- ance on weathered surface ; finely crystalline. Fossils abundant 380 ' b. Limestone, crystalline, massive, light gray, with small brownish fossil fragments scat- tered through it. The upper 10 feet is a conglomerate of red, often cellular lime- stone. Fossils iO a. Limestone, massive, light gray, similar to No. 28 15 31' 31 30 Is 29 Limestone, light gray and brown, very finely crystalline or granular; well bedded, with layers 10 to 20 feet thick of brown or cream-colored limestone. Certain layers are banded with light-colored chert, weathering bufi' or brown; these layers carry corals and fossil shells 85 28 Limestone, crystalline, light gray, generally massive, but in places more thinly bedded, and striped with brown. The rock is often magnesian and impure. Fossils 200 27 Limestone, dark gray and butf, very argillaceous, thick and thinly bedded. Fossils from the upper portion and the lower portion of these beds are Lower Carboniferous. This limestone is very much like the bed beneath it 50 b. Limestone, more massively bedded than the underlying bed and coarser in crystal- lization; a quite pure limestone, full of fossil fragments 15 26 \ a. Limestone, fissile and thinly bedded, impure and argillaceous. The fossils occur in lower and upper beds 60 I 75 r ^-a SS hS 20 1 ^ ir (C iii I^ -n Ui i- I. (0 0) n C ID u7 <'!; q: ^Jr o i^ 7 10 S s ,:; o :c u: (U u. 03 UJ o o c z ^ ^n*: z 'S o h >-h < ■= 0) _l _J 0 <55 UJ I c 1- i2 M. ^^ o £! 5 UJ 0) c — .t: nj > _1 < 1^<^ C U S GEOLOGICAL SURVT^ MONOQRAPHXXXII.PARTIIPL V (K'OSS SKC.TIOXS SIIOWINO MOUNT HOI.IVIKS I5YSMAT()I,IT1I I.l-.OKMn CARBONIFEROUS DEVONIAN "3J~] ^ NEOCENE DnuitR- porphyiy. dp Scale or Miles MOUNT HOLMES HYSMALITH. 19 southwest, and tlirougli Mount Holmes and Trilobite Point. These cross tlie contact i)lane between the bysmaUtli and the strata with the inclosed laccolith. Owing to the crystalline character of the rock constituting the bys- malitli, there is little doubt that it soliditied beneath a covering of strata. The crystals are larger than those forming the mass of the Indian Creek laccolith. A possible reconstruction of the position of the strata after the intrusion is given in PI. V, fig 4, in which all of the formations up to the top of the coal-bearing Laramie are represented — a total thickness of 9,000 feet. The upper parts of the mountains into which this intrusion has been carved are barren and rocky above 9,000 feet, with comparatively smooth slopes covered with loose fragments of porphyry. The peaks are pointed in some cases and rounded in others, as may be seen from PI. IV. The rock is very uniform in appearance throughout the entire extent of the mass. It is light gray to white, aphanitic to fine crystalline, with a slightly porphyritic structure in part. It shows small flakes of biotite and indistinct phenocrysts of feldspar. It is massive, with irregular joint ci'acks, and weathers into angular blocks and. slabs. Its megascopical chai'acters are quite uniform throughout the greater part of the mass, which varies slightly in grain. But near the margin of the body the rock becomes denser and more aphanitic, showing a broad banding parallel to the walls of contact with the surrounding rocks. These walls are nearly vertical in the moun- tain west of The Dome, on the saddle east of Mount Holmes, and also on that of Echo Peak. In all cases examined, the neighboring limestones dip away at angles of 40° to 55°, and the adjacent andesite-jiorphyry has been crushed anr])liyry. 11 6. Liinestoiic, rather tliiuly bedded, dark bliic-gray with lighter weathered surface. 6 7-10 5. Limosloiies, f'oiuiing the great ledge of the monutaiii side. Many beds are of a crystalline, fine-grained, dark-gray and dense limestone seamed with calcite. Weathers light gray, often rusty. At the base is thinly bedded, breaking readily into small angular pieces. At top, beds are slightly cherty and fossil- iferous. In ci'ntcr, beds are massive and appear irregularly bedded. Strike N.Si*^ E. and dip 3'^ N 225 Dacite-porphyry, probably an offshoot of the Holmes bysmalith 25 6 4. Limestone, compact, brown, weathering gray 20 5 3. Slialy beds, micaceous and schistose, with thin bands of limestone 50 2-4 2. Interval, no exposure 300 1 1. Gneiss. It will be seen from the above section that the andesite-porphvry of the laccolith immediately overlies the limestone No. 6 of this section, which con-esponds to the Flathead limestones of the Crowfoot Ridge section. The laccolith has therefore been intruded in the upper shale belt of the Flathead formation, the shales being 150 feet thick in the Crowfoot section. The occurrence of the laccolithic intrusion is the same at the base of Tliree River Peak, where above the porphyry a part of the shales is found beneath the limestones that form the highest beds of the Flathead forma- tion. At Antler Peak the laccolith incloses parts of the Flathead limestones, as well as a thin belt of limestone and fragments of the underlying shale. Along the base of steeper slopes toward the northeast, the drift has covered all exposures; even the beds of the great limestone ledge are partially hidden. Over these beds we find a platform where the overlying shale and poi-phyry have been eroded, leaving the limestones underneath intact. That the bench is due to the erosion of the shale seems probable; easilj^ yield- ing to disintegrating agencies, it has been carried away, undermining the porphyry, which has also been swept off by glacial action. The lowest bed noted above the laccolith is a finely crystalline, light- di-ab limestone, probably the upper beds of the Flathead limestone of the general section. The following succession of strata is exposed on the northeast spur of the mountain from the summit of the peak down to this bed: 22 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Crowfoot aectioD. 31 S g1 30(1,6 29 26o 25 24 27, 28 < 22 Num- ber. 81 21 20 Antler Peak section. Limestone, crystalline, moderately dense, brown, weathering grayish, witli rough pitted surface, and breaking readily into small angular pieces. Dip, N. .50 E., 20= Limestone, less splintery than bed above, light brown, fissile, with fossil layers. Limestone, finely crystalline, light gray with buff or pink, finely granular, weathered surface. Very fissile, plates warped Limestone, brown or purplish brown, very fissile and platy. Fossils abundant. Limestone, massively bedded, light drab and brown, breaking readily into frag- ments. Fossils somewhat abundant. Dip, 5" NE Limestone, finely crystalline, light and dark gray and gray-brown, weathering bntf, with smooth, finely granular surface. Layers thickly and thinly bedded, with very fissile fossiliferous strata near base Limestone, mottled, massive, and seamed with calcite. Lenticular arrangement of light-brown in darker mass gives appearance of bedding Limestone, very fissile and containing fossils Limestone, massive, purple, containing white fossil fragments Limestone, alternating layers of very fissile, gray, and fossiliferous limestone and more massive rock Limestone, coarsely crystalline, without chert; is fossiliferous and seamed with ;alcite Cherty limestone, forming a prominent ledge shown in Holmes's sketch. Hard, dense, crystalline; contains corals and crinoid stems and much blue chert in bands and nodules. The rock is somewhat seamed with calcite Feet. 100 40 15 100 50 100 15 5 15 170 50 100 23 22 21 20 19c 19 18 17 16 15 14 13 111 Limestone, somewhat massive and thickly bedded (5 to 10 feet), light gray, with lifht, very rough, and irregular weathered surface. Few fossils and a little light-colored chert 40 Limestone; alternating beds of dense light-drab limestone and brown arena- ceous sandstone, with rough and pitted weathered surface and fetid odor, parts of it resembling No. 16 of this section. Extends up to base of cone top. The rock is an arenaceous limestone, dark brown-gray, weathering brown 130 Limestone, compact, dense, hard, dark gray, weathering very light brown-gray, with finely granular surface 20 Limestone, dark brown-gray, weathering straw-color and rich brown. Is an arenaceous limestone 5 Limestone, white, pitted and rotted, with harder mottled places 6 Interval, no exposure 10 Limestone, brown, dense 5 Limestone, light creamy yellow mottled with gray, thinly bedded, breaking into small cuboidal blocks. Strike, N. 5° W. Dip, 3° W 35 Limestone, finely crystalline, white 30 15-19fc 10 Limestones, grading at top into cherty limestone. 14 9 Mottled limestone, but 30 feet exposed I- (11 8 Interval, no exposure. 7 Limestone, finely crystalline, light drab. 160 50 THREE ElVEB PEAK. 23 West of the eastern summit the edges of" the lower beds outcrop, and the Galhitin Hmestone is exposed in the saddle. On the northeast spur of the peak the Flathead limestones are exposed, the dip being- N 30° E., 10°. THREE RIVER PEAK. Three River Peak is a shaq) point whose position at the head of the Gallatin River and of branches of the Gardiner and Madison rivers makes the name appropriate. The slopes rise abruptly from the head of Indian Creek Valley on the east, while to the north an almost vertical wall rises above the deep blue waters of Gallatin Lake. The peak occurs on the western side of the Indian Creek laccolith, and the beds composing it, like those forming- the summit of Antler Peak, consist of Paleozoic strata ranging from the Cambrian limestones to those of the Carboniferous. The sedi- mentary rocks are, however, penetrated by several sheets of intrusive rocks which are much decomposed, but represent phases of the Mount Holmes bysmalith. The following section shows the sequence of rocks exposed on the northern spurs of the peak from Indian Creek Pass to the summit: . Three River Peak section. Crowfoot Num- seetion. ber. 26a 2.T .12 in 10 24 n^ «g 03 J 23 21-22 15-20 .U 13 r 3 f Feet. 75 30 15 25 30 5 35 50 10 17 5 25 Limestone, thinly bedded, dark and light gray, magnesiau 130 Limestones, in a series of beds, not individually noted 160 Limestonfl, thinly bedded 70 Mottled limestone, matrix light brown, mottled with black; due to aggrega- tion of black grains of matrix 40 Gray, blue-gray, brown, and black limestones, with layers of "glaueonitic" limestone, the grains black instead of green. Is fosaillferous. Thickly and thinly bedded, with some yellow argillaceous layers and one conglomerate bed 100 12 Limestone, crystalline, gray, fossiliferous; contains crinoid stems Limestone, light gray, dense, massive, cherty Porphyry, fissile, much decomposed, yellow and purple Limestone, light gray Porphyry, fissile, decomposed and yellow at base ; upper half massive and fresher Limestone, crystalline, light gray, with granular, weathered surface Limestone, brownish gray, weathering a light brown; massively bedded; with splintery fracture Porphyry, light colored, nearly white, weathering brown, fissile; thoroughly decomposed Limestone, baked by porphyry Porphyry, fissile, yellow and rusty gray, thoroughly decomposed Limestone, black and rusty, much baked Porphyry, dense, compact, looking like quartzite 24 GEOLOGY OF THE YELLOWSTOI^E NATIONAL PARK, The shores of the Galhxtin Lake, and the small hills adjoining, are formed of the laccolith rock, audesite-porphyry. The western boundary of this rock runs northward along a gully, west of the di-ainage from the lake, and through a small shallow pond to the saddle of Bighorn Pass. To the south the porphyry extends to the base of Three River Peak in the rear of the lake, and forms the saddle in the pass between Indian Creek and the valley of the Gallatin River; from here northward the exposure extends along the western base of the ridge to Bighorn Pass. The position of the strata seen in the precipitous northern face of tins peak is shown in PI. VII. At the western base of this mountain they dip sharply over the edge of the laccolith, changing from nearly horizontal to 50° or 70° W., and gradually decreasing again westward. Into the axis of this abrupt bend a vertical offshoot from the andesite-porphyry has been intruded, showing that the limestones were ruptured at this place. The limestone strata of Three River Peak are traversed by dikes of lithoidal igneous rock at various angles. One broad dike, 100 feet thick in places, cuts diagonally across the northern face, appearing on the eastern slope about halfway up to the si;mmit. Another, about 10 feet thick, without phenocrysts, lies horizontally between the strata and might easily be mistaken for a compact sandstone. A narrower dike cuts nearly verticallv throuo-h the western side of the mountain. At the west base of the peak the gneiss is faulted against the lime- stones by the soutliern extension of the Gallatin fault. The position of the sedimentary beds which abut against the gneiss, as well as their fracturing, shows clear evidence of the presence of the fault. An intrusive body of igneous rock related to the Mount Holmes rock occurs at this locality. On the saddle between Three River Peak and Echo Peak, near the contact of the Holmes bysmalith with the andesite-porphyry and lime- stone, the latter rocks are seen to have been turned up, so as to dip 40° N., away from the bysmalith, and to be greatly shattei'ed and dislocated, producing slickensides and a pulverizing of the rock along the fracture planes. BIGHORN PASS. Bisrhorn Pass is a low divide between the head waters of the Gallatm River and the drainage of Panther Creek, and affords an easy passage from the valleys west of the mountains across the range to the central region of EIGIJOUN I'ASS. 25 the Park. The pass is cut in the Paleozoic sedimentary rocks, which are sH^htly tihed by an intruded sheet of andesite-i)orphyry that is the northern extension of the Inchan Creek hiccohth. A dark, Liinprophyric rock occurs at the lowest })oint in the pass, where it is seen to form a sheet 50 feet thick intrusive in the Cambrian shales. The hjoh ridgfe extending north from the head of Indian Creek to Bighorn Pass is formed of sedi- mentary beds that overlie the northward extension of the Indian Creek laccolith. Above the andesite-])orpliyry of the laccolith which forms the Indian Creek Pass the green Flathead shales are exposed, overlain by the upper limestone series of the Flathead, which are here 100 feet thick and resemble quite closely the beds of this horizon as developed in Crow- foot Ridge. The summit of the ridge is formed of the Gallatin "mottled limestone," which dips to the northwest and makes a well-defined ledge, with a cliff" face 30 feet high and a rounded but hummocky surface, -the result of glacial planing. Near Bighorn Pass the beds are locally affected by an intrusion of the laccolith, and dip more steeply than the beds north of the pass, there being a difference of 5° to 8°. Two sections of the Paleozoic rocks were measured in this vicinity; the first was made on the ridge running south, the second from Bighorn Pass to the summit of Bannock Peak. These sections show the following sequence of beds, arranged in descending order: Bighorn Pass section. Crowfoot Num- section. ber. Feet. ^J H "-5 Cherty sandstones .and limestones, brown and gray, chert nodules, witli whitened surface 11 21 Quartzose conglomerate ; matrix a light-gray limestone 20 33 20 White beds of sandstone, quartzite, and limestone, generally saccharoidal 325 32 19 Limestone, crystalline, light colored. The upper portion is a brecciated and nearly pure limestone. The lower beds are dense, finely crystalline, weath- ering white, with granular surface. Magnesian, and containing sparsely disseminated chert. Strike, S. 30^ W.; dip, 10° NW 275 32 18 Limestone, very finely crystalline, with calcite strings, brown, dense, massive; nearly pure 25 31 17 Limestone, breccia ; the matrix is similar to the bed below ; the fragments resemble the beds above and below. The lower beds are slightly siliceous, light-gray limestones weathering pale yellow 50 31 16 Limestone, crystalline, light brown, with granular weathered surface; mass- ively bedded, and is vertically jointed and contains some chert in bands 75 26 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 29 28 Bighorn Pass section — Continued. Crowfoot Num- sectioD. ber. Feet. 30 15 Cherty limestone. The lower 30 feet ia a brown fossiliferous limestone, over- lain by 70 feet of a moderately coarsely crystalline gray rock, weathering brownish. One bed is a compact brown limestone, full of criuoul stems and fossil fragments, which appear as crystalline masses of calcite on fresh fracture, but on weathered surface show their true nature. The upper portion of No 15 is cherty and massive 225 14 Limestone; the lower portion light brown, shading to gray; massive, with cherty band near center. The upper part Is rich in coral. This limestone varies in crystallization, being both fine and coarse 30 13 Limestone, gray, weathering brown, finely crystalline and compact 12 12 Limestone, linely crystalline, white, cherty. Chert is light gray, weathering rusty or black 5 11 Limestone, blue, finely crystalline, very splintery 6 10 C'hprty limestone, white, finely granular 30 9e Limestone, coarsely crystalline, light drab, with few fossils; runs down to saddle 25 9b Limestone, finely crystalline, compact, massively bedded, light drab, vertically jointed. Dip 18-, N. 20^ W 20 9a Limestone, very light gray, coarsely crystalline, containing crinoid stems and other fossils 50 8 Limestone, snmewhat coarsely crystalline, compact, white; the base concealed by talus of No. 9 of this section 30 7 Limestone, fine grained, fissile, dark gray, weathering blue; certain layers are quite fossiliferous 90 27 6 Limestone, dark gray, often brownish gray; cherty and siliceous near base. The upper 50 feet more friable and soft; contains numerous fossils, shells, crinoid stems, and corals 250 5 Limestone ; finely crystalline, with quartzose band near top ; gray, weather- ing creamy. The top is concealed by the talus of No. 6, and the thickness should be increased about 40 feet iO 4 Limestune, dense, massive, dark blue-gray, impure (argillaceous) 20 3 Limestone, alternating beds of massive, steely gray, arenaceous limestone, weathering brown and containing corals, and fissile, light-gray, and dense limestone ''O ) 2 Limestone, at the base dark blue-gray and very compact, changing to a browu-giay arenaceous limestone. Dip 15°, N. 10° W 10 ) 1 Limestone, light drab, finely crystalline and dense, somewhat cherty. Chert light and dark gray ; thickly bedded. The dip of the lower beds of the section is 15°. Five hundred feet above the pass it is 18°, and near the summit of Bannock Peak it is 10°. The direction of the dip also changes from N. 11° W. to NW., becoming N. 41° W. on the summit. The beds appeared to be perfectly conformable throughout. GALLATIN VALLEY. 27 It will be observed that the thicknesses given in the foregoing section to the beds niindx'red 16 to 10 inclusive differ considenibly from those of the Crowfoot Ridge section The correlation of the beds seems to be correct; the error can not ])e large either in this or in the estimates of thicknesses, as the white Quadrant sandstones above and the arenaceous Jefferson lime- stones form a check on the work. This difference amounts to nearly 400 feet and is believed to occur in the upper beds of the Madison limestones. West of Quadrant Mountain and Bannock Peak the range consists of a rugged region drained by the Gallatin River. This stream, which heads in Gallatin Lake at the base of Three River Peak, flows through a valley that is one of the most beautiful parts of the park. Broad open meadows, diversified with clusters of pines and spruces, alternate with small patches of forest that cover the broad valley bottom. To the south the slopes rise steeply to the peaks of Crowfoot Ridge, while bold cliffs of white limestone wall in the valley upon the north. The river flows rapidly, in a succession of rapids and clear pebbly reaches, cutting the heavily bedded limestones that form the valley floor. CROWFOOT RIDGE AND GALLATIN VALLEY. On the west side of the ridge along which the chief stratigraphic section was studied a branch of Grayling Creek has cut a deep gulch, trending toward the northwest. This follows the outcrop of the Flathead shales, and has the gneiss and steeply dipping basal sandstone on the south side and the massive Paleozoic Ihnestones on the north. About a mile down the gulch a fault crosses the country in a direction east of north, letting down the block of sedimentary rocks and crystalline schists on the west side of the fault, so that the strata dip at a more uniform inclination of 15° to 20°, and also 30°, NE. This throws the basal quartzite at least 800 feet lower down than the west end of the crest of Crowfoot Ridge, and brings the Quadrant quartzite back to the summit of the west spur of Crowfoot Ridge, from which it extends down its northern slope. At the western base of the end of this mountain ridge the sedimentary rocks are lost sight of beneath a deep accumulation of glacial drift, which obscures the contact between these rocks and the rhyolite lava that has buried them and the underlying crystalline schists, as already pointed out. The north and south ends of the fault just noticed are lost beneath the same drift. 28 GEOLOGY OF THE YELLOWSTOJTE NATIONAL PARK. East of the high ridge along which the sedimentary section was made, abeady referred to as Crowfoot Ridge, the strata are folded and faulted in a pronounced, though not an extreme, manner. In the short spur between the two branches of the drainage east of the ridge there is a marked bend in the beds of limestone, which in the higher part of the spur di)) steeply and can be traced continuously into the main body of the ridge, but at the lower end of the spur are nearly horizontal. There is thus a short fault line west of the spur, which runs out in the head of the gulch, and probably joins a longer fault which terminates somewhere near the junction of this drainage with the Gallatin River, as shown on the map There is also evidence of horizontal thrust in the telescoping of the limestone layers, which is seen on the east escarpment of the ridge. The next spur east of the one called Section Ridge is a long low ridge, formed of nearly horizontal beds, with a slight syncline across its middle, the axis of the syncline being about northwest and southeast. At its south- ern end the beds turn up abruptly against the gneiss ridge, and the shaly horizons are eroded down, and do not rise in a high spur as erroneously drawn on the general map. Tliere is a fold or bend in the strata as they come from Section Ridge, the beds curving down towai'd the east so as to permit the strata in the low spur to lie at a low angle. This is probably accompanied hj slight faulting, with north-south trend, situated near the bottom of the drainage. It was not obseiwed, however, in the field. Between this spur and the next large spur, about a mile east, there is a broad fold in the strata. The beds that dip at a low angle of about 20° to the noi'th and northeast, arch over to an abrupt pitch with steep angle at the east side, near the south end of the east spur. This general arch is compli- cated by minor folds, not indicated on the map. The changes in dip and the differences in hardness of the shales and limestones show themselves in the topography, which is modified by glaciation. The easier degradation of the shaly layers leads to sink holes beneath stronger limestone layers. One has been made in the lowest micaceous shale, with the first massive limestone layers to the north. Farther east a small rock -bound glacial lake occurs on the gneiss at its contact with basal quartzite. North and north- east of this lake the lowest belt of Cambrian limestone forms a bench and a long slope down to the drainage, which flows west of north. Here the general dip of the strata is 30° NE. Near the lower end of the slope just mentioned are four small folds of the strata, with axes trending about UALLATIN VALLF.Y. 29 N. 10° W. The upper part of tliis drainage is located on the upper shale belt in the Cambrian, l)nt leaves it lower down the slope. The upper shale belt may be traced across country by its influence on the topography, form- ing saddles where it crosses spurs which trend north, and giving rise to lateral drainage channels, feeding larger ones running north, or forming basin-like depressions with sink holes, as already noted. The head of the gulch cut in the shale belt just mentioned is not shown on the map, but it is (|uite strongly marked, being narrow and deep and trend- ing north, and receiving the drainage of the small pond southeast of the larger lake noted above. The west wall of this gulch is formed of the lowest belt of Flathead limestone, with the lower micaceous shales of the Flathead formation to the west. At the spot where the drainage from the small j^ond falls into the deep gulch, these strata are inverted, dipping 60° or 70° W. ; strike, north and south. Hence the lower beds appear to overlie the upper ones. The gneiss is only a short distance west. The inverted beds can be traced northward into vertical beds, and then into others dipping toward the northeast. To the south the inverted beds continue in the same position until they abut against the gneiss. It is evident that there has been some faulting and displacement of the basal formations for a short distance in the neighborhood of the unconformity just mentioned. The portion of the high ridge east of the shale gulch and the ponds previously mentioned is in general a syncline with a flat anticlinal fold at its northern end, which is south of the saddle crossed by the fault to be described. The dip of the strata, which are very steep near the gneiss, changes from almost 45° NE. to 15° farther north, flattening to the syncline already mentioned. The axis of the synclinal fold is somewhat west of north, and the same fold may be observed to the southeast of this ridge. Southeast of the southern end of the ridge a drainage channel follows the line of the upper shale belt in a southeast dkection. The southern side of this drainasre is formed of the lowest massive belt of limestone, and south of this parallel gulches have been worn in the lower shale belts. These drain either through cuts across the belt of massive limestone or in sink holes beneath it. Here again the strata are inverted, with a dip of 50° to 80° SW., changing in places to vertical and also to steep dips to the northeast. Near where the gneiss ridge is faulted by the north-south fault, the basal beds of the sedimentary series are inverted, with dip of 20° to 50° SW., 30 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. and form a narrow wedge between this fault and the gneiss. The Gallatin fault, which crosses the west base of Three River Peak, trends in a north- northwest direction, crossing Crowfoot Ridge three-quarters of a mile west of Three River Peak, and crossing the ridge north of it at the saddle one mile north of the gneiss, thence following down the drainage, to die out where it joins the short fault east of Section Ridge. The trend of the fault is nearly jjarallel with that of the Gallatin River, as will be seen on the map. The maximum displacement is about 2,000 feet. The long, low, flat-topped ridge lying between this fault and Gallatin River consists of nearh' horizontal beds of Carboniferous limestone capped by the white Quadrant quartzite or sandstone occun-ing at the top of the Carboniferous series. The dip of the beds is about 5° NE. From this it is evident that there must be a fault or a fold between this ridge and the higher one east of Gallatin River. A fold exists west of Bighorn Pass, but it was not followed down the valley. On both sides of the low ridge west of Gallatin River are bodies of intrusive igneous rock, related to the dacite- porphyry of the Holmes bysmalith in composition and petrographical character. The rock is lithoidal and holds small mica phenocrysts; it is fissile near the contact with sedimentary rocks, and mas.sive a few feet dis- tant. It crosses the fault line and is found on its western side intnided in the axis of an anticlinal fold in Cambrian rocks. Its intrusion followed or accompanied the faulting. On the eastern side of the flat ridge it apjjears as an intrusive sheet, about 50 feet thick, forced between beds of Carbonif- erous limestone. This exceptional occurrence of igneous rock as an intru- sive sheet in massive Carboniferous limestone is of limited extent and is in the immediate neighborhood of a fault, with which it is dii-ectly connected. Similar rock has been intruded into the west base of Three River Peak, and it may be assumed that the Holmes bysmalith was connected with the same line of faulting. The intrusion of this mass has been shown to have been subsequent to the upheaval that permitted the intrusion of the Indian Creek laccolith; hence it follows that the more steeply upturned position of the ffneiss and Cambrian strata west of this fault was due to a later movement than the general uplifting of the body of the range. This steeper uplift was limited on the east b}^ the fault last mentioned, and by that cutting across the northwest end of Crowfoot Ridge, which faults are probably contempo- raneous and were accompanied by a slight faulting east of Section Ridge. THE GALLATIN MOUNTAINS. 31 QUADRANT MOUNTAIN, BANNOCK PEAK, AND THE VALLEY OF THE GALLATIN KIVER. In the less disturbed eastern portion of the GaHatin Range the Cam- brian and Devonian strata pass northward with a low northeasterly dij), dis- appearing beneath the more massive beds of Carboniferous limestone alone- the base of the mountains north of Panther Creek. The bold southern escarpments of Quadrant Mountain and Bannock Peak exhibit almost the entire section of Carboniferous strata, since they are topped near the summit of the former mountain by Juratrias beds. The nearly horizontal beds form massive cliffs that extend with gentle inclination along the eastern escarp- ment of this mountain, in lines parallel to the slope of its plateau-like top, and that sink beneath the level of the valley as Fawn Creek is approached. They may be plainly made out in Mr. Holmes's panoramic sketch of the Gallatin Range, PI. IV. Their character in Bannock Peak is seen in PI. VIII. From here they extend westward along both sides and the bottom of the valley of the Gallatin River, forming the cliff along its northern side and dipping at a low angle toward the southeast, while on the south they form a high ridge and the mountainous spur of Crowfoot Ridge. BANNOCK PEAK. Bannock Peak is a sharp mountain summit north of the head of Panther Creek. Resting upon the more readily eroded beds of the Silurian and Devonian terranes, the massive Madison limestones form the main mass of the mountain and are capped by the resistant beds of the Quadrant quartzite, whose white ledges form a bold escai-pment that encircles the peak. On the northern side of the mountain a section was made of the strata exposed in the wall of the amphitheater cut between this peak and the broad plateau summit of Quadrant Mountain. This amphitheater, though appar- ently open, as shown on the map, is divided by a spur pi'ojecting southward from the extreme western end of Quadrant Mountain. This section was made from the bed of Panther Creek up the center of the amphitheater to the crest of the ridge dividing this from the amphitheater at the head of Fawn Creek. The beds are exposed in a series of steps or benches, the lowest strata being the arenaceous Jefferson Hmestones, the underlying beds being covered by drift. The beds dip N. 21° W. at 8°, the determination being made on No. 4 of the section 32 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Crowfoot Num- sectioD . ber. (o) 33 23 f22 21 32 < 31, 20 as 30a, 6 12 29 11 28 10 28 9 28 8 2 26 1 Bannock Peak section. „ , Feet. White beds, sandstones and quartzites with interbedded limestone 325 Limestone, drab, finely crystalline, hard, forms knoll of saddle 100 Limestone, dense, well bedded, very light gray-brown, compact, weathered surface, very finely granular 30 Limestone, forming great ledge of amphitheater saddle. At the base this limestone is brecciated, being a gray limestone with brown and blue frag- ments. The limestone is generally splintered, the lower two-thirds well brecciated and splintered and weathering in pinnacles, recesses, etc. This weathering is further facilitated by the occurrence of great seams of caloite, 4 inches thick, and pockets of the same material. In general the rock is finely crystalline, gray, weathering gray-brown 200 Limestone breccia 10 Limestone, light gray-brown 15 Limestone, very linely crystalline, splintery, dense, light gray 15 Limestone, finely crystalline, brown, weathering same color 20 Limestone, finely crystalline, very light brown, well bedded and banded. No fossils seen 30 Limestone, coarsely crystalline, massively bedded, splintery, brownish, weath- ering gray-brown ; is fossiliferous, and forms a ledge 50 Interval 125 Limestone, coarsely crystalline, brown-gray, weathering a lighter tint. Con- tains fossils 50 Limestone, white or very light gray, crystalline, compact, massive, not splintered; with small scattered calcite crystals, weathered surface, finely granular. The upper beds are more coarcely crystalline and sometimes indurated 165 Limestone, brown, banded with darker fossiliferous layers, the rest denser; weathers with buff granular surface, often pink or light red. Breaks into fragments 2 to 8 inches across 30 Limestone, brown, fissile, contains fossils 6 Limestone, dense, blue-gray mottled with buff-brown, with occasional thin layers of coarsely crystalline limestone 100 Limestone, fissile, purple-red, fossiliferous, and resembles the limestone of the saddle of Antler Peak 5 Limestone, brecciated, fragments sparsely scattered, fossils abundant 5 Limestone, crystalline, gray, crumbly, containing fossils, weathers gray and exposes fossils and crinoid stems. Beds 2 to 6 feet thick, and strike jointed. Becomes darker and more finely crystalline near top. Strike, S. 70° W. ; dip,8°N 80 Limestone, cherty, crystalline, gray-brown, weathers light with finely granular surface, sometimes pinkish, the chert weathering a rust color 25 Limestone, crystalline, cherty, gray, thinly bedded (2 to 6 inches) ; few crinoid stems; blue chert; fossils more abundant in upper layers. Slope of beds, 70 NW 125 Interval, probably a blue limestone, crystalline, dense 50 Limestone, crystalline, light gray and gray, very arenaceous, somewhat granular, with rough, pitted, and honeycombed weathered surface. This bed underlies any seen in the east face of Bannock Peak 60 a Quadrant quartzite. THE GALLATIN MOUNTAINS. 33 QUADRANT MOUNTAIN. The broad sumrnit of Quadrant Mountain is an open and grass-covered area, above wliicli a bold pyramid formed of the red Teton sandstones rises quite abruptly. Snow fields cover the summit in early spring and remain through the summer, nourishing streams that flow in cascades over the walls of the Pocket. The upper slopes, which lie beneath the cliffs of white Quadrant sandstones, are dark with the lichen-covered debris from the overhanging walls, while the slopes beneath are thickly timbered. The sujnmit of the mountain slopes northward with an angle of 3° to 4°, con- forming very nearly to the bed of the rocks. The flatness of the mountain top is clearly due to the resistant natui'e of the Teton limestones, as the overlying clays and sandstones are rapidly removed by erosion. This mountain block is of very simple stratigraphical structure. The beds are slightly flexed, without faulting, and are undisturbed by intrusives. The beds forming it are the Madison limestones, covered by the white Quadrant quartzites overlain by the cherty beds of the Teton formation. The strata forming the mountain are clearly a continuation of those of Antler Peak and Panther Creek Canyon; on the west the bods are seen to be connected with those of Bannock Peak through the saddle of the amphitheater, while on the north the Quadi-ant quartzites form the floor of Fawn Creek Valley and pass under the slopes of Little Quadrant Mountain. Eastward the beds end in a cliff and steep slope along that north-south line which separates the sedimentaries of the range from the lavas of the plateau. The general dip of the beds is a little west of north, about 8°, so that the slope of the summit corresponds approximately to the dip of the beds. The summit of the mountain has been carefully examined. West of the Pocket the cherty Teton limestone covers the surface, which, when examined closely, is seen to be rough, gullied, and hummocked. The red hill on the summit of the mountain, southeast of the Pocket, is composed of the red Teton sandstones. This point is about 200 feet higher than the surrounding summit. On the east, south, west, and northwest these beds commence at the very foot of the hill ; on the northeast the area extends about one-fifth of a mile farther. The general summit from the red jDoint north is formed of the Teton cherty limestone and its associated lingula-bearing limestone, down to 9,200 feet, where the red beds again cover a portion of PT II 3 34 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the mountain. Eastward the cherty beds have been removed from the bench, and the white beds of Quadrant quartzite are exposed. On the summit of the 9,100-foot hill a small outcrop of the red and yellow sandstone (No. 38 of section below) is exposed. West of this hill is a deep cut, into which the small drainages of this part of the summit flow. The surface of the area covered by the red beds is generally smooth and grassy; the shales are exposed in cuts, but appear only as detritus on the summit. On all sides of the mountain the white beds of Quadrant sandstone form an escarpment, often capped by the cherty limestone. This Teton cherty limestone varies greatly in character. Often it is a cherty sandstone with little if any calcareous material in it; again it is a true limestone; and these two extremes grade into each other. The chert seems to be formed of sand, for the transition between the sandstone and the chert is often very gradual. The color is a grayish brown. Crow- foot sec- tion. Nuni ber. -39 38 38 37 37 36 o 1' 36 35 35 34 34 33 32 31 30 29 28 27 T 33 26 25 24 23 22 21 20 Section of beds exposed at the southeastern end of Quadrant Mountain. Feet. Sandstone, red and orange colored, coarsely granular, weathers in blocks 15 Calcareous shale, dark slate colored, fossiliferons 5 Limestone, bright yellow, fissile, with platy debris, grading into yellow and red spotted calcareous sandstones below 40 Shales, light greenish drab, changing to red and grading into overlying beds 75 Conglomerate of red and gray quartz pebbles in limestone matrix 10 Cherty sandstone, the lower part without chert, is brown; slightly calcareous at base, becoming more so above 100 Limestone, dense, white, weathering same color 10 Sandstone and limestone in alternating bands 15 Limestone, light gray and dense and pure 12 Quartzite, pure whi te, thin bedded, forms a persistent band along face of mountain . . 6 Quartzite, more thickly bedded, white 65 Limestone, very light gray, somewhat dense, containing very small fragments of light-colored chert 10 Quartzite, white, calcareous, with intercalated bands of limestone carrying quartzite fragments 30 Limestone, light gray, with angular fragments of sandstone 5 Quartzite, white, weathering pink and rust color, but appearing black when Been from a distance, owing to the growth of lichens upon it 130 Limestone, light gray, dense 2 Sandstone, well banded, white, saccharoidal 6 Sandstone, very calcareous, saccharoidal, white and rust color 10 Talus slope of sandstone blocks; also of cherty limestone 100 QUAUKANT MOUNTAIN. 35 Section of beds exposed at the xoutheastern end of Quadrant Mountain — Continued. Crow- foot nee- tlou. 32 Num- ber. 19 Feet. 18 17 16 15 f 14 13 12 U 31 29^ 3 30 28 28 Liiiii'stoiio breccia. Tbo lower 30 foet ia a white limestone, weathering cream, cnn- taininj; angular fragments of bine, brown, and buff limestone, from one-eighth of an inch to 2 inches in diameter. The matri.'i is coarsely granular, and grades above the first .30 feet into a crnshed and splintered limestone similar to the iniitrix Just mentioned. The outcrop is massive, rough weathering, often pinkish. Kock is slightly clierty. Dip, 12^' N. ; strike, S. 78'^ W Limestone, finely crystalline, gray, weathering light gray, with granular surface. Generally massive, though bedded at base. No fossils seen; is splintery and weathers rough Limesti>ne, very light brownish gray, splintered and cemented by calclte in strings, and by blue limestone Limestone, brecciated at the base; matrix gray, fragments angular, brown and brownish gray ; above this the limestone is massive and gray. Seamed with cal- cite and carries much of that mineral in pockets. It is somewhat cherty at the base Interval; no exposure Limestone, finely crystalline and granular, brown, somewhat cherty Limestone, very fine grained with spai'sely disseminated chert, but varying to a very coarse-grained blue-gray rock. Color in general a light brown-gray. Weathers into irregular warped plates, due to jointing Limestone, coarsely crystalline, brownish gray, weathering gray with granular surface. Irregularly bedded ; fossiliferous; much broken by vertical jointing. .. Limestone, finely crystalline, generally thinly bedded, sometimes dark gray, but mostly brown, with granular weathered surface, or a blue-gray more coarsely crystalline limestone. Dip, 5° N 10b Limestone, similar to No. 10a, but well banded. The fossilii'erovis layers weather- ing blue-gray ; the nonfossiliferous bands denser, granular, weatheriug light brown , and 1 to 3 inches thick lOo Limestone, in alternating layers of light gray, finely crystalline and darker, coarsely crystalline and fossiliferous. Dip, 4° NW .1. Interval ; no exposure Limestone, finely granular, light brown, weathering same color; fissile, contains remains of fossils. Talus indicates a greater thickness than that given Interval; no exposure Limestone, light gray, finely crystalline, with gray and granular, glistening, weath- ered surface Interval; no exposure Limestone, coarsely crystalline, dark gray, weathering the same color; fossiliferous fragments Limestone, forming a well-marked and prominent ledge extending around the mountain; massive, light drab, weathering dark gray and brown with glossy beaded crust. Contains corals and other fossils 2 Interval ; no exposure 1 Limestone, cherty, crystalline but not granular, compact, massively bedded. The upper part fossiliferous, containing crinoid stems, corals, and spirifers. Dip, about 5° N 135 65 35 50 80 10 75 25 90 10 25 25 5 10 12 65 15 45 60 60 36 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. lilTTLE QUADRANT MOUNTAIN AND FAWN CREEK YALIiEY. LITTLE QUADRANT MOUNTAIN. Nortli of Quadrant Mountain is another flat-topped elevation, known as Little Quadrant Mountain, wliich is clearly defined from tlie adjacent moun- tains by the deeply incised valleys of Fawn Creek and the headwaters of the Gardiner. The mountain is carved out of a block of Mesozoic strata, into wliich numerous sheets of andesite-porphyry, offshoots from the Gray Peak intrusion, have been injected. The resistant nature of these intruded sheets has produced the marked terracing which now forms so characteristic a feature of the southern slopes. The following section, made by Mr. Geoi'ge M. Wright, represents the beds exposed on the southern side of the mountain, the lowest strata being the brecciated limestone forming the top of the Madison limestone series, through wliich Fawn Creek has cut a small canyon at the forks of the stream: Section of beds exposed on south side of Little Quadrant Mountain. Kum- ber. Feet. 4 Sandstone 20 Interval with no exposure (broad bench about 300 yards wide) 75 Mica-hornblende-andesite-porphyry 50 3 Cherty, arenaceous, and calcareous beds : Limestone 2 Interval with no exposure 35 Cherty, arenaceous, and calcareous beds 40 Teton limestone. 77 Quadrant quartzite. 2 Sandstone and limestone : (6) Limestone, white, much of it brecciated and mixed up with sandstone 20 or 25 (o) Sandstone 175 200 Interval with no exposure r- 100 Madison ( 1 Brecciated limestone, having some layers compact, not brecciated; in walls of limestone, i miniature canyon at junction of branches of Fawn Creek 40 The total thickness of this section is not given, owing to the uncer- tainty of the exact thickness of two of the intervals above mentioned. Above the beds of the section just noted there is a long steep slope, rising 300 feet or more to a prominent cliff formed of the Ellis sandstones. LITTLE QUADRANT MOUNTAIN. 37 Another section, made by Mr. Wrij^ht, sliows the sequence and thickness of the beds from this liorizon to the summit of the mountain. Section of beds exposed on south side of Little Quadrant Mountain. Num- ber. Feet. Colorado . * Mica-horDblende-porpbyry 125+ Dakota Ellis sandstoDe. | I Ellis limestone. I 11 Carbonaceous sbalos. Interval with no exposure 100 or 150 10 Sandstone. Interval with no exposure .50 Additional interval with no exposure 175 Mica-hornblende-porphyiy several feet thick, with sandstone in small exposures below it in slope showing no other exposures. Number of feet given is height of slope 100 9 Sandstone and conglomerate. These are here overlain by the mica-horn- blende-andesite. The sectiou was again continued at a place about 100 yards southeast from the last-menC med exposure 25 Interval with no exposure 340 8 Soft gray and drab beds, weathering into light-green shales 10 7 Calcareous sandstoue and limestone 50 Interval with no exposure 75 6 Oolitic limestone 2 I Fossiliferous shales, occurring as follows: Shalef, gray, soft 15 Interval with uo exposure 60 Shales, gray, clayey, in cut of stream flowing from pass at west end of Little Quadrant Few. Limestone 30 At the west end of Little Quadrant Mountain a branch of Fawn Creek has cut back to a low divide separating this mountain from Gray Peak. The lowest beds exposed by this stream are the Ellis limestones, which are exposed in the gulch 25 feet deep near the forks of the stream. The beds dip N. 25° W. at 10°. The strata contain numerous fossils and are quite like the beds described later in the Fan Creek section. In the stream channel above, there is an exposure of very fissile calcareous sandstone in a ledge 5 feet thick, which is overlain by very arenaceous, granular, cross- bedded, gray limestone, containing fossils which are mostly comminuted and broken. This exposure is 20 feet thick, and the bed is overlain by a sandstone containing a few scattered pebbles. The strike is S. 35° W., and the dip is 10° NW. Above this the stream flows over a small exposure of Dakota conglomerate, which is overlain by andesite-porphyry, forming a cliff 75 feet high, over which the stream flows in a succession of cascades This rock, which is an extension of the Gray Peak intrusion, is hornblendic, 38 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. generally much decomposed, and shows no megascopic mica. This por- phyry forms a bench north of the stream which extends back to the base of the cliffs where Dakota conglomerates occur. In the stream channel a brownish-gray sandstone speckled with black, and belonging to the Dakota series, is overlain to the east by the andesite-porphyry, forming the two 9,000-foot hills shown on the map. These higher beds, forming the west end of Little Quadrant, are tilted up by the porphyry intrusion. The following section, made by Mr. Wright, shows the sequence and thickness of the beds exposed in ascending the creek, the beds being given in descend- ing order. The thicknesses are estimated and approximate, and are given in feet: Num- ber. Section on north side of head of Faion Greek Valley. Feot. Dakota ... Ellis Bauds tone. Ellis limestone. Teton limestone. Quadrant quartzite. 50 50+ 50 {Mica-hornbleude porphyry ..."| Limestone > 300 Mica-hornblende-porphyry ...J 7 Sandstone 6 Conglomerate ^ Interval with no exposure ^) Sandstone Few. Hornblende-porpliyry, in sloping belt across an interval 165 4 Sandstone, very calcareous 15 3 Limestone, very arenaceous 25 Interval with no exposure— steep slope 365 Mica-hornbleuile-porphyry 40+ Interval with no exposure 100 2 Cherty, arenaceous, and calcareous beds 35+ Interval with no exposure 100 1 Sandstone in bed of Fawn Creek. Total thickness of section 1, 295+ Total thickness (approximate) of intruded porphyry 505 Total thickness of sedimentary rocks and intervals 790 The slopes on the northern side of the west end of the mountain show a succession of beds very similar to that of the section just given. The meas- urement made of the series from the Dakota conglomerate to the summit of the ridge showed the 100 feet of conglomerate and sandstone, which was assigned to the Dakota, overlain by 45 feet of compact gray limestone considerably altered by intrusive sheets of porphyry, which occur both above and below the bed and also spKt it in half. The overlying sand- stone, which forms the summit of the Dakota series, is a pure white, rather FAWN CltEKK VALLEY. 39 soft and fine-grained, massive bed, whose outcrops often weather a light- brown. The thickness is 50 feet, and it is overhiin by carbonaceous shales which are (juite arenacetms at tho base and become more argillaceous above. These beds form the cliffs extending eastward around the sides of the crescent-like amphitheater cut in the northwestern wall of the mountain. The black shales extend eastward along the crests of the cliffs of the crescent ann)hitheater for nearly a mile, when they break down and the sandstone forms the summit of the cliff. In the northwestern slopes of the mountain, sandstone is exposed in nearly all the lateral gullies and stream channels, the upper sandstone bed of the Dakota being especially prominent and forming a persistent ledge that extends ai'ound the north spur of the mountain and constitutes the wall of the amphitheater cut iu its eastern face. Beneath the cliffs which form the wall of the northwestern part of the mountain an andesite-porphyry sheet has furnished the material for a great morainal accumulation of ang-ular rocks, concealing all expos- ures and rendering travel difficult. The persistent nature of these andesite- porphyry sheets is shown by their occurrence iu so many localities at the same stratigraphic horizon. In the stream channel noi'th of Little Quadrant the sheet of andesite-porphyry occurring between the Dakota limestone and the conglomerate is well exposed at 9,000 feet. In the vicinity of the lakes at the head of the valley the porphyry forms low rounded knolls, whose surfaces are scored and polished by glacial action. The lower slopes east of Little Quadrant have been carefully examined, but the morainal drift obscures all outcrops. FAWN CREEK VALLEY. The valley of Fawn Creek shows good exposures of the Carboniferous rocks, overlain by the softer Mesozoic series. In a little gulch near the forking of the creek, the Quadrant quartzite series is well exposed. On the south fork of the stream, just above this junction, a green magnesian bed, whose surface is red from the wash of the weathered outcrop, is also exposed. The overlying bed is a dark pm-plish-red rock spotted with green, highly ferruginous and argillaceous, being a very impure dolomite. This rock is overlain b}^ an outcrop of brecciated limestone, which is believed to repi'esent the highest bed of the Madison limestone series. This brecciated character and the granular weathered surface of these 40 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. limestones are persistent features of the upper beds of the IMadison series in this vicinity. These beds are overlain by the white Quadrant quartzites, which are well exposed in the stream channel. In the bottom of the amphi- theater at the head of Fawn Creek, a coarsely crystalline brown Hmestone is well exposed. The rock is fossiliferous, but the fauna presents no features different from those of the underlying limestones. The beds dip 10° N. The amphitheater floor is heaped up in places with great piles of debris, but presents many smooth exposures of a dark, slaty limestone and of the coarsely crystalline rock just mentioned. In the latter there are numerous large sink holes or "swallow"^ holes, in which the waters flowing from the snow banks of the amphitheater walls pass underground, to reappear two miles down the valley as a large stream which forms the headwaters of Fawn Creek. The section of beds exposed in the amphitheater walls to the east has already been given in the account of Quadrant Mountain. Nowhere is the character of the Quadrant quartzite and of the immediately underlying Madison limestones better shown than it is in the walls south of Fawn Creek Valley. The sections which have already been given show the relative thickness of these beds and the development of the impure argillaceous dolomites whose red ledges form so prominent a feature of the rock outcrops. A comparison of the sections of the Quadrant quartzites made on the walls of Quadrant Mountain is given in the following table. A precise separation of the sandstones from the interbedded limestones is not always possible. Many of the sandstones are very calcareous, and in some cases would perhaps be classed as arenaceous limestones. I Handbook of Physical Geology, A.. J. Jukes-Brown, p. 87, London, 1884. REGION NOltTII OF (iALLATIN RIVER. Com})ari8on of sections of Quadrant formation. 41 "Pocket." Feet. "Amphitheater." Feet. "yiiailninl." southeast corner. FePt. r, q. Sandstone 15 Sandstone with in- r. Limestone 10 p. Limestone 6 terhodded 1 i m e - p, (/. Sandstones . ^ 15 5 stone 265 0. Limestones . S n. Limestone 15 n. Limestone 12 m. Sandstone 18 k-m. Qnartzite 71 1. Limestone 2 j. Limestone 10 k. Sandstone, etc . 148 /. Limestone 4 i. Limestone h. Limestone 30 5 209 e. Sandstone 3 f,f,9- Qnartzite 130 272 283 d. Limestone 2 d. Limestone .. .. 2 c. Sandstone 6 c. Sandstone 6 h. Lime.stone 10 b. Limestone 10 a. Sandstone 36 a. Talus 100 326 401 Madison limestones beneath above series. On the summit of the ridge west of Fawn Creek amphitheater, the Teton limestone is well exposed, the dip being 15° and the direction N. 26° W. These beds are undoubtedly tilted by their proximity to the Gray Peak bysmalith mass, although the tilting is not uniform, as the red sandstones forming the hill farther north have a dip of but 10° in the direction N. 15° W. REGION NORTH OF GALLATIN RIVER. As already pointed out, the escarpment wall on the north side of Gallatin River consists of massive Madison limestones topped by the white sandstone or qnartzite of the Quadrant formation. These beds dip at an angle of about 10° NE. throughout the greater part of the distance, having a more northerly dip in the vicinity of Bannock Peak, and at the western end of their exposure curving over from a northeasterly to a northwesterly dip of 5° to 10°, bending down toward the profound fault plane that bounds them on the west and brings them against subaerial breccias of andesite. Within the limits of this low anticlinal arch the sandstone is in places broken and polished with slickensides accomjDanying slight displacement 42 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. of the rock. A well-marked bench occurs along the top of the steep slope or escarpment, its surface in places sloping with the dip of the strata. It is most pronounced when above the harder beds, especially where these are overlain by the more friable sandstone and soft shales of the Juratrias formations. The bench is well developed on both sides of the drainage channel running west from Fawn Pass. Upon entering the terrane of the Juratrias formations, which are mainly fissile limestones and shales, passing down- ward into the sandstones of possible Triassic age, and passing upward into the friable sandstones underlying the Dakota conglomerate,' we again encounter intruded sheets of igneous rock. These intrusive sheets are nearly conformable with the sedimentary strata, following the shale belts for long distances, and only occasionally breaking up across the strata to follow higher horizons. The first of these intrusive sheets met with above the Carboniferous limestones occurs in the base of the Juratrias shales below the Ellis shale beds, and forms a cliff rising above the bench west of Fawn Pass. The sheet of aiidesite-porphyry is possibly 200 feet thick at this place. It can be traced west and east from this exposure, con- tinuing at nearly the same horizon. The shale in contact with the poi'phyry is more or less baked, and, like the igneous rock, resists erosion better than the altered shales, thus leading to the formation of blutfs or ledges. Above this porphyry cliff the country slopes gradually and stretches eastward to Fawn Pass, rising abruptly to the triangular peak 1^ miles southwest of Gray Peak. This comj^aratively level country occupies the axis of a flat synclinal arch that dips to the northwest. The strata bend around from the gentle northeast dip through a northwesterly one to a southwest dip of 15° to 20°, in which position they form the triangular peak just mentioned. It is evident, from a study of the region, that this southwesterly dip is due to the intrusion of a large body of igneous rock connected with the bysmalith of Gray Peak. The highest sedimentary rock in the triangular peak is Dakota conglomerate. It occurs again high up on the west spur of Gray Peak, where it dips toward the northeast. The ridge between these points traverses an anticlinal arch of Jurassic beds that bend over the igneous mass already mentioned. The shales include at least two thin sheets of igneous rock, each from 40 to 100 feet thick. One of these, in the mass of the triangular peak, thins out perceptibly toward the REGION NORTH OF GALLATIN RIVER, 43 southwest. The coiTesponding intrusive sheets beneath the Dakota con- glomerate in the southern slope of Gray Peak thin out towai-d the east, and near the end of the spur one of them breaks upward as a dike-like body across the Dakota conglomerate. The porphyry forming the axis of this small arch extends south, constitutmg the ridge of Fawn Pass. It extends east down the valley of Fawn Creek as an intrusive sheet near the base of the Juratrias shales, and extends south of Fawn Pass as an intrusive sheet at the same horizon, and has been traced as a ledge along the ridge south and westward to the cliff first described north of Gallatin River. It becomes thinner as it is followed farther from the bysmalith, and it is e\'ident that the intrusive sheets in this vicinity proceeded from the Gray Peak intrusive mass. The sedimentary beds forming the mountain side south of Gray Peak dip into the mountain toward the north and northeast at a low angle and encounter the igneous rock of the bysmalith which forms the highest portion of the mountain mass from Gray Peak to Joseph Peak, and extends down the east slope to a level of 9,000 feet and down the west side to below this altitude. The igneous rock extends along tlie north face of the ridge west of Gray Peak. From it also proceed sheets of porphyry intruded between the Juratrias strata which are exposed along the south face of Little Quadi-ant Mountain and may be traced around the northern slopes. On the northern side of the mass the sedimentary beds dip- toward the southeast, into the igneous core Again, as at the southern side of this body, the highest horizon is that of the Dakota conglomerate which is found at the summit of Joseph Peak in contact with the intruded mass. As may be seen from the map and cross sections (Pis. IX and X), there is a quaquaversal arching of the strata, the center of which is located in the head of Fan Creek, northwest of Joseph Peak. From this point the beds dip south, southeast, east, northeast, north, and northwest. In the three valleys heading against the ridge surrounding this arch the beds dip to the east, northeast, and north at angles not far from 10° — in some cases reaching 25°. At the west end of the ridge north of this part of Fan Creek, the beds arch over to the west and southwest with a dip of 20°, and pitch against the same fault plane noted north of Gallatin River which let down the volcanic breccia. Between the sedimentarv strata, sheets of andesite- 44 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. poi-phyry have been intruded exactly as on the southern and eastern sides of the bysmahth. The lowest one exposed, however, is beneath the Juratrias beds, immediately above the Carboniferous limestone. It appears around the head of Fan Creek, thinning- out northward. Within the Ellis shales, beneath the Dakota conglomerate, there are five thin sheets of intrusive rock on the northern slope of Joseph Peak. Three of these have been recognized north of the saddle between Fan Creek and Gardiner River. They grow thinner and less noticeable to the northwest, and may be traced down the east slope of Joseph Peak, where, on account of the position of the beds, they form isolated patches. These sheets vary in thickness from 16 or 20 to 100 feet. Above the Dakota conglomerate and sandstone, the shales and sand- stones that alternate with one another through a thickness of nearly 3,000 feet, constituting the Colorado and Montana formations, take part in the quaquaversal arching already described — that is, on the northern side. On the south they have been removed by erosion. In the ridge noi'th of Fan Creek they dip to the northwest and north, curving over to a northeasterly dip in the ridge connecting this with Electric Peak, throughout which latter ridge they maintain a generally uniform dip to the northeast, con- tinuing the same attitude beyond the boundary of the Yellowstone Park to the synclinal trough at Horr. In the ridge between the head branches of Gaidiner Kiver, these beds curve from an easterly dip near its west end to a northeasterly one farther down the ridge, and in Little Quadrant Mountain they also maintain a general northeasterly dip, as already noted. The alternation of shales and sandstone layers seems to have been particularly favorable to the intrusion of sheets of igneous magmas. The fissile shale offered numerous planes of weakness and parting, while the sandstone layers tended to stifi"en the strata and cause the splitting to follow more nearly constant horizons, for though there is some cross fracturing of the sedimentary beds, where the igneous rock may be seen crossing the strata to higher horizons, yet the persistency of the intrasive sheets is one of their marked features. This is observed both upon actual exjjosures over long distances and upon the comparison of geological sections made across the strata by several observers in numerous localities. In the ridge north of Fan Creek the Colorado shales form the northern slope and steep spurs and a small portion of the western end. Directly THE FAN. 45 above the Dakota oong-lonierate tlie shales are spht by two thin sheets of aiidesite-porphvry, and also by a massive layer that appears as a small lac- colith constituting- the northwestern end of the ridge. The petrographical character of the sheets is not the same in all cases, but the distinctions are slig-ht and will be discussed in Chapter II. In the high ridge between the head branches of Gardiner Kiver, at least five different sheets of andesite- porphyry were observed, having the general dip of the shales and sandstones, with occasional ruptures across the beds. They were also found crossing the valley to the north and forming part of the ridge leading to Electric Peak, as represented on the map. Their thicknesses are not constant, as may be seen in their exposui'es, but the actual variation is greatly exaggerated in appearance by the positions of the exposures, whether directly across the thickness or more or less parallel to the sheet. This impression is still further increased by the appearance produced by the more persistent talus slopes of the harder porphyry, which often obsciire more easily removable areas of the softer shale. The same sheets occur in the shales in the upper part of Little Quadrant Mountain. THE FAN. Fan Creek drains the mountainous area whose various spurs converge to the west at the ribs of the Fan, from which resemblance the region derives its name. The encircling ridge which forms the divide between the waters of Fan Creek and those of the Gallatin and Gardiner drainages culminates in two prominent peaks, one of which. Gray Peak, has already been described. The other, lying to the north, is named Joseph Peak, and occupies a commanding position just west of Little Quadrant Mountain. The southei'n fork of Fan Creek is named Stellaria Creek. At the head of this stream the high ridge which is the southwestern extension of Gray Peak is formed of Mesozoic beds, having a strike of N. 20° E. and a dip of 10° W. The peak is formed of Dakota sandstone resting upon the Jura- trias beds, and is cixt by intrusive sheets of andesite-porphyry from the Gray Peak bysmalith, as already described on page 42. 46 GEOLOGY OF THE YELLOWSTONE NATIONAL TARK. The following section represents the beds exposed on the northern slopes of this ridge at a point just west of the 9,900-foot peak: Section at ridge southwest of Gray Peak. Num- ber. Feet. 3 Dakota conglomerate and sandstone; pebbly in layers, but much of it a fine-grained sand- stone, buff with red and white blotches, and cross bedded 60 2 Shaly beds, very arenaceous and light brown at top; softer and more argillaceous below, where the layers are generally a blue-black and contain some splintery limestone. The typical rock is a soft argillaceous sandstone, light gray, weathering brown 50 Andesite-porphyry, dark gray, compact; rock occurring irregularly columnar in ledges, with two or three layers of brown altered porphyry with fine concentric weathering 35 1 Limestone, gray with rusty speckling, saccharoidal texture. The upper 8 feet soft and purple shale, weathering brown 18 Strike, N. 20'^ E. ; dip, 8^-10^^ W. On the west side of this peak, 100 feet below the summit, the black shales are well exposed and form the crest of the ridge down to the saddle. West of the saddle they give place to the Dakota sandstone, which extends westward to the cliffs indicated upon the map. Farther west the ridge shows a succession of light-gi-ay limestones overlying the red Teton sand- stones. The latter beds form red slopes that extend westward to the andesite-porjihyry hill shown upon the map. The central ridge of the Fan, lying north of Stellaria Creek and west of Joseph Peak, is a long flat-topped mass with grassy meadows and dense forests of pine. On the western end of this ridge exposures are scarce and must be sought for in the stream channel. A short distance above the forks of Fan Creek, Stellaria Creek has cut a gorge through the intrusive sheet of andesite-porphyry. This rock is also exposed on the south slopes of the ridge to the north for a distance of 2^ miles above the mouth of Stellaria Creek. The rock is generally much decomposed, of a light-buff color, with numerous decomposed acicular hornblende and white plagioclase phenocrysts. The porphyrj^ forms great heaps of tabular dc^bris, often arranged in ridges running apj^roximately east and west and separated from the solid rock by the hollows between the cliffs and these morainal ridges. These hollows are often without outlet, and sometimes hold small ponds. From the junction of the stream eastward the summit of the ridge shows no outcrops of sedimentary rocks, the covering of the porphyry sheet just noticed having been removed by erosion and the summit being now hea\aly mantled with glacial drift, which seems to be at least 100 feet thick in the JOSEPH PEAK. 47 transverse drainage channel. This transverse drainage channel, which runs northward to join Fan Creek, forms the natural boundary line between the sedinientaries on the east and the andesite-porphyry on the west. The sedimentary rocks are light-gray limestones, having a strike of S. 20° W., and a dip of 10° W., which would carry the beds under the drift forming the summit of the ridge to the west. The higher slopes to the east show good exposm-es of the sedimentary rocks. A western spur of Joseph Peak shows the following section of sedimentary rocks, the lowest bed exposed being part of tlie Quadrant quartzites. Joseph Peak section. Num- ber. Feet. {5 Ked bed.s, calcareous sandstones, etc. 4 Sandstone and limestones, fissile, gray, weathering brown-gray 25 3 Limestone, gray, compact 10 Teton > limestones \^ Cherty sandstones and limestones 100 Quadrant niiart?itps ' ^ Sandstones, quartzites, and interbedded gray limestones 300 > 1 Sandstones, quartzites, and interbedded gray limestones . At the base of this spur the summit of the ridge is nearly flat and is largely strewn with chert weathered out of the Teton limestones. The beds here apparently dip SE. 10°, Avhich takes them underneath Joseph Peak. The cherty beds of the Teton series are here quite well exposed. The chert occurs in both banded and nodular forms, and is so abundant that the remaining material, which is generally sandstone, forms but a minor feature. In seams and patches, however, the rock is free from chert, and is then much more calcareous and contains fragments of fossils. North of the spur from Joseph Peak the Teton limestone beds dip W. 8°, and strike S. 8° E. Farther north the flat summit of the ridge is formed of a fine-grained andesite-porphyry, whose rust-colored exposures much resem- ble those of the sedimentary rocks. This rock forms the summit of a bold cliff to the north. This cliff", which is about 500 feet high, shows excellent exposures of the Quadrant quartzites resting upon Madison limestones, forming the channel of Fan Creek, and capped just beneath the andesite- porphyry by the cherty beds of the Teton series. This exposure shows a total thickness of 350 feet of Quadrant quartzite and 125 feet of the Teton limestone. The character of the cherty limestones varies from a dove- colored, nearly pure limestone to a granular brown sandstone which is not 48 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. calcareous. The talus at the base of the cliffs, like that of the andesitic intrusive of Stellaria Creek, is arranged in morainal ridges, with a depres- sion between these heapings and the base of the cliff. The valley of Fan Creek has been cut in the low anticline, exposing the Madison lime- stones overlain by the Quadrant quartzites, with the softer Mesozoic rocks forming higher slopes to the north. In the small drainage cutting the slopes north of the creek the following section was measured: Fan Greeh section. Num- Feet, ber. ( 15 Dakota conglomerate and sandstone, the latter gray, with white spots, * °'" (14 Sandstone, rusty yellow, blotched with piuk, slightly calcareous 125 (•13 Limestone, dark gray, crystalline 5 12 Limestone, fissile and shaly, gray 15 lie Arenaceous limestone, gray, crumbly, rusty 1 EDig 116 Sh.iles and crumbly limestones 2 sandatoue. 1 Ha Limestone, crysfcilline, gray, dense, splintery, argillaceous 1 10 Arenaceous limestone, or calcareous sandstone, light brown-gray 15 9 Limestone, grading at top into No. 10. The limestone is pure and full of fossils 15 8 Limestone, argillaceous, soft, crumbly 10 7 Argillaceous limestones, crumbly, containing fossils, and with interbedded layers of harder crystalline limestone 140 6 Red shales 20 5 Green and blue shales 30 4 Interval (?) 3 Cherty beds 125 2 AVhite sandstones, etc 300 1 Limestone, crystalline, creamy, with patches of red magnesian limestone 30 Ellis J limestone. | Teton I shales. | Teton ) limestone. \ Quadrant ( quartzite. ^ Madison limestone The summit of the ridge north of Fan Creek, already mentioned on page 43, forms what might be termed the northern rib of the Fan and is capped by Dakota beds, whose persistent nature, combined with that of the intrusive sheets of andesite-porphyry, has left the ridge sharply defined. The Dakota conglomerate is but 20 feet thick and is overlain by buff-colored and pink sandstones similar to those mentioned in the section just given. At the head of Fan Creek a depression in the mountain ridge forms a pass to the headwaters of Gardiner River. The western slopes of this pass are thickly covered with soil and vegetation, and no exposures are seen, but to the east the beds are well exposed where the streams from the snow banks of the ridge have washed the surface of the rocks bare of Ellis limestone FAN.PASS. 49 soil. The saddle itself is toniu'd of liiuestoues broken throiiii-h hv juidesite- porphyr\-. The folhtwiug- section shows the series of beds exposed from the pass to the snnnnit of the peak to the north: Fan I'ass section. Num- l"r. Feet. Dakota. S Dakota coiiu'lomerate and saudstono; creamy, pink, broken tlirongli by an- de.'iite porphyry ^0 ( 11) I>iniestone, bard, gray, crystalliuo, weathering brown 10 7« Limestone, granular, arenaceous, light drab 15 Ellis J (! Limestone, more or less arenaceous in certain bauds, fossililerons. Strike, sandstone. 1 N.45-' W.; dip, 2.")- N 75 I oft Limestone, soft and sandy ; 1q \ 5a ]>imestone, arenaceous, gray-brown 5 I ib Ked shale, crumbly and soft g in Sliite ; metamorphosed by audesite-porphyry 2 .Vndesite-jiorphyry- 3 Limestones, soft, crumbly, very argillaceous, with harder crystalline layers; very fossil iferons 5g 2 Limestone, finely crystalline, weathers brown, somewhat slialy 5 1 Limestone, shaly, broken through by andesite-porphyry 45 To the east of Fan Pass an extension of the anticlinal uplift noted to the west brings up the red shales and sandstones from the upper portion of the Teton formation. From the summit of the mountain peak north of Fan Pass the ledge extends in a northwest direction until it meets the long southwestern spur of Electric Peak. The Dakota conglomerate forms the crest of the ridge as far as the second peak north of Fan Pass, and, as already noted, the same rock extends westward, forming the crest of the encircling ridge The summit of the second peak north of Fan Pass is formed of andesite-porphyry. This rests upon Dakota conglomerate and is overlain by cherty limestone, which is apparently part of the Dakota limestones, but is of different habit and carries light greenish-yellow chert. Between this point and the 10,100-foot peak to the northeast a succession of beds is exposed in which the shales are cut by intrusive sheets of andesite-porphyry. The Dakota limestone, somewhat metamorphosed, but •showing the crystalline marks and the little gasteropod shells so character- istic of this horizon, is overlain by very splintery greenish-yellow shale, weathering brown. This in turn is capped by a baked sandstone about 20 feet thick, which is overlain by the upper quartzite belt of the Dakota series, the bed being here 30 feet thick. The carbonaceous shales of the Benton formation form the ridge from this point eastward to the slopes of MON XXXII, PT II 4 50 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Electric Peak. The shales are cut by numerous intrusive sheets of andesite-porplivry and b}' a few dikes, one of which cuts the 10,100- foot peak already noted. In the sandstone bed intercalated in the lower part of the Benton shales the little oyster, Ontrea anomioides, occurs abundantly. The beds here have a dip of 10° N., the strike being N. 75° E. The andesitic sheets noted on this ridge ai-e continuous for long distances, their ledges being traceable along the slopes ou either side of the ridge. In general, the andesitic sheets, being less easily eroded than the soft black shales, form the high points and mountainous summits of the ridge, while the saddles are cut in the softer rocks. ELECTRIC PEAK. Electric Peak is the highest and most imposing summit of the Gallatin Range. Its apex rises boldly above the adjacent mountains, and the long ridges which form its foundations dominate the country for many miles. The mountain is composed of sedimentary rocks of Cretaceous age, broken through and in part largel}' altered by igneovis rocks. The sedimentary rocks only will be treated here, as these igneous rocks and their occurrence are of such interest that a special chapter is devoted to them. The sedimentary rocks composing the mountain embrace the most recent strata of the sedimentary series to be found in the Gallatin Range, including a thickness of 4,300 feet of Cretaceous beds, whose uppermost portion is coal-bearing and belongs to the Laramie. Complete sections may be studied at two localities. One is the southeastern spur of the peak, where the beds are sharply upturned against the Gallatin fault; the other is the long northern ridge of the peak which terminates in that mass of upturned and exposed strata known as Cinnabar Mountain. Although the latter locality lies just outside the limits of the Park, the section there exposed is typical for the region, and, combined with the sections already given of the Teton, Ellis, and Dakota formations, it forms a complete sec- tion of the Mesozoic strata of the range. Section of beds exposed on southeast sjmr of Electric Peak. Nam- ber. f 22 Carbonaceous sliale '40 Anilesite-porphy ry ■10 Feet. s g ' 5 ' Carbonaceoiis shale 100 « o Andesite-porpby ry ^0 I Carbouaceous shale 300 .500 9 U S GEOLOGICAL SURVEY MOHooFAPH XXXII, fart:; ?L ll< CROWFOOT RIDGE OUNT HOLMES EMIGRANT PEAK THE CRAGS «gn SEPULCHRE MOUNTAIN ELECTRIC PEtt- GRAY PEAK JOSEPH PEAK ELECTRIC PEAK EMIGRANT PEAK SEPULCHRE MT- GEOLOOICAL SKCTIONS ACHOSS CALLATLX HANOK I.KIVKNL) CRETACEOUS JURATRIAS CARBONIFEROUS CAMBRIAN ik/h i^' h B H Hi' 'CK Scale oF Miles r^y^ ELECTRIC PEAK SECTION. 51 Scctimi of beds c.qjoscd on southeast spur of Electric I'eal- — Continued. Niini- bor. 21 Cnlcareous saiidstonos, chan;;ing to pure Siindstoues at the bottom 20 S;iii(lsti)iio, mottled and carbonaPrDiis ly Sandstone, indurated and argiUaeeous , 18 Sandstones, speckled Andesite-porpliyry, much decomposed 17 Calcareous sandstone 16 Sandstone, indurated, argillaceous Andesite-porphy ry Interval, no exposure 15 Limestone, very impure, argillaceous and arenaceous Interval, no exposure 14 Indurated sandstone 13 Shales, very dark slate-colored, argillaceous rocks which are poorly exposed 12 Sandstone, indurated to granular quartz ite 5 Interval, no exposure 75 Indurated sandstone 10 11 Lio f 9 r 6 I 5 W I i: J ^ V Sandstones and arenaceous limestones, -with two intruded sheets of andesite-por- phyry aggregating 15 feet in thickness Interval, no exposure, hut showing debris of dark-colored carbonaceous shales belonging to bed helow Andesite-porphyry, much decomposed Carbonaceous, argillaceous shale Sandstone Interval, no exposure Limestone Interval, no exposure Conglomerate and sandstone, broken through l)y andesite-porphyry Arenaceous limestone Arenaceous limestones, passing downward into sandstones, cross bedded, and chang- ing to limestones near base Interval, no exposure 4 Sandstone, dark gray, mottled with carbonaceous matter, fine grained and not indu- rated Interval, no exposure 3 Limestone Interval, no exposure 2 Quartzite and highly indurated calcareous sandstones ^) IS L Limestone, light cream colored; bands of red limestone exposed along north bank of Gardiner River, 200 feet below top Limestone, brownish gray, dense Ft-et. 175 1)1) 20 10 15 30 50 30 10.) 10 100 10 300 (10 160 300 15 100 20 50 5 50 5 45 50 5 100 100 15 200 250 50 Total thicliness of section. Thickness of intrusive sheets 3,47« 148 Total thickness of sedimentary rocks •. 3, 330 52 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The audesite-porphyvies of this section occur as sheets intruded along the planes of bedding- of the sedimentary rocks. With one exception intrusion is regular and does not break across the bedding planes of the shale. The dip and strike of the beds vary in passing upward from Gardi- ner River to the summit of the peak. In many cases this change of dip is apparent in the exposure, but in most cases the outcrop is not suffi- ciently extensive to make the flexure apparent. The long southwestern spur of Electric Peak, which has already been noted, shows sheet after sheet of andesite-porphyry cutting across the crest of the ridge and intruded in the dark shales of the Colorado formation, the beds dipping NE. about 10°. Three different bodies of andesite- porphyry have broken through one another in the high point southwest of the peak. One of these intrusions may be traced eastward along the southern slope of the mountain for some distance. The western slope of the mountain shows the sedimentary and igneous layers in strong relief, and they may be distinguished at a distance. The inclination of these ledges is about 10° N., corresponding to the greater dip, which is to the northeast. The sheets of igneous rock are seen to follow the bedding planes of the strata for considerable distance. Only one sheet was seen break- ing up across the strata and proceeding along the higher horizon. The direction of this uprising is from sovith toward the north, and this occur- rence, together with observations made on the eastern side of the moun- tain, showing a similar rise from the west to the east and a thinning out of the sheets in the same direction, indicates that these intrusive masses were injected from the southwest— that is, probably from the center occu- pied by the Gray Peak bysmalith. The intrusive sheets vary from a few feet to a hundred or more feet in thickness. The rocks differ slightly in petrographical character and will be described more fully in Chapter II. The peak itself is formed of the soft shales and thinly bedded sandstones belonging to the Colorado and Montana formations. These rocks are penetrated by a number of intrusive dikes of andesite-porphyry, and the sedimentary series is much altered by the great intrusion of igneous rock forming the volcanic core east of the peak. On the summit of the peak the normal sandstones and shales are altered to slates and quartzites, the rocks being much shattered by joints and breaking readily into short, angular ddbris. The beds dip N. 10° to 20°. ELKCTUIC PEAK, 53 The intrusive sheets extend, in Jiininishin<>' numbers, northward in tlie north ridge of Ek'ctrii' Peak. The}' i-esenibk^ the sheets intrudei PLEISTOCENE CRETACEOUS LEGEND JURATRIAS CARBONIFEROUS DEVONIAN SILURIAN Phs Pal Pgd Km Kc M ' Je " Jt ' Cq 'i Cm tfr: Sj Hot Springs AUnviran. Glacial Montana Coloraflo Dakota Ellis Totoii Quadrant Madison formation drift. formatioii-. formatioii. fomiatioiL formation, formation, formation, limestone. CAMBRIAN NEOCENE EOCENE Thi"eot()rt(s limestone. ARCHEAN JetfersoH limestone. H Nbst Nrh Nel Nebb Eeab dp anp -fl^n — Gallatin PJathead limestone, formation- Basalt. Rliyolite. Khmiiir Kersanlite. Earlv basic f^ailv acid UaciUi- Andtisite- intrusives. breccici. breccia. porphyry, porphyi'y. Graiiilo and s^nciss. Yaoilts. ^-^-^£-^-S- Scale 12SOOO ■ f f ? CONTOUR INTERVAL lOO FEET. MADISUN liANGE. 57 sedimentary strata and their tilting' iKirthward, followed by extensive erosion at the south prior to the extravasation of tlie andesitic breccia. We have already jjointed out the connection between the hitrusion of the Holmes bysmalith and the fault traversing the eastern end of Crow- foot Rido-e, noting their probable contemporaneity. The intrusion of the Holmes mass nuxst have been followed by extensive erosion before the cr'S'stalline schists were exposed at the level they now occupy relative to the Holmes mass, after which erosion the andesitic breccias were thrown ujjon them. This separates the eruption of the Holmes bysmalith and that of the andesitic breccias by a very considerable length of time. No definite time relation has been made out, however, between the two great intrusive bodies at the southern end of the Gallatin Range — Indian Creek laccolith and Holmes bysmalith — and the more complex intrusion of Gray Peak and the associated sheets of andesite-porphyry in the northern part of the range. Though separated by only a small distance, there is no structural feature which connects their intrusions in point of time, except the general fact that the}^ are all much older than the eruptions that centered at Electric Peak. EASTERN FliANK OF THE MADISON^ RANGE. In the extreme northwestern corner of the Yellowstone Park there is a small area of mountainous country that is part of the eastern flank of the Madison Range. This area lies wholly within the Montana portion of the reservation. The Gallatin River has cut a narrow valley across this tract, exposing folded strata, in which the same sedimentary series seen in the Gallatin Range is developed, the lowest rocks belonging to the Cambrian and the highest being of Colorado Cretaceous age. These strata are flexed about a laccolith of andesite-porphyry. This mountain area is terminated on the south by the northern end of the rhyolite plateau, whose lavas cover the southeastern flanks of the high mountain east of the Gallatin River and also occur in small isolated patches upon the mountain slopes to the north and west. Topographically this little tract consists of parts of four distinct moun- tain masses. The largest lies east of the Gallatin and is embraced between that river and Fan Creek. This block and that north of it, and the flat- topped mountain west of the Gallatin River, are all parts of the lacco- lithic uplift, which has been cut through by the river. The east bank Three Forks and Jefferson. 58 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. of the Gallatin shows an excellent exposure of the contact between the andesite-porphyiy and the Cambrian shales, the latter being altered by contact metaniorphism for a few feet from the andesite-porphyry. The Cambrian shales are overlain l^y limestones in which there are intruded several sheets of andesite-porphyry, and are capped by cliffs of a heavily bedded white limestone of the Madison formation, with basic intrusions, near tlie summit of the mountain. The following partial section shows the series found immediately above the laccolith : Section east of Gallatin River, below Fan Creel: Feet. Madison. Limestones carrying cdrals, thickly bediled, of a dense texture, drab or dark-gray colored, and holding black chert. Limestone shale of pink, red, buff, and pnrplish colors, carrying a few fossils and underlain by dark-blue (almost black) limestone 200 Andesite-porphyry, poorly exposed 25 Granular, dark-brown and black limestone, sometimes banded, and of Silurian aspect 15 Thinly bedded and fissile light-gray limestone, dense and not crystalline, impure and carrying argillaceous matter 5 Uark-colored granular limestone, carrying Obolella 12 Limestone, thinly bedded and with a knotty texture, dark blue in color, of typical Cambrian aspect, and evidently of shallow-water origin 30 Limestone shale, blue and olive gray in color 5 Limestone, dense in texture and dove colored 5 Limestone, becoming shale ; dip mO"^ to the east 5 Shales, green or olive colored, seldom exposed 15 Limestone, mottled, of typical Cambrian aspect 15 Shale 5 Andesite-porphyry laccolith. West of the Gallatin River the mountain slopes show andesite-porphyry extendino- up nearly to the summit of the flat-topped mountain, but the stratified rocks are seen both to the north and to the south, forming great cm-ved plates, with dip away from the intrusion in every direction. A stream from the west has cut its valley in the dome, exposing the sedi- mentary rocks on the valley walls. The mountain opposite the mouth of Fan Creek is composed entirely of Paleozoic strata, which are not affected by the laccolithic uplift, but dip to the east and northeast, away from the axis of the Madison Range. The lower slopes show Cambrian beds, which are overlain by the Silurian rocks, of which the most prominent strata are quartzitic in nature and form heavy, massive beds that cap the summit of the mountain and extend east- Gallatin. MADISON RANGE. 59 ward down to tlie valley of the Gallatin Kiver, the dip being about 20°. The summit of the mountain is flat, and shows Carboniferous limestones dijiping northeast at gentle angles. This mountain and the one north of it both show the characteristic flat-to2')ped topography noticed in the lesser marginal peaks of the Madison Range. The andesite-porphyry of the laccolith is (p^ite like those rocks in the Gallatin already described, and its petrographic description is given in another chapter. A chai'acteristic feature of the exposures seen of this rock is the occurrence of numerous included fragments of gneiss, schist, and hornblende-porphyry. The two patches of rhyolite which occur upon the slopes rest directly upon this andesite-porphyry, showing a thorough dis- section of the laccolithic fold before the outpouring of the rhyolite flows. CHAPTER 11. THE INTRUSIVE ROCKS OF THE GALLATIN MOUNTAINS, BUNSEN PEAK, AND MOUNT EVERTS. By Joseph Paxson Iddings. Having described the occurrence of the igneous rocks that have been intruded within the sedimentary beds of the Gallatin Mountains, or have been thrown over their surface, so far as their occurrence is related to the history of the dynamic events that brought about the present structure and topography of the range, we may now describe their petrographical characters in relation to the mode of their occurrence, ^vith special reference to the size of the various bodies of rock and then* geological position. From what has already been shown as to the relative age of the different intrusions, it will be proper to consider them in the following order: Indian Ci'eek laccolith; Holmes bysmalith and connected outliers; Bighorn Pass sheet; Gray Mountain intrusive and connected sheets; Electric Peak stock and dikes, together with the extrusive breccias and intrusive dikes of Sepulchre Mountain; and the breccias west and south of the Gallatin Range. In this connection may also be described the Buusen Peak intrusive and the intrusive sheets in Mount Everts. INDIAIi^ CREEK LACCOLITH. HORNBLENDE-MICA-ANDESITE-PORPHYRY. The rock constituting this laccolith and its two sheet-like apophyses to the south is an intrusive mass, quite uniform in mineral composition throughout its whole extent. It exhibits a limited variability in texture and habit, ranging from those of a compact aphanitic or lithoidal lava to those of a minutely crystalline porphyry-like rock. Its predominant min- eral constituents are lime-soda feldspar, hornblende, and biotite, with a small amount of magnetite and, in the coarser-gi-ained forms, quartz. For this reason it may be called an andesite-porphyry with andesite facies. Its 60 INDIAN CKEEK LACCOLITH. 61 chemical coin]iositinn is rr'wen below. The portion of tlie rock analyzed was the unalt(;reil coarser-g-rained form (55)' occurring in the middle of the laccolith on the north side of Indian Creek. ,1 iKilysis of hornhlende-micaandesite porphyry. [Analyst, J. E. Wliitfleld. 1 Coustitueut. sio, TiOj AI2O3 FecO:, FeO MnO MgO CaO Li;0 NajO K.O P2OB SO-, H;0 Total Per cent. 61. 50 None. 17.42 4.66 1.09 Trace. 1.26 5. 33 .03 3.99 1.29 .60 .35 2.44 99.96 The main body of the laccolith, where it is about 1,000 feet thick, is a light-gray rock crowded with small crystals of feldspar, mica, and horn- blende, with a subordinate amount of groundmass, whose component grains are not discernible with the naked eye. The phenocrysts are 1 or 2 mm. in diameter and smaller; occasional ones reach 3 mm. The rock is distinctly massive, cracking with irregular joints into angular or somewhat tabular fragments, and exhibiting columnar jointing hi only one locality, on the southeast slope of The Dome. Under the microscope the most crystalline portion of the laccolith (57), which proved to be the eastern- central part of the mass on the south side of Indian Creek, is seen to consist of the pheno- crysts already named, cemented together by a holocrystalline aggregation of quartz and feldspar with scattered grains of biotite, hornblende, and magnetite (PI. XI, lig. 1). The areas of quartz inclose minute idiomorphic feldspar, in part, if not wholly, lime-soda feldspars, probably oligoclase. The quartz is allotriomorphic and has a micropoikilitic structure, the grains ' Numerals in brackets used in connection with the petrography in this monograph refer to the specimen numbers in the Yellowstone Park collection. (32 GEOLOGY OF THE YELLOWSTONE XATIO^STAL PARK. ranging from 0.08 to 0.2 mm. in diameter, the inclosed feldspars being about 0.04 mm. long and 0.008 mm. wide, and upward. Somewhat finer-grained forms were found in the central portions of the mass north of Indian Creek. In these there is a more marked difference between the groundmass and phenocrysts. When seen under the microscope, the microstructure of the groundmass is more evenly granular, the grains averaging about 0.04 mm. in diameter in one case (56), and about 0.024 mm. in another (55). This degree of crystallization corresponds to grade 20 of the table for the rocks of Electric Peak (Table XVII), for the first case, and to grades 11 and 9 of the same table for the last two respectively. The last is shown in PI. XI, fig. 2. The phenocrysts are not sharply outlined, and have numerous inclu- sions of irregular grains or streaks of quartz and feldspar. The feldspar phenocrysts are all lime-soda feldspar, in part labradorite, in part andesine. They are frequently shattered, with irregular cracks, and are penetrated by irregular streaks of quartz and feldspar, whicli are sometimes granular. In places it looks as though the groundmass of the rock had penetrated cracks in the feldspars before it solidified. The feldspar individuals in one rock section are not all equally fissured, and not always in the same direc- tion, so that the cracking appears to antedate the solidification of the rock. The biotites exhibit very slight dislocation or bending in some cases, which may be referred to the same i:)eriod. The biotite is dark brown, with mod- erate absorption and occasional twinning. The outlines, often idiomorphic, are sometimes very irregular, there being marginal inclosures of quartz and feldspar, and sometimes of magnetite, but not often. The hornblende is green, with moderate pleochroism from strong green to light bi'own. The outlines are quite irregular, and inclusions of the other minerals are fre- quent. There is sometimes a chloritic mineral present in small pseudo- morphs, which may possibly l)e altered pj^roxene. In some instances it is decomposed hornblende. Magnetite is present in microscopic crystals, often idiomorphic; and apatite forms colorless microscopic crystals. Both hornblende and biotite take part in the composition of the groundmass in the more crystalline varieties. Somewhat finer-grained microcrystalline structures are found in the rock, where it forms the thinner sheets, 100 to 150 feet thick, beneath Trilo- bite Point (72, 73). Here the structure is confused, being partly micro- poildhtic, partly nncrogranular. In the still finer-grained modifications the U. S. QEOLOaiCAL SURVEY MONOGRAPH XXXII PART II PL. XI rA) % 29 rsj X 3 1 0 1 KeO NiO MnO MgO CaO Trace. 4.33 4.73 BaO SrO Na:0 K;0 Li,0 4.02 4.20 .13 ■ 68 .24 .22 [ 1.74 PjO, CI SOi HjO below 110'^ H-O above 110" Total 99.86 100. 18 .05 100. 09 .04 Less 0 for CI ' 100. 13 100. 05 The cliemical composition of the sheet is not hke that of any of the igneous rocks of Electric Peak and Sepulchre Mountain, being- lower in silica and proportionately higher in alkalies. It approaches the composition of shoshonite (Chapter IX), and indicates that the magma is a more highly differentiated form of the general magma. The two parts of the sheet cor- respond in chemical composition more closely to absarokite and shoshonite (q. v.), and are the results of a differentiation in which the separation was according to mineral molecules, as it was actually the settling of pyroxene crystals. The ratio of the alkalies to one another in the two parts is nearly constant, indicating that they remained in combination. The u^iper part of the rock, 10 feet from the top, consists of feldspar, most of which is plagioclase, and is striated. It is partly in tabular or equidimensional crystals, with allotriomorphic outlines, partl}^ in lath-shaped and rectangular crystals, more nearly idiomorphic and generally of smaller size. The extinction angles are low, often nearly zero, indicating oligoclase. 84 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Some of the feldspars exhibit no poly synthetic twinning and have low extinction angles, and are probably orthoclase. The substance of the feld- spar is clouded by minute secondary grains. There is also considerable colorless malacolite or diojjside in small irregular crystals and in short stout prisms, besides partly altered magnetite and abundant long needles of apatite; also abundant green and brown secondary mineral in irregular aggregations, which in places resembles microcryptocrystalline aggregates of chlorite or serpentine, and in other places appears to be microscopic crystals of brown mica. Biotite is also sparingly present in long shreds or crooked plates and in stout crystals. About 10 feet from the bottom of the sheet the lath-shaped feldspars are more abundant, long prismatic crystals of malacolite are numerous, and magnetite or ilmenite occurs in small grains and in greater numbers. There are some porphj-ritical malacolites and felds])ars, besides patches of brightly polarizing micro-fibrous material with larger needles of actinolite scattered through it. The portion of the rock filled with large malacolite crystals consists of these large crystals, more or less idiomorphic in outline, in a subordinate amount of feldspar matrix, composed of lath-shaped feldspars, like those already described, besides small crystals of malacolite and iron oxide. There is nnich actinolite in thin needles, and in a greenish, microscopic felt, which is bright green or pleochroic in some places and colorless in others. Around the grains of magnetite the felt is colored brown. The large mala- colites are to some extent altered to fibers of actinolite that lie parallel to the prismatic axis of the pyroxene. It is a question whether the patches of actinolite felt may not be altered olivine. This seems probable from the shajje of some of them, but no unaltered olivine is observed in the thin sections of the rock. GAIiLiATIN RIVER liACCOLITH. DACITE-PORPHYRY. In connection with the iutnisive bodies in the Gallatin Movmtains should be mentioned a laccolith-like mass situated on the Grallatin River just west of the l^order of the Yellowstone Park. It is within and near the base of the Paleozoic strata. The rock is a dacite-porphyry with prominent pheno- cr5rsts of feldspar and abundant smaller ones of hornblende, besides small rounded crystals of quartz. In thin sections the large feldspars are seen to INTRUSIVE SHEEia IN MOUNT EVERTS. 85 be andesine-labradorite with marked zonal structure, and with cracking- and secondary inchisions simihir to those in the andesite-porphyries ot" this rejifion. Thecjuartz crystals are sometimes idiomori)hic pyramids, or are nearly spherical, or are irregularly shaped. They contain bays and inclusions of groundmass and many liquid inclusions with cubes and gas bubbles ; rhombohedral cleavage is occasionally developed. The hornblende is green and more or less chloritized. A few crystals of biotite and of sphene were noticed. Magnetite occurs in small individuals, and colorless apatite in comparatively large ones. AUanite is present in brown jileochroic crystals, witli idiomorphic form and zonal structure. Strongly pleochroic epidote in irregular grains is sparingly present as a secondary mineral. The groundmass is fine grained, microgranular, with minute idiomorphic quartzes and abundant crystals of magnetite (168, 169). INTRUSIVE SHEETS IX MOUNT E^^BTS. There are a number of intruded sheets of igneous rock within the Cretaceous strata of Mount Everts, the lowest being exposed near the base of the south side of the mountain, and the highest at the top of the west escarpment. The rocks as a group are dark greenish and brownish grays to slate color. They are dense and aphanitic to very fine grained, and for the most part are free from prominent phenocrysts. The rocks are altered holocrystalliue andesites and andesite-porphyries. The coarsest-gi'ained form occurs in a sheet 20 to 30 feet thick at the base of the south face of the mountain (365). The rock is greatly fractured, with joints along which there has been sliding about parallel to the bedding of the inclosing sedimentary strata. It consists of nearly idiomorphic lime- soda feldspars, with low extinction angles and low dovible refraction, about 0.4 mm. long, the marginal part being unstriated and cloudy. A few are phenocrysts 2 mm. long. There is considerable serpentine and a little pale- green augite not yet altered. Magnetite occurs in small crj'stals, and colorless apatite is abundant in minute thin prisms. Numerous shreds of red-brown biotite may be secondary. The rock is a pj-roxene-andesite- porphyry. In the west escarpment several thin sheets were observed by Mr. Wright. They are aphanitic and porphyritic (356, 357), with phenocrysts of feldspar and decomposed pyroxene. The feldspar is parti}' altered, and is probably labradorite. The groundmass is extremely fine grained and is 86 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. comjjosed of pi'isms of plag-ioclase, much serpeutiue or chlorite, and altered magnetite, wliich is now light yellow by incident light. There are sugges- tions of crystals of pyroxene, now altered. The structure is andesitic and the rocks are holocrystalline pyroxene-andesites. There is much calcite scattered through the rocks. The intrusive sheet near the top of the northern part of the west escarpment, which can be distinguished even at a long distance from the inclosing sand.stones, because of its dark color, is about 20 or 30 feet thick in places, but much thinner in others. It lies parallel to the bedding of the strata, except for short distances, where it breaks across the beds. In ])laces it exhibits prismatic parting at right angles to the contact surfaces, and in other places the spheroidal suiidering is well developed. The rock is dark and dense, with few phenocrysts of hornblende (360, 361, 362). It contains segregations of hornblende. The same sheet of rock is exposed lower down the northwest spur of the mountain, near the line of the forty-fourth parallel of latitude (363, 359). It is a holocrystalline pyroxene-andesite, or pyroxene-andesite-porphyry, carrying a small amount of hornblende. Its habit is like that of similar andesites of Sepulchre Moimtain, there being innumerable small phenocrysts of labradorite and pyroxene in a groundmass of still smaller crystals of the same minerals, with magnetite and some micropoikilitic quartz. The rock is considerably decomposed in part, the pyroxenes having suffered most. Portions of it contain fresh augite and altered hypersthene. The hornblende is brown, with a border of magnetite and pyroxene. Near the contact planes of the sheet the groundmass of the rock is still finer grained. These rocks are similar to the intruded sheets in the Cretaceous strata of Electric Peak, and it is possible that they may have been connected with them before the faulting of the region by the great north-south faults on both sides of Sepulchre Mountain. THE BinVSEK PEAK MASS. DACITE-PORPHYRY. The Bunsen Peak mass is an intrusive body that broke through Creta- ceous strata, which are exposed in contact with it on the Gardiner River near the mouth of Glen Creek, and which dip away from it northward at an angle of 10°. Erosion has removed the sedimentary covering, leaving an isolated, dome-like mountain, whose base has been surrounded on all sides by THE BUNSEN PEAK MASS, 87 streams of rliyolitir and basaltic lavas. The rock is litrlit gray and fine grained, with abnndant small phenocrysts of feldspar and biotite. It is a mica-dacite-i)t)rphyry, \vlu)se chemical comjjosition is as follows: A nalysia of Bunsen Peak micadacite-porphyry. Constituent. (102) SiO. 70.52 Trace. 15. 85 2.28 .36 .09 .09 2.59 Trace. .3.93 3.43 .17 .29 .35 TiO. ALO, FeO, FeO MnO MgO CaO Li,0 Na^O K.O P.Os SO, HO Total 99.95 This analysis was made from the rock at the summit of Bunsen Peak. It is nearly the same as that of the rock from Mount Holmes (p. 65), beino- a little lower in alumina and higher in lime and potash. The mineral composition and microstructure of the rock vary but slightly throughout the body. Under the microscope it is seen to consist of a holocrystalline groundmass of feldspar and quartz, with abundant flakes of biotite and a little magnetite Small crystals of apatite and minute prisms of zircon are present. There are numerous phenocrysts of irregularly outlined biotite, idiomorphic feldspar, and a few corroded crystals of quartz. The feldspar phenocrysts are almost all polysynthetic twins of lime-soda feldspars, oligoclase-andesine, also twinned according to the Carlsbad law, and having marked zonal structure. A few appear to be labradorite. Some unstriated feldspars may be orthoclase. They have few inclusions, and exhibit very little decomposition in some parts of the rock. The cracking and secondary minerals characteristic of the feldspar phenocrysts in the intrusive rocks of the Gallatin Mountains also occur in parts of this rock. The biotite is brown, with strong absorption and few inclusions. It is for the most part unaltered. Quartz phenocrysts are much corroded and carry 88 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. few inclusions. They are scarce in most sections of the rock, and are more numerous in the linest-gi'ained portions at the northeastern extension of the mass. The groundmass in the coarsest-grained forms, which occur about the middle of the northern and western sides of the mountain, is micro- crystalline, and consists of lath-shaped and rectangular feldspars and micro- poikilitic quartzes, about O.Oo mm. in diameter and smaller, with some magnetite crystals and a few flakes of biotite. The microstructure is shown in PI. XIX, fig. 1. The poikilitic quartzes are more pronounced in some parts of the rock than in others, and exhibit a tendency toward idiomorphism (105, 106, 108). The same structure occurs in smaller grain at the summit of the mountain, on its southeastern face, and at its uortliern base, where the rock is exposed in knolls near Grardiner River and elsewhere. Where the dacite-porphyry comes in contact with a large mass of sandstone, probably included within the igneous mass, the porphyrj- exhibits platy part- ing pai'allel to the plane of contact, which disappears a short distance away. The microstructure of the rock near the contact is indistinctly micropoiki- litic, the quartz patches being very minute. In spots it is microcryptocrys- talline. The finest-grained forms occurring near the contact with sedimentary rocks on Gardiner River below the mouth of Glen Creek, and in the spur of the plateau west, are microgranular, with minute idiomorphic quartzes, averaging 0.01 nun. in diameter. A coarse-grained mass resembling granite occurs in the base of the clifi^ on the northern side of the mountain, and consists of quartz, feldspar, and biotite, with the grain of fairly coarse granite. It is a crystallization from the same magma as the dacite-porphyry, for the crystals of feldspar along its margin project into the porphyry groundmass with idiomorphic outline. It is not a broken fragment of some foreign rock inclosed during the eruption of the porphyry. Tlie mineral constituents are the same as those of the porphyry, both in kind and in general character. The biotite has the same color and has similar inclusions of magnetite. The feldspars are orthoclase and oligoclase, with some crystals of andesine-labi'adorite. The quartz is allotriomorphic with respect to all the other minerals, and contains gas inclusions, with a small amount of liquid. Magnetite, apatite, and zircon occur as in granite. This is clearly a coarse-grained crystalliza- tion of the magma, due to some cause not known, and presents the true granite equivalent of the dacite-porphyry. Similar coarse-grained masses occur in the dacite-porphyry of the Holmes bysmalith, near Echo Peak. CHAPTER III. THE IGNEOUS ROCKS OF ELECTRIC PEAK AND SEPULCHRE MOUNTAIN. By Joseph Paxson Iddings. GEOLOGICAL SKETCH OF THE REGION. As already stated in Chapter II, the series of eruptions that broke through the synclinal fissure in what is now the eastern part of Electric Peak are so plainly related to the lavas that form the volcanic pile of Sepulchre Mountain and the foothills at its southwestern base, and the character of this relationship is of siich petrographical importance, that these rocks will be treated conjointly.^ It has been shown that the erap- tions that accompanied the synclinal folding and Assuring' in the eastern part of Electric Peak were subsequent to the intrusion of the sheets of andesite-porphyry between the beds of shale and sandstone. The general character and form of Electric Peak are exhibited in the accompanying map and illustrations. The Peak is the highest point in the Gallatin Mountains, being 11,100 feet in altitude, and is situated upon the northern boundary of the Yellowstone Park, the forty-fifth parallel of latitude passing just south of the summit. For this reason it is not well shown on either of the atlas sheets north or south of this parallel. The accompanying map (PL XVI) shows its relation to Sepulchre Mountain, as well as its geological structure, which has been explained on pages 50 to 55, where the character of the sedimentary formations and their position and the nature of the intruded sheets of andesite-porphyry were described. The sharply pointed peak has broad, steep slopes on the west and south, where streams have cut 3,000 feet below the summit of the mountain. ■ Iddings, J. P., The eruptive rocks of Electric Peak iiud Sepulchre Mountain, Yellowstone National Park: Twelfth Ann. Kept. U. S. Geol. Survey, 1892, pp. 569-664. 89 90 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. A narrow spur or ridge connects the peak with the mountains to the south- west, while a broad, high ridge on the north carries the gently dipping Cretaceous strata to the abrupt synclinal fold south of Cinnabar Mountain. On the east and northeast of the summit deep gulches have been carved into the heart of the inass, reaching depths of -4,000 and 5,000 feet below its highest point. The valley of Reese Creek marks the line of faulting between Electric Peak and Sepulchre Mountain. Only the eastern half of Electric Peak is involved in the consideration of the series of volcanic eruptions here discussed, the central stock or conduit of eruption being located in the middle of the deep gulch east of the peak and in the rocky spur north of the gulch, and the apophyses and dikes extending only short distances across the southeastern and north- eastern spurs. The accompanying view of the eastern face of the mountain (PI. XIII) shows the jagged northeastern spur on the right, with its steeply sloping base, and the deep east gulch in the middle, with light-colored morainal accumulations of rock fragments covering the bottom like a glacier. The long southeastern spur is on the left, with its short, steep branch imme- diately south of the gulch. The barren slopes, partly covered with slide- rock, are easily recognized. The southeastern spur is formed of upturned beds east of the synclinal axis. The black shales which constitute the greater part of the spur have been baked and indurated in the vicinity of the stock, so that tliey have withstood erosion sufficiently to form the pyramidal mass bounding the east gulch on the south. The main mass of Electric Peak and the greater portion of the northeast s^Dur consist of less disturbed strata dipping toward the northeast. The structure of the mountain is shown in the walls of the deep gulches draining east and northeast, as well as in the bare slopes on the south and west sides. The differences in the topography of the two halves of the mountain are due to the influence of the vertically intruded rocks, which have metamorphosed the neighboring sandstones and shales, i-endering them hard and resisting, and leading to the production of rugged and pinnacled ridges, Avith precipitous walls hundreds of feet in height. The east gulch forms an amphitheater at the base of the peak, which surmounts a precipice of nearly 1,500 feet. The walls of this amphitheater are shown in the panorama, PI. XIV. The gulch crosses the synclinal axis and the stock of igneous rock, part of which is covered by debris. The can- 13 U. 8. GEOLOGICAL 6URVEV MONOGRAPH XXXII PART It PL. XIII -^^■r^.'^^P^ ELECTRIC PEAK, FROM SEhuLCHRE MOUNTAIN- 14 U. a. QEOLOOICAL euOvEv MON00P*PH X)(!C(I HEAD OF EAST GULCH OF ELECTRIC PEAK. ELKCTRIC PEAK AND SKPdLOHRB MOUNTAIN. 1)1 Tral portion of tlie stock is located on the northeastern s])ur of the mountain, where it is surrounded by sandstones. It is well ex])Osed throug-h a vertical distance of a thousand feet. \ large a])0])hysis extends up the crest of this spur, forniiufi- dark-colored pinnacles, shown on tlie right-hand side of the panorama. The southwestern end of the stock is ex])osed in the southern wall of the ani}ihitheater (left side of the panorama). It is a high wedge of crystalline rock, reaching to within a few hundred feet of the top of the cliff. The crest of the southeastern spur, from an altitude of 10,000 feet to the summit of the peak, is serrated by numerous narrow gulches and rocky points, caused by the unequal weathering of dikes and of upturned intrusive sheets. The nearly vertical dikes are frequent between the wedge of crystalline rock and the fault to the west. They become fewer toward the summit of the peak and do not occur farther northwest. They extend across the southeastern spui", appearing on its southern slope in Avails rising above the black shales. They do not occiu* at the eastern base of the spur. Where dikes and upturned intrusive sheets are parallel it is difficult to distinguish them from one another. The sheets, however, usually exhibit signs of crushing and displacement. The dikes are more numerous and thicker nearer the area of metamorphism. They are not more than a mile and a half long, and radiate from a center on the northeastern spui', which is about the location of the stock. They range thr(jngh 45° from south to southwest. Sepulchre Mountain, east of the great fault, located near the line of Reese Creek, consists of andesitic tuff-breccia. With this mass of breccia, which also forms the low ridge south of the mountain, is associated a set of dikes and broad intrusive bodies that have broken up through the breccia. The breccia is 3,000 feet thick, and rests upon Cretaceous and older strata exposed along the northern and eastern bases of the mountain. It is well exposed in bold escarpments on the northern side of the mountain, the southern and southwestern sides being smooth, glaciated slopes with few outcrops. The contrast between the northern and southern sides of the mountain is shown in PI. XV, the view having been photographed from the northwestern spur, looking southeast. The breccias are but crudely bedded; in places not bedded at all. With them are a few massive lava streams. The whole mass is distinctly a' olcanic. The dikes in the western part trend mostly in a north and northeasterly direction, radiating from the vicinity of Cache Lake. A few trend east. 92 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. It is probable that, instead of the broad bodies of intrusive andesite and dacite represented on the map, there are a number of smaller bodies of similar rocks intersecting one another, but the data at hand are iusuflftcient to enable their more accurate representation. In the northwestern spur of the mountain the dikes are well marked, from 5 to 25 feet wide, and not perfectly straight. Some of the intrusive bodies carry inclosed masses and small fragments of black shale, and where the fault plane traverses the massive igneous rock the latter has been crushed into angular fragments, which are cemented together by particles of the same rock, producing a crushed breccia, somewhat resembling the tutf- breccia. The rhyolite that occurs over the breccia in Glen Creek Valley is part of the great rhyolite sheet, and is of much more recent date, following the faulting and erosion (if the Electric Peak and Sepulchre Mountain masses. The accompanying map (PI. XVI) shows in a simple manner the chief geological features of a limited area embracing the rocks to be described. The sedimentary terranes are colored according to the period in which they were formed, embracing the Carboniferous, Juratrias, and Cretaceous. The sheets of igneous rocks intruded between the strata are not drawn continuous, as they exist, owing to the fact that the data are insufficient. They are more numerous than represented on the map, and are thinner. The same is true of the dikes. Although the two mountains were at one time geologically connected and the eruptive rocks were in a sense a geological vmit, it will be conven- ient and profitable to describe them separately at first, and afterwards to consider their correlation. THE INTRUSIVE ROCKS IN ELECTRIC PEAK. The intrusive rocks in Electric Peak, west of the fault, occurring in the stock and its apophyses and in dikes, form a group of diorites and diorite- and andesite-porphyries of variable composition and structure. They grade into one another Ijy transitions in composition and structure. The coarse-o-rained granular rocks — diorites — occur almost wholly within the stock and its larger apophyses, while the finer-grained porphyritic rocks — porphyries — occur in the dikes and smaller apophyses, and in places along the margin of the stock, in contact with sedimentary- rocks. The greater part of the stock is diorite, which varies in structure and INTRUSIVE ROOKS IN ELECTRIC PEAK, 93 composition, in some places rapidly aiul (juite irregulai'ly. Moroovei', there are abundant evidences of the successive eruption throuoh the fissure or conduit of different molten magmas. The porphyries also differ from the main body of diorite in the character of their pheuocrysts — that is, in those minerals which were present in the magma when it came to rest. Most of the porphyries contain phenocrysts of hornblende and biotite, but none of p-\'roxene. In some of the diorites there was an early crystallization of brown hornblende and of pyroxene, but none of biotite. In most of the diorites there is no evidence of any development of phenocrysts. They were magmas free from crystals at the time of their eruption. In order to understand the relation of the various dikes to the stock rocks, let us consider the possible course of events that would follow a synclinal Assuring of sedimentary sti'ata when the dynamical action was repeated and when igneous magmas were forced up through the cracks. Evidently the first magma would penetrate all the small crevices connected with the larger fissures and fill them with its material, which would solidify rapidly as narrow dikes. The magma in the large fissure would remain molten much longer, consolidation setting in along the sides and in the narrow portions. A subsequent eruption would force out the molten por- tion and replace it by other material. It would fill any new crevices made at the time of its eruption. The number of such crevices would probably be smaller toward the end of the series of eruptions than at the beginning. Hence the number of dikes of the later magmas would be smaller. The magma that closed the conduit would in such a case be represented by few dikes. If the final action was a violent explosion, the reverse would be true. At Electric Peak the final eruption was comparatively weak, and is represented by a small body of quartz-diorite-porphyry within the stock and in six or eight narrow dikes trending southwest. These rocks form a very complex group, so intimately connected geologically and exhibiting such gradual transitions in composition and structure from one extreme to another that there appears to be no simple method of describing them or of discussing their various relationships. For convenience of petrographical description they will be treated in the follow- ing groups : . I. The greater number of dike rocks and some of the contact forms of the stock, probably older than the main body of the stock. 94 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. II. The main body of the stock, most of its contact forms, and most of the rocks that have broken through it, with some apojihyses, probably contemporaneous with the main mass. III. The quartz-mica-diorite-porphyry that broke through the stock and also produced some dikes. I. THE DIKE ROCKS AND CERTAIN CONTACT FORMS OF THE STOCK. Porphyries. — The porpliyrics forming most of the dikes, which are from 1 to 25 feet in width, have a g-enerally uniform habit. They are dense and aphanitie, filled with small phenocrysts of feldspar and ferromagnesian silicates, mostly hornblende and biotite. They have a uniformly speckled appearance, with occasional spots of white feldspar or black ferromagnesian silicates. Variations in habit are due to differences in color, caused b}' the relative propoi'tions of light and dark colored phenocrysts, and to the nature and amount of the groundmass. The color varies from dark greenish and purplish gray to light gray of different tints. The dike rocks are in some cases fresh and compact, in others decomposed and disintegrated. In thin sections under the microscope the groundmass of all these dike rocks is found to be holocrystalline, and the phenocrysts are lime-soda feld- spar and hornblende, generally with biotite, occasionally with pyroxene. The relative proportions of these minerals vary gradually among the rock bodies, so that the specimens collected may be arranged in the follow- ing subdivisions, according to the relative amounts of the ferromagnesian silicates : Table I. — Mineral variatioH of the andesite-porphyries of Electric Peak. Besides the phenocrysts of biotite there are shreds of this mineral that belong to the period of crystallization of the groundmass. There is a DIKE ROCKS OF ELECTRIC PEAK. 95 gTiulual variation iu the kiiuU ot lime-soda t'eldspjir accoinjjaiiyiuy that ot the lerroiuagnesian minerals. But transitions in the possible isomorphous series of hornblendes or pyi'oxenes were not detected. The variation iu min- eral composition affects the microstructure of the groundmass, an inci'ease of quartz being- accompanied by an approach to a granular structure. Altliouffli the coarseness of jjrain and at the same time the character of the microstructure vary to some extent with the size of the dike, and to a g-reater extent with the rate at which the mass cooled, for each of the mineralogical subdivisions indicated in the table, still, the conditions under which these various magmas cooled having been quite similar, the variations in the composition and microstructure of the groundmasses of the subdivi- sions named bear a marked relation to the composition of the rock as a whole and to the variations in the phenocrysts. This will appear from the following descri2:)tions of the rocks belonging to the subdivisions in Table I: (a) Groiiudniass with micropoikilitic structure, the quartz graius iu ono case being 0.09 mm. to 0.43 mm. in diameter, and containing lath-shaped microlites of feldspar, gas cavities, and microscopic hornblendes and biotites. Abundant phenocrysts of lime-soda feldspar, 1 to 2 mm. long, and, smaller ones of hornblende and biotite. The relative proportions of the latter minerals dift'er in diti'erent specimens. As the total amount of ferromagnesian minerals increases, the relative amount of hornblende increases. .Small amounts of magnetite, apatite, and zircon occur iu all these rocks. (h) The rocks of the second subdivision are nearly the same as those of the first. (e) In the third division the micropoikilitic structure is not well marked and grades into one in which lath-shaped feldspar microlites are more prominent. (d) and (e) Micropoikilitic structure is wanting. The groundniass is composed essentially of lath- shaped microlites and grains of feldspar, approaching a fel; like or pilotaxitic structure. This change accompanies a diminution in the amount of (juartz. In these five subdivisions pyroxene is entirely absent. (/) and ((/) These are similar to the last two subdi\'isions in microstructure and composition, but pyroxene was originally present as phenocrysts and has been nralitized. Biotite is only present in shreds in the groundmass and does not form phenocrysts. (A) is represented by a coarser-grained rock, but slightly porphyritic. It consists of lath-shaped feldspars 0.4 mm. to 0.7 mm. long, between which is a very small amount of irregular grains of feldspar and quartz and ferromagnesian silicates, amphibole, and mica. There is much uralitized pyroxene, which formed the largest idiomorphic crystals. (i) The rock of this division is like the last in microstructure, but is more porphyritic, with pheno- crysts of plagioclase and pyroxene, the latter iu part uralitized. Near the contact of this rock with metamorphosed sandstone the pyroxene is almost colorless, difl'erent from the varieties common in the pyroxene rocks of this region. It resembles the secondary pyroxene whicli has resulted from the alteration of hornblende in other varieties of porphyry in this neighborhood. The more quartzose porphyries and the coarse-grained modifications cutting the stock will be described later. The microscopical characters of the minerals constituting the dike rocks are nearly the same throughout this series of rocks. 96 GEOLOGY OF THE YELLOWSTON^E NATIONAL PARK. The feldspar in all cases is lime-soda feldspai-, with the usual poly- synthetic twinning. In sections the forms of the feldspar crystals are lath- shaped, rectangular, and tabular, the general habit being tabular parallel to the clinopinacoid. Zonal structure is pronounced. Their range appears to be from labradorite to oligoclase, the former prevailing in the more basic dike rocks, the latter in the more siliceous varieties rich in biotite. Primary inclusions of glass or of other minerals are scarce. Secondary inclusions are more numerous, and are gas cavities or needles of am]diibole. The feldspars are more distinctly idiomorphic than the hornblendes, and are sometimes hvclosed in hornblendes. More rarely hornblende is inclosed in feldspar. Primary hornblende phenocrysts are generally idiomorphic, but not always. In the prism zone the unit prism (110) and clinopinacoid (010) are well developed. Terminal planes are seldom observed. Twinning is common, parallel to the orthopinacoid (100). The color varies from brown to green, through reddish brown, greenish brown, and light brown, brownish gi-een, and olive gray, sometimes with a reddish tint approaching violet gray. The olive gray and violet gray are common in many hornblendes of these dike rocks. The pleochroism is, then, ohve gray || C, olive brown || Ij, light brown || a. The absorption is C>lJ>a:. The color is sometimes in-egu- larly distributed in the crystal, the darker shades being usually in the center, but zonal structure is rare. In the less siliceous rocks of this series the hornolendes are somewhat darker colored, approaching chestnut brown. There are no characteristic inclusions. When associated with biotite the two minerals are so intergrown as to suggest synchronous crystallization. In some cases biotite is inclosed as a secondary mineral. The hornblende is in various stages of preservation, sometimes fresh, sometimes jiartially or comjjletely altered. The usual alteration products are chlorite and epidote, with calcite and quartz. Sometimes compact hornblende has been changed to fibrous, "reedy" amphibole. Biotite forms six-sided plates, occasionally twinned parallel to the cleavage plane. It is dark reddish brown with normal absorption. It is sometimes partially bleached, the light-colored spots containing bundles of rutile needles. It may be completely altered to chlorite and epidote, with calcite and quartz. Pyroxene was not found in an unaltered condition, and was only identified by its form. The iron oxide is probably magnetite, with 15 U. S. GEOLOGICAL SURVEV MONOGRAPH XXXll PA^IT II PL. SEPULCHRE MOUNTAIN, FROM ITS NORTHWEST SPUR, 16 U S GEOLOGICAL SURVEY. MONOGRAPH XXXII,PARTII,PL XVI, STOCK HOCKS AND ArOPlIYSES. 97 sonic titanium. Apatite is more al)un(lant In the more micaceous rocks. The same is true of zircon Secondary pyroxene occurs in porphyries within the metamorphosed sandstones, apparently derived from liornblende. The feldspar and biotite phenocrysts are quite fresh, and the general microstructure of the ground- mass is normal for a hornblende-mica-andesite-porphyry. The augite substance is colorless and compact, with pyroxenic cleavage. It occupies spaces with hornblende outlines in cross section, the plane of synnnetry for both minerals being the same No pyroxene outlines were observed. Its refraction and double refraction are high, and the extinction angle is large. It sometimes forms irregular grains and minute aggregations not immediately connected with a hornblende crystal. In some cases the hornblende is not entirely changed to pyroxene. The process by which this alteration took place has not been made out. II THE STOCK ROCKS AND APOPHYSES. The diorite forming the body of the stock varies in the size of its crystals. Most of it is medium grained, consisting of clusters of feldspars, and others of ferromagnesian minerals, from 5 mm. to 2 mm. in diameter, and smaller. The coarsest is shown in fig. 1 of PI. XVII, photographed natural size. The size of the component crystals is smaller than that of the clusteiii, and is from 1 mm. to 2 mm. A medium-grained form is shown in fig 2 of PI. XVII. The grain sinks to fine grained and to microcrystalline. The variation in grain is gradual in some parts of the mass and rapid in others. The finer-grained portions are darker colored. While a gradual transition from coarse to fine grained and from light to dark-colored rock can be traced in some places, the two extremes are in juxtaposition in others, with a sharp line of demarcation between, veins of the light-colored rock cutting the dark colored. In places also there are fragments of various modifications of the diorite inclosed in diorite, which appears to be a later intrusion. The dioi'ite also varies in mineral composition. For the most part the ferromagnesian and the nonferromagnesian minerals are in about equal proportions. In places the former preponderate. In other parts of the rock the other minerals are in excess. The minerals recognized megascop- ically are lime-soda feldspar, hornblende, and biotite. In places biotite is MON XXXII, PT II 7 98 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. abundant. The lighter- colored varieties of the rock exhibit quartz. The finest-grained porphyritic forms show only feldspar and pyroxene pheno- crysts, but most of the rock is evenly granular, with no porphyritic structure. When examined microscopically, the constituents are found to be hyper- sthene, augite, hornblende, biotite, lime-soda feldspar, orthoclase, quartz.- These are not all in every modification of the rock. Their range of variation is indicated in Table II, in which a, b, etc., represent different mineralogical modifications of the rocks. Table IL — Mineral variation of the diorites at Electric Peak. Pyroxene. Hornblende. Biotite. Labradorite. Oligoclase. Orthoclase Quartz. a .. h... c... d -. Little... Some . . . Much . . . Much ... Much . .. Much ... Much... Much .. . Some . . . Some ... Little . . . Some . .. Little. Little. Some. Much. Much. Much . Much. Muih ... Little . . . Much ... Much... Much... Some .. . Little... Some . .. Some . . . Some . . . Much . . . Much .. . Much .. . Little . . . Little... Little . . . Little... Some ... 0 f Much . .. The diorite is traversed by veins or dikes of equally coarse-grained, lighter-colored diorite, sometimes approaching granite in composition. In one case the rock is fine-grained granite (fig. 1 of PI. XVIII). In .places there are narrow seams of feldspar and quartz, which grade into rock containing some biotite and hornblende, and finally into quartzose diorite. Such seams of feldspar and quartz appear to be the extremities of fissures or cracks in the early solidified magma, into which the fluid portion of sub- sequently intruded magma has been forced. They are of truly igneous origin, and consist of the most liquid portion of the magma, or that part which is the last to crj^stallize. Segregations rich in fen-omagnesian minerals are abundant in some parts of the rock. The marginal portions of the diorite core are diff"erent in difi'erent places. In some there are porphyiy-like modifications, indicating the more rapid cooling of the margin of the mass. In other places the coarse-grained rock is directly in contact with the wall of the conduit, showing no indica- tion of chilling. In the first case the surrounding rocks must have been cooler than the igneous magma. In the latter case they must have been DIOKITES OF ELECTRIC PEAK. 99 equally hot, or nearly so, iii(li('atiii<^ the previous heating' by earlier magmas. For convenience of description these rocks will be subdivided into the following' grou])s : llrt. Vtu'ieties in which the dark-colored and the light-colored minerals are in nearly the same i)roportions. 116. Varieties in which the lig-ht-colored minerals are in excess and the amount of quartz is moderate. lie. Like 116, but with much quartz. The dai'k-colored minerals include fen-omagnesian minerals. The others are feldspar and quartz. Ilrt. VARIETIES IN WHICH THE DARK-COLORED AND LIGHT-COLORED MINERALS ARE NEARLY EQUAL. This group includes most of the stock rocks, and is the most basic. It embraces a series of varieties that grade into one another chemically, mineralogically, and structurally. As regards the degree of •ciystallization, or the size of the grain of the rocks, they naay be classed under 27 different grades, from fine to coarse. But no attempt has been made to establish a scale of uniform degrees. The arrangement is shown in Table VIII, Column Ila. At the coarsest- gi-ained end of the series are the diorites of the stock. Their structure is hypidiomorphic granular. Some of the mineral constituents have their proper crystallographic outline, but most of them are irregularl)^ shaped. The constituents are lime-soda feldspars, hornblende, augite, hyper- sthene, biotite, and quartz, with magnetite. The feldspars are more nearly idiomorphic than the other constituents. They are rectangular to lath- shaped, with outlines modified by the juxtaposition of other minerals. Quartz forms cementing grains, wholly allotriomorphic. Hornblende, pyroxene, and biotite seldom exhibit crystal boundaries, and penetrate one another intricately. Magnetite is mostly found in the ferromagnesian sili- cates. Apatite is colorless and in crudely formed crystals. Zircon is rare. The diorites of the seven highest grades of crystallization, Table VIIT, Column 11a, have a structure similar to that just given, but vary in the relative abundance of the constituent minerals, as shown in Table V. In the coarsest form the feldspars are from 2.5 mm. to 1 mm. long, and the quartz grains 0.25 mm. in diameter. The structure is shown in PI. XIX, 100 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. fig 2. In the seventh grade from the coarsest end the feldspars range from 1.25 mm. to 0.5 mm., and the quartzes are about 0.12 mm. As the grain becomes smaller, idiomorphic forms are more numerous, especially of hornblende and biotite. And these are more idiomorphic when quartz is more abundant, since they are always idiomorphic with respect to this mineral (PI. XIX, fig. 3). A gradual change of this character can be followed to grade 26 of the table, where the average size of grain is 0.23 mm. Here there is a slight tendency to porphyritic structure, which does not show megascopically. Porphyritic structure becomes noticeable in grade 24 (PI. XIX, fig. 4), and still more so in grade 14. This has a groundmass composed of grains of feldspar and quartz with poorly defined outlines, besides microscopic pyroxenes and magnetites. The phenocrysts are lime-soda feldspar, hypersthene, augite, and some irregular patches of biotite. There is no hornblende. The finest-grained forms of these rocks, grades 17 to 13, have similar structures, and might be called pyroxene- andesite- porphyry . This group of rocks presents a continuous series from fine-grained andesite-porphyry, with phenocrysts of hypersthene and plagioclase, to coarse-grained honiblende-mica-diorite with a variable percentage of pyroxene. In two instances the transition is represented by specimens collected within short distances of one another. Thus, Nos, 268 to 271, 279, and 287 (PL XIX, fig. 3) were 1 foot apart in a continuous rock mass, and No. 266 is from the same mass. Nos. 277, 278, 281, 284, and 289 are from one rock mass exhibiting a gradual change of grain through a distance of 4 feet. No. 267 is from the same mass. The microscopical characters of the constituent minerals are much the same throughout the series, but there are certain featm-es that vary with the coarseness of grain of the rock. The feldspars are mostly labradorite, and to a less extent andesiue. The idiomorphic crystals and the zonal portion of the allotriomorphic ones increase in size as the grain of the rock becomes larger. Their twin lamellae become broader, the number of inclusions of pyroxene and other ferromag- nesiau minerals and of magnetite diminish with increasing grain, and the abundance of minute dots and needle-like inclusions increases. The feldspars, forming irregular grains in the groundmass of the andesite- porphyries, crystallize as a border around the idiomorphic feldspai-s in the U. S. QEOlOOICAL SURVEY MONOGRAPH XXXII PAHT II PL. XVII H DIORITES. A. Coarse grain ; /?, Medium grain, U. S. GFOLCKICAL SURVEY MONOGRAPH XXXII PART II Pl.XVIII .1, GRANITE. li, DIORITE-PORPHYRY DIOUITES OF ELECTUIC PEAK. 101 coarser-grained varieties. The border is allotriomorphic and more alkaline than the center. Orthoclase is recognizable in the coarsest-grained rocks. Quartz occurs in aHotriomorphic crystals, nearly contemporaneous with the orthoclase, which is also allotriomorphic. The gas and fluid inclusions in the quartz increase in number and in size with the size of the quartzes and with the grain'of the rock. Hypersthene and augite form idiomorphic and allotriomorphic indi- viduals in the porphyries. They are much more irregularly shaped in the coarsest-grained rocks, and are in larger individuals. When grown together, the hypersthene is always the older, being inclosed by the augite; rarely they mutually penetrate one another, as though their crystallization was synchronous. Primary brownish-green hornblende occurs in a similar manner. It fre- quently surrounds the pyroxenes more or less completely, and is usually the younger growth. Occasionally it appears to be contemporaneous with augite. It is more abundant as the grain of the rock becomes coarser. Dark-brown hornblende sometimes is present as an independent crystallization. Biotite is mostly in allotriomorphic crystals. The ferromagnesian min- erals occur isolated from one another to some extent, but are generally inter- grown in the most intimate manner. Though there is an apparent order in the time of their crystallization, beginning with hypersthene and augite and ending with biotite, still in most cases they have grown synchronously. This is specially true in the coarser-grained rocks. Magnetite has two periods of crystallization in the porphyritic rocks, but only one in the uniformly granular ones, the size of the crystals increasing and their number dimini.shing. Apatite forms abundant minute idiomorphic crystals in the finer-grained rocks, and fewer, larger, poorly shaped indi- viduals in the coarser-grained rocks. Zircon is more noticeable in the coarser rocks and is in larger crystals. All of these variations of character plainly indicate that the physical conditions that brought about the variation in the texture of the rocks affected the crystallization of the earliest-forming minerals, and since these conditions were localized in the stock, it follows that portions of the igneous magma were completely liquid when they arrived in this part of the conduit. The intergrowths of green hornblende with pyroxene, which are the results of primary crystallization in these diorites, find their analogies in 102 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. similar intergrowths of hornblende and pyroxene in unaltered, often pumi- ceous, glassy lavas. They are to be distinguished from the formation of hornblende from pyroxene by secondary processes of metamorphism, which may also lead to the production of compact green hornblende. The transformation of both pyroxene and compact hornblende into fibrous amphibole has taken place in some of these rocks to a limited extent. They are in general very fresh and unaltered. II&. VARIETIES IN WHICH THE LIGHTCOLOEED MINERALS ARE IN EXCESS, BUT IN WHICH QUARTZ IS NOT EXCESSIVE. These include the more feldspathic facies of the diorite, whether within the main body, on its margin, or as dikes or veins within the mass. There is considerable quartz and a range of ferromagnesian minerals that connect them with the preceding varieties. The finer-grained forms approach the dike rocks in microscopical characters, and are possibly connected with them geologically. Hornblende, pyroxene, and biotite are similar to the same minerals in the main body of diorite, and exhibit the same relations to one another when in juxtaposition, but vary more widely in their relative proportions, as shown in Tables V and VI. The feldspars are somewhat more alkaline, and have a slightly different habit from those in the main diorite. The quartz plays a somewhat difi"erent role. Its crystals occasionally possess a crudely idiomorpliic form, and because of their greater abundance the microstructure exhibits more of a granitic appearance than in the less siliceous diorites. The coarsest-grained variety (313) consists of broad plagioclase feld- spars from 1 mm. to 2 mm. long, with numerous small quartz grains located along the line of junction of the feldspars; hornblende and biotite occur in irregularly shaped anhedrons, the hornblende being in part phenocrystic. Magnetite and apatite are also present. When the grain of the rock becomes smaller the feldspars stand out more prominently in a fine-grained groundmass. The porphyritic texture is quite pronounced in specimen 308 from near contact with sedimentary rocks. Its grade of crystalliza- tion is 27. The large feldspars and hornblendes are idiomorphic. The crystals composing the groundmass exhibit an approach to idiomorphism, especially the feldspars, and to some extent the quartzes. This structui'e is shown in fig. 1, PI. XX. QUARTZ MICA-DIOKITE. 103 II f. VARIETIES WITH AN EXCESS OF LIGHT-COLORED MINERALS, IN WHICH QUARTZ IS AKUNDANT. These include very quartzose and very feldspatliic varieties of diorite, approaching' granite in conii)()sition and structure (320 to 323, 275a and 286a). Tliey Jii"e mostly coarse-grained dikes or veins cutting the diorite mass. They correspond to grades 37 and 40, Table VIII. In this group are also placed certain apophyses (314-319) from the stock that penetrate the sedimentary rocks. These rocks are very similar to those of Group II&, but contain more quartz, and the feldspars appear to be still more alkaline. Oligoclase- andesine is the predominant feldspar, but there is some labradorite and some orthoclase. Orthoclase is very abundant in one modification of the rock, which is in ftict a fine-grained granite. It forms a large body on the northeast spur of Electric Peak, in the rugged mass of dark-colored diorite needles. Its crystallization is about grade 35, and its microstructure approaches panidiomorphic, as shown in PI. XX, fig. 2. The other varieties are more properly quartz-mica-diorites. In the coarsest-grained forms the ferromagnesian minerals are biotite and hornblende, with no pyroxene, and with biotite in excess of hornblende. The microstructure of one of the coarser-grained varieties (321), grade 37, is shown in PI. XX, fig. 3, and that of the finest-grained one (314), grade 19, in PI. XXI, fig. 1. The latter is a pronounced porphyry. lie'. Certain narrow apophyses in the immediate ^dcinity of the stock are rich in quartz, but contain more calcic feldspar and a variable amount of pyroxene, besides biotite and hornblende. They appear to be quartzose facies of the pyroxene-diorite of the stock, and have not been found cutting the main body or forming dikes at any considerable distance from the stock. Their mineralogical composition is indicated in Table Vll by the first six numbers (314 to 319). "With increase of quartz the micro- structure becomes more evenly granular. III. QUARTZ-MICA-DIORITE-PORPHYRY. The last magma erupted through the Electric Peak conduit formed quartz-raica-diorite-porphyry. It is a broad wedge-shaped mass cutting the main diorite, narrower toward the north, and sending- out dikes into the sedimentary strata to the southwest. The rock is light gray to white, with 104 GEOLOGY OF THE YELLOWSTONE JfATIONAL PARK. abundant small pheuociysts of feldspar, quartz, and biotite. Its habit is like that of the other porphyries, and is produced by the great number of small phenocrysts. The groundmass is hardly recognized megascopically, except in the finest-grained varieties. The coarsest varieties occur within the stock; tlie finest-grained ones in the narrow dikes cutting the southeast spur of Electric Peak. Their grades of crystallization are shown in Table VIII, Column III. The rock is intermediate between quartz-diorite-porphyry and granite- porphyry. It varies slightly in mineral composition and in chemical com- position, and the extremes would be classed under these two kinds of rocks. Besides biotite there is a little hornblende in some cases, but it is almost entirely absent from most of the rock. The biotite is partly chloritized, and the feldspars are more or less altered. In the finest-grained varieties the groundmass is microcrj^stalline, approaching microcrj'ptocrj'stalline. The phenocrysts of feldspar, quartz, and biotite are sharply defined. The feldspar is mostly oligoclase, with possibly a little orthoclase. The quartzes are smaller than the feldsj)ars. Most of them exhibit, in thin sections, straight-edged crystallographic out- lines. Others are rounded more or less completely. Both forms occur together in the same rock section. In some cases the outlines are irregular because of bays or pockets of groundmass let into their sides. These occur in otherwise straight-edged and in rounded quartzes. They appear to be original inclusions rather than the results of corrosive action of the magma on idiomorphic crj^stals. There are bipyramidal inclusions of glass and others of gas and fluid. In coarser-grained groundmasses the outlines of feldspar and quartz phenocrysts are not so sharply defined, but are jagged. Around some quartzes there is a narrow border of groundmass, part of which extinguishes light in unison with the quartz phenocryst, showing that the quartz in this part of the groundmass has> one orientation parallel to that of the quartz phenocryst. The con-esponding rock within the stock is much coarser grained, with larger and more numerous phenocrysts, so crowded together as to leave but little groundmass. The feldspar phenocrysts are similar to those in the finer- grained rocks, but those of quartz gradually lose their idiomorphic shape as the groundmass becomes coarser, and, extending out among the smaller crystals of feldspar, take on a very irregular outline (PI. XX, fig. 4). There U. S. GEOLOGICAL SURVEY MONOGRAPH XXXII PART II PL. XIX r.-i ) < 36 re; X 28 ( D)x 29 PHOTOMICROGRAPHS OF ANDESITE-PORPHYRY AND DIORITE THE HELIOTYPE PRINTING CO., BOSTON U. 8. QEOLOOICAL SURVEY MONOQRAPH XXXII PART II PL. XX I Aj ^ 16 rBjx 13 fCj % 22 (J)j < 20 PHOTOMICROGRAPHS OF DIORITE AND DIORITE-PORPHYRY THE HELIOTVPE PRINTING CO.. BOSTON U. 8. OEOLOOICAL SURVEV MONOGRAPH XXXII PART II PL. XXI (B) % 33 PHOTOMICROGRAPHS OF DIORITE-PORPHYRY AND DACITE THE HELIOTYPE PRINTING CO., BOSTON MINERAL COMPOSITION OF DIKE ROCKS. 105 is a gradual transition from the sliarply idiomorphic quartz plienocrysts of the fine-grained poqihyries to allotriomorphic crystals, such as occur in granites and in the coarser-grained porphyries. This shows that the por- phyritical quartzes were the last ])lienocrysts to crystallize, and that their crystallization in the coarser-grained varieties continued into the period of crystallization of the groundmass without evidence of interrujition. GENERAL CONSIDERATION OF THE MINERAL AND CHEMICAL COMPOSITION OF THE INTRUSIVE ROCKS IN ELECTRIC PEAK. MINERAL COMPOSITION. In order to convey an idea of the variations in mineral composition of the rocks just described, recourse has been had to tabular statements of the relative abundance of the constituent minerals in the different grouj^s of rocks. The tables serve not only to condense into very compact space many data, but place them in such form that they may be comprehended at a glance, while at the same time the formal arrangement of the data often conveys ideas of transitional relationships not easily expressed otherwise. The same is true of data relative to degree of crystallization, which will be explained later on. In the dike rocks constituting GroujD I, and in the dikes of Group III, the mineral variations most readily noted affect the phenocrysts, and more particularly those of the ferromagnesian minerals and quartz. Variations in the feldspars may be recognized, but with more difficulty, and may be expressed in general terms by saying that those in the more basic rocks are richer in calcium, while those in the more siliceous rocks are richer in sodium, and that the transition between the extremes appears to be gradual. The variations in the phenocrysts other than the feldspars are indicated in Table III, in which the first column contains symbols of mineralogical subdivisions to be used for correlation in subsequent tables. In this table no account is taken of the degree of crystallization. 106 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table III. — Mineral variation in the dike rocks of Electric Peak. Mineral groups. Specimen numbera. Phenocrj'stB other than feldspar. Pyroxene. Hornblende. Biotite. Quartz. d, d, da d, d» de...:.. d, dn d9 din dn f 232 I 233 234 235 f 236 1 237 f 238 I 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 256 257 255 258 259 260 261 262 263 264 265 Much Much Much Some Some Some Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Some Some Little Little Little Little Little Little Little Little Little Little . Little Little Little Little Little Some Some Some Much Much Much ... Much Much Much Much Much Much Much Much Much Much Little Much Much Much Much Much Much Much The transition indicated in the table is from acidic rocks with much porphyritical quartz and biotite and very Httle hornblende, through inter- mediate rocks with much porphyritical biotite and hornblende, to basic rocks with pyroxene and little or no porphyritical hornblende or biotite, but which, being more coarsely crystalline, contain some biotite as a product of the final consolidation of the groundmass, which is related in its occrn'rence CRYSTALLIZATION OF DIKE EOGKS. 107 to the biotite in the diorite. The gradual nature of the transition from one extreme to the otlier is apparent at a ghxnce. The impossihiUty of considering certain rocks as definite types with which to compare other rocks in the region is also evident when it is observed that tlie mineralogical variation takes place within certain limits in one rock body (Nos. 247, 250, 255, 256, and 257 are from the same dike), and that what appears to be a mineralogical modification of one particular rock body is the characteristic combination of another, and its modification is something different. Field observation shows that in this locality the greater number of dikes are composed of rocks with variable percentages of porphyritical hornblende and biotite, and that the other varieties are less numerous. In another region other varieties ^predominate. The chemical variations which are indicated by the silica percentages range from 57.12 in subdivision ds to 61.85 in (!■„ and probably reach 69.00 in rfij. They indicate a correspondence between the mineralogical and chemical variations for this group of rocks. Table IV. — Grades of crystallization of the dike rocks of Electric Peak, Grades of crystal- lization. Mineralogical grouping indicated in Table HI. d, d. da di d. d. d. ds d. dio d.i 6 259 260, 261 262, 263 264, 265 7.. 240 8 238 9. • ■ 241,242 243 244, 245 258 10 246 11 25.5, 256 257 12 239 249, 250 251 252, 253 254 13 14 247, 248 16 235 19 20 25 232 233 236,237 234 Table IV expresses the range in degree of crystallization of the ground- mass of these rocks, which are arranged in columns corresponding to the mineralogical grouping of Table III. It is to be remarked that the speci- mens were collected from different-sized dikes and from different parts of the dikes, so that the variations in grain can not be compared very closely 108 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. with the mineral composition. But when the size of the dikes in each case is taken into consideration it becomes even more evident than from the table that the coarseness of grain bears a very considerable relation to the chemical composition of the rock. The variation in grain between the sides and center of a dike and between dikes of different widths, for rocks of nearly the same composition, is not so great as the variation between rocks of different composition where the size of the dikes in which they occur is somewhat similar. Thus, specimen No. 233 is from the center of a 4-foot dike, and No. 232 from the contact wall of the same; and specimen No. 247 is from the center of an 8-foot dike, and Nos. 257 and 250 are from the contact walls of the same; Nos. 264 and 265 are from 4-foot dikes, and No. 263 is from a 2-foot dike. They all occur at nearly the same altitude, but it is possible that the pyroxene-bearing rock, No. 233, may have been intruded in rocks which were more heated at the time of its intrusion and so have acquired its degree of crystallization through slower cooling, but this is not so likely to have happened in the case of rock No. 234, which is in the same part of the mountain as No. 235, but is in a dike 10 feet wide and is very much coarser grained than No. 233. (See Table VIII.) The groundmass of the rock with porphyritical quartz and biotite, No. 265, is made iip of minute grains of quartz and feldspar, about 0.015 mm. ua diameter, while the groundmass of the pyroxene-bearing variety. No. 233, is made up of lath-shaped and irregularly shaped feldspar about 0.10 mm. to 0.14 mm. in length, and the groundmass of No. 234 is composed of lath- shaped feldspars 0.5 mm. to 0.7 mm. in length. The character of the gi-oundmass changes from an even granular structure in the acidic rocks, through one made up of irregular grains and latli-shaped feldspars in the intermediate rocks, to an aggregation of lath- shaped feldspars with almost no irregular grains in the basic varieties. The tendency of basic rocks to crystallize more completely and with larger groundmass crystals than acidic rocks is constantly observed among the extrusive rocks, such as basalts, andesites, and rhyolites. The same law appears to obtain among the intrusive rocks. It is of course necessary to compare rocks that appear to have crystallized under very nearly the same physical conditions. The rocks of Group II have been described in greater detail on account of their number and importance, and have been subdivided into three sub- MINERAL COMPOSITION OF DIOKITES. 109 grou]is, Ilrt, II/>, He. The tables presenting the results of this part of the work have a ditierent form and are arranged separately for each subdivision. They are Tables V, VI, and VII. Table V. — Mincralogical variation among the diorites of Group Ila. 1 1 1 o «■ ga ^ Amount uf <|ujirtz. Kclative iiiiioiint of pyroxene and hornblende. Uelative amount of pyrox- ene, hornblende, and bio- tite. Little. Mod- erate. Con- sider- able. Much. p. P>h. p=h. pb. {ph)=b. (ph)h. p=h. pft)>6. {ph)=b. (phXb. 301 302 303 304 305 306 307 308 309 310 311 312 313 301 302 303 301 302 }3 304 305 306 307 308 301 3 yi 65.60 3 303 304 304 65.94 305 306 307 308 }9 310 311 12 313 305 306 63.78 307 3 )8 309 310 311 12 64.07 3 *309 t310 65.11 311 312 3 3 64.85 313 313 ] * This rock belongs 'witb 288, resembles it in structure and character, but is higher in silica and feldspar, t An exceptional variety, from talus. Table VII. — Mineralogical variation among the diorites of Group lie. 1 s 9 a 1 1 Cm O Xit, O CD O Amount of quartz. Relative amount of pyroxene and hornblende'. Relative amount of pyrox- ene, hornblende, and bio- tite. Little. Mod- erate. Con- sider- able. Much. P- P>h. p=h. Pb. (ph=b.) lph)6 275, 276 97 277 308 98 278 279 280, 281 282, 283 284 |- 285 I 286,287 288 289 99 30 31 ^9 33 1 SA 309 310 311 35 { 318 319 320 321, 286a 334 36 37 290 291 294 295 296 297 298 299 300 38 312 313 39 40 { 275« 322, 323 41 49 1 43 45 Table VIII expresses the relative degree of crystallization of all the intrusive rocks collected from the stock and dikes of Electric Peak. They are an-anged in the groups already described. The breaks in the different columns do not signify breaks in the gradation of crystallization in the rock bodies in the field, but simply that the specimens collected are not from all the different structural phases of the different rocks. However, the clus- tering of the numbers in particular parts of the scale indicates the prevailing grain of the rocks as they are exposed at the present time. CHEMICAL COMPOSITION OF ELIX'TUIC PEAK KOCKS. 1 15 It is not possible to draw a liiu' of (U'luarcatiiiu anywlieiv iu the scale based on the dej^ree of crystallization between rocks that occur in narrow dikes and those that form parts of much larger bodies. A relation between the degree of crystallization and the size of the rock bod}' does not at first appear when all of these occurrences are considered together. The very important influence of several other factors, however, becomes apparent. One is the chemical character of the magma, the more basic magmas tend- ing to crystallize coarser than the more siliceous ones under similar physical conditions. Another factor is the previous temperature of the rocks into which the molten magmas were injected, and the consequent differences in the rate of cooling which the molten magmas experience. There niay also be other factors which influence the crystallization in certain cases, but they are not evident in the occuiTences at Electric Peak. In this locality the chief factor influencing the crystallization appears to have been the temperature of the inclosing rocks at the time of the diff"erent intrusions. The next most influential factor appears to have been the chemical character of the magma itself, and the third the size of the intruded mass. In another region the relative importance of these factors may be different. CHEMICAL COMPOSITION. The chemical composition of the intrusive rocks at Electric Peak is shown by the analyses in Table IX. Nos. 272 and 3(i9 were made by Mr. W. H. Melville, the remainder by Mr. J. E. Whitfield. All are from rocks occurring in the stock and its immediate apophyses. They represent the composition of various forms of the diorite and diorite-porphyry. The first four analyses, Nos. 295, 267, 273, and 272, are from the main body of the stock, and belong to Subgroup Ila. The next four analyses, Nos. 309, 313, 311, and 303, are from modifications of the main body of the diorite and from one of the lighter-colored veins or dikes which traverse it. They belong to Subgroup Ilh. Two more varieties of the main stock are repre- sented by analyses Nos. 323 and 321. They are quite siHceous, and belong to Subgroup lie. Analyses Nos. 329 and 326 are from the large body of quartz-mica-diorite-porphyry, the first being a basic variety of it, and the second corresponding more nearly to the general character of the body of the rock. 116 OEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table IX. — Chemical analyses of intrusive rocks from Electric Peak. Constituent. 295 267 273 272 309 61.07 313 311 303 65.60 329 323 321 326 SiO; .... 56. 28 57.38 58.05 61.22 64.85 65.11 65.97 66.05 67.54 69.24 TiO, .... .84 Trace. 1.05 .61 .45 .91 .71 . 75 .42 .34 .80 .65 Al,03 ... 14.23 16.86 18.00 16.14 15.82 16.57 16.21 17.61 16.53 16.96 17.02 15.30 FegOs ... 4.69 2.49 2.49 3.01 3.40 2.10 1.06 .95 2.59 2.59 2.97 L72 FeO .... 4.05 5.17 4.56 2.58 1.44 2.15 3.19 2.76 L72 1.38 .34 .69 NiO .09 Trace. .05 Trace. MnO.... .16 Trace. None. None. None. None. None. None. Trace. Trace. CaO .... 7.94 7.32 6.17 5.46 4.43 4.01 3.97 3.72 3.37 3.37 2.94 2.98 MgO.... 6.37 5.51 3.55 4.21 3.39 2.14 2.57 1. 49 ! 2. 11 2.08 L51 .95 LiiO .01 .39 None. None. .04 .03 .09 None. .03 None. Na,0.... 2.98 3.33 3.64 4.48 4.06 3.71 4.00 4.36 3.41 4.20 4.62 4.46 K:0 1.23 L45 2.18 1.87 2.27 3.10 2.51 2.36 1 2.67 2.53 2.28 2.52 P,Os .... .40 Trace. .17 .25 .18 .14 .02 .16 Trace. Trace. Trace. Trace. SO, Trace. .21 .07 Trace. Trace. Trace. . 13 .03 .26 .27 CI H:0 .... Total. .17 .93 .17 .42 Trace. .86 None. .35 None. .94 None. 1 . 09 Trace. .15 .55 Trace. 1.30 .44 .52 .59 1. 23 . 69 100. 28 100. 70 100. 79 100.36 100. 08 100. 03 100. 33 100.38 '100.33 '100.22 101.01 100.08 Less 0 1 for CI . .04 .04 j .02 .03 100. 24 100.66 100. 31 100.98 Table X. — Silica percentages of rocks from Electric Peak. Sheet rocks. Dike and stock rocks. SiO^. I. Ila. i 116. lie. III. 53.72 55.23 55.64 56.28 56.33 53.72 55.23 55.64 56.28 56.33 57.12 57. 38 58.05 58.10 58.11 58.49 58.87 59.64 60.54 57. 12 57.38 58.05 58.10 58.11 58.49 58.87 59.64 60.54 SILICA PERCENTAGES OF ELEOTKIO PEAK ROCKS. Table X. — Silica percentages of rocks from Electric Peak — Continued. 117 Sheet rocks. Dike null 8tuck rocka. SiO,. 60.36 60.89 61.50 61.85 63.01 63.78 64.85 65.11 65.48 65.60 65.80 65.94 65.97 66. 05 67.54 69.24 I. IIo. 116. He. in. 60.56 60.89 61.50 61.85 63.01 63.78 64.85 65.11 65.48 65.60 65.80 65.94 65. 97 66.05 67. 54 69.24 • Fio. 1. — Variatiou oT silira perceutayes of rocks Irom Electric Peali. Tlie silica percentages of a number of varieties of these rocks were determined and are given in Table X, together with those from the complete analyses. In a measure they supplement these analyses and demonstrate what is evident from the. microscopical study of the thin sections, namely, that the diorites and porphyries pass through all possible gradations from one extreme to the other. The character of this transition is shown by the diagram, fig. 1, in which each determination is given the same weight. The series is arranged according to the increase of silica, and the silica percent- ages are plotted as ordinates. 118 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Ill Table X the percentages are all placed in the extreme right-hand column, and also in separate columns corresponding to the groups described in the first part of the paper. From this it is seen that the main body of the diorite varies from 53.72 to 60.56 per cent of silica, and in certain con- tact forms reaches 67.54 per cent. The dikes of later rocks related to the diorite and cutting the main body of the stock range from 63.78 to 69.24 2)er cent. Of the various bodies of magma that have followed one another through the conduit at Electric Peak, there is a variation in chemical com- position in each, the different series of changes overlapping one another. Thus the average chemical composition of each subgroup of varieties shifts somewhat, and is more basic for one than for another. But the end varieties of each subgroup overlap, so that tlie most basic modification of the more acid group is more basic than the most acid end of the more basic group which immediately preceded it. Since the rocks of Grroup I belong to outlying dikes of the main stock and are contemporaneous with it, their silica percentages may be placed in the proper subgroup of the stock rocks, making Subgroups lift and II & practically continuous. It apjiears from Table X that the succession of magmas which came up through the vertical fissures was from a basic one to more and more acid ones, and that the previous intrusions which formed the sheet rocks were of a magma of medium chemical composition. The variations of the other chemical constituents of these rocks are beet comprehended by comparing their molecular proportions. This has been done graphically in the accompanying diagram, fig. 2, in which the molecular proportions of the principal oxides are plotted as ordinates, those of the silica being taken as abscissas. The origin of abscissas is located some distance to the left. The first impression derived from the diagi'am is that of the irregularity of the variations in all the oxides besides silica, especially in the magnesia. Moreover, these variations appear t(i be independent of one another. But this apparent independence disappears on closer study. The most striking evidence of connection between the molecular proportions exists in the case of the two oxides of iron; the ferrous and ferric oxides are noticeably inversely proportional to each other, an increase of ferrous oxide being accompanied by a decrease of ferric oxide. The total amount of iron MOLECULAR VARIATION OF ELECTRIC PEAK ROCKS. HiJ varies iiTo<>ularly, decreasing from the basic to the acid end of the series. While each of tlie iron (^xides is quite independent of the magnesia, it is found upon reducing all the iron to the ferrous state that there is the greatest accord between the iron and the magnesia, both varying in like directions and to nearly the same extent. The ]nagnesia drops rapidly at first, and is very erratic in the more siliceous end of the series, where it becomes very low. The most regular variation is in the lime, which decreases steadily from the basic to the acid end of the series. It exhibits little or no connection AbQiJjaf ^-^ OSiOz .03& UaSU^ Fig. 2. — Molecular variation of the rocka at Electric Peak. with the other constituents. The molecular proportions of the alumina, though quite irregular between certain limits, maintain a uniformly high position, and are much greater than those of any one of the other constitu- ents except silica. At the extreme basic end of the scale, however, they are equaled by those of both the magnesia and the lime. The alkilies are most like the alumina in their variations, and remain very nearly uniform, increasing somewhat toward the acid end of the series. The soda mole- cules are more than twice as numerous as those of potash, which is one of the most noticeable characteristics of the rocks of this locality. In the basic end of the series the alkilies vary together in the same direction. 120 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. while in the more sihceous end they vary in opposite directions. There is a marked accordance between the soda and the alumina, both varying in the same direction, with one exception, though not to the same extent. There is a more strongly marked discordance between the alumina and the magnesia, which, with one exception,. vary in opposite directions. These irregular variations take place not only among allied varieties of rocks, but even in different parts of one and the same rock body. They find expi-ession in variations in the proportions of the essential minerals. The origin of this variation is undoubtedly to be sought in the chemical differentiation of the molten magma. The development of the constituent minerals in the solidified rock is the result of physical forces that combine the chemical constituents of the magma in a variety of ways to form closely analogous crystal compounds. A discussion of the possible molecular condition of molten magmas will not be taken up in this place. A few obvious relations between the mineral and chemical variations, however, may be pointed out. The inverse variation between alumina and magnesia, and the accordance between alumina and the alkalies, affect the relative proportions of feldspars and ferromagnesian silicates, which vary in an inverse ratio. The decrease of the alkaline earths with the increase of silica and the alkalies shows itself in the diminution of the ferromagnesian silicates and the calcium feldspars, which accompanies an increase in quartz and the alkali feldspars. The reciprocal variation of the ferrous and ferric oxides indicates the variable oxidation of preexisting ferrous molecules. This should naturally be in accord with the development of minerals containing more or less ferric oxide, the most prominent of which are hornblende and liiotite. Such a coimection seems to be made out, but data for its complete demonstration are not at hand. It is most significant on account of its bearing on the question of the development of these two minerals in the coarser-grained forms of rocks whose magmas maj^ crystallize under other conditions free from either mineral. It may tlu'ow light on the possible action of water vapor as a mineralizing agent. The order in which the constituents crystallized out of the molten magma to form diorite may be learned by considering the relative ages of the component minerals. It has been pointed out that some crystallized almost synchronously, but that they began to separate from the liquid VOLCANIC KOCKS OF SEPULCHRE MOUNTAIN. 121 magma at ditterent times. The order in which tlio ditl'ereut minerals began to crystalHze in that portion of the magma which formed diorite appears to have been as follows: Magnetite, liypersthene, augite, labradorite, horn- l)lende, biotite, oligoclase, orthoclase, quartz. The feldspathic minerals started to crystallize liefore an}- of the ferromagnesian minerals had com- menced; and the last of the series undoubtedly crystallized after all of the feiTomagnesian minerals had been completed. So far as the siliceousness of the minerals is concerned, the series of ferromagnesian silicates and that of minerals free from iron vary in opposite directions. In the former the range is from highest silica to lowest; from the metasilicate, liypersthene, to the orthosilicate, biotite. In the second it is from the least siliceous, labra- dorite, to the most siliceous, orthoclase, or to free silica, quartz. THE VOLCANIC ROCKS OF SEPULCHRE MOUNTAIN. The igneous rocks of Sepulchre Mountain are partly extrusive, partly intrusive. By far the greater mass consists of subaerial breccias and tuffs, with a small amount of massive lava flows The intrusive rocks form dikes and larger bodies traversing these breccias. The breccias and flows are andesites of various kinds. The intrusive bodies are andesites and dacite, grading into porphyry-like modifications in places. The tuff-breccia is separable into an older and a newer, or into a lower and an upj^er, l^reccia. THE LOWER BRECCIA. , The lower breccia is about 500 feet thick, and consists mostl}' of frag- ments of hornblende-mica-andesite, and is generally light colored. It carries a large amount of fragments of crystalline schists, which do not occur in the overlying upper Ijreccia. It is probable that the lower breccia was ejected from some neighboring center of eruption located in an area of Archean rocks. Such a center occurs a few miles north, at the west base of Sheep Mountain. The lower breccia passes into fine tuff in places, and at the extreme end of the northwestern spur of the mountain it is distinctly bedded, with layers containing bowlders of a rhyolite-porphyrj^, which has not been found in place in this region. In places the upper part of the breccia is green and partly decomposed, as though weathered before the upper breccia had been thrown iq^on it. In the northwestern spur of the mountain the upper breccia is seen to rest upon an uneven surface of the lighter-colored 122 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. • bottom breccia. There appears to have been a distinct time break between the ejection of the lower breccia and that of the upper breccia. The occur- rence of fragments of crystalHne schists in the bottom Hght-colored breccia and their absence from the overlying dark-colored breccia is a characteristic difference between these two breccias wherever they have been observed along the northern boundary of the Yellowstone Park. The andesites from the lower breccia at Sepulclu-e Mountain vary somewhat in mineral composition, color, and microscopical habit. They are mostly light colored — gray, white, and red; in places dark colored. Some fragments have comparatively large phenocrysts; others are crowded with small ones. The greater number of fragments are hornblende-mica-andesite ; some have little mica, and grade into hornblende-andesite. Others are dacite, having quartz phenocrysts. The microstructure of the ground- masses of these rocks ranges from glassy and microlitic to microcrystalline. The characters of the minerals and the microstructures are the same as those of the light-colored acid breccias on the Yellowstone River in the neig'hborhood of Crescent Hill, and also those in the vicinity of Cook City. It is important to note that there is associated with the lower acid breccia of Sepulcher Mountain an obscure body of massive, vesicular basalt with porphyritical augites and decomposed olivines. Its exposure is of small extent, and its exact relation to the breccia was not seen. It is ariiygdaloidal with quartz, agate, and calcite. It does not resemble the recent basalts in the neighborhood, but is similar to basalt associated with the bottom acid breccia at Crescent Hill and in the valley of Cache Creek. Its petrographical character is more fully discussed in Chapter IX, where it is classed with shoshonites. THE UPPER BRECCIA. The upper Ijreccia, overlying that just described, is dark colored at its base and lighter colored in the upper portion. It is at present 3,000 feet thick through the summit of the mountain. The lower portion consists almost wholly of pyroxene-andesites, with little or no hornblende. Many fragments are vesicular and basaltic in habit, without megascopic pheno- crysts. At the south base of the mountain there are vesicular massive bodies of pyroxene-andesite, with large phenocrysts of pyroxene and VOLCANIC ROCKS OF SEPULCHRE MOUNTAIN. 123 felds])!!!-. The u])per portion of tliis breccia is iiiore hoi-iibleudic, and horiil)k'iide-j)yroxene-;nul('sitcs predominate. The transition from tlie pyroxene-andesite ])ortion to the liornl>U'nde-pyroxene-andesite portion appears to he <>ra(hi;d. The hiter breccia is accom^janied by vesicular flows of simihu' andesite, often cpiite porous. It is hghter colored in gen- eral, but parts are quite dark, witli prominent hornblendes, the habit being andesitic, not basaltic. There are no evidences of any considerable In-eak or interruption between the higher and the lower parts of this breccia. They appear as a continuous geological body, composed of fragments and flows of andesite which were ejected from one center of eruption during a considerable period of time. The andesitic material composing this breccia varies somewhat in min- eral composition and in megascopical habit, as will be seen from the following descriptions. The variation in tlie phenocrysts present other than feldspar in the specimens examined is indicated in Table XI. They are andesites with glassy groundmass and phenocrysts of plagioclase, hypersthene, and augite in some cases, and with these minerals and hornblende in others. Table XI. — Mineral variation in the upper breccias of Sepulchre Mountain. I Mineral groups. Specimen uumber. Phenocrj'sts other than feldspar. Pyroxene. Hornblende. Biotite. Quartz. 1 B, ....\ B, .... B, .... 385 386 387 388 390 391 392 393 394 396 397 398 400 401 402 403 404 Much . Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Much Little Little Little Little Little Little 1 Some ""{ Some Some Some 124 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table XI. — Mineral variation in the iq)per breccias of Sepulchre Mountain — Cont'd. Mineral Group. Specimen number. Pbeuocrysts other than feldspar. Pyroxene. Hornblende. Blotite. Quartz. ' B^ .... Bs .... 405 406 407 409 410 411 412 413 414 415 416 417 418 419 420 Much Much Much Much Much Much Much Much Much Much Some Some Some Some Some Much Much Much Much Much Much Much Much Much Much Much Much Much : Much Little The varieties without hornblende, Bj — that is, pyroxene-andesites — have a groundmass of g-lobuUtic brown glass, in shades from dark to light, filled with microlites of feldspar, pyroxene, and magnetite. The size and abmidance of the microlites vary. The feldspar microlites are plagioclase with low extinction angles. Two of the varieties examined are basaltic in appearance, with a few decomposed olivines among the phenocrysts. The pyroxenes are both hypersthene and augite, having much the same general appearance in the same rock. Their crystal outline varies consid- erably in one rock section. Some individuals are bounded by distinct crystal planes, while others are rounded. Some have irregularly jagged outlines, with tongues of glassy gTOundmass ^^I'ojectiug into tlie crystal. These forms appear to be the result of irregularities of growth rather than of solution by the magma before its solidification. Inclusions of glass are common; also those of magnetite, and fewer of apatite. The hypersthene is pleochroic; green parallel to C, ^^ellow parallel to a, light red parallel to h- It is generally light colored in thin section. But one darker-colored crystal with strong pleochroism incloses thin brown plates, aiTanged in lines at right angles to the vertical axis of the crystal. These inclusions are like those in hypersthene in many coarsely crystalline VOLCANIC ItOCKS OF SKPULCUKE MOUNTAIN. 125 rocks. In tins case the nxrk is f^lassy and vesicular, and shows no signs of any kind of nictainorj)hosin3. V>t, U„ D,. D„I>„D,. D,„,1),„D„. 1. 394,396 416. 2... 385, 38fi, 387, 388, 397, 398, 421, 422, 423, 427, 428. 401,405,417 459. 3... 390, 391, 392, 393, 400,429. 402, 403, 406, 407, 409, 410, 411, 412, 413, 418, 431, 432, 433, 434. 4... 404,414,415, 419, 443,460,461,474.. 476, 420. 5... 445,462,463 446,464,465 481, 482, 496. 477,484,485 486,487... 6... 424 436,437,439 498 508 509 7... 425 466,467,468,475.. 499, 510, 511, 512, 523. 8 .. 447 448 449 470 478, 488, 489, 490. . 500, 501, 502, 503, 513, 514, 515, 471, 472, 469. 516, ;i7, 524, 525. 9... 451, 452, 453. 454. 455. 491,492,497 .504 .518 tilQ 10... 11.. 456, 457, 473 . , 526, 12 .. 440 479, 480. 13... ' 505, 527. 14... 15... 426 441 493. 16... 458 494. 17... 18... 520. 506, 507, 521, 522. 19 495 20... 442. 21... 22... 23... 24... 25... 430. . 132 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The microstructiire of the acid varieties is not the same as that of the basic, so that it is diflficult to compare the grain of one directly with that of the other; but since the intermediate rocks 230ssess microstructures intermediate between these extremes, it is possible to estabhsh a kind of relationship between them, and it is admissible to place them in the same line across the table, it being understood that the correspondence is an a^jproximation. A glance at Table XIII shows that a large majority of the varieties are very fine-grained forms that have only reached the crystallization of the few smallest-grained forms of the Electric Peak rocks. A small num- ber of them are more coarsely microcrystalline and correspond to the grain of the dike rocks at Electric Peak. A large number are finer grained than any of these rocks, or are glassy. The coarsest-grained forms have been attained by the most basic varieties, but they do not represent bodies of any considerable extent. Specimen No. 430, grade 25, comes from a small exposure with no definite limits, surrounded by much finer-grained rocks. It is properly a diorite-porphyry, and carries much biotite of final consoli- dation, which has not been reckoned with the phenocrysts. The coarsest- grained forms of the acid varieties, however, represent larger bodies and are more abundant in the field. In explanation of the degrees of crystallization indicated in the table, it may be said that the first three are glassy groundmasses, the first one having fewer microlites than the second. In the third the microlites are closely crowded together. The next two represent microlitic structures in which no glass can be detected; they appear to be holocrystalline. In the sixth grade the form of the microlites is more indistinct, but the general structure is the same as before. Beyond this the diff'erent deg-rees indicate increasing grades of a structure which may be described in general as follows: Commencing with the lowest order, the groundmass is composed of a multitude of indistinct microlites of lath-shaped feldspars; between crossed nicols this aggregation extinguishes light in small patches Avhicli bear no fixed relation to the position of the microlites within them. As the dimensions of the lath-shaped feldspars become larger it is observed that the patches of light and darkness arise from the cementing material between these feldspars. This cement possesses the same optical orientation for small spaces which in cross section produce the patches just alluded to. In CRYSTALLIZATION OF SEPULCHRE MOUNTAIN ROCKS. 133 still coarser-fjraiiied fornis it becomes apparent that the cementing material is quartz which has crystallizod in irregularly shaped patches inclosing many smaller Feldspars. The size of thes(i feldspars and of the interstices between them is taken as the grain of the rock, and not the size of the patches of quartz. For it is observed that as the rocks become more coarsely crystalline the felds[)ars, which are plagioclase, increase steadily in size and each quartz patch cements fewer of them, until in still coarser grades the quartz forms allotrioraorphic individuals between the plagio- clases and does not surround any, so that in these varieties of rock the size of grain is judged by the dimensions of the plagioclases and the interstices of quartz. The patchy structure just described is that called micropoikilitic. In the most siliceous varieties of the rocks the microstructure is differ- ent. The smallest-grained forms appear to approach a granular structure, in which, however, the feldspars exhibit a more or less rectangular shape and the quartz shows a tendency to appear in minute, poorly defined dihexahedrons. As the grain becomes larger the form of the quartz grains becomes more pronounced (PI. XXII, fig. 2). They are rudely idiomorphic, with sections that are in many cases equilateral rhombs, extinguishing the light parallel to their diagonals. In the coarsest-grained forms of the dacites these imperfectly idiomorphic quartzes are characteristic of the groundmass, and reach a diameter of from 0.08 mm. to 0.10 mm. (PI. XXI, fig. 2). Their surface is indented with the ends and corners of small plagioclases, the structure of the groundmass being hypidioraorphic. These quartzes often contain minute colorless inclusions in negative crystal cavities, which have every appearance of being glass and correspond to the glass inclusions in the quartz phenocrysts of the same rocks. The partially diomoi-phic quartzes in the groundmass are to a slight degree porphyritical with espect to the other constituents, but belong to the final consolidation of the magma. 134 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, GENERAL CONSIDERATION OF THE MINERAL AND CHEMICAL COMPOSITION OF THE ERUPTIVE ROCKS OF SEPULCHRE MOUNTAIN. MINERAL COMPOSITION. The mineral variations in tlie group of rocks forming Sepulchre Momatain are much simpler and require much less discussion than those of the intrusive rocks of Electric Peak. They have already been expressed in Tables XI and XII. From these tables it is evident that the so-called transitional forms of the rocks are as numerous and as important as those forms which would be considered type rocks. There is no particular mineralogical modification of the rocks at this place which from its gi-eater abundance or its special mode of occurrence renders it a type rock. On the contrary, the whole accumulation of eruptive rocks which are subsequent to the bottom breccia, with its admixture of Archean fragments, must be considered as a series of volcanic rocks that vary in mineral composition through gradual changes from pyroxene-andesite to dacite. Starting with those rocks which carry phenocrysts of pyroxene and plagioclase, it is observed that as the hornblende makes its appearance and increases in amount the pyroxene decreases. Biotite accompanies the hornblende in the more acid varieties, and increases in amount with the acidity of the rock. Quartz first appears in small quantities, and increases with the acidity of the rock, the hornblende decreasing at the same time. To this rule there are exceptions, which are indicated in the table. Biotite is found to a slight extent in some of the homblende-pyroxene-andesites, and pyroxene occurs in small amounts in some of the hornblende-mica- andesites. It is, of course, understood that this relation between the essential minerals may be different for groups of andesites in other regions. CHEMICAL COMPOSITION OF SEPULCUKE MOUNTAIN ROCKS. 135 CHEMICAL COMPOSITION. The chemical composition of the ei-uptive rocks of Sepulchre Moun- tain is shown in the accompanying table of chemical analyses: Tablk XIV, — Chemical analyses of rocks from Sepulchre Mountain, Constltaent. 4«1 471 407 386 409 487 494 521 523 SiOj 55.83 1.05 17.11 4.07 3.75 None. 7.40 55.92 .94 17.70 3.16 4.48 Trace. 5.90 56.61 .79 13.62 5.89 2.60 .35 6.61 .14 5.48 Trace. 3.13 2.71 .06 (?) None. 2.27 57.17 1.03 17.25 2.48 4.31 None. 6.61 4.83 Trace. 3.44 2.03 .05 Trace. Trace. 1.20 60.30 .76 16.31 4.35 1.41 .13 5.62 .15 2.39 Trace. 3.99 2.36 .20 .10 None. 2.50 64.27 .32 17.84 3.36 1.29 None. 3.42 2.00 .03 3.84 2.48 .16 Trace. None. L32 65.50 .45 14.94 1.72 2.27 .20 2.33 .13 2.97 Trace? 5.46 2.76 .09 .06 None. L37 65.66 1.37 15.61 2.10 2.07 None. 3.64 67.49 .13 16.18 1.30 1.22 .08 2.68 TiO. AljOa FesOa FeO MnO CaO BaO MeO 5.05 4.34 2.46 1.34 SrO LiaO None. 2.94 1.71 .21 Trace. None. .09 4.08 2.28 .18 Trace. None. .36 3.65 2.03 Trace. .13 .12 Na>20 4.37 2.40 .13 K2O P2O6 SO3 CI COi H20.. 1.28 1.42 1.07 2.69 Less 0 for 01. 100. 40 100. 45 100. 26 100.40 100. 57 100.33 100. 25 100. 27 .03 100. 01 100. 24 Nos. 421, 471, 386, 487, and 521 were analyzed by Mr. J. E. Whit- field; Nos. 407, 409, and 494 were analyzed by Dr. T. M. Chatard; and No. 523 was analyzed by Mr. L. G. Eakins. The first, 421, and the fourth, 386, are analyses of pyroxene-andesites which carry no hornblende. The first is from a dike near tlie summit of the mountain; the other is from a surface flow at its southwest base. Nos. 407 and 409 are of hornblende-pyroxene-andesites, occurring as breccia in the upper part of the mountain. No. 471 is of hornblende- andesite, which is an intruded body in the small hill northeast of Cache Lake, at the head of Reese Creek. No. 487 is a hornblende-mica-andesite from the same locality, also an intrusive rock. No. 494 is the same kind of andesite from an intrusive mass at the north base of Sepulchre Mountain, 136 GEOLOGY OP THE YELLOWSTONE JNATIONAL PARK. and Nos. 521 and 523 are dacites from the lidge south of Cache Lake. The structure of 521 is shown in PI. XXI, fig-. 2. The range of variation in the percentage of sihca is about the same as that of the rocks at Electric Peak. The character of the variations of the other oxides in these rocks is shown by the accompanying diagram, fig. 3, whicli represents the variations in the molecular proportions of the essential oxides, and has been plotted in the manner already described. A glance at this diagram shows that it has the same form as that of the group of analyses of the rocks from Electric Peak. The variations in M,i03J60i CkLO 132 M^-IZG Fig. 3 — Molecular vari.ition of the rocks of Sepulchre Mountaiu. the oxides other than silica are quite irregular for a gradual change in the silica. The alumina varies rapidly in 2Dlaces and retains a high position in the diagram. The alkalies gradually increase with the silica, the soda mole- cules being twice as numerous as those of potash, and their variations being alike, with one exception. Magnesia varies most widely, and in striking contrast to the alumina; in each instance they vary in opposite directions. The lime is nearly as irregular as the magnesia, both decreasing rapidly from the less siliceous to the more siliceous end of the series. The two oxides of iron are strikingly reciprocal in their variations, the significance of which has been pointed out in discussing the diagram for Electric Peak. IGNEOUS ROCKS WEST OF GALLATIN MOUNTAINS. 137 III the group of analyses from Sepulchre Mountain the oxidation of the iron bears a noticeable relation to the presence of hornblende, biotite, and magnetite in the rocks. From a study of these analyses it is evident that the chemical varia- tions in this group of rocks are the same in character and extent as those in the intrusive rocks of Electric Peak. Moreover, it appeal's that the variations between similar varieties of andesite — such as those between dirtVrent ])yroxene-andesites — are as great as, and in some cases greater than, the variations between varieties of andesites which are distinguished mineral- ogically from one another. Thus, Nos. 421 and 386 are pyroxene-andesites without hornblende, Nos. 407 and 409 are hornblende-pyroxene-andesites, while No. 471 is a hornblende-andesite. It is not possible to point to any chemical character of these rocks that is distinctive of this mineral varia- tion, with the exception of the oxidation of the iron, which, though slight, is an important one ; for it undoubtedly relates to forces that did not alter the fundamental relation between the bases in the magma, but simply modified it by changing the oxidation of one of them. The last four analyses are of hornblende-mica-andesites and dacites. The chemical varia- tions between them are as pronounced as those between the more basic members of the series, without there being the con-esponding differences between the kinds of ferromagnesian silicates, so far as it can be detected microscopically. They all carry hornblende and biotite, and no pyroxene, the relative proportions of these minerals varying. The character and amount of the feldspars differ in these rocks, and so do the abundance and mode of occurrence of the quartz. In Nos. 521 (PI. XXI, fig. 2) and 523 quartz appears as pheuocrysts; in the other rock it is confined to the groundmass. THE EXTRUSIVE IGKEOUS ROCKS WEST AND SOUTHWEST OF THE GAIiLATlN MOUNTAINS. These are mainly tuff-breccias of andesite, with rarely a massive lava flow of andesite, more numerous flows of basalt, and the great rhyolite lava sheet. Andesitic breccias form the north-south i-idge west of the headwaters of Fan Creek, and extensive accumulations of these rocks underlie rhyolite in the northwestern corner of the Park, where they are connected with the range of volcanic mountains farther north. There are other isolated areas of andesitic breccia in the gneissic mountains west of Mount Holmes. In 138 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. all of these localities the tufF-breccias have the same genei-al character as the tuff-breccia of Sepulchre Mountain, just described They vary some- what in compactness. In all, the fragments are small. The general color is dark, but that of the individual fragments is varied — dark and light grays, with tones of red. There are abundant small phenocrysts in most instances; some fragments are almost free from them, while others carry larger and more prominent ones. The mineral composition varies slightly among the fragments in any considerable mass. The greater part are hornblende-pyroxene-andesites and pyroxene-andesites. Hoi-nblende-andes- ites without pyroxene are less abundant. Still less frequent are hornblende- mica-andesites, representing the most siliceous rocks, while the least siliceous are olivine-bearing pyroxene-andesites or andesitic basalts, which are much rarer. These -s'arieties naturally grade into one another and are inter- mingled in the tuff-breccias. The microscopical characters of the various andesites from these local- ities correspond to those of the Sepulchre Mountain andesites. The ground- masses range from glassy to microcrystalline and microlitic. Some of the glasses are colorless, others brown and globulitic. The hornblendes in most cases are brown and reddish brown, seldom green (543), which con- trasts them with those in the andesite-^Dorphyries. They often have black borders, especially in the more basic rocks, where they are sometimes paramoi'[3hosed to magnetite and pyroxene. The feldspars are plagioclases, more calcic in the less siliceous rocks. They are characterized by numerous glass inclusions and marked zonal structure. The pyroxenes are hypersthene and augite. The olivine in two rocks where it was observed is serpentinized. COMPARISON OF THE ROCKS FROM EIjECTRIC PEAK AlVD SEPUIiCHRE MOUNTAIN. The geological structure of Electric Peak and of Sepulchre Mountain and the occurrence and character of the igneous rocks in each locality having been desci'ibed, it remains to point out the relationship of the two groups of rocks to each other and the petrological deductions which may be drawn from their investigation. To arrive at the relationship of the volcanic I'ocks of Sepulchre Moun- tain to the intrusive rocks of Electric Peak, it is necessary to observe, in review of the facts already presented, that the latter cut through Cretaceous CORUELATION OF THE ItOUKS. 139 shales and sandstones, and have imparted to tliem sufficient heat to meta- nior])h()se tliein for a fj-reat distance, indicating- the ])assa<'e of large (juanti- ties of molten magma through the fissures, while the lavas of Sepulchre Mountain i-est on Cretaceous strata and also caiTy large blocks of black shale inclosed within them They plainly show by their crushed and dragged portions that a ])rofound fault has separated the block of Sepulchre Mountain from that of Electric Peak, drojjping the former down consid- erably more tlian 4,000 feet. Consequentlv the volcanic rocks of Sepulchre Mountain once occupied a higher elevation than the present summit of Electric Peak and its bodies of intrusive rock. In Electric Peak there is a system of fissures that radiate outward toward the south and southwest, as shown by the dikes of porphyry. At the west base of Sepulchre Mountain there is a system of dikes and intruded bodies that radiate outward toward the north and northeast. These fissures antedate the great faulting just mentioned and represent the east and west halves of a system of fissui-es trending from north and south around to northeast and southwest, which crossed one another at the point where the broadest body of intruded rock is now found. The axis of this system appears to have been inclined toward the east — that is, to have dipped toward the west — and was cut across by the great fault which dropped Sepulchre Mountain. The igneous rocks that broke through the strata of Electric Peak consist of a series of andesite-porphyries, occurring in sheets between the strata, and another seiies of diorites and andesite-porphyries that were erupted through the vertical fissures just alluded to. The central fissure or fissures became the conduit through wdiich the molten magmas followed one another after successive intervals of time. In the outlying naiTow fissures the magmas solidified as dikes of porphyry, while within the heated conduit they consolidated into coarse-gi-ained diorites of various kinds. The magmas of this series of eruptions became more and more siliceous. Their succession is indicated in the table on the next page. 140 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table XV. — Order of eruption of the rocks at Electric Peak and Sepulchre Mountain. Succession of ernptioDs at Electric Peak. Snccession of ernptions at Sepulchre Monntain. A. Intrusion of sheets of andesite-por- A. Extravasation of andesitic breccia from phyry from the southwest. some Archean area. B. Intrusion of dike and stock rocks in B. Eruption of andesitic breccias and the following order: dikes in the following order: Pyroxene-porphyries, grading into Pyroxene-audesites, breccia, and do ws, passing into pyroxene- and hornhlende-diorites pyroxeue-hornblende-andesites, brec- with biotite of tin.al crystallization, cia, and flows, with dikes of similar with dikes of pyroxene- and horn- andesites, grading into blende-porphyries, grading into hornblende-biotitediorites with bio- hornblende-biotite-andesites, in dikes, tite of early crystallization, with grading into dikes of hornblende-biotite-porphy- ries J quartz- biotite-diorite-porphyry with dacites with phenocrysts of quartz, some hornblende, with dikes of biotite, and some hornblende. quartz-biotite-porphyry. The igneous rocks that formed the breccias and lava flows of Sepulchre Mountain, with their dikes and larger intruded bodies, constitute a series of andesites, basalts, and dacites, which reach a degree of crystallization that places part of them among the porphyries. They commenced with an andesitic breccia that is filled with Archean fragments, which must have been thrown from some neighboring center of eruption located in an Archean area. Such a center exists a few miles to the north. This was followed by a series of magmas that were at first somewhat basic and became more and more siliceous. The series is represented in the right-hand column of Table XV. From this it is seen that the succession of eruptions in each locality was the same after the first period. A, in which the magmas evi- dently came from different sources. Each series of the second period began with basic magmas and ended with acid ones. Their division in the table into four groups is not intended to convey the idea that they belong to four distinct periods of eruption; the whole series in each case is, rather, a single irregularly interrupted succession of outbursts of magma that grad- ually changed its composition and character. Upon comparing the rocks which have resulted from the corresponding phases of these series of erup- tions, the similarity of the porphyritic forms is immediately recognized. CORRELATION OF THE KOGKS. 141 Tlie nature and distribution of the phenocrysts in the different varieties of andesite and dacite, which determine their inegascopical habit, liave their exact counterpart in the different varieties of porphyries. The microscopical characters of the phenocrysts in the corres})onding varieties of porphyries and of the intruded andesites and dacites are identical The character of the various groundmasses, however, is different in tlie two groups, being more highly crystalline in the porphyries — many of the andesites being glass}'. Many of the tiner-grained diorites have a habit, derived from the distribution of the ferromagnesian silicates and larger feldspars, which resembles that of some of the andesites and dacites that correspond to them chemically. Finally, the study of the chemical composition of the intrusive rocks of Electric Peak and of the volcanic rocks of Sepulchre Mountain proves that these two gi'ouj)S of rocks have identical chemical compositions, for the varieties that have been analyzed are but a few of the many miner- alogical and structural modifications assumed by these magmas on cooling. The analyses serve as indications of the range of the chemical variability of these magmas From the geological structure of the region, then; from the corre- spondence between the order of eruption of the two series of rocks; from the resemblance of a large part of the rocks of both series, megascopically and microscopically, and from the chemical identity of all the rocks of both groups, it is conclusively demonstrated that: I. The volcanic rocks of Sepulchre Mountain and the intrusive rocks of Electric Peak were originally continuous geological bodies. II. The former were forced through the conduit at Electric Peak during a series of more or less interrupted eruptions. III. The great amount of heat imparted to the surrounding rocks was due to the frequent passage of molten lava through this conduit. We have, then, in this region the remnant of a volcano, which has been fractured across its conduit, faulted, and considerably eroded, and which presents for investigation, on the one hand, the lower portion of its accumulated debris of lavas, with a part of the upper end of the conduit filled with the final intrusions, and on the other hand, a section of the conduit within the sedimentary strata upon which the volcano was built. 142 GEOLOGY OF THK YELLOWSTONE NATIONAL PARK. CORRELATION OF THE ROCKS ON A CHEMICAL BASIS. Correlatiuy the two groups of rocks according to their chemical composition and arranging them as in Table XVI, we see that the hornblende-mica-andesites, Nos. 487 and 494, are the equivalents of the quartz-mica-diorites, Nos. 313, 311, 303, 323, and 321, and of the quartz- pyroxene-tnica-diorite, No. 309. The dacites, Nos. 521 and 523, are the equivalents of the quartz-mica-diorite-porphyries, Nos. 329 and 326. The hornblende-pyroxene-andesites and the pyroxene-andesites, Nos. 421, 471, 407, 386, and 409, are the equivalents of the coarse-grained pyroxene-mica- diorite. No. 295, with variable percentage of quartz, and of the fine-grained diorites, Nos. 272 and 273, and of a fine-grained variety. No. 267. The dacites and hornblende-mica-andesites included within this cor- relation are intruded bodies within the breccia of Sepulchre Mountain, and have the same nrineral conijiosition as the corresponding porphyries and diorites of Electric Peak. They diff'er from them in structure and degree of crystallization, as already described. The glassy andesites, with pyroxene and hornblende phenocrysts, however, present the utmost contrast to the chemically equivalent coarsely crystalline diorites. In the former the hypersthene, augite, hornblende, and plagioclase are sharply defined idiomorphic crystals in a groundmass of glass, which is crowded with microlites of plagioclase and pyroxene, besides grains of magnetite. The hornblende is brown, occasionally red, and the other phenocrysts have all the microscopical characters which distinguish their occurrence in glassy rocks. In the diorite the hornblende is green; in some cases brown ; and the hypersthene, augite, and hornblende are accom- panied by biotite, and are all intergrown in the most intricate manner, with evidence that they commenced to crystallize in the order just given. The labradorite is often clouded with minute opaque particles, which are charac- teristic of its occurrence in many diorites. It is surrounded by a shell of more alkaline plagioclase, which, with occasional individuals of orthoclase and considerable quartz, closed the crystallization of the magma. Magne- tite, apatite, and zircon are the accessory minerals. The quartz contains fluid inclusions, which complete the correspondence of this diorite with typical diorites of other regions. From the structure of this region, which has been so finely exposed CHEMICAL COHRkLATION OF THE ROOKS. 143 by faultiiiji' aiul erosion, it is evident tluit of the diflFerent magmas enipted a part found tlieir way into vertical fissures and took the form of dikes; part reached tlie surface and became hiva flows and breccias, while other portions remained in the conduit. Therefore the various portions of the miio-nias solidified under a variety of physical conditions imposed by the dirt'erent geological environment of each, the most strongly contrasted of which were the rapid cooling of the surface flows under very slight pressure and the extremely slow cooling of the magmas remaining within the conduits under somewhat greater pressure. Table XVI. — Correlation of the two groups of rocks upon a chemical basis. S'O, No. Volcanic rocks of Sepulchre Mountain. Intrusive rocks of Electric Peak. Essential minerals. Name. Name. Essential minerals. Phcnocrysts. Groundroass. 69.24.. 67.54.. 67.49.. 66.05.. 65.97.. 65.66.. 65.60.. 65.50.. 65.11.. 64.85.. 64.27.. 64.07.. 326 321 523 323 329 521 303 494 311 313 487 309 quartz mica-diorite- porpbyry. quartz-mica-diorile . quartz-raica-diorite . quartz-mica-diorite- porphyry. quartz-mica-diorite . quartz-mica-diorite - quartzmica-diorite - quartz-pyroxene- mica-diorite. quartz, biotite, plagioclase and alkali feldspar, horn- blende. biotite, hornblende, plagio- clase (ortboclase), quartz. biotite, hornblende, plagio- clase (ortboclase), quartz. biotite, hornblende, plagio- clase (ortboclase), quartz. biotite, hornblende (pyrox- ene), plagioclase (ortbo- clase), quartz. biotite, hornblende, augite, byperstheue, plagioclase (ortboclase), quartz. hornblende, biotite, plagio- clase (ortboclase), quartz. biotite, hornblende, augite, hypersthene, magnetite. plagioclase (ortboclase) , quartz. (lacite quartz, biotite, horn- blende, plagioclase. holocrystalline, quartz, feld- spar. dacite quartz, biotite, horn- blende, plagioclase. holocrystalline, quartz, feld- spar. hornblende- mica ande- site. hornblende, biotite, plagioclase. holocrystalline, quartz, feld- spar. horn bleu de- mi ca-ande- eite. hornblende, biotite, plagioclase, mag- netite. holocrystalline, quartz, feld- spar. 144 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table XVL — Correlation of the two groups of rocks upon a chemical basis — Continued. SiO. "Volcanic rocks of Sepulchre Mountain. Intrusive rocks of Electric Peak. per No. Essential minerals. cent. Name. Name. Essential minerals. Phenocrysts. Groundmasa. 61.22 272 pyroxene-mica - dio- rite. biotlte, hornblende, augite, hypersthene, magnetite, ' plagioclase (quartz). 60.30.. 409 horn blend e- pyroxene- andesite. hornblende, augite, Lypersthene, plagio clase, magnetite. glassy, micro- litic. 58.05.- 273 pyroxene-mica - dio- rite. hiotite, hornblende, augite, hypersthene, magnetite. plagioclase (qiiartz). 57 38 267 pyroxene-porphyry. augite, hypersthene. l)io- tite, magnetite, plagio- clase, quartz. 57.17.. 386 pyroxenc- augite. hyperstbene, brown glass. aiidesite. plagioclase. niicrolitic. 56.61.. 407 bornblende- pyroxene- bornblendf. augite. glassy, niicro- hyperstbene, plagio- 1 litic. andesite. clase. pyroxene-mica-dio - rite. hiotite, hornblende, augite, hypersthene. magnetite. plagioclase, quartz. 55.92.. 471 hornblende- andesite. hornblende, plagio- clase. microcryatal- liue. 55.83.. 421 pyroxeue- andesite. augite, hyperathene, plagioclase. glassy, niicro- litic. The effect of this diversit}'- of conditions upon the degree of crystal- lization of the various portions of these rocks is well shown in the accom- panying Table XVII, which has been derived from Tables VIII and XIII. In this table are presented all of the specimens from Sepulchre Moun- tain and Electric Peak. They are arranged in four principal divisions: First, the breccias and lava flows; second, dikes and larger bodies intnided in these breccias; third, dikes in the Cretaceous strata of Electric Peak; fourth, the main stock and its immediate apophyses. These groups are still further subdivided into columns which coirespond to mineralogical differences in the rocks, and bear the same letters as the mineralogical subdivisions in Tables III, VIII, XI, and XII. Consequently each of the four principal groups has the most basic members at the extreme left and the most acid ones at the extreme right. The mineralogical range is therefore repeated four times. The table illustrates a number of facts. It exhibits the relative degree of crystallization of the breccias, lava flows, Taiu.e Wll. —Cornhilion nj ;/niittA of / the ruvkn J'rvm Seimkhrv Mountain and Electric i'eak. Gradtw oT crystilliu- Udu. Sepulutira MuuDlaiu. Electric Teak. 1 Breccias. Dike nickS: Dikt, rook*. StMkiwiki. B. 394,396 397,398 400 B. B. 416 417 118 4151,420 D. D. 1>> D. D. l>. D, u. D. D,. D„ Dit a, J. .u 0. •1. d. .1, .1. a. 1 462, 463 416 ! 164,46^ 6 424 436,437,439 475 177 425 466, 467. 46(1 4611,470,471, 472 510, 611, 512 513,514,515, 516,517 518, 519 523 521, 525 ■aa 447, 448, 449, 450 461,452,453, 454,455 478 ■ 497 502, 503 504 241,212 243 244,245 246 256,256 257 258 45U, 457 473 526 440 479,480 239 219,250 251 252,253 13 ... . 505 i>27 .1. 14 426 441 493 217,248 IB 18 . .. 458 494 236 254 17 t 18 520 521, 522 19 495 506, 507 232 236,237 20 142 333 21 326, 327 328.329 330,331 332 22 ! -m 272 ' 273,274 23 24 310 430 234 26 275,276 277 ■ 278 279 280,281 283,283 284 285,^, 387 288 280 308 309 310 3.1 ... 1 27 318 331 28 29 30 31 ' 32 33 34 35 ) 36 319 320,321, 286' 290 391 394 395 296 297 298 299 390 38 312 39 313 40 275",322. 41 323 1 15 j 1 1 1 1 MON XSXII, I'T II Face page 144. CORRELATION OF THE ROCKS. 145 (likes, and stock rocks, and shows that a great number of intermediate steps can be recognized between the most ghissy andesite and the coarsest diorite. It shows that the dike rocks furnish the connecting link between these two extremes, and that the dike rocks of Electric Peak have the same range of grain as the majority of those of Sepulchre Mountain. But many of those at Sepulchre Mountain are still finer grained, and some are glassy, being vesicular also. Between these rocks there is the closest possible resemblance megascopically, and the two groups miglit have been described conjointly, so far as their })etrographical characters are concerned. The variation of grain within each of the four principal divisions is very significant when taken in connection with the geological occurrence of the different rocks. The limited range of variation in the first group is in accord with the fact that all of these rocks are surface ejectamenta. The range in the third group from more crystalline basic rocks to less crystalline acid rocks, as already pointed out, shows the greater tendency of the basic rocks to crystallize. And since the dikes here represented are of nearly the same size, this variation of grain corresponds to differences in the chemical com- 23osition of the rocks. On the contrary, the variations in the second group indicate a slightly greater crystallization of the acid rocks. This, however, is dtie to the fact that the basic rocks in this group, with a few exceptions, occur in small dikes, while the acid rocks for the most part form broad intruded bodies several hundred feet wide. In these cases the size of the mass has had more influence on the degree of crystallization than has the chemical composition of the magma. In the fourth group the basic rocks exhibit a wider range of grain than the acid, being much coarser and also considerably finer grained than the latter. This arises from the fact that the basic rocks form a much larger mass and exhibit great variation of grain, having fine-grained modifications that have been fully discussed in an earlier part of this chapter. These diorites and others that cut the volcanic lavas in several locali- ties in this region correspond to the andesdiorites and andesgranites of Stelzner, who described stocks of granular rocks penetrating the andesitic tuffs in Argentina. The study of these Tertiary granular rocks led him to the conclusion that the degree of crystallization of eruptive rocks is in no way dependent on their age, but depends on the physical conditions MON XXXII, PT II 10 146 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. under which the nimeralogical differentiation and the cooling of the magma took place/ Study and comparison of the chemical analj^ses of the two groups of rocks under investig-ation demonstrate that the magmas that reached tlie surface of the earth in this place had exactly the same chemical compo- sition as those which remained inclosed within the sedimentary strata. They prove with equal clearness that the different conditions attending the final consolidation of the ejected and of the intruded magmas affected nrA only their crystalline structure, hut their essential mineral composition. The most marked illustration of this is in the occurrence of biotite in the two series. In the volcanic rocks of this locality biotite is an essential constit- uent of the more siliceous varieties, and is only rarely found as an acces- sory constituent of the varieties with less than 61 per cent of silica. In the intrusive rocks it is an essential constituent of all the coarse-grained varie- ties, even the most basic. In the finer-grained, porphyritic forms it is a constituent of the groundmass to a variable extent. The second most notice- able difference is the presence of considerable quartz in the coarse-grained forms of the basic magmas and its absence from the volcanic forms of the same magmas. From these observations, then, we see that in this region there are chemically identical rocks which have distinctly different mineral compo- sitions, but which were once parts of a continuous body of molten magma. We are led, therefore, to the conclusion that — The molecules in a chemically homogeneous fluid mayma can combine in various ivays, and form different associations of silicate minerals, producing mineralogically different rocks? ' Stelzner, Alfred, Beitriige zur Geologie und Paleontologie der Argentinischeu Kepublik, Cassel and Berlin, 1885, p. 207. " Sie [die Andengesteine] wird uus, wie ich meinerseits glaube, immer mehr uud niehr erkeoDen lassen dass die grossere oder geringere krystallinitat ernptiver Gesteine keiiies wegs, wie man so lange nnd so hartnackig beliauptet hat, von deui Alter der letzteren abhiingig ist, sondern lediglich von den phvsikalischen Umstiinden, unter deneQ die mineralische Differeuzirung iind Erkaltuug der gluth- fliissigeu Magmen vor sich ging." '^This conclusion is tbe same as that stated by Justus Roth: "Es kijnneu mineralogisch gauz verschiedene Gesteine in dieselbe Gruppe gehiiren, denn feurig- fliissige Massen von gleieber oder sehr uabe gleicher chemiscber Zusammeusetzung konnen in ver- schiedene Mineralien auseinanderfallen. Die Ursachen, welcbe diese Erscbeinung bediugen, lassen sich bijchstens muthmasseu und miigen in Unterschieden des Druckes, der Teniperatur, des ungebeiiden Mediums der Unterlage u. s. w. gesucht werden." Die Gesteins-Analysen in tabellarischer IJbersieht und mit kritischeu Erlauterungen, Berlin, 1861, p. xxi. CORRELATIOISr OF THE KOGIvS. 147 In this refj-ion of Electric Peak and Sepulchre Mountain the greatest minoralogical differences accompany the greatest differences in structure or degree of crystallization; hence we may assume that the causes leading to each are coexistent. The source of these caiises must be soug-ht in the differences of geological environment, and these affect the rate at which the heat escapes from the magmas and the pressure they experience during crystallization. It is to be remarked that the most essential mineralogical difference between the intruded rocks and their chemically equivalent extrusive forms is the much greater development of biotite and quartz in the intruded rocks, these minerals being abundant even in the basic intrusions and absent from their basic volcanic equivalents. That their simultaneous development is naturally to be expected in many cases is evident from a consideration of the character of their chemical molecules and that of other minerals com- mon to these rocks. For if we assume that biotite is made up of two molecules, coiTesponding respectively to KgAlgSieOai and Ri2Si6024, and compare these with the molecules of orthoclase, KgAlaSieOig, of olivine, RaSiOi, and of liyperstheue, RSiOg, we see that molecules which under some conditions might have taken the form of olivine or hypersthene and potash feldspar, which latter may have entered into combination with lime- soda-feldspar molecules to form somewhat alkaline feldspars, may under other conditions combine as biotite with the separation of free silica or quartz ; in which case also the feldspars of the rock would be less alkaline. Another mineralogical difference between the two groups of rocks just mentioned is the greater development of hornblende in the intruded rocks in place of augite, which is chemically similar, though it has not been determined Avhether in this case the hornblende of the diorite has nearly the same composition as the augite of the andesite. The proba- bility is that there are considerable differences between them. The crystallization of quartz, biotite, and hornblende in fused magmas, according to our present knowledge, requires the assistance of a mineraliz- ing agent; for it has been demonstrated by synthetical research that these minerals will not crystallize in the forms they assume in igneous rocks when their chemical constituents are fused and simply allowed to cool under ordinary atmospheric conditions. But they have been produced artificially with the aid of the mineralizing action of water vapor and of other gases. 148 GEOLOGY OP THE YELLOWSTOJSfE NATIONAL PARK. Now, there is ample evidence, both in the ejected lavas and in the coarsely crystallized rcicks in the conduit, that water vapor was uniformly and gener- ally distributed through the whole series of molten magmas, and there is no evidence that there existed in the magmas which stopped within the conduit any more vapors than those which existed in the magmas that reached the surface, or that they were different in the two cases. Hence we conclude that: The efficacy of these absorbed vapors as mineraUsing agents was increased by the conditions attending the solidification of the magmas within the conduit. Moreover, if mineralizing agents are universally present in igneous mao-mas, and if their action, so far as we can observe it, is controlled by the physical conditions imposed by the geological history of each eruption, we should not regard the presence or absence of certain minerals, relegated to the influence of mineralizing agents, as evidence of the presence or absence of these agents in the molten magma; but we should see in it the evidence of special conditions controlling the solidification of the magma, and should seek the fundamental causes of the mineralogical and structural variations of a rock in the geological history of its particular eruption. CHAPTER IV. DESCRIPTIVE GEOLOGY OF THE NORTHERN END OF THE TETON RANGE. By Joseph Paxson Iddings and Walter Harvey AVeed. INTRODUCTION. The Teton Range is the highest and most imposing of the mountain ranges that environ the Yellowstone Park. The three highest peaks, whose spire-like summits and perpetual snow fields are visible from every outlook of the Park, form a well-known feature of Wyoming scenery, giving the mountains the familiar name of the Three Tetons. Only the northern spurs and lesser peaks of this range occur within the region surveyed — that is, north of the forty-fourth parallel of latitude. This northern part presents none of the impressive features of height and scenery that occur in the main portion of the range farther south, yet geologically this limited area is of great interest, since it includes the northern end of the Ai-chean nucleus of the range, with the flexed and upturned sedimentary rocks encircling it. The great epochs of geological time are all represented in the stratigraphic section exposed in these northern peaks, while the relations of the eroded range to the accumulations of basic volcanic breccias and to the great rhyolite flows of the Park Plateau are here revealed. The area shown on the map (PI. XXIII) includes an aecidented region that is the divide between the waters of Falls Ri-\-er Basin and those of the valley of the Snake. The two most ^jrominent streams, Owl Creek and Beny Creek, cut deeply into the uplifted rocks, exposing Archean gneisses and the overlying Paleozoic strata. Two prominent summits, known as Survey Peak and Forellen Peak, rise above the general level of the rhyolite plateau. The region is well wooded, but is diversified by parks and grassy valleys that add to its attractiveness. The recently built road 149 150 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. extending southward from the Upj^er Geyser Basin and the Yellowstone Lake to the southern limit of the Park, and the wagon trail from the Mormon settlements of the Falls River Basin to the great natural meadows of Jack- son Lake, make the region readily accessible. Sedimentary series. — The Sedimentary rocks begin with the Middle Cambrian, which rests directly upon the crystalline schists. The Sheridan quartzite has not been found in this vicinity, nor have any beds resembling the Algon- kian been noticed in the area mapped as Archean. The Paleozoic includes beds of Silurian and Devonian age, whose character and relations appear to be the same as those of like age in the Grallatin Mountains. The Carboniferous series presents no features different from those noted in the northern ranges. The Juratrias, on the contrary, presents a far greater development than in the Gallatin Range, and its typical member, the Teton sandstone, forms bright red outcrops that are especially prominent features of the scenery wherever exposed. The Ellis limestones appear in full development and include the impure, shaly, fossiliferous beds which contain an abundant marine fauna, and the overlying littoral deposit whose character varies from a conglomer- ate or coarse sandstone Avith comminuted shells to a pure crystalline lime- stone. The Cretaceous, as noted in Chapter V, in the description of the region lying east of the one here described, is essentially a series of sand- stones in which the usual subdivisions are not readily recognizable. The Dakota has been mapped liy the occurrences of the basal conglomerate, and the Colorado has been delimited by the upper belt of dark shales that occurs in the sandstones. The Montana group is represented by coarse yellow sandstone, containing numerous fossils. The Laramie has not been found in the exposures of this locality, but is probably buried beneath the rhyolite flows of Pitchstone Plateau. The most northern extension of the Teton Range is a small outlying area of sedimentary rocks which have been upturned by the dacite-porphyry that forms the summit of the Birch Hills, 8 miles north of Survey Peak. The structure of the Teton region shows that it is the end of an anticlinal uplift, modified by faults parallel to the axis of the fold; thus, in Forellen Peak the crystalline schists have been faulted against Carboniferous beds, a small area of the Flathead quartzite remaining attached to the gneissic mass. To the west, in the amphitheater at the head of Conant Creek, Cretaceous shales have been faulted agJiinst volcanic rocks. us GEOLOGICAL SURVEY. MONOGRAPH XXXII.PART II.PL XXIIl GEOLOGICAL MAP OF THE ^ORTHEKNT END OF TETON RANGE , YELLOWSTONE NATIONAL PARK. LEGEND PLEISTOCENE CRETACEOUS JURATRIAS CARBONIFEROUS DEVONIAN SILURIAN Pal Pgd Kr Kc Kd Je Jl „, ^^, , Cm Sj Anm-him Glacial Montmia Colorado I);ikola EDis Teton Qujidiaiil Madison Threeforks Jofler anil. iormation. formalion. formation, formation, formation, formation, limeslone. limestone, limest son limestone. CAMBRIAN NEOCENE ARCHEAN 1 €| €f ; Nbst Nrh NIbb dp /Rgn GalJatin l-'lallwad Basalt. Hltyolite. Lalol)asii- Dacite- Granite and Faults nmestone. fonnation. breccia. porpWiy. giuiiss. Scale 125000 ^ T- ,_^^ CONTOUR INTERVAL lOO FEET. NOUTHHKN END OF TIOTON RANGK. 151 TOPOGKAIMIIC FKATITRES. The reffion is about 10 miles wide from east to west, and 7 miles from north to south, alon<>' the western side of Snake River Valley. The highest point, Forellen Peak, is 11, 700 feet in altitude, while others of 9,200 and 8,900 feet occur north of Berry Creek. The district is almost completely transected by two deeply cut valleys, those of ()\y\ an^hat resembling schist. In this part of the rhyolite the lamination which corresponds to the planes of flow in the lava dip to the north, indicating that the lava had been moving over a northward-sloping surface. REGION WEST OF THE CRYSTAELINE AXIS. West of the fault that bounds the western side of the body of crystal- line schists the sedimentary rocks have been u^^turned at a high angle, causing them to dip steepl)^ at about 80° W. for a short distance, beyond which they become flatter. This structure is seen in the mountain south of Owl Creek and in Forellen Peak and Survey Peak. In the western 158 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. summit of the mountaiu south of Owl Creek, steeply upturned limestones dip 80° W. and appear to be continuous with those, to be described, west of the summit of Forellen Peak. Directly west of them, on the di-vdde south of the head of Owl Creek, massive limestone abuts against them with a low easterly dip. These are the eastern portion of a flat anticlinal arch, whose axis trends north along the western side of the amphitheater at the head of Owl Creek. The western portion, with slight westerly dip, forms the ridge between the headwaters of Owl and Conant creeks, the most northerly point of which is Crimson Peak. Crimson Peak. — Here thc Strata strike S. 50° W. and dip 7° NW. The dips farther down the northwest spurs varj^ from 7° to 10° in the same general direction. The red color of the summit, which is so prominent when the mountain is seen from a distance, is due to the red magnesian streaks and patches Avhich occur in the higher beds of the Carboniferous limestones. The summit of the peak, which is 10,300 feet above sea level, shows good exposures of the white Quadrant quartzites, the rocks weathering in great cubical blocks; being of very compact texture, they resist erosive agencies and are in striking contrast to the same series exposed near the junction of Owl and Berry creeks. Fossils collected from the northeastern spur of the mountain prove to be of lower Carboniferous age. Farther down the spur, on the saddle of the divide southwest of Forellen Peak, a horizon of fossiliferous limestone, carrying peculiar con- cretions of chert, occurs above a brown arenaceous bed that is correlated lithologically and by its stratigraphic jjosition with the Devonian of the Grallatin section. This sandy limestone, which is believed to correspond to the Three Forks limestone, is underlain by fine-grained and dense gray limestone, Avhose peculiar rough, pitted, and guttered surface makes it a readily distinguishable horizon. This bed corresponds to the Jefferson limestone of the Gallatin Range. These strata continue northward along the western slope of Forellen Peak, having a low dip to the west. They adjoin the nearly vertical limestones that have been faulted against the gneiss in the same manner as in the mountain south of Owl Creek. Forellen Peak. — Ncarl)' vcrtlcal liuiestoues form the western summit of For- ellen Peak and the steep narrow spur down its northern flank. The beds forming the summit of the peak are Carboniferous, and 100 feet below them stratigraphically is the dark-gray massive limestone, weathering with SITRVKY PEAK. 159 guttered surface, that has just lu'cii noted. 'I'he heds liave a general strike N. 35° W., and dip «0^ 8W. Upon the gneiss, directly east of the fault, there is Flathead quartzite, dipping ;it a low angle toward the northwest. The fissile Cambrian formations liave Ix'en completely displaced at this point. The displacement noted on Forellen Peak jjrobably diminishes north- ward and may fade out east of Survey Peak, tlie steeply dipping strata continuing through this mountain into the hills north of it. Here the light- gi'ay and brown stri})ed limestones of the ^ladison formation, which form the naain mass of Survey Peak, strike N. 25° W. and dip 70° SW. At the eastern base of the mountain they have the same strike, but a lower dip, about 25° SW. Survey Peak. — Ou the slopes soutlieast of Survey Peak the gneiss is well exposed, immediately overlain by the rusty Flathead quartzite with strike N. 70° W. and dip 15° N. Above this ledge no exposures are seen for 50 feet, when limestones outcrop, the ledges being conformable in dip and strike to the quartzites below. These limestones are dark gray, mottled with butf spots of sandy material, and resemble the limestones occurring in the Flathead shales. Above these beds the slopes show poorly exposed limestones, eroded by glacial action into well-marked benches. Six hundred feet above the gneiss the beds consist of chocolate-colored cherty lime- stones, alternating with gray crystalline limestones containing traces of fossils and much cut up by veins and jjatches of calcite. On the east slope of the mountain the beds are well exposed, forming rough, bare ridges devoid of soil or timber. The best section of the Paleozoic rocks is to be found north of the creek, in the slopes which fall away from the eastern flanks of Survey Peak. Here we have a continuous series of beds from the Archean to the red shales and clays of the Teton formation. The section given on the next page was measured at this point. 160 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. dum- ber. Survey Peak section. Feet. Teton 18 Quadrant ... 17 ri6 15 14 13 12 11 Madia, m \ 10 9 6 5 4 3 Three ForkH f ., ^ 1 Cherty sandstone, forming slopes of Sur%ey Peak. Quartzite, white, etc., forming summit of peak. Limestone, with red streaks, etc., near top 1, 000-|- Liniestone, gray, splintery 25 Limestone, brecciated 50 Limestone, gray, similar to beds below 50 Limestone, brown, containing peculiar chert balls 10 Limestone, cherty, fossiliferous, steely gray 300 Limestone, gray, weathering brown, with smooth surface 30 Limestone ; not exposed 25 Limestone, gray brown, obscure traces of fossi Is 30 Limestone ; not e.xposed 30 Limi stone, dense, gray 10 Limestone, brown, with rough, guttered surface. Strike N. 5-' W. ; dip 30^' W 100 Limestone, light yellowish green ; laminated 10 Limestone, light gray, cherty 25 Limestone, dark gray, cherty. .Strike N. 10° E. ; dip 5= W 10 Limestone, great ledge of rough brecciated rock at base of east slope of the peak 150 The summit of Survey Peak is formed of the cherty sandstones which occur at the base of the Teton formation, but the western flank of the mountain is covered by a narrow strip of rhyohte that connects the rhyolite sheet near the head of Berry and Conant creeks with the rhyohte plateaus which sweep northward to the geyser basins. This rhyolite west of the peak is about one-fourth of a mile wide, its upper limit being 8,600 feet, and it forms a bench terminated westward by bold cliffs, some 200 feet in height, that form the wall of the Boone Creek amphitheater. The bottom of the sheet dips to the west. The surface of the rhyolite is quite irregular, as tlie sheet rests upon the steeply upturned Teton shales which have slipped beneath its weight, forming great tissures of varying width, from a few feet to many yards across and often many yards long. Huge masses have become detached and have slid down to the bottom of the amphi- theater valley. To the south the rhyolite thins out against the cherty sandstones, but on a projecting point extends to the flat summit at the head of Beny Creek. Beneath the rhyolite the walls of the amphitheater show the red Teton shales and sandstones well exposed and dipping steeply to the northwest. These Teton sandstones probably extend under the gravel- \capped ridge to the west, but no exposures were seen. CON ANT OKEIiK. 161 conant Creek. — Tlu* Cai'boniforous limostones of Crimson Peak south of the head of Herry Creek extend down tlie northern spur Avith a dip of 7° to 10° NW., as ah-eady stated, and form the divide to Conant Creek and the creek south of it; but the}' are covered with rhyoHte farther north, appearing beneath it in several spurs projecting into the valley at the head of Conant Creek, llie lower portion of the rhyolite sheet is dark coloreil and glassy, becoming lighter colored and lithoidal higlier up. On the small spurs the lamination of the lava dips to the northwest, showing that the slope was in this direction. On the divide between Conant Creek and the creek south the limestones terminate abruptly against soft clays and sandstones, pre- sumably of Cretaceous age, but of which there are no good exposures, while to the south the massive lime'^tones can be traced along a western escarpment to where the}' overlie sandstone and gneiss, which form a group of peaks northwest of the main Teton Range. The soft clay shales and friable sandstones on the low saddle south of the head of Conant Creek dip toward the west and extend northward across the basin at the head of Conant Creek. Their close proximity to the Car- boniferous limestones indicates a fault and considerable displacement between the two, which, however, nia}^ not exist farther north; for west of Survey Peak there is sufficient distance between the Teton formation and the north- ward extension of the shales to allow of the intermediate formations being in place. The divide between Conant Creek and the head of Boone Creek is a narrow ridge composed of well-rounded gravel, mostly quartzite. This also forms the lower ends of the two short spurs south. The exact relation of this gravel to the adjacent rocks was not discovered. Its character and geuei'al appearance are those of a recent deposit connected with the glacia- tion of the region. Volcanic breccia. — The sedimentar}^ area is bounded on the west by an accumulation of volcanic tuff-breccia that is exposed for a distance of 6 miles north and south, and again farther north in the neighborhood of Birch Hills. The actual extent of the breccia is unknown, since it is partially covered by rhyolite. A portion of it has been uncovered in Berry Creek. It is well exposed in the valleys cut through it by Boone and Conant creeks. The rocks exhibit rude assorting, but are not bedded, the coarse agglomer- ates occui'ring with tuffs and fine breccias without order or arrangement. MON XXXII, PT II 11 162 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The material consists of basic andesites and basalts, some of which are absar- okite and contain orthoclase as an essential constituent. Petrographically the}' are like tlie basaltic breccias of the Absaroka Range. The breccias are dark colored and often weather into fantastic towers, pinnacles, and cliffs, whose dark rich shades of red, brown, purjile, and gray render them highly picturesque. The fragments are angular and sub- angular and often are several feet in diameter. The best exposures occur just l)el()w the amphitheater at the head of Boone Creek. On the north side of Conant Creek, where the exposure is nearly 1,000 feet high, there are indications of rude bedding, dipping westward. The breccias were thrown upon the surface of deeply eroded and faulted sedimentary rocks, and undoubtedly were considerabl}^ eroded themselves before being buried beneath the rhyolite, which forms the western slopes and sjjurs and extends beneath the later basalt sheets of the Falls River Basin a long distance westward. The canyons of Boone and Conant creeks cut into it 400 feet and more without reaching the underlying rocks. The rhyolite is porphyritic and lithoidal as a whole, but at the bottom of the sheet, in contact witli the underlying rocks, it is dark-colored obsidian. Birch Hills. — The Birch Hills, whose summits rise prominently above the western border of the plateau, present the most northern exposures of the sedimentary rocks of the Teton uplift. Separated from the north- ern spurs of that range by the southern extension of the great rhyolite plateaus of the Park which so effectively conceal all the earlier rocks, this small area, which recent denudation has again exposed to view, presents clear evidence of the same sequence of events S(i clearh' outlined in the range itself The hills consist of a group of pointed eminences, with gentle eastern slope and steep western declivities. The surface, formerly heavily wooded, is now densely covered with a shrubby gi'owth of black birch, concealing the fallen timber that everywhere strews the ground. North of Falls River, whose beautiful Rainbow and Terrace falls are near by, the hills consist of dacite-porphyry, forming the two main sununits. This rock is light gray and compact, with phenocrysts of feldspar and quartz, and small biotite plates. It is a holocrystalline, intrusive body, resembling the rock of Bunsen Peak in composition and structure, but more distinctly BIRCH HILLS. 163 ])(>rj)liyritic, tlio i)henocrysts being larger and fewer. They are: Oligoclase in line idioniorpliic crystals, with marked zonal structure and little ])olysyn- thetic twinning, sometimes suggesting ortlioclase; biotite, in thick idicmior- phic crystals, with munerous magnetite inclusions; and corroded quartz, with glass inclusions. The groundmass is microgranular with idiomorphic quartzes, the average grain being about 0.02 mm. in diameter. It consists of quartz and feldspar, with small amounts of magnetite and biotite. Apatite occurs iu comparatively large colorless crystals, nuich cracked. Zircon is present in minute prismatic crystals. The chemical composition of the rock is shown in the following analysis, and is nearly identical with that of the Bunsen Peak rock: Analysis of daciie-porphyry of the Birch Mills. [J. E. Whitfield, Analyst.] Constitaent, Per cent. SiOj 70.24 Trace. 17.36 1.38 .79 None. .53 2.74 3.69 2.65 None. Trace. Trace. .71 TiOj Al^Oa Fe^Oa FeO MnO MgO . . CaO '. Na-O K.O Li 0 P2O5 SO, H,0 Total 100.09 Eastward this rock jjasses beneath the rhyolites, which reach almost to the summit of the hills. On the westward slopes steeply upturned limestones, somewhat altered, dip toward the igneous rock. The foot slopes show a remnant of the basic breccias covering the eroded limestones and porphyry, and covered in turn by the ubiquitous rhyolite. The west spur of the northern hill is formed of altered limestones, whose beds strike S. 40° E., and dip 70° NE., toward the dacite-porphyr-s'. The limestone is dense, gray, mottled with yellow, and underlies thinly 164 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. liedded glaucouitic limestones whose litliological character and sequence place them in the Flathead formation of the Cambi'ian. Similar rocks are exposed in the bed and Avails of Falls River belov?^ the Rainbov\^ Falls, where they are covered by a light-colored andesitic tuff or breccia, generally fine grained and much decomposed. This breccia forms low rounded hummocks at the base of the hills, and is not yet cut throup-h bv the river, whose bed it forms for a mile above the meadows. The exposure in the river bank shows rude bedding, with northwest dip. South of Falls River the hills are continued in an irregularly accidented area. The rhyolite plateau terminates in a wall several hundred feet high, a deep but narrow depression separating the bluff from the sedimentary ridge to the west. These hills south of the river jjresent exposiu-es of the Carboniferous and Triassic beds, forming jjarallel ridges with benched slope and trending N. 70° E., the rocks dipping 30" N. The red, fissile Teton sandstones are well exposed in the lower slopes, weathering into a reddish soil not easily distinguished from that of the red patches of the Quadrant formation. These red sandstones are here underlain by the cherty horizon of the Teton, resting upon the Quadrant quartzites. The chert occurs in charac- teristic rolls, rods, and nodular masses, having a chalky surface, and grading at times into the inclosing arenaceous rock. The Quadrant quartzites cor- respond closely in character to the formation as developed in the Gallatin, consisting of white granular quartzite and interbedded limestones that are often good marbles. West of the sedimentary area just noted there is an exposure of hornblende-andesite-porphyry. The rock is clearly intrusive and cuts through the Carboniferous limestones. The Birch Hills, by reason of the compact character of their rocks, present excellent evidences of former glaciation of the region. The rocks occur in rounded ice-worn hummocks, covered with glacial scorings and groovings with general east-west trend. In general the eastern and northern slopes are gentle, while steep cliffs bound the hills to the west and south. CHAPTER V. descriptivp: geology of huckleberry mountain and big game ridge. By Arnold Hague. GEISTERAL FEATURES. The country described iit this chapter embraces a mountainous area iiTegular in outhne and of great diversity of form. It consists mainly of a series of ridges, trending northwesterly and southeasterly, composed for the most part of Mesozoic rocks. Older sedimentary rocks are well exposed in a number of localities, as Avell as areas of coarse breccia and broad fields of rhyolite, but the region is essentially one formed of rocks of Cretaceous age. The southern line of the area descriljed here is sharply defined by the forty-fourth parallel of latitude, coinciding with the southern boundary of the Yellowstone Park forest reservation.^ The broad valley of the Snake separates it from the mountains and uplifted sedimentary rocks of the Teton Range lying on the west side of the river. On the northwest and north the rhyolites of the Park Plateau, reaching their southern limit, rest directly against the upturned edges of the sedimentary beds. In much the same way the western border of andesitic breccias of Two Ocean Plateau sharply delimit this area of sedimentary rocks from the unbroken mass of basic lavas which stretch far away eastward in broad plateaus and seiTated ridges. In striking contrast to these areas of breccias and rhyolites that surround it, this region stands out strongly marked by its physical features. In a certain way this group of sedimentary ridges rises as an island, or rather as a projecting- promontory, into a vast sea of lavas. The irregular ' See map of Yellowstone National Park aocompanyiug Part I, aud Geologic Atlas U. S., folio 30, 189(). 165 166 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. outline is in great part due to the sinuous border of accumulated lavas that abut against the steep slopes of uplifted strata. Across its broadest expan- sion, from Snake River to Two Ocean Plateau, it measures about 20 miles. In length it measures nearly 22 miles, stretching northward with decreasing breadth across the forest reservation, gradually dying out in a narrow ridge projecting into the rhyolite body which skirts the west shoi'e of the south arm of Yellowstone Lake. All of the ridges and mountain masses which make up this region are clearly defined by salient topographic features, delimited by deeply eroded valleys, and yet they are all so knit together by outlying spurs and elevated passes as to present a single mountain grouj), with a somewhat complex topographic structure and an intricate drainage system. The principal physical features are Big Game Ridge and its extension north- ward, Chicken Ridge; Piiiyon Peak and Bobcat Ridge; HucklebeiTy Mountain and Wildcat Peak. Several of the high mountains of the Park country are found here, a number of them attaining elevations of over 9,500 feet, but only one, Mount Hancock, the culminating point of Big Game Ridge, reaches an altitude of over 10,000 feet above sea level. With the exception of a narrow strip of country pouring its waters into Yellowstone Lake, this entii-e region is drained by Snake River or some of its many tributary streams. The main branch of Snake River takes its rise along the west slopes of Two Ocean Plateau, flows northerly around the east base of Mount Hancock, and thence, with a sharp curve around the end of Big Game Ridge, runs southerly at the west base of the same mountain. With a gentle sweeping curve it encircles the northern end of Huckleberry Mountain and enters the broad, open plain lying west of this mountainous region. Continuing its course southward, it crosses the forest reserva- tion, and soon after widens out into Jackson Lake, a short distance south of the limit of the map. With this circuitous course, as thus defined. Snake River nearly surrounds this group of mountains, and on leaving the forest reservation has become a wide, deep stream. Across the broadest expanse of these mountains there runs, in an approximately east-west line, a well- defined watershed from Snake River to Two Ocean Plateau. North of this divide such fine streams as Coulter, Wolverine, and Fox creeks pour large volumes of water into the main Snake. Several mountain torrents, notably Lizard, Gravel, and Mink creeks, flow southward into Pacific THYSIOAL FEATUHKS OF nUCKLEBERRY MOUNTAIN. 167 Creek, which tinally adds its waters to those of the Snake soon after the latter stream crosses tlie soutliern boundary of the area mapped. The physical features of the country present strikinj^ly varied outlines of mountain, ridfje, valley, and upland, with abrupt changes in coniiguration. Constantly changing- rock formations, with accompanying modifications of topogi'a{)hic forms, make the region singularly pictui'esque, and the alterna- tion of gently undulating and roughly accidented areas causes the region to stand out in sharidy deiined contrast to the more monotonous Park Plateau. i\Iuch of the country, especially the more elevated portions, are timber- less, but large areas of mountain slope present a diversified park-like appearance, covered with a vigorous growth of coniferoiTs forest. Faulting- and folding of strata, with frequent changes in the inclination of beds, have produced conditions favorable to the flow of springs, the many mountain torrents making the region a highly favored one in its water supply. The region is well adapted to the haunts of Avild animals, and the dominant ridge of the country, characteristically named Big Game Ridge, in former years furnished abundant sport for the hunter in search of bear, elk, deer, and mountain lion. Unlike the areas of sedimentary beds which make up the Gallatin Range and form the slopes of the Teton or Snowy ranges, the sedimentary rocks of this region do not rest directly upon any exposed bod v of Archean rocks, nor do they dip away in any one direction from a central mass. Within this region no x\rchean rocks are known. Southward, in the Wind River Range, the Archean presents a bold unbroken mass of pre-Cambrian rocks, but its geological relations with the uplifted sediments of this region can not be determined, owing to the accumulated volcanic material, which conceals everything beneath it in the intervening country. In much the same manner the breccias of Two Ocean Plateau and the rhyolites of the Park Plateau prevent any precise interpretation of the structural relations of this region with the country to the north and east. It is evident that the powerful forces which uplifted this mountain mass acted from several different centers and produced a somewhat intricate structure. The uplifting of the mass was accompanied by profound fault- ing and folding, and in places by marked compression of strata. Subse- quent orographic movement produced secondary faulting, adding much . in 168 GEOLOGY OF THE YELLOWSTONE NATIOlsTAL PARK. certain localities to the difficulties of determining structure. The later intrusion of igneous rocks tended in some places to break \\\i and confuse the position of beds, but only in limited areas is such action especially noticeable, and it may be said to have affected the larger mountain blocks singularly little as regards the disturbance of beds. Sandstones of the Montana and Laramie formations constitute the moi*e elevated portions of the ridges. Both formations are conformable, and throughout their entire development, from base to summit, the prevailing- beds consist of a coarse yellowish-brown sandstone, of varying degrees of purity. In the absence of a characteristic fauna discrimination between the two formations is very difficult, and in most instances impossible with- out much detailed work, with results not commensurate to the labor. Fort Pierre beds, which are mainlj^ arenaceous, pass down into nearly similar sandy deposits of the Colorado. The fauna which characterizes these lower beds is one possessing a wide vertical range throughout the Cretaceous sandstones, and the line of demarcation between the Montana and Colorado is not always easy to draw. It is possible that beds provi- sionally placed in the Montana may upon further investigation be found to belong to the Colorado, the assignment being based upon their faunal relations rather than upon their lithological habit. REGION OF WILDCAT PEAK AND HUCKLEBERRY MOITNTAHST. Snake River sharply defines this group of mountains on the west and north. Above the broad valley of the Snake the niountains rise abruptly over 2,500 feet in long rugged ridges whose outlines are more or less obscured by dense forests. Northward, along the gorge of Snake River, the mountain slopes are precipitous and in places rise like canyon walls above the stream. Coulter Creek, named in honor of the distinguished botanist. Prof. John M. Coulter, may be taken as the eastern boundary of these moun- tains. It drains, by numerous tributaries, nearly the entire eastern slope, and pours a large volume of water into the main stream, being the first impor- tant affluent above the gorge of the river. The summit of the mountains at their northern end, with an average elevation of 8,700 feet, presents a broken, gently accidented country, easy to traverse and singularly attractive from its park-like character. All the dominant peaks attain nearly the same WILDCAT PEAK. 109 elevation, are fiat-topped, and easily aci-essible. Numerous groups of conif- erous trees, broad areas of grassy upland, and an abundance of water add great charm to the region. South of Wildcat Peak the country falls away in long monotonous ridges, with narrow inter\'eiung valleys, uniform in out- line and dreary in aspect. Structurally this uplifted mass, in its simplest form, presents a synclinal fold, whose axis, with a broad sweeping curve, strikes obliquely across the mountains northwest to southeast. This struc- ture is accompanied by local crumpling and folding of beds. Apparently the force uplifting the beds upon the southern side of the fold came from the direction of the Teton Range. Wherever observed these beds dip persistently into the mountains and away from the Archean mass which forms so broad and continuous a body to the southwest. Owing to the crumbling nature of the beds and the amount of soil, good rock exposures are rarely seen. Along- the banks of Lizard Creek and the adjoining- valleys to the east and west the beds lie inclined from 20° to 30° NE. The axis of the syncline trends across the southern and western slopes of Wild- cat Peak, and is lost beneath the rhyolite forming the steep slopes toward Snake River. Wildcat Peak. — At tlic basc of Wildcat Peak, near the head of Lizard Creek, the beds dip slightly to the northeast, but those forming the summit of the peak belong to the opposite side of the syncline and are highly inclined, many of them standing on edge. Here they trend diagonally across the ridge, with a dip varying from 65° to 70°. The strata are thinly bedded sandstones, presenting- long rows of slab-like exposures. These are underlain by black arenaceous shales, in turn followed by other thin layers of sandstone. The beds striking across the ridge give rise to narrow lateral spurs, with deeply eroded ravines between them. Along the summit of the ridge the same beds may be traced eastward with apparently the same dip and strike. In the open park-like country northwest of Wildcat Peak and west of Huckleberry Mountain the beds show a southerly dijD, indicating the north side of the syncline. The beds found on both sides of the axis of this fold have been referred to the Montana formation. It is possible that they include a series of beds which should be assigned to the Colo- rado, but, owing to the present state of knowledge and the very limited number of organic forms as yet obtained from this region, it has been found impossible to draw any line of demarcation between the two periods 170 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. of the Cretaceous. All the sediments are more or less impure sandstones, and even those cliaracterized by argillaceous deposits are usually sandy. While the org-anic forms found here niay be such as occur elsewliere in the Colorado shales, they are also forms tliat extend upward into the sandstones of the Montana. These arenaceous shales are well developed in the valley of Lizard Creek, and along the east side of the stream are exposed in a number of localities above the stream bed. From them have been obtained Ostrea, Anomia, Inoceraraus, and the widely distributed middle Cretaceous species, Gardium iMuperculiun. Beds similar in lithological habit are exposed in the valley to the west- ward, which in its topographic outline closely resembles Lizard Creek, and still farther westward these rusty sandstones crop out from beneath thin cappings of rhyolite at a number of localities on both sides of the Snake River trail. One such exposure is seen along the trail not far from where it crosses the summit of the spur which extends westward to Snake River. On the east side of the river, opposite the mouth of Berr}^ Creek, a small exposiire of sandstone and shale occurs, striking nearly due east and west and dipping north. Owing to the limited area exposed and the fact that the surrounding- country is mainly covered by drift the outcrop is not indicated on the map. According to Prof J. P. Iddings, this sandstone carries a seam of coal 4 inches in thickness. Northward, and on the extreme western spur of the ridge, the sandstones and shales are exposed, extending up the hill slope for several hundred feet. Here they strike northeast and southwest, with a dip of 25" NW. It is possible these beds belong to the Colorado fox-ma- tion, but in the absence of all organic remains they have been placed in the ^Montana, together with other beds of similar lithological character found in tliis region. Huckleberry Mountain. — Tlic ccutral mass of tlus gToup of mouutaius has been designated Huckleberry Mountain. Its summit is formed of a broad sheet of rhyolite, slightly inclined toward the south. On nearly all sides this rhyolite capping rises above the underlying rocks as an abrupt Avail, Avhich along the east side forms an escarpment over 100 feet in height. This east wall limits the rhyolite in this direction, and the entire eastern slope of the mountain, down to Coulter Creek, exposes only strata of the Montana formation. The beds dip at low angles to the southeast. Beneath HUCKLEBERRY MOUNTAIN. 171 tlie rliyolite of the summit the Montana beds present a very uneven surface, and at one point tlie sandstones ])roject tln'ou^^li tlie capping' of lava, which elsewhere forms the top of the mountain. On both the east and west slopes of lluekleberry Mountain the underlying strata ])resent many of the same general features, being fissile, friable sandstone, crumbling easily, and in places showing signs of cross bedding and other evidences of shallow-water deposition. On the west side, where the sandstones are exposed by erosion of the rliyolite, the beds have yielded Card'mm paHperciiliim, and on the east side, just below the base of the rliyolite, the same species has been obtained from nearly similar rock. Again, near the east end of the long spur making out toward Coulter Creek, in fissile sandstone, inclined 10° S., there were found the same Cardium, associated with Ostrea anomioides. North of HucklebeiTy Mountain the country suddenly falls away several hundred feet to a narrow saddle, where the Montana shales are ag-ain well shown. Beyond this saddle the country again rises in a prominent point, which, for want of any distinctive appellation, may be designated as North Huckleberry Mountain. In elevation it falls but little below the more southern point, and commands to the north a still more comprehensive view. Geologically the two points possess much in common. A sheet of rhyolite, resting upon the Montana sandstone, forms the top of the table, as already described for Huckleberry Mountain. Probably at one time the two points wei'e connected by a continuous sheet of rhyolite, erosion having since worn away the rock upon the saddle. In the case of North Huckle- berry Mountain the rhyolite escarpment faces northward, and the prominent wall of Montana sandstone stretches far away to the eastward till buried beneath the ovitlying masses of late basic breccia. The fissile sandstones of the Montana beds are well shown all along the northern slopes of the mountain and in the valley of the stream tributary to Coulter Creek. Northward, the Montana sandstone still forms the summit of the main ridge and eastern slopes, till, near the northern end of the mountain, the beds become decidedly argillaceous, with sandstone occur- ring as intercalated layers. Although no evidence of a fauna was obtained, the beds, upon their lithological habit in distinction to the arenaceous beds above, have been assigned to the Colorado formation. Their continuity westward is obscured by overlying rhyolite. Montana sandstones occur as the underlying rocks along the entire western slope of this mountain mass, 172 GBOLOGl OF THE YELLOWSTONE NATIONAL PARK. and extend from the open plain of Snake River Valley to the summit of the ridge. At one locality just south of the Park boundary Cretaceous clays are exposed in a precipitous bluff at the river, but the slopes of the hills are for the most part obscured by alluvial material, followed higher up by extensive deposits of glacial drift and broad areas of rhyolite, the latter in places extending from the summit to the plain. An overlying sandy soil nearlv everywhere mantles the mountain side, and large fox'est areas conceal the structure of beds, rendering it most difficult to follow the con- tinuity of strata. Observed dips and strikes indicate that in general the sandstones lie inclined eastward, toward the mountain mass, but with many local displacements. Rhyolite. — By reference to the map it will be seen that the rhyolite is represented as forming a continuous body from the extreme northern end of the mountain south to the forty-fourth parallel of latitu.de. This rhyolite is very irregular in outline and represents a comparatively thin flow of lava. Over a large part of the area covered by rhyolite it is doubtful if the lava sheet is more than 100 feet in thickness. In places it has been entirely removed by erosion, leaving isolated patches of sandstone exposed upon the surface. In two localities it caps the westward spurs from the summit to Snake River, and at other points lies high up on the mountain sides. It caps the sandstone on the long ridges trending southward, and presents a somewhat striking appearance with its long monotonous flows, scarcely 100 feet in thickness, resting upon the deeply eroded arenaceous strata. These long flows stretch southward nearly to Jackson Lake. This rhyolite body possesses a fairly uniform appearance from one end to the other; that is to say, it does not vary throughout its mass more than many areas of equal extent on the Park Plateau; indeed, it closely resembles the rhyolite of the Park. It is in general purplish gray in color and lithoidal in texture. In places it is fissile, and upon Huckleberry Mountain, and in several other localities along the summit, it occurs in horizontal beds with jointing planes. On North Hucklebeny Mountain it is thinly bedded and fissile, the debris slopes being made up of irregular fragments of lithoidal rock. Dacite. — Near the junction of the Cretaceous rocks with the rhyolite, due west of Huckleberry Mountain, occur two or three exposures of igneous rock, that rise in low obscure mounds above the general level of the sand- SNAKK IIIVER GORGE. 173 stone. In outline these exposures are strikiugly different from the sand- stone, fuid in tht'ir mode of weathering stand out in strong contrast with the surrounding rliyoUte. An examination shows that these rocks are to be chissed as dacite. In composition the}' are more basic than the rhyoHtes, and carry a larger proportion of })lagioclase, and, in distinction from the rhyolites of the region, hold a considerable amount of biotite. Apparently they are older than the rhyolite and are exposed by the erosion of the latter rock. Petrographically they are closely related to a dacite occurring in a number of exposures on the west side of Snake River Valley, and their interest lies in the fact that they are among the few instances known in the Park of rocks with a dacitic facies related to rhyolites. REGION OF SNAKE RIVER GORGE. From Lewis River to the mouth of Coulter Creek the course of Snake River makes an irregular curve of nearly 180°, closely encircling the northern end of the Wildcat Peak and Huckleberry Mountain mass, the mouth of Coulter Creek lying 7J miles due east of Lewis River. Snake River runs through a deeply eroded gorge, which for several miles above Lewis River sharply defines the rhyolite flows of the Sheridan volcano on the north side from the uplifted sedimentary rocks on the south. Against the abrupt wall of Paleozoic rocks the rhyolites were piled up to a great height, and it is along this contact that the river has cut its picturesque gorge. On the north side the rhyolites stand out in a precipitous wall, nearly 400 feet above the river, and thence rise gradually toward the centi-al portion of Mount Sheridan. On the south side a massive wall of limestone rises 1,000 feet to the summit of the mountain. The beds are highly crystalline, light in color, and belong to the Madison limestone. It is possible that older beds, represented by Three Forks and Jefferson limestones, are exposed in the gorge along the base of the mountain, but the mantle of drift is so heavy and the timber so dense that they have nowhere been recognized. Above the Madison limestone come the brilliant red sandstones and shales of the Teton formation, standing out conspicuously in contrast with white and blue limestone. Along the summit of the mountain the Quad- rant quartzite has nowhere been recognized. Arenaceous limestone lies 174 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. directly beneath the Teton beds, but nothing similar to the compact siliceous deposits which characterize the Quadrant quartzites iu the Gallatin Range has been observed. Overlying the Teton beds come the drab limestone, marl, and fine sandstone which mark the Ellis formation, everywhere defined by Jurassic fauna. Fine-grained sandstones which form the uppermost beds of the Ellis formation pass gradually into a coarser and more compact series of sandstones, which here represent the Dakota beds. These in turn are followed by impure sandstones and black shales of the Colorado fornaa- tion, and these again b}^ the Montana. The latter have ah-eady been referred to in describing the geological features north of Huckleberry Mountain. This entire mass of uplifted sediments dips to the south, forming a part of the general syncline which constitutes the Wildcat Peak and Huckleberry IVIountain orographic block. About 5 miles east of LeAvis River the phys- ical features of the canyon wall change. The Madison limestone, dipping eastward, dies out, and the Mesozoic strata, which to the west are seen only hifdi up on the cliffs, turn and pitch down the mountain slope toward the river. The Mesozoic strata are much faulted and crumpled, and lie inclined at varying angles. Overlj'ing the Madison limestone the Teton red beds incline to the southeast, but the dip soon changes, and the beds which make up the long ridge stretching down to the river dip for the most part to the southwest. Both the Teton and Ellis formations are exposed along the south side of the river, but neither the Dakota nor Colorado have been recognized along the river bank. Good exposures are few. The Dakota conglomerate is not characteristically developed, and the slopes for 200 feet above the river are largely covered by glacial drift. On the ridge south of the river and west of Coulter Peak, where the Ellis beds are well exposed, dipping at a low angle to the southwest, the drab limestone has furnished Ostrea sfrigilecda, Camptonectes, and Bhijnchonella myrma. Several hundred feet higher up the ridge, in the arenaceous limestone passing into sandstone, the same species were obtained, together Avith R. gnathophora, and at still another locality on the ridge the beds yielded Gryphcea planoconvexa. As regards the relative position of the horizons furnishing these species nothing definite can be stated. Still higher up the ridge the coarse sandstones assigned to the Dakota formation ai-e well exposed, and above the Dakota RED CREEK SANDSTONE. 175 nunuTous drainatjo channels, triltutarics of the western affluent of Coulter Creek, aH'orcl i^ootl exjjosures of the higher Cretaceous formations. KKOION IJKTWKKN UKI) AND BASIN CREEKS. East of Red Creek the gorge of the river narrows, and the clear shallow water presents a striking ap})earance, flowing for more than half a mile over a smooth, polished floor of Teton red beds, with the highly colored sandstone forming the brilliant banks on both sides of the stream. On the north and east side of Snake River, between Red and Basin creeks, there is a mountain area consisting mainly of Mesozoic rocks. It extends back from the river about 5 miles, and across its broadest expansion meas- ures somewhat less than 4 miles. Rhyolite surrounds it on all sides, except along the river gorge, effectually isolating it from adjoining areas. Geo- logicall}- this region is closely related to the Mesozoic rocks on the south side of the river, every formation being represented, from the Teton to the Montana, inclusive. Red Creek, which is appropriately named from the red rocks found on both sides of the stream, marks the eastern boundary of the rhyolite flow, stretching southward from the Sheridan volcano. Red Creek enters Snake River through a narrow chasm cut in the sedimentary rocks. At the mouth of the creek there is a bluff of red arenaceous limestone, similar to the Carboniferous limestone found elsewhere underlying the red sandstone of the Teton formation. It has been designated on the map as the Madi- son limestone, but it may belong to the Quadrant formation, for the upper beds are nearly pure sandstone. Passing up Red Creek the limestone soon disappears and is overlain by the red sandstone. The stream for nearly its entire length has carved its channel in these beds, which are here exceptionally well exposed, show- ing the varying character of the sandstones and the intercalated red clays and marls. The formation here has an estimated thickness of 400 feet, the beds dipping north and east. Between Red Creek and Basin Creek the beds are pressed into a syncline, followed by a sharp anticline. Overlying the Teton beds of Red Creek come the Ellis and Dakota formations, followed by the black clays and arenaceous shales of the Colorado, which lie in the syncline, the latter formation being characteristically shown in a depression between two ridges of less easily eroded beds. 176 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. To the east of this depression the sandstones assigned to the Dakota formation are clearly defined along the west side of the prominent ridge separating Red and Basin creeks. They pass gradually, without any sharp line of demarcation, over into the Ellis beds, which form the summit of the ridge. The axis of the anticline lies in the Ellis limestone, which is here nearly 200 feet in thickness, and is characterized by a small but well- defined Jurassic fauna. Among the species found here are Gryphcea calceola var. nebrascensis, Campfonecies pertenuistriatus, Gervillia, Fseudomonotis curta, ModioJa suhimhricata, Ammonites. At the east base of the ridge and on the opposite side of the anticline the Dakota sandstones ag-ain come in, dipping eastward until finally lost beneath the rhyolite which skirts the edge of the upturned sedimentary beds. East of Basin Creek the valley of the Snake is broad and open, show- ing wide alluvial meadow lands, diversified by occasional growths of pine. A short distance below the mouth of Basin Creek the river flows through a narrow chasm before it enters the wider valley near its junction with Covilter Creek. At the upper entrance of this chasm the river cuts through a ridge of coarse breccia, showing a mural face nearly 300 feet in height. This breccia rests upon Montana sandstones, which form the greater part of the hills on the west side of the river. On the east side of this chasm, about half a mile above the junction of the river with Coulter Creek, occur two outcrops of coal, exposed just above the river bank. These seams of coal along the outcrops measure about 15 inches in thickness. They are over- lain by fine conglomerate and underlain by black arenaceous clay. These coals are more or less impure by reason of thin bands of carbonaceous clay. The beds caiTying the coal strike N. 30° W. and dip from 15° to 20° E. The bedded sandstones carrying the coal seams pass under the river, but are not exposed on the o^iposite side, owing to the accumulation of glacial drift. Below the junction of C.oulter Creek with the Snake the sandstones dip to the northeast, away from the river, while, as already noted, they dip to the southwest on the opposite side of the stream. Notwithstanding the occurrence of coal these sandstones are regarded as belonging to the Montana formation, and probably to the iipper part, or the Fox Hill terrane. Owing to the great uniformity in the sedimentation SNAKE KIVEK HOT SPUINCS. 177 of these beds and tin- absence of orij^anic^ remains, it is impossible to deter- mine with precision the position of these coals. Unlike the Montana sand- stone north of the Park, these rocks fre([ueTitly carry well-defined coal seams, alth(Hi<>;h Vieds of economic value are foiuid mainly in the Laramie. This coal is probably of the same age as that exposed in the banks of the Snake River west of Wildcat Peak. SNAKK lilA'EU HOT SPllINGS. On the sonth side of the river, below the mouth of Red Creek, occurs an interesting- group of hot sj)rings, more than half hidden by dense tindier, which at this point come.s down to the water's edge. A low cliff of bine cherty limestone is exposed along the bank, beneath which, from a line of springs, there issues a large volume of warm calcareous waters. Near by is a long bench of rhyolite, rising slightly above the stream, and the only one observed on the south side of the river. The thermal waters are probably closely related to this body of rhyolite, but their mineral constituents are derived mainly from the limestone. These springs divide naturally into three groups, but their mode of occurrence is much the same and they are similar as regards the mineral composition of the deposits. The travertine deposits in their moimds, basins, and terraces resemble those found at the Mammoth Hot Springs. They were visited by the writer in 1886 and again in 1891; they presented but slight changes after this interval of five years. The most picturesque and ])owerful of the springs are situated farthest up the river and are built out over the stream upon the edge of an old meadow. It was estimated in 1886 that the volume of water running from these springs reached 50 gallons a minute. This group of springs is shown in PI. XXIV. For beauty of color and orna- mentation of the rim they are unsurpassed by any of those at the Mammoth Hot Springs, although by no means equal to them in magnitude of the deposits or in volume of calcareous water poured forth. The clear water is of the most delicate turquoise-blue color, and the basin is lined with a soft white travertine of extremely fine texture, impalpable to the touch. The basins which surround the pool are tinted with orange, brown, and red colors, derived from the hot-water algse. Mr. W. H. Weed has furnished trom his notebook the following MON XXXII, PT. II 12 178 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. description of the springs lying to the westward, written at the time of his visit in the antunni of 1891: One sj^riug. issuing from sandy mire, is 2 feet in diameter, and has built up about tbe orifice a deposit of white calcite. It will, however, be buried beneath more sand with the jirst fi-eshets of tbe river. The two main springs of the group lie to the west of this one. Beyond these a dark ledge of limestone projects over the slopes termi- nating the timber bench some 20 feet above the river. The first of these two springs is a bowl with a wide terraced mound of great beauty, the deposits being dense porcelain like travertine, like that of the first spring noted. The spring attracting most attention throws up a splashing, steaming body of water between 2 and 3 feet in height. The smooth, round surface of the bowl is a snowy white, very dense and compact travertine. The outlet appears as a break in a marble bowl and is a foot deep. Between this bowl and the springs to the east of it there is a hot-water out- tiow of the type common at the Mammoth Hot Springs. The spring waters have formed mushroom nodules in the channel and a fungus-shaped border about the waters. There are also a number of warm-water springs along the edge of the stream, but the springs issue from the gravel and have no well-defined basin and no deposits. The old travertine deposits form a low bench about 5 or 6 feet above the river, at a place where the higher bench and the limestones retreat to the south. The area covered does not exceed one fourth of an acre. The actual area occupied by the sijrings is, however, more extensive, for following the grassy, willow-covered bench there is an extension of the travertine level to the west, where the rocky bluff again comes out to the river. At the foot of a higher bench back of these low hills there is a stream of hot water which flows west from a recess in the meadow to the base of the cliff and along it to the river. The stream is from 3 to 8 feet wide near its source. The water is warm, but not hot, probably not over 120° F., judging from the algeous growths, but the volume of water is very considerable. The photograph from which the illustration is made is a view down the Snake River gorge and northwest across the river to the walls of rhyo- lite on the opposite side. Forest Creek, which runs through a deep trench in the rhyolite, is shown on the north side of the river, with a gently inclined mass of lava abruptly terminated along the gorge. In the spring the river is a rushing torrent, subsiding after the first melting of the snows, leaving low, broad benches, made up of coarse gravels and bowlders. The view was taken in late autumn, when the water stands at its lowest level. COULTER OKEEK. 179 UEGION OF COl LTKU CHEEK AND BOBCAT RIDGE, Coulter Creek. — Coiilter C'vook, l)of()re eniptyinw' into Snake lliver, flows throufjli an open basin, and is yreatlv aujiinented by the drainage of two such hvrge streams as Harebell and Wolverine creeks. All these streams liave brought down large accumulations of drift material, and the underlying sedimentary rocks are for the most jjart obscured by a thick mantle of gravel, sand, and tine breccia. The mountain slopes surrounding this little basin are well terraced, and five sharply defined benches rise one above the other to a height of nearly 200 feet. Coulter, Harebell, and Wolverine creeks all enter this basin through narrow defiles cut in breccia, with perpendicular walls 300 feet in height in places. Coulter Creek, for nearl^^ 4 miles, has cut its way through this breccia, and it is practically impassable from the number and size of the bowlders which lie piled up along the valley. From beneath this dark, somber breccia Cretaceous sandstones and shales crop out at a number of localities and on the west side of Coulter Creek extend along the base of the mountain, with the breccias lying above. The main tributary of Coulter Creek from the west has cut through the breccia, and erosion has carried it away from the mountain slopes so as to expose Montana sandstones all the way from Huckleberry Mountain to Coulter Creek. In the region of Coulter Creek the underl3^ing sandstones possess a very irregular surface, and in many places the breccia rests upon them as a thin flow or crust. The sandstones show a prevailing dip to the southwest. This body of breccia stands by itself, completely isolated from the vast pile of breccias of Two Ocean Plateau and the Absaroka Range. It is very irregular in outline and measures about 8 miles in length, stretching from the source of Coulter Creek northward along the west slopes of Mount Hancock. On the east side of Coulter Creek the breccia attains an elevation of 8,500 feet, and on the slopes of Mount Hancock reaches nearly the same elevation. Throughout the entire body the breccia presents much the same general habit, a coarse, firmly compacted agglomerate, dark brown or black in color, with a lighter-colored cementing material. Some portions of it are exceptionally coarse. Fragments of well-rounded gneiss and quartz have been observed embedded in the mass. In general it is free from evidence of bedding, as is well shown in the exposures along the main stream. At 180 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Mount Hancock its mode of weathering is well brought out by the many- abrupt walls of rough, jagged surface and numerous deep trenches along the mountain side, which make travel very difficult and well nigh impossible. The breccia, while closely resembling the imposing mass of Two Ocean Plateau, and probably allied to it in age, is a distinct body, having its source along lines of displacement west of the Big Game Ridge uphft and the continuation northward of the Bobcat Ridge fault. It was the result of a powerful local eruption of coarse agglomerate, imiform in its composi- tion, violent in its explosive action, and oiih' dimmed in interest by its close proximity to the larger masses of the Absaroka Range. It consists mainly of pyroxene-andesite and basaltic fragmental material. Near the source of Coulter Creek broad sheets of purple lithoidal rhyolite occur, resting directly upon these basic breccias. On the west side of the stream there occurs an isolated body of rhyolite, lying on the breccia and completely surrounded by it. This exposure is interesting, as it is evidently a remnant left by erosion, and probably at one time was con- nected with the larger fields to the east. High up the mountains Coulter Creek bifurcates and the two branches encircle a broad table of rhyolite which lies in the middle of the mountain valley. It is not known on what this rhyolite rests; tlie base of it is being deeply buried beneath an accumu- lation of glacial drift and coarse quartz gravel, derived from the Eocene conglomerate of Pinj'on Peak. Bobcat Ridge. — Bobcat Ridgc is one of the marked physical features of this part of the country, standing out prominently above the surrounding rido-es by reason of its great elevation. The ridge trends northwest and southeast, and measures about 6 miles in length. It is a singularly narrow rido-e, having an average elevation of over 9,000 feet, with a number of peaks scattered along the summit, which attain altitudes of 9,500 feet or more. At its northern end it is connected with the Wildcat Peak mass and the hio-h country around the head of Coulter Creek. At its southern end it falls away in long dreary spurs toward the valley below, lying just outside the limits of the area shown on the map. Both the east and Avest sides of this rido-e are abrupt and present a rather dreary, monotonous aspect, with little standing forest, as the mountain sides over large areas are covered with fallen and dead timber. Greologically Bobcat Ridge has not been studied much in detail. A WOLVERINE CREEK. 181 fault runs along the west base ot" tlic lidge, but tlie line of (lis])la(;eineut can not be traced, aiul its northern end is lost in the breccias and rhyolites. At the extreme nortiiern end, near tlu' bend of (youlter Creek, there is a capjjing of rhyolite, but l)et\veen this rhyolite and the higher jjarts of the ridge the top of the mountain is covered with loose sand and coarse gravel, derived from the wearing away of Pinyon Peak conglomerate. The entire ridge is apparently made up of yellowish-brown sandstones of the Montana formation. In places the sandstone is massive, but in others it is well bedded. Wherever observed the beds dip to the southwest, and the entire ridge is probably a massive block of upper Ci-etaceous sandstones, dipping awa-\- from Mount Hancock and Big Game Ridge. REGION OF WOLVERHSTE CREEK. Wolverine Creek finds its source high up on the west slopes of Big Game Ridge, and flows westerly for 9 miles, joining Coulter Ci'eek a short distance above the mouth of the latter stream. Compared with other high mottntain streams in this region tributary to the Siiake, it runs through a broad open valley, rough and rugged nuich of the way, but intei'spersed with green meadows and wide areas of alluvial bottom. The mountains rise high above the stream, the valley being practically shut in by steep slopes and high walls on all sides. On the north side the long steep spurs of Mount Hancock tower above the valley for 1,500 feet to the summit of Big Game Ridge. On the south side the mountains stand out witli even greater abruptness, and are more irregular in outline, with the lower slopes largely covered with timber and heavy accumulations of glacial drift. For the greater part of the distance the valley is cut in sandstones assigned either to the Montana or to the Laramie forma,tion. Near the mouth of Wolverine Creek stands a grand escarpment of somber breccia, presenting a fine section in many ways typical of large masses of this rock. Beyond this wall the stream bottom is impassable, and the trail ascends a steep hillside, crossing a spur of the mountain for 2 miles through a densely wooded country covered with soil and without any good rock exposures. This spur forms a part of the main mass, lying between Coulter and Wolver- ine creeks, and as exposed on both streams consists mainly of basic breccia resting upon a base of Cretaceous sandstone. According to Prof. J. P. Iddings, this mass is capped by a broad table of rhyolite 3 miles in length, 182 GEOLOG^Y OF THE YELLOWSTONE NATIONAL PARK. which at its western end is superimposed upon the breccia. The north slope of this ridge, forming the south wall along Wolverine Creek, consists mainly of bedded sandstones and impure shales inclined to the southwest, but, owing to the mantle of soil, both the dip and the strike are most difficult to determine. The mountain slopes along the north side of Wolverine Creek present a remarkable exposure of massively bedded yellow sandstone, with prevail- ing dips to the south and southwest — that is, toward the valley. No fossils have been obtained from these beds, but they have been assigned to the Montana formation. Higher up the valley they pass by insensible grada- tions into beds less regular in their sedimentation, cai-rying clays and earthy material with interbedded ferruginous sandstones. The latter series of beds, from their lithological habit, have been placed in the Laramie, but without any sharp lines of demarcation between the two formations. They lie conformably on the older beds to the north and west, and pass beneath the valley, dipping into the ridge on the opposite side. Due north of Piu- you Peak, and rising as an abrupt wall on the south side of Wolverine Creek, stands a somewhat prominent hill, several hundred feet in height. It affords an excellent exposure across characteristic Laramie strata nearly 200 feet in thickness. These consist of yellowish-brown sandstones, with interbedded blue and black clays, rusty sandstones, and thin carbonaceous layers. Along the stream bed are exposed outcrops of five distinct, thin seams of impure lignite with more or less fragmentary impressions of plant remains. The beds strike northwest and southeast, and dip from 25° to 30° SW., passing under the mass to Pinj^on Peak. Higher up the valley at several localities the banks along the .stream expose arenaceous blue clays and black shales with evidence of carbona- ceous material, and in places carrying well-preserved leaves. These beds also dip to the southwest. Again, on the divide between Wolverine and Gravel creeks, and due east of Pinyon Peak, similar beds of arenaceous clays are exposed along the ravines and in the banks cut by numerous small streams. These beds along the summit of the pass dip to the southwest and west and are finally lost beneath the conglomerates of Pinyon Peak. The divide between these two creeks, which lies at an elevation of 8,500 feet above sea level, is cut entirely in the Laramie sandstones. WOLVERINE CREEK FLORA. 183 Wolverine Creek flora. — Theso clays 5111(1 saiicly betls i)f tlie Laramie have so far tailed to yield any evidence of an invertebrate fauna; at least nothing has been found sufficiently well preserved to determine their specific char- acters. Plant remains have been obtained from several of these localities bv (liferent members of tlu^ Survey, but mainly by Dr. A. C. Gill, who was a member of the field party in the sununer of 18S7. Although the collec- tion embraces few species, they have proved to be highly important, not only as determining by the evidence of organic remains the Laramie age of these beds, but also as indicating the geographical distribution of Cretaceous plants and the association of species found in the same strata. Prof F. H. Knowlton, who has studied these plants, has determined seven species, which he has described in detail, with illustrations, iu Chapter XIV of this volume. The following is a list of species from the Wolverine Creek beds, extending from the north slope of Pinyou Peak to the low pass at the head of Gravel Creek: Asplenium haguei, Onoclea minima, Paliurus minimus, Sequoia langsfonlii. Viburnum rotundifolium, Trapa micropliylla, and Paliurus sizyphoides. Of these sjjccies the first three are described for the first time by Pro- fessor Knowlton. P. minimus is closely related to P. sizyphoides, a true Laramie species from Black Butte, with which it is here associated. The last four species are also found in the Laramie of Black Butte and Point of Rocks. Asplenium haguei, a small delicate fern, in its relationships is more closely allied to certain Cretaceous species from Greenland than to those as yet recognized from the Rocky Mountains of the United States. Onoclea minima is also closely related to forms from Black Butte and Point of Rocks. The most interesting among these species is Trapa microphylla, which is here represented by several fine specimens. It was first described from Point of Rocks, Wyoming. This identification and grouping of plants carries the Laramie flora of central Wyoming, as developed at Black Butte and Point of Rocks, north of its limits as heretofore recognized. The Wolverine Creek beds undoubt- edly belong to the conformable series of Cretaceous sandstones upturned by the orographic movement which took place at the close of the Laramie epoch. They lie near the top of an immense series of sandstones every- where uptilted at high angles. 184 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. REGION OF PINYOK PEAK. Pinyon Peak, from whatever poiut of view it is looked at, stands out promiiieiitl}' above the surrounding country. It rises boldly above Wol- verine Creek for over 2,000 feet, and for more than 1,500 feet above the connecting saddles which relate the peak to the mountains both east and west. To the south the country falls away rapidly, and the jjeak presents a still more isolated appearance when seen from that direction. In outline it resembles a truncated pyramid rising from an elevated base. Dense timber covers the peak on all sides except where the abrl^pt cliffs which form so conspicuous a feature of the mountain are too precipitous to permit growth of vegetation. Pinyon Peak attains an altitude of 9,600 feet above sea level. The summit is flat topped, and the long ridges putting- out in all directions from the central mass resemble a very slightly inclined plane, with occasional points rising above the general level. It is this peculiar feature of the peak which, from a distance, gives it the form of a truncated pyramid. Resting upon the Laramie rocks, which everywhere form the base of Pinyon Peak, comes a remarkable deposit of coarse conglomerate, measur- ing nearly 600 feet in thickness. This conglomerate forms the greater part of the summit of the peak and the many long ridges radiating from the central body. Nine-tenths of the conglomerate consists of smootli, highly polished, waterworn material of various-colored quartzites. The prevailing colors are red, white, and yellowish brown, but all so mingled tog'ether as to give a general tone of reddish gray to the abrupt walls and escarpments which form so prominent a feature of the deposit. This siliceous niatei'ial varies from gravel to coarse pebbles and quartzite bowl- ders measuring 10 and 12 inches in diameter, although the largest are by no means common. Much of the conglomerate is indurated and held together by fine sands and ferruginous material. Occasionally thin beds of finable sandstone are encountered throughout the conglomerate, but they are insignificant in amount and do not ajjpear to be very persistent over any great distance, occurring as lenticular bodies in the coarse conglom- erate, then as well-defined strata. Everywhere on the slopes of Pinyon Peak the beds vary greatly in thickness and in continuity. In general it may be said that the conglomerate formation carries more sandstone PINYON PEAK CONGLOMERATE. 185 near the base tlian it does liig-lier up in the de}M)sits. Mingled with the (juartziti' are found rounded and poHslied ])el)bles <»f granite, gneiss, argillite, and indurated slates, jjrobably derived from Archean and pre- Candirian land surfaces. Occasional fragments of andesite have been found, indicating- a volcanic origin for some of the detrital material. Such pebbles, however, are hard to find and play no part in the great mass of the deposit. Possibly they may have been derived from the capping of the breccia foinid on the top of Pinyon Peak, as described later. Pebbles of sandstone, limestone, and other sedimentary rocks have been picked up in the conglomerate, evidently derived from neighboring Paleozoic and Meso- zoic sources. Neai the base of the conglomerate waterworn fragments of coal have been observed associated with grav sandstone and resembliusr that known to occur in the Laramie. Throughout the entire mass of the conglomerate the bowlders present much the same general appearance from base to summit. The characteristic forms of the long ridges radiating from the culminating mass of the peak are due solely to the peculiar erosion of the indurated coarse conglomerate. Erosion has worn deep recesses into the very core of the jieak, with broad amphitheaters encircled by nearly perpendicular walls for long distances, absolutely impossible to scale. Along their tops many of these ridges are mere knife edges, barely permitting one to walk in safety. In places the vertical Avails rise for over 300 feet without any perceptible change. Enormous amounts of the conglomerate have been swej)t away by erosion, the material Avhen once disintegrated being easily transported. Every- where the lower slopes of Pinyon Peak are covered by loose pebbles and bowlders brought down from higher elevations. Coulter and Wolverine creeks are literally clogged up with quartzite bowlders, and Gravel Creek, draining the southwest slopes of Pinyon Peak, derives its name from the huge piles of reassorted bowlders which line the valley for miles. For many years the gravels along Snake River and Pacific Ci'eek in the neighborhood of Jackson Lake have been known to yield a slight amount of gold to mining prospectors, but not in remunerative quantities. Evidences of gold may be found by washing with a pan almost anywhere in the streams coming down from the conglomerate. It is quite likely that this gold has in great part been dei'ived from the conglomerates of the Pinyon Peak formation. In many places the indurated conglomerate and 186 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. associated sands are distinctly bedded. They lie in a nearly horizontal position, or at a low angle of deposition, resting upon the upturned edges of tlie Laramie rocks. Local faulting and displacement in the conglomerate may be observed, but this may be attributed to fracturing and shpping of limited masses, due to the wearing away of underlying beds or to ice filling the numerous cracks and ravines found in the rock mass, causing landslides on a grand scale. That the conglomerate has been subjected to great pressm-e and movement within the mass is everywhere apparent l:)y the action of the quartzite pebbles on one another. Field study of these pebbles is most interesting from the curious modifications they have undergone under pressure. In some instances they are flattened and rolled; in others they are indented and forced, one into the other. Many of these pebbles are cracked and crushed, in some cases almost ground up, so great has been the pressure exerted upon them. It is curious to observe how these flattened, almond- shaped quartzite pebbles, with the pointed end fractured, have been sharply cut off" by dislocation and movement of the mass. Many of the smaller fractured pebbles have smooth surfaces, as if cut off by some sharp instru- ment. A vast number of the pebbles show a peculiar mottled appearance, being covered by white spots of varying size, probably produced by pres- sure of the pebbles against one another. The top of Pinyon Peak is capped by a heavy bed of dark basic brec- cia, made up of angular fragments in every way resembling the breccia, ah-eady described, at the junction of Coulter and "Wolverine creeks on the west and Two Ocean Plateau on the east. According to Professor Iddings, who studied the west slo^ie of the peak, the breccia is 300 feet thick. It rests directly on the conglomerate, stretching for nearly half a mile along the east face of the mountain, projecting out like a lava flow over several of the characteristic long ridges. On the west side of the peak it stretches westward or terminates abruptly, with the conglomerate coming to the surface from beneath the breccias. The conglomerate was evidently deposited before the laying down of the breccia. No animal or vegetable remains have as yet been found in these conglomerates and indurated sandstones, consequently no definite state- ment can be made as to their precise age. Tliat they are younger than the Laramie rocks is evident, as they were deposited unconformably upon the riNYON PEAK OONGLOMEUATE. 187 unturned Cretaceous sandstones. In all probability the breccia capping the conoloiueratc is of the same age as tliat forming the great mass of Two Ocean IMatcau. It is quite impossible that this enormous muss of basic breccia should have been poured out over so large an area of elevated country before the deposition of the conglomerate and not have furnished a considerable amount of material to the latter deposit. A discussion of the age -of this conglomerate will be found in Part I of this monograph. Evidence is there adduced to show that the basic breccia of this region is in all prob- ability of Miocene age and followed the conglomerate. The conglomerate has been referred provisionally to the Eocene period, and has been regarded as a distinct geological formation, to which the name "Pinyon Peak con- glomerate" has been given, after the locality where it is so characteristically exposed. Southwest of Pinyon Peak and connected with it by a long ridge 8,500 feet above sea level, stands an east-west ridge whose culminating point attains an elevation at least 1,000 feet higher. This prominent ridge, which has never received any distinctive appellation, measures over 2 miles in length, standing out from the surrounding country like a broad rampart. The underlying rocks of the ridge are apparently all Cretaceous sandstones and have been referred to the Laramie formation, although it is quite pos- sible that Montana strata may be represented, passing by insensible grada- tions into higher horizons. The summit of this ridge is capped by a thick deposit of Pinyon Peak conglomerate, which was evidently at one time connected with the main body of Pinyon Peak. The north slopes of this ridge are covered by dense vegetation and by soil, which completely obscure the underlying rocks. On the south slopes the sandstones are exposed for a long distance, but near their base the glacial drift comes in and buries everything beneath it. From the divide at the head of Gravel Creek there is a descent of over 1,000 feet in 5 miles, the country south of Pinj'-on Peak falling away steadily toward Pacific Creek, which lies just south of the limits of the mapped area. Grravel Creek, characteristically named from the gravels which line its banks, trends due south along the west base of Big Game Ridge. A north-south fault probably runs along the west base of the ridge, although its course has never been determined. The area of country lying between 188 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Big Game and Bobcat ridges and Pinyon Peak to the north is undei'laiu by sandstone. Over the sandstone occur large areas of Pinyon Peak con- glomerate, and much of the country is strewn with iinassorted coarse gravel, derived from the disintegration of the more compact conglomerate. Accumulations of glacial material cover large areas. It is a broken, hilly country, with great diversity of topographic features, but picturesque and dotlednvith groves of scattered pine. It is fairly well watered by numerous small streams, but the gravel deposits are usualh' dry. BIG GAME RIDGE. Big Game Ridge is a narrow mountain uplift about 15 miles in length, and rises abruptly above the valley of Pacific Creek along the southern limit of the forest reservation, with a trend slightly west of north as far as the slopes of Mount Hancock. From the latter mountain, the culminating point, the trend of the ridge changes to northwest, gradually falling- away toward the open valley near the junction of Heart and Snake rivers. The eastern boundarj' of the ridge as far as Crooked Creek is defined by the Snake River fault, which approximately coincides with the course of Mink and Fox creeks, the fault crossing the narrow divide separating the two streams. From Crooked Creek the deeph' trenched but narrow valley of Snake River defines Big Game Ridge from Chicken Ridge. Geologically Big Game Ridge is formed mainly of Ci'etaceous sand- stones, singularly uniform in color and texture from one end of the ridge to the other. The}- have been referred to the Montana and Laramie forma- tions. In broad masses at certain localities the two formations may readily be distinguished b}^ their lithological habit, l^ut they resemble each other so closely near their junction that any line of demarcation must of necessity be drawn somewhat arbitrarily. In the great thickness of Montana sedi- ments developed here, coarse yellowish-gray sandstones are everywhere the prevailing rock, and nowhere has the Pierre shale been recognized as such by its lithological habit. Evidences derived from organic remains ai'e entirely wanting. Rhyolite skirts the ridge in a number of ])laces, and, as described farther on, caps the very summit of Mount Hancock, and basic breccias cover the lower slopes north of Harebell Creek. Gravel Peak. — Tliis pcak Is situatcd 3 miles north of the southern limit of the mapped area, midway between Gravel and Mink creeks. It has an BIG GAME KIDGE. 189 elevation of 9,600 feet above sea level, and is the culminating- point of the southern end of the ridge. Its interest Hes mainly in the conglomerates, which form the upper 400 feet and which rest upon the mountain in much the same wa}' as they do upon Pinyon Peak. The gravels are in every way identical, and belong without doubt to the same horizon. Abrupt walls of this i-onglomerate face east and north, oftering good expo.sures across coarse gravels with polished and crushed i)ebbles held firmly together by sands. They rest directly ujion Laramie sandstones, which dip to the east at low angles, and near the base of the ridge abut unconformably against Madison limestone lying along the east side of the Snake River fault. Isolated patches of Pinyon Peak beds, left by erosion, rest upon sand- stones west of Gravel Peak. They lie at different elevations, but their position may be due to a series of small parallel faults found along that side of the ridge. The block of sandstone north of Gravel Peak Ridge and due east of Pinyon Peak presents a northward continuation of the same Creta- ceous strata. The ridge trends a few degrees east of north and west of south, with beds dipping at low angles to the east. Beds typical of the upper portion of the Laramie make up the entire ridge. The sandstones are rusty brown in color, with numerous thin layers of ferruginous material interbedded with friable white sands. Clay bands and thin, shaly, impure sandstone with evidence of cross bedding characterize both slopes. Fragmental and imperfect plant remains lie scattered over the surface, and certain strata seem to carry a considerable amount of carbonaceous material. Specimens of leaves and twigs were collected, indicating a vig- orous flora, but all too imperfect to pemiit of specific identification. Over the top of the ridge are strewn smoothly polished quartzite pebbles derived from the Pinyon Peak conglomerate, but no beds of the same were found in place. North of the pass from Wolverine Creek to Fox Creek the ridge still shows the lithological habit of the Laramie sandstones. At the north end the massive white beds dip from 5° to 10° SE.; in fact, all the beds in this region dip to the southeast. The line of demarcation between the Montana and Laramie formations is drawn along the southeastern slopes of Mount Hancock, as will be seen by reference to the map. The basal rocks of the Laramie, as thus defined, trend in a general northeasterly direction. Starting at the south base of Mount Hancock, 190 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. in the valley of Wolverine Creek, tliey cross the summit of Big Game Ridge, and pass down the steep east slopes, where they are well exposed on both sides of Snake River just below the mouth of Crooked Creek. It can not be said with any degree of assurance that this line is correctly laid down, but no sandstones to the north or west of it have been recognized as possessing the lithological characters of the Laramie. In the great thickness of sedimentary sandstones represented in the several orographic blocks it is possible that Laramie beds may occur, Avithout geological evi- dence as to their age. Mount Hancock. — Mouut Haucock is uot only the most prominent mountain of Big Game Ridge, but it stands out as one of the most commanding- points along the southern border of the Park. It was named after General Hancock by Maj. J. W. Barlow, who ascended the peak in August, 1871. On a clear day the view from the summit is unsurpassed, either for detail of topographic features immediately beneath or for the more distant pano- ramic outline. It commands the Tetons, the dominant peaks of the Wind River Range stretching far southward, the entire west face of the Absarokas, the Park Plateau with its great lakes, the Snowy Range to the north, and the Gallatin and Madison ranges to the west. Mount Hancock rises above Snake River at its east base for over 2,000 feet, and above the valley of the Snake at its west base for 2,500 feet. The greater part of the mountain consists of yellowish-gray and white massively bedded sandstone, which extends to within 400 feet of the summit. All the beds forming the upper portion of the mountain have been assigned to the Montana formation, although no organic remains have been obtained from them. The southeastern slopes offer the best exposures of these rocks, which dip to the southeast. It is estimated that there are over 3,500 feet of sandstones. On the nari'ow ridge of sandstone just south of the summit the beds strike north and south and dip 30° W. The western spurs of the mountain are largely covered by forests and glacial drift, rendering it difficult to obtain good exposures, but the beds for the most part apparently dip west. North of Harebell Creek basic breccias similar to those found on Coulter and Wolverine creeks, and part of the same mass, extend along the west base of Mount Hancock. They present a most irregular outline, the higher portions reaching an altitude of over 8,000 feet above sea level. On the summit of Mount Hancock a capping of dark rhyolite stands out boldly, in contrast with the yellowish underlying sandstones. It rises CHICKEN KIDGE. ' 191 over 400 feet in jjrecipitoius walls, faciiif^- north ;uul east, l)nt on the south falls awav witli drliris slopes, permittinj^' ascent to the summit. Tlie mass has a slight inclination to the east, and the greater part of it is lithoidal, very brittle, and jointed in thin fissile layers. At a distance on the slopes it resembles a d(jbris pile of cherty indurated argillites. This ntck is dark gray in color, with small phenocrysts of feldspar and grains of quartz. Obsidian and gray and red pumices are well shown here, with the varying nioditications found elsewhere in the Park and described in detail in Chapter X of this volume. Mount Hancock is perhaps remarkable for the variations in color of its obsidian. Black, brown, and various shades of red are noticeable, and some of them Avhen highly polished are singularly brilliant. It is this dark, turret-like mass of rhyolite that makes Mount Hancock so conspicuous a landmark over the Park region. The great elevation and complete isolation of this small body of rhyolite are by no means easy to explain. North of Mount Hancock the slopes of Big Game Ridge fall away rapidly for 4 miles in long timber ridges, mostly buried beneath glacial drift and soil. No rock exposures were observed other than the Montana sandstones and the low rhyolite hills which border the uplifted sedimentary beds. CHICKEN RIDOB. Chicken Ridge presents a narrow north-south chain of mountains about 12 miles in length. It is a prominent and persistent orographic block, with several culminating points between 9,000 and 9,600 feet above sea level. Over the greater part of this area the mountain slopes are well timbered and well watered. The southern end of Chicken Ridge rises abruptly on the east side of Snake River at its junction with Crooked Ci'eek, nearly due east of Mount Hancock. Along its east base the ridge is sharply defined from Two Ocean Plateau by the valleys of Crooked and Grouse creeks and the narrow north-south depression lying between the two streams. The Snake River fault, which is described later in this chapter, follows the course of these streams, and the marked contrast, both geologically and topographically, between the opposite sides of the fault serves to accentuate the eastern boundary of the ridge. Northward Chicken Ridge projects into Yellowstone Lake, and its gentle slopes along the base, with broken, accidented hills rising above them, form the picturesque shores of 192 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the south arm of tlie lake. The deeply trenched valley of Snake River limits the mountains on the south and southwest, and the rhyolites of the Park Plateau, stretching from Heart River to Yellowstone Lake, submerge between an accumulation of lava the western flanks of the mountains to heights varying from 8,000 to 8,500 feet. Topographically Chicken Ridge is closely related to Big Game Ridge, the latter trending off to the northwest, while the former has a nearly north-south course. Geologically the relationship is still closer, and the Cretaceous strata of Big Game Ridge can be easily traced crossing the river at several localities. This is speciall}' well shown at the southern end of Barlow Peak, just north of Crooked Creek Barlow Peak. — Barlow Peak is named by the writer in honor of Maj. J. W. Barlow, of the Engineer Corps of the Army. He conducted the first official exploration to the headwaters of Snake River in 1871. The peak attains an elevation of 9,500 above sea level, and rises 1,500 feet above the river. It forms a well-defined mountain block between Crooked and Sickle creeks, the former stream encircling its southern base, and the latter cutting a deep trench directly across Chicken Ridge, flowing into Snake River 4 miles farther downstream. Just below the mouth of Crooked Creek, beds assigned to the Larajnie are found on both sides of Snake River, dipping to the sovitheast and east. They ci'oss the spur of the mountain, continuing eastward until lost in the accumulation of drift, and are finally cut off by the Snake River fault. The Laramie sandstones reach nearly to the summit, and along the crest of the ridge are underlain by yellowish-gray sandstones similar to those found high up on the slopes of Mount Hancock. The Montana sandstones cap the summit of Barlow Peak, aiid along the east slope dip 10° to 15° E. From this point they can be traced northward across Sickle Creek, still inclined in the same direction. Passing down Sickle Creek the underlying beds gradually grade into thinly bedded sandstones, limestones, black shales, and argillaceous sand- stones, and are well exposed on both sides of Snake River. Lithologically these beds bear the closest resemblance to the sedimentation of the Colorado formation found elsewhere. The thickness of these black clay shales and interbedded sandstones has been estimated at 600 feet. On the north liank of Snake River, about a quarter of a mile above the mouth of Sickle CHICKEN ItlDUE. 193 Creek, there were found in the shale a cross-bedded sandstone 3 feet in thickness, carrying' a number of characteristic Colorado fossils. From this collection Mr. T. AV. Stanton has identified the following species: Inoceramus tiudahundus, I. uinhonatus, I. flaccidus, I. acutepUcatus, BacuUtcs asper, Sca- phifcs ventricosus. Along Snake River the base of the Colorado formation is nowhere exposed; consequently no estimate can be made of its thickness; but there ai'e at least 400 feet of fissile impure sandstones and limestones above the heavy shale belt assigned to the Montana. The Colorado formation extends along Snake River for more than £ miles, the deep trench of the river exposing a sharp anticline in the shales. A mile below the mouth of Sickle Creek, on the northwest bank, occurs an exposure of blue clays inclined nearly 70° SW., while half a mile upstream the beds dip 30° NE. Near the point where the Colorado fauna was obtained the shales dip from 10° to 15° NE. Along the south and west banks of the river the Colorado beds, on the west side of the anticline, rapidly pass beneath the Montana sandstones at the base of Big Game Ridge. On the bottom of Heart River, the stream having cut completely through the flow of rhyolite, there is an exposure of dark clay shale which has been referred to the Colorado and may prove to be an extension northward of the Cretaceous shales exposed between Sickle and Crooked creeks. Between Sickle and Outlet creeks Chicken Ridge is made up mainly of yellowish-gray, brown, and white sandstones, which in their lithological habit closely resemble those found on Mount Hancock and Barlow Peak. Along the southern slope the upper beds are a very dense steel-gray rock. North of Coulter Creek the beds strike obliquely across the ridge, but northward trend with the ridge in a nearly north-south direction. The general dip varies from 20° to 30° E. South of Overlook Mountain the sandstones are well exposed, and are incHned 30° E., toward Grouse Creek, with evidences of local faultino- accompanied by variations in dip. Underlying these beds on the west side of Chicken Ridge fissile sandstones with interbedded arenaceous shales prevail. Lithologically these latter beds resemble the Pierre shales of the Montana, and have been con-elated with them, although no evidences of organic remains were secured. They form the slopes until obscured by the rhyolite flows, which attain elevations of between 8,200 and 8,300 feet above MON XXXII, PT II 13 194 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. sea level. A sharp contrast is seen between the steep rounded slopes of the sandstone and the irregular outline of rhyolite. The latter is marked by long, naiTOw drainage channels, with steep bluffs on the west side, parallel to the valley of Heart River. These bluffs stand out from 20 to 50 feet above the depression. The intervening ravines are the result of ice movements and are occupied by small ponds and meadows carved out of glacial drift. OUTliET CANYON. This impressive gorge cuts a deep, broad passage completely through Chicken Ridge. In the strict use of the word it is a true canyon, quite unlike any other canyon or drainage channel in this part of the country, and is one of the most interesting geological features to be found within the Park. It affords an instructive section across the range from Grouse Creek to Heart River, with the Montana sandstones constituting the center of the ridge, flanked on both sides by rhyolite hills. Overlook and Channel mountains, on opposite sides of the canyon, form a part of the same mono- clinal uplift, the strata striking- with the ridge. The interesting feature about Outlet Canyon is that it at one time served as the discharge for the waters of Yellowstone Lake. This mag- nificent sheet of Avater, which now flows northward and drains to the Atlantic through the famous Yellowstone Canyon, formerly discharged by way of the south arm through Outlet Canyon to Snake River and thence onward to tlie Pacific. The discovery of Ovitlet Canyon as an ancient drainage channel for Yellowstone Lake was made by the writer in 1889. For several years he had been firmly convinced, by geological reasoning that seemed unanswerable, that this grand lake at one time must have discharged southward, and consequently into the Pacific. All attempts to locate such outlet proved futile till the autumn of that year. It was hidden by dense forests, obscured by glacial drift, and abandoned as a waterway. After the discovery of this old and neglected channel all fresh observations tended to strengthen and confirm the arguments that the lake formerly found its outlet to the south. In the chapters treating of the physiographic features of the Park, in Part I of this monogra^ih, the problems connected with the ancient drainage of Yellowstone Lake are discussed at some length and Outlet Canyon is described in detail in its ANCIENT OUTLET OF YELLOWSTONE LAKE. 195 bearinh, weathered surface, but so far as observed do not carry fossils and are not cherty. Another exposure nearer Soda Butte Creek is found 200 feet above the river, tlie most prominent ledge being a fissile limestone 20 feet thick, carrying variegated chert and Carboniferous fossils. These beds dip west of south at 10°. These limestones forn\ tlie low flat- topped knolls which are so distinct a topographic feature of the southeast base of Druid Peak, as they are quite unlike the topography prevailing in the breccia areas. On the shores of the small lakelet which a landslide of breccia has formed on the lower slopes of the peak the beds are tilted, dipping west at 55° and striking north and south, but it is probable that they have been dislocated by a landslide. PEBBLE CREEK. Light-gray, massively bedded limestones are exposed at the mouth of Pebble Creek, forming a rounded knoll on the south side of the stream. The rocks contain rather scanty fossil remains, which prove that the beds belong to the Madison formation. These beds also outcrop along the north base of Abiathar Peak, 1,300 feet above the creek bottom. Pebble Creek has cut a narrow gorge through the limestone, whose beds form vertical walls 100 feet high. The strata are nearly horizontal and are exposed for 300 feet above the channel of Soda Butte Creek. Above the mouth of the stream the valley of Pebble Creek shows heavily wooded slopes, with no exposures until, near its head, limestone again appears, being exposed on both sides of the valley beneath a capping of andesitic breccias, as shown in the accompanying plate (PI. XXVI). Above the creek on the spur just outside of the Park boundary occurs a thickness of 800 feet of limestones, the beds dipping at a low angle to the southwest. The west base of Baronet Peak and the ridge of which it is the highest point show limestones dipping from 1° to 5° S. On the south side of Pebble Creek, just north of the limits of the area mapped, but within the Park, about 100 feet lower than the low saddle that indents the ridge, occurs a mottled Cambrian limestone carrying fragments of trilobites, the rocks being nearly horizontal. 212 GEOLOGY OF THE YELLOWSTONE NATIOISTAL PARK. SODA BUTTE VAL,I.EY. For some distance above the mouth of Amphitheatre Creek the valley of Soda Butte is narrow, the stream flowing through a gorge cut in volcanic rocks. Its upper course is, however, through a broad valley, with flat gravelly bottom and with striking cliff's of limestone appearing on either side. The limestones exposed at the mouth of Pebble Creek extend up the western side of the Soda Butte Valley to near the mouth of Amphitheatre Creek. As no exposures appear on the east side of Soda Bvitte Creek, it is evident that the sedimentary rocks were cut away before the deposition of the volcanic breccias. An examination was also made of the rocks exposed on the south slopes of the high limestone mountain that is capped b}" breccia and lies north of Soda Butte Creek. The lower slopes of this peak are covered with large blocks of limestone, the talus from the cliffs above. The lowest exposures are of strongly mottled dark-colored limestones, overlain by limestone conglomerates, with light-gray, chert-bearing, massive-bedded limestones above. These rocks show an old surface that is quite irregular. The andesite rests upon a cemented mass of large blocks and fragments of limestone. The heavy limestone belt of Soda Butte Creek above this point is exposed some 500 feet above the stream, the rocks being nearly horizontal. The following sections, made by Professor Iddings, show the sequence and character of the sedimentary rocks exposed in this vicinity: Section of beds on north si fie of Soda Butte Creek. Feet. {Gray limestones, carrying fossils and chert 10 White limestones, much crackled and biecciated 20 Massively bedded, light-gray limestones, forming cliff 200 f No exposure 50 Thinly hedded limestones, carrying trilobites 50 Thinly bedded limestones and limestone conglomerates, carrying abundant fossils near top. The limestones are glauoonitic, thinly bedded, and weather with a yellowish surface, often studded with fossils in relief 190 Tallatin Thinly bedded limestones and much limestone conglomerate. The rock is a dense light-gray limestone, and the conglomerate is formed of flat and very thiu beach pebbles, and the rocks carry trilobites and .i few shell remains at summit of exposure. The conglomerate is intraformational; that is, the pebbles , are of the same limestones 60 Mottled dark-colored limestone, forming a massive bed that is generally a cliff 100 feet in height 100 r Trilobite remains occur in a black limestone that is oolitic, full of dark glauconitic Flathead J grains, and is quite characteristic for this horizon. The thickness of limestone probably does not exceed 100 feet. It is underlain by soft laminated shales 400 SODA BUTTE VALLEY. 213 The forefroinar section was observed on tlie north side of Soda Butte Creek, near the forty-fifth meridian, the locaht}' being- a mile west of tliat just noted. Mottled limestones form the lowest strata exposed, occurring- 100 feet above an exposure of (juartz-porphyry. The lowest bed is a fissile, dark-colored limestone, carrying numerous fragments of trilobites and over- lain by a massive, dark-colored, mottled limestone, which is the base of the Gallatin formation, and which hei'e forms a cliff fully 100 feet high. This is the lowest horizon seen on the north side of the creek, but on the south there are patclies of sliale which belong to the Flathead formation. Above the dark, coarsely mottled limestone cliffs are more thinly bedded, gray limestones and limestone conglomerates. Fossils collected from this hori- zon are of Cambrian age and were obtained 60 feet above the top of the cliff". At 1,050 feet above the stream similar limestones form projecting ledges, and the rock carries many trilobite spines and a few fossils. The rocks 50 feet higher up are similar and carry similar fossils and a few cri- noid stems, which in this region are not commonly found at this horizon. A heavy belt of light-gray limestone, weathering with a rough surface and showing no fossils except crinoid stems, and representing, it is believed, the JeflFerson formation, occurs at 1,150 feet above the stream. This belt is about 200 feet thick and is overlain by a white, much brecciated limestone about 20 feet thick, overlain in turn by gray limestones 5 to 10 feet thick, carrying traces of fossils and some chert. These limestone beds are nearly horizontal, although at the west end of the low saddle between Pebble Creek and the Soda Butte Valley they dip 30° SW. This sudden change in dip is probably due to intrusive quartz-porphyry that may form a laccolithic mass under the horizontal beds that occur at the highest point. Section of beds at north base o/Abiathar Peak. Feet. i' Andesitic breccia, forming summit of mountain. Limestones, carrying Carboniferous fossils 150 Massive belt of indurated, gray limestone in which no fossils were found 175 I Beds generally covered by talus from the clift' above. At the base the ledges are fossiliferous and carry au abundance of shell remains, which are of Devonian types. The rock is a tine-grained buff or yellow limestone, varying to abrowu- gray limestone, very finely crystalline and carrying an abundance of finely stri- I atedshells 200 (^Purplish and red limestones, thinly bedded and c.irrylng gastropod remains 20 C Brown, earthy, and argillaceous limestone conglomerates -. , I Light and dark colored, thinly bedded limestones \ 200 1 Crackled white limestones ' l Massive bed of light-colored limestone, forming peisistent cliff 200 Three Forks. 214 GEOLOGY OF THE YELLOWSTONE l^ATIONAL PAEK. {Limestone conglomerates and thinly bedded limestones, with trilohite remains.. ■. Massive belt of dark-green mottled limestone, resembling the same formation > 850 in the Gallatin Range ' Flathead Shales. This section was made on the high limestone bluff at the north base of the north spur of Abiathar Peak. At the northwest base of the spur the strata dip to the southwest. The dark-colored, coarsely mottled limestone belt which is the base of the Grallatin formation is again exposed, overlain by finely bedded limestones bearing trilobites and by limestone cono-lomerates. Higher up the slope the massive belt of light-colored limestone belonging to the Jefferson formation Aveathers in an almost insurmountable cliil' extending along the valley wall for a long distance. The top of this bed is about 1,000 feet above the creek. It is overlain by a stratum of broken limestones, followed by light and dark limestone beds without noticeable fossils up to 200 feet above the gray belt. At this point a purplish layer carrying gastropods overlies a brown earthy and clayey layer of limestone conglomerate with a fossiliferous ledge 20 feet above. Fossils collected from these beds show that it belongs to the Three Forks formation. The talus slope for 200 feet above these Devonian strata shows no exposures until we reach the base of a massive limestone about 1,500 feet above the cliff of Jefferson limestone. The limestones composing this upper belt are indurated and not fossiliferous, but the strata exposed above it, at 1,675 feet above the stream, contain numerous fossils. The limestones extend 150 feet higher, where the eroded surface is overlain by dark-colored basic breccias. The limestone bluffs extend along both sides of the Soda Butte Valley to Cook City and continue up RepubHc Creek for 2 miles. CrystaUine schists are exposed on the road 100 feet above the Republic Creek road, and also on the lower slopes of Mount Henderson, the gneiss forming obscure outcrops. The Flathead shales are exposed higher up the slopes, at 700 feet above the stream bottom. Above them the dark-colored and mottled Gallatin limestone is exposed, but the rock is much altered and mineralized. Still higher on the south slope of Mount Henderson, east of the road, are altered shales and limestones with hornblende-mica-andesite- porphyry well exposed. The summit of Mount Henderson consists of heavily bedded mottled limestone, broken through by intrusive rock, which cuts across the bedding and also forms intrusive sheets. CHAPTER VIT. THE DISSECTED VOLCANO OF CRANDALL BASIN, WYOMING. By Joseph Paxson Iddings. INTRODUCTION. The exploration of the country in the northeastern corner of the Yel- lowstone Park and immediately east of it led to the discoveiy of a volcano so eroded as to expose its internal structure and to permit the connection or relationship between coarsely crystalline and glassy forms of the same mag-mas to be distinctly made out.^ More or less satisfactory demonstra- tions of this relationship have been made at different times within the last twenty-five years, but few of them have been based on occurrences where the evidences of the former existence of a typical volcanic cone have been unquestionable. The classic studies on "The secondary rocks of Scotland,"^ by Prof. John W. Judd, and his memoir "On the ancient volcano of Schemnitz, Hungary,"^ describing the "basal wrecks" of Tertiary volcanoes in these regions, while accepted by many as conclusively demonstrating the con- temporaneity of the granular rocks and volcanic lavas at these localities, failed to convince a large number, who imagined that the observations might be susceptible of othev interpretations. The dissected volcano of Tahiti, visited in 1839 by James D.Dana,* was considered by him to have been sufficiently eroded to disclose a granular core, but there was no opportunity offered at the time of his visit to exjjlore ' Jour. Geol., Vol. 1, 1893, p. 606. ^ Quart. Jour. Geol. Soc. Loudon, Vol. XXX, 1874, pp. 2l'0-302. ' Idem, Vol. XXXII, 1876, p. 293. PLEISTOCENE Cim^Mierale Cm i> CARBONIFEROUS ~Sj I j> SILURIAN H €f > CAMBRIAN Ibrjiiation. n\\./ Ngd, Gabhro diiirite iiilrusivii rocks . Nrh Nlab Lale acid- breccia. Nebl Nbst Nebb Earty basic breccia. Eeab "]> EOCENE Earb' acid breccia. /Bgn I y ARCHEAN Granite and gnedss. CEOLOGIC.y. MAP OF THE VOLCANO OF CRANDALL BASIN,. ABSAROKA IL\NGE Scale Scale CONTOUR INTERVAL 500 FEET =3 ?"' MILES GHXKUAL FEATURES. 217 by Crandall Crook, extondiufj" a short distance into the Park. It is defined by the aceoinpanvinfi- map (PI. XXVII). Tlie area of voUianic rock.s liere re})resented is but a small portion of the great belt of igneous material that forms the mountains of the Absaroka Range, which stretches along the eastern margin of the Yellowstone Park from the Bowlder Plateau on the north to the Wind River Mountains on the south. The volcano of Crandall Basin is one of a chain of volcanic centers situated along the northern and eastern border of the Yellowstone Park, which are all distinguished by a greater or less development of radiating dikes, and by a crystalline core, eroded and exposed to a variable extent. Electric Peak and Sepulchre Mountain constitute one of these centers. Since the volcanic ejectamenta forming the Absaroka Range have been thrown from numerous centers situated at no great distance from one another, it would be impossible to separate the materials which have origi- nated from the different vents, since they must have intermingled; and it would be incorrect to assume that any particular area of volcanic rocks had been derived exclusively from one center of eruption. But since the material ejected from closely associated vents may be considered to have come from the same general source, or to belong to a connected series of eruptions, we may regard the volcanic rocks occurring in the immediate vicinity of a well-marked center of eruption as representing the various results of volcanic activity which have existed at that place. The area embraced within the limits of the map may not be sufficiently large to include all of the material thrown out from the minor centers of eruption, which, during the period of volcanic activity, must have shifted about within the region of Crandall Basin, but it is large enough to furnish data from which the geological history of this particular volcano may be derived. To understand the geology of so limited an area as that represented on the map it will be necessary to explain the general features of the sur- rounding region. A high and massive range of Archeau granite and gneiss forms the country north of Clark Fork and stretches in a northwest-southeast direction. The river channel is situated within this granitic district, near its southern margin. The Paleozoic strata which overlie the Archean rocks have been greatly eroded, leaving an irregular layer of limestone, which dips gradually to the southwest. This limestone forms a cliff along the south side of Clark Fork and extends for considerable distances up the 218 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. valleys of the streams emptying into it from the south. It also extends down the valley of Soda Butte Creek near to the mouth of Amphitheatre Creek, and disconnected areas of it occur at the mouth of Pebble Creek and near Soda Butte, as described in the previous chapter. It also forms the head of Pebble Creek and the valley of Slough Creek, a small portion of which is shown in the northwestern corner of the map. The limestone embraces the Cambrian, Silurian, and Devonian, which attain a thickness of only 1,800 feet, the strata of the last two jDeriods being very poorly developed and not exceeding in thickness 400 feet. In most places the limestone extends up into the Carboniferous. The whole series is very jjoor in fossils within the area of the map, and the identification of the horizons rests on evidences obtained from neighboring sources. The very irregular form of the eroded surface of the limestone is shown by the variable heights of the limestone cliffs, which range from 400 to 2,400 feet. The highest within the area are in the peak southwest of Cook City, in Hunter Peak, and in the escarpment south of the mouth of Cran- dall Creek. The extensive erosion which preceded the ejection of the lavas was stibsequent to the orographic movement that involved the coal-beai'ing Laramie strata in this region. Upon this greatly eroded surface were thrown volcanic tuffs and scoria, with occasional streams of lava, until the accumulation exceeded in thickness 4,000 feet. The breccias were traversed in various directions by dikes of lava which filled the crevices made during the later eruptions. The close of volcanic acti^aty in the vicinity of Crandall Basin was followed by another period of erosion which removed the upper portion of the volcanic accumulation, leaving over 4,000 feet of it in the form of high ridges and peaks, with deeply cut valleys between. The occurrence of nearly horizontal layers of massive lava alternating with crudely bedded tuflfs and breccia, which in places are piled one on another to the number of twenty or more, gives rise to j^recipitous mountains, which are quite inaccessible from most points of approach. The highest of these is Index Peak, whose steeple-like summit, 11,700 feet in altitude, has not yet been scaled. A view of this peak from Clark Fork gives an idea of its sharpness. (PI. XXVIII.) The readiness with which the scoriaceous breccia and tuflfs are eroded causes the di'ainage channels to be narrow and rocky, so that the valleys traversing this region are in general very difficult to travel through. EARLY ACID BRECCIA. 219 After erosion had reduced the breccia coiintr}' to very near its present configuration, the region to the southwest was flooded Ijy an immense body of rhyolitic lava. One edge of this rhyolite covered a portion of the breccias in a thin sheet, remnants of which are found in the southwestern part of the district. They occur in the most unlooked-for places, as, for instance, at an elevation of 10,000 feet on a narrow spur near the summit of Saddle Mf>untain and at various altitudes over its slopes; also near the bottom of Cache Creek Valley, where they form a bench between the levels of 7,500 and 8,000 feet. The rhyolite was erupted from a distinctly different center and after the volcano of Crandall Basin had long become extinct, so that it need not be considered in connection with the history of this volcano. After the rhyolite had been in turn eroded and the valley of Lamar River had been cut 500 feet below the surface on which the rhyolite had flowed, basalt was again erupted and filled the bottom of the valley. The source of this eruption has not been discovered. The period of volcanic activity may be considered as not yet ended, though it is at present con- fined to such manifestations as are found in geysers, hot springs, and fuma- roles, some of which occur within the district under discussion. The general features of the region having been sketched, the geology of the volcanic rocks within the area of the map may be taken up and described in greater detail. EARLY ACID BRECCIA. The breccias and lavas covering the country are essentially basaltic, but there are remnants of an older breccia which is acid. The term brec- cia is used for subaerial accumulations of tuff and scoria and fragments of I'ock dei'ived from explosive action, and it will be seen how great a pro- portion of all of the material has been subjected to this kind of action. The acid breccia is found underlying the basaltic lavas in several locali- ties in the district. It is exposed about Republic Creek, where it is rudely bedded, the bedding being produced by layers of different mixtures of tuff and angular fragments. They pitch steeply to the south and pass under basaltic breccia, which also is rudely bedded at the bottom, but becomes well bedded higher up. The lower layers dip steeply to the south and southwest, but the upper layers are nearly horizontal. The acid breccia is light colored and variegated, and consists of horublende-mica-audesite 220 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. mixed with some pyroxene-andesite. It is also exposed in the valley of Cache Creek in two places, the larger exposure extending for about 8 miles. Here it is light colored and consists of the same kinds of andesite. It is indurated and somewhat decomposed, and its surface indicates that it was eroded before the basaltic breccia was thrown on it. A much smaller body of honiblende-mica-andesite-breccia occurs in the heart of the district within a mile of the center of the volcano. It is at the junction of Closed Creek and Timber Creek, and rests directly on limestone, as it also does in the vicinity of Republic Creek. It appears to have been at one time on the outskirts of the earlier volcanic district, for its lowest portion is composed of layers of andesitic gravel which were deposited by water. It passes tip into light-colored breccia of liorublende-mica-andesite, which carries frag- ments of Archean rocks. Fragments of gneiss and schist characterize the early acid breccia wheiever it has been found along the northern boundary of the Yellowstone Park. They have already been mentioned as occurring in that which forms the base of Sepulchre Mountain, and they occur in that at the base of the Washburne volcano. This early acid breccia has been shown by Mr. Hague ^ to belong to the Eocene period, and to correspond to the Fort Union horizon. Throughout the remainder of the district the basaltic breccia rests directly on tlie sedimentary strata, or forms the bottom of the valleys where erosion has not yet cut through them to the underlying rocks. It is to be remarked that the basaltic lavas pass under a second series of acid breccias of hornblende-mica-andesite, which are like the older ones in mineralogical character. The younger or late acid breccias form a considerable part of the Absaroka Range south of Lamar River. Neither the older nor the younger of these accumulations of hornblende-mica- andesite appears to have been erupted from what we have called the volcano of Crandall Basin. This was essentially a basaltic center, the last erujDtions of which became acid, and in part more basic, but were of small extent. BASIC BRECCIA AND FLOWS. A conception of the magnitude and pi-oportions of this volcano must be derived from a study of the geological structure of the basaltic breccia and flows — early basic breccia — for nothing remains to indicate a single line of the original form of the mountain. In place of a volcanic cone . ' Hague, Arnold, The age of the igneous rocks of the Yellowstone National Park : Am. Jour. Sci., 4th series, Vol. I, 1896, p. 450. IJEDDED BASIC BRECCIA. 221 there is a system o{ narrow ridges and valleys, three of the deepest valleys passing- through what was the center of the volcano. The arrangement of the rocks, however, is so marked that there can be no doubt about the loca- tion of the center of volcanic activity or of the general nature of the mountain. DISTINCTLY BEDDED HUECCIA. The geologist who approaches the region by way of the Lamar River is impressed with the great masses of almost horizontallj^ bedded breccia which form the chocolate-brown mountains on either side of Soda Butte Creek. They are finely shown in the panoi-amic sketch by Prof. W. H. Holmes in his report on the geology of the Yellowstone Park,^ notices of this portion of the country being found on pages 44 to 49. The sketch is as faithful to nature as it is artistic, and it is possible to calculate the point from which it was made by reference to the map. The breccias rise from 2,000 to 3,000 feet above the river, and appear so uniformly bedded as to give the impression that they have been water- laid; but a nearer view shows their irregularity and proves their subaerial deposition. Upon examination the bedding is found to be crude and ill defined, the layers consisting of tutf with various-sized fragments of scoria and compact rock. Between the layers are occasional sheets of massive lava. In some places the tutfs are quite light colored and are very notice- able among the dark-brown beds. The deposits contain the stumps and roots of trees, whose erect position shows that they have not been distm-bed since they were buried beneath showers of dust and stones. Their situa- tion at different horizons in the breccia and their large size indicate how great a time must have elapsed between the explosions which covered the country with ddbris in beds from 1 to 3 or more feet in thickness. A more or less distinct and nearly horizontal bedding is characteristic of the breccias forming the mountains west of Cache Creek, including the ridge from Mount Norris through The Thunderer to the great wall sur- rounding Amphitheatre Creek. The east face of this ridge is shown in PI. XXIX, from a photograph which was taken from the divide at the head of Republic Creek. The same breccias form the jjrecipitous ridges on both sides of Pebble Creek, and are well exposed in the face of Baronett Peak, 10,300 feet in altitude. 'Twelfth Ann. Eept. U. S. Geol. and Geog. Surv. Terr., Part II, 1883, pp. 1-62. 222 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The horizontally bedded breccias and lava flows extend eastward across the head of Cache Creek to Index Peak and the range of peaks immedi- ately south, but the lower portions of these mountains are irregularly bedded. The upper parts, above 10,000 feet, consist chiefly of basalt flows resting one upon another, with occasional intercalated layers of breccia. This is also the case at the summit of the mountains northeast of Amphi- theatre Creek, and southward to the summit of Mount Norris. The ridge between Cache Creek and Crandall Basin, with its western spurs, is composed of nearly horizontally bedded breccias with few lava flows. They carry numerous silicified trunks of trees, which are exposed in a standing position on the western slopes of the Needles. Similarly bedded breccias extend south of Cache Creek across Calfee and Miller creeks, and form the plateau west of Lamar River and the high mountains south of its head. Here, again, in the upper thousand feet massive basalt flows prevail, forming the top of the plateau and the upper portion of the peaks just mentioned. In this vicinity the basalt sheets are plainly seen to slope gradually to the Avest and southwest, their highest present altitude of about 11,000 feet being found on the summits of Castor and Pollux peaks. Basalt sheets to the thickness of 400 feet cap the summit of Saddle Mountain, at 10,400 feet altitude, where irregularly shaped flows of vesicular and scoriaceous basalt indicate by their position and by the arrangement of the columnar cracking that they flowed down an uneven surface, appar- ently a drainage channel, sloping toward the southwest. Occasional flows of massive basalt occur in the lower portions of the series of basic breccias and tuffs. A notable one is found near its base over the limestone on Soda Butte Creek and Lamar River, but the great bulk of the lava sheets is at the top of the series. Columnar structure is common to all of these flows except when very thin and scoriaceous, and they possess all of the superficial characteristics and variations of surface flows of basalt. None of those observed in the localities just described appear to have been intruded sheets. CHAOTIC BRECCIA. In striking contrast to the almost horizontally bedded breccias and flows are the chaotic and absolutely orderless accumulations of scoriaceous breccia which form the mountains and ridges about the head of Lamar o ^ s i CHAOTIC BKECCIA. 223 River aiitl MilliT Creek .ind the ceiitriil })ortiun ot ('raiidall Basin. To one who has spent inui-h time among- the; well-be(hled breccias of Two Ocean Phiteau and of tlie greater portion of the Absaroka Range, nothing could be more noticeable than the difference of structure exhibited by the breccias in the locality just mentioned. It is to be remarked, however, that while this difference is so noticeable in extreme cases, there is no sharp line to be (b'awn l)etween the different areas in the field, and from the nature of their origin they often merge into one another. The most typical exposure of chaotic breccia has become well known for the grotesqueness of the shapes assumed by the rock when cut by erosion into pinnacles and buttresses. The heterogeneous agglomeration of scoria and tuffs with angular masses of various sizes has been carved into turrets of the most irregular and remarkable shapes, whose dark color and forbidding aspect suggest to a fanciful imagination goblins and demons, popularly termed "hoodoos." The Hoodoo Basin, at the southern base of the mountain of the same name, is the best example of this form of erosion. Other occurrences of this character are found in various localities in the district Some of the grotesque pinnacles are shown in PI. XXX, from a photograph taken by Mr. Weed. The rocks, though dark chocolate-brown as a whole, often appear on closer examination to be brilliantly colored and variegated, ranging from brick red to purple and pink, and being in places bluish and gi-eenish, and also yellow and brown. These colors are characteristic of the chaotic breccias in a number of localities; as, for example, on the eastern slope of Parker Peak, on the divide between Miller and Papoose creeks, and on that east of the head of Lamar River. There is a noticeable increase in the number of large masses of rock occurring as fragments in the breccia, which often exceed a diameter of 8 feet, some being 20 or more feet thick. The petrographical character of the rocks forming large areas of this breccia is more uniform than in the outlying region of well- bedded deposits, where fragments with quite different habits maj^ be found intermingled. The whole accumulation is, besides, more scoriaceous and slag-like. 224 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. DIKES. A Still more noticeable feature of the central portion of tlie district is the occurrence of dikes which form prominent walls of rock traversing the country in all directions. They are specially numerous in the region of chaotic breccia, but are not confined to it. Owing to the importance attached to the position and trend of the dikes, it has been thought advisable to describe tliem in considerable detail, in order to assure the reader that their location on the map is the result of careful observation. In the southwestern part of the district they are most noticeable cross- ing the spurs at the head of Miller Creek, where they were observed by Superintendent Norris. They are nearly all parallel, and trend northeast and southwest, a few having a more westerly direction. Eight of them cut the slope of the amphitheater at the northern base of Parker Peak. They are from 3 to 8 feet wide, and often rise from 3 to 15 or 20 feet above the ground. They are nearly vertical and parallel, almost straight, with slight curves and sometimes sharp bends, and may be traced by the eye across the spurs in a north-northeasterly direction. The long spur south of the branch of Miller Creek is crossed hj several dikes having a northeast trend. They consist of the same kinds of rock as two dikes cutting the summit of Saddle Mountain, Avhich also have the same trend and appear to be continua- tions of these dikes. Hoodoo Mountain and the ridge between Lamar River and Timber Creek are traversed by numerous dikes, some of which trend about N. 10° W. and N., and others S. 30° E. and SE. Most of these dikes are from 3 to 8 feet wide. Proceeding- from Hoodoo Mountain northwest and north, one finds that the divide between Miller and Timber creeks is cut by dikes trending northeast; and the high ridge through Indian Peak, and the Peak itself, are traversed by dikes trending N. 30° E. and N. 20° E. In this peak, as at Saddle Mountain, the dikes cut the massive flows of basalt, which were therefore some distance beneath the surface of the volcano when the dikes were injected. The valley of Timber Creek is covered with a heavy growth of pines and firs, which obscures the geology and prevents the location of dikes except by closer study than there was opportunity to bestow on it. But the long narrow ridge north of this branch is bare of timber on its crest, DIKES IN CRANDALL BASIN. 225 iind is deeply furrowed by lateral •■■ulches with r(ick\' spurs, wliose U])])er slopes are thiulv elad. 'i'lio geological structure of this ridge is specially significant and was carefully studied. The breccia composing it at its southern base is l)asaltic and scoriaceous, with massive flows of vesicular l)asalt of the same j)etrographical habit. On one f)f its southern spurs, about 5.^ miles from its eastern end, a number of dikes trend N. 70° E. Near the toj) of the ridge two trend N. 80° E., and one trends east. They vaiy in width from 18 inches to 8 feet. A narrow dike near the top trends S. 10° E. On the crest of the ridge, about a mile and a half from its western end, there is a light-gray indurated tuff, in places containing small frag- ments of rock and carrying some })lant remains. The northern face of the ridge at this point is an almost vertical precipice, exposing breccia without a trace of bedding, utterly chaotic, slaggy, and scoriaceous, containing large fragments of massive basalt. In some places it is composed of small angular fragments; in others it is brightly colored, and is cut by dikes which trend a little north of east, very nearly parallel to the crest of the ridge. About a mile east of this point the breccia consists of vesicular basalt, with A'ery large feldspar phenocrysts. Some masses of this rock are 20 feet in diameter. Near this an amphitheater on the north side of the ridge exposes alternating layers of breccia and lava flows, having a rather steep dip to the southeast. They appear to have been part of a small cone at one time. This part of the ridge is cut by dikes trending a little north of east, and also by a broad dike, 10 feet wide, trending north and south, with a steep hade to the west. Farther east on the crest of the ridge the breccia becomes indurated and weathers into small fragments. It continues to be indurated eastward as far as explored. It is traversed by dikes trending N. 50° E., and by one dike, 18 feet wide, running S. 85° E. Farther east there are other dikes cutting the ridge in a northeasterl}' direction and trending toward the two deep gulches on Hurricane Mesa, on the northern side of Closed Creek brancii of Crandall Creek. Some of the dikes are narrow, but several are quite large, one being 10 feet and another 18 feet wide. Along the portion of the ridge ex^jlored b}^ the writer, a distance of about 4 miles, there are 31 dikes; of these 26 are basalt and 5 are hornblende-mica-andesite. They are not uniformly distributed along the crest of the ridge, but occur in groujjs of from 3 to 8, the largest groups MON XXXII. PT II 15 226 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. beinar situated at the east. Besides these dikes others were observed at the eastern end of the ridge, and 6 or 7 were found by Mr. Weed at the western end, making over 40 in all. From the distribution and trend of these dikes it is evident that they radiate from that portion of Hurricane Mesa which is situated between the deep gulches just alluded to. The dikes are not absolutely straight, but trend in general toward this spot. They are more numerous directly south of it, where the ridge is nearest to this center, and are less frequent toward the west, where the ridge is more remote. The southern slope of the ridge north of Timber Creek is traversed by dikes of the same kinds of rocks as those occurring on the crest, and having similar trends, leaving no doubt that they are continuations of the same dikes. The breccia cut by these dikes is indurated where they are close together. It is to be remarked that all parts of the country in this vicinity which were explored were found to be traversed by dikes, but, owing to the limited amount of time and the difficulty of traveling, a thor- ough exploration of the country was not made, and only those dikes which were observed, sometimes from a distance, have been mapped, their probable continuations being indicated by dotted lines. On the end of the northeastern spur of Indian Peak there are dikes, some of which trend west of north toward the center on Hurricane Mesa, while others trend northeast. Dikes trending northeast occur on the ridge between Papoose and Hoodoo branches of Crandall Creek. The structure of Hurricane Mesa and the ridge west is clearly seen from the ridge south of it. A sketch of it was made from a point on the northeast spur of Indian Peak (PI. XXXI). It shows the ridge with its eastern table-land, from 10,000 to 10,600 fee; in ahitude, and the western chain of peaks, reaching heights of from 10,400 to 10,800 feet; the valley of Closed Creek, whose bottom has been eroded down to 8,000 and 6,800 feet; the steep narrow ridge south of the latter, whose high point in the middle ground is 9,600 feet, and the valley of Timber Creek, with the divide to Cache Creek, at about 9,500 feet. To the right is the outline of Hunter Peak, at the mouth of Crandall Creek. The western head of the valley of Closed Creek, which is the divide to Cache Creek, consists of horizontally bedded breccia with a slight dip to the southwest. It contains a few intercalated flows of basalt and is cut U S.GEOLOOtCAL SURVEY MONOGRAPH XXXII PA«T II PL XXXI J-Plddinja HURRICANE RIDGE DIKES IN ORANDALL BASIN. 227 by dikes trending east and west. The bedded breccias continue eastward across the saddle to the tirst peak of the ridge west of Hurricane Mesa. Near the suniniit of this peak they are cut off and overlain by beds of breccia dipping slightly toward the east. These beds pass under the massive rocks which form the upper 600 or 700 feet of the western half of this ridge. The massive rocks form nearly horizontal sheets capping the peaks of this part of the ridge and constituting the top of the flat eastern half or mesa. They exhibit prismatic cracking, and appear to be sheets of basalt intruded in the breccia. Beneath them the breccia shows no bedding, and in the eastern part of the ridge — that is, in the mesa — it is highl)- indurated and weathers like massive crystalline rock with long talus slopes of small fragments. On the southern side of the head of Closed Creek the bedded breccias of the Cache Creek divide are cut off near the top of the ridge between Closed and Timber creeks, and are overlain by chaotic slaggy breccia, which exhibits a rude bedding, with steep dip to the eastward. Halfway up the northern slope of the ridge, beneath this point, there is a large iiTegularly shaped body of massive columnar rock intruded in the breccia. Exposures of massive hornblende-mica-andesite were observed by Mr. Weed on the southern side of the ridge opposite to this body. The southern slope of the ridge west of Humcane Mesa is traversed by dikes rvmniug east and west and more or less parallel. As already remarked, the eastern half of the ridge is a high table-land, whose top, at 10,200 feet, consists of a horizontal sheet of basalt, 200 to 300 feet thick. On the south there are steep slopes and spurs, with much slide rock and little vegetation. On the north are four deep amphitheaters, with precipitous walls, and high rocky spurs between them. In the middle of the table-land on the southern side are two narrow gulches encircling a round-topped spur. At the western end of this table-land dikes are numerous. Across its southwestern spur there are 11, from 2 to 10 feet wide, trending N. 70° E. and S. 70° E. At the northwestern end of the plateau there are dikes trending northwest, which are well exposed in the wall of the amphitheater. A 10-foot dike follows the ridge along the saddle and cuts the turreted peak to the northwest. The dikes also cut the basalt sheets. The long spur north of this end of the plateau is traversed by 18 narrow dikes trending toward the northwest and converging southeastward toward the round- 228 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. topped spur in the middle of the plateau. Small dikes cut the northern edge of the plateau and a small spur from it, and trend toward the north- west at various angles. They can be seen at a distance of 4 or 5 miles traA'ersing the country to the north in the same direction, but of course it is onl}' the largest and most prominent that can be recognized in this way. The basalt sheet on top of the plateau is massive and is jointed in large rectangular blocks. The walls of the amphitheater appear to consist of similar massive rock for a depth of a thousand feet, but they are highly indurated breccia. The western half of the mesa is cut off by the gidcli west of the round-topped spur, and presents a cliff facing eastward. This is intersected by numerous dikes, one of which is 12 feet wide. The cliff passes south into the pinnacled spur west of the gulch. A high and narrow ridge extends around the northern side of the head of the twin gulches, and consists of massive rock cut by a few dikes trend- ing north. From it a high spur runs toward the northeast. It is composed of chaotic breccia, which is somewhat indurated and is traversed by a numljer of dikes ti'ending northeast. The i)ortion of Hurricane Mesa east of the twin gulches is less indurated than that immediately west, and contains fewer dikes. Its northern side was not explored, but undoubtedly exhibits some dikes. Across the upper part of the southern slope there is a long straight dike trending south of east; and several others occur lower down the slope, and trend toward the round-topped sjjur. The southeastern spurs are traversed by 10 dikes, which trend toward the northeast and converge toward a point in fche gulch which drains the eastern end of the mesa. Near this point on the long eastern spur the breccia is indurated and a large body of fine- grained crystalline rock is exposed, which is probably connected with the center toward which this group of dikes converge. Near the junction of Closed and Timber creeks a number of dikes were observed, most of which trend toward the northeast. There is a large one trending toward the round-topped spur. Where the two systems of dikes intersect, tlie dikes from the round-topped spur are found to be the younger, since they cut those trending toward the eastern center. These observations have been plotted on the map in such a manner as to show where the dikes have been actually found, the dotted lines being THE COKE OF TllK UlfANDALL VOLCANO. 229 introduced to emphasize the structure and indicate where the dikes would have been found if tliere had been sufficient time to liunt them out. Slide rock and forest obscure ])arts of the country, and })arts of it have not been visited, as the o-eneral character of the geology was recognizable from a distance. From the data obtained there can be no reasonable question as to the arrangement of the dikes. The great majority of those in Craudall Basin radiate from the middle of Humcane Mesa. A smaller number radiate from a second center, 3 or 4 miles east of the first. It was during the study of the district, which was traversed along much the same lines as those along which it has just been described, that the conviction forced itself upon the writer that the locality toward which the majority of dikes converged nuist have been the center of great volcanic activity, and would prove to be the location of what was once the conduit or throat of an ancient volcano, and mig-ht ijossibly exhibit rocks represent- ing a coarsely crystalline development of the magmas which had filled the dikes. It was, consequently, with great expectations that he led his pack train over the uninviting and even forbidding countrA' drained by Crandall Creek, from Miller Creek across the densely timbered valley of Timber Creek, and over the precipitous ridge into the bottom of Closed Creek ; and having reached the gulches draining the suspected core, it was with great satisfaction that he found himself surrounded bv blocks of gabbros and diorite of decidedly coarse grain. Here Avas in reality the core of an ancient volcano, the conduit through wliich lava had risen to the surface, from which it had escaped in lateral fisures through the surrounding rocks, and in which it had eventually solidified. A description of this core necessarily involves a consideration of the petrographical character of the rocks composing it, which in the case of the other rocks of the district has been deferred to a subsequent part of this chapter; and in order to maintain a logical sequence in the study of all of the rocks of this volcano the detailed description of the granular core will be given in connection with the jjetrography of the rocks. A general statement of its character, however, will be in place here. The round-topped spur between the twin gulches, frequently referred to, consists of granular gabbro which grades into diorite. Grabbro also forms the bottom of the gulches and extends up the flanks of the precipitous spurs encircling the gulches. The greater part of the spur on the west 230 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. above the timber is gabbro, which here attains its highest degree of crystal- hzatiou. The outhne of the gabbro mass is not well defined against the surrounding breccias, for several reasons. The breccias become highly indurated as they approach the core, and finally appear as dense aphanitic rock, with jointing planes like those of the finer-grained parts of the massive intruded rocks, and evidences of their originally brecciated character are almost obliterated. Moreover, the gabbro becomes finer grained and darker colored near the encircling rocks, and in some places is so fine grained as to be distinguished with difficulty from the metamorjjhosed breccia. The shape of tlic granular core is very irregular and indefinite, for it is found ujion investigation that it does not consist of one continuous body of solidified magma, but is made up of smaller bodies diff"ering in grain and mode of crystallization and in mineral composition. Many of these bodies appear as dikes or veins cutting one another and the larger masses of gabbro. They penetrate the breccia as dikes of crystalline ])orphyries, whose identity with the more distant, finer-grained dikes is shown by then* megascopical habit and mineralogical character. It is evident that in the immediate neighborhood of the heated conduit they cooled at a rate which permitted them to assume a higher degree of crystallization than that assumed by the dikes in the cooler breccias. The transition in grain from the core outward is rapid, and, owing to the variability in the size of the dikes and the diff'erences of crystallization due to this cause, no definite ratio of change was noted. Returning to the consideration of the distribution of dikes, it is to be remarked that they abound in the breccias lying north and also east of Cran- dall Creek. In the most easterly mountain of breccia on the map, and on the northwestern spur of Windy Mountain, the breccia of which consists of basaltic scoria and flows, there are numerous dikes, some of which trend a little east of south and others a little west of south. The high limestone escarpment north of Windy Mountain is cut by many small vertical dikes, whose black color contrasts strongly with that of the whitened limestone containing them. In different localities in Crandall Creek where the lime- stone is cut by dikes it is whiteiied in the same manner in the vicinity of the intruded rock. These dikes also trend east of south, and it is to be observed that there were no signs of a radiation of dikes within the limestone, but the dikes appeared to be located along a system of parallel joints. DIKES IN ORANDALL BASIN. 231 No (liki's of volcanic rocks were found in the g-neiss and g-ranite alonj^ Clark Fork, altliough the baro and smootldy glaciated surfaces offered ample opportunity for detecting tlieni if jjresent. The stiaicture of the high ridge north of the upper portion of Crandall Creek is shown in the escarpment on its northern side — that is, along the southern side of Clark Ft)rk and of the creek south of Index Peak. Tlie basaltic breccias appear to be rudely bedded at various angles and are cut by numerous dikes. The top of the western end of the ridge, as already stated, consists of twenty or more basalt sheets, which are nearly horizontal. When viewed from Hurricane Mesa it appears that the low, rugged peak about 4 miles north of the gabbro core consists of rough beds of breccia dipjiing steeply eastward. In the middle of the ridge which is being described there is a low arch of breccia beds that ai-e rouech and irregular. Higher up on the peaks to the west the bedding is more regular and dips at a low angle to the southwest. At the eastern end of the ridge the breccias resting on the limestone are traversed by dikes trending S. 10° E. One of special importance is 3 feet wide and trends S. 25° E. It rises 8 or 10 feet above the surface of the ground and exhibits horizontal prisms. It will be referred to again on account of its composition and of the presence of large crystals of primary quartz. The southeastern spur of Index Peak is cut by dikes trending north- west and southeast, and some more northerly. Numerous dikes cut the northern and northwestern spurs of the same mountain, and a few were observed on the ridges surrounding Republic Creek. In the neighborhood of Cook City we aj^proach another center of eruptive action, which manifests itself in the form of intrusive sheets of porphyry that occur within the Cambrian strata along the valley of Soda Butte Creek, and more especially in the mountains north of Cook City, just beyond the limits of the mapped area. Dikes of similar rocks cut the breccia of Mount Miller, one of the peaks of this group of moun- tains. Several intrusive sheets occur in the limestone south of Cook City, and are located on the map. They include a dense porphyry, a fine- grained gabbro-porphyry, and hornblende-andesite. A few miles west of Cook City there ai-e two small intrusions of dacite-porphyry. 232 GEOLOGY OF THE YELLOWSTO^fE NATIONAL PAEK. EXTENT OF EROSION. As already stated, the volcanic ejeetamenta were thrown over the sur- face of greatly eroded sedimentary rocks. It appears from a study of the adjacent region that an apparently conformable series of deposits from Cambrian to the Laramie of the Cretaceous had been greatly dislocated and faulted, and in places entirely eroded down to the crystalline schists, before the volcanic lavas of Crandall Basin were erupted, thus representing a period of great orographic movement and denudation. It becomes equally evident from a study of some of the areas of volcanic rocks that, after the earlier of these rocks were extravasated, both orographic movement and denudation took place on a grand scale. The region of Electric Peak and Sepulchre Mountain exhibits the extent of the faulting which cut in two that andesitic volcano. But in tlie region of Crandall Basin, which seems to have escaped serious disturbance since the accumulation of the basaltic lava, we may discover a measure of the erosion which has affected this portion of the country subsequent to the completion of this volcano, which must have been active in upper Miocene time.^ However, it should be confessed at the outset that all such calculations must be of the crudest and most general character. A consideration of the geological structure which has been briefly sketched, and which has been indicated on the map and in tlu-ee vertical sections across the district through the gabbro core, leads to interesting con- clusions. The profile sections (PI. XXXII) are drawn to natural scale and exhibit the steepness of some of the mountains. The first passes through the core in a direction N. 24° E., and cuts Pollux, Parker, and Indian peaks, the narrow ridge south of Hurricane Mesa, and the low hills north, ending in the gneiss on Clark Fork. The second lies N. 20° 30' W., pass- ing from the di^^de between Crandall and Sunlight basins, through the gab- bro core and Index Peak, to the gneiss at the head of Soda Butte Creek. The third passes S. 77° 30' E., from Druid Peak across the valleys of Soda Butte and Cache creeks, cutting the ridge of The Thunderer where it is narrowest, and, traversing nearly the whole length of Hurricane Mesa, passes through the summit of Windy Mountain. The chaotic accumulations of scoriaceous breccia and the occuiTences of steeply dipping beds and lava flows throughout the area of Crandall Basin ' Hague, Arnold, loc. cit., p. 4.52, 32 n S GEOLOGICAL SURVEY. DRUID PEAK I MONOGRAPH XXXII, PART ILPL >DCZII THE THUNDERER - -- rJebb" — HURRICANE MESA "TliJb TiiniLi]iiiimiri[iii[[it( mTinii|!;i|iiiiii|ii|||irinniiTmifiaif[IliiiiiiiiiiliiiiMiiJli/illlIill HURRICANE MESA INDEX PEAK Nebs POLLUX PEAK y?!^N e b s HURRICANE MESA lebb Nebb J, A-To. Lllli Baltbnol GEOLOGICAL GROSS SECTION'S OF THE YOLCiVNO OF CKANDALL BASIN, .VBSAll()IL\ RANGE CARBONIFEROUS DEVONIAN SILURIAN CAMBRIAN NEOCENE EOCENE ARCHEAN Cm sj «« N^d Nrh | Nebs Hebb /Rgn Scale oT Miles 1 i o EliOSION OF THE CKANDALL VOLCANO. 233 and the country south of it show this to have been the scene of great voU-anic activity, which shifted about from place to pLvce, building up and blowing to pieces cone after cone of moderate proportions. The unifonnly bedded tuffs, breccias, and lava flows, which dip at anffles not exceeding 5° and form the mountains west and southwest of Crandall Basin, show with equal clearness that they cover an area of inac- tion, where the ejectamenta and lava streams remained undisturbed during their accumulation. The same is? true of the nearly horizontal beds of lava and breccia which cap chaotic breccias, as at Index Peak. Since they began to accumulate the region beneath them must have remained quiet, however active it had been previously, for they exhibit no evidences of upheaval. These subaerial deposits and flows must have been derived from some neighboring center or centers of eruption. The slope of the lava flows toward the west and southwest and their petrographical character prove conclusively that they have been erupted and ejected from centers situated in Crandall Basin. While it is evident that the breccia within this basin and the lower portion of the bedded breccia surrounding it came from shifting vents, it seems necessary to assume that the lava streams which occupy high positions near the summits of the present mountains must have flowed from still higher vents on the slopes or summit of some great volcano. The exploration of the region has led to the discovery of one large central conduit and a multitude of radiating channels Avhicli extend to distances of from 7 to ] 2 miles from the center, besides another smaller center. The great conduit and its radiating channels belong to a period suc- ceeding that in which the chaotic breccia of Crandall Basin was thrown out, and to one in which the volcanic energy had concentrated into one place, for the dikes from this gabbro core traverse the country in nearly straight lines, and have not been thrown into confusion b}' the breaking out of new centers of eruption. They belong, in fact, to the latest phase of volcanic activity in the district. The coarsely crystalline character of the rock at the top of the core, as it is exposed at 10,200 feet, as well as the topography of the country, makes it clear that very considerable erosion has taken place since the volcano was active. Hoav great the erosion may have been will appear when the attempt is made to combine the facts just mentioned and to com- pare them with what is known of great volcanoes which are still active. 234 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. One of the largest and most thoroughly investigated active volcanoes is Etna, whose majestic cone rises from the sea to a height of 10,835 feet. According to the elaborate study of Etna by Sartorius von Waltershauseu, as completed by von Lasaulx,^ the central mass and basal portion of this mountain consist of thick beds of tuff (or breccia) traversed by dikes of massive rock, filling clefts which are for the most part nearly vertical. Between the layers of tutf or breccia are sheets of crystalline rock. These are partly connected with the dikes, and have been injected horizontally in the tuff, or they are in part surface flows of lava. The beds in the central jjart of the mountain dip as steeply as 29°, and show by their positions and by the different groups of radiating dikes that the centers of eruption have been shifted from southeast to northwest. The lower flanks of the volcano are composed of more numerous lava flows, and slope at angles of from 2° to 5°. These lavas have been mostly erupted from lateral or parasitic cones, the arrangement of which on the surface proves that they all belong to grovips in more or less straight lines which exhibit an exactly radial direction from the center of eruption — that is, the present crater of the volcano. In the earlier period of the building of the mountain, as at present, fissures were formed from the center outward, radially. These fissures often lay close together, and were then almost parallel; through them the molten lavas rose and formed dikes; and where they reached the surface they gave rise to parasitic cones. Modern fissures that are radial to the present crater are those of 1669, 1792, 1811, 1852, 1865, 1874, and 1879. There are many others which are approximately radial, and others exhibiting no such arrangement. The lava flows on the flanks of the volcano have reached the surface through the radial fissures connected with the central conduit. The profile of Mount Etna along a vertical section through the summit, from Catania to Randazzo, drawn to natural scale, is shown in PI. XXXII. The scale is the same as in the profiles across Crandall Basin — i25;ooo. The diameter of the volcano in the direction taken is about 27 miles. Etna is of very recent age, geologically considered, for its lowest rocks rest on Diluvial, or Pleistocene, deposits, since which period it has piled up scoria and lava to a height of nearly 11,000 feet. From the foregoing there appears to be a close analogy between the 1 Der ^tna, Leipzig, 1880. COMPARISON WITH OTHER VOLCANOES. 235 conditions at present existing- in the active basaltic volcano of Etna and tliose which |)rol)ably olitained in the basaltic volcano of Craudall Basin. In the last-named region, as it is now exposed, four-fifths of the volcanic material is fragmentary ejectamenta, forming subaerial breccias of angular pieces of massive and. scoriaceous lava with tuff or dust. But in the upper pai"ts of the outlying mountains massive flows of lava predominate. In the case of Mount Etna it is known that the central mass, as exposed in the Val del Bove, is mostly fragmentary ejectamenta, but the surface of the vol- cano consists of lava flows to a very great extent. In Vesuvius there is a cone of nuich steeper slope, consisting largely of tuff-breccias, which dip at high angles in the slopes of Monte Somma. The latest eruptions, which form the cone of Vesuvius, have been quiet outflows of lava. A meridional profile of Vesuvius on the same scale as that of Etna is placed under the latter for comparison (PI. XXXII). It is to be remarked that the subaerial breccias and tufts of Monte Somma, while differing in mineral and chemical comjDosition from those of the Crandall district, resemble them most closely in outward appearance and in the manner of their agglomeration. The subaerial breccias of the Yellowstone Park and its vicinity are for the most part more compact than those of Monte Somma, but exhibit the same structure. Many of them, however, present the same degree of cohesion and all the characteristics of recent ejectamenta. The volcanoes of the Hawaiian Islands are said to be the results of non-explosive eruptive action, very little fragmentary material entering into the construction of the mountains. But it must be borne in mind that the central portions of the great volcanoes there are not exposed and their true character is not definitely known. Assuming that the volcano which must have existed in the region of Crandall Basin resembled closely the type represented by Etna, and neglect- ing the erosion which undoubtedly removed material from above the outlying peaks of horizontally bedded lavas, we may gain some idea of the original form and proportions of this volcano by constructing above the profile sections through its center the outline of Etna, as represented in the plate of sections. Placing the crater of Etna over the center of the dikes of Crandall Basin (PL XXXII), and allowing its outer slopes to rest on the sum- mits of the surrounding mountains, we obtain theoretical elevations of the 236 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Crandall volcano, which, if reckcmed from the level of the ancient surface of the limestone in the neighborhood of the g-abbro core, are 13,000, 13,400, and 13,800 feet. These results are sufficiently close to one another when it is noticed that the jieaks used as datum points lie in an arc of 133° and at distances of from 9 to 14 miles from the center — from Index Peak in the north to Pollux Peak in the south. Moreo^-er, the highest altitude is obtained by using Pollux Peak as a base of reckoning, and this mountain lies within the radius of other volcanic centers near the head of Stinking-- water River, and has probably been built up by lavas from two great centers. A volcano 13,400 feet in elevation with a radius of 20 miles is not so large as man}" in existence at the present day. The volcanoes of Hawaii are familiar examples. Of these. Manna Loa, with an altitude of 13,675 feet, has a maxinuim radius of about 40 miles and a minimum radius of 20. Mauna Kea, 13,805 feet in height, has an average radius of 20 miles. These estimates, it should be remembered, are taken from the sea line. The heights of these volcanic piles above their actual base, and the real diameters of their cones, are not known. The profile of Kea is shown on the same scale as that of Etna and has nearly the same outline (PI. XXXII). A volcano with the profile of Vesuvius, if as large in diameter as Etna, would be 5,800 feet higher, or about 16,600 feet in height. The conclusion, therefore, that the ancient volcano of Crandall Basin rose to an elevation of 13,400 feet above the preexisting surface of the limestone is within reasonable limits, and is probably too low. Upon this basis we find that the gabbro core in Hurricane Mesa must have solidified at a distance of 10,000 to 12,000 feet below the level of the ancient crater. Erosion must have removed 10,000 feet from the highest portion of the volcano to the level of the mountain tops, and 4,000 feet more into the val- leys between them, thus cutting 14,000 feet vertically below what was once the summit of the volcano. At Index Peak the present topography shows an erosion of nearly 5,000 feet from the summit of the peak to the valley of Clark Fork. The foregoing estimates were based on the assumption that the tops of the highest mountains of horizontal lava flows had not been materially afPected by erosion; hence we must regard the calculated amount of erosion as a minimum. There seems to be no way of avoiding this conclusion, EAULY ACID BRECCIA. 237 unless we conceive the last act of vulcanisin to have been the greatest and imagine a gigantic explosion to have blown the ui)p(o- })ai't of the volcano into the air and t(» have left no evidence of such a culmination of events. On the contrar}-, the evidence furnished by the structure of the granular core indicates that the last eruptions were feeble, injecting narrow veins of rock into the body of the core. It is to be remembered that the erosion which has thus laid bare a basal section of so great a volcano was accomplished after the accumulation of this vast pile of Miocene ejections and before the extrusion of the immense Hood of rhyolitic lava forming the jdateau of the Yellowstone Park. In the region of Electric Peak and Sepulchre Mountain there are evidences of orographic movement accompanying this period of denudation, shown in the profound faulting which cut in two that audesitic volcano ; but the region of Crandall Basin seems to have escaped serious orographic disturbance. PETROGRAPHY OF THE ROCKS OF THE DISTRICT. The extn.^sive rocks of the volcano of Crandall Basin are in the main the same as those found in various parts of the Yellowstone Park, those of Sepulchre jMountain having been described in Chapter III. It will not be necessary to repeat in detail the characteristics of most of the I'ocks, but the petrographical features that are distinctive of this volcano will ])e fully described. EARLY ACID BRECCIA. The early acid breccia consists of small fragments and dust of hornblende-mica-andesite, hornblende-andesite, and hornblende-pyroxene- andesite. The microscopical characters are quite normal. The andesites are partly holocrystalline and partly glassy. The structures of the groundmass are typical of andesites, and the phenocrysts of plagioclase, hornblende, biotite, hypersthene, and augite exhibit the usual characteristics. The color of the hornblende varies from reddish brown and brown to brownish green, green, and bluish green, and is often strongly pleochroic. In one occur- rence there is a little quartz in microscopic ^phenocrysts. There is a consid- erable range of composition, and the rocks grade into varieties which are like the more siliceous andesites of the overlying breccias, a small portion of which is hornblende-pyroxene-andesite. They also appear to pass upward into the basic breccias in certain localities, though in others there are evi- dences of an intermission accompanied by erosion. 288 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. BASIC BRECCIA AND LAVA FLOWS. The basic breccia is, with some exceptions, dark colored, gray, and reddish brown, and is as a whole basaltic. Variations in mineral composi- tion occur within narrow limits, and are most noticeable in the amounts of olivine and hypersthene. All proportions ot olivine exists. According to the preponderance of one or the other the rocks may be classed as basalts or pyroxene-andesites, though their other characters remain much the same. Variovis modifications of the rock are mingled in the breccias, but to a different extent in different localities. In some cases the material is very uniform in its habit. Of the specimens collected two-thirds are liasalt. Hornblende-bearing varieties are extremely rare, and occur in the neighbor- hood of the early acid breccia. In most instances the rocks exhibit no lai'ge phenocrysts, but carry a nmltitude of minute tabular feldspars and somewhat larger pyroxenes, with more or less olivine. There are modifications of the rock — which are more numerous within the region of chaotic breccia — that carry tabular feldspars 5 to 8 mm. long, and still others with the same form of feldspar 30. mm. long, the large feldspars being crowded with inclusions. The rocks are very generally vesicular and scoriaceous, but a part are dense and compact. In thin sections the groundmass possesses an andesitic habit, and consists of brown and red globulitic g-lass, which is occasionally colorless, with microlites of feldspar and grains of pyroxene and magnetite. In some instances it is opaque through an excess of iron oxide, and in other cases it is holocrystalliue. The phenocrysts are plagioclase, augite, magnetite, and more or less hypersthene and olivine. The microscopical characters of these minerals are the same as in other occurrences in this region. A basalt with andesitic habit from Saddle Mountain is shown in PI. XXXIV, fig. 3. Hypersthene is more abundant as olivine is less so, and is absent from the rocks with much olivine. Occasionally hypersthene is surx'ounded by augite with parallel orientation. In some cases augite is brown at the center, with a zonal structure. In most cases it is pale green. The olivine is unaltered in many occurrences and completely serpentinized in others. In general the rocks are very fresh, with slight indications of weathering, and only an occasional development of zeolites An unusual and interesting variety of the latter mineral was collected and investigated by Prof. L. V. BASALT FLOWS. 239 I'irssou, who determined it to be mordeiiite.' Very j^lassy t'onns of rock are found in the breccia on the ridge south of Indian Peak. Some are fragments of black glass with a few small phenocrysts of tabular feldspar. Others are gray and exhibit spheroidal cracking, and constitute masses of considerable size. The black fragments are basalt-andesite glass, which is dark brown and almost o]>aqne in thin section, with few scattered microlites. In some sections the glass is mottled and streaked with light brown. The microlites consist of feldspar needles and grains of magnetite surrounded by halos of colorless glass, besides a few small augite crystals and serpen- tinized olivines. There are somewhat larger plagioclases with inclusions of brown glass. The chemical analysis of this rock (analysis 6 on page 260) proves it to be intermediate between basalt and andesite. The gray glassy varieties belong to pyroxene-andesite. In thin section this glass is colorless to light brown, Avith small crystals of plagioclase and fewer of magnetite, augite, and hypersthene, and in rare instances hornblende. The variety of basalt with feldspar phenocrysts 30 mm. long is char- acterized by a slightly different microstructure. The groundmass consists of tabular feldspars, composed of kernels of labradorite with margin of orthoclase, besides smaller augites and magnetite, through which are scat- tered larger microscopic crystals of the same minerals, with patches of serpentine. The phenocrysts are small megascopic labradorite, augite, decomposed serpentine and magnetite, besides extremely large tabular labradorite. Avith abundant inclusions of glass or groundmass. These basalts are intermediate between normal basalts and the shoshonite described in Chapter IX. BASALT FLOWS. The lava flows intercalated in the breccias are all basalt, with variable amounts of olivine, judging from the thirty specimens of them which were collected. None proved to be andesite. In general they come from higher parts of the volcano, and represent later phases of its eruption. But some of them occur among the earlier products, and while it may be said that the basalts formed almost the whole of the later outflows of the volcano, and that the magma became more basic iip to this period, it must not be forgotten that the eruptions varied constantly within narrow limits, and that ' On mordenite : Am. Jour. Sci., 3d series, Vol. XL, Sept. 1890, pp. 282-237. 240 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. ill the earlier history of the volcano this variation was within such a part of the chemical scale of variation that the resulting rocks might be called andesites or basalts, but that this difterence of name corresponds to no greater difference in composition than that between the varieties of basalt of the later period. It is also probable that flows of pyroxene-andesite occur among the lava streams, but that they were not distinguished in the field. The greater part of the basalt flows are andesitic in habit — that is, in microstructure — and are like the basalts forming the breccias. None of them are ophitic. The groundmass is in most cases glassy; in others, holocrystal- line. Some of them carry large phenocrysts of feldspar and resemble the same variety of breccia in microstructure. Some contain a little orthoclase in the groundmass, and are intermediate between normal basalt and shoshonite. INTRUSIVE ROCKS. OUTLVlNe DIKES. As already pointed out, the dikes belong to several converging groups, the largest of which centers in the gabbro core and a smaller one in a focus a few miles east, while a great number of dikes in the southern part of the district belong to an outlying volcanic center situated near the headwaters of Stinkingwater River. The rocks constituting these dikes exhibit more variation than the brec- cias, though the majority of them are like the breccias in composition and habit, being basalt. But toward the end of the period of volcanic activity, as we learn from the structure of the granular core, the composition of the magma became more and more siliceous, and the volume of the lava erupted, or the size of the fissures from which we estimate this volume, became smaller. At the same time we learn from certain dikes that peculiar phases of the magma made their appearance, the rocks of which deserve special consideration. It is to be remarked that while the most siliceous modifications of the magma occur within the core, the most basic phases of it are found at considerable distances from the center, with one exception. This accords with the idea that the more siliceous products of differentiation will occur near the center of the reservoir in which differentiation takes place, presumabl}' beneath the crater of a volcano, while the less siliceous products BASALT DIKES. 241 will occur near the niarjicin of the reservoir, away from the crater.' More- over, it is to be noted that while many of the exceptional modifications of the magma appear to be connected with the center of eruption in Crandall Basin, they are more numerous in the southern district, about the head of Stinkingwater River. In describing the intrusive rocks we shall com- mence with those which resemble most closely the breccias and surface flows. Basalts. — The basalts of the dikes exhibit the same megascopical habit and variability as those of the breccias. Part of them have a multitude of small pheliocrysts of tabular labradorite and augite, and part carry very large labradorites. They appear to be the same varieties of magma which have cooled in dikes, and consequently possess a slightly different ground- mass. In a large number of cases the groundmass consists of lath-shaped labradorite and crystals of augite and magnetite in a small amount of microlitic base. The augite is occasionally slightly pleochroic. The pheno- crysts are tabular labradorite, augite, and olivine, with magnetite and stout colorless apatite. In a number of dikes the groundmass contains orthoclase as margins around the microlites of labradorite. One of the most pro- nounced of these varieties (1325) forms a dike on the ridge south of Closed Creek. Its chemical composition is given by the third analysis on page 260. It is closely related to shoshonite, as pointed out in Chapter IX. Others contain less orthoclase and are intermediate between shoshonite and normal basalt. To this variety belong most of the dikes at the head of Miller Creek and those cutting the summit of Saddle Mountain. In some cases the groundmass contains microlitic and globulitic glass base; in others it is holocrystalline. A glassy basalt from Hunter Peak contains microlitic needles of feldspar, slightly curved, and magnetite grains pointed at the corners, besides augite microlites with magnetites attached. In some occurrences these needles are coated with magnetite and resemble thin black lines. It is often observed that the face of a dike along the plane of contact is glassy, while the center is holocrystalline. In one instance this contact facies consists of almost opaque brown globulitic glass with much iron oxide in minute rods, and thin feldspar needles with long forked longitudinal sections shaped like an H, the groundmass extending to near the middle of ' L. V. Pirsson, ComplemeDtary rocks ami railiatinj; dikes : Am. Jour. Sci., 3d series, Vol. L, 1893, p. 120. MON XXXII, PT II 10 242 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the crystal. Cross sections are square, with large square inclusions of groundmass. Ilmenite occurs in many of the rocks in rod-like crystals, and a small amount of serpentine is present in most of the groundmasses. Olivine is decomposed to serpentine in most instances, and originally formed small as well as large crystals. In one of the fresher rocks the groundmass contains many small olivines, which are probably the mineral from which the serpentine in the groundmass of the more altered rocks was derived. As a whole, the basaltic dikes are not so fresh as the breccias surrounding them, although they are the younger rocks. Those with large tabular feldspars acquire a very characteristic appeai-ance through the whitening of these crystals, which are strongly contrasted with the dark dense groundmass. The large dark- colored augites are also distinctly noticeable. Gabbro- and diorite-porphyries and andesites. The rOCks wllicll WOuld be plaCed under this division in consequence of a microscopical examination jjrobably belong quite as closely to the basalts. With one exception they all occur in close proximity to the granular core, and some of them are included in it. The one exception is a narrow dike of pyroxene-andesite, the ground- mass of which is filled with serpentine, indicating the former presence of a magnesian mineral, possibly olivine. The rocks of this division exhibit all of the modiiications of mega- scopical habit shown by those just described, and resemble them closely in hand specimens. They are, however, more crystalline and present micro- structures both distinctive and characteristic, which are related to differences in mhieral composition. A few of the andesitic dikes which cut the summit of the plateau west of the core are very fine grained and are considerably altered, and contain chlorite and epidote. The absence of olivine from most of the more crystalline forms of these rocks appears to be due to the causes which influenced the crystalli- zation of the rocks and not to their chemical composition, for the hand specimens in some cases show what seem to be decomposed crystals of olivine, which in thin section are found to be paramorphs after this mineral. This group of rocks includes the intrusive sheets on top of Hurricane Mesa and certain dikes. In the immediate neighborhood of the core and within the zone of indurated breccia the massive sheet of intrusive rock appears dense and aphanitic (1359, 1361, 1369), and carries abimdant tabu- GABBRO AND DIOUlTE-rOKPUYRIES. 243 lar feldspars 5 mm. lonn(le is surrounded by a pleochroic halo. The chemical composition of this rock (analysis 14 on pa<)e 2()1) is that of a (piartz-mica-diorite rich in orthoclase — that is, banatite. iri<;her up the spur, at 10,000 feet, the main body of rock (1429) becomes finer p-aiued, the feldspars are more nearly idiomorphic, and the quartz forms large, irregular individuals with raicropoikilitic structure, inclosing small felds])ars (PI. XXXIII, fig. 4). The plagioclase is andes- iue, and contains rectangular inclusions resembling glass. Orthoclase is not so abundant. Tliere is considerable biotite, with augite, hypersthene, and magnetite, but no hornblende. A still finer-g-rained form of this quartzose facies of the core occurs north of the top of the middle spur. It is a very fine-grained gray rock (1414), without phenocrysts. In thin section it exhibits a structure similar to that last mentioned, the idiomorphic labradorite-andesine having a border of allotriomorphic feldspar. There is a moderate amount of augite and hypersthene, which occur in groups of small grains rather than in compact individuals, besides magnetite and very little biotite. The chemical analysis (No. 13 on page 261) shows its resemblance to 1427, as well as the chemical differences between them, which correspond to difference in min- eral composition, the latter rock being richer in biotite, orthoclase, and quartz, with more hornblende than pyroxene. In some of the thin sections from the body of the core there are traces of decomposition, producing a little chlorite and serpentine, and in some cases uralite accompanying evidences of slight crushing in the feldspars. But the rocks are to a very great extent perfectly fresh and unaltered. The quartzose facies of the gabbro is younger than the main mass of more basic I'ock, for it is found cutting it as dikes. Thus, a fine-grained variety (1419), with the same microsti'ucture and composition as the fine-grained form (1414) on top of the core, cuts the aphanitic zone of more pyroxenic rock at the base of the middle spur. It grades directly into more granular rock (1420), which has the structure and composition of the lower part of the main mass of the spur represented b}' 1 425. There is also a 20-foot dike of this quartzose variety which cuts the gabbro on the southwest spur at 9,100 feet and trends toward the southwest, while a body of similar rock, whose form was not observed, occurs on the crest of the same spur, more within the core. The rock from this body (1400) has the same composition as that at the base of the middle spur 254 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. (1425), with more hornblende intergrowths. The pyroxenes have the char- acteristics of those in the gabbro. The microstructure is coarser than that of the 20-foot dike, which is represented by specimens 1407, 1405, the finer-grained form (1405) being about grade 28. Rock 1400 has less ferro- magnesian minerals and resembles in outward appearance the fine-grained rock from the top of the core (1414). Its structure is shown in PI. XXXIV, Two small dikes of similar quartzose diorite-porphyry cut the aphanitic zone at the base of the west spur. They are dense and crystalline, without noticeable phenocrysts (1385, 1386). The coarser of the two resembles the rock last mentioned in mici-ostructure, and is about grade 27. It has the same mineral composition as the finer-grained rock which occurs in a dike 1 foot wide. The latter (1385) differs from it slightly in microstruc- ture, and is about grade 18. Its phase of crystallization is specially inter- esting. In thin section it consists of lath-shaped feldspars of varioiis sizes, and small grains of feldspar, with considerable quartz, which has a micro- poikilitic structure. The groundmass also contains magnetite, biotite, augite, and altered hypersthene. Its most notable characteristic is the development of small phenocrysts of orthoclase in Carlsbad twins with irregular outlines. The outer portion of these crystals incloses the ferro- magnesian minerals, and occasionally plagioclase. There are few pheno- crysts of plagioclase. The orthoclase appears to belong to the period of crystallization when the quartz formed in poikilitic individuals of nearly the same size as the orthoclase, but inclosing more plagioclase. The outline between the quartz and the orthoclase is irregular. Thus the porphyritical orthoclase crystals are younger than the lath-shaped plagioclase and ferro- magnesian minerals of the groundmass of the rock. The rocks are banatite- porphyry. There are still more quartzose facies of the magma, which cut the dioritic facies of the middle spur in dikes or veins. A coarsely crystalline variety (1428) forms a 4-foot dike cutting the main body of rock (1429), which is somewhat finer grained and has been described. The dike rock is about grade 40, and is like the main part of the spur lower down (1425), being of the same degree of crystallization. The microstructure is like that of the latter rock, but there is more quartz and feldspar and less DIOIUTE AND DIOlUTE-rOKPHYKY. 255 ferromag'nesian minerals, which are liiotite and a Httle chlorite, but no pyroxene. Some of the chlorite carries zircon with i)leochroic lialos, and bunches of rutile needles. Magnetite, zircon, sphene, and stout apatite crystals are the accessory minerals. The rock is a quartz-mica-diorite, approaching granite in composition. It has the same microstructure, degree of crystallization, and mineral composition as the quartz-mica-diorite or honiblende-granite (323) which occurs at Electric Peak. The latter, however, contains hornblende besides biotite, and has no chlorite, which in the rock in Hurricane Mesa may in part replace hornblende. The chemical composition of the rock at Electric Peak has been determined. Its silica percentage is 66.05. A still more quartzose and feldspathic variety (1424) forms a vein 10 inches wide on the middle spur. It has the general habit of the rocks of this facies, but is lighter coloi'ed and carries less ferromagnesian minerals. Its texture is saccharoidal. In thin section it has a granular structure about grade 40, and is composed of quartz, orthoclase, and oligoclase, with biotite and magnetite, very little hornblende, and some chlorite. The accessory minerals are the same as in the previous variety. It is a fine-grained granite, whose chemical composition is shown in analysis 16 on joage 261. Its microstructure is shown in PI. XXXIII, fig. 3. There are also narrow veins of white rock, composed of quartz and feldspar, with little ferro- magTiesian minerals, and numerous small cavities lined with crystals of quartz and feldspar. These veins present the most highly siliceous facies of the rock. A porphyritic form of the very quartzose facies also occurs on the mid- dle spur. It is not noticeably porphyritic in the hand specimen (1423), but in thin section is distinctly so, with a granular quartzose groundmass, grade 23. It exactly cori-esponds in microstructure and degree of crystallization, as well as in mineral composition, to the quartz-mica-diorite-jjorphyry (331) of Electric Peak. The phenocrysts are biotite, andesine, and quartz, and occasionally orthoclase. Their outlines are nearly idiomorphic, but the quartz in some individuals loses its proper form by merging into the smaller quartzes of the gi-oundmass in the manner described for the rocks at Elec- tric Peak. There is considerable sphene and zircon. Its chemical compo- sition (analysis 15 on page 261) is like that of the rock (329) of Electric 256 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. Peak, and is quite the same as that of the quartz-mica-diorite (1427) in which it occurs. From its chemical composition it should be classed with banatite. Less quartzose dioi'ite-porphyries were collected from talus at the south- western base of the southwest spur, and from that under the cliff west of the lake at the head of the west gulch. Having been led from the petrographical study of the breccias and flows of glassy basalt and pyroxene-andesite along the converging lines of microcrystalline dikes of like composition to the coarsely granular core of gabbro of the same chemical composition which rei:)resents the highest phases of crystallization of these basaltic magmas, and having found the gabbro passing into more siliceous facies which have been erupted after the main mass of gabbro, and from which have proceeded dikes of finer-grained rocks of similar composition, we may follow these more siliceous dikes out into the surrounding country, and consider in connection with them the less numerous dikes whose variations of mineral composition express a still fur- ther development of facies of the basaltic magma. These dike rocks exhibit a wide range of composition, and, together with the dikes already described, form a natural group. The latter repre- sent the main body of magma in this region, of which the rocks to be described may be considered facies by differentiation, the variations being, on the one hand, toward more siliceous and more feldspathic rocks, and, on the other hand, toward less siliceous rocks, some of which are highly feld- spathic, while others are high in ferromagnesian minerals. These dikes appear to have been erupted after the greater number of basalt dikes Avere formed, but the exact relationship between them was not observed in every case. Hornbiende-mica-andesite-porphyries. — Commeuciug witli tlic more siliceous Varie- ties, we have a group of light-colored rocks in various tones of gray, which are compact, and are filled with small plienocrysts of feldspar, hornblende, and biotite. There is a striking similarity of habit throughout the rocks of the group, which corresponds to the habit of the fine-grained quartz-mica- diorite -porphyries already described. Within the granular core they form a few dikes, one of which cuts the gabbro on the crest of the southwest spur, and another, 10 feet wide, cuts it a little higher and trends west. These hornblende-mica-andesite-porphyries HORNBLENDE MICA-ANDESITE-rORPHYKIES. 257 (1401, 1408) are not quite so rieh in quartz as the diorite-poqihyries of the core, l)ut tlun' carry consiih'ralile tjuartz in tlie ground inass, and a few crystals of it occur as phenocrysts. Their crystallization is fii'rade 23 in the first case, and grade IH in the second. Near the base of the west spur there is an S-foot dike of this rock (1 384), trending west of south, and still- lower down the slope there is another (1381). A small dike of this rock cuts the soutliAvestern edge of the top i>f the middle spur, and in the cliff west of the lake thei'e is a 15-foot dike of it (1367), trending N. 45° W. Besides these there are indications of other bodies of the same kind, fragments of which are found in the talus in various places. These rocks are fine grained, and resemble the remainder of the dikes of hornblende-mica-andesite-porphyry so closely that a general description will serve for all of them. The outlying dikes of this character are found in the immediate neigh- borhood of the core, the longest noted extending about 5 miles to the south- west. A 10 -foot dike of it forms the saddle northwest of the plateau of Hurricane Mesa and trends northwest, being- in line with the 15-foot dike west of the lake. On the narrow ridge south of Closed Creek there are a nuinber of these dikes, which cut the ridge at a ^jlnce southwest of the core. Five were noted, three of which are 10, 18, and 20 feet wide and trend toward the south and southwest. They fork and branch out in these directions, and dikes of identical rock are exposed on the southern slope of the ridge, having the same general trends. They may be traced almost continuously, in some instances diagonally, across the steep spurs. In thin section the rocks are holocrystalline and fine grained, ranging from grade 18 in the dike (1381) at the base of the southwest spur of the core to grade 10 in the most remote dike (1319), which is 4 or 5 feet wide. The habit of the rocks is andesitic, passing into that of andesite-porphyry at the more crystalline end of the series. The groundmass consists of tabular plagioclase in a matrix of irregular grains of feldspar with a little quartz, besides idiomorphic crystals of magnetite, biotite, hornblende, and pyroxene. Through this are scattered larger crystals of the same minerals. The mega- scopic crystals are abundant, and are andesiue-labradorite .with zonal struc- ture and variable amounts of inclusions; and idiomorphic hornblende, brown- ish green with a brown Ijorder, in places intergi'own with augite in the MON XXXII, PT II 17 258 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. same manner as in the rocks of Electric Peak. Augite is pale gi'een, and occurs in small amounts. Hypersthene is often decomposed. Biotite is abundant in the groundmass of some of the rocks when it does not form large cr^-stals. In other cases it is abundant as phenocrysts. Some of the more altered rocks carry chlorite and epidote. Apatite and zu'con appear as accessory minerals. When the biotite has been altered to chlorite the zircon inclusions are sometimes surrounded by pleochroic halos. There are more siliceous and feldspathic varieties of the rock, in which biotite preponderates over hornblende. The groundmass carries less ferro- magnesian minerals, and a distinctly micropoikilitic structure is recognized in the quartz. From the foregoing it is evident that we have followed this fades of the magma from the core out int(i microcrystalline forms, which may be classed as andesitic forms of hornblende-mica-andesite-porphyry, or as holocrystalline andesites. The chemical analysis of the most distant dike of this rock (1319) (analysis 12 on page 261) shows that it belongs to a less siliceous phase of the general magma than the quartz-mica-diorite of the core. No highly siliceous dikes were found outside of the core in connection with this system of intrusions. Similar rocks occur in the neighborhood of Cook City in such a ma;mier as to indicate the presence of another center of eruption near that place. The more basic dikes which remain to be described, though they are scattered over the district and are somewhat sporadic, may properly be considered to belong to the Crandall center, since varieties of them occur within the core, although the extreme forms do not. They are less numerous than those just described, and vary considerably in mineral composition. Hornbiende-pyroxene-andesite. — There are ouly two of thcsc dlkcs wliicli may be classed as hornblende-pyroxene-andesite, but dikes of this rock are more numerous in the neighborhood of Cook City. One of these rocks (1317) forms a dike on the ridge northeast of Indian Peak and trends toward the gabbro core. The other (1368) was found on the top of Hurricane Mesa east of the core, but not in place. It carries large black crystals of horn- blende from 10 to 20 mm. long. Both of the rocks mentioned are compact, with hornblende, as the only prominent phenocrysts. In thin section the groundmass is andesitic and holocrystalline, and consists of lath-shaped plagioclase microlites with tluidal arrangement, besides small patches of MINERAL AND CHEMICAL VAKIATIONS OF KOCKS. 259 quartz with iiiayiietite aiul altered pynixeiie. Tlio plieuocrysts vary in aiiu»uut and size, and are plagioclase, auyite, and lijperstliene, witli larger crj'stals of hornblende, which is brown and brownish green and in one of the rocks has a narrow border of magnetite. Lamprophyric rocks. — The remaining dikes do not constitute a distinct group which may be sharply separated fntm the majority of the rocks of the dis- trict, though certain of them possess marked characteristics. Their chiet distinction, is an unusual mineral combination, but they are connected with the ordinary rocks of the district by mineralogically interniediate varie- ties. In general appearance they resemble the rocks with which they are associated. They are fine-grained rocks, characterized by an abundance of biotite and other ferromagnesian minerals, including augite and olivine, with feld- spar subordinate in some cases, and partly alkaline, while analcite appears as a secondary mineral in some modifications of the rock. In other cases the rocks are distinctly feldspathic. Because of their unusual composition, and of the occun-ence of similar rocks in dikes and lava flows in other parts of the Yellowstone Park, their petrographical description is deferred to Chap- ter IX, where they are classed as absarokites, shoshonites, and banakites, and are considered as exceptional facies of the normal magma of the region. They seem to represent less common differentiations of this magma than the more numerous varieties of igneous rocks do, and for this reason may be discussed separately. MINERAL AND CHEMICAL VARIATIONS OF THE ROCKS. The variations in minei'al composition of the igneous rocks of this dis- trict are evidently dependent on more than the chemical composition of the magmas from which they have crystallized, rocks of the same or of similar chemical composition ha^'ing diff'erent mineral components, which has also been shown to be the case at Electric Peak and Sepulclu'e Mountain. The range of mineral variation among the extrusive rocks, when con- sidered in the order of their eruption, is from siliceous andesites with biotite and hoi-nblende, through those with hornblende and pyroxene, to pyroxene- andesites, which grade into basalt by decreasing percentages of hypersthene and increasing amounts of olivine. This is succeeded in a neighboring part of the country by a recuiTence of the same series from hornblende-mica-andesite to basalt, and finally by 260 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. rhyolite and basalt. There are three distinct periods of basaltic eruptions and an indefinite number of minor outbursts of the same rock. The study of the whole region shows the frequent recurrence of certain lavas. Among the intrnsive rocks the mineralogical variations differ according to the phase of crystallization of the rock. In the finer-grained dike I'ocks they range from olivine-augite-labradorite-basalts, through those with little or no olivine, to hornblende-pyroxene-andesites and to still more siliceous mica-hornblende-pyroxene-andesite-porphyries, and in another direction to more basic rocks, which range from olivine-augite-mica rocks, through augite-mica rocks, to augite-hornblende-mica rocks with orthoclase and plagioclase. There is also a mineral variation which accompanies the degree or phase of crystallization of the rock. It is illustrated by the transition from basalt to gabbro. The character of the variation will be shown by a com- parison of the mineral composition of rocks whose chemical composition has been determined to be similar. An alynes 0 f rochs from th e Cranilall volt ano. Constituent. 1 2 3 i 5 6 7 8 SiO, 51.81 .77 52.09 .39 52.11 .53 53.56 .68 53.71 .74 53.89 .49 55.93 .81 56.21 .88 TiOa AI5O3 15.24 17.84 16.58 16.07 18.00 18.81 18.32 18.24 Fe^O:, 3.66 4.27 3.66 3.21 3.99 4.92 2.39 3.26 FeO 4.86 4.36 4.99 5.29 4.05 2.81 4.91 3.69 MuO .08 .14 .23 .11 .24 .17 .14 .17 MgO 8.89 5.33 6.87 7.23 5.19 3.29 3.97 3.38 CaO 9.06 8.03 6.43 8.77 6.88 5.42 6.17 5.91 NajO 2.83 3.39 3.25 3.06 3.50 3.65 4.29 4.15 KiO 2.08 1.98 3.20 1.94 3 10 2.98 2.62 3.02 p„05 .18 .27 .63 .18 .38 .52 .56 .64 NiO CI 1 1 H:0 Total .67 1.77 1.99 .19 .55 2.99 .22 .78 100. 13 100.06 100. 47 100. 29 100.33 99.94 100.33 100. 33 1. Gabbro-porphyry ; core ou Hurricane Mesa, CrandaU Basin (1388). 2. Basalt; flow, north side of Timber Creek. C'raudall Basiu (1252). 3. Basalt; dike, ridge south of Hurricane Mesa, CrandaU Basin (1325). 4. Basalt-porphyry; core. Hurricane Mesa, CrandaU Basin (1383). 5. Gabbro (with raica) ; core, Hurricane Mesa, CrandaU Basiu (1430). 6. Basalt-andesite glass, breccia; ridge south of Indian Peak, CrandaU Basin (1241). 7. Orthoclase-gabbro-dioriti; (rich in raica) ; core, Hurricane Mesa, Crandal] Basin (1399). 8. Orthoclase-gabbro-diorite (rich in mica); core, Hurricane Mesa, CrandaU Basiu (1396). OHliMlCAL ANALYaKS OF KOOKS. Analyses of rockn from the Crandall volcano — Continued. 261 CoDStltuent. 9 10 11 12 61. 16 .23 16.17 2.89 2.18 Truce. 3.89 4.26 3.87 3.20 .13 13 63.42 .35 17.16 3.09 1.50 .04 1. 64 4.65 4. .51 3.04 .26 .19 14 15 16 SiO. 57.26 .76 19.40 2.49 3.29 .16 2.57 5.68 4.21 2.95 .51 57.32 .62 17.29 3.89 3.03 .06 3.50 5.81 3.89 3.04 .50 .10 57.64 .77 18.43 3.63 2.84 .10 3.32 5.49 4.03 3.33 .34 63.97 .4X 15.78 2. 35 1.87 .05 2.84 8.71 4.36 4.01 .40 Trace. 64.40 .40 15.77 2.47 1.15 .04 2.12 3.54 4.10 3. HI .16 .17 71.62 TiO. .08 ; 14.99 , 1.27 j 1.01 .17 .74 1.33 3.62 4.81 Trace. AliOj Fe Oj KeO MnO MgO CaO Na.O K.O p .0, NiO CI Trace. .51 HO .86 .63 2.09 .44 .58 2. 24 .41 - Total 100. 14 99.74 100. 43 100.07 100. 29 100.40 100. 37 100. 05 9. Dioritic facies of gabbro; core, Hurricane Mesa, Crandall Basin (1436). 10. Monzonite; east core. Hurricane Mesa, Crandall Basin (1442). 11. Pyroxene-diorite-porphyry. approaching iiiouzonite-porpliyry; intrusive sheet, Hurricane Mes.i, Crandall Basin (1372). 12. Honibleudemioa-andesite-porpbyry ; dike, ridge south of Hurricane Mesa, Crandall B.TSin (1319). 13. Quartzdiorite (tine grained) ; core. Hurricane Mesa, Crandall Basin (1414). 14. Quartz-mica-diorite; core. Hurricane Mesa, Crandall Basin (1427). 15. Quartz-niica-diorite-porphyry ; core. Hurricane Mesa. Crandall Basin (1423). 16. Aplite; dike in core. Hurricane Mesa, Crandall Basin (1424). The chemical analyses show what is known of the composition of the sm'face flows, dikes, and stock rocks of this district, exclusive of those classed as absarokites, etc. Of these analyses, Nos. 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, and 16 were made by Mr. L. G. Eakins, and Nos. 10, 13, 14, and 15 by the late Dr. W. H. Melville, in the chemical laboratory of the United States Geological Survey. They are arranged according to the increasing percentage of silica, which varies from 51.81 to 71.62. The range of silica is greater than in the rocks of Electric Peak and Sepulchre Mountain, most of the analyses showing less than 58 per cent silica. The more siliceous rocks in both localities are similar. The variability of the chemical composition of the rocks of this district has been discussed in another place.^ The analyses shoAv that the basalts of the district vary in composition within certain limits. 'Iddings, J. p., The origin of igneous rocks: Bull. Philos. Soc. Washington, Vol. XII, 1892, p. 151. 262 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. Comparin^'^ the first three analyses (1, 2, 3), it is seen how closely they agree with one another. The first has slightly less alumina and somewhat more magnesia and lime. The second and third are of basalts, the second being a surface flow, and the third a dike. They are rich in olivine, augite, and magnetite, without hypersthene. The third contains large pheno- crysts of labradorite, and can'ies a little orthoclase in the groundtnass. The first of the three analyses is of the finest-grained form of one of the series of specimens from the core, and is a gabbro-porphyry. Its compo- nent minerals are plagioclase with much augite, hyperstliene, biotite, and magnetite, and a little olivine. Although it is richer in magnesia and has only two-thirds as much potash as the third rock, it has developed a great amount of biotite, much hypersthene, and onl}- a little olivine, while the third rock has abundant olivine and no biotite or hypersthene. Comparing the next three analyses (4, 5, 6), we find a close corre- spondence in chemical composition, with a smaller amount of alumina and alkalies in the first and a greater amount of iron, lime, and magnesia. The fifth analysis holds an intermediate place between the fourth and sixth. The greatest variation is in the magnesia, which is twice as great in the fourth as in the sixth. The rocks represent three very different phases of consolidation. The sixth (1241) is a glass with few crystals of olivine, augite, and plagioclase, and microlites of magnetite, augite, and feldspar. The fourth is a fine-grained basalt-porphyry, composed of plagioclase, augite, hypersthene, biotite, and magnetite, with no olivine. The fifth is coarsely granular gabbro, composed of plagioclase with some orthoclase, a little quartz, much augite (diallage), some hypersthene, considerable biotite and magnetite, and a few crystals of olivine. The next two analyses (7, 8) are only a little higher in silica than the previous three, and are very similar to that of the basalt-andesite glass (1241) in all other respects. They are analyses of coarsely crystalline gabbro-diorite, which grades into less siliceous rock (1388) within a short distance. There are no analyses of extrusive rocks from this district with the same percentage of silica with which to compare them, but at Sepulchre Mountain there are andesites whose chemical composition has been determined, and with which these may be compared. CHEMICAL ANALYSES OF ANDliSITES. 263 Analygcx of andesUen from Seiinlclirf Mountain. CoilMf itiU-llt. 4'JI 171 407 388 SiO- 55.83 1.05 17.11 4.07 3.75 Niine. 7.40 55.92 .94 17.70 3.16 4.48 Trace. 5.90 56.61 .79 13.62 r.. 89 2. 60 .35 6.61 .14 5.48 Trace. 57.17 1.03 17.25 2.48 4. .31 None. 6.61 TiO. AU> Fe.-O:, FcO MuO CaO BaO Mg( » 5.05 4.34 4.83 .SrO LiO Nunc. 2. 94 1.71 .21 Trace. None. .09 4.08 2.28 .18 Trace. None. Trace. 3.44 2.03 .05 Trace. Trace. Na,0 K,0 3.13 2.71 .06 P,Or, SO:, CI CO. None. 2.27 HO 1.28 1.42 1.20 LessO forC'l 100. 40 100. 45 100.26 100.40 These analyses are liig-her in magnesia and lime and a little lower in alumina and alkalies. The rocks from wliich they were made are pyroxene- andesite and hornblende-pyroxene-andesite, without mica or olivine. Their coarsely crystalline equivalents at Electric Peak are pyroxene-andesite- porphyry and pyroxene-mica-diorite. The rocks from which analyses 7 and 8 were made are orthoclase-gabbro-diorite. They consist of plagio- clase with some orthoclase and a little quartz, much biotite, augite, hyper- sthene, and magnetite, and a little hornblende, but no olivine. When compared with the corresponding granular rocks at Electric Peak, they are found to differ from them in having less hornblende and more augite and hypersthene, with less quartz and considerable orthoclase. The next three analyses in the table (9, 10, 11) are .shghtly more siliceous, and are all from intrusive bodies. They are similar to the pre- vious analyses, but the ninth shows more alumina and less magnesia. This rock is very coarse grained and feldspathic, and is a diorite facies of the gabbro. The tenth is the fine-grained monzonite with the poikilitic ortho- clase and little biotite, besides much augite, hypersthene, and magnetite, and 264 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. very little, if any, quartz. The eleventh is a pyroxene-diorite-porphyry approaching monzonite-porphyry, which is very fine grained and is com- posed of plagioclase, augite, h}-persthene, magnetite, and some biotite and a little quartz, Avith no olivine, but paramorphs after olivine, now consisting of augite, l^iotite, and magnetite. It also contains microscopic feldspars, which are in part orthoclase. The twelfth analysis is still higher in silica, with somewhat lower alumina, lower lime, and about the same alkalies. The rock is a dike of hornblende-mica-andesite-porphyry with phenocrysts of andesine-labra- dorite, hornblende, and biotite, besides a small amount of augite and hypersthene. The groundmass is microcrystalline, and consists of feldspar and the ferromagnesian minerals just named, with considerable magnetite. There is a little chlorite or ser[)entine. It is interesting to compare this rock with that of the Indian Creek laccolith. The next three analyses (13, 14, 15) are of diorites that form part of the core of the volcano. They have nearly the same percentage of silica, but that with lowest silica has highest alumina and lime and low- est magnesia and potash. This rock also differs from the others miner- alogically. It is a very fine-grained rock without phenocrysts. It consists of labradorite-andesine and a small amount of orthoclase and quartz, besides a moderate amount of augite, hyjjersthene, and magnetite, and very little biotite. The second of the three, with G3.97 per cent of silica, is of a coarser-grained quartz-mica-diorite, composed of andesine with a nearly equal amount of orthoclase and quartz, besides considerable biotite and hornblende, some magnetite, and a little pyroxene. The third of these three analyses is of a quartz-mica-diorite-porphyry, with abundant quartz. The phenocrysts are biotite, andesine, and quartz, and occasionally ortho- clase. It corresponds chemically to the diorite last described, and is almost exactly the same mineralogically and structurally as one of the quartz- mica-diorite-porphyries (331) of Electric Peak, and chemically it resembles another of those rocks (329). The sixteenth analysis is of a fine-grained granite which forms a 10-inch vein in the diorite. It consists of quartz, orthoclase, and oligo- clase, with biotite and magnetite, besides a very little hornblende and some chlorite. CHYSTALLIZATION. 265 From till' t'orcji'dinji- it is evident that magmas which may crystallize into extrusive mcks whose essential minerals are plagioclase, augite, and olivine may crystallize into coarsely granular rocks with plagioclase, augite, Inpersthene, and biotite, with a small amount of orthoclase and quartz, with or without hornblende; and that olivine may be present in some cases, when the other magnesian nu'nerals will be less abundant. Hornblende, which is so important a constituent of the diorite of Electric Peak, jdays a very subordinate role in the granular rocks of Hurri- cane Mesa. Biotite becomes more pronounced as the rocks become more granuhu'. Hypersthene also develops under the same conditions. And orthoclase and quartz make their apjjearance in the granular equivalents of many basalts. Thus we find minerals that are chai'acteristic of more and more siliceous members of the series of extrusive rocks developed in basic magmas under conditions which render the magmas more highly crystalline and more or less granuhir. These minerals, then, are in part functions of the chemical composition of igneous magmas, while in part they are functions of the phase of crystal- lization of chemically identical or similar magmas. This is another demon- stration of the law that "the molecules in a chemically homogeneous fluid magma combine in various ways and form quite different associations of silicate minerals, producing mineralogically different rocks." CRYSTALLIZATION. It may be well to call attention to some of the conditions under which the molten magmas within the dikes and the core of the Crandall volcano must have solidified. Referring to the profile sections of the district and the probable outline of the ancient volcano (PI. XXXII), it is evident that the magmas which cooled within that portion of the core which is now exposed, and those in the dikes within a radius of 2 miles, must have occu- pied positions at nearly the same distance beneath the surface of the volcano. And if the former may be considered to have solidified 10,000 feet below this surface, then the latter must have solidified 10,000 feet below the surface. The one is as deep seated as the other, and yet their degrees of crystallization range from glassy to coarsely granular. The influence of jjressure alone on the crystallization of these rocks is not recognizable in the size of the grain or in the phase of crystallization. 266 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, The changes of crystallization may be traced horizontally in the imme- diate vicinity of the core, increasing from the outlying bodies toward the core, the change being rapid near the core and accompanied by induration and metamorphism of the surrounding rocks. It is in great measure inde- pendent of the size of the body, since nari'ow dikes within the core are coarsely crystalline, while much broader ones in the surrounding country are very fine grained. It was unquestionably the diiferences in the temperature of the core rocks and of the outlying- breccias which determined the degree of crystal- lization. The core was undoubtedly much more highly heated than the surrounding rocks, and the bodies of magma that solidified within it cooled much more slowly than those injected into the outlying parts of the vol- cano, or even within a mile of the central conduit. From this it follows that the application of the terms "deep-seated" and " abyssal " to coarsely crystalline rocks is misleading, since it is not distinctive and applies equally well to rocks of totally different crystalline characters. The depth at which a magma has solidified appears to be of little moment in comparison with the temperature of the rocks surrounding it. DEVELOPMENT OF PHENOCRYSTS. A consideration of the various mineralogical phases of rocks which have the same chemical composition, as they occur in this district, leads to important conclusions regarding the crystallization of phenocrysts. The great majority of the basaltic dikes carry porphyritical crystals of olivine, augite, and plagioclase in a microcrystalline groundmass of plagioclase, augite, and magnetite. In other varieties the phenocrysts are almost wholly olivine and augite. Within the core there are rocks with pheno- crysts of augite and plagioclase, sometimes with olivine, sometimes with paramorphs after olivine. The outlines of these crystals show that their crystallization continued uninterruptedly into the period of crystallization of the groundmass. These rocks are more generally the fine-grained forms. The greater part of the gabbro does not carry olivine, or at least oidy in occasional crystals, while the augites possess characters different from those in the basalt; besides which, hypersthene and biotite have developed in crystals as large as those of augite. It is also observed that the apatite and magnetite ai-e differently developed, being in larger and fewer individuals in the coarse-grained rocks. DEVELOPMENT OF PHEXOCRYSTIS. 2H7 From this it is evident that inrt«i:inas of similar cliomical comjiositinii, which were erupted at diti'ereut times, reached positions of Hke elevation within the volcano in different stages of crystallization. 8ome can-ied large crystals of plagioclase, augite, and olivine, some only aiigite and olivine, and others had no crystals developed in them. For, as shown in the chapter on Electric Peak (Chapter III), the molten magmas must have been completely fluid when they reached those places in the conduit where the character of crystallization referable to the surrounding conditions affected all of the constituent minerals, including the apatite and zircon. From the fact that the magma which was forced into the outlying dikes nuist have been the advanced portion of that which stopped in the conduit in any particular eruption, and since the dike rocks are more usually porphyritic, and the core or stock rocks show by their micro- structure and mineral development that they Avere generally completely fluid when they came to rest in the conduit, it may be inferred that the phenocrysts of the dike rocks were formed in the advanced portion of the magma of a particular eruption, and that the rear part of the magma was in most cases free from them. The magma having been assumed to be chemically homogeneous, and the influence of pressure not being recognized in the crystallization of these rocks, the most variable condition which remains is the temperature of the rocks through which the magma flowed, and the consequent difference in the rate of cooling of the advanced portion of the magma and of the rear portion. The former would cool more rapidly. While the magma advances through hot rocks it may cool gradually, but when it enters less highly heated rocks the cooling will be more rapid. There are many reasons for concluding that the phenocrysts of porphy- ritic rocks are the result of crystallization which has taken place very shortly before the final solidification or crystallization of the whole rock mass, and that they are comparatively rapid growths, and are not minerals that have existed within the molten magma for any considerable length of time prior to its solidification. As indicating their rapid growth, we may cite the abundant inclusions of mother liquor with gas cavities, which are of common occurrence in phenocrysts in extrusive rocks; and that they could not have existed for any great length of time within the molten magma is proved by the 268 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. uniform distribution instead of the segregation of the heavier minerals in feldspathie magmas, such as j^henoerysts of augite and magnetite in rhyohte. Tlie specific gravity of the former, about 3.3 and 6, is so much greater than that of even the sohdified magma in the form of obsidian, 2.3, that it is difficuh to imagine how fairly large crystals of these minerals could have remained suspended for any length of time in this matrix when it was in a fluid state. Cross ' has called attention to certain large crystals of orthoclase in dacite-porphyries ("quartz-porphyrites ") and in granular diorites in Colo- rado, which appear to have crystallized after the magmas of tliese rocks had been erupted and had come to rest. And Pirsson has presented, in a paper read before the eleventh annual meeting of the Greological Society of America, further evidence of the relatively late growth of phenocrysts in many por^jhyritic rocks. ' Cross, W., The laccolitic mountain grouiisoi Colorado, Utah, ami Arizona : Fourteenth Ann. Kept. U. S. Gcol. Survey, 1895, p. 229. CHAPTER VIII. THE IGNEOUS KOCKS OF THE AH8AR0KA RANGE AND TWO OCEAN PLATEAU AND OF OUTLYING PORTIONS OF THE YELLOWSTONE NATIONAL PARK. By JosETH Paxson Iddings. INTRODUCTION. The volcanic lavas that were erupted from the chain of ancient vol- canoes situated along the eastern border of the Yellowstone Park, and from minor vents lying outside of this range, were to a very great extent tuffs and fragrnental material. They were thrown over large areas of country, and often traveled long distances, so that after erosion had reduced the size of these vast accumulations of tuff- breccia, not only wei'e the original forms of the bodies destroyed, but deposits that may have been at one time connected have become separate. Thus, it is not always possible to decide whether isolated areas of volcanic breccia belong to neighboring larger bodies or are the result of local eruptions. In the present chapter no attempt will be made to describe the mode of formation or the history of the lavas of these portions of the Park, or the topographic features of the Absaroka Mountains. Descriptions of these will be found in chapters by Mr. Arnold Hague in Part I. I'he petrographic treatment of the rocks in this chapter will be confined to an account of their field occurrence and distribution and to a systematic description of their mineralogical characteristics and composition. The account of their occurrence and distribution must of necessity proceed along geographical lines, which may be followed either upon the map of the Yellowstone Park accompanying this monograjjh or on the atlas sheets of folio 30 of the Geologic Atlas of the United States, issued by the Geo- logical Survey. For convenience, we shall start at the northern boundary 269 270 GEOLOGY OF THE YELLOWSTOJS^E ^^ATIOJSTAL PAEK. of the Park, and mentiou the lavas forming the mountains east of the Yellowstone River, from the northern boundary southward. Those in the vicinity of Soda Butte Creek and east of Lamar River have been described in connection with the dissected volcano of Crandall Basin, but their men- tion again here will serve to make clear the connection of that volcano with others that combined to form the Absaroka Range. In proceeding from the north southward, the rocks encountered will follow one another more nearly according to the order of their eruption, the youngest being found farthest south. EARXrY ACID BRECCIA. The volcanic ejectamenta of the Absaroka Range rest upon crystalline schists and sedimentary rocks in the vicinity of the northern border of the Yellowstone Park. The contact is exposed along the valley of Clark Fork, Soda Butte Creek, Slough Creek, and lower Lamar and Yellowstone rivers. In all of these localities there are exposures of light-colored andesitic breccia, often variegated in color. These represent masses of various dimensions, sometimes very large. They rest immediately upon the schists and sedimentary rocks, and are overlain by dark-colored breccia. In some places the two grade into each other gradually; in others there is a well- defined plane of contact, and evidences of a period of erosion, between the deposition of the two breccias. The gradation between the two indicates continuous deposition, or that both belong to a prolonged series of erup- tions, during which the composition of the lavas changed. A precisely similar relation between lower acid and upper basic breccias obtains at Sepulchre Mountain, where the volcanic activity was synchronous with that of the volcanoes of the Absaroka Range. Exposures of the early acid breccia are few, and their areas are com- paratively small, in the region about to be described In the vicinity of Junc- tion Butte, immediately over the gneiss there is tuff-breccia of light-colored acid andesite and trachytic rhyolite, quite the same as those west of Yellow- stone River in the neighborhood of Crescent Hill, and undoubtedly part of the same formation. These breccia deposits have been more or less worked over by water and rearranged, and include many fragments of gneiss and schist. Similar lavas and Ijreccia with buff-colored tuff (1025, 1026, 1032) and some massive hornblende-andesite (1024) form the top of the north- western end of Specimen Ridge. The trachj'te is brecciated with lumps of EARLY ACID lUtKOOlA, ABSAKOKA KANGE. 2'('l turt' and iilteivd pcrlite liavinfr distinct, perlitic stnictnre (1027, 102«, 1031, 10i{2). Trarlivtt' also tornis the base ot" Junction Uutte, and rests upon the ••neiss directh' noith. It also forms the banks of" the river at the mouth of Slou"h Creek. The acid andesitic breccia extends several miles farther up the Lamar Kivcr and is o\erlain by a lava sheet of j)orphyritic basalt (112!l). The ])reccia is dense and dark colored and might be mistaken for l)asic breccia, but contains nuich biotite and even minute phenocrvsts of (juartz. The acid breccia is cut by a 3-foot dike of pyroxene- andesite, which is dark colored and has small phenocrysts of pyroxene and feldspar (1038), The relative age of these rocks is thus plainly shown in this locality. Mica-bearing andesitic breccia occurs at the northern base of Speci- men Ridge, about a mile west of Crystal Creek. It is green, com])act, and carries dark-colored frag-ments. It may be a mixture with more basic andesites. The onh- other exposures of the earliest acid .breccia in this viciuit)' are in Cache Creek and near Cook City. These have been described in connection with the Crandall volcano. The acid breccias in all of these localities are the same. But in some cases thei'e is more or less of an admixture of basic material. Of course there are localities where the basic breccia rests directl}' upon the nonvolcanic rocks. Either the first acid breccia was not so extensive as the basic breccia or it was com- pletely removed by erosion in some places. The microscropical study of specimens collected from bodies of the earliest acid breccia shows it to var}* in mineral composition, the varieties falling under three classes : Hornblende-mica-andesite, hornblende-andesite, and hornblende-pyroxene-andesite. The fragments constituting any large mass often differ considerably among themselves iu habit, color, and min- eral composition. Sometimes their characters are nearly constant for large bodies of breccia. Massive bodies occur either as lava streams or as intru- sive masses. In most places mica-bearing varieties abound. They are seldom absent. But the relative proportions of the different varieties is not constant enough to permit a close estimate to be made of the average com- position of the whole. The following analyses represent the chemical composition of the three varieties, one of which has been already given in connection with the description of the Electric volcano. 272 GEOLOGY OF THE YELLOWSTONE I^'ATIONAL PARK. Analyses of rocks occur rim/ in early acid breccia, Absaroka Range. Constituent. 1 2 ' 3 SiOi 61.56 ; .87 14.73 4.47 1.23 .34 3.57 4.87 64.61 Noue. 18.62 2.78 .95 Trace. .85 4.20 67.95 .45 14.98 2.33 .95 .09 1.42 3.98 .23 4.39 2.86 TiO A1>0,.-- - YeiO:, FeO MnO MgO CaO BaO Na.O .5.10 2.24 4 37 2.36 .01 .30 KO LiO PO, .04 .07 .11 .37 .61 SO Loss lit 105° H,0 1.42 .93 100.44 : 1 99. 88 100. 79 The first is a massive rock iu the early acid breccia near the head of Tower Creek. The second is from the breccia of Crescent Hill, and is above the average in percentage of silica, jvidging from the mineral com- position of the breccia as a whole. The third is from early acid breccia of Sepulchre Mountain, and is considerably above the average for silica. It is probable that the average percentage of silica for the whole of these earlv acid breccias is 62 or 63. These rocks are usually lig-ht gray, with greenish, reddish, and purplish tones, sometimes having darker colors. The appearance of the breccia is g-enerally variegated. It may be loosely aggregated, but is oftener com^iact and indurated. The habit of the andesite fragments varies from those with aljundant small phenocrysts of feldspar, biotite, hornblende, and pyroxene to those with fewer and larger phenocrysts of the same minerals, which seldom exceed 5 mm. The groundmass is glassy in some cases, usuall}' colorless glass filled with rectangular and prismatic crystals of feldspar and fewer microscopic crystals of the other constituent minerals, including pyroxene in many cases. C)r the groundmass may be microlitic with little or no glass, or holocrystal- EARLY AUID BRECCIA, ABSAROKA RANGE. 273 line ofi'i^'liiij? into niicropoikilitic structures, wliicli indicate that the rock frag- ments are broken portions of voU-anic cones where the hivas had crystal- lized us dikes and other intrusive bodies. The shape of the fragments, usuallv angular, is such as to show that most of the breccia was formed by the explosion of ah-eady solidified lavas, which had consolidated near the centers of volcanic action. Few, if any, exhil)it the slaggy surface of bombs. The phenocrvsts are sharply idiomorphic, and zonal structure is well developed in the felds[)ars, wliich often contain numerous glass inclusions. The feldsjiars are almost wholly polysynthetic twins, in the lime-soda feldspar series, their optical properties indicating oligoclase and oligoclase- andesine. Sanidine is seldom present; in fjict, is almost entirely absent. It is found in some associated tufts, but may have been derived from the trachytic lava occun-ing in the vicinity of Junction Valley. The feldspars are sometimes quite free froni inclusions; in other cases they contain minute crystals of the other constituent minerals, as well as portions- of the gToundmass. Biotite forms six-sided plates, often rather thick. Its color is brown to red, with marked absorption parallel to the plane of cleavage, and some- times with strong pleochroism between orang-e, red, and light yellow. Grreenish yellows also occur. Frequently the hornblende exhibits the same colors as the biotite in the same rock, both being red, or both brown or greenish brown. Apparently tlie same cause affected the color of both minerals at the same lime. Often the biotite is brown when the hornblende is greenish brown, or even green. Biotite resists decomposition longer than hornblende in many cases. It is often free from inclusions, but fre- quently contains magnetite, apatite, or zircon, and less often the other mineral constituents. In some cases it has a border of magnetite grains, or may be more or less completely changed to a pseudomorph of magnetite with or without pyroxene. This is usually accompanied by like changes in the hornblende. Hornblende has its customary stoiit prismatic forms, usually with colors like those of biotite, but green tones occur more frequently than in biotite. The pleochroism is that ordinarily observed. Often free from inclusions, it sometimes abounds in them, glass and magnetite being the common kinds. Paramorphism to magnetite and augite occurs, as with biotite. Intergrowths with pyroxene are occasionally seen. Pyroxenes are more numerous in -18 274 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. those rocks in which biotite is scarce, but both also occur together, accom- panying' hornblende. The pyroxenes are nionoclinic and orthorhombic species. Malacolite or augite is pale green in thin section, with no ple- ochroism. Hypersthene is more or less pleochroic with pale colors in thin section; green parallel to the prismatic axis, and reddish perpendicular to it. The optical characters are the same as those of these minerals in the pyroxene-andesites, and they will be more particularly described under that heading. Quartz phenocrysts are occasionally seen in the more siliceous rocks approaching dacite in composition. Microscopic quartz is abundant in the groundmass of the more crystalline varieties. Magnetite is always present in microscopic crj'stals, and a^jjjears to be the form of iron oxide common to this group of andesites. Titanium oxide is present in only small amounts. It is to be remarked in this connection that titaniferous iron oxide occurs in the rhyolites of this region, where it shows itself in the cb.aracter of the alteration product, which appears to be leucoxene. Apatite, in short stout crystals, is usually colorless, but is sometimes gray, yellowish, or red. The latter colors occur when the bio- tites and hornblendes are more or less reddened. Zircon is always present in small amounts and in minute crystals. The subdivision of rocks into hornblende-mica-andesites, hornblende- andesites, and hornblende-pyroxene-andesites is based on the relative pro- portions of the ferromagnesian minerals. All three — biotite, hornblende, pyroxene — may be present together, those in very small amounts being left out of the name of the rock. In general, the first group is the most siliceous, the second next, and the third least of the three. But the tran- sition through the mineralogical series is not strictly coordinate with the transition in the chemical series, so far as the silica is concerned. More- over, we know that the mineral composition of a rock is not rigidly con- cordant with the chemical composition. So that rocks that might be classed as hornblende-andesite and others that are hornl^lende-pyroxene-andesite may be alike chemically. As already said, some fragments of the overlying breccia are mingled in places with the acid breccia; hence the collections from these masses in some cases contain basic andesites, such as pyroxene-andesite. EARLY BASIC liRKCCIA AND FLOWS. 275 EARLY BASIC BRECCIA AND ASSOCIATED BASALTIC FLOWS. This breccia includes all of the darker-colored breccia, with some light- colored breccia, which directly overlies the early acid breccia and which consists mainly of pyroxene-andesites, with some hornblende-pyroxene- andesites and basaltic andesites and l)asalts. By correlation it corresponds to the basic breccia of Sepulchre Moun- tain and that west and south of the Gallatin Mountains. It constitutes the great accumulation of basic breccia that formed the bulk of the volcano of Crandall Basin, including the mountain masses from Index Peak, through those on both sides of Soda Butte Creek to Sloug-h Creek, south through Fossil Forest and Slirror Plateau, to the mountains surrounding the drain- age of Lamar River and the drainage of Crandall Creek. Basic breccia connected with this extends along the mountain range east of the head of the Stinkingwater River and west up to the tributary canyons, and under- lies the summits of the northern half of the Absaroka Range within the boundary of the Yellowstone Park. Basic breccia forms the mountains north of Lamar River, including Bison and Druid peaks and the high ridges on both sides of Pebble Creek and Soda Butte Creek, the bedding in all of these masses being nearly horizontal, with a slight dip toward the south. They appear to be continu- ous with the breccia south of Lamar River, and, as akeady pointed out in Chapter VII, they may be considered as the outlying base of the Crandall A'olcano. In these breccias pyroxene-andesite is the prevalent rock, horn- blendic varieties being less common, and basaltic varieties subordinate. Associated with these breccias — that is, intercalated in them at the base — are several sheets of basaltic rock, which are exposed in disconnected bodies along the bottom of the valley of Lamar River and Soda Butte Creek. They distinctly underlie the great mass of the basic breccia where they are exposed on Soda Butte Creek and near its junction with Lamar River. They also overlie some of the same kind of breccia. The charac- teristics of these basaltic rocks are sufficiently pronounced to distinguish them from a much more recent basalt, whose eruption was posterior to the excavation of the present valley of Lamar River, and which will be described later on. The older basaltic rock is found over the acid breccia and trachytic breccia in the vicinity of Junction Butte and about the mouth 276 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. of Slough Creek. A remnant caps the breccia on the east side of Yellow- stone Canyon, opposite the hot springs above Baronett Bridge (1126). It is dark, dense, and crystalline, with a slightly resinous luster. It has large tabular phenocrysts of plagioclase, some 8 or 10 mm. long, but none of augite or olivine. Another sheet of basalt at the north base of Specimen Ridge is dark and dense, with many medium-sized phenocrysts of tabular plagio- clase, and fewer of augite (1127). A somewhat similar basalt overlies the acid breccia just east of the mouth of Crystal Creek. It is dense and full of medium and large phenocrysts of feldspar and augite. It is partly amygdaloidal with agate and quartz (1128). Over it is another sheet of dense basalt, dark and crystalline, with many large phenocrysts cf rec- tangular and tabular feldspars, and fewer and less noticeable augites (1130). A similar basaltic rock occurs farther east, at the south base of Bison Peak. It is dense, has a slightly resinous luster, and is filled with large brilliant feldspars and numerous smaller augites, and contains some amj^g- dules of zeolite (1131). Similar basalt occurs at the southwestern base of Druid Peak (1132). It is underlain by a massive sheet, which is dense and crystalline, with abundant large phenocrysts of tabular plagioclase 10 mm. long, and fewer and smaller augites (1133). Farther east, at the first gulch below the mouth of Soda Butte Creek, basalt similar to the last is exposed 200 feet above the river (1135). Three miles up Soda Butte Valley a basalt cliff exposes a sheet of dense black rock, with abundant small phenocrysts of feldspar and augite (1137). These rocks have a peculiar mineral composition that distinguishes them from ordinary basalts. They are like some of the basaltic lavas occun-ing in the upper parts of this breccia, or overlying it, which are char- acterized b}^ a varying content of orthoclase, and since they have never been described in detail their specific characters will be given in Chapter IX, which is devoted to a general description of all similar rocks occurring within the Yellowstone Park. The basic breccias belonging to the main mass of the Crandall volcano, and forming the mountains on Cache and Calfee creeks and the body of Saddle Mountain, extend across Lamar River toward the west and south and constitute the basal portion of Mirror Plateau and of the mountains between Lamar River and the head of Stinkingwater River. Overlying this breccia in Mirror Plateau are numerous sheets of basalt, EARLY BASIC BKEOOIA AND FLOWS. 277 with some intercalated layers of scoria and breccia, forming a compound sheet 700 to 1,000 feet thick. This massive sheet caps the northeastern spurs of Mirror I'lateau and forms the eastern half of its top, passing west- ward under rhyolite. The basalts of this sheet differ somewhat in outward appearance. Some are dark and dense, with small phenocrysts. Others have a semi waxy luster and belong to the orthoclase-bearing varieties already mentioned. West of the mouth of Cold Creek irregularly bedded basic breccia forms the lower thousand feet of the ridge between this creek and Willow Creek. Immediately over it is a sheet of porphyritic basalt, with pheno- crysts of felds})ar and jDyroxene. This sheet is 200 feet thick, and consti- tutes the base of the broad shoulder which sets back from the steep face of the ridge. East of the mouth of Cold Creek basic breccia fomns the lower 1,500 feet of the northern end of the flat-topped mountain east of Pyramid Peak, and rises still higher in the next peak east, which is just beyond the one hundi-ed and tenth meridian. Here, at 9,850 feet elevation, it forms the northern summit of the peak, the breccia being rough and ulibedded and dark gray in color (1472). The northern face of the peak is precipitous, and consists of rudely bedded breccia can-3'ing masses 3 feet in diameter. The rock bears abundant phenocrysts of pyroxene and feldspar, and is mostly dark colored, in places red. On the southern slope of this ^^eak it is composed of very small fragments (1473) in a jnn-plish-red matrix. Horizontal basalt flows cap the next peak south, whose summit is about 10,025 feet in altitude, and also form the top of the ridge to the east and the smooth table-topped mountain lying southeast. The basalt on the peak is dense, with few phenocrysts of olivine (1475, 1476). It proves to be a leucite-bearing shoshonite, described in Chapter IX. Other flows of basalt in this neighborhood are more porphyritic. The precipitous exposures on the ridge east, and on the south face of the twin peaks Castor and Pollux, show the lower .parts of these mountain masses to be made of similar dark, rough, and rudely bedded or unbedded breccia. But the upper thousand feet, above the 10,000-foot line, consists of nearly horizontal sheets of basalt of various thicknesses. The slope of the top of the table mountain south is at a slight inclination westward. The basalt sheets extend westward across the saddle at the southeastern 278 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. end of the flat-topped mountain east of Pyramid Peak, and form the upper 600 feet of this mountain, the bottom of the sheets lying' at about 9,000 feet altitude, and resting on basaltic breccia. The character of the different sheets varies somewhat, a highly vesicular and strongly porphyritic basalt (1477) being found at the northern end. Glaciation has left its marks upon the surface of these table-lands, having planed out lake basins and deposited rounded drift. The extension of the basalt sheets westward is clearly indicated by the topography of Pyramid Peak. From the saddle northward there is a flat bench or series of benches along the eastern base of the pyramidal peak, which Ijroaden out into a flat-topped spur between the branches of Cold Creek. The basalt passes beneath the upper thousand feet of this mountain and descends steeply into the valley of Cold Creek, thence across a broad spur into Mist Creek, north of which it forms the basalt ledges already noticed, which are con- tinuous with those of Mirror Plateau. The same or similar basic breccia, topped by sheets of massive basalt, continues southward along the base of the mountain forming the west wall of Stinkingwater Canyon, and extends far up the valleys draining the region lying east of the watershed of the Yellowstone Lake. As in the vicinity of Lamar River, these breccias and lava flows I'epresent the ancient slopes of basaltic volcanoes lying east of the one hundi'ed and tenth meridian. Along Jones Creek, Crow Creek, and Middle Creek basaltic breccia forms the lower portion of the eastern end of the mountain ridges. It is overlain by successive sheets of porphyritic basalt, which, on the northern side of Middle Creek, attain a total thickness of between 900 and 1,000 feet. In each of these three valleys the basalt ledges have given rise to high-shouldered spurs and benches on either side of the valleys, in the same manner as on Cold Creek. The surface of the basalt flows descends gradually to the westward, and disappears beneath more recent breccia in the heads of the valleys. The character of the basalt is similar to that near Lamar River. Some of the flows are full of large phenocrysts of feldspar and pyroxene (1530); others exhibit only large olivines (1527). This early basic breccia, with its associated basaltic lavas of peculiar composition, continues beyond the divide at the head of Middle Creek, through Sylvan Pass, and forms the mountains and ridge as far as the shore of Yellowstone Lake at Signal Point. It also occurs in isolated patches at EARLY BASIC BRECCIA AND FLOWS. 279 the head of the southwestern brancli of ^MicUHe Creek, and on the other side of the divi(U' at the head of Hocky Creek, beneath more recent Hght- coh>red acid brt^ccia. On the southern side of Sylvan Pass breccia of pyroxene-andesite is highly indui'ated by the many dikes that traverse it, and the pyroxenes are more or less iiralitized. At the forks of Middle Creek, east of this, it is full of larjji'e ])hent)crysts of pyroxene and resembles much of the basalt of the Crandall Basin, and at Si<>nal Point and near Park Point, on. Yellow- stone Lake, there are basalts and breccia of this type (1616-1619). Signal Ridge and the mass of Grizzly Peak are composed of pyroxenic breccia without prominent phenocrysts, with some olivine and little or no horn- blende, while hornblende ajipears in the breccia at the summit of Grizzly Peak (1521-1625). An isolated exposure of basaltic rocks belonging to this series occurs at the head of the southeastern branch of Beaverdam Creek and just north of Coulter Creek. At this place there are two horizontal sheets of porphyritic basalt, one upon the other, and over them is a light-colored tuff of trachytic rock, with many inclosed fragments of basalt and andesite. This tuff cor- responds to the trachytic tuff in the neighborhood of Junction Butte. Almost precisely similar basaltic lavas and trachytic tuff occur at Two Ocean Pass, beneath the basic andesitic breccia which forms Two Ocean Plateau, and though the exact period of eruption of these basaltic lavas, as compared with the basalts of the Crandall volcano, is a matter of uncertainty, still on purely petrographical grounds they may be described in this con- nection. On the northern side of Two Ocean Pass there is a ledge of basaltic rocks conaposed of five sheets resting directly one on another. The basalt of the different sheets varies somewhat and belongs to the group of sho- shonites. That of the top one is a dark, dense rock, with rather small phenocrysts of feldspar, augite, and decomposed olivine (1715). The top surface is red, the middle of the flow dense, and the bottom somewhat vesicular. The top has probably been eroded. The sheet below is similar, with numerous large feldspars and altered olivines (1716). ■ It is vesicular in the upper portion, dense in the middle, and slightly vesicular at the bot- tom, and is 25 feet thick. Beneath this is a layer of scoria 2 or 3 feet thick, having the character of the imderlying flow, which is full of large feldspars, 280 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. is dense in the middle, but vesicular for 2 or 3 feet at the bottom (1717). It is about 20 feet thick and is filled with zeolites (1722) and calcite, which line cavities and cracks. This sheet rests directly on the slaggy, scoriaceous top of the next lower one, which is a basalt with only a few phenocrysts of pyroxene (1718). It is distinctly vesicular for some depth (1719). The lowest sheet is a dark, dense basalt with numerous phenocrysts of augite and olivine (1720). The top and bottom of the sheet are vesicular (1721). This basalt extends across the valley south. It rests on assorted basic breccia, and may be traced west along the northern side of the valley for 2 miles (1724), where it is similar to the upper two sheets at Two Ocean Pass. The more crystalline forms of these basalts have a slightly resinous luster. The petrographical character of the rocks constituting the early basic breccia is variable within limits, and is slightly different in the two princi- pal localities mentioned, Sepulchre Mountain and Crandall volcano. In all cases it is pyroxeue-andesite in large part, grading into hornblende- pyroxene-andesite on the one hand and into olivine-bearing andesite and basalt on the other. At Sepulchre Mountain the hornblendic end of the series is more pronounced and the basaltic end is subordinate. But it is to be remembered that the size of the mass of this mountain is insignificant when compared with that of the groups of mountains embraced in the Crandall volcano. The breccias more directly connected with the Crandall volcano are largely pyroxene-audesites, only a very small jJi'opoi'tion of which carry hornblende. Basaltic forms are very abundant, and true basalts preponderate in the upper parts of the volcano. The bulk of this breccia lies within the district already described as the dissected volcano of Crandall Basin, and its petrographical characters have been given in Chapter VII. The basaltic lava flows or streams connected with this breccia, as already pointed out, occur partly near its base, as do the flows ex2)osed in the lower Lamar River Valley and in the valley of Soda Butte Creek. The greater part constitutes the thick accumulation of lava sheets forming Mirror Plateau and the summits of the mountains immediately south of Lamar River. The petrographical character of these rocks is somewhat variable. A large number of sheets consist of normal andesitic basalt — that is, basalts with abundant phenocrysts of lime-soda feldspar (labradorite-bytownite), ACID BRECCIA OF PYRAMID PEAK. 281 aufjite, ami olivine, and occasionally hyperstliene, in different proportions in different cases. In some rocks the phenocrysts are large; in others, small. Augite is usually tlie most prominent mineral. The groundmass is glassy and microlitic, or holocrystalline, with lime-soda feldspar, augite, and mag- netite, and having the various modiiications of microstructure characteristic of basic andesitic lavas. Olivine, which is abundant, is in some cases partly decomposed to green serpentine, in others to orange or red serpentine, which apjK'ars to pass into the mica-like mineral having similar colors and indices of refraction, but marked pleochroism, with strong absorption for rays vibrating parallel to the plane of perfect cleavage. The perfect cleavage appears to be parallel to some plane in the prismatic zone of olivine. Other bodies of these rocks have an exceptional composition, and for this reason will be described in detail in Chapter IX, together with other similar rocks in the region. XiATE ACID BRECCIA. Overlying the massive basalts that top the early basic breccia, and in marked contrast to their dark-gray or black color, are breccias and tuffs of light-colored and brightly variegated andesites. This superposition is clearly shown in Pyramid Peak and on the flat-topped mountain east of it. West of the ponds on the latter mountain there are scattered exposures of compact and also of friable beds of light-gray tuff, composed of small frag- ments of horubleude-mica-andesite and hornblende-andesite, with larger rounded and subaugular pieces of the same kinds of rock (1481, 1482). Just west of the saddle east of Pj'-ramid Peak the basalt is exposed with overlying beds composed of fine grains of hornblende-mica-andesite, acting as a cement for fragments and rounded masses of vesicular basalt, similar to the basalt of the neighborhood. Above this the pyramidal mountain is formed of light-colored andesitic breccia and tuff to its summit. The whole mass is exposed in bold escarpment, and consists of nearly hori- zontal beds of tuff and breccia, with layers of large fragments that are subangular, rounded, and also angular. There is great variety of color and habit in the andesite. The greater part is hornblende-andesite, some is hornblende-mica-andesite, and some pyroxene-andesite ; portions of it are dense and compact, other portions porous. The beds are brown and gray, some being very thick without distinct bedding. At the southern end of 282 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK, the escarpment there is much gray ash with leaf impressions (1478, 1479, 1480). Similar liarht-colored breccia extends south and west and forms the upper part of the mountain ridge through Cathedral Peak, lying between Cold Creek and Jones Creek. It constitutes the main mass of Mount Chittenden and the low mountains north to Raven Creek, and beyond to Pelican Cone and the ridge west (1160, 1161). In these low mountains the character of the andesites constituting the breccia varies considerably, and acid and basic andesites are often intimately mingled, many fragments being hornblendic, while others are wholly pyroxenic. However, it is evident in numerous places that the more siliceous and hornblendic andesites predominate in the lower parts of the mass, and are overlain by distinctly later accumulations of basic andesite. Thus, at the falls on Raven Creek, at about the 8,200-foot contour of the map, and within a short distance of the limits of the older basalt, hornblende- andesitic breccia is exposed in indurated beds which cany rounded bowlders of the same rock. It is also found iimnediately south of this point on the summit of the ridge, where it is capped by dai'k-colored basic breccia, which is well bedded in places. On the southern side of the meadow at the head of Mist Creek and near the limits of the older basalt, compact breccia of hornblende-andesite is exposed in such a manner as evidently to be over the basalt, although an immediate contact was not discovered. Similar breccia, not so indurated, however, forms the ridge south of this locality. Many of the fragments are hght colored, with phenocrysts of feldspar and hornblende; others are darker, have less noticeable phenocrysts, and are more pyroxenic (1483). At the knob about the middle of this ridge the hornblendic breccia is capped by a remnant of dark-red basic breccia, the line of contact between the two being plainly visible (1484). Similar relations exist between horn- blendic breccia and basic breccia on the ridge across the head of Mist and Cold creeks (1485, 1486). The various altitudes at which the overlying basic breccia is found indicate a very irregular surface for the previously accumulated hornblendic breccia. Tiie breccia west of Raven Creek forms the mass of Porcupine Cone, which is hornblende-pyroxene-andesite at its summit (1159), mostly light colored. West of the mud springs on Pelican Creek similar andesite occurs, ACID BKECOIA OF MOUNT CHITTENDEN. 283 that on the top of the ridge bein}^- liornblenfle-mica-andcsite (1160, llGl). Hestin<;' upon the ' water action. Laj'crs of tine sand and gravel and large masses alternate with one another, but the bedding is decidedly irregular. The layers are not of uniform thickness, and ai:e in places cross bedded. This condi- tion continues for about 1,000 feet above the valley, the upper 1,000 feet consisting of true breccia without waterlaid layers. Here, as elsewhere in the breccia, there are evidences of the former existence of localized bodies of water. The matrix is light colored, with angular fragments of all sizes up to those 6 feet in diameter. The andesites vary in' character; some are dark, others light; some dense, others vesicular. They carry plieno- crysts of feldspar and pjroxene, with occasional hornblende or olivine. The whole mass has a distinct but irregular bedding, clearly seen at a distance. The surfaces of the layers are rough and irregular. They are generally denser at the bottom of each, so that the top of each weathers more easily and causes the line of bedding to become pronounced in exposures. Where layers ditfer in color and can be traced for any distance, they are observed to thin out laterally, and are not persistent for long distances. Horizontally bedded breccias form the plateau ridges about Jay Creek and those west of the Yellowstone River, and also the mountains at the head of Buffalo Fork of the Snake River, which are the southern extension of this region. Here they have a slight dip to the northeast. They also form the body of Two Ocean Plateau, and are ex^iosed in the lateral canyons cut into it by the tributaries of the Yellowstone. From Atlantic Creek to north of Lynx Creek the petrographical character of the rocks is the same, and there are places where the material has been assorted and rearranged by water action. But the great bulk of the material is purely subaerial ejectamenta. At the head of Lynx Creek, on the continental divide, are remnants of a surficial flow of basalt which extends down the 300 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. present vallej' for a short distance, and is therefore hiter than the period in which the valley was eroded. The basalt is light gray and somewhat vesicular, with small phenocrysts of olivine (1734, 1735). A similar basalt occm's on Chipmunk Creek (1736). A small hill on the divide between Fox Creek and Mink Creek is formed of a massive flow of pyroxene-andesite, which is jointed into great slabs and is thinly fissile in places. It resembles many occurrences of rhyolite. It is partly massive and vesicular, and is light gray, with small phenocrysts of feldspar and pyroxene (1727). It carries segregations of feldspar and pyroxene, and has cavities containing tridymite (1726). Other portions of the same lava sheet are darker and denser (1728, 1729, 1730). The breccia along the western margin of the plateau is basic, and in places there are remnants of porphyritic basalt. At the southern end of the valley of Fox Creek it is composed of fragments of basic andesite in a light-red matrix, and on the limestone hills east of the mouth of Crooked Creek it is also basic. Isolated areas of basic andesitic and basaltic breccia occur overlying very irregular surfaces of sedimentary rocks on the peak south of Pinyon Peak, in the valley of Coulter Creek, in the vicinity of the northern end of the Teton Range, on Berry, Boone, and Conant creeks, and at Birch Hills. The last of these occurrences are described in connection with the general geology of the northern end of the Teton Range (Chapter IV). Those in the region of Coulter and Wolverine creeks and Pinyon Peak are described by Mr. Arnold Hague in Chapter V, devoted to the descrip- tive geology of Big Game Ridge and Huckleberry Mountain. Of 116 specimens from the upper basic breccia, one-half contain olivine in variable amounts, and may be classed as basalt and basaltic andesite ; the other half are free from it, and are pyroxene-andesites and hornblende- pyroxene-andesites, the last-named rocks being much fewer than the pyrox- ene-andesites. Hornblende-pyroxene-andesite. TllC fcW SJlCCimeUS of tllis kiud of audesite which were studied prove to be glassy microlitic modifications, some with dark-brown glass, one with red glass. Reddish-brown hornblende with magnetite border, or an outer zone of pyroxene, magnetite, and plagioclase, is the usual variety. In one rock brown hornblendes without any border of foreign material occur so closely associated with pyroxene as to inclose I'YKOXENE-ANDKSITES. 301 it in a variety of ways. Tlicv form a narrow zone of small prisms around a larji^c au^ite in one instance, and in another case liornljlende contains small grains of angite as inclusions. It is also intergrown with pyroxene in the manner already described in othi'r occurrences. pyroxene-andesites. — 'I'he jiyroxeiie-andcsites of the late basic breccia are quite the same as those of the late acid breccia just described. Most of them have glass}' microlitic grounchnasses, the glass being brown in the majority of cases. Some have holocrystalline groundmasses. The habit of most of the modifications is that jjroduced b}" abundant small plieuo- crysts and a microlitic groundmass. In some cases distinct phenocrysts are wanting, but there are many microscopic prismatic feldspars in the groundmass, usually aiTanged in curving parallel lines, nroducing fluidal structure. In a few rocks these rectangular microscopic feldspars are in excess of the microlitic groundmass. In the holocrystalline varieties the dark color of the groundmass gives way to gray shades. The degree of crystallization does not exceed that of holocrystalline-microlitic or finely microgranular. The phenocrysts are lime-soda feldspar, hypersthene, and augite, with small crystals of magnetite. Rarely hornblende or olivine is present in small amounts. The feldspars are labradorite-bytownite, with marked twinning and zonal structure, and generally rectangular outline in cross section. Glass inclusions are frequent. In some varieties of this rock the feldspar phe- nocrysts are anorthite. Hypersthene and augite have the same colors, forms, and microscopical characters as in the pyroxene-andesites already described. In some cases pale-yellowish augites are twinned on the ortho- pinacoid, and, being cnt so as to exhibit symmetrical extinction angles on both sides of the twinning plane, furnish an inclination of the bisectrix a equal to 42° to the trace of the twinning plane, indicating hedenbergite or augite. Zonal structure is occasionally exhibited between crossed nicols, and sometimes by variations in color. Glass inclusions are often present. The pyroxenes are mostly fresh and unaltered. An alteration of hypersthene to pale-green pleochroic amphibole is sometimes observed, the fibers of amphi- bole lying parallel to the vertical axis of the hyijersthene. A narrow opaque border and a darker-colored margin are sometimes present. Occasionally a serpentinous mass is included and suggests the former presence of olivine. 302 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The pyroxene-andesite occurring as a massive lava flow west of the head of Mink Creelc lias a habit somewhat different from that of the pyroxene-andesites already described. It has a smaller number of pheno- crysts, which are labradorite, distinctly pleochroic hypersthene, and augite, the pyroxenes being more prismatic than usual. The groundmass when very dense is globulitic and microlitic glass, which is dark colored where the microlites are very minute. Through it ai-e scattei'ed long prismatic microlites of hypersthene, augite, and feldspar. In varieties with larger microlites the color is lighter, and it is seen that pyroxene is more abundant than feldspar; magnetite also is abundant. Apatite occurs in comparatively few large crystals, Avith brownish color and distinct pleochroism. Tridy- mite is present in small aggregates. Basaltic andesite and basalt. — These rocks are like the pyroxene-andesites in habit, both megascopically and microscopically. They consist of an aphanitic groundmass witli multitudes of small phenocrysts of feldspar and pyroxene and more or less altered olivine. In some varieties the phenocrysts are almost absent, or are of microscopic proportions. The colors of the rocks are darker as a whole than those of most of the andesites. Dark grays to black and red are most common. Light grays occur. Many of the rocks are porous or finely vesicular. In thin sections the groundmasses are seen to be glassy, with abundant microlites of feldspar, pyroxene, and magnetite, the latter minerals being rather more abundant than in the j)yi'oxene-andesites, and being equal to, or sometimes more numerous than, the feldspar.s. The microlitic pyroxenes appear to be augite. The feldspars are lime-soda feldspars, apparently about andesine-labradorite, but not always of the same kind. The glass is usually brown globulitic, when in noticeable amount. Holocrystalline modifications occur; they are very fine grained and are formed by the o-rowinsT together of microlites. Groundmasses so crowded with iron oxide as to be opaque, even in very thin sections, are common. The feldspar phenocrysts are labradorite-bytownite, in some rocks being more calcic than the proportion Aug Ab,, in other cases having the optical properties of this variety of labradorite. The forms are mostly rectangular and prismatic, tabular forms being common in some rocks. The twinning is according to albite, pericline, and Carlsbad laws, usually all three combined; occasionallv only two. Zonal structure is pronounced, especially BASALTIC ANDESITE AND BASALT. 303 ill those sections exliibitino- little polysyiithetic twiiiiiing. In ii few instances there is a central core of feldspar, first recognized between crossed nicols, and this is invariably more calcic than the marginal feldspar. Glass inclu- sions are the same as in the feldspars of the ])yroxene-aiidesites. Con- temporaneous crystallization with pyroxene is occasionally observed. The pyroxene phenocrysts are augite in nearly all the rocks in which olivine is abundant. In a few cases hypersthene is also present, but in smaller amount than augite. Transitional varieties with hypersthene and olivine in reciprocally varying proportions have been mentioned in connection with the rocks in other parts of this region. The augites have the same appear- ance and characters as in the andesites. The same is true of the hyper- sthene when present. Olivine occurs in very small idiomorphic crystals, yielding rhombic and characteristic six-sided sections. It is iu most cases wholly altered either to green serpentine or to the red and orange pseudo- morphs which often result from weathering. In the few cases where olivine is still preserved it is colorless in thin section. The serpenthiization is quite normal. Both modes of alteration are frequent, but the green serpentiniza- tion is probably more common. They do not occur by the side of one another in one rock section. In only one instance was anything like a combination of the two observed. The processes appear to be due to local causes, for it is found that all the varieties, with olivine, that were collected at any one locality bear the same kind of pseudomorphs. Occasionally colorless olivine is coated with opaque iron oxide, which is red by incident light. It occurs in minute grains penetrating the crystal in rows normal to the side planes. The shape of the grain suggests that the original oxide was magnetite. In cross sections the coating appears as an opaque border of variable width. In one rock olivine is replaced by calcite. The irregular and amygdaloidal cavities in these rocks are sometimes filled with secondary minerals, of which chalcedony and hyalite or opal and several zeolites are the commonest kinds. The first two are often associated together, chalcedony coating the walls of the cavity in a spheru- litic layer, opal filling the central portion. In one of the pyroxene- andesites the chalcedony of the margin passes into fibrous or platy quartz, which fills the center of the amygdule, the two being continuous optically as well as in substance. In some sections thi-ough such amygdules the central quartz exhibits undulatory extinction, not very unlike that produced 304 GEOLOGY OF THE YELLOWSTONE NATIONAL FARK. in quartz by dynamic forces. It is, liowever, in this case the result of ao-o-resrate crvstalhzation. Such sections exhibit uniaxial interference crosses wliich are optically positive. The aggregation appears to be made up of thin hexagonal plates, parallel to the basal pinacoid. The aggrega- tion of plates into spherical masses takes place in tridymite, as is well known. Spherulitic aggregations being only modifications of spherical ones, such structures may be produced by the attempts of thin plates to form spherical clusters. The rods would then be at right angles to the vertical axis of the mineral — that is, the apparent fibers would be parallel to a, the direction of vibration of the swiftest-traveling ray. The lighter specific gravity of chalcedony, as compared with quartz, would seem to be due to inclusions, probably of hyaline silica, since minute inclusions are observed in thin section, and a variable percentage of water is found upon chemical analj^sis. Opal replaces the feldspars in a few of the rocks studied. Sometimes the amygdules consist of minute zeolites with very low double refraction and a marked pinacoidal cleavage with parallel extinc- tion. It is probably heulandite. The spaces between these crystals are filled with a colorless, low-refracting substance, apparently composed of minute spherules or plates, resembling tridymite. But the whole mass is spherulitic, with delicately fibrous rods that are optically positive. The double refraction is low. There seems to be no structural relation between the minute spherules and the spherulitic structure. One appears to be subsequent to the other. The chemical character of this substance was not discovered. Similar mineral with stronger double refraction occurs in other varieties of the rock. Other secondary minerals, probably zeolites, are present in a few cases (1682, 1675). rHKES AISTD SURFICIAIi FLOWS. VICINITY OF SYLVAN PASS. Subsequent to the accumulation of the late acid and basic breccia of the Absaroka Mountains there broke out a series of eruptions whose center of activity was in the vicinity of Sylvan Lake. In this neighborhood the breccias are traversed in all directions by dikes of rocks which have a wide range of composition and which also attained great variety of crystalline structure. DIKES NEAU SYLVAN PASS. 305 In tlu' vjilley of Sylvan Pass and on tlio slopes of the mountains on both sides the hreccius have been hig'hly indurated by tlu; intrusion of dikes close to one another, and of larger bodies of magma. This is particularly the case on the southern side of the valley. This metamorphism is limited in extent north and south, but continues a greater distance east and west. The induration of the breccia and the presence of massive rocks produce mountain slopes ver}- different in character from those of the breccias of the region. The indurated and massive rocks weather in small angular frag- ments that form long, bare talus slopes, giving to the southern flanks of Avalanche Peak and of the mountain southeast a smooth, light-colored appearance, which is quite distinctive. The southern slope of Avalanche Peak has the character just noted. It consists of indurated breccia of hornblende-andesite, traversed by intru- sive bodies of horublende-mica-andesite and of hornblende-andesite. Some of these bodies have been crushed and fractured so as to I'esemble breccia in places. They furnish evidence of dynamic movements. One body of hornblende-mica-andesite (1532), whose outline is obscured by talus, is altered considerably. The phenocrysts of mica are large, as are also some of hornblende and feldspar It is finer grained and fissile near the south- ern contact wall, and is distinctly mottled in planes parallel to this contact, and carries inclosed fragments of other rocks. The southern end of the summit of the mountain is formed of a broad dike of hornblende- andesite (1533), compact and gray, with abundant small phenocrysts of hornblende and feldspar. The trend of this dike is east and west, and that of three or four others cutting the siunmit of the peak is northwesterly. These are hornblende-andesite. Another dike on this summit, trending south and north, is hornblende-mica-andesite (1534). It is greenish g'ray and dense, Avith a multitude of small phenocrysts — white and prominent feldspai's, altered hornblendes, and fresh biotite. The northern end of the summit consists of massive rock with horn- blende and pyroxene phenocrysts. The northern mass of the peak is com- posed of chaotic breccia of hornblende-andesite not specially indurated. Six dikes cut the northwestern spur, five having a general east- west trend, and one, lower down, a north-south trend. Three dikes cut the north- eastern spur. They have a northeast trend. On the eastern spur there are MON XXXII, PT II ^20 306 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, three dikes with a soiitherly trend. One of these dikes consists of horn- blende-andesite with many phenocrysts of hornblende and feldspar. The rock is colnmnar, with horizontal prisms. In the gulch west of Avalanche Peak the breccia of hornblende- andesite is indurated, and is cut by bodies of horublende-andesite that have been much fractui-ed and cracked. Similar indurated breccia forms the ridge west, and is traversed by ten or more dikes of hoi'nblende-andesite with variable trends, mostly north and south or northeasterly. On the west end of this ridge are other dikes, whose trends were not observed. Other dikes of liornblende-andesite cut the ridge from Avalanche Peak to Mount Chittenden. They have a general north-south trend, as indicated on the map, several trending northeast and one east. Dikes may be seen cutting the southern face of Silver Tip Peak. At the head of Crow Creek several of the dikes traverse the sheet of massive hornblende-pyroxene- andesite, cutting it in different directions. These dikes extend into the head of Jones Creek, the most northerly intersecting the eastern edge of the summit of Mount Chittenden. Here this dike is 50 or 60 feet wide, is horizontally columnar, and trends a little east of north. The rock is hornblende-andesite (1498 to 1600), dense, fine grained, witli abundant small phenocrysts of hornblende, sometimes in stellate groups, and less prominent feldspar. No dikes were observed in the mountains northeast of Mount Chittenden, or in those in the vicinity of Pyramid Peak, or in Castor and Pollux peaks. In the region of Sylvan Pass, the mountain mass of Hoyt Peak consists of indurated breccia of hornblende-andesite with some pyroxene- andesite. It is traversed in various directions by dikes, some trending northeast and east, and others southeast. Those cutting the northern crest of the mountain are mostly hornblende-andesite. They are from 4 to 10 feet wide, and in one instance 20 feet. The rock of the 20-foot dike (1535) is dense, light gray, with a hackly fracture, and is crowded with small phenocrysts of minute feldspars and larger hornblendes, with a very little mica. One of the andesite dikes is very fine grained, with few phenocrysts. The dikes on the south slope are largely covered by talus. Their general trend is toward the southeast. Among them, near the bottom of the slope, are several dikes of quartz-mica-dacite, with phenocrysts of these minerals. Farther down the slope, just east of the divide, there is DIKES NEAR SYLVAN PASS. 307 an intrusion of honiblende-mica-autlesito (1545), Avhich is dense and dark "■ray, with abundant liexa'mite (1611, 1610). It also has the same microscopical characters. A surhcial flow of pyroxene-andesite occurs on the summit of the ridge north of ^liddle Creek, already mentioned in another place. TRACIIYTIC RHYOIilTE. Closely connected with the early acid breccia on Yellowstone River in the neighborhood of Crescent Hill and Junction Butte are remnants of a lava stream of light-colored lithoidal rock whose most pronounced miner- alogical feature is the presence of abundant phenocrysts of sanidine without any of quartz. It passes into breccia in places, and appears to have been contemporaneous with the earlier acid andesitic breccia of the region. Whether the scattered occurrences of this rock in the bottom of one large valley were originally connected and were parts of one large sheet, or whether they belong to several eruptions, is not definitely known. Areas of this rock occur along the south side of Yellowstone River, forming a cliff at about 6,400 feet altitude from Geode Creek around the north base of Crescent Hill to Yanceys. It occurs somewhat higher on the north side of the Yellowstone River west of Hellroaring Creek, lying between 6,600 and 7,200 feet altitude. It extends east around the north end of Junction Valley and forms the base of Junction Butte east of the river. It occurs on the north of Lamar River opposite the butte, and 500 feet above the river, and also near the mouth of Slough Creek. Patches of it are found on the end of Specimen Ridge 1,500 feet above the river. Lavas similar to this occur as intimately associated with the basic andesitic breccias north of the Yellowstone Park, on Buffalo Plateau and on the flanks of Sunset Peak. The rock is generally light colored, and varies from white and gray to yellow, buff, brown, red or pink, purplish, and green. In most places it is -21 322 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. litlioidal to earthy; also compact and deuse. lu one locality it is glassy and greenisli gray, in part perlitic, passing into dark-gray and black glass, and constituting a pitchstone (683, 684). In nearly every instance it is mottled with Avhat appear to be inclosed fragments having a different character, and which are mostlv tuif of the same rock. They are often flattened, giving the rock a distinct flow structure. The phenocrysts vary in abundance and size in different modifications of the rock. They are sanidine, plagioclase, and biotite. Sanidine is generally perfectly fresh and exhibits a brilliant cleavage surface, while the plagioclase is often decom- posed and is fresh in oidy a few cases. Biotite is subordinate in amount. In places the rock carries many fragments of andesite and of crystalline schist, and passes ujjward into breccia filled with the latter, and merges into andesitic breccia similar to that already described as underlying it This relation may be observed at the northern base of Crescent Hill and on the ridge opposite the mouth of Hellroaring Creek. It was the product of eruption of an exceptional modification of magma, rich in sanidine, which occurred early in the period of the extravasation of the hornblende-mica- andesite, Avhen crj^stalline schists formed the surface of the country through which the eruptions took place. This light-colored porphyritic lava consists of an abundant groundmass, which is in nearly all cases megascopically lithoidal and under the micro- scope is highly varied in structure. In this groundmass are numerous phenocrysts of sanidine and lime-soda feldspar, which in numerous cases is decomposed. Ferromagnesian minerals are scarce. The only ones recog- nized megascopically are small biotites. In thin sections of the rock pyroxene is seen, in some cases in almost microscopic crystals. A -very little green hornblende occurs in a few cases. The sanidine crystals are 2 mm. long and smaller, and are usually twinned according to the Carlsbad law. Their cross sections are generally rectangular, but they often have iri'egular outlines, as though fragments of former well-shaped crystals. The same is also true of plagioclase. The sanidines are very free from inclusions of foreign material; occasional inclusions of glass, apatite, and zircon occur. The pinacoidal cleavages are often well developed, but some crystals are almost free from cleavage cracks and are easily mistaken for quartz. The lime-soda feldspar is similar to sanidine in size and general form, but exhibits polysynthetic twinning according to albite, pericline, and Carlsbad laws. In TKAOUYTIC RHYOLITE. 323 a number of cases tlie synimetrical extinction angles tested by Micliel Levy's nu'tli(Kl indicate that the feldspar is labradorite as high in lime as Abo Ang. In other rock sections tlie only syniiuetrical extinction angles are Ioav, but they are few, and may possibly belong to labradorite. These feldspars also are quite free from inclusions. They are more easily decomposed than sani- dine, and in a luimber of rock sections are completely altered, while the sanidine is fresh. The usual alteration is to a microcrystalline aggregate with low double refraction, probably kaolin. Occasionally the feldspar is replaced by calcite. Biotite occurs in irregularly outlined crystals of very small size. It is brown and has a very small optic angle. Augite, when present, forms idioinorphic and also irregularly shaped crystals, apparently fragments of lai-ger crystals. Its colors and general character are the same as those of the augite in the associated andesites. The same is true of the few small fragments of green and brownish-green hornblende. Ilmenite, or titaniferous magnetite, is jweseut in comparatively large microscopic crystals and grains. Its character is indicated b}' its alteration product and its form, since it alters to a white opaque mineral crossed by lines in three directions. It is similar to the occurrence of titaniferous iron oxide in the rhyolite of the region. With it are associated colorless apatite and zircon. There are a few yellow, almost isotropic, pseudomorphs, possibly after hypersthene. The groundmass is in many cases brecciated, and is made up of patches with diiferent kinds of microstructure. It also contains fragments of other rocks, such as andesite and the crystalline schists. Large fragments of the latter are found in places, and the massive lava grades into tiiff-breccia in some localities. Only a small part of the rock is glassy and unaltered (683). Numerous thin sections show that the rock was once glassy in many places but has become more or less completely devitrified. The glassy form con- sists of glass that is globvilitic and brown in places, with streaks and lumps that are colorless, and microlitic and trichitic, with pyroxene and magnetite, quite like some rhyolitic glasses. It has eutaxitic and flow structures and is spherulitic in places. Perlitic cracking is developed to some extent. Small lumps with beautiful brown glass full of microlites, and others con- taining augite and hypersthene, and holocrystalline pieces of jjyroxeiie- andesite in this glassy lava, suggest that its eruption was subsequent to that of pyroxene-andesite, which is the case for similar trachytic lava farther 324 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. north on Bnffalo Plateau and southeast of Sunset Peak. These rocks are filso identical microscopically with this glassy modification of the trachytic lavas north of Crescent Hill. Other parts of the rock are l3recciated flows, with lumps that are devitrified perlitic glass, with raicrogranular and microcryptocrj-stalline por- tions. These retain the small phenocrysts and microlites intact. Some are composed of minute fragments of glass with very irregular shapes, welded together as in many rhyolites. They are devitrified and microcryptocrys- talline. Some of the groundmasses are colored yellow, orange, or red by clouded particles of hydrous oxide of iron. Less often the color is green, from chloritic infiltration. The grouudmass is wholly devitrified in many cases where the feldspar phenocrysts are still fresh. In a number of instances the rock is wholly altered, both kinds of feldspar having been reduced to kaolin, and the other phenocrj'sts being decomposed and the groundmass reduced to a micro- crystalline to microcryptocrystalline aggregation. One modification of the rock is somewhat andesitic, all of the feldspar phenocrysts being lime-soda feldspar (709). The chemical composition of the rock is shown by analysis 1. It is of a variety (679) which has fresh phenocrysts of sanidine in abundance and fresh labradorite and a little biotite. The groundmass is devitrified, and there is some chlorite. The loss upon ignition is high and indicates partial alteration. If anhydi-ous the silica would be 66 per cent, and the rock would be about on the dividing line between (piartz -soda- trachyte or highly siliceous soda-trachyte and rhyolite. The presence of labradorite in a rock with so little lime and so much soda is surprising, and it is evident that the orthoclases must be rich in soda. The chemical composition of the very similar rock near Sunset Peak on Bear Gidch, mapped in the Livingston folio (No. 1) of the Geologic Atlas, is shoAvn in the accompanying analysis 2. It is higher in silica and in allvalies, the potash being exceptionally high for rocks of this region. This rock is chemically trachj'tic rhyolite. Mineral- ogically all of these rocks are characterized by the absence of quartz as phenocrysts. The groundmass is highly siliceous, and quartz is present in the microcrystalline modifications. TKACUYTIG KHYOLITE. 325 Analyses of trachytic rhyolite. [Analysts: 1, J. E. Whitflcld; 2, L. G. Eakins.] Coii.stitut'nt. 1. 2. SiO- 64.65 Trace. 17.80 2.33 2.10 Trace. 69.45 .19 14.92 3.16 .23 .07 .03 1.19 .05 TiO. Al 0, Fe.Oi FeO MuO BaO CaO 1.73 .81 .17 4.18 2.83 Trace. .43 3.06 MgO •- Li,0 NaO 3.19 5.95 .06 K .0 P,0^ SO, H,0 1.69 ■ 100. 09 100. 18 Trachytic tuffs similar in composition occur in two other locahties in the Park. One is on the south fork of Beaverdam Creek, where it overHes shoshonite, and the other is at Two Ocean Pass, where it occurs in the bottom of the andesitic breccia near the basaltic lavas (shoshonite). They are all alike in being composed of a glass;,' groundmass, with phenocrysts of sanidine and lime-soda feldspar, besides biotite, magnetite, or ilmenite and many inclusions of other rocks, pyroxene-andesites for the most part (1650, 1722, and 1725). In the rock from Two Ocean Pass there are labradorite crystals and fragments and numerous broken augites, as well as pieces of andesite. In this rock it is possible that the labradorite crystals may have been derived from the andesite dust. The presence of labradorite in association with orthoclase in parts of this rock corresponds to the simi- lar association of these two feldspars in shoshonite and banakite, and indi- cates a genetic relationship, which is also indicated by the close association of these rocks in the field. CHAPTER IX. absarokite-shoshonitp:-banakite series. By Joseph Paxson Iddings. INTRODUCTIOIS^. There are certain basaltic-looking rocks associated with the older andesitic breccias in various localities within the Park, which form lava flows in most cases and dikes in others, and which more rarely constitute part of the basic breccia itself. They are usually quite subordinate in amount, judging from the extent of their exposures, but, considering the probable size of their original masses, before being exposed by erosion thev must have had very considerable volumes. As flows they are basaltic in character, being dark colored and heavy, with olivine among the pheno- crysts in most cases. They are massive and compact or vesicular. They are jjorphyritic in some cases, but not noticeably so in others, and generally exhibit a semiwaxy luster that suggests the presence of nepheline, which, lio^ever, is not present. The waxy luster is due to the alkali feldspar in the groundmass. They are often dull greenish black owing to the serpen- tinization of olivine. As dikes they are basaltic in some cases and trachytic in others, l^eing gray in vaiious shades, and having a somewhat waxy luster in the rocks of darker shades. The luster, as in the case of the flows, is due to the alkali feldspars, as there is no uepheline. They are porphyritic or not in diff"erent cases, and range from aphanitic to phanerocrystalline. As will be seen later, they represent a rather wide range of composition, both chemical and mineralogical, and though genetically related and con- nected by gradual transitions, so that they constitute a natural group, they could not be embraced by any one definition and must be divided into several classes. 326 ABSAUOKITE AND SHOSifONITE. 327 The cliiot" chnractevistics of the most basic class are the presence of abuiidant phenocrvsts of olivine and angite and the absence of any of feld- spar. The groundniass may be anything- from a dark glass to an almost phanerocrystalline light-gray mass. It is oftener aphanitic and dark greenish gray. The phenocrysts are large and pronounced in many cases, but are very small in othei's. The microscopical characteristics will be given at length. Chemically they are low in silica, from 46 to 52 per cent; low in alumina, from 'J to 12 per cent; high in magnesia, from 8 to 13 per cent; comparatively high in alkalies, with potash considerably higher than soda, except in one case. The molecular ratio of the alkalies to silica is 0.08 and 0.09. After the crystallization of abundant phenocrysts of olivine and augite the remainder of the magma, owing to the low alumina and to relatively high alkalies, was so constituted that alkali-feldspathic minerals, in the form of orthoclase or leucite, might crystallize out, which they did or not according to the conditions under which solidification took jjlace. The principal characteristic of the second class is the presence of phenocrysts of labradorite, together with those of augite and olivine, in a gi'oundmass that is usually dark greenish gi'ay, with a semiwaxy luster, but which may be glassy or phanerocrystalline, and which when distinctly crystallized contains a notable percentage of orthoclase. They range from varieties rich in olivine and augite, which, with decreasing labradorite, grade into rocks of the first class, to varieties with few olivines or augites. Chemically they contain from 50 to 56 per cent of silica. Alumina is moderate to high, from 17 to 19.7 per cent. Lime and magnesia are moderate to low, the former from 8 to 4.3 per cent, the latter from 4.4 to 2.5. The alkilies are moderately high, with potash comparatively high for rocks of this region, with like amounts of silica, from 3.4 to 4.4 per cent, the soda ranging from 3 to 3.9 per cent. The molecular ratios of the alkalies to silica is 0.10 and 0.1 1 . After the crystallization of phenocrysts of labradorite, olivine, and augite, the remainder of the magma was rich in alkali-feld- spathic material, usually that of orthoclase, which shows itself in the ground- mass according to conditions of crystallization. Rocks corresponding chemically to both of these classes occur with no megascopic phenocrysts, and in various phases of crystallization, from glassy to holocrystalline, and almost phanerocrystalline ; consequently they differ from them not only in microstructure but in the minerals that have 328 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. been developed. They occur both as lava flows and as dikes, but no special characteristics can be connected with either mode of occurrence, except that the more highly crystallized forms are found as dikes. Not all the dikes, however, are more crystalline than all the lava flows. Rocks of the third class are known mostly in the form of dikes, and in only a few localities. The rocks are highly feldspathic, with small amovmt of ferromagnesian minerals, and these chiefly biotite with sub- ordinate augite. The ])henocrysts are labradorite in a groundmass rich in orthoclase. Chemically they have 51 to 61 per cent of silica, 16.7 to 19.6 per cent of alumina, 3.5 to 6 per cent of lime, 1 to 4 per cent of magnesia, 3.8 to 4.5 per cent of soda, and 4.4 to 5.7 per cent of potash. The ratio of alkalies to silica is 0.13 and 0.14. Since much of the calcium and sodium goes into the phenocrysts of labradorite, the feldspathic groundmass is rich in potash and is largely orthoclase. The rocks stand at the end of the series, representing the variation reached when all the phenocrysts are labadorite and when biotite occurs instead of olivine and augite. The division of the series into three parts is wholly artificial and for convenience. There is gradation from one end to the other, and from the middle of the series into the normal basaltic rocks of the region, which will be pointed out later. Tlie three classes will be described under the names absarokite, shoshonite, and banakite. ABSAROKITE. All of the rocks here classed as absarokites carry abundant phenocrysts of olivine and augite, except two (1282 and 1624). These are classed with them on the ground of chemical identity. The rocks occur in the Absaroka Range, and also in other parts of the Yellowstone Park, being found upon Mirror Plateau (1151, 1152), within the region of the Crandall volcano (1282, 1277, 1306, 1307), at Signal Point, Yellowstone Lake (1617, 1618), at Two Ocean Pass (1719, 1720), on Coulter Creek (1743), about the head- waters of Conant Creek (1745, 1751), and in the Ishawooa Canyon (1698). The absarokite is found as bowlders on the west shore of Yellowstone Lake, south of Bridge Bay, probably coming from Signal Point, on the east shore. CHEMICAL COMPOSITION OF ABSAROKITE. 329 Tlio chemicfil composition of six of these rocks is shown l)y the follow- ing auulvses, the characteristic features of which have already been indicated : Analyses of absaroMtes. Constituent. 1 2 3 4 5 6 SiOj 48.28 .88 11.56 3.52 5.71 .13 48.95 .49 12.98 3.63 4.68 .13 48.36 1.18 12.42 5.25 2.48 .13 .29 9.36 8.65 1.46 3.97 .84 Trace. 51.76 .47 .12.36 4.88 4.60 .11 49.71 1.57 13.30 4.41 3.37 .17 .46 7.96 8.03 1.49 4.81 .66 Trace. 51.68 1.08 14.07 4.71 4.57 Trace. TiO. Al.On KeO, FeO MuO B-iO MgO 13.17 9.20 2.73-2.89 2. 17-2. 22 .59 11.73 7.66 2.31 3.96 .67 9.57 7.14 1.99 3.83 .56 7.72 6.65 2.45 4.16 .72 SO3 . 13 LijO Trace. 2.09 CaO Na:0 K.O PiOs Cr O CI .18 2.96 HjO 3.16 5.54 3.05 4.07 Total Less 0 for CI 100. 08 .04 100. 35 99.93 100. 32 100. 01 100. 03 100.04 1. Leiicite-absarokite, Ishawooa Canyon, Wyoming. Analyst, J. E. Whitfield. (1698.) 2. Absarokite, dike at liead of Lamar River. Analyst, L. G. Eakius. (1306.) 3. Absarokite, dike south of Clark Fork River. Analyst, L. G. Eakins. (1277.) 4. Absarokite, lava flow, head of Raven Creek. Analyst, L. G. Eakins. (1151.) 5. Absarokite, dike, divide east of Cache Creek. Analyst, L. G. Eakins. (1282.) 6. Absarokite, lava flow. Two Ocean Pass. Analyst, J. E. Whitfield. (1720.) The six analyses are arranged according to decreasing percentage of magnesia. The first two have the highest; the second two, over 9 per cent; the fifth and sixth have 7.96 and 7.72, which are not very high for a rock so low in silica. There is an increasing range in alumina and in potash. The second, third, and fourth analyses are closely alike. The first and last two are not so much alike that they might not be considered separately. The chief dijfferences are in the magnesia and alkalies, but they are related in other respects. They all exhibit considerable loss upon ignition, corre- sponding to the amount of hydration due to alteration or to the presence of zeolitic minerals. As already said, the rocks here grouped together diifer somewhat in 330 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the mineral composition of the groundmass as well as in its microstructure. The rock with the largest grain and most highly developed crystallization is that whose chemical composition is given in the first analysis (1698). It was not found in place, but was collected from a bowlder 3 or 4 miles from the junction of the streams in Ishawooa Canyon. It is nearly holocrystal- line, and was probably an intrusive rock in the form of a dike. It consists of abundant phenocrysts of olivine and augite, about 3 mm. in diameter and smaller, and of a subordinate amount of gray crystalline "groundmass. In thin section the olivine is colorless and very free from inclusions, with almost no serpentinization. The augite is pale green, with high extinction angle, reaching 42°.. It incloses some olivine and magnetite. The form of these phenocrysts is only partially idiomorphic, the outline being quite jagged in some cases, and the reentrant angles being occupied by orthoclase, as though the crystallization of the olivine and augite had continued into the period in which the felds]3ars of the groundmass were forming. There was no hiatus between the crystallization of the phenocrysts and that of the o'roundmass. The two were connected and continuous. The groundmass consists of crystals of orthoclase and leucite, which are nearly idiomorphic, although the mass is holocrystalline, except for occasional possible remnants of glass base, wliich form angular patches between the crystals. There are also small irregularly shaped crystals of augite and olivine, with magnetite and much apatite in long slender needles. The orthoclase and leucite are not uniformly mingled, but are clustered in groups. The orthoclase is in rectangular prisms, twinned according to the Carlsbad law, and about 0.4 mm. long and smaller. Very rarely they contain minute cores of lime- soda feldspar, with symmetrical extinction angles of 30°, corres]Donding to labradorite. The substance of the feldspar is very fresh and unaltered. The leucite is partly idiomoi-phic, partly allotriomorphic, and in some cases exhibits the characteristic double refraction, though most crystals are isotropic. Central aggregations of minute augite grains occur. In places a cloudy alteration has set in, resulting in a zeolitic mineral whose exact nature has not been determined. Owing to the small amount of material collected, no separations or partial analyses were attempted. The determi- nation (if the alkalies was repeated and found to accord closely with the first determination. The needles of apatite are very delicate and traverse the feldspathic ABSAHOKITE. 331 crystals of the groumlinass in all directions, but do not ])enetrate tlie jilieno- crysts of olivine and aug'ite, indicating- tliat tlie formation of the a})atite was not anionji' the earliest of the crystaHizations, but took place when the groundmass crystallized.' The development of orthoclase and leucite from a magma so low in alkalies and with so little potash is notable. The almost total absence of lime-soda feldspar is plainly due to the low percentage of alumina, which was nearly all combined Avitli the alkalies to form alkali-feldspathic min- erals. It is evident that both the orthoclase and leucite must be rich in soda. The formation of leucite was undoubtedly controlled by the low percentage of silica, which if higher would have formed a polysilicate of all the aluminum and alkahes, instead of a metasilicate and polysilicate. The earliest compovinds to crystallize — olivine and augite — consumed the magnesia and lime, with iron oxide and some alumina, and possibly some soda. It is evident that the remaining magma contained lime in sufficient amount to satisfy the phosphoric oxide, besides a little that combined with alumina and silica to form labradorite. Moreover, the alkalies and alumina were left in the proper proportions to form alkali-feldspathic minerals. In a molten condition they did not exist as molecules of these minerals, yet we see the indication of an influence that controlled the proportions of the partially dissociated elements. At the time of the crystallization of the alkali-feldspathic constituents there were small amounts of ferromagnesian silicates still liquid, which crystallized at this time. The rock most closely related to the one just described in chemical composition occurs as a dike, 4 feet wide, on the divide between Lamar River and Crandall Creek, south of Hoodoo Mountain. It is dark colored (1306, 1307) and aphanitic, with abundant large crystals of augite 5 to 10 mm. in diameter and smaller phenocrysts of olivine. On the sides of the dike a thin layer of the rock is glassy and black. In thin section the body of the dike is holocrystalline and very line grained. The groundmass consists of indistinctly outlined lath-shaped feld- spars with low angles of extinction, besides an indistinct feldspathic mineral as cement, which is cloudy. The lath-shaped feldspars appear to be, in part at least, orthoclase with minute latli-shaped cores of lime-soda feldspars. ' Arnold Hague, Notes on the occurrence of a leucite rock in the Absaroka Range, Wyoming Territory: Am. Jour. Sci., Sd series, Vol. XXXVIII, July, 1889, pp. 43-47. 332 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Nothing resembling leucite or suggesting it is present. This feldspar matrix is crowded with microscopic crystals of augite, magnetite, and brown biotite in thin tablets and long narrow crystals which often resemble hornblende. In one part of the rock ilmenite accompanies magnetite. The groundmass of the edge of the dike is brown glass with microlites of augite and some of plagioclase. These microlites have dark-browiji clouds attached to their ends, or in the case of augite are colored brown. The augite phenocrysts are light green in thin section and are filled with irregularly shaped inclusions of crystalline g-roundmass containing ilmenite rods, which are not generally found in the grovindmass of the rock outside of the augites. These ilmenite rods within the inclusions of one augite lie in several orientations, apparently with rhombohedral symmetry. Although they are confined to the inclusions of groundmass and do not penetrate the augite substance, their shape and arrangement suggest the microscopic rod-like inclusions in the diallage and hypersthene of gabbro, which may possibly be ilmenite. The augites also inclose small crystals of olivine and magnetite. The olivine phenocrysts are sharply idiomorphic and of very pure sub- stance, with small inclusions of magnetite and glass and occasionally bays of groundmass. It is sometimes twinned in pairs of attached crystals, the twinning plane being (Oil). There is a slight serpentinization along the surface and cracks in some cases. The olivine crystals are much smaller than those of augite, but are more numerous. The appearance of this rock in thin section is shown in PI. XXXVI, fig. 1. It is to be observed that the glassy groundmass of the marginal surface of the dike is unlike the groundmass of the main body of the dike in mineral composition. Biotite is not developed, and the only feldspars are the microlites of plagioclase, which may correspond to the cores in the lath-shaped orthoclases of the main body of rock. As compared with the leucite-bearing I'ock from Ishawooa Canyon (1698), it is to be noted that the phenocrysts of augite and olivine in the dike rock just described are not quite so numerous as in the Ishawooa rock, while there is much more augite in the groundmass, besides abundant biotite. The microscopic crystals of feldspar are not so large and distinct, and nothing corre- sponding to leucite can be seen. Chemically the rock is richer in potash, with about the same per cent of soda. Alumina is slightly higher, and U. S. QEOLOOICAL SURVEY RT II PL. XXXVI (B) X 37 PHOTOMICROGRAPHS OF ABSAROKITE THE HELIOTYPE PRINTING CO., BOSTON ABSAROKITE. 333 mafj-nesiii and lime are sli'notite i\i\(\ aug-itejand some colorless apatite. The t'eldspar plienocrysts are labradorite, while the feldspar of the ground- mass is mainly orthoclase, with kernels of fresh feldspar that has the optical characters of oligoclase. There is very little quartz, and some little chlorite or serpentine. The feldspars of this rock are quite fresh, as are also the biotites. A coarser-grained and more altered modification of this rock occurs in another dike near the head of the main stream (1467). The feldsjiars of the groimdmass are not idiomorphic, but acicular, with the microstructure characteristic of syenite-porphyries. The mineralogical analogy between banakite and shoshonite is chiefly in the association of labradorite phenocrysts with orthoclase microlites. Biotite and augite are common to some varieties of both, while olivine is present in one variety of banakite and is connnon to most shoshonites. These rocks are the highly feldspathic modification of shoshonite magma, and are complemen- tary to absarokite, which rejjresents the least feldspathic modification of the same magma. SIMILAR KOCKS IN MONTANA. Rocks almost identical with absarokite occur in the region about Boze- man, Montana, and have been thoroughly described by MerrilP in a bulletin of the United States National Museum. They are intrusive bodies in part, and have been described under the head of questionable basalt and lampi*ophyre. They are more or less decomposed in some cases and quite fresh in others. Their mineral composition and habit are like those of the rocks here called absarokite. The phenocrysts are olivine and monoclinic pyroxene, whose chemical composition in the case of the rock from near Fort Ellis is that of chrome-diopside. The rock itself is imusually rich in magnesia and comparatively low in iron oxide, so that it is probable that the monoclinic pyroxenes in the other absarokites are not such pure diopsides, but are most likely malacolites or augites. The pyrox- ene in the coarse-grained shonkinite of Square Butte, Montana, which is related to absarokite chemically, has been shown by Weed and Pirsson to be augite. There are no phenocrysts of feldspar, and the groundmass con- tains orthoclase, or when not distinctly crystallized is found to be compara- tively rich in potash and soda. The chemical compositions of the rocks ' Merrill, Geo. P., Notes on some eruptive rocks from Gallatin, Jeflferson, and Madison counties, Montana: Proc. U. S. Nat. Mus., Vol. XVII (No. 1031), 1895, pp. 637-673. 352 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. described by Merrill are shown in the first four analyses in the table, which is introduced here for comparison with those of absarokite in the Yellowstone Park. Analyses of absarokite and similar rocks. Constitaent. 1 2 3 4 5 6 7 SiO.2 46.90 .41 10.17 .33 1.22 5.17 .10 20.98 6.20 1.16 2.04 .44 49.13 .42 9.05 .39 3.57 5.05 .15 17.21 5.68 2.01 2.24 .38 .05 50.82 .59 11.44 .03 .25 8.94 .19 14.01 8.14 1.79 3.45 .20 .06 51.65 .55 13.89 .80 2.70 4.80 .15 11.56 4.07 2.99 4.15 .21 .19 .19 1.30 1.89 50.03 .61 14.08 Trace. 2.92 6.11 .08 10.73 7.46 1.46 2.64 .42 .04 52.33 .14 15.09 54.15 Not det. 18.92 TiO.2 AI.O3 'Cr.iOs FeiO 1 4.31 4.03 .09 6.73 7.06 3.14 3.76 1.02 .07 1 6.79 Not nesia and lime are fairly liij^h. In the two rocks of S(iuare Butte the shonkinite is like that of Yoyo I'eak, but alumina and alkalies are somewhat lower, and mag-nesia and lime hii)-lier. The syenite of Square Butte, the complementary rock of shonkinite, is high in alumina and alkalies and very low in magnesia and lime, with very high potash. In these two cases we find shoukinites as extreme forms of differ- entiations in connection with syenitic rocks quite different from one another in chemical composition, one being comparatively low in alumina and the other high, the sum of the alkalies in one case being 8.85 per cent and in the other 12.74 per cent. In each instance the associated rocks are facies of one igneous mass. A comj^arison of the series of differentiation products just described shows to what extent they may differ from one another in neighboring regions. CHAPTER X. THE RHYOLITES. By Joseph Paxson Iddings. INTRODUCTIOIf. The rhyolite (if the Yellowstone National Park occurs almost whollj'- as extrusive surficial lava flows in the form of nearly horizontal sheets, some having enormous proportions. In only one locality does it assume the character of a volcanic mountain, in which place it occurs as breccia and also as intrusions and surface flows. It constitutes the great plateau of the Park, and sends out arms into valleys in the surrounding ranges of moun- tains, and is found in isolated remnants upon their slopes. Owing to its great areal extent, and also to the fact that it is in places more than 2,000 feet thick, its volume is very large. It is exposed to view in many clifl"s and bare slopes tlu'oughout the region, and has been studied in detail in many places. Its two most striking petrological characteristics are the uniformity of its composition chemically and mineralogically and the multiformity of its physical aspect. With a range of only 5 per cent in the silica, and of much less in the other constituents throughout miles of material, there is the greatest diversity in the appearance and texture of the rock, even within the limits of a few feet. Its color may be white, black, yellow, red, brown, or grays of various tones, which may be uniform for broad areas, or mingled in blotches, streaks, and layers, or finely speckled in small spots. Its luster may be dull and stony or vitreous and brilliant, and its texture may be rough or smooth as the rock is porous, vesicular, and pumiceous, or dense and compact. In some localities the characters are quite uniform for a large extent of rock; in others they are highly diversified. In order to convey a proper idea of the relations of these various modifications to one 356 t> KHYOLITE NEAR JIAMMOTII HOT SPKINGS. 357 another and to show their orij^iu, it will he necessary to descrihe the field occurrence and niegascopicul characteristics in a number of localities within the Park, and afterwards to treat systematically the microscopical characters. MEGASCOPICAIi CHAllACTERS. VICINITY OF MAMMOTH HOT SPRINGS. The rhyolite at the Golden Gate, where the road to the Geyser Basins passes alonjf the face of a rocky cliff at the south end of Terrace Mountain, is a dense, light purplish-gray rock, separated into distinct horizontal layers, and jointed by irregular vertical cracks, which cause it to weather in pinnacles of angular blocks. In the lower part of the cliff the rhyolite is dense and dark purple, passing up into lighter-colored and more porous fonns, with occasional flattened ca\'ities and yellow spots. The rock has a stony lithoidal groundmass, in which glisten small crystals of quartz and sanidine (1775, 1776). It also forms a prominent cliff, 100 to 150 feet high, along the top of the southern portion of the west escarpment of Mount Everts, which is well shown in the panoramic view of this mountain, by W. H. Holmes, wliich accompanies his report on the geology of the Yellowstone National Park.i I Here the rhyolite is massive, with a rude columnar structure. It is reddish purple and lithoidal, with many small jihenocrysts of quartz and feldspar. Near the northern end of the sheet, on the summit of Mount Everts, it passes into a grayish-white rock, finely porous in spots (1762). Beneath the rhyolite sheet there is a deposit of 1-hyolitic dust or ash about 4 feet thick, in places more, which, as Holmes has pointed out, is beautifully and delicately laminated in light and dark grays, brown, and bufts. The top of the sandstone strata on which this ash rests is covered with a thin layer of small fragments of the same kind of sandstone and sandy soil, only a few inches thick. Ujjon this is a layer of rhyolitic ash or sand, passing up into very fine white dust (1763), formed of microscopic angular particles of glass and a small amount of crystalline grains. This is thinly laminated. Over it are alternating layers of coarser rhyolitic sand and finer dust, all laminated, with the thinnest possible lines, wliich are 'Twelfth Aun. Rept. U. S. Geol. and Geog. Stiiv. Terr. (Hayden), for 1878; Part II, PI. XXXII. 358 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. persistent and perfectly parallel to one another and to the plane of contact of the overlying- massive rhyolite. This friable portion passes npward by insensible gradations into dark-purple dense rock with abundant pheno- crysts, almost indistinguishable from the overlying rock, from which, however, it is separated by a thin layer of black perlitic glass (1769) less than one-fourth of an incli thick. A similar deposit of dust iniderlies the rhyolitic sheet in the mountain north of TeiTace Mountain, where it has been indurated in the same manner. The rhyolite sheet of j\Iount Everts extends over the whole southern half of the top of the mountain and down the slopes of the southeastern spurs to the valley, and overlies a thin sheet of vesicular basalt which is exposed in a number of places. It is found near the top of the plateau wall south of Lava Creek, where it is about 150 feet thick, and extends south into the gi'eat plateau. In the neighborliood of Osprey Falls, east of Bunsen Peak, the same rhyolite sheet is exposed in the cliff near the falls. Beneath it is a deposit of light-gray rhyolitic dust, which grades upwai'd into more compact rock and tlien into dark glassy rock immediately beneath the massive rhyolite. The rhyolite sheet is from 100 to 150 feet thick and overlies 8 sheets of basalt, which are superimposed nearly hoi'izontally, and it is in turn overlain by a 50-foot sheet of basalt, the whole series, including the rhyolite, being finely columnar. The surfaces of the columns of the rhyolite and of those of basalt are very similar in color, owing to weathering and to the lichens, so that the two rocks are scarcely distin- guished from one another at a distance, the rhyolite appearing as dark as the Ijasalt. Near the falls, however, the rhyolite columns are longer and straighter, and become granular at the upper ends, where they weather into pimiacles. The rhyolite forming the cliff at the Golden Gate contiimes as a nearly horizontal sheet northward beneath the travertine deposit on Ter- race Mountain, and forms the top of tlie hill north of this, where it is from 150 to 200 feet thick. It is exposed in a bold cliff heading an amphitheater on the northeast side of this mountain, and has the same characters as in the cliff on Blount Everts. It is dark purple, lithoidal, and full of rather large phenocrysts. In the top of the cliff it is in places glassy and perlitic, and contains large vesicles. Beneath the sheet, as already mentioned, there is a deposit of rhyolitic dust, whose upper portion is indurated like that on OliSIDIAN CLIFF. 35i) Jlount Everts, the nuiteriiil from Ijotli loealities being' identical. The rhyohte sheet continues north luitil it rtiuches the an(U?sitic breccia forming the southeast spur of Sepulchre Mountain, upon which it rests, its lower portion inclosing fragments of andesite. It extends along the base of the south slope of Sepulchre Mountain west to the divide between Glen and Reese creeks, and forms the bench of dark-])urple rock with small phenocrysts south of Cache Pond, and also an isolated remnant of light- reddish earthy rhyolite overlying the andesite on the west base of Sepulchre Mountain. From this we see that in the neighborhood of the Mammoth Hot Springs the rhyolite has a very uniform character, being mostly lithoidal, except in one place on the old Norris road northwest of Terrace Mountain, where a small mass of dark-coloi'ed rhyolitic perlite is exposed, which, as Holmes has remarked, "is similar to that forming the under surface of most of the rhyolitic flows in this region." In this vicinity, however, the under surface of most of the rhyolite sheet has only a thin iilm of perlitic glass along its contact with the underlying rhyolitic tuff. The tuff deposit has not been observed on Glen Creek, nor at the head of Reese Creek, nor does it underlie the most northern remnant of rhyolite which occurs on the west side of Bear Gulch, north of the Park boiuidary. OBSIDIAN CLIFF. The rhyolite which forms the plateau country and the flat-topped bluffs, 300 or 400 feet high, on both sides of Willow Park along Obsidian Creek is a lithoidal to earthy rock, reddish purple in darker and lighter shades, and filled with brilliant phenocrysts of quartz and sanidine, the latter exhibiting a blue iridescence in man)- localities. Rhyolite of the same character continues to form the plateau as fa^- south as the Norris Geyser Basin, being well exposed all along the road. It also extends east to Lava Creek and forms the west base of the mountains west of Tower Creek, overlying andesitic breccia and reaching an altitude of 8,800 feet. At the noiihern end of Beaver Lake the lithoidal rhyolite is overlain by a great flow of rhyolitic obsidian, which covers the high country to the east in a sheet 75 to 100 feet thick and has accumulated in an ancient valley to the depth of 200 feet. The stream erosion of this thicker mass has 360 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. formed Obsidian Cliff/ whose shining black columns of g-lass rise 100 feet above the road. The cliff stretches for half a mile from the outlet of Beaver Lake along the east side of Obsidian Creek, being 150 to 200 feet high near the lake and becoming lower northward. The upper half is a vertical face of rock, the base of which is obscured by debris of large blocks of the same material. The obsidian sheet extends eastward up the rude benches to the top of the plateau 400 feet alcove Beaver Lake. Along the west edge of this table-land it forms a cliff' about 50 feet high, which extends south to the Lake of the Woods. Following the obsidian back from the face of this upper cliff, over the hummocky surface of the plateau, the black glass becomes filled with gas cavities and passes into banded ])umiceous rock, and finally into light-gray pumice. This covers the surface of the plateau for 2^ miles eastward, to the valley of Solfatara C'reek. Here again the lava flow is exposed in a cliff, the lower portion of which is lilack and red ob.sidian. Toward the south the obsidian flow extends a mile beyond the Lake of the Woods, and northward it crosses the east-west drainage that cuts off the higher jwrtion of the plateau a distance of some 5 miles. The original thickness of this lava flow is not known, since the upper pumiceous portion has been eroded to a variable extent. The denser obsidian portion is from 75 to 100 feet thick. The point at which the obsidian broke through the older rocks has not been discovered, but it is evident that the lava forming Obsidian Cliff flowed down from the high plateau in a northwest direction into a preexist- ing valley. The planes of flow in the lava clearly indicate that it crept down the slope back of Obsidian Cliff and accumulated in the bottom of a channel between rhyolite hills. The most noticeable feature of this body of obsidian is its columnar structure, which is confined to the southern end of the cliff. It is shown in PI. XXXIX. The glassy columns rise from a talus slope that extends 50 feet up the cliff. They are vertical prisms 50 or 60 feet high, and vary in width from 2 to 4 feet near the south end of the cliff, the width of each column being quite constant throughout its length. (Jn the south face of 'Idding8, J. P., Obsidian Cliff, Yellowstone National Park: Seventh Ann. Kept. U. S. Geol. Survey, 1888, pp. 249-295. U. 5. GEOLOOrCAL SURVFv MONOGRAPH XXXII PART II PL XL TOP OF COLUMNS, OBSIDIAN CLIFFS. COLUMNAR OBSIDIAN. 361 this end of the cHff the columns are the same, but grow less clearly defined toward the oast, where a sharp bend in the lava sheet has fV)nned gaps in the rock and has destroyed the ciuitinuity of the mass. Beyond this tlie colunnis incline considerably toward the west, as though the underlying surface of contact sloped toward the west also. The columns in the main face of the cliff are tilted If)" to the eastward, and the planes of flow which cross them have an average dip of 10^ E., indicating that the underlying surface at this place sloped toward the east. The colunnis become broader to the north, the largest being 20 feet in width, and with the change in the character of the rock from glassy to lithoidal they grade into massive blocks formed by vertical cracks farther apart. The columns have four, five, and six sides, which are unequally developed, but at a distance the general effect is quite regular. The obsidian forming the lower part of the columns is dense and black, and transparent only on verj' thin edges. It is traversed by bands or layers of small gray spherulites. In this part of the columns there are almost no cavities or lithophysfe, and but little contortion of the layers. Higher up, the obsidian is less massive and contains large lithophysEe flattened parallel to the plane of flow. The tops of the columns pass into -obsidian, which for 10 feet is quite dense, but above this is full of large cavities which honeycomb the mass. This may be seen in the photograph of the columns (PL XL). This upper portion, about 50 feet thick, is divided by vertical cracks into broad quadrangular blocks. The sides of the columns are comparatively straight, and are independent of the flow stiTicture within the mass, which is indicated by the spherulitic layers that traverse the rock in parallel planes more or less contorted These layers pass through the columns at all angles, exhibiting abrupt folds and curves, which have been cut across sharply by the colunmar cracks. The crystal- line spherulitic layers formed planes of weakness, along which transverse cracks were produced. There is another kind of pai-ting, which took place while the lava was still molten, but when it was so viscous that in places where vertical layers pulled apart in flowing down the slope the gaps did not close up. These are of only exceptional occurrence. The columnar portion of the west face of the cliff extends for only a few hundred feet northward, the character of the rock also changing in this direction. The spherulitic and lithoidal layers also become more frequent, 362 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. until the black glass appears as thin bands in a light-gray rock, and finally the whole mass is a laminated lithoidal rock. The lithoidal form of the rock is not found in the thinner portions of the lava flow, but only where it has accumulated in the ancient channel. It is split into thin plates along the planes of flow, owing to the differences in texture of the alternating layers, which vary in degree of crystallization. This delicate lamination and variability of crystallization will be referred to again, after the micro- scopical characters have been described. Owing to the fact that the spherulitic structure, which is highly devel- oped in the obsidian at this place, is typical of that which occurs in a great number of other localities in the Yellowstone Park, it seems advisable to describe it in considerable detail, in order to give a clear impression of this very characteristic mode of crystallization. The spherulites form isolated spherical bodies or groups of spheres, often so intimately intergrown as to form layers in the rock. Their substance is lusterless and stony, dull bluish gray and pink. They are of various sizes, the larger ones frequently being hollow or porous. The simplest :form of the megascopic spherulites is that of small dark- blue spherules, about the size of a mustard seed, embedded in the black obsidian. When broken, they appear lighter gray within, have a dense porcelain-like texture, and exhibit slight indications of a radially fibrous structure. They are usually located along fine lines of minute dots on the surface of the obsidian. The small blue spherules are generally crowded together along these lines, or more properly along the planes of which these lines are the traces, and which are planes of flow. Sometimes a number of layers will lie close together with the thinnest possible sheet of black glass between them, or they will unite to form a baud a fourth of an inch thick, whose surface is covered with protruding hemispheres. Occasionally groups of spherules are prolonged in one direction, forming parallel ropes through the black glass. The surface of the spherules is brown or red, and constitutes a plane of weakness between the siiherulite and the glass, along Avhich the two separate with ease, leaving a dull pitted surface on the obsidian. The arrangement of the spherulites in the plane of flow is quite iiTegular, though occasionally in arborescent figures. Spherulites about the size of peas have an agate-like banding in con- SPHERULITES IN OBSIDIAN. • 363 centric shells, combined with a radially tibrons structure. Their form is more or less spherical, sometimes l)ein<^ depressed on one side, or they are eloufjated into lit gray, carrying abundant phe- nocrvsts of feldspar, most of which a'v white or yellow and exhiliit brilliant striated cleavage planes. There are none of (juartz. This rock resembles that forming the bluti" at the southeast corner of Geyser Meadow. It is exposed in the rounded hills back of the Splendid Geyser (1924), and in tabular masses back of the Grand (1926), and forms the west bank of the Firehole Kiver east of Old Faithful Geyser. The microscopical features will be described in another place. Its extent and its relation to the normal rhvolite of the neighborhood were not made out. Perlite with large spherulites occurs on the bank of the Firehole River a short distance above Old Faithful Geyser (2166, 2167). Above the Upper Geyser Basin the road along the Firehole River traverses rhyolite like that of the plateau, for the most part lithoidal, and weathering into crumbling sand. Through it the river has cut a narrow rocky channel which is tilled with great masses of rhyolite that have fallen from the steep sides. Just below Keplei's Cascade the river passes through a narrow gate in a channel not more than 2 feet wide. The cut exposes vertical layers of spherulitic rhyolite, mostly lithoidal (1933), the layers ci'ossing the stream at right angles. Following the southeast branch of the Firehole River to the pass of the old trail near the north end of Shoshone Lake, one traverses country covered with lithoidal and glassy rhyolite. For long distances the road lies in a line glassy sand derived from the disintegration of perlite. The clitf that stretches for 3 miles along the south side of the road presents a variety of phases of rhyolite. At its western end it is lithoidal and very porous and vesicular, with here and there patches and streaks of glassy rock. Farther east the glassy rock predominates, with smaller masses of lithoidal rhyolite. Near the pass south of the road well-banded lithoidal rock abounds, and at the • pass glassy and spherulitic modifications occur, as varied as those of Obsidian Cliff. The vesicular lithoidal rock at the west end of the cliff is lig-ht bluish gray, discolored by brown and yellow stains. It carries numerous phenocrysts, which are so transparent as to be easily overlooked. The small irregular vesicles are not distributed uniformly through the rock, as is usually the case in basalt, but are very unequally scattered, being abundant in some spots and almost absent from others. This is a very common mode of occurrence in the lithoidal rhyolite of this region (1934, 1935). The 374 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. well-banded lithoidal portiou near the pass is dark slate colored, striped witli layers of light purplish gray, often of the utmost delicac)', in this respect resembling the laminated lithoidal part of Obsidian Cliff. There are occa- sionally small cavities with transparent tabular crystals of sanidine and some of quartz. The phenocrysts are abundant, and consist of sanidine, plagioclase, and quartz, with numerous rusted crystals of a ferromagnesian mineral, which has been found to be augite. The longer phenocrysts lie more or less parallel to the lamination (1937). Some of the obsidian contains small black spherulites, the size of small shot. Other parts of it are streaked with red and brown glass (1936). The most perfect perhtic structure is developed in places, together with curiously crenulated cavities that traverse the rock in streaks and are coated with crystalline grains, which in some instances appear to be fragments of broken phenocrysts of feldspar (1939-1940) that have been dragged apart along the line of the cavity. MADISON PLATEAU SOUTH OF THE GEYSER BASINS. The whole of this plateau is rhyolite, mostly black glassy obsidian, with porphyritical crystals, in places spherulitic. This alternates with pumiceous glass, which occurs in bands or layers. The alternation of dense and pumiceous glass is very persistent over the whole top of the plateavi, but the majority of outcrops consist of the denser obsidian, since the pumiceous portions of the rock have been more easily eroded. The character of the country and of the rocks is very monotonous and uniform, varied only in the neighborhood of Summit Lake by small areas of hot springs and fuma- roles. The top of the plateau soutliwest of tlie Upper Geyser Basin is glassy, but the lower part of the bluff along Iron Spring Creek is lithoidal gray rhyolite, more or less porous and vesicular. The shallow drainage channels, as the}^ approach the edge of the plateau, drop into deep ravines, where are large streams of water which are not met with on the top of the plateau. The water comes from the edge of the plateau, out of the mass of the rhyolite, the upper portion of which is porous and vesicular, while the lower part is dense and compact. The smaller of the streams draining south- westerly into Boundary Creek, east of Buffalo Lake, cuts a gulch 150 feet in the edge of the bluff which forms the east wall of the basin of Buffalo Lake. The gulch has vertical, rocky walls, exposing a fine section of the rhyolite lava, the flow of which has been greatly contorted. The lowest MADISON PLATEAU. 375 portions of the cliflf are l)luisli-}.Tay litlioidiil rli^-olitc, passin<-- up into black and red obsidian (19')!) with small plienocrysts. Tlie rock is richly spher- ulitic, witli large lithophysa' in thick layers. Tlie lava sheet is slaggy on top, with layers that have been stretched and cracked transversely. From the structure of the lava it is evident that the flow poured down a steep slope westward into the valley basin of Buffalo Creek. The jiresent eastern wall is a bluff 150 to 200 feet high. Farther down Boundary Creek, as far as the bluff north of Falls River Basin, the rhyolite is lithoi- dal, but the bluff west of the falls of lioundary Creek, forming the edge of the plateau, is black and red spherulitic and porphyritic obsidian (1950). The same observation was made by Professor Penfield in traveling from Madison Lake across the southern end of the plateau to Falls River Basin. The whole surface of the country is black obsidian and grayish-white pumice (1941, 1942), which is porphyritic with large sanidines and smaller quartzes, but as the level of the basin is approached the rock grows lithoidal. On the continental divide south of Madison Lake the black obsidian is in some places finely vesicular and in others spherulitic, with small litho- physfe coated with tridymite pellets and containing a small amount of fayalite. It incloses many angular fragments of very fine-grained basalt, which is often highly vesicular and which has the petrographical characters of the so-called "recent basalts." Similar inclosed fragments of basalt were found in various places northwest of this locality. They indicate the existence of basalt flows in this vicinity prior to the outbreak of the top sheet of rhyolite, but no large body of basalt was observed. BECHLER CANYON. Bechler River cuts a fine canyon through the great rhyolite mass, thus separating Madison Plateau from Pitchstone Plateau. The canyon trends in a northeast-southwest direction and exhibits a very marked diffei-ence between its western and eastern walls. The former is a rather i^ersistent bluff 800 feet high, while the latter is from 1,000 to 2,000 feet in height, presenting the greatest thickness of rhyolite exposed within the Park. The rock of the country forming the northern head of Bechler River has the character of that on the surface of the plateaus, the rhyolite being mostly glassy and pumiceous, in some places crowded with spherulites, in 376 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Others perlitic. Parts of it are lithoidal. Before the valley commences to canyon, at an altitude of about 7,900 feet, the stream cuts its way through lithoidal rhyolite, well laminated and much contorted, with most of the layers standing in a vertical position. Below this the stream continues to cut through dark-gray porphyritic rhyolite, which is lithoidal and finely banded, while on the top of the western wall at the upper end of the canyon pi-oper the rock is glassy and beautifully spherulitic in irregularly shaped forms, inclosing grains of obsidian, and producing the appearance of large axiolites on the surface of the rock in a manner already described. It also contains small hollow spherulites, distinctly fibrous (1946), and passes into highly vesicular to pumiceous lithoidal rock, light bluish gray in color (1945). Half a mile above the mouth of Bechler Canyon the rock exposed in the stream bed is dense lithoidal rhyolite (1949). It forms the bed of the stream up to near Colonnade Falls, which is about a mile above the mouth of the canyon. Here the rhyolite is overlain by a horizontal sheet of basalt which is at the same altitude as that of the great basalt sheet in Falls River Basin, a tongue of which must have flowed up into the canyon. It gives rise to Colonnade Falls, where the stream drops 60 feet from a ledge of rock into a basin partly inclosed by a semicircular wall of colunmar basalt. At the base of this wall the large vertical columns are 30 feet high; they pass up into irregularly cracked basalt, which at the top is massive and vesicular, forming a layer which projects over the face of the wall. The wet columnar rock forms a dark background for the free-falling water with its rainbowed mist, while the banlcs, kept moist by the shifting spray, are covered with a luxuriant growth of ferns on the one side and of flowers on the other. A hundred yards upstream is Iris Falls, about 40 feet higli, of diff'erent character. It is broad and is broken by large masses of rock at its base. The rock is porphyritic rhyolite, which is a later flow than the basalt, and must have been a small one in the bottom of the canyon. The lower portion of this later flow of rhyolite is glassy, being a spherulitic obsidian (1961), and is brecciated with inclosed masses of older rhyolite. It grades upward hito lithoidal rock which is light gray colored (1948). This passes up, at the top of the falls, into black, glassy, and spherulitic forms again. Half a mile farther upstream is another waterfall, of 60 feet, having the same general character as the last. It cuts through the later FALLS ItlVER BASIN. 377 sheet of rhyolite, which is finely exposed on the east wull. In tlie bottom portion of the flow nix' h>r<>t' masses of inclosed rock. The central layer is massive, with well-marked planes of flow. A short distance upstream are fine double cataracts, and above these are others in continuous succession, the river descending in all about 150 feet. The rocks on both sides of the can\'on appear to be soaked with water, which runs into the river from a multitude of small streams and springs along the base of the walls. FALLS RIVER BASIN. Falls River Basin, which in reality is a terrace of the great plateau, at an altitude of from 6,300 to 6,500 feet, is about 15 miles long and 8 miles wide. It is a portion of the vast rliyolitic lava flow, which is partially covered by a thin sheet of basalt. The river has cut its way down to the rhyolite, which forms the bed of the stream from a point 1 mile below the mouth of Boundary Creek down as far as explored, below Boone Creek. The rhyolite is lithoidal and fissile, and at the falls below the mouth of Falls River there is evidence of more than one flow of rhyolite. The upper of these falls is a cataract. The middle one is a beautiful fall, 15 or 20 feet high and about 200 feet wide, with a cascade in low steps above it. At the west end of this fall there is a low arched cave, formed by a sheet of dense, gray, glassy rhyolite, with small pheuocrysts (1952), overlying a mass of brecciated glassy rhyolite, which is more easily eroded. Above the gray layer the rhyolite is glassy and spherulitic (1956), passing up into banded lithoidal rock. The exposure appears to be that of the bottom of a lava flow. The third waterfall is broad and low, not more than 5 feet hia-h. About 2 miles above the mouth of Boone Creek there is another fall, where the river cuts 50 feet into the rhyolite, leaving isolated blocks of .the rock standing like monuments in the stream. The rhyolite forms a bench on both sides of the river, with bluff's of basalt 100 feet high standing back a short distance. This branch canyon of the Snake River begins to assume the same geological character which the deeper canyon of the main stream possesses in the neighborhood of Shoshone Falls, Idaho, where numerous sheets of columnar basalt overlie a glassy and lithoidal dacite of peculiar characters, which closely relate it to the rhyolite of the Yellowstone National Park. The valley of Conant Creek, just north of the forty-fourth parallel of 378 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. latitude, is cut into litlioidal rhyolite, which is somewhat spherulitic and is filled with small phenocrysts (1955). This rhyolite continues south beyond the limits of the area explored and forms the northwestern base of the foothills of the Teton Range up to an elevation of over 8,000 feet. Where it has Ijeen cut across by the valley of Conant Creek its contact with the underlying rocks is seen to be very steeply pitched to the west, indicating how steep the preexisting surface must have been at this place. The rhyo- lite near the contact is rudely columnar. It is part of the great lava flood which buried the slopes of the northern foothills of the same range, and is found overlying sedimentary and Archean rocks and volcanic breccias of andesite which had accumulated on them. About the head of Conant and Boone creeks and along Berry Creek thin tongues of the rhyolite sheet, continuous with the heavy mass of Pitchstone Plateau, have been left in favored places, and have escaped the erosion which must have considerably modified the contour of the surface in the vicinity of this high range of mountains. These portions of the lava lie at higher altitudes than the top of the plateau north, and even exceed in some places the highest elevation of the main body of Pitchstone Plateau. In two points north of Berry Creek the altitude of the pi'esent surface of the rhyolite is 8,900 feet, and just east of Forellen Peak it reaches 9,300 feet, resting in a thin sheet on sedimentary rocks. The petrographical character of tlie rhyolite varies somewhat in this neighborhood, but the variations are mainly due to the fact that the exposures are in many cases at or near the bottom of the lava flow, where it has been aff'ected by coming in contact with underlying rocks. Thus, on the west slope of the mountain north of the head of Conant Creek the mass of the rhyolite is lithoidal and but slightly porphyritic, but near the bottom of the flow it is in places black obsidian (1958) with a fine mottling that is almost imperceptible and is more pronounced in a gray, glassy form of the rock (1954) fi'om the same locality, which is similar to that at the middle falls on Falls River (1952). In places the lithoidite is light bluish or purplish gray and has large flattened vesicular cavities intimately related to hollow spherulites and lithophysoe (1953, 1957). These exhibit characteristic V-shaped cracks, and have evidently resulted from the gaping open in spots of a viscous substance. They are coated with yellow- stained crystals of the same minerals as those which occur in lithophysae, FALLS RIVER BASIN. 37i) and around tlie cavity the rock is lif^liter colored. Another modification of the rock, which lias numerous small i)henocrysts of quartz, occurs 2 miles northeast of Survey Peak. It is laminated and fissile in thin ])lates, resem- bling a schist (1960). A similar form of rhy elite is found on the long spur east of Snake River, opposite the mouth of Owl Creek. The rhyolite cap- ping the limestone on the divide between Berry and Conant creeks belongs to the nevadite tyi)e, being filled with phenocrysts. Near its contact with the limestone it is dark slate colored, glassy, and spherulitic (1959). It grades upward into lighter-colored, purplish, and yellow lithoidal nevadite, full of irregularly shaped ca^^ties. It weathers in great rounded and roughened masses like granite. The same is tiaie of the rhyolite in the neighborhood of Birch Hills, in the valley to the northeast, and at Terrace Falls. Here the coarsely jjorphyritic, reddish-purple rhyolite, or nevadite, has been weathered and eroded into great rounded towers 100 feet high, which resemble exposures of coarsely crystalline granite. It is to be remarked that while the rhyolite in the vicinity of Birch Hills is lithoidal along the valleys cut by both forks of Falls River at altitudes of from 6,700 to 7,000 feet, j^et within the amphitheater at the head of Mountain Ash Creek the stream at 7,000 feet cuts a narrow canyon through porous and glassy rhyolite, which also forms the spur on the north side of the amphitheater at 7,350 feet, where it is black porphyritic obsidian and perlite. This is 1,200 to 1,500 feet below the edge of the Pitchstone Plateau, where the rhyolite is black and red spherulitic obsidian with many phenocrysts (1972). Farther down Mountain Ash Creek, at an altitude of 6,800 feet, where two branches unite at the crest of Union Falls, 80 feet high, the rhyolite is lithoidal. The occurrence of glass)" forms of rhyolite in the bottom of this amphitheater overlying lithoidal ones indicates that this was the surface of a flow, aiid not the interior jjortion of one which has been exposed by the erosion of a vast amphitheater. PITCHSTONE PLATEAU. One of the most interesting exposures of rhyolite is that furnished by the high spur between the branches of Glade Creek, a tributar}- of the Snake River, which enters the latter about 5 miles north of the forty-fourth parallel of latitude. The spur is from 600 to 1,000 feet high, and at its southern end presents a high bluff of lithoidal rock, exhibiting greatly 380 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. contorted bands of flow. Its base consists of a talus of large blocks. The rhyolite is dark gray, speckled with white and brown. It bfears many phenocrysts of white plagioclase and fewer of quartz and sanidine, besides many small rusted crystals of augite (1964, 1966, 1967). Through the rock are scattered cavities of various sizes and shapes with gray or white walls, which are coated with brilliant crystals of quartz, tridymite, or sani- dine, with opaque crystals of faj-alite. The quartzes have been studied b}^ Professor Peniield, who has found them to have a simple but very unusual development. In addition to the common quartz forms — prism and unit rhombohedrons — there are steep rhombohedrons (3032), 3/2 and (0332), 3/2, and narrow trapezohedral faces rb 3/2-3/2.^ The same rare forms occur on the quartzes in the lithophysse at Obsidian Cliff" and in other localities within the Yellowstone Park. The white walls of these cavities vary in thickness from mere lines to an inch, and some of them have a distinctly spherulitic structure with widely gaping centers. They are in part hollow spherulites of a peculiar character, very closely related to the irregular cavities in the rock, which could not be termed spherulites. The outei- margin of the hollow spherulites is not shai-ply defined against the groundmass of the rock, as in most instances. The radial fibration is not recognizable V)y the unaided eye, and a concen- tric zonal structure is observed in only a portion of them. The most characteristic feature of these hollow spherulites is the occurrence of com- paratively large quartz crystals in two habits, usually in diff"erent parts of the cavity. One form of the quartz consists of stout crystals, seldom over 2 mm. in diameter, in one iiistance 6 mm., very transparent, with a pale smoky to amethystine color. The others are slender white prisms, 10 nmi. long. The transparent crystals are often located on a nearly flat side of the cavity, while the white prisms, intersecting in all directions, form a kind of network which occupies the thicker part of the center of the spherulite. The light-colored streaks and more crystalline parts of the rock are punc- tured with minute round holes. Along the cliff" to the westward the rock passes into laminated lithoidal rhyolite with open layers incrusted with the same minerals as those in the cavities just described. The rhyolite on the second ridge east of Glade Creek is black and I Iddings aud Pentield, Tho minerals in hollow spherulites of rhyolite from Glade Creek, Wyo- ming: Am. Jour. Soi., 3d series, Vol. XLII, 1891, p. 39. MOUNT SHBKIUAN. 381 brown Dbsidijui, witli iiiiiiiy plu'iiocrysts and small splnTulites. The splieru- lites have crystallized around plienocrysts as nuclei in many cases. There are also small crenulated cavities, which lie indiscriminately in the glass and spherulites and are coated with minute crystals (1968, 1969). These curious cavities occur in the rock ot" Obsidian Clitf and elsewhere in the Park. RED MOUNTAINS. On the edg-e of the plateau of" rhyolite which lies between the Yellow- stone Lake and Snake River rises a small group of mountains, whose highest peak at the eastern end is ]\Iount Sheridan (10,200 feet). It is an east-west ridge with four prominent spurs trending north and south, sejjarated by deep amphitheaters. Its summits are from 1,500 to !2,000 feet above the plateau, but the eastern peak is 2,700 feet above Heart Lake, which lies at its base. The slopes and spurs on the east and north are short and steep, and only the southern ones fall away gradually to tlie level of the jilateau. These mountains are of rhyolite, whose character in the body of jMount Sheridan ditfers somewhat from that of the plateau. On the steep north- eastern spur south of the Heart Lake Geyser Basin much of the rhyolite is white and gi'ay lithoidal rock, with a moderate number of small phenocrysts, in some places very few, and belonging to the variety liparite. The main mass of Mount Sheridan and the ridge immediately west is composed of this dense liparite, which is light purplish gray in color and fissile in thin plates (1980). Similar rhyolite occurs near the top of the ridge and on the summit of Mount Sheridan, where it is coated with hyalite in places and contains many transparent crystals of tridymite in thin fissures (1984). The rhyolite on the top of the ridge and on the upper northern slope and summit of Mount Sheridan is brecciated, but it is com- pact, and is evidenth* brecciated flow rock and not an aggregation of loose fragments and dust, which is the case with almost all of the andesitic breccia of this region. In places on the summit the rhyolite is brown and glassy, and the brecciated portion is intersected by dikes of massive banded lithoidal rhyolite of no considerable extent. This appears to be the only instance in which anything resembling a dike of rhyolite has been observed in the Yellowstone Park. All of the rhyolite exposures observed b}^ the writer appeared to be surface flows of lava resting upon older rocks. In the cases where later bodies of rhyolite have been recognized they have always been 382 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. ill the form of surficial flows, the orifices or fissure through which they reached the surface not being exposed to view. This is most noticeably the case in the outlying remnants of thin sheets whose jjlane of contact with the underlying rocks is frequently observed. The eastern face of Mount Sheridan is composed of massive white and gra}' liparite, like the northeastern spur. The upper portion of the long northern spur consists of a heavy flow of rhyolite, about 700 feet thick, which appears to have the same character as the plateau rock. In the neighborhood of Lewis and Sho.shone lakes the rhyolite exhibits variations from lithoidal to glassy forms. The bluff west of Lewis River at the crossing of the old trail, 2J miles below Lewis Lake, exposes very fine lithoidal rhyolite, mottled dark and light gray, which is porphy- ritic and banded (1971). The top of the plateau west and north of Lewis Lake is mostly glassy or hyaline rhyolite — black and red obsidian and perlite, which is spheruhtic and porpliyritic (1973). This may be observed along the trail between the two lakes. The character of the rhyolite on the east side of Shoshone Lake near its outlet is particularly varied. It is porpliyritic and is streaked with black and red glass and blue spherulitic layers, besides blue lithoidal portions, weathering pink on the exposed surface. The lake l)each is made up of very irregularl}' shaped pebbles of this rhyolite, wliich are but partially rounded and form a beautiful variegated sand. VICINITY OF YELLOWSTONE LAKE. The most striking A-ariability in the rhyolitic lava, however, is found along the shores of the Yellowstone Lake. The many miles of coast offer numerous bluffs which have been cut into the surface of the great rhyolite sheet, and the slightly glaciated hills of the plateau country immediately west of the lake shore present all possible modifications of this variable lava. A good example of this is found in the cliff on the second point south of the mouth of the West Arm of the lake and the first one north of Flat Mountain Arm. Here red and black glassy forms occur, separately and also intimately mixed. The rock is porphyritic and more or less spheru- litic. There are masses of black obsidian completely shattered by irregular tracks, which cause it to crumble readily into small angular fragments, and WEST OF YELLOWSTONE LAKE. 383 otliers t)t' dark and liglit bruwuisli-red obsidian canying- dark-blue splieru- lites with gray, brown, or i)urple outer shells, also completel}' crackled. lilack and red streaked obsidians alternate in layers with bands of densely spherulitic material, and occasionally of porous spherulites. In places the lamination is ,very pronounced, and thin spherulitic layers, when l)rokeu from the obsidian, are covered Avith wart-like excrescences, which are protruding- spherulites, ribbed with parallel lines corresponding to the planes of lamination of the rock. Parts of the rock are fissile and consist of lioht- brown glass streaked with black and red in small blotches, and even rather large lumps, wliich have been di-awn out into lenticular shapes during the flow of the rock (1994 to 1998). Pumiceous glassy rhyolite forms the top of the plateau in many places about the West Arm of the lake. Southwest of Riddle Lake the drainao-e exposes light-gray pumice overlying black, glassy, porphyritic rhyolite or obsidian. Lower downstream, near the forks, the rhyolite is lithoidal, purplish gray, and banded, and is accompanied by black glassy varieties carrying spherulites, which are the commoner kinds over this part of the jjlateau. In the immediate vicinit}' of Duck Lake light and dark gray pumice and perlite form a brecciated flow (1986 to 1989), while farther west the rhyolite is in places lithoidal. At Rock Point porphyritic obsidian with small spherulites occurs in a brecciated mass. The surface of the spheru- lites and of the glass immediately in contact with them, as well as that of the obsidian blocks, is dark red, like other portions of the body of obsidian in many places. There is also black perlite with small lithophysfe; and light-brown and black, streaked and blotched perlite, and silvery-grav fibrous pumice (2003, 2004). An idea of the great diversity of the rhyolite along the west shore of the lake may be gotten from several typical exposures in the neighborhood of Bridge Bay, from which extensive collections have been made. On the south side of Bridge Creek, about a mile west of the lake, a branch stream has cut into brecciated pumiceous and hyaline rhyolite. It is porphyritic and partly spherulitic crackled obsidian and perlite, with many small roughened cavities. The brecciated portion contains some fragments which are 2 feet in diameter. A highly vesicular modification of it is almost fibrous, owing to the elongation of the vesicles, which have been drawn out 384 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. in thin tubes. This form of the rock is microspheruhtic or lithoidal, with some glassy portions, and the breccia, which is largely composed of this material, is the same as that which occurs on the Firehole River a short distance below the Lower Geyser Basin (2020 to 2023). A more varied occurrence is crossed l)v the trail in a coulee about a mile south of Bridge Creek. It is mostly glassy and is full of phenocrysts of quartz and feldspar. One black ])rojecting mass of rock consists of finely vesicular to pumiceous perlitic obsidian. This grades into a light reddish-brown pumiceous breccia inclosing fragments of white pumice with light-brown borders and small fragments of light-brown pumice and pieces of black obsidian. This passes into a dense red ^Jerlite mottled with black and gray, and the latter grades into reddish-br(iwn and also dark drab-colored perlite, which in turn passes into spherulitie obsidian banded with minutely spherulitic or lithoi- dal layers full of small roughened cavities. It is scoriaceous in places and exhibits a great variety of colors on weathered surfaces (2013 to 2019). All this variation of texture and color takes place within a distance of 100 feet. Farther south the rhyolite becomes more lithoidal in places, purplish lithoidal and spherulitic bands being intermingled with obsidian and jjerlite. It is often roughly vesicular and slag-like (2014). The modifications of rhyolite just described constantly recur over the plateau in this vicinity. A still more varied assortment of rhyolite is found in a low bluff on the lake shore half a mile south of Bridge Bay. It consists of brecciated pumice and scoria, with some massive lava, and appears to be the surface or the forward end of a flow of porphyritic rhyolite. The colors of the rock, all of whose varieties appear to be textural modifications of one magma, range from jet black through different shades of gray to almost white, besides reds which are dark liver colored to pink, and browns that are reddish and others that approach yellow. These colors occur separately in large masses or are combined in brecciated bodies in blotches and streaks, or as mottlings and bandings in massive rock. The greater j^art of the rock is glassy, but some of it is lithoidal. There is black crackled obsidian grading into per- lite banded by delicate layers of spherulites. Some of it is more spherulitic and carries hollow spherulites, which are distinctly fibrous on the inside and are coated with tridymite pellets. There is dense black obsidian so filled with hollow spherulites as to appear like a porous or vesicular rock. Black, red, and brown obsidians occur together, with and without spherulites, some of which are blue and red, while others are porous and RIIYOLITE SOUTH OF BRIDGE BAY. 385 hollow. A pitcliN- MiU'k obsidian with l)luish metallic luster is filled with minute pores that give it a rough fracture surface, besides some larger pores which are pumiceous and generally occur about the phenocrysts, some of the larger feldspars appearing to have been fractured and dragged apart. Another form of obsidian is so finely vesicular as to be almost a pum- ice; it is dark gray colored, with grains of black glass scattered through it. Others are lighter gray, and the most pumiceous rock is silvery white and fibrous. In the larger cavities the glass has been drawn out to the finest threads, like spun glass. Among the phenocrysts the few light-green augites are plainly recognizable. There is black glass with bright yellow pumi- ceous spots, and sanidine crystals which have split open down the middle lengthwise, and others irregularly cracked and piilled apart, the cracks not having become filled with the glass, which must have been expanding into pumice at the time. This grades into rock in which the yellow pumice preponderates over the black glass.- There is perlite of black, red, and brown glass intimately mingled and banded, with feldspars arranged nearly parallel to the planes of flow; also a light-red dense perlite with small black spots. There is a light-red, lithoidal, fibrous, vesicular variety with irregular patches and remnants of black glass, besides light-gray lithoidal rock, with streaks of dark-gray and black glass and porous and scoriaceous portions. Some of these forms of the rhyolite are masses in the breccia, but the more finely brecciated material presents a still more variegated appearance. The most striking breccia is a light-red, also reddish-brown, finely porous glass filled with lumps of light-gray glass of all sizes which is finely porous and minutely crackled, besides others of dark-gray pumice and rounded lumps of highly inflated vesicular black glass. Some of the black glass is compact and occasionally spherulitic. Another form of breccia consists of fragments of black and red obsidian in a matrix of smaller fragments of the same, most of which are red, appar- ently cemented together by a porcelain-like material, which is pink or white. There is distinct evidence of plasticity and flow in the form and arrangement of the small pieces of glass, and the porcelain-like portion is a crystalline modification of the magma, which can be traced into spheru- litic patches. The reddening of the glass seems to have occuired subse- quent to its breaking up, for the fragments of black obsidian have a red margin or surface of variable thickness. MON XXXII. PT II 25 386 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. NATURAL BRIDGE. Bridg-e Creek has received its name from a small natural bridg-e of rhyolite wliich sjians a narrow g-ulch through which runs a tributary to the main creek. Tliis bridge, which is shown in the illustration (PI. XLVIII), consists of two vertical slabs of lithoidal rhyolite, parts of the contorted layers of lava flow, which stand about vertical in this place. The vertical layers just east of the north end of the bridge are shown in PI. XLIX. They are slightly curved and are separated by open crevices with rough- ened scoriaceous walls. Of' the two slabs forming the bridge the eastern, or that seen in the illustration, is 2 feet thick at its ends and thinner in the middle. There is a space of 2 feet between it and the western slab, which is 4 feet thick. The span of the arch is about 30 feet and its rise about 10 feet, the top of the bridge being some 40 feet above the creek. The eastern slab is traversed by two vertical cracks, and by horizontal ones just below the base of the arch. The rhyolite is porphyritic and lithoidal, dark blue- gray, mottled with light gray, and distinctly banded in places. It bears numerous holloAv spherulites of considerable size and many small lith- ophysse with delicate concentric shells, but no small megascopic dense spherulites. The lithoidal rock alternates with glassy layers of black perlite having dense spherulitic bands and some large dense spherulites (2048 to 2052). The large hollow spherulites have been crushed while the matrix was plastic, though not liquid, for the broken shells have been dislocated and the sides of the spherulite forced in and the cavity partly tilled by the matrix. But this was not liquid enough to enter very far into the hollow cavity, nor has it filled up the cracks on the outside of the shells. It is evident that there was miition in the lava after the large hollow spherulites had formed, and that they were rigid crystalline bodies. It is quite as evident that the delicate lithopliyste of various sizes Avere not formed before the lava came to rest, because they have not been crushed in any case, although their shells are often much thinner than those of the hollow spherulites. Moreover, their eccentric and irregular shapes are more or less in accord with the crooked and distorted banding which marks the planes of flow in the rock. They Ivdve the same character as tliose at Obsidian Clitf and are highly crystalline; but the fayalites have been changed to light-yellow opaque pseudomorphs, and the iron has been NATURAL BRIDGE, EAST SIDE OF YELLOWSTONE LAKE. U. 8. GEOLOGICAL SURVEY MONOORAPH XXXII PARI II ri. XLIX VERTICAL PLATES OF RHYOLITE, NATURAL BRIDGE RHYOLITE OF ELEPHANT BACK. 387 concentrated to stout tablets of hematite, with brilHaut crystal faces, some of them set upon the fayalite ))seu(lomorplis, and of later ()rii)in. In some of the lithoi)hysa» hematite occurs without pseudomorphs of fayalite. The Natural Bridge is one of the best localities for the study of these hollow fonns of crystallization. NORTH AND EAST OF YELLOWSTONE LAKE. The spur of the plateau lying west of the outlet of Yellowstone Lake, and known as the Elephant Back, is ribbed and grooved b}' numerous drainage channels that cut deep gulches down its slopes and permit the nature of the mass of lava forming it to be observed. The surface of the slopes and the top of the plateau consist for the most part of glassy forms of rhj^olite, strongly porphyritic. Black obsidian, passing into red pumiceous breccia like that south of Bridge Creek, is the prevailing rock, with occa- sional areas of lithoidal rhyolite. The obsidian is markedly banded with parallelly oriented feldspars and layers of spherulites, some of them red, porous, and distinctly fibrous, with white pellets of tridymite, the feldspar fibers radiating trom the center of the spherulite, though often separated from it by an open space (2066, 2068). But as the drainage channels are followed from the top of the plateau downward the glassy forms become less abundant, and in the deeper gulches the whole mass of the rock is lithoidal and well banded (2067). This relationship between the lithoidal and the glassy forms of rhyolite is the usual one for the large flows; the upper surface is glassy and more or less pumiceous, the lower part of the mass is lithoidal, and the bottom of the flow, when exposed, is glassy for a variable thickness in many cases, but not in all. Along the Yellowstone River 3 miles below the outlet of the lake, about opposite the mouth of Thistle Creek, the rhyolite is lithoidal and purplish gray, not noticeabl)^ banded, and full of phenocrysts, of which the quartzes are more perfectly crystallized than in the greater number of cases noticed. This characteristic becomes more pronounced in the vesicular brecciated rhyolite which forms a massive exposin-e about 2 miles below the head of Thistle Creek. In this rock well-developed double pyramids of quartz, with smooth crystal faces, project into the cavities of the rock and from broken surfaces. The saiaidine is iridescent in blue and some- times in more brilliant prismatic colors. Farther iip the creek the rhyolite 388 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, is dense and dark colored. But on the summit of the peak, 9,000 feet high, at the head of the creek, it is light pink and gi'ay, earthy in texture, and brecciated like a tutf, with fragments of andesites, and with phenocrysts like the vesicular brecciated rock lower down the creek. There is no evidence, however, that it is a tuff, but it appears to be a finely brecciated massive rock, of the same kind as the rhyolite opposite the mouth of Thistle Creek, except that the latter is denser and not brecciated (2059 to 2064). Along the east shore of Yellowstone Lake the rhyolite extends from the vicinity of Pelican Creek on the north as far south as Brimstone Basin, a small area of hot springs 2 miles south of Columbine Creek. It forms a sheet of lava which constitutes the table-land and flat-topped spurs between the lake and the Absaroka Mountains, reaching an elevation of about 8,500 feet. Tongues of it extend up the long valleys and are found at still higher altitudes. In the valley of Sylvan Lake it forms a massive bluflp on the north side, which reaches 8,700 to 8,800 feet elevation. This is several hundred feet higher than the divide in Sylvan Pass; still it has not been found east of the watershed in the valleys draining into the Stinkingwater River. In the next valley north of that of Clear Creek the rhyolite sheet is found at 9,000 feet. The rock throughout the greater part of this area is massive, lithoidal, purplish, and porphja-itic. The glassy and pumiceous parts which probably formed its sui-face have been eroded away. VICINITY OF YELLOWSTONE RIVER. The surface of Central Plateau, which extends from the Elephant Back west to the head of Nez Percti Creek, and around the west end of Hayden Valley northward, is covered, like the countiy south, with glassy rhyolite. It is mostly porphyritic black obsidian, more or less spherulitic, and is in places vesicular. On the south branch of Alum Creek, a short distance from the road, the obsidian is spherulitic and carries lithophyspe and hollow spherulites from 1 to 6 inches in diameter (2072, 2073). The obsidian in jjlaces is traversed by jointing planes, along which the surface of the rock is smooth and polished, but slightly uneven and warped. The crystals of quartz and feldspar have been cut across smoothly in most instances, though in many cases the plane of jointing has curved around the end of a crystal, or followed the cleavage of the feldspar when this was nearly coincident with the plane of jointing. A small elevation and depression extends for CENTRAL PLATEAU. 339 a short distance i'rom each of the larger crystals, all being parallel and pointed in one direction. They appear as though they had resulted from the resistance offered by the jjlienocrysts to a slieariug stress. The hill south of the hot springs east of j\Iarys Lake is formed of porphja-itic perlite, full of small hollow spherulites and lithophysa^, which have been partly altered by the action of heated vapors, which come up throuo-h it and deposit crystals of sulphur. The phenocrysts of feldspar and the spheru- lites are much decomposed, the quartzes and grouudmass remaining unal- tered. The hollow spheruHtes are partly filled with opal, and less often with sulphur (2070). The top of the plateau from the north side of Hayden Valley to Gib- bon River and Grebe Lake is covered with porphyritic glassy rhyolite or obsidian, in places spherulitie. This is the character of the rock along the road from the Yellowstone Falls to the valley of the Gibbon, and along the west bank of Yellowstone River from Alum Creek to Cascade Creek. At the north side of the mouth of Otter Creek there is much silver-ora^^ pumice, which is beautifully fibrous, exhibiting a satin-like sheen Avhen the light is reflected from the sides of the fibers, but appearing dark gray and vitreous on transverse surfaces. It is filled with phenocrysts (2084 to 2089). A somewhat similar pumice, or more correctly, a highl}^ vesicular porphy- ritic perlite, occurs in a small gulch west of the Upper Falls of the Yellow- stone. It forms a loosely adliering breccia of pumice and perlite. Some masses of perlite are quite dense, with only small vesicles, but most of it is greatly inflated, Avith flattened cavities. In places the perlitic structure is not complete, lea^-ing kernels of iiTegularly sliaped obsidian, which weather out and cover the ground with black sand (2080 to 20S3). In the meadow of Cascade Creek south of Dunraven Peak the rhyolite exposed in the creek bed is finely vesicular lithoidal rhyolite, purplish gray, with many phenocrysts of plagioclase and fewer of sauidine and quartz (2092, 2093). The rock closely resembles that which forms the bluff at the southeast comer of Geyser Meadow and also the rock of the Upper Geyser Basin. VICINITY OF THE GRAND CANYON OF THE YELLOWSTONE. Since the topographic and scenic features of the Grand Canyon, and the character and condition of the rocks forming it, are described in detail by Mr. Arnold Hague in Part I of this monograph, it is not necessary 390 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. to repeat any of the petrograpliical description of the rhyoHte in this, its most notable, exposure. There is, however, an occurrence of cokimnar cracking in an inconspicuous locality which is of considerable petrological interest on account of its bearing on the general question of the production of jirismatic parting, and which may properly find a place in this chapter. The fine columnar parting on the east side of the canyon north of Agate Creek are described in Part I. Here the columns are 80 feet long and several feet in diameter. But the prismatic cracking to be described occurs in a small gulch on the west wall of the canyon a mile south of Deep Creek. The rhyolite forming the upper part of the plateau at this place is lithoidal and porphyritic, light purplish gray, with a rough fracture. It is jointed in broad blocks which weather into rough granite- like masses. This passes downward into more distinctly columnar, denser rhyolite, which is exposed on the south side of the gulch in a beautifully columnar cliff 300 feet high. The vertical columns are so regular in shape that they may be easily mistaken at a little distance for basaltic ones. On the north side of the gulch thei'e is a ledge of columnar basalt 100 feet thick resting upon gravel and andesitic breccia. Immediately overly- ing the basalt is the bottom contact of a younger flow of rhyolite. The lowest portion is tuffaceous and yellow, passing i;pward into denser material, and this into dark-gray, brownish, porphyritic glass, which has cracked in thin, straight prisms, some quadrangular, others irregularly shaped. The prisms vary in size from 4 to 8 inches long and from one-third to three- fourths of an inch thick, and thicker. This glass grades into lithoidal purplish rock, which is also cracked into small prisms and columns. Some of these are 3 or 4 feet long and 4 inches thick; others are very small, about 6 inches long, and irregularly shaped, like prisms of starch. They are more or less curved, and occur grouped together in the form of large blocks, whose relation to the original form of the whole mass was not made out. They appear to have resulted from a shrinkage within these blocks. The jointing planes which constitute the faces of these prisms or columns intersect the many porphyritical crystals of quartz and feldspar, producing smooth faces, which show that the groundmass of the rock was rigid Avhen the. cracking took place. The small columns, in their shape and arrange- ment, are precisely like those formed in dried starch. RIIYOLITR NEAR THE LAMAK RIVER. , 391 NORTHEASTERN CORNER OF YELLOWSTONE PARK. Toward the northeast the rliyolite sheet thins out and overhes the andesitie and okler rocks, which had previously been , 12 (C) X 12 (D) % 12 PHOTOMICROGRAPHS OF SPHERULITIC STRUCTURES THE HetlOTYPE PRINTING CO., BOSTON BUANCniNG FELDSPAR MIGR0L1TE8. 415 developed than tliu (»tlior.s. In scime cases the sections are twinned parallel to the broad plane. In the rhombic sections the extinction is diagonal and no twinning is noticeable. The long prisms »>r needles are twinned in nearly all instances, the composition plane being parallel to the length of the prism. The direction of vibration of the fastest ray is nearly parallel to the direction of the length of the prisms, proving them to be elongated parallel to the clinoaxis. The twinning is after the Manebach law; and the cross sections show that the crystals have a clinodome with basal plane and possibly with clinopinacoids. These crystals branch ont in two different ways. In some cases they appear to split, the parts being slightly inclined to one another at first, and becoming more divergent farther on. This is shown in the right-hand half of PI. LIII, fig. 2. Both parts are twinned in the same manner and have the same optical orientation — that is, each is a prism parallel to the clino- axis. By this method a succession of branchings takes place, the prisms becoming more and more numerous and thinner, often terminating in a spherical surface, the aggregation in thin section resembling a rounded bush of branching stems, especially when the prisms terminate in broad leaf-like fronds, which often happens (PI. LIV, fig. 3). In other cases the branching of the long, twinned prisms is seen to obey a cr}'stallographic law. Short prisms project from opposite sides of the Manebach twin at an angle corresponding to that between the vertical axis and clinoaxis, about 64° (left-hand half of PI. LIII, fig. 2). These branches are prisms parallel to the vertical cr3'stallographic axis. They are sometimes loug and slender, and are curved to a position parallel to that of the prism or stem from which they branch; in such cases the bundle of feldspar needles will consist of numerous prisms elongated parallel to the vertical axis, and a central one elongated parallel to the clinoaxis. The optical orientation of prisms parallel to the vertical axis will differ according as the plane of the optic axes lies in the plane of symmetry or is at right angles to it. In the first case the direction of vibration of the slowest ray will always make a small angle with the axis of the prism, or be parallel to it. In the second case the speed of transmission of the ray vibrating in the direction of the prism axis will sometimes be less and at other times greater than that of the ray vibrating at right angles to it, according to which side it is ^dewed from. Closely allied to these gi-owths and associated with them are delicate rays 416 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. or needles of feldspar which are composed of minute stout prisms attached to one another end to end, in parallel position, producing a rude microscopic rod with uneven sides. These jirisms are elongated jmrallel to the vertical axis, and for the reason just given are optically sometimes negative and sometimes positive, or they may all be positive. They form branching arborescent growths, and constitute rays of spherulites, usually of consid- erable size. A phase of this kind of spherulitic growth is shown in PI. LVI, fig. 3. Between the feldspar rays there are minute grains of tridy- mite, which are often clustered in small spherical pellets with cavities between them. Such spherulites are porous. In the more coarsely crys- talline spherulites, with large cavities, the same kind of feldspar crystals may be seen with a low magnifying power. Both kinds of feldspar prisms often occur in the same spherulite. Some spherulites are composed of a dense, micrographic spherulite at the center, which passes outward into the branching variety, Avhicli may be porous to a greater or less degree, the free silica being in the form of tridymite. In some areas of the tridymite grains between comparatively coarse prisms of feldspar (PL LVI, fig. 2) there are crude spherulitic aggre- gations of tridymite, probably composed of interpenetrating tablets. LITHOPHYS^E. The microstructure of the lithophysse can not be studied so easily as that of the more compact spherulites, because of the slight coherence of the crystals composing them and the difficulty of preparing thin sections. But in many cases the component crystals are large enough to be seen with a pocket lens, and their character and arrangement can be made out. It is evident in the case of hollow or gaping porous spherulites, which are one phase of lithophysse, that the mass consists of short prisms of orthoclase or sanidine attached to one another end to end, in a manner already described for some spherulites. These jointed rods of feldspar radiate from what was the center of the spherulite, the gaping appearing to have taken place after their crystallization. With them are associated tridymite, quartz, and fayalite. When there is no marked banding in the surrounding rock mass, the hollow spherulite may have the form represented in cross section in PI. LVII, fig. 1. When pronounced banding is present in the groundmass. LITIIOPIIYS.E. 417 it often truversos tlie hollow splierulite aiul the fj-apiiiy or spaces are between the layers, as in fig-. 2. In lithophysjy proper there are eoneentric shells of (-rA-stals and con- centric spaces between them, as in fig. 3 of the same plate. The mimxte feldspar prisms in the shell stand radially with respect to the center of the litho{)hys3e; the other minerals have no definite arrangement. Often the tridymite occurs in minute pellets, dotting the shells. The concentric shells correspond to the concentric l)ands of coloi- and of varying composition which characterize certain solid spherulites. They probably result from a pulsation in the act of crystallization, such as has been observed in the growth of crystals and spherulites of artificial salts when the latter grow very rapidly. It is due to the lowering of the saturation of the surrounding mother liquor, caused by the sudden liberation of heat in the act of crystalli- zation, and to the rapid extraction of crystallizing molecules. The spasmodic advance of the crystallization appears to have produced layers that were more coherent than others, and the latter became the open spaces upon the shrinkage of the partly crystallized magma before its final crystallization. The position of the quartz, tridymite, and fayalite upon the surface of these shells in some cases indicates that they formed after the spaces did. When the groundmass is markedly banded the lithophysfe are often modified, as in fig. 4 of PI. LVII. Similar structures occur in hemispherical lithophysfe, as shown in figs. 5 and 6. The presence of these cross walls proves that the shells are not the result of expanding gas bubbles, but must have been formed by the contraction of the magma within the boundary of the litho- physa at the time of its formation. In a very few cases there appear to be evidences of a slight expansion, which is shown in the arching of the layers of the groundmass over the lithophysa, as in fig. 7. But it is quite possible that the cur\'ing of the layers may have antedated the formation of the lithophysa, and have led to its formation. When we consider that the known condensation of mass in the passage of anhydi'ous glasses of ortho- clase and quartz into the crystal form is about 10 per cent in the first case and 16 per cent in the second, and when we remember that hydrous glasses possess still greater volume than the anhydrous ones, we are prepared to understand the comparatively large cavities which often occur in these forms of rapid crystallization. In the case of the dense spherulites, we must assume that the condensation was more gradual, though rapid, and MON XXXn, PT II 27 418 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. was uniformly toward a center, the surrounding magma closing in about the growing crystals, which must always happen in the case of phenocrysts, though generally by inappreciable stages, owing to the comparative slowness of their growth. The r)rigiu of lithophysa' must be due to the more abundant presence of water vapor in spots in the magma, the greater viscosity of the sur- rounding magma and its generally viscous condition, the very rapid crystallization of jointed rods of feldspar and attendant condensation, fol- lowed by the further condensation of the remainder of the mass upon the crystallization of the silica, which must have taken place in the presence of highly heated water vapor. The minerals produced are like those crystallized artificially in closed tubes in the presence of highly heated water vapor.^ In certain cases the spherulitic growths appear to be little more than incipient crystallizations, although the spherulites may be megascopic. They are only faintly doubly refracting, and probably consist of extremely minute fibers. Where such spherulites occur in colored banded glass the irregularly twisted bands pass through the brownish- gray spherulites with- out interruption, but their bright colors are changed to brown, with the formation of opaque grains (PI. L, fig. 4). Within such spherulites in some cases there are delicate branching trichitic needles, radiating from the center, which are probably augitic, besides other delicate curved needles with high index of refraction and strong double refraction, whose character was not made out. In some forms of rhyolite the appeai'ance of welded glass fragments or veil structiire is retained, although the mass is faintly doubly refracting and mav be spherulitic in part, incipient spherulitic needles traversing the rock in various directions without regard to the former lines of flow, which are marked by opaque dustlike pai-ticles. In these cases it is evident that the spherulitic crystallization took place after the molten mass had come to rest. ' Friedel and Sarasin, Bull. Soc. miiK^ialogie, 1879, vol. 2, p. 1158; ibid., 1880, vol. 3, p. 171; Comptes rendns Acad, sci., Paris, 1881, vol. 92, p. 1374; ibid., 1883, vol. 97, pp. 290-294. K. von ChrustBchoff, Am. Chemist, 1883; Tschermaku mineral. Mittheil., vol. 4, p. 536. Stanislas Meunier, Comptes rendus Acad, sci., Paris, vol. 93, 1881, p. 737. De Haldat, Anuales chimie, vol. 46, p. 70; Neues .Tahrbuch fiir Mineral., 1833, p. 680. A. Daubree, fitudes syuthetiques, etc., Paris, 1879, pp. 154-179. For a historical review of the theories regarding the fbriiiatiou of lithophysir, scr page 287 of the author's paper on Obsidian Cliif, in the Seventh Annual Report of the U. S. Geological Survey. AXIOLITIC EHYOLITE. 419 Tn rcrtain kinds of rlivolito, apparoiitly composed of welded glass fraji'ineiits, tliere is a iiiicrosplu'rulitic gmwth wliicli l)ears a definite relation to the form of the supposed glass fragments. The feldspar fibers are in groups, which are approximatel}' normal to the outline of the fragments, and radiate inward. Where the fragment had a rudely triangular shajje the central part often attained a greater degree of crystallization than the margin, ;uid sometimes consists of distinct crystals of feldspar with tridymite or (juartz and a small amount of ferromagnesian mineral. Where the fragments were long and narrow the si)herulitic growth from the sides inward produced the effect of parallel fi'inges — "axiolites" of Zii-kel. This tendenc'S' to develop spherulitic growths from old suifaces or cracks is shown in another modification of the rock in which the axiolitic structure can be seen megascopically. In hand specimens these varieties appear to be dark lithoidal or glassy rocks, traversed in all directions by narrow spherulitic bands. In the glassy forms of the rock the black glass inclosed by the lithoidal bands occasional!}- falls out, like a kernel from a shell, proving the spherulitic portion to be a growth along intersecting planes. In thin section it is observed that the spherulitic bands have a dark line along their centers, as though the}' were ancient cracks. They inter- sect one another in some cases, but are not persistent in others. Their behavior toward phenocrysts when present is the same as that of perlitic cracks. They encircle them, but never traverse them (PI. LV, fig. 4). They do not often occur in as many concentric circles as ordinary perlitic cracking, but they are unquestionably of the same general character, namely, the cracking- of an amorphous glassy substance. The spherulitic crystallization is subsequent to the cracking and is located along the cracks. It is like other forms of spherulitic growths in these glasses, and is evidenth' only a special case. In one instance similar spherulitic growth had formetl about the edge of an open crack in such a manner as to show that the magma had been so viscous jjrevious to its last movement that a small gap in it was not closed. Upon its walk pellets of tridymite formed. It nmst have been after it had reached this highl}- viscous state that this jjarticular spherulitic crystallization took ])lace. In cases where perlitic glasses contain spherulites it is observed that the perlitic cracks encircle spheralites in the same manner as they encircle phenocrysts, and do not traverse them. The perlitic cracking is subsequent to the spherulitic crystallization and is 420 GEOLOGY OF THE YELLOWSTONE I^ATIONAL PAEK. confined to the glassy grouudmass. In the . rather uncommon occurrences just noted, where a crackmg has been followed by crystallization, it is probable that the shrinkage and cracking took place in a highly heated, stiff mass, which was sxibsequently welded together, as the collapsed pumice may have been — that is, it may have been surrounded by a hotter portion of the same lava flow and its temperature may have been raised to some extent. Instances of this kind of structure are found on the continental divide south of Madison Lake and on the summit of the west wall of Bechler Canyon, 5 miles from its mouth (1945, 1946), and also in the vicinity of the Lower Geyser Basin. From the foregoing it appears that certain forms of crystallization which unquestionably take place in molten magmas at or near their point of solidification, and which niaj' be classed as pyrogenous and primary, may take place in a mass at a time subsequent to the development of fea- tures which seem to be dependent upon a certain amount of rigidity of the magma, such as the formation of cracks. Such rigidity is generally supposed to indicate perfect solidification and completed pyrogenous crystallization; and undoubtedly it does in most cases. But rigidity has a relative significance, and what is rigid with respect to a force acting through an extremely short period of time may be plastic toward the same force acting through longer time. Hence a highly viscous magma may be torn to fragments by an explosion, or be highly inflated by the sudden expansion of vapor, and in some cases be still viscous. Generally, however, the sudden expansion and escape of inclosed vapors tend to lower the tem- perature of the magma and increase its viscosity. But it may not necessa- rily be solid or rigid. Similarly, shrinkage cracks may be produced in a '/iscous mass by sudden contraction before the mass has solidified and while it is still highly heated, the fracturing being due to the rapidity of change of volume, and not necessarily to the absolute amount of contraction. Such sudden contraction of imsolidified lavas is not of common occurrence, it would seem, but the instances of postperlitic spherulitic crystallization just described indicate its occasional occurrence. In the massive glasses which are striped and marked with bands of various color it is sometimes noticed that lines of color traverse the mass like ancient fractures which closed up before the solidification of the mass. They pass across the lines of flow, which sometimes end abruptly against INTEKSFHEKULITIC CRYSTALLIZATION. 421 these lines, appearing as tliougli faulted and displaced to a slight extent. In many instances the arrangement of the streaks of color is such as to indicate that the compact mass was once an aggregate of fragments of similar magma, the lines of flow having various orientations in the different fragments. They have been welded into one contiiuious homogeneous mass. In those varieties of rhyolite in which the first kind of spherulites are developed — namely, the compact ones which are closely related to micrographic intergrowths — there are irregularly shaped areas bet^^'eeu bands and clusters of mici'oscopie spherulites which exhibit a different sort of crystallization. They are more highly crystalline — that is, the size of the individual crystals is larger. The spherixlites bordering these areas generally terminate in distinct prisms oi orthoclase, which have already been described, while isolated crystals of orthoclase of similar habit and size lie in various positions within the more crystalline area. The cement to these crystals in some instaiaces is trid}'mite, in minute grains or in well- developed twinned crystals with characteristic wedge-shaped cross section. In other cases the quartz forms the cement, and is wholly allotriomorphic, producing a micropoikilitic structure (PI. LIV, fig. 4). In places some of the feldspar prisms are nearly parallel to one another, so that the interstitial quartz appears in the shape of thin strips or needles, which is misleading, producing the effect of idiomorphic crystals. This quartz is unquestion- ably of igneous or of aqueo-igneous origin, occupying the same relation to the orthoclase as does the tridymite in the other cases, the development of one or the other depending on very slight differences of 23hysical condi- tion, as demonstrated by experiment. In some experiments both forms have been produced together. Often the tridymite is accompanied by gas cavities of variable dimensions. With the orthoclase and quartz oi- tridy- mite are some magnetite and small amounts of ferromagnesian minerals. The latter differ in character in different occuiTcnces, and may be faj^alite, mica, or tourmaline, and in rare instances possibly garnet. The fayalite forms comparatively large individuals, allotriomorphic with respect to the feldspar, sometimes with an opaque border, which raaj- entirel}' replace the original individual. Tourmaline and mica are found in minute crystals about 0.025 mm. long and 0.01 mm. thick. They are abundant in places, or lie scattered through the tridymite and quartz, and also in the margin of the bordering 422 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. splienilites. Sometimes they occm- together, but usually independently. The tourmaline is recognized by its strong absorption and by its other optical properties. Its color is brownish green to colorless. The mica is green, and also yellowish brown to reddish. The green mica is easily confounded with the toiu-maline, but may be distinguished by the direction of the absorption. The tourmaline and mica are idiomor})hic, and must have crystallized just before the outer jiortion of the small spherulites did, and also before the tridymite and quartz in which they lie. They are con- fined to the region of these interspherulitic spaces and are not found scattered indiscriminately through the spherulites. A mineral which is probably garnet occurs in ' the same manner as tounnaline and mica, and forms irregular graiias, which are colorless and isotropic and have a high index of refraction. Occasionally the more coarsely crystallized quartz and feldspar in the interspherulitic spaces are traversed by opaque material segregated in curved layers, suggesting the structure of Eozoon. In PI. LV, fig. 2, these streaks appear to be continuations of the lines of trichites that traverse the spherulites and originally marked the flow planes in the lava. They have been displaced by the crystallization of the larger crj^stals of feldsijar and quartz. In the banded lithoidal rhyolite the layers, often microscopic in size, consist of minute spherulites alternating with various modifications of the crystallizations just described. These are really holocrystalline, with gas cavities, a phase of miarolitic structure. The size of the cavities is some- times consideralile, and may be observed megascopically, giving rise to planes of weakness in the rock along which it splits. The microspherulitic layers may also grade into glassy layers, so that holocrystalline and glassy layers alternate with one another in some modifications of rhyolite, notably in certahi parts of Ob.sidian Cliff. This is illustrated in PI. LVI, fig. 4, representing a section across laminated lithoidite. Microspherulitic layers alternate with layers containing comparatively large feldspar crystals with quartz and tridymite. In one layer the coloring matter is segregated in streaks, like ribs. MICROGRASrUIiAR STRUCTURE. While the glassy and spherulitic structures are those most commonly found in the rhyolites of the Yellowstone Park, several modifications of U. S. QEOLOGICAL SURVEY MONOGRAPH XXXII PART II PL. LVI (A) X 13 (B) I 20 (C) I 12 ( D) X 12 PHOTOMICROGRAPHS OF SPHERULITIC STRUCTURES AND FELDSPAR MICROLITES THE MELIOTYPE PRINTING CO.. BOSTON U. 8. OEOLOQICAL SURVEY MONOORAPH XXXII PART II PL. LVtl ^' ris^rvv?iJ,5^?^^K?^yT"'\^^ Ni,SX^\\\.);s\ss\\\\X\\\\\\\\\\X-^Tains nre so minute as not to be distinctly discernible. In some cases this structure accompanies a distinct How structure which is marked by opaque grains. In others no flow structure is noticealjle. It appears to be a primary crystallization in many cases, even where a flow stnicture is observed, when it must have been a crystallization accompany- ing the final solidification of the rock. But it is undoubtedly secondaiy in some instances, which are not of frequent occurrence among the extremely little altered rhyolites of the Yellowstone Park. RELATIONS OF THE VARIOUS MICROSTRUCTURES TO ONE ANOTHER IN THE ROCK MASS. The various microstructures which have been described in detail in a systematic manner occur together in quite diff'erent combinations. Pumice is found associated with dense glass, and grading into it. Usually the surface of a flow is pumiceous, as at Obsidian Clifi", but the easily abraded pumice has undoubtedly been carried away by glaciation in most places. It is not, however, a necessary accompaniment of obsidian flows, as is shown by such lava streams in the island of Lipari. It was probably more frequent in the Yellowstone region. Pumiceous and compact glass is often intermingled over the surface of the plateaus. The dense glass is usually microlitic and often spherulitic, but in no ease has pumice been found to contain spherulites. They occur in vesicular obsidian. The various kinds of microlitic glass may be found in close association with one another, and all the diff'erent forms of incipient crystallization and spherulitic aggregation may be found in a single specimen of rock, even in one thin section. It oftener happens that a particular form of spherulitic growth prevails throughout a considerable mass of rock. But in such occurrences as the rhyolitic flow at Obsidian Cliff there are parts of the mass in which there is great variability in the microstructure within short distances. In a great many localities it is clearly seen that the thick flows of rhyolitic lava were pumiceous and glassy at the top and glassy for some distance downward, usually with megascopic spherulites. They then became lithoidal by the development of microspherulitic structure, as in the lithoidite at Obsidian Cliff". The microcrystalline to microcryptocrystalline 424 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. modifications exist in some cases near the bottom of the lava sheet, but no definite mode of occurrence has been made out. In places the bottom part of the flow is glassy and dense ; in places it rests on a bed of pumiceous tuff and is lithoidal; that overlying the rhyolitic tuff on Mount Everts is microcrystalline (1762). The indurated tuff, indistinguishable from the overlying massive lava, exhibits a fragmentary glass structure, with some axiolites, and occasional spherulitic structure independent of the outline of the fragments, while parts of the mass are isotropic. LAlMIlSrATION AND BANDING. Lamination and banding are highly developed in the lithoidal portion of the rhyolitic flow at Obsidian Cliff. They are very generally present in a higher or lower degree in all the rhyolites of the Park. In fact they form one of the commonest characteristics of acid lavas, and are equally uncommon among the basic ones. They are clearly due to the spreading out through flowage of a more or less heterogeneous caseous fluid. Homo- geneous portions of the mass, of whatever shape, will spread out and flatten during the flow of the whole body of lava, becoming thin lenticular layers if the spreading or flow is sufficiently extended. A mass consisting of por- tions which differed from one another in color or composition would become, after spreading out upon the surface of the earth, a body made up of layers of different color or composition, which Avould wedge out in thin edo-es between one another. A cross section of such a body would exhibit a more or less streaked, banded, or laminated structure according to the original size of the different portions and to the extent of the spreading. In the case of the lithoidite at Obsidian Cliff, it can be shown that the cause of the differences in the layers was unquestionably the different amounts of water vapor present in them. For in the lithoidite the layers differ in their degree of crystallization, some being glassy, others microspherulitic, others more coarsely so and porous, while others are microgranular with larger cavities. Some layers have locally developed crystallization in the form of large spherulites and lithophysse. In the obsidian the differences consist in layers of spherulites, large and small, in bands of lithophysse, and in layers abounding in micrographic feldspars, microscopic spherulites, microlites, and trichites — that is, in the different phases of crystallization. Near the surface of the lava flow the laminated LAMINATION OF RHYOLITES. 425 condition of the rock sliows itself in layers of compact <)lass full of micro- lites wliicli alternate with layers full of gas cavities and with little or no microlites. And in the highly pumiceous part of the flow it is seen that the inflation of the glass is more marked in some layei's, while there are spots in which the inflaticm is specially pronounced. These differences in the pumiceous parts of the rock are due to variable amounts of water vapor in the layers of the lava; and similar differences must have existed in lo'\\'er parts of the same lava sheet. Moreover, the kinds of minerals crystallized are those whose formation is known to be aided by the pres- ence of water vapor and other vapors. Further, the localization of more abundant water vapor, which gave rise to specially inflated spots in the pumice, is undoubtedly the cause of the crystallization of isolated spheru- lites in the compact glass. The greater frequency of lamination and localized crystallization in acid lavas as compared with basic ones is a conseqvience of the generally greater viscosity of acid lavas at the time of their eruption. The basic rocks have a considerably lower melting point and are much more liquid up to very near the temperature of solidification. Hence diffusion would take place more rapidly and the magma would be more homogeneous, other things being equal. The heterogeneity of the acid lavas, so far as known, is confined to the distribution of vapors, presumably of water, and suggests that the water thus irregularl}- disseminated has not existed within the magma long enough to become uniformly diffused. It must therefore be looked upon as water absorbed near the earth's surface. Whether there may also have existed water vapor in the magma having a much longer connection with it, is more difficult to demonstrate, though it is highly probable. 426 GEOLOGY OF THE YELLOWSTOISTE Is'ATIONAL PARK. I Si IS ® CO o o IM •^ y^ , ' ^ ^ H "*~ '*~ (r> =x> Ifi (TJ lO 05 lO X CO lO no CO c- rH o 1-1 CO o C5 in o -# N ac crs Oi 00 o o CO o r-t o o o o 03 C5 o o O rr. Oi o o o (35 o 8 c o o o OS C5 o G o ffl o o 1-H »-r rH iH rH •"• rH 1-t rH § o m CO 1-1 lO Ir- ^ CO Ol CO 01 Ol CO ^H m cr CO CO m t- -^ ^ T-H i^ m CO CO X ^ CO 00 cc CO '-< ^ -^ M i t~ : 1- 1 CS J 03 Ol N 00 d" w < CO c^ • I c^ ■ !M ■^ CO OJ ai o ; ; : ■ ■ ■ d o § 6 a5 t^ QO © © -* a © <6 a 2 2 © n © a © a (k i^ o o o o o H '^ jH !zi H !zi a 12; a '/r, iHi o o ;2; o 1 (N • (M e CD rH o i 1 1 i ; O ; O H O o O 1-1 lO CO ip ^ Cl (M on IM cq CO t^ lO eo CCl er CO Ifi 05 71 CD -1" UO X CO C^ o CO i-H X CO •^ t~ Oi 1 M C^l IC -^ C^ CO ■^ "^ CO tM in « -# CO -^ iq eo CO ^ co' 1 o m CO 00 C^ CO CO 00 or o CO- y-i CO 1 S ^ 1-1 Ol (N ■^ IM er in t- in CO (M ITS o -^ Tj •^ 1—1 CO w r^ Cl eo iH CM tH »H fH rH -H - o CM in cr lO ^ O I^ r— r^ C^ rN r^ ^_, lO ^^ r^ (- 00 o cc c; Cl X -r ^ t-~ c^ o o rH C^I e^ » <1 in 1-* 1-1 in CO iH Jh OJ — CO CO Ol CO rH M -^ o CO CD t- c^ t^ t- c- t- t- t- c^ c- t- t^ , -u u \ * u ^ >^ * ; ; ; i a □ o ' rl ' o ^ ' 1 ^ r a ■? * 3 O ©' ■ CD © o X •a '« c:) ce !9 s a 2 C -a o : ;s^ »!^ .^ O O) _j O © a - O 1 1 ^ « 4A c o CD 5 S O S s CO © 60 12 s ■ CO CJ © a O o 9 I 'x o o s C © 3 o 1 .a O a 3 0 o 8 o *n a — ^ M ^H c t» 4: r- Ol Ch CO cc ^ O = 5 Ol cc I' X CO CO ira c tH 1— 1 O »-i CIO IN J CO w c- iH !N Observations. — Tliis spccies from the Upper Cambrian may be compared with the Middle Cambrian 0. (L.) ferrugineus of the Atlantic Basin fauna. Compared with the Rocky Mountain species it is intermediate between 0. (i.) manticiilus and 0. (L.) rotundatus. It may also be compared with 0. (i.) granvillensis of eastern New York, upper Olenellus fauna. What appears to be an identical species also occurs in the upper beds of the Secret Canyon shale just beneath the Hambm-g limestone, 1,200 feet lower in the Eureka district Cambrian section. 446 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Formation and locality: Upper Cambrian, Gallatin limestone, Crow- foot section, Grallatin Range, Yellowstone National Park; Hamburg shale near Hamburg mine, Eureka district, Nevada. A variety also occurs in the Secret Canyon shale 1,200 feet below the Hamburg shale. DICELLOMUS Hall. Dicellomus Hall, 1873 : Twenty- third Ann. Kept. New York State Cab. Nat. Hist., p. 246. Obolella Hall, 1892: Pal. New York, Vol. VIII, Pt. I, p. 72. When proposing that the genus Dicellomus include Obolella polita, Pro- fessor Hall stated that the grooving or emargination ot the apices of both valves and the thickening of the edges of the shell on each side below the apex, together with the form and character of the muscular impressions, would separate the species from Obolella. Again, in 1892, Messrs. Hall and Clarke gave a fuller description of Dicellomus politus, but owing to the poor character of the material, he did not feel confident that it should be recog- nized as generically distinct from Obolella chromatica. Material now in the collections of the Greological Survey clearly shows that Professor Hall's provisional conclusion was correct, and that Dicellomus ])olitus is generically distinct from Obolella chromatica. The generic characters are also finely shown by specimens of Dicellomus nana (M. and H.) from the Little Rocky Mountains of Montana, and also by the interior of the ventral valve, figured by Meek and Hayden. The cast of the interior of the ventral valve is shown by fig. 3c, PI. LX, and the interior of the ventral valve from the Black Hills by fig. M, PI. LX. These will be found to differ from the illustrations of Obolella polita given by Professor Hall,' but the material fx'om which the figures were drawn was poor, and, to a certain extent, the drawings are somewhat constructive, as stated by Professor Hall.^ From the specimens before me, as shown by figs. 4, 4a, PI. LX, it is clear that Dicellomus politus and D. nanus are congeneric. Further illustrations of the characters of D. politus will be given in a review of the Cambrian Brachiopoda. 1 Sixteenth Ann. Rept. New York State Cab. Nat. Hist., 1863, PI. VI, figs. 20, 21. »Pal. New York, Vol. VIII, PI. I, p. 72. GAM BRIAN FOSSILS. 447 DiCELLOMus NANUS M. and H. sp. PI. LX, figs. ,3, 3a-d. Obolella nana Meek and Hayden, 1861 : Proc. Acad. Nat. Sci. Philadelphia, 2d series, Vol. V, i>. 435. T?illings, 18G2: Paleozoic Fossils, Vol. I, p. 07. Hayden, 1863: Am. Jour. Sci., 2d series. Vol. XXXIII, p. 73. Meek and Hayden, 1864: Pal. Upper Missouri, Pt. I, p. 4, PI. I, figs. 3a-d. Whitfield, 1880 : U. S. Geog. and Geol. Surv. Rocky Mountain Region, p. 340, PI. II, figs. 14-17. Hall and Clarke, 1892: Pal. New York, Vol. VIII, Pt. I, p. 69. Only a single specimen of the outer surface of a ventral valve of this species occurs in the collection. It has the characteristic appearance of the species. The species also occurs in abundance in the Little Rocky Mountains to the north, in Montana, and also to the eastwai'd in the Black Hills. The specimen from the Park is illustrated, and, in addition, the types from the Black Hills and two specimens from the Little Rocky Mountains. Formation and locality: Upper Cambrian, Gallatin limestone (upper portion); Crowfoot section, Gallatin Range, Yellowstone National Park. IPHIDEA Billings. Iphidea sculptilis Meek. PI. LX, figs. 5, 5a-e. Iphidea (??) sculptilis Meek, 1873: Sixth Ann. Rept. U. S. Geol. and Geog. Surv. Terr., for the year 1872, p. 479. Kutorgina minutissima Hall and Whitfield, 1877: U. S. Geol. Expl. 40th Par., Vol. IV, p. 207, PI. I, figs. 11, 12. Kutorgina sculptilis Walcott, 1884: Mon. U. S. Geol. Surv., Vol. VIII, p. 20, PI. I, figs. 7, la-h; PI. IX, fig. 7. In the description of Iphidea (!?) sculptilis, Mr. Meek decided that, as the shell had a very narrow, slightly flattened margin on each side, repre- senting a false area, and as there seemed to be a wide, open, triangular foramen, it could not be referred to the genus Acrotreta or the genus Iphidea. He was not jjositive that there was not a permanent pseudo- deltidium present, but, assuming the absence of that structure, and with the probability that when all the characters of the shell were known it would be found to belong to a different genus, either of the Brachiopoda or of some other group, he would propose for the genus the name " Micromitra." 448 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. A study of the material collected from tlie same horizon at a point not far distant from the original locality shows the presence of a false area and a pseudo-deltidium of the same character as that of Iphidea hella, the type of the genus Iphidea. There is, however, a difference in the two forms that might possibly be considered of subgeneric value. The surface of Iphidea hella is covered with fine concentric strise, while the surface of Iphidea sculptilis is marked by very fine, sharp, elevated, concentric lines that coalesce or bifurcate irregularly, imparting a peculiarly interrupted wavy appearance that is highly characteristic. The variation in the surface character is continued still further in Iphidea piannula White, in which the surface is marked by a very fine network of oblique raised lines that divide it into minute porelike pits, which cause it to resemble under the lens the texture of finely woven cloth. The difference in character of surface between Iphidea p)ammla and /. sculpUUs is the same difference as between the surface characters of Trematis and Lingulella; and the difference in surface characters between the two species mentioned, on the one hand, and Iphidea hella and I. labradorica, on the other hand, is equally important, as the latter have the plain concentric strise and lines of growth that are characteristic of the species, while the former have highly ornamented sur- faces. If we should find the genus on the surface characters of the shell, it would be necessary to place I hella, I. lahradorica, and J. prospectensis under one genus, I. ornatella (Linnarsson) and /. sculptilis under another, and I.pannula and I. cailata under still another. There are, however, specimens of I. pannula on which the outer portions of the shell show the surface characters of J. hella; and more or less complete transitions may be found between the varying types of surface ornamentation. There are too many similarities in form to warrant us in removing I. sculptilis from Iphidea without the evidence of interior markings to prove that it is generically distinct. Formation and locality: Middle Cambrian, Flathead terrane (lowest fossiliferous bed) ; Crowfoot section, Gallatin Range, Yellowstone National Park. It also occurs in the Middle Cambrian shales of Antelope Springs, Utah. CAMBRIAN FOSSILS. 449 Iphidea sp. uiitlet. PI. LX, lif;-. (;. Dorsal valve semicircular, slig-htly convex. Hin^e line somewhat shorter than the width of the shell below; nearly straight, tlie rostral angle about 180°. Beak small, not elevated. Surface ornamentation consists of extremely tine i-adiating and undulating concentric striai that can be seen in detail only with a strong magnifying glass. Shell substance horny. This form is associated with /. scidptilis, and, judging from external characters, is closely related to it. The sui-face ornamentation is of the same character, and, in the absence of the ventral valve, it is difficult to distinguish any specific characters on which to base a new species, although the shell is much larger than that of typical t. sciilpt'tlis. Formation and localitj^: Same as last, for Ipliidea scidptilis. ACROTRETA Kutorga. ACROTRETA GEMMA BilliugS. PI. LXII, figs. 2, 2a-e. Acrotreta gemma Billings, 1865: Pal. Foss., Vol. I, p. 216, figs. 201«-/: Acrotreta subconica Meek, 1873: Sixth Ann. Kept. U. S. Geol. Surv. Terr., p. 463. Acrotreta attenuata Meek, 1S7 3: Ibid., p. 463. Acrotreta pihridicida White, 1874: Geog. and Geol. Expl. Surv. W. 100th Merid.: Prelim. Eept., Invert. Foss., p. 9. White, 1875: Ibid., Final Kept., Vol. IV, p. 53, PI. Ill, flgs. 3a-d. Acrotreta gemma Walcott, 1884 : Mon. U. S. Geol. Surv., Vol. VIII, p. 17, PI. I, figs. Irt, h, d,f; PI. IX, flgs. 9, 9a. Walcott, 1886: Bull. U .S. Geol. Surv. No. 30, p. 98, PI. VIII, flgs. 1, Iff, h. Walcott, 1891: Tenth Ann. Rept. U. S. Geol. Surv., p. 608, PI. LX VII, flgs. 5. 5a-e. Hall and Clarke, 1892 : Pal. New York, Vol. VIII, Pt. I, p. 102, figs. 55-57. ( "?) Matthew, 1895 : Trans. New York Acad. Sci., Vol. XIV, p. 126. This species was described and illustrated by me in Bulletin No. 30, Monograph VII, and the Tenth Annual Report, of the United States Geo- logical Survey. It occurs with both the Middle and the Upper Cambrian faunas in the Park. Formation and locality: Middle Cambrian, Flathead terrane, ranging from the lowest terrane; Gallatin ten-ane, upper beds; Crowfoot section, Gallatin Range ; spur at southeast head of first branch from head of Gallatin Valley, south side; Yellowstone National Park. -29 450 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. BILLINGSELLA Hall. Billvu/sella Hall aud Clarke, 1892: Pal. New York, Vol. VIII, Pt. I. p. 230, PI. VII A, figs. 1-9. BiLLINGSELLA COLORADOENSIS SllUUiai'd. PL LXI, figs 1, la-d. Orthis coloradoensis Shumard, 1860: Trans. St. Louis Acad. Sci., Vol. I, p. 627. Orthis pepina Hall, 1863 : Sixteenth Ann. Kept. New York State Cab. Nat. Hist., p. 134, PI. VI, figs. 23-27. Hall, 1867 : Trans. Albany Institute, Vol. V, p. 113. Whitfield, 1882: Geol. Wisconsin, Vol. IV, p. 170, PI. I, figs. 4, 5. Orthis f {Orthisina?) pepina Hall, 1883: Second Ann. Eept. New York State Geol- ogist, PI. XXXVII, tigs. 16-19. Billingseaa pepina Hall aud Clarke, 1892: Pal. New York, Vol. VIII, Pt. I, p. 230, PI. VII, figs. 16-19; PI. VIIA, figs. 7-9. This species was described by Shumard, in 1860, as from the Potsdam sandstone of the IS! ew York series, near the head of Morg-ans Creek, Burnett County, Texas. He states that "tlie general form of the shell is very similar to a species in my cabinet from the Potsdam sandstone of Minnesota." In 1863 Professor Hall described a similar shell, from the sandstone al)ove Lake Pepin, Minitesota, under the name of Orthis pepina, stating that when compared with Orthis coloradoensis from Texas the species is much smaller, the length of the ventral valve is greater, and the strife are finer. However, a comparison of an extended series of specimens collected in the Upper Cambrian of Burnett County, Texas, leads me to believe that the specimens from widely separated locaUties all belong to the one species BillingseUa coloradoensis. The size and form of these species appear to be remarkably constant wherever found, as is also the surface ornamentation, which consists of fine concentric stria? and slender radiating costte, which are often unequal in size. The concentric striae are unusually well shown in the material from Texas, while the radiating costaj are ver)' faint. On specimens from the St. Croix sandstone of Lake Pepin, Minnesota, the costse and the concentric striae and lines of growth are strong and well shown in the casts of the outer surface of the shell. The generic characters are finely shown by specimens from the Gallatin Range in the Park, in which the charactei-istic muscular scars of the ventral valve of BillingseUa are well preserved; also CAiMUKIAX FOSSILS. 45^ the high, nearly vertical area, and the large delthyrimn, partially closed by a convex deltidiuni. Formation an.l locality: Upper Cambrian, Gallatin terrane, Crowfoot section, (Jallatm Kange ; also on the north slope of the Crowfoot Rid-e on the south side of the Gallatin Valley, and on the divide between Panther Creek and the Gallatin Kiver. ORTHIS Dalman. Okthis (?) REMNicHA Winchell. PI. LXI, ligs.3, 3a; PI. LXII, figs. 1, la-d Ortlns remnicha WiucheU,lSSG: Fourteeuth Anu. Eept. Geol. and Nat. Hist. Surv Mmuesota, p. 317, PI. II, flg. 7 . Shell of medium size, usually slightly transverse, with an oblong, oval outhne tor the ventral valve, and a subquadrate to semicircular outHne for the dorsal valve. Valves moderately convex, with an almost straight hino-e line that vanes in length from nearly the greatest width of the shell to two- thuds the greatest width; cardinal angles varying from 90° or less in the extreme forms, with ears somewhat angular, to the other extreme, where they are very obtuse and have the appearance of being almost rounded their angle being not less than 120°. Cardinal area narrow but well devel- oped on each valve, and divided by a rather large delthyrium. The ventral (pedicle) valve has in some specimens a shallow mesial depression, and in some examples it is slightly flattened toward the cardinal angles; beak small and curving down toward the hinge line, beyond which It projects slightly. Dorsal (brachial) valve slightly less convex than the ventral. Beak small, scarcely projecting beyond the hinge line _ Surface marked by bifurcating, radiating cost^, that vary on shells of similai- size from 16 in the space of 5 mm. to 3 in the same space This variation is shown in the specimens from the Park, as well as in those from lexas and Wisconsin. In well-preserved specimens very fine, radiatino- raised stri^ occur both on the costae and on the intervening depressiont. W-'r Tw-""" ~' '^'" '"'*' "^ '^'' ^^^^"^ ^^-^^'^ *1^^ S*- C^-oix sandstone of Wmhe d, Wisc.->nsin, and on the larger shells from the limestones of the upper Middle Cambrian horizon of Texas and the Park The interior of the ventral (pedicle) valve shows a slightly raised, 452 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. rather small muscular area, and the interior of the dorsal (brachial) valve a slightly elevated area upon which occurs a naiTOw, short median septum. The crural plates are also well shown. In casts of the interior from the St. Croix sandstone of Wisconsin the dental lamellae of the ventral valve are finely shown, and in the dorsal valve the median septum and crural plates. This is one of the most variable shells that occur in the Cambrian fauna. Its range of variation is such in all of the widely separated locali- ties in which it occurs that one would scarcely hesitate, if in possession only of the extremes, to identify two well-marked species. The variation is not only in the radiating cost?e, but also in the general form of the shell. It is proposed to illusti'ate this variation somewhat fully in a memoir on the Brachiopoda of the Cambrian fauna. Formation and locality : Near base of Upper Cambrian, Gallatin ter- raue, Crowfoot section, Gallatin Range, Yellowstone National Park. It also occurs at a slightly lower horizon on the south side of the Gallatin Valley, and specimens were collected farther to the north by Dr. A. C. Peale, opposite the mouth of Pass Creek, in the Gallatin Valley, Montana. Orthis (?) SANDBERGi Winchell. PI. LXI, figs. 2, 2a-d. Orthis sandbergi Winchell, 1886 : Fourteenth Ann. Kept. GeoL and Nat. Hist. Surv. Minnesota, p. 318, PI. II, figs. 8, 9. Shell small, transverse, subquadrate in outline, exclusive of the acute angular ears. Valves slightly convex, with a straight hinge line longer than the greatest width of the shell ; cardinal area naiTOw l3ut well devel- oped on each valve and divided by a rather large open delthyrium. The ventral (pedicle) valve slightly flattened at the ears, rising toward the center with a convex triangular swelling, broadening from the narrow beak to the front ; beak small, rounded, and extending slightly beyond the hinffe line. Dorsal valve flattened at the ears, with well-marked rounded ridges rising between the ears, and a rather broad, well-detined median sinus ; beak very small, slightly encroaching upon the hinge line. Surface marked by fine, regular, radiating strife, between which one or more faint intermediate strife are sometimes visible; under favorable con- OAMBIilAN FOSSILS. 453 ditious very fine concentric stria; can ])e seen, and there are also usually present more or less distinctly marked lines of growth. The generic cliaracter of this species has not been fully ascertained, but the material from the Park and specimens from the typical locality at Red Wing, Minnesota, lead me to think that this can not l^e referred to the genus Billingsella. It appears to be an Orthis of the Plectorthis group of Hall and Clarke. A comparison with specimens of Orthis sandhergi from the typical locality at Red Wing, Minnesota, shows the two shells to be specifically identical, as far as the comparison of casts in sandstone can be made with well-jireserved shells on the surface of a limestone slab. This is the only species of the type known to me in the Cambrian fauna. It is a type that is developed in the Ordovician fauna, and I think it will be found to occur in the Calciferous-Chazy fauna of New York and the St. Lawrence Valley. Formation and locality: Upper Cambrian, north side of Elk Pass, between Buffalo and Slough creeks, Yellowstone National Park. PLATYCERAS Conrad. Platyceras primordialis Hallf PI. LXIII, fig. 1. Platyceras primordialis Hall, 1863, Sixteenth Aim. Kept. New York State Cab Nat Hist., p. 136, PL YI, fig. 28. ^ A single species of Platyceras occurs on a slab of limestone in asso- ciation with BiUingsella pepina, Ptyclioparia (L.) wisconsensis, and Ptijcho- paria (1) diadematus. So far as can be determined from a comparison of the single specimen, it is probable that the forms are identical. Formation and locality: Middle Cambrian, Gallatin terrane, north side of Soda Butte Creek, below saddle on ridge between Pebble Creek and Soda Butte Creek, Yellowstone National Park. 454 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. HYOLITHES Eichwald. Hyolithes primordialis Hall. PI. LXIII, figs. 2, 2a. Theca primordialis Hall, 1861 : Aun. Eept. Progress Geol. Surv. Wiscousin, p. 48. Hall, 1862: (ieol. Kept. Wisconsin, Vol. I, p. 21, fig. 5. Hall, 1863: Sixteenth Ann. Eept. New York State Cab. Nat. Hist., p. 135*, PI. VI, figs. 30, 31. Pugiunciilus primordialis Hall, 1863: Ibid., p. 135*. Theca (Ptigiunculus) gregaria M. and H., 1861: Proc. Acad. Nat. Sci. Philadelphia, 2d series, Vol. Y, p, 436. M. and H., 1864 : Pal. Upper Missouri, Pt. I, p. 5. HyolitheS {Theca) primordialis Hall and Whitfield, ]873: Twenty-third Ann. Eept, New York State Cab. Nat. Hist., p. 242, PL II, fig. 3. Hyolithes primordialis f White, 1874: Expl. Surv. West 100th Merid., Prelim. Eept., Invert. Foss., p. 6. Hyolithes primordialis White, 1875: Ibid., Final Eept., Vol. IV, Pt. I, p. 37, PI. I, figs, 5rt-e. Whitfield, 1883 : Geol. Wisconsin, Vol. IV, p. 175, PL I, fig. 12. Walcott, 1884 : Mon. U. S. Geol. Surv., Vol. VIII, Pal. Eureka District, pp. 23, 24, Forms of this species occur at several localities, and are identical with those found in the Middle Cambrian St. Croix sandstone of Wisconsin. They vary in length from 1 to 5 cm. The young individuals when grouped together in the limestone are very closely related to, if not identical with, Theca grefiaria} The type specimens of the latter were found near the head of Powder River in the Bighorn Mountains of Idaho Territory, now in Wyoming. Formation and locality: Middle Cambrian, Flathead formation. Crow- foot section, Gallatin Range; Clark Fork Valley, south side, between Lodge Pole and Reef creeks; and blufiF on south side of Pebble Creek, north of saddle to Soda Butte Creek, Yellowstone National Park. AGNOSTUS Brongniart. Agnostus interstrictus White. PL LXIII, figs. 3, 3fl. Agnostus interstrictus White, 1874: Geol. and Geog. Expl, West 100th Merid., Prelim, Eept., Invert. Foss., p. 7. White, 1S75: Ibid., Final Eept., Vol. IV, Pt. I, p. 38, PL II, 5a, h. Walcott, 1886: Bull. U. S. Geol. Surv. No. 30, p. 149, PL XVI, figs. 6, 6o. A comparison of the specimens from the Gallatin Range with the type specimens from the Springhouse Range of Utah leads to the conclusion ' PaL Upper Missouri, Pt. I, 1864, p. 5. CAMBRIAN FOSSILS. 455 that they represent the siuiie species. Tliere are no good specimens of the head, but tliere is one very well preserved pygidiiini. This and the type specimen are illustrated. Formation and locality: Middle Cambrian, Flathead formation. Crow- foot section, Gallatin Range, Yellowstone National Park. Agnostus bidens, Meek. PI. LXIII, figs. 4, ia. Agnostus bidens Meek, 1873: Sixth Aim. Kept. U. S. Geol. aud Geog. Surv. Terr., for 1872, p. 46.3. Walcott, 1884: Mon. U. S. Geol. Surv., Vol. VIII, p. 26, PI. IX, figs. 13, 13rt. The specimens representing this species include the head and pygidium only. There is considerable similarity between this species and A. inter- str ictus and A. josephus, the latter from the St. Croix sandstone of Wisconsin. They all belong to the Middle Cambrian fauna, and it will be only after a careful examination with an extended series of specimens that the speciiic characters are well determined. The originals of the type specimens were found on the east side of the Gallatin River, above the town of Gallatin, they being associated with essentially the same fauna as that with which they occm- in the Gallatin Range. Formation and. locality: Middle Cambrian, Flathead formation. Crow- foot section, Gallatin Range, Yellowstone National Park. Agnostus tumidosus Hall and Whitfield. PI. LXIII, figs. 5, 5rt. Agnostus tumidosus Hall aud Whitfield, 1877; U. S. Geol. Expl. 40th Par., Pt. II, p. 231, PI. I, tig. 32. This species is represented by a small cephalic shield, and there is an associated pygidium that is referred to it. The species was founded upon a small head discovered in the Eureka district of Nevada. It is a strongly marked species and not liable to be confused with any other species of the genus from the Cambrian rocks of the Rocky Mountain region. Formation and locality : Middle Cambrian, Flathead formation. Crow- foot section, Gallatin Range, Yellowstone National Park. 456 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. PTYCHOPARIA Corda. Ptychoparia penfieldi u. sp. PI. LXV, tigs. 4, 4a, b. Of this species there are in the collection the central parts of the head, the interior of one free cheek, and one pygidium. The general form of the head is trausvei'se, semicircular; the frontal rim strong, rounded, and separated from the frontal limb and free cheeks b}^ a well-defined rounded furrow; postei'ior lateral angles prolonged into slender spines. Glabella truncato-conical ; nearly as broad at the base as long; marked by three pairs of glabella furrows, which penetrate about one-fourth the distance across ; the posterior pair bend slightly backward and penetrate toward the center. Fixed cheeks narrow and separated from the glabella by a well- defined dorsal furrow, from the narrow posterior rim by a rather broad, clearly defined furrow ; anteriorly they merge into the rather narrow frontal limb. Palpebral lobes narrow and clearlj'- defined by a groove from the fixed cheek; they are nearly one-tliird the length of the cheek; ocular ridges barely discernible above the general surface of the cheek. The posterior lateral lobe of the fixed cheek extends outward, so as to give a total length from the glabella outward somewhat greater than the width of the glabella at the base. The associated free cheek has a strong marginal rim and well-marked furrow between it and the main body of the cheek, which reaches up to the palpebral lobe. Pygidium small, semicircular; axial lobe strongly defined and marked by three segments and a short terminal portion; lateral lobes marked by thi-ee rather broad segments that merge into the smooth outer rim. Surface apparently smooth. Formation and locality: Middle Cambrian, Flathead terrane, Crow- foot section, Grallatin Range, Yellowstone National Park. Ptychoparia antiquata Salter sp. PI. LXV, figs. 7, la. Conocejphalus antiquatus : Quart. Jour. Geol. Soc. London, Vol. XV, p. 554, tig. 2. This species was founded on an entire trilobite sent to the great exposi- tion in London in 1851. It was said to have been discovered somewhere OAMBIIIAN FOSSILS. 457 in the State of Georgia. From the occurrence of laro-e numbers of entire specimens on nodules in the Coosa VaHey, in Alal)ama, a few miles west of the Georg-ia State line, it is thought pnjbaljle that the specimen referred to came from that locality. A comparison of a series of specimens from the Coosa Valley locality with the Gallatin Range specimens shows a very close resemblance between them. The Alabama specimens have two marked ^-ariations in the frontal limb and border; in one the limb is gently rounded to a marked groove that separates it from a strong rounded frontal rim; in the other, the groove in the frontal rim curves backward from each side toward the glal^ella so as to indent the frontal limb. As a result of the comparison, it is found that the range of variation among the individuals ol P. antiquata includes not only the Gallatin species but also the varieties of it. Formation and locality: Middle Cambrian, Flathead formation. Crow- foot section, Gallatin Range; bluff on south side of Pebble Creek, north of saddle to Soda Butte Creek; on ridge near Crowfoot section, Gallatin Range, Yellowstone National Park. East of Dead Indian Creek, Absaroka Range, Wyoming. Ptychoparia (E.) afpinis Walcott. PI. LXV, fig. 8. Ptychoparia (E.) affinis Walcott, 1884: Mou. U. S. Geol. Surv., Vol. VIII, p. 54, PI. X, fig. 12. With the material at hand it is impossible to make a positive identifi- cation Avith the type species from the Upper Cambrian of the Eureka district, Nevada. There is, however, a striking similarity in the only por- tions we have for comparison, the center of the head. A similar species occurs in the Cambrian beds of Honey Creek, Bur- nett County, Texas, and it is probable that the specimens from the three widely separated localities are identical. Formation and locality: Middle Cambrian, Gallatin limestone, Liv- ingston section, at head of Davis Creek, Snowy Range, Montana. 458 GEOLOG^Y OF THE YELLOWSTONE N ACTIONAL PAKK. Ptychoparia llanoensis Walcott (?) PI. LXIV, fig. 4. Ptychoparia llanoensis Walcott, 1890: Proc. U. S. Nat. Miis., Vol. XHl, p. 272, PL XXI, flgs. 3-5. The fragments that have been compared and provisionally identified with this species show only the central portions of the head. The frontal rim and border, separated by a narrow, raised, crenulated line on the cast of the under surface of the test, and the glabella, appear to be identical with those of some of the specimens of P. llanoensis. Formation and locality: Middle Cambrian, Livingston section, at head of Davis Creek, Snowy Range, Montana. Ptychoparia sp. undet. PI. LXIV, fig. 5. This is a rather strongly marked form, of which only the central por- tion of the head is preserved. It differs from other described species in having the frontal rim project inwardly almost to the front margin of the glabella. A figure is presented of the onl}^ specimen in the collection. The head may be compared with the head oi Ptychoparia teucer, from the red sand rock of Highgate Springs, Vermont.^ It is possible that this is a strongly marked variety of P. anfiqnata. Formation and locality: Middle Cambrian, Flathead tVirmation, near Crowfoot section, Grallatin Range, Yellowstone National Park. Ptychoparia (?) sp. undet. PI. LXIV, fig. 3. This is a clearly marked form, represented by the central portion of the head. The small eye lobes and strong postero-lateral limbs suggest Ptychoparia eryon Hall," but the glabella is less elongate and the frontal limb is marked by a rounded rim. Formation and locality: Middle Cambrian, Crowfoot section, Gallatin Range, Yellowstone National Park. • Tenth Ann. Kept. U. S. Geol. Siirv., 1891, PI. XCVI, fig. 3. 2 Sixteenth Ann. Rept. New York State Cub. Xat. Hist., 1863, PI. VIII, Hgs. 16, 31. CAMBRIAN FOSSILS. 459 CRE PICE PH ALUS Owen. Crepivephalm Owen, 1852: Kept. Geol. Siirv. Wisconsin, Iowa, aud Minnesota, p. 57(1, PI. I, fig. S; PI. lA, tigs. 10, 1(5, 18. Hall, 1803: Sixteentli Ann. Rept. New York State Mus. Nat. Hist., p. 147. Hall and Whitfield, 1877 : Rept. Geol. Expl. 40tli Par., Vol. IV, Pt. 11, p. 209. Whitfield, 1870: Rept. Reconnaissance from Car- roll, Montana, to Yellowstone National Park (Ludlow), p. 141. Whitfield, 1880: Rept. Geology and Resources of the P>lack Hills (Jenuey), p. 341. Whitfield, 1882: Geol. Wisconsin, Vol. IV, p. 182. Walcott, 1884: Bull. U. S. Geol. Surv. No. 10, p. 30. Walcott, 1880 : Bull. U. S. Geol. Surv. No. 30, pp. 206, 207. Attention was called to this genus in 1886,' but in giving an entire figure of C. texunus I will repeat the description given by Dr. Owen, and also add a few remarks. Dr. Owen projiosed the generic name Crepicephalus for some fragmen- tary remains of trilobites, the characteristic features of the central portion of the head of which he described, and he also gave figures of the associated pygidia. The description of the central portion of the head is as follows: The rather flat slipper-shaped glabella is tapering and slightly acuminated anteriorly, with a faint ridge in the median line; two small and very superficial depressions, and a posterior faint furrow, very partially divide the glabella. The facial sutures run nearly parallel to the margin of the glabella, and join a thickened, cordlike, anterior narrow border, inclosing a convex area, narrower in front than at the sides. Oblique plications can sometimes be traced on the cheek plate, in advance of the eye, converging toward the apex of the glabella. In his remarks on the genus, he refers to figs. 10, 16, and 18 of PI. Ia, as illustrating the central portions of the ceplialic shield of the genus. The comparison of these figures with typical specimens of Crei)icephalus (Owen's Dikellocephaliis) iowensis shows clearly that the types of the genus Crepicephalus should have been referred to this species. He also refers to the associated pygidia which are illustrated by his fig. 8 of PI. I and fig. 16 of PI. Ia, a comparison of the pygidium of Crepicephalus iowensis with these figures showing it to be identical. In the description of fig. 13 (PI. I) the species tvisconsinensis is referred with a (?) to the genus Crepicephalus. No reference, however, is made to it in the text. Professor Hall, in referring to the genus,^ speaks of this as the only species designated by Dr. Owen, and states that it off"ers no distinction, in regard to the head, from a species placed under the genus Lonchocephalus. ' Bull. U. S. Geol. Surv. No. 30, pp. 206, 207. ^Loc. cit., p. 147. 460 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. He considered it difficult to sustain this genus, or either of them, upon the characters given, and referred all to the genus Conocephalites. Messrs. Hall and Whitfield, in describing Cambrian trilobites from Utah and Nevada, discussed the genus Conocephalites and revived Crepi- cephalus as a subgenus equivalent to Loganellus of Devine. They did not, however, describe the genus Crepicephalus, but refen-ed a number of species to it which possess more or less distinctly marked "slipper-shaped" glabellte. Professor Whitfield subsequently used the genus in his description of Crepicepludus (LoganellMs) montanensis;^ also in the Paleontology of the Black Hills of Dakota." But later (1882) he omitted reference to Loganellus in describing Crepicephalus onustus? In 1884 I stated that Crepicephalus might be used as a subgenus of Ptychoparia on account of its peculiar pygidium, but, from a recent study of an entire specimen of the type species and of C. fexanus, I think that we can with propriety use it as a full generic term. The essential elements of the head are genericall}^ identical with those of the head of Ptychoparia striata, but the pleura of the thoracic segments and the pygidium vary in a marked manner. The pleura terminates in the graceful backward-curving acu- minate points so characteristic of many species of Paradoxides. This may not be considered a character of generic value, but it gives a marked aspect to the body of the trilobite in both C. ioivensis and C. texanus. The pygidium of C. iowensis is short, broad, and provided with two long postero-lateral spines which appear to be an extension of the border, but in reality are the lateral extension of one of the segments of the pygidium. This feature is more clearly shown in the pygidium of C. texanus. The combination of characters in the head, thorax, and pygidium clearly distinguishes the genus from Ptychoparia and other genera of the Conocephalidae. Crepicephalus texanus Shumard sp. PI. LXV, fig. 5. Arionellus {Bathyurus) te.ramis Sliumard, 1861: Am. Jour. Sci. and Arts, 2d series. Vol. XXXII, p. 218. Arionellus tripnnctatus ^Yhit&eld, 1816: Kept. Reconnaissance from Carroll, Montana Terr., on the Upper Missouri, to the I'ellowstone National Park (Ludlow), p. 141 PL I, figs. 3-5. Numerous heads of this species occur in a dark-greenish-colored oolitic ' Bull. U. S. Geol. Suiv. No. 30, p. Ul. ^'Loc. cit., pp. 341-343. sLoc. cit., p. 182. CAMUlilAN FOSSILS. 4GI limestone, with a few frao-ments of the pygidium. The material is too poor to properly illusti'ate tlie species, and a tif>-ure is introduced that was di-awn from specimens collected in the Middle Cambrian shaly beds of the Coosa Valley, Alabama. A detailed desci'iption of the species and full illustrations will be given in a memoir on the Middle and Upper Cambrian faunas, now being jn-epared. The type specimens of the species were described by Dr. Shumard from Llano County, Texas. I collected a series of specimens from the type locality, and a comparison of these with those from Moss Agate Springs, near Cami) Baker, Montana (described as Arionelliis tripunctatus by Whit- field), and the Coosa Valley, Alabama, shows them to belong to one species. Formation and locality : Middle Cambrian, Flathead terrane, north side of Soda Butte Creek, below saddle on ridge between Pebble Creek and Soda Butte Creek ; Flathead terrane, Crowfoot section, Gallatin Range, Yellowstone National Park. PTYCHOPAKL-i (LoNCHOCEPHALUS) HAMULUS Owen! Lonehocephalus lianmlus Owen, 1852: Geol. Kept. Wisconsiu, Iowa, and Minnesota, p. 576, PI. lA, figs. 8, 12. Conocephalites hamulus Hall, 1863: Sixteenth Ann. Eept. New York State Mus. Nat. Hist,, p. 166, PI. VII, figs. 43, 44; PI. VIII, figs. 25, 26. One imperfect head is all there is in the collection on which to base the presence of this species. Little more can be said than that there is a form which represents it. Formation and locality: Middle Cambrian, Flathead formation, north side of Soda Butte Creek, on ridge between Pebble Creek and Soda Butte Creek, Yellowstone National Park. Ptychoparia (Lonchocephalus) WISCON.SENSIS Owen sp. PI. LXIV, figs. 1, la-c. Grepicephalus ( 1) loisconsensis Owen, 1852 : Eept. Geol. Surv. Wisconsin, Iowa, and Minnesota, description, PI. I, fig. 13. Dicellocephalus latifrons Shumard, 1803: Trans. St. Louis Acad., Vol. II, p. 101. Conocephalites loisconsensis Hall, 1863: Sixteenth Ann. Eept. New York State Cab. Nat. Hist., p. 164, PI. VII, figs. 39-41; PI. VIII, figs. 22-24, 27, 28. This species occurs in abundance in thin-bedded limestone in the northeastern portion of the Park. It is associated with Ptychoparia (f) dia- 462 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. demata, an association which also occurs in the Middle Cambrian St. Croix sandstone of Wisconsin. Numerous heads occur, but only one fragmentary pygidium has been seen. An illustration of the pygidium is taken from a specimen found in the St. Croix sandstone 4 miles southeast of Lake City, Minnesota. Formation and locality: Middle Cambrian, Flathead foi-mation, north side of Soda Butte Creek, below saddle on ridge between Pebble and Soda Butte creeks, Yellowstone National Park. PtYCHOPARIA (?) DIADEMATA Hall Sp. PI. LXIV, figs. 2, 2a-c. Conocephalites diadematus Hall, 1863: Sixteenth Ann. Kept. New Y^ork State Cab. Nat. Hist., p. 107, PI. VII, figs. 36-38; PI. VIII, figs 18, 21. This species is associated with Ptychoparia (L.) tvisconsensis. The cen- tral portions of the head are quite abundant and associated with the sepa- rated free cheeks. Two finely preser^-ed hypostomas and one imperfect pygidium also occur on the slabs of limestone. The pygidium is illustrated by a specimen from the St. Croix sandstone, found in the bluff near Hudson, Wisconsin. Formation and locality: Middle Cambrian, Flathead formation, north side of Soda Butte Creek, below saddle on ridge between Pebble and Soda Butte creeks, Yellowstone National Park. ARIONELLUS Barrand. AriONELLUS LEVIS u. sp. PI. LXV, fig. 1. It is with little doubt that the specimen illustrated is referred to this genus. It has a strougl)^ convex, minute head, 4 mm. in length; glabella nearly as Ijroad as long, narrowing slightly toward the broadly rounded front; glabella furrows barely visible as four shoi't, slightly depressed lines. It is separated from the fixed cheeks and frontal limb by a narrow groove, which is all that breaks the general convexity from the frontal margin back to the occipital furrow. The occipital furrow is deepl}' impressed between the glabella and the very narrow depressed occipital ring. Fixed cheeks slightly convex, sloping abruptly toward the facial sutures; anteriorly they CAMBRIAN FOSSILS. 463 pass into the rather l)roa(l tVoiit;i1 hiiil), which shipcs directly downward to the frontal niaryin, without any frontal groove or rim. The palpebral lobes are situated oj)posite a point about two-thirds the distance from the jjos- terior to the anterior mar<>'in of the glabella. Formation and locality: Middle Cambrian, Gallatin limestone, Crow- foot section, Gallatin Range, Yellowstone National Park. Arionellts sp. undet. PI. LXV, fig. 2. Only the central portion of the head of this species is known. It is so distinct a type that I do not hesitate to refer it to the genus Arionellus. The glabella is elongate, subcorneal; the glabella furrows are indicated by very slight depressions, and the occipital furrow is almost obliterated. Fixed cheeks as broad as the glabella and merging into the broad, rounded, anterior frontal limb. The palpebral lobes are broken away and there does not appear to be any frontal rim, the gently rounded slope from the glabella to the margin being unbroken. The specimen strongly recalls specimens of Arionellus from the Paradoxides zone of Newfoundland. Formation and locality: Middle Cambrian, Flathead formation, north side of Soda Butte Creek, below saddle on ridge between Pebble and Soda Butte creeks, Yellowstone National Park. LIOSTRACUS Angelin. LlOSTRACU.S PARVUS U. Sp. Pi. LXV, fig. 6. This form is I'epresented by the central portions of three small heads. The glabella is a little longer than broad; sides subparallel, broadly truncated in front; three pairs of small glabella furrows are slightly indi- cated ; occipital furrow narrow and slightly impressed ; occipital ring narrow at the sides, broader at the center, and provided with a short occipital spine. Free cheeks broad, convex, and separated from the glabella by a well- defined dorsal furrow; anteriorl)^ they merge into the narrow frontal rim; ocular ridges narrow, passing almost directly outward from a point opposite the anterior pair of glabella furrows to the anterior end of the small, narrow palpebral lobe; anterior rim nearly flat and distinguished from the 464 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. frontal lobe by its smoothness and by being nearly flat ; posterior lateral limb of fixed cheeks strong and extending obliquely outward and backward from the base of the palpebral lobe; posterior rim narrow. Surface slightly granular under strong magnifying power. Formation and locality: Middle Cambrian, in bluff south side of Pebble Creek, north of saddle to Soda Butte Creek, Yellowstone National Park. SOLENOPLEURA Angelin. SOLENOPLEURA ? WEEDI. PL LXV-, figs. 9, 9a. Of this species, only the central portions of the head occur in the col- lection. The entire individual attained considerable size, as the laro-est head has a length of 20 mm. The characteristic features of the head are also shown in heads 9 mm. in length. The glabella is obtusely conical, having a width at the base in the largest specimen of 10 mm., and a length from the center of the occipital furrow to the frontal limb of 13 mm. It is separated from the strong rounded occipital ring by a relatively broad, well-defined furrow. The posterior pair of glabella furrows is indistinctly shown by very shallow grooves in the case of the largest individuals; on the smaller individuals it is not shown, except by a smooth spot. The glabella is separated from the fixed cheeks and frontal limb by a well-marked dorsal furrow, and as it is quite convex it stands out in clear relief from the general surface of the head. Frontal limb short, 1.5 mm. in length in the large specimen. It is separated from the strong rounded frontal rim by a well-defined groove; laterally it passes into the free cheek, which is of medium width. The pal- pebral lobe is of medium size and situated at a point opposite the transverse central line of the glabella. A faintly defined occular ridge extends abruptly backward across the fixed cheek from a point a little back of the front of the glabella to the front angle of the palpebral lobe. It is defined more by the presence of a slight groove in front of it than by the elevation of the ridge itself. The posterior lateral limb of the fixed cheek extends outward two-thirds of the width of the glabella at the base ; it is separated from the posterior rim by a well-defined furrow. CAMBRIAN FOSSILS. 465 Fragnit'iits of tin- free cheeks associated willi the glal)ella slmw tliat they are convex and tliat the strong rounded rim is sejjarated from the cheek |)roi)er l)y a well-marked groove. The entire surface of the head, with the exception of the occijiital groove and the groove within the outer rim, is strongly pustulose, the pustules being scattered irregularly over the surface. Where the true test is broken awa}' the jjustules are shown on the surface of the cast. This species resembles Bathyurus coniciis Billings, from the Calciferous formation of northeastern New York and St. Timothy, Canada. It differs, however, in the strongl}- marked frontal rim and the form of the glabella.^ It may be also compared with Hall and Whitfield's Crepicephalus (L.) macuJosm} Formation and locality: Middle Cambrian, Flathead formation, Crow- foot section, Gallatin Range, Yellowstone National Park. ZACONTHOIDES Walcott. Zaconthoides sp. undet. PI. LXV, fig. 3. Head moderately convex ; glabella convex, subclavate, narrowino- very slightly from the anterior toward the posterior end; marked by three pairs of slightly impressed glabella furrows, the posterior pair cutting in obliquely backward toward the occipital fuiTOw. Occipital furrow narrow but distinctly impressed; occipital ring strong and provided with a short strong spine, which projects from the upper posterior margin; fixed cheeks narrow anteriorly and a little less than half the width of the o-labella opposite the posterior margin of the palpebral lobe; anteriorly they pass down to the frontal rim, there being practically no frontal limb, the glabella extending directly down to the margin The palpebral lobe is nearly half the length of the glabella; anteriorly it extends to a point opposite the anterior glabella furrow and posteriorly to a point opposite the occipital furrow. The largest specimen of this species is 3 mm. iu length; a second, a smaller one, occurs on the same piece of limestone. It is possible tliat thev ' Geol. Surv. Canada, Pal. Fossils, Vol. I, 1865, p. 353, tig. 3416. = U. S. Geol. Expl. Fortieth Par., Vol. IV, 1877, j). 215, PI. II, tig. 24. MON XXXIl, PT II 30 466 GEOLOGY OF THE YELLOWSTO^^E NATIONAL PARK. represent the young of Z. spinosus} The head diflPers in details, but not more so than between the young- and adults of Z. typicalis} Formation and locality: Middle Cambrian, Flathead formation, Crow- foot section, Gallatin Range, Yellowstone National Park. BATHYURISCUS Meek! PI. LXIV, flg. 6. A single specimen of the pygidium is placed provisionally under this genus. Its principal characters are well shown in the figure. It is associated with HyoUthes primordialis, and is probably from the Middle Cambrian liorizon. The genus Dolichometopus Angelin might include this form, but with the material at hand it is difficult to make any detailed comparison of generic characters. Formation and locality : Middle Cambrian, Flathead formation, east of Dead Indian Creek, Absaroka Range, Wyoming. ' Bull. U. S. Geol. Survey No. 30, p. 184, PI. XXV, fig. 6. '^ Loc. cit., PI. XXV, flg. 2, 2a. PLATE LX. 467 PLATE LX. Page. Fig. 1. Obohis (Linf/iilepis) aciiminatiis var. meeki 444 1. Ventral valve, x 3. 1((. Dorsal valve, x 3. Fig. 2. Obohis ( LhifiuleJla) desideratus 445 2. Ventral valve, s 6. '2a. Dorsal valve, x 6. Fig. 3. Dicellomiis uana 447 3. Ventral valve, from Gallatin Range, x 6. 3a. Dorsal valve, from Little Rocky Mountains, Montana, x 6. 3h. Ventral val\e (type specimen of Meek anil Hayden) from Black Hills, South Dakota, s 6. 3c. Cast of interior of ventral valve, from Little Rock Mountains, Montana, x 6. 3d. Cast of interior of ventral valve (type specimen of Meek and Hayden), from Black Hills, South Dakota. Fig. 4. Dicellomits jmlitiis 446 4. Interior of dorsal valve, x 6. 4a. Interior of ventral valve, x 6. Fig. 5. Iphidea sculptiUa 447 .5. Summit view of ventral valve, x 4. 5a. Side view of fig. 5. x 4. 5ft. View of the broken false area and pseudo-deltidinm of iig. 5. x 4. 5c. Surface of fig. 5, greatly enlarged. p'ig. 6. Iphidea sp. undet 449 6. Dorsal valve described in the text, x 4. 468 U. S. OEOLOOICAL SURVEY MONOGRAPH XXXII PART II PL. LX I ^ > w ' \ # d la # 3c 3a /■ 3cl 4a 5a Sb 2a 3b '-^ -ir " '^ ^~ *~ 5c ^ i CAMBRIAN THE HELIOTYPE PRINTING CO., BOSTON PLATE LXI. 469 PLATE LXI. Page. Fig. 1. BiUinijsella colovadoensis '150 1. Ventral valve, from Gallatin Range, x 2. la. Dorsal valve, from same locality as fig. 1. x 2. lb. Interior of dorsal valve, from same locality as fig. la. x 3. Ic. Interior of ventral valve, from same locality as fig. 1. s 3. Id. Cast of interior of ventral valve, Gallatin Range, x 3. Fig. 2. Ortltis (?) sandbei-gi 452 2. Veuti'al valve, x 3. 2o. Dorsal valve, x 3. 26. Interior of dorsal valve, x 6. 2c. Interior of ventral valve, x 3. 2d. Enlargement of fig. 2c. x 12. Fig. 3. Orihis remnicha - 451 3. Interior of dorsal valve, x 3. 3a. Interior of ventral valve, x 3. 470 U. S. QEOLOQICAL SURVEV MONOORAPH XXXn PART II PL. LXI CAMBRIAN THE HELIOTVPE PRINTING CO., BOSTON PLATE LXII. 471 PLATE LXII. Page. Fig. 1. Orihis remnicha ).") 1 1. Rather strongly costate dorsal valve, x 2. la. Finely costate ventral valve, x 3. 11). Finely costato dorsal valve on same bit of rock as fig. 1«. x ,3. Ic. Strongly costate ventral and dorsal valves, x 3. Id. Dorsal and ventral valves, showing fine radiating stria' on costic. x 3. Fig. 2. Acrotreta gemma 449 2. Suuimit view of ventral valve, x 6. '2a. Posterior view of ventral valve, x 6. '2b. Side view of ventral valve. 2c. Summit view of cast of interior of ventral valve, x 6. 2d. Uorsal valve, x 4. 2e. Interior of dorsal valve, x 6. ' 472 U. S. OEOLOOICAL SURVEY MONOGRAPH XXXII PART II PL. LXII CAMBRIAN THE MELIOTVPE PRINTING CO., BOSTON PLATE LXIII. 473 PLATE LXIII. rage. Fig. 1. Platyceraa primordtalis 453 1. Ca^t of interior of shell. Fig. 2. Hiwlithes pi-imonliaHs 454 2. View of (lat side and two sections of a large specimen. 2a, Reprotliictiou of photograph of a slab of sandstone, with numerous specimens of H. primordialis, from the St. Croix sandstone of Wisconsin. Tho small shells are identical with H. gregaria of M. and H. Fig. 3. Agnostiis interatrictus 454 3. Entire specimen, from Antelope Springs, Utah. 3a. Pygidinm, from Gallatin Range, x 6. Fig. 4. Agnostus bidens 455 4. Cephalic shield, x 6. 4a. Pygidium. x 6. Fig. 5. Agnostus tiimidosus 455 5. Cephalic'shield. x 6. 5a. Pygidium, associated with fig. 5. x 6. Fig. 6. Hagnia spharica 442 6. Reproduction of photograph of thin section, x 8. 6a. Drawing of thin section, x 9. The light-colored spaces are the flllingB of the canals. They correspond to the darker spaces of the photograph. 474 U. 8. OEOLOOICAL SURVEY MONOGRAPH XXXII PART II PL. LXIII (p-? ■S' 4a 3a 5a CAMBRIAN THE HELIOTYPE PHINTtNfl CO. SOBTON PLATE LXIV. 475 PLATE LXIV. Page. Fig. 1. rti/cliojMfia (L. ) ivisconsensis ^^l 1. Central portions of head aiul side outline of median section of head and occii>ital spine, la. Free cheek associated with fig. i. 16. Central portions of head of specimen from the !St. Croix sandstone of Wisconsin. After Hall. Ic. Pygidium from the St. Croix sandstone of Wisconsin. Fig. 2. Ptijchoparia (?) (Uademata "^^^ 2. Central portions of head. 2(1. Free check associated with fig. 2. " 26. Hypostoma, associated with fig. 2. 2c. Pygidium from the St. Croix sandstone of Wisconsin. Fig. 3. Fttjchoparitt .sp. uudet ■15° 3. Central portion of head, x 3. Fig. 4. rttjclwpuvia Uanoensis - *58 4. Reproduction of illustration of the type specimen. Fig. 5. Ptychoparia ap. undet ^-^^ 5. Central portion of head of the only specimen in the collection. Fig. 6. Bathyiiy'isciia sp. undet ^^^ 6. Figure of the specimen referred to in the test. 476 U. 8. QEOLOaiCAL SURVEY MONOGRAPH XXXII PART II PL. LXIV CAMBRIAN THE HELtOTVPE PRINTrNG CO.. BOSTON PLATE LXY. 477 PLATE LXV. Page. Fig. 1. Arionelhia levis 462 1. Central portions of head of type specimen, and side outline, x 4. Fig. 2. Arionellus sp. uudet 463 2. Figure of specimen referred to in text. Fig. 3. Zacanthoidea sp. undet 463 3. Central portions of head, x 5. Fig. 4. Ptychoparia penfieMi 456 4. Central portions of head. 4a. Free cheeks, associated in same layer with fig. 4. 46. Associated pygidium. Fig. 5. Crepicephalus texanus 460 5. Partially restored drawing from specimens in the Middle Cambrian shales of Ala- bama. Fig. 6. Liostracua parvua.... i 463 6. Central portions of head of type specimen, x 6. Fig. 7. Ptychoparia aniiquata 456 7. Entire individual, slightly restored, x 2. la. Side outline of head of a variety of this species, x 2. Fig. 8. Ptiichoparia ( E. ) affinia 457 8. Reproduction of figure of type specimen. Fig. 9. SoJenopIeura (?) iceedi 464 9. Central portions of head of type specimen. 9a. A small head, showing same general characters as fig. 9, 478 U. 8. QEOLOOICAL SURVEY MONOGRAPH XXXII PART II PL. LXV CAMBRIAN THE MELIOTfPE PRINTIHO CO., BOSTON Section II.— DEVONIAN AND CAKBONIFEROITS FOSSILS. By Geoege H. Girty. INTRODUCTION. In the following pages are described the Paleozoic faunas, with the exception of the Cambrian, which have been found in the Yellowstone National Park. The point of interest in this connection is the presence of the Devonian and the apparent absence of the Coal Measures in this region. The Ordovician and Silurian are also absent, and the only Paleozoic forma- tions indicated by the collections are the Cambrian, the Devonian, and the Lower Carboniferous. The great bulk of the material was furnished by the Madison limestone, whose fauna, though showing close relations only with that of the Kinder- hook period, may have survived nearly through the Mississippian. The fauna is essentially that described by White and by Hall and Whitfield,^ but it is more extensive than that recorded by them. Devonian types are rare and constitute a fauna more scanty, though nearly akin to that described by Meek and by Walcott from the Rocky Mountain region of Nevada. The collections which I have had the privilege of examining were made by the geologists of the Yellowstone National Park survey, whose careful stratigraphic observations rendered easier the solution of many 'As is well known, the principal literature dealing with the paleontology of the Devonian and Lower Carboniferous in the Rocky Mountain region consists of a report by Meek and another by Hall and Whitfield in King's U. S. Geol. Expl. 40th Par., Vol. IV, 1877; a report by White in Wheeler's Expl. and Surv. W. 100th Merid., Vol. IV, 1875; and a monograph by Walcott, Hon. U. S. Geol. Survey, Vol. VIII, Pal. Eureka District, 1884. Meek has also identified certain Mississippian horizons in this region: Prelim. Rept. U. S. Geol. Surv. Wyoming, etc., Hayden, Fourth Ann. Kept., 1871, p. 288; ibid.. Fifth Ann. Rept., p. 76; ibid., Sixth Ann. Rept., pp. 432-433. 479 480 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, problems that would otherwise have been left in doubt. To them I desu'e in this place to make ample acknowledgments, and especially do I wish to express my obligation to Mr. Charles Sclmchert, of the United States National Museum. A preliminary study of this collection Avas made by him before the work was assigned to me, and he also supplied me with facil- ities in the National Museum, gave me free access to the Museum collec- tions for comparison, permitted the use of his Bibliography of North Amer- ican Brachiopoda, then unpublished, and placed at my disposal his fine col- lection of brachiopods and his no less extensive knowledge of the same. It gives me pleasure also to acknowledge my obligations to Mr. John L. Ridgway, by whom the greater number of the drawings accompanying this report were made. DEVONIAN. The inaiterial believed to be of Devonian age is unsatisfactory in that it is scanty and often poorly preserved, while the species represented are almost the worst that could have been selected for stratigraphic correla- tion. Consisting mostl}^ of corals, with a few gastropods and brachiopods, it would be difficult, unassisted by the richer though related fauna of Nevada, to affirm of some of the local representations anything more than that they are older than the Carboniferous and younger than the Ordovician. The strata represented fall into three groups, distinguished somewhat by their lithologic character as well as by the fossils which they carry. More extensive collections would probably show a closer connection than now appears. The age of the exposure on the north side of Soda Butte Creek has not been detinitely ascertained. It is represented only by an undetermined species of Favosites, in a fragmentary condition. The most likely reference would be to the Silurian or Devonian, for if Carboniferous the coral belongs to none of the few related species known in Cai-boniferous rocks. The locality is therefore provisionally referred to the Devonian, since no fossils of Silurian age have been recognized in the Yellowstone Park. The locality at Wall Canyon, Clark Fork Valley, stands by itself. It is represented only by Pleiirotomaria isaacsi {f) (a solitary specimen), both fossil and matrix being highly siliceous. P. isaacsi was described from Lower Devonian strata, probably of the age of tlie Schoharie grit, but its range is not known, and my identification is questionable. DEVONIAN FOSSILS. 481 Fntiii the base of the bluff nn Little Sunlight Creek only Atrypa reticu- laris is known, a small coarsely plicate variety. It is similar to, perhaps identical with, the type figured b>- Walcott (Mon. U. S. Geol. Survey, Vol. VllI, 1884, PI. XIV, figs, (j, it(t, (!/;), and mentioned as occurring in the upper part of the formation (p. 150). Meek cites the same form (King's Kept. U. S. Geol. Exi)l. 4()th Par., Vol. IV, 1877, p. 3:») from Pinon Station, Treasure Hill, White Pine district, etc., and figures it on PI. Ill, figs. 6, Ga. The horizons of Bighorn Pass, Gallatin Range, near the divide between Gallatin Valley and Panther Greek; the east slope of Antler Peak, Galla- tin Range; and the south slope of the same, can be correlated with one another and constitute a separate group. The matrix is a calcareous sand- stone; and the included fossils, almost exclusively corals, are cnxdely silici- fied. The common fossils are Cladojiora si)., PachuphjUum s])., CyathophyJlHm ccespitosum (?), and Actinostroma sp. Every indication points to the Devonian age of this bed. The genus Actinostroma is characteristic of, though not restricted to, Devonian rocks. Ci/afhopJu/Uitm. ccBspifosiim, as identified in this country, occurs in Upper Helderberg strata. The genus Pachyphyllum is characteristically Devonian, and Claclopora sp. is more closely related to certain Upper Helderberg forms than to aijy I have found described. The material from the south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range, from northwest of Abiathar Peak, Soda Butte Canyon, and from the north side of saddle west of Mount Miller, Absaroka Range, represents, perhaps, the same horizon as that from The Gate, Fossil Hill, and Eureka district, whose fauna, as described by Meek and by Walcott (loc. cit.), is quite similar, as far as it goes. In the Yellow- stone Park this consists of Atrypa missoiiriensis, Spirifer eiigehnanni, Athyris vittata var. triplicata n. var., PJeurotomaria (f) sp., PacliyphyUum. sp., Cyatho- phyUiim ccespitosum (f), etc. Atrypa missouriensis is, I believe, the same form figured by Walcott as A. desquaniata Sow. (loc. cit. PI. XIV, figs. 4, 4«), and by Meek as A. reticularis var. As in their collections A. missouriensis was associated with the small, coarsely plicate Atrypa, which I have found alone at Little Sunlight Creek, it might perhaps be better to regard the latter as forming one of the group of localities under consideration. This group, on the other hand, is connected with the otlier previously mentioned (Bighorn Pass and Antler Peak) by having in common CyathophyUiim ccBspitosiun (doubtful identification) and Atrypa missouriensis. A bed at the south side MON XXXII, PT II 31 482 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Eaiige, is unique in the collection, and may fitly be called a gastropod limestone. The rock consists of comminuted organic remains cemented by a shaly limestone, and carrying certain small gastropods in great abundance. Two of the types represented are described below, under the names of PJafystoma minutmn and Loxonema deUcatum, but the others, of which there are perhaps three or four genera and some half diizen species, are too jjoor for either identification or description. They ai-e small, and nearly all badly eroded, and often concealed by a matrix from which they are not easily separated. It has therefore proved difficult or impossible to acquire data even for certain generic references ; but Loxonema, Pleurotomaria, Murchisonia, Platystoma, and perhaps other genera are probably present. The associated brachiopods show this fauna to be of Middle Devonian age. It can be affirmed beyond question that all the localities here discussed occur below the Carboniferous. Indeed, there is a decided faunal break between them and the great series of beds regarded as representing the base of that formation, so much so that the two groups have not a single species, and scarcely even a single genus, in common. • At the same time, I believe that the lower series is neither wholly nor in part Silurian, but that it was in fact laid down in Lower or ]\Iiddle Devonian time, repre- senting the Hamilton, or perhaps the Upper Helderberg, of the New York system. Many of the generic identifications strongly suggest a Devonian facies, or, at worst, are ambiguous, while the specific references, though often doubtful, all point to the Devonian rather than the Silurian age of these strata. Finally, the fauna seems to be rather closely related to that of the White Pine district, etc., above referred to, of which Meek says (loc. cit., p. 6): "Hence Ave can not doubt that these beds belong to the Devonian, and probably to about the horizon of the Hamilton group of the New York series." DEVONIAN AND LOWER CAKBONIFEliOUa FOSSILS. 483 Table vonian species. •2 >?5 c i 1 S =5 a Gallatin er Creek, llntin Ka P4 ^ a 5": M P o a: . II Species. His n? §53 •-.5 ■S.3 ^"^i -<1S S:^ 1*5 g.^ B£S C3 o A "^^ *s« !l ^" •a <§ P4 2 >.ft So 09 •s-j 12£ ®3 II 0) "fa ^ .t^M 9 SS X X X X X X X Ovtliotlietes init'Oiifilis . X X X X X ! X X X Derbva keokuk (?> X Lept;i*na rhoniboidalis X X X X X X X X X X X X X X X X X X X X X X X X Profliictt'lla coonereiisis X Pi'oductGlla alitera ii. 8d Prodiictua scabriculus ..... ^ X X X X X X PiNKluctus ijallatineii.sis n. 80 - .. X X X X X X X X X X X X X X X X X X X Procluctus semireticulatus . ... ........ X Catuarotcechiii herrickana 11. sp .... ......-- X X X X Camarotoecliia luetallica -. X X X X X Camarotfpcliia sappho (?) X X X Caniarotcechia sp X ... Liorhy nchus haguei n. sp X X X X ...-.- Dielasma utab X X X X X X X X X X X X X X X X X X Spiiifer centroiiatus Spiriferceutrouatusvar. semifurcatusu.var Spiiifer subattenuatus Spiiifer sp X Spirifer marionensiB(?) _ X Spirifer sp X Spirifer striatus var. madisonensis n. var. . . X X X Martinia rostratan. sp X X X X X X X X X X X X IJeticularia cooperensis X X X Eeticularia cooperensis var Reticularia ( ?) peculiaris X X Eeticularia (?) subrotuntTata Syringotliyris carteii X X 486 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table showing the ranye of Lower Carboniferous species — Coiitiuued. Species. Number of bed. 24 25 26 27 28 29 30 31 32 Eumetria venieuiliaua X X X X X X f X Seminula madisonensis vav. pusilla u. var. Spiiiinnln, liuiiiilis ii. sv) X X X X X X X X X X X X X Cliotbyris crassicardinalis Cliothyris crassicardiiialis var. nana u. var. X X X X X X X X X Conocardiuiu pulchellum { ?) i X X X X X X X X X X X The following data are derived from the table just given, and go to show that the Madison limestone fauna is practically a unit, evincing very- little progressive differentiation, and not affording sufficient evidence to warrant its subdivision upon paleontologic considerations. Seventy-nine species have been recognized in the nine beds which go to make up the formation. Of these, 4 species have not been assigned to any particular lied, because it has not been ascertained what position the locali- ties from which they came would occupy in the type section. These, with 5 species of Platyceras and 5 of Fenestella, have not been taken into con- sideration in collecting the following data. Therefore only 65 species have been considered in making up the tables from which these data are sup- plied. Of these 65 species, 29 are found to be rare and scattered among single beds, but some 17 or 18 are common, and may be said to range from the bottom to the top of the formation. If the nine beds constituting the Madison limestone be artilicially divided into three groups of three beds each, the central group is represented by 38 species, only 6 of which are not found in the upper or the lower group, LOWER CA1U50NIFEK0US FOSSILS. 487 wliili' tlu' uppiT Madison,' represented by 33 species, and tlie lower Madi- son by 47 species, have 21 species in common. In other words, 64 ))er cent of the forms found in the lowest beds occur also in the middle beds, wliile 45 per cent survive into the upper beds; (iO per cent of those in tlie middle beds are found also in the upper, and 64 per cent of those in the upper are introduced in the lower Madison. These percentages include spet'ies which were found in only a single locality, and which, though per- haps alien to the beds in which they are not recorded, at the same time can not be said to be characteristic of that which alone provided them. Although the table (see p. 484) shows a number of species in the upper portion of the Madison which have not yet been found in the beds below, it would scarcely be tiiie to say that they materially changed its character. The fauna of the Madison limestone is closely related to that which was described in reports by White,^ by Hall and Whitfield,^ and probably also by Meek.* The close relationship of this fauna with that of the Kinderhook formation of the Mississippi Basin was recognized by the authors mentioned. Writing in regard to this correlation in 1877, White says (loc. cit): "The collections of the expedition contain fossils from only three localities that I have definitely referred to the sub-Carboniferous period. These localities are Mountain Spring, Old Mormon road, Nevada ; Ewells Spring, Arizona (upper horizon), and a place below Ophir City, Utah. The collection made at the first-named locality is the most charac- teristic and important one of all, and is referred to the horizon of the Kinderhook formation, to which horizon it is not improbable the others also belong." And again: "The case is far different, however, with the collec- tion from the Mountain Spring locality, which I refer without hesitation to I In makiDg out these percentages certain species, as f:ir as my data go, are fonnd to have skipped one or more beds in vertical distribution. In such case the species Iiave been counted as occurring uninterruptedly between the points of highest and lowest occurrence. 2 Wheeler's Rept. U. .S. Geog. Surv. W. 100th Merid., Vol. IV, 1M77, pp. 12-17, p. 79 et seq. 'King's Rept. Geol. Expl. 40th Par., Vol. IV, 1877, p. 2.51 et seii. ■•Hayden, 1873, Prelim. Rept. U. S. Geol. Snrv. Wyoming, etc., Sixth Ann. Rept. (for 1872), pp. 432-433. Meek here cites a fauna from Mystic Lake ; canyon, e.ast side of Madison River ; Bridger Peak near Fort Ellis; Blacktail Deer Crrek, north side of Gros Ventres Butte: Flathead Pass, north side Henrys Lake; canyon west of GalLitin River (all in Montana), and Camp 19, Idaho, of which he says (p. 433) : " In looking over the collections from these localities I have been quite impressed with the similarity of their geueral focies ( without being quite sure that any of the species are identical) to the fauna of the Waverly group of Ohio, now known to belong to the Carboniferous." Most of these localities are in the vicinity of Yellowstone National Park, and probably are in the Madison lime- stone. 488 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the Kiiidei-liook g-roup" (p. 14). The fauna of this locaUty seems to include the following species : PJaUjcrinus sp., Actinocnnm viaticus, Pro- ductiis })arvus, Strophomena rhomboidaUs, Spirifer centronatus, S. striatus, S. extenuatus, S. (Martinia) pecidiaris, Spirigera monticola, S. ohmaxima, Tere- hratula (Dielasma) hnrUngtonensis. The Madison limestone contains the following equivalent or identical species : Platycrinus symmetricus of the same type as the form figured by White ; Prodiwtus parviformis n. sp., con- sidered to be different from P. jyarvus M. and W., but the same as P. parvus White; Leptcena rhomhokkdis ; Spirifer centronatus; S. striatus var. madison- ensis n. var., which I believe to be varietally different from S. striatus of White, though corresponding to it in the fauna : Syringothyris carteri, repre- senting the closely related S. extenuatus^ oi Whita's fauna; Beticularia (f) peculiaris ; Athyris incrassata.- Dielasma utah, which I ha-s'e recognized in the Yellowstone National Park collections, is probably the same as D. hurUngtonense ; at least, with the limited material at my command, I am unable to find any characteristic difference. Some of the species from the other localities also have their analogues in the Madison limestone fauna. S. harveyi White may be one of the two species of Syringopora described below, although the original description is insufllcient for identification. Conocardium pukhellum (f) of this report is certainly of the same type as, and may be identical with, C. trigonak White, which is unfortunately unidentifialjle, while Euomphahis luxus is represented by Straparollus titahensis, both closely allied forms. Hall and Whitfield also describe a similar fauna from the limestone of Dry Canyon, Oquirrh Mountains; and from Ogden, Little Cottonwood, and Logan canyons, in the Wasatch Range, Utah. This fauna is described and figured under the name of the Waverly group, and is said (loc. supra cit., p. 201) to contain an assemblage of fossils considered to be "of about the age of the Waverly group of Ohio' and the yellow sandstones of Bur- ' Some of the specimens which I have identified as S. carteri can not be said to differ in any essential particular from that figured by White as S. extenuatus. = This form is very close indeed to White's Spirigera ohmaxima in form and general characteristics. Strictly speaking, A. incrassata is a true Athyris, while Spirigera ohmaxima belongs to the subgenus Cliotliyris. In point of fact I have not been able to discover spines on White's specimens, and they may prove to bo the same as the form which I have called J. incrassata. ■'The Waverly group of Ohio is now known to be composite in its nature and to contain several different faunas. The lower portion, Herrick has been led to believe, is Devonian, and the upper portion corresponds to the Kinderhook and the Burlington-Keokuk phases of the Mississippian. A close acquaintance with the Waverly faunas, involving several years of collecting and study, has convinced me that Herrick is altogether mistaken iu this view. The whole of the Waverly, including LOVVliR CARBONIFEROUS FOSSILS. 489 lino-ton, Iowa, wliirli li:i\X' been referred to the same aj'e.'" The foHowing species are described as "Fossils of the Waverly - may be mentioned as identical or cognate forms occurring- in the Madison limestone: Mkhelinia placenta (probably the same as MichcUnia sp. of Hall and Whitfield's report), Orthothetes incequalis (the same as Streptorhynchus equivalvis), Leptmna rhomhoidalis, Chonetes loganensis, Spirifer centronatus (S. alha-pinensis seems to be only an insignificant varia- tion from this form), Martinia rostrata n. sp. (the same as Athyris planosid- cata (J) of Hall and Whitfield), Camarotachia metaUica (the same form -which Hall and Whitfield identify as Rhynchonella piistidosa (f) ), Bielasma utah, Straparollus utahensis, Proetus peroccidens, and P. loganensis. Of the forms grouped vmder the heading "Fossils of the Lower Carboniferous" (p. 265), Productus semireticidatus, P. Icevicosta, and Spirifera setigera (probably the form recognized below as Eeticidaria cooper ensis var.) are found in the Madison limestone. ]\Ieek' cites a fauna from various localities in Montana and one in Idaho which is probably identical with that of the Madison limestone. The lists which accompany this notice are of a preliminary character, and but few species are identified specifically. Still, the genera involved, together with such brief descriptions as are appended, as well as the close relation geo- graphically of his localities to the Yellowstone National Park, i-ender it probable that he was dealing with the Madison limestone fauna. Meek expresses himself as being impressed with the similarity of its general facies to that of the Waverly group of Ohio. The faunal lists given by Peale^ constitute essentially the same fauna the Bedford shale and .iscending to its hitest stratum, is undoubtedly Carboniferous. The fauna of the Cuyahoga shale, using the term to include the outcrops at Lodi, Medina, Bagdad, Weymouth, and the lower (?) beds at Riclitield, which Herrick wishes to refer to the Devonian, is certainly the same as that of the Chouteau limestone, which Meek includes as typical in his description of the Kinderhook period (Am. Jour. Sci. (2), Vol. XXXII, 18(il. pp. 169 et seq., 288). Above the Cnyahoga shale follow representatives of the Hurlington and Keokuk horizons. It is probably that portion of the Waverly faunas which is found in the Cuyahoga shale that Hall and Whitfield have in mind in this reference, as they mention the yellow sandstones of Burling- ton, which, with the Chouteau limestone, are supposed to be typical Kinderhook. 'Sixth Ann. Kept. U. S. Geol. Surv. Wyoming, etc. (loc. cit., pp. 432-433, 465 et seq.) ^The Paleozoic section in the vicinity of Three Forks, Montana: Bull. U. S. Geol. Surv. No. 110 1893, pp. 33-39. 490 GEOLOGY OF THE YELLOWSTOXE NATIONAL PAEK. as that of the Madison limestone, and had the material been worked hj the same hand the specific determinations wonld doubtless have been more uniform. The two areas are geographically closely related. Considering the favina of the Madison limestone as a whole, it can be pointed out that, of the 79 species known from this formation, 29 were described from or have been identified in Kinderhook beds of Ohio, Michi- gan, and the Mississippi Valley — that is, aljout 37 jier cent of the Madison limestone fauna consists of Kinderhook species. These are: JliclieUnia placenta, Platycrinus symmetricus, Cra/nia Icevis, Rhipidomella michelini, Orfho- thetes incequalis, Berbija keokuk (f), Leptcena rJiomhoidalis, Chonetes loganensis,^ Chonetes ornatus, Productella cooperensis, Prodiictus Icevicosta, P. semireticu- latus, Camaroplioria ringens, CamarotcecMa herrickana n. sp., C. metaUica, C. cainarifera (.**), C. sappho (.''), Dielasma utah,^ Spiriferina solidirostris, Spirifer centronatus, S. suhattenuatus, S. marionensis (.^), Betkidarla cooper- ensis, B. (.^) 2>'^culiaris, R. (f) suhrotimdata, Syringotliyns carteri, Athyris lameUosa, Cliothyris crassicardinaUs, and Conocardium pulchelluin (.**). After making the necessary deductions from this list, some of whose identifications are rather in the nature of approximations, it still niust be apparent that the fauna of the Madison limestone has many peculiarities of the earlier Mississippian, and in particular shows a marked affinity through- out with the Kinderhook fauna. Taking a more general view of the fauna, the presence of Syrinr/othyris speaks for lower Mississippian, since it is not known there above the Keokuk, and the same is true of Leptcena rhomhoidalis, since it does not occur above the lower Burlington. It umst be noted, however, that these forms appear to be restricted to the lower portion of the ]\Iadison also. The absence of Productus punctatus from this formation is evidence in the same direction, as it is introduced in America in the Keokuk, and in general there is to be noticed in the Madison limestone fauna an absence of those highly difi'erentiated and often peculiar species which characterize the beds of the middle and upper Mississippian. This is perhaps most noticeable in the Spiriferoids and Productoids, for they are the conunonest forms. In the Madison tliese comprise a few comparatively simple, stable, and persistent 'A form, probably the same, is common in the Cuyahoga shale of northern Ohio, passing usually as C ilUnolsenais. •Probably a synonym for /'. hiirUinjtoiieiise. LOWER CARBONIFEROUS FOSSILS. 491 forms, often real Kin6 GEOLOCiY OF THE YELLOWSTONE NATIONAL PARK. Sjiiriferina solidirostris, Liorliynclms haguei n. sp., Cnmarotoechia metallica, ProdncteUa cnopcrcnsis, Chonefes ornaUis, Orthothetes injiatus, Crania Jcevis, rtilopora sp., Fe)ie,st€Ua sp. Of these L. haguei, Naticopsis (f) sp., Plati/ceras sp.. Crania Icevis, Ptilopora sp., and Fmestella sp. have not been identified elsewhere in the Madison limestone, with whose fauna, however, that of these localities is very closel}' related. The red beds exposed at the head of Conant Creek, Teton Rang-e, may also be separated frcim the ]\Iadison limestone, with which lithologically as well as famially they are slightly connected. The matrix is a red cal- careous shale, more shalj- than is common in the Madison limestone, in which the fossils are, as a rule. Aery Ijadly crushed. The fauna, which is scantil}- known and, on account of the condition of the material, inadequatel)' identified, consists of Semimda madisonensis n. sp., Spirifer ■marioneniiis (?), Orthothetes sp., and Eridopora (/) sp. None of these is unquestionably identical with species found in beds below, thougli they are perhaps cjuestionably distinct. This locality is jDrovisionallj" referred to bed 32, the highest in the formation. More evidence may show it to be later than the Waverly- DESCRIPTIONS OF SPECIES. DEVONIAN. C(ELEXTERATA. ACTINOSTROMA Nicholson, 1886. ACTINOSTROMA SJl. At least one species of Stromatoporoid is represented in this collection ; but the material, badly weathered and poorly silicified, scarcely affords the pronnse of more than a generic identification. Therefore it has not been studied by means of microscopic sections. A careful examination shows a larffe concentricallv laminate coenosteum. The laminae are moi'e or less contorted, and the division into latilamiuse is not apparent. The very fine laminae are connected by minute radial pillars, which on favorably exposed surfaces are seen to be continuous. This is the well-known characteristic structure of the genus Actinostroma, very al^undant in Devonian strata in both hemispheres. DEVONIAN FoasiLS. 497 Formation and locality: Three Forks limestone, near the divide between Gallatin Valley and Panther Creek, Bighorn Pass, Gallatin Kange, bed 21 ; S. L. Penfield. East slope of Antler Peak, Gallatin Range; A. C. Gill. South slope of Antler Peak, Gallatin Range; J. P. Iddings. PACHYPHYLLUM Edwards and Haime, 1850. Pachyphyllum sp. Corallum attaining large size (the present specimen measures 150 mm. in longest diameter and is fragmentary). Corallites small (9 to 10 mm. in diameter), separated by mural zones of about 2.5 mm. Septa, 32 to 34 in number, and alternating in size. The specimen studied is a massive weather-worn fragment, which does not show the external surface of the corallum, nor the nature of the calyces. The rock has also suffered considei'ably from compression, for, though the limestone is scarcely altered, the corallites are flattened and the lines of the septa and spongy exothecal and dissepimental tissue often broken and discontinvious. The corallites vary much in size, owing probably to difference in age, but are more uniform where the corallum is crowded. The average of mature cells is, perhaps, as above stated. That measure- ment, however, relates to the septate portion only. The mural tissue is very finely vesicular and is not penetrated by the septa, which are about 34 in number. They are strong, but have not the Acervularia-like expansion so strongly developed as in P. devoniense. Longitudinal sections show alter- nating stripes of finely vesicular mural tissue and the longitudinally banded septate portion. This is occupied by dissepimental plates, but the presence of complete tabulse has not been ascertained. While I am convinced that this species is as yet undescribed, and although the characters established are sufficient to enable one to distinguish it from any forms known and to recognize it again at the type or adjacent localities, yet I have not felt justified in proposing for it a new name, since the material is scarcely suitable for illustration; and it is not improbable that from other stations, more or less remote, new types will subsequently be described, which it will not be possible to separate from this, owing to the imperfections of the latter. The only species which, so far as I am aware, have been referred to MON XXXII, PT II 32 498 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. this genus in this country are the three mentioned by Miller in his North American Geology and Paleontology, viz: P. devoniense, P. woodmani, and P. solitarium. The last mentioned of these can scarcely be referred to the genus Pachyphyllum, since it is described as a simple coral with an epitheca (or theca) and without exothecal tissue. PachjplujUum tvoodmani was originally mentioned by White as Smithia tvoodmani} Hall and Whitfield describe and figure it - under the name of PachjphjUum tvoodmani, saying "the exsert form of the cells, and their limitation by an outer wall, are features which do not exist in Smithia, but pertain to the genus Pachyph}^- lum." In point of fact, Pachyphyllum seems to be a synonym of Smithia. The genus is characterized by Edwards and Haime as follows: "Corallum compound, increasing by lateral gemmation. Corallites not separated by an individual epitheca, but united in their lower portion by a large develop- ment of costJB and exothecal tissue; septa and tabulfe well developed. Pachyphyllum is distinguished from all othei' Cyathophylloids by the development of the costaj and exothecal tissue.'" The descrijDtion of P. houchardl, the type (ibid.), accords with the generic description, but, unfortunately, by some oversight, it was not figured by the authors. Although there is the usual reference heading the specific description, there is no corresponding plate or description of plate in the accompanying atlas. I am not aware that it has subsequently been figured. Smithia is described by the same authors in the following terms: "Corallum compound, astrei- form, multiplying by submarginal gemmation. Corallites intimately connected, having the same structure as Acervularia (i. e., with two walls; septocostal structure well developed between the walls; much less in the central area. No columella. Tabular little developed), except that they lack external walls and that the septocostal rays are more or less confluent. No columella." (Loc cit., p. 142.) A comparison of the two genera shows that they are at least very closely related. One great distinction, implied rather than expressed, is that in Smithia the one wall is regarded as homologous with the inner wall of Acervularia, the intercellular tissue being then simply confluent intermural tissue of adjacent cells. In Pachyphyllum, on the other hand, 1 Geol. Kept. Iowa, 1870, Vol. I, p. 188. 2 Twenty -third Ann. Kept. New York State Cab. Nat. Hist., p. 231, PI. IX, fig. 9. 3 Hist. NAt. des Coralllaires, Vol. Ill, Paris, 1857, p. 391. DEVOVIAN FOSSILS. 499 the imperfect wall is regarded as equivalent to the theca of most rugose corals, the outer wall of Acervularia, while the surrounding tissue is exothecal in nature, a sort of cocnenchyma. If this distinction can be established, the two genera would be widely different in fact, however diffi- cult it would be to distinguish them in practice. However, there seems to be little if any reason why the single, imperfect central walls in both genera should not be homologous with each other and with the imperfect inner wall of Acervularia. Thus the two differentiating characters mentioned by Hall and Whitfield fall to tlie gi-ound, for in neither genus are the corallites limited by an outer wall. As to the exsert form of the cells, this character is not mentioned in the generic description of Pachyphyllum, but P. bouchanli is described with "Walls strong and distinct; calyces circular, deep, with edges rather elevated." This character, then, is not regarded as of generic value, and in the type species is not especially striking. The chief points of distinction which can be drawn from Edwards and Haime's description (leaving out their view of the homologies of the inner wall, which I hold to be questionable) come to this, that Pachyphyllum -has very extended tabulse, while Smithia has them only slightly developed, a character which, taken alone, is of doubtful generic importance. Smithia is generally regarded as a synonym for Phillipsastrsea, but Edwards and Haime claim that it is distinguished from the latter by the presence of a columella. If constant, this would seem to be a good character. After studying the type species, Nicholson states that Phillips- astrsea (= Smithia) has essentially the structure of Heliophyllum — i. e., with carinate septa, fossula, and without an inner wall. If Smithia is indeed synonymous Avitli Phillipsastrsea, then Pachyphyllum is a quite different thing. But if Smithia and Pachyphyllum are as Edwards and Haime have described them, it seems probable that the latter is a synonym of the former. It is possible that three types are included among the five species referred to Pachyphyllum. One of these, P, soUtarium, I think, beyond a doubt, must be placed elsewhere. Or, is it perhaps the initial cell of a Pachyphyllum colony? Another type which is structurally near Smithia is that represented by P. houchardi and P. woodniani. A third type is found in P. devoniense and the form above described. It is 500 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, characterized by a mural zone of vesicular tissue, which is not penetrated by the septa. Edwards and Haime say that in P. devoniense this zone is traversed by the costaj, which are not very pronounced, but distinct. This is scarcely apparent in the figure, but, if so, the form represents an inter- mediate stage between P. houchardi and Pachyphylliim sp., where the thick costse terminate in the mural zone without penetrating it. Formation and locality: Three Forks limestone, north side of saddle west of Mount Miller, Absaroka Range ; Louis V. Pirsson. CYATHOPHYLLUM Goldfuss, 1826. Cyathophyllum c^spitosum Goldfuss (f) CyaihophyUum ccmpitosum Goldfuss, 1826. Petrefacta Germanic, p. 60. In the calcareous sandstone, associated with specimens of Actiuostroma, Pachyphyllum, Atrypa, etc., is a species of Cyathophyllum, which may be identical with G. ccespltosum Goldf It consists of isolated fragments of cylindrical corallites, which have about forty alternately long and short septa, a tabulate central portion, and a vesicular outer zone. In size, general character, and in specific detail, as far as determinable, these strongly resemble Goldfuss's species, and may, like it, when entire, have grown in tuftlike masses. Indeed, the small diameter and the cylindrical form of the corallites are favorable to such an interpretation. C. ccespitosum is already known to occur in American strata, being found in Upper Helder- berg rocks. Formation and locality: Three Forks limestone, near the divide between Gallatin Valley and Panther Creek; Bighorn Pass, Gallatin Range, bed 21; S. L. Penfield. East slope of Antler Peak, Gallatin Range; H. C. Gill. North side of saddle west of Mount Miller, Absaroka Range; Louis V. Pirsson. CLADOPORA Hall, 1852. Cladopora sp. Like the other corals from the same bed, specimens ot Cladopora are coarsely silicified and considerably weathered. The branches are circular, and about 5 mm. in diameter. The pores are nearly circular, small (about 0.25 mm. in diameter), and separated from each other by a distance about DEVONIAN FOSSILS. 501 equal to their own diameter. What the shape of the orifice may have been originally it is impossible now to determine. In its present condition the con-allum resembles C. lahiosa and C. inngms, both of Romiuger/ but more especially the form figured as a variety of C. lahiosa} The form under discussion resembles C. lahiosa in the slendeniess of the stem, but the pores are more distant, and at present not labiate. It resembles C. pinfjuis in the thick interstitial tissue between the cells and in the less labiate condition of the latter ; but the branches are less robust and the cell apertures a])j)arently smaller. Formation and locality: Three Forks limestone, near the divide between Gallatin Valley and Panther Creek, Bighorn Pass, Grallatin Range, bed 21; S. L. Penfield. FAVOSITES Lamarck, 1812. Favosites sp. PI. LXVI, fig. 8rt. Corallum rather small, about 50 mm. (I) in diameter; cells small, very closely tabulate, tabulae being about 0.5 mm. apart. Number of rows of mural pores, character of the same, and nature of the epitheca, not known. The material submitted was not found in place. It consists of a frag- mentary silicified example, which, while showing some characters very plainly (e. g., the tabulation), has others obliterated so that specific identi- fication of the form is impossible. It can, however, be affirmed that it does not belong to any Carboniferous representative of the genus, at least such as are yet described, and it can therefore with great probability be regarded as belonging to Devonian or Upper Silurian time. Formation and locality : Three Forks limestone, north side of Soda Butte Creek, Absaroka Range; J. P. Iddings. 'Geol. Surv. Michigan, Vol. Ill, PL II, 1876, pp. 52-53, PI. XXI, figs. 2, 3. '^ Loc. cit., fig. 3, lowest specimen. 502 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK. BRACHIOPODA. ATRYPA Dalmau, 1827. Atrypa reticularis Linud. PI. LXVI, flgs. la, lb, If. Atrypa reticularis Linac^, 1767 : Systema Naturse, ed. xii, Vol. I, p. 1132. Hall, 1852 : Pal. New York, Vol. II, p. 72, PL XXIII, figs. 8, Sa-8»; p. 270, PI. LV, flgs. 5a-5u. Billiugs, 1863: Logan, Geol. Surv. Canada, Eept. Progress 1843-1863, p. 318, figs. 335a-335c; p. 384, figs. 4160-4160. Hall, 1867 : Pal. New York, Vol. IV, p. 316, PL Lll, flgs. 1-3, 7-12; PL LllI, flgs. 3-19; PL LIIlA, flgs. 22, 23. Meek and Wortheu, 1868: GeoL Surv. Illiuois, VoL III, p. 432, PL XIII, flg. 11. Meek, 1877: King's U. S. GeoL Expl. 40tli Par., VoL IV, p. 38, PL I, figs. 7, 7a; PL III, flg. 6. White, 1880: Second Ann. Kept. Indiana Bureau Statistics and Geology, p. 502, PL V, flgs. 7, 8, 9, Walcott, 1884 : Mon. U. S. GeoL Surv., Vol. VIII, p. 150, PL XIV, figs. 6, 6a, 6b. Beecber and Clarke, 1889: Mem. New York State Mus. Nat. Hist., p. 51, PL IV, figs. 12-20. Hall and Clarke, 1893: Pal. New York, VoL VIII, Pt. II, p. 165, fig. 153; PL LV, figs. 1-17. Herrick, 1895: GeoL Oliio, Vol. VII, PL XX, fig. 7. This well-kuowu and uuiversally distributed form needs no further description. It has as yet been identified from but one locaUty in the Yellowstone National Park, is represented entirely by casts, and is a small, coarsely plicate form, similar to that from the Lockport (often called Niag- ai-a) Hmestone, and identified by Walcott fi'om Upper Devonian strata. Formation and locality: Three Forks limestone, base of bluff, Little Sunlight Creek; Arnold Hague. Silurian and Devonian throughout the world. Atrypa missouriensis Miller. PL LXVI, figs. 2a, 2b, 2c. Atrypa reticularis (var.) Meek, 1877: King's U. S. GeoL Expl. 40tli Par., VoL IV, p. 38, PL III, fig. 6a. Atrypa desquamata V/alcott (uou Sowerby), 1884: Mou. U. S. GeoL Surv., Vol. VIII, p. 150, PL XIV, figs. 4, 4a. Atrypa missouriensis Miller, 1894: Eigbteeuth Ann. Kept. State Geologist of Indiana, 1893, p. 315, PI. IX, flgs. 19-21. Shell rather small, subcircular, variable in shape. Dorsal and ventral valves moderately and equally convex, finely striate, not at all or only obscurely marked by distant concentric striae, which, moreover, are not DEVONIAN FOSSILS. 503 sqiianiose. Beak of the veutial valve small, not much incurved; area small. Anterior margin distinctly but not strongly sinuate. There can be little (U>ubt that this is the same form for which Miller proposed the name Atnjpa inissouriensis, and which had been previously referred to by Meek as Atrypa reticularis and by Walcott as Atrypa desqua- muUi (loc. cit). A. missoiiriensis is described from Middle Devonian rocks (probably Hamilton age), and the type locality is 3 miles from Otterville and 17 miles west of Sedalia, Missouri. A form, probably referable to Miller's species, is found at Fulton, Missouri, in rocks of Hamilton age, and with this the material from the Yellowstone National Park is very closely allied, perhaps specifically identical. It is possible that the finely striated variety of A. reticularis, mentioned by Walcott^ and said to resemble a variety fi-om the Hamilton and Chemung groups in Iowa, may also be placed in the list of synonyms. ^i. missouriensis occurs in considerable abundance at several localities in the Yellowstone Park, but it is rarely found associated with Atrypa reticularis, which is known from the same region. The two forms are thus distinct in distribution as well as intrinsic character, when this region alone is contemplated, and the natural tendency is to refer them to diff'erent species, but in view of the almost universal distribution of A. reticularis, and its equally extensive range of ^'ariation, perhaps a varietal distinction is all that is warranted. Only a monographer will be com- petent to determine specific limitations in this protean type. A. desquamata in this country is nothing more than A. reticularis with an erect beak, area, and unconcealed foramen ; and the same appears to be equally true of the European forms. This character or group of characters seems scarcely of specific value, but in any case the same peculiarities of surface, etc., which distinguish A. missouriensis from A. reticularis serve to diff'erentiate it from A. desquamata also. Although it is a mature form, A. missouriensis is characterized by neologic traits, and agrees very closely with young examples of A. desquamata as figured by Davidson." Still, full-grown shells are the only ones with which we are justified in comparing it. 'Mod. U. S. Geol. Surv., Vol. VIII, 1884, p. 150. "British Fossil Brachiopoda, Vol. Ill, Part VI, PI. XI, tigs. 6, 6o. 504 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Formation and locality : Three Forks limestone, south slope of Antler Peak, Gallatin Range ; south side Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. North side of saddle west of Mount Miller, Absaroka Range; Louis V. Pirsson. Near Otterville and Sedalia, Missoui-i. SPIRIFER Sowerby, 1815. Spirifer engelmanni Meek. PL LXVI, figs, :^a, 3b, Sc, 3d. Spirifera engelmanni Meek, 1860: Proc. Acad. Nat. Sci. Phila., p. 308. Meek, 1877: King's U. S. Geol. Espl. 40tli Par., VoL IV, p. 41, PI. Ill, figs. 3-3a. Spirifer engelmanni Meek, 1876: Simpson's Rept. Expl. Gt. Basin. Terr. Utah, p. 316, PI. I, figs. Irt-lc. There is only one example of this species. Though otherwise appar- ently identical with the smaller forms of S. engelmanni, it is abnormal in this, that the strong plication bounding the sinus bifurcates, the two inner ribs lying upon the sides of the sinus. 1 have not observed this in S. encielmanni from Nevada, but have seen dorsal valves with a shallow median sulcus on the fold, so that there is little reason for believing that such irregularities do not occur on the other valve as well. The specimen could scarcely be a young individual of S. disjunotm, for that species has finer plications, which are distributed in large numbers on both fold and sinus. Formation and locality: Three Forks limestone, south side Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. Middle Devonian, Neils Valley, Utah; White Pine District, Nevada. ATHYRIS McCoy, 1844. Athyris vittata var. triplicata n. var. PI. LXYI, figs, la, 4&, 4c. Shell small, subcircular. The two valves moderately and equally convex. Ventral valve marked by a broad, shallow median sinus. On either side is a faint sinuation separated from the median one by a sharp ridge. Dorsal with well-defined, square fold, bounded on either side by an angular depression, after which follow, one on each side, two other slight folds. All the plications of this shell are discernible for only a short distance back from the margin. Width, 9 nun. ; length, nearly the same. DEVONIAN FOSSILS. 505 The shell is so badly exfoliated that its surface characters are unknown, and the generic reference, as a whole, is donbtful. It resembles Athyris ritfnfa of the Corniferoiis and Hamilton groups, and A. nngelica of the Hamilton, some examples of which approach this shell, though not very closely. It finds a close ally in A. (OHjclira var. occidentalis Whiteaves (Cont^ Canadian Pal., Vol. I, Pt. HI, 1891, p 227, PI. XXXII, figs. 3-3a), from which it differs chiefly in having an additional low fold on either side. The two forms resemble each other more than either A. anffeUca or A. vittnta. Whiteaves's shell is probably worthy of specific distinction, and the relation between it and the form from the Madison limestone would be best expressed by making the latter a variet}' of the former. The name of my shell would then be Athyris occidentalis var. triplicata. Formation and locality : Three Forks limestone, south side of Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddiugs. GASTROPODA. PLEUROTOMARIA Defrance, 1824. Pleurotomaria ISAACS! Hall and Whitfield. (!) PI. LXVI, figs. 5a, 56. Pleurotomaria isaacsii Hall and Whitfield, 1873 : Tweuty-third Kept. New York State Cab. Nat. Hist., p. 238, PL XII, figs. 6, 7. The form which I have referred to Hall and Whitfield's species occurs as an isolated specimen of a large gastropod shell. As far as the somewhat imperfect condition of the material permits a comparison, the specimen from Yellowstone National Park is very close to P. isaacsi. It is a large flattened shell, about 59 mm. in diameter, agreeing in size, general proportion, and peritreme section with the species to which I have referred it. On the other hand, the spire is a little more elevated than the specimen figured by Hall and Whitfield, the whorls a little more angular in section, with the upper surface obliquel)^ plane or slightly concave. The shell appears to be without ornamentation. Pleurotomaria isaacsi is from the Lower Devonian, probably the Scho- harie grit. Formation and locality: Three Forks limestone. Wall Canyon, Clark Fork Valley; Arnold Hague. Lower Devonian, near Raymond Station, Iowa. 50(3 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Pleurotomaria(?) sp. A rather large gastropod shell, broken and embedded m limestone. Height, about 22.5 mm.; diameter at base, 25 mm.; whorls, five or six. Umbilicus extending through three or four whorls. Apparently without ornamentation. Cross section of whorl subquadrate, the upper and lower faces converging centripetally, the distal and proximal faces converging toward the apex. Shell thick, interior section of whorl nearly circular. The matrix inclosing the specimen is weatherworn so as to form a transverse section somewhat more than half through tlie shell. From this the above notes were taken. The surface as reijresented by section is unornamented, for the line representing the outer face is simple and entire. Although a certain identification is impossible, this fact operates against refeiTing the form to Pleurotomaria. It may go with the genus Palseo- trochus, but is distinct from anything yet referred thereto. Formation and locality: Three Forks limestone, north side of saddle west of Mount Miller, Absaroka Range; Louis V. Pirsson. LOXONEMA Phillips, 1841. LOXONEMA DELICATUM n. sp. PI. LXVI, fig. 6a. Shell very small, elongate. Spire consisting of about five volutions; whorls well rounded and suture line depressed. Aperture nearly circular. The specimen described is a cast, not showing any surface characters. It is foimd associated with Platijstoma minutum and other gastropods (see ante, p. 482). Formation and locality: Three Forks limestone, south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range; J. P. Iddings. PLAT Y STOMA Conrad, 1842. Platystoma minutum n. sp. PI. LXVI, figs. 7(1, Ih. Shell extremely small, conical, flattened. Spire low and consisting of about three volutions. Aperture somewhat oblique, elongate, elliptical. Surface nearly smooth, ornamented, if at all, only with lines of growth. LOWER CARBONIFEROUS FOSSILS. 507 This species occurs at the south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range, associated with Loxonema delicatmn and a number of other gastropod forms too imperfect for description (see ante, p. 482). Formation and locaHty : Three Forks Hmestone, south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range; J. P. Iddings. LOWER CARBONIFEROUS. PROTOZOA. ENDOTHYRA Philhps, 1845. Endothyra baileyi var. parva n. var. PI. LXXI, flgs. 13rt, Ub, 13c. This form is known only by microscopic sections and therefore very inadequately ; but the correctness of the reference to Endothyra seems unquestionable, and I am even in doubt whether it is varietally distinct from Hall's species. So far as my observations go, it is never much over half the size of Endothyrahaileyi,'^ and is more simple — i. e., less numerously chambered. Although these characters are ordinarily of questionable diag- nostic value, appearing as it does in quite different associations, the Western form seems worthy to be classed as a distinct variety. And it is not improb- able that a study of the shell under auspices more favorable than by microscopic sections will more fully justify the distinction. This form should be compared with E. howmani Phillips and E. lobata Brady, which Brady '^ considers to be the same as E. bailey i. They are less robust and more simple forms. Formation and locality: Madison limestone. White Mountain, Absaroka Range; Arnold Hague. Amphitheater east of Bannock Peak, Gallatin Range, bed 30; Snake River Valley, west of Two Ocean Plateau; W H Weed. ' See PI. LXXI, figs. 12a, 126. Si PaliBontographical Soc, Vol. XXX, p. 92, PI. V, figs. 1-4. 508 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. PORIFERA. HOLASTERELLA Carter, 1852. HOLASTEEELLA WRIGHTI var. AMERICANA 11. var. PI. LXXI, fig. 11a. The only trace of sponge remains which has been observed in Yellow- stone National Park consists of two or three delicate silicified spicules, which, for lack of a better designation, I have called by the above name. While closely related to Carter's species,^ I think it is undoubtedly distinct. At the same time, in view of the limited amount of material at my disposal, I do not feel justified in proposing a new specific name, Avhile the occurrence of the form seemed worthy of notice and a name of some sort desirable. The spicules in question are of the regular hexactinellid type. The six arms are stout and short, each quickly subdividing into four long tapei'ing branches. These are set at an acute angle with one another, and ornamented with fine nodes, which tend to an arrangement in transverse rows, giving the branches a finely annulated appearance. The genus Holasterella, so far as I am aware, is restricted in its range to Lower Carboniferous strata; and this is the first notice of its occuiTence in this country. Formation and locality: Madison limestone, divide between Gallatin Valley and Panther Creek, near Bighorn Pass, Gallatin Range, bed 24; Arnold Hague. C(ELENTERATA. AULOPORA Goldfuss, 1826. AULOPORA GEOMETRICA n. Sp. PL LXVII, fig. 6a. Corallum free ("?), spreading. Coralhtes small, each regularly budding off two other individuals, which diverge at an angle of about 120°, so that the colony as a whole presents a regular network with hexagonal openings. Length of corallites about 5 imn.; diameter, from 1.25 to 1.5 mm 1 See Carter, 1880: Ann. Mag. Nat. Hist., Vol. VI, p. 209, t. 14b, figs. 1-17; and Hinde, 1883: Cat. Foss. Sponges, Brit. Mus., p. 153, PI. XXXII, figs. i-ig. LOWER CAUBONIFEROI a FOSSILS. 509 This species is interesting as being the first rejiresentative of the genus Aiilopora described from the Carboniferons rocks of this country. The form in question presents some apparent divergences from typical Aulopora habit and stracture, such as, if they could be established, would be suffi- cient for generic differentiation. However, I have but one specimen of the species, and it does not afford conclusive evidence on the points in question. The corallum appears to have been free, or at all events to have outrun the surface on which it was creeping, and the unaunexed portion to have been broken away; for there is no evidence of attachment in its present condition. The corallites are small and cut up internally by infundibuliform dissepimental tissue, somewhat as in Syringopora. At least, there are usually to. be seen one or more cylindrical walls internally concentric with the theca. It may be thought, and perhaps correctly, that this is the initium of a Syringoporoid colony. As against this view, it may be stated that no such colonies are known from the locality in question, nor would the hypothetical colony restored from this initium probably agree specifically with any yet discovered in the Yellowstone Park. Formation and locality: Madison limestone, Bighorn Pass, Gallatin Range, cherty belt; Arnold Hague. SYRINGOPORA Goldfuss, 1826. Syringopora aculeata n. sp. PI. LXVII, figs. 5a, 56. Corallum large, never favositiform ; corallites small, radiating, sepa- rated by distances varying from one-half to five or six times the diameter of the average corallite. Usually about 1 diameter apart. Corallites about 1.5 mm. in diameter. Septa represented by spines set in about twenty-five vertical rows. The number appears to be varia- ble, and can not be stated with exactness. The spines are long and very numerous, so that they form a striking feature in any transverse or longitudi- nal section. Dissepimental structures well developed, spinose, vesiculose infundibuliform, the dissepimental plates converging very gradually. Formation and locality : Madison limestone. White Mountain, Absaroka Range; Arnold Hague. Crowfoot Ridge, Gallatin Range, bed 29; J. P. Iddings and W. H. Weed. 510 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. Syringopora surcularia n. sp. PL LXVII, figs, ia, ■lb. Similar to the above, but larger. Average diameter of individual corallites, 2.5 mm. Walls thickened by stereoplasma. Infundibuliform di.ssepimental tissue well developed, spinulose; the spines appear as nodes of greater or less prolongation, often radially directed between parallel dissepiments. They are irregular, however, have no constant connection with the spiniform septa, and never give the corallite the septate appearance of rugose corals. This species is, in a general way, very close to the preceding, but the eye differentiates them at a glance on the basis of size. The walls of S. sur- cularia are more thickened by stereoplasma than are those of S. aculeata, and the septal spines, which are embedded in it, appear to be relatively not so long, so numerous, nor in so many rows. Both species are easily distinguished from S. multaUenuata McChes., by the fact that the corallites in the latter often grow in contact and are scantily supplied Avith septal spines. Formation and locality: Madison limestone. White Mountain, Absaroka Range; Upper Gallatin Valley, west of Bighorn Pass; Arnold Hague. Crowfoot Ridge, Gallatin Range, bed 28; J. P. Iddings and W. H. Weed. Head of Gallatin River, west of Three River Peak; Arnold Hague. MICHELINIA DeKoninck, 1842. MiCHELINIA PLACENTA White. PL LXVII, tigs. 3a, 36. Michelinia {?) placenta White, 1883: Twelfth Anu. Kept. U. S. GeoL Geogr. Surv. Terr., Pt. I, p. 157, PL XXXIX, figs, la-1^7. This species is known at two localities in the Yellowstone National Park. It appears to be the same form described by White, from Sedalia, Missouri, where it occurs at tlie top of the Chouteau limestone. I have not seen specimens from White's locality, but his description and figures show the two forms to be very similar. Formation and locality : Madison limestone, east side of Gallatin River west of Electric Peak; divide between Gallatin Valley and Panther Creek, near Bighorn Pass, Gallatin Range, bed 24; Arnold Hague. Top of the Chouteau limestone, Sedalia, Missouri. LOWEK CARBONIFEKOUS FOSSILS. 511 MENOPHYLLUM Milue Edwards and Haime, 1850. MeNOPHYLLUM (!) EXCAVATUM H. sp. PL LXVII, figs, la, lb, Ic, hi, le. If. Corallum simple, regularly and rather rapidly expanding, very slightly curved. Length of an average specimen, 41 mm.; diameter at the top, 23 mm. Septa of two series. Calyce verj- deep, half or more than half the entire length of the corallum. In the calyce the primary septa are short and the secondary septa shorter still. Below, only the primary septa are well developed. They are there sometimes so thickened by stereoplasma as to make the bottom of the corallum almost solid. There is no columella nor dissepimental development, but a well-marked fossula is always present. The deep calyce uninterrupted by transverse partitions, the smaller number of septa, and large fossula, strongly characterize this form There is only one species of Menophyllum known heretofore, M. tentii- marginatmn; and M. excavatum is, so far as I am aware, the first reference made to the genus in this country. This reference may, however, perhaps justly be called in qviestion, since M. tenuimargin'atwn is said to possess crescent- shaped tabulfe, and to be allied to Amjjlexus, while M excavatum is without tabulae and dissepimental tissue. On the other hand, as seen in transverse sections, the structure of the two forms seems to be so closely analogous that I can not but believe that, if not congeneric, M. excavatum is at least nearly allied to M. tenuimarginatum. It resembles the genus Cyathaxonia in being without tabulae or dissepiments, but differs from it in lacking a columella as well. I have avoided the genus Petraia, which is pei'haps founded on a similar type, for it is little known and can scarcely be regarded as well established. Nor do I believe a reference to Zaphrentis to be war- ranted, for, as before stated, M. excavatum is without endothecal structure except the septa, and the manner in which the ends of all the septa are bent to form an inclosing wall for the fossula is very characteristic. Compared with M. tenuimarginatum, M. excavatum has fewer primary septa, and those of the second order are not so well developed. The structures of the earlier corallum of this coral have not been observed. The secondary septa attain only an inconsiderable development. There are about twenty-six primary septa, which are bent at the ends and so united as to leave a large fossula, reaching to the center of the theca. The 512 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. fossula is bisected by a cardinal septum, which also reaches to the middle and is there connected with the other septa. The theca and all the septa, except the cardinal septa, are sometimes so thickened by stereoplasmic deposits as to form a nearly solid mass, obscuring details of arrangement. This description is taken from a section below the calyce, well down in the septate portion. A section through another coral, apparently at a somewhat later stage than the above, shows a very interesting condition. The septa on one side of the theca, about fifteen in number, are inclined toward a point, eccentric, and lying within the diametral segment under discussion. Their ends are bent and connected by a thick stereoplasmic deposit into a counterseptal wall. There are twelve other septa. Of these, six on one side and five on the other are inclined toward the visceral wall aforesaid, and their bent ends are united into a partition which, in one case, appears to connect with the counterseptal wall, and in the other is still free. This leaves a wide terminally inflated fossula, but the septum occupying it, or cardinal septum, is very short. There is no stereoplasmic thickening. Another section through the same specimen, at a point farther from the apex, shows the primary septa (twenty-nine in number) inclined and Avith bent terminations as before described, but not extended so as to form by their ends three visceral partitions — a counterseptal and two alar. The secondary septa are represented by low ridges. The fossula is strongly marked. It is partly distinguished by the nondevelopment of the fossular septum, which is scarcely more strong than the two secondary septa between which it stands; and all the septa diminish in size as they approach the cardinal septum. Another section, farther toward, yet still some distance from, the mouth of the calyce, shows thirty short primary septa with as many still shorter secondary septa. The general position alone of the fossula is indicated by the obsolescence of the septa in that region. Formation and locality: Madison limestone, near sixmmit of ridge, west end of Hunter Peak, Absaroka Range; Upper Gallatin Valley west of Bighorn Pass ; Arnold Hague. Crowfoot Ridge, Gallatin Range, bed 25, lower part of bed 27, bed 31 ; J. P. Iddings and W. H. Weed. South of Forellen Peak, Teton Range ; S. L. Penfield. South base of Quadrant Mountain, Gallatin Range ; J. P. Iddings. Crowfoot Ridge, Gallatin Range, cherty limestone, top of bed 24 ; A. C. Gill. LOVVBK CARBONIFEKOUS FOSSILS. 513 LITH08TR0T10N Lliwyd, 18G9. LlTHOSTROTlON sj). Conilhim coTni)Oun(l, massive. Corallites small, about 7 mm. in diameter, polygonal. There are usually in the neighborhood of thirty radiating septa, alternately long and short. The longer ones extend almost to the center. Transverse sections show that the whole interseptal space is more or less vesicular. Toward the penphery the vesicular tissue is coarse, stretching in extended loops, among Avhich, in some individuals, the periph- eral ends of the septa lose themselves. In others the septa can be traced quite to the inclosing wall. Toward the center the vesicular appears to give place to dissepimental tissue, and regularly a series of these dissepi- ments equally distant from the center are thickened and joined together to form a sort of inner wall. This inner wall is circular in section, having a diameter of about 4 mm. The septa, too, appear thicker and denser at this point, so that the demarcation between the inner and outer zones is well marked. In the inner zone is found localized dissepimental tissue, which usually unites to form one or two concentric sheaths about the columella. The latter is linear, often united at either end with two opposite septa which bisect the corallite and give it a conspicuous bilateral symmetry. The other primary septa terminate in one of the columella sheaths, as do often all the primary septa. The calyces are deep, flaring toward their mouth. The columella projects from the center of each, high, thin, and knifelike above, but below thicker and complicated with ridges. About thirty alternating septa are present, of which the primary ones descend into the calyce and unite with the columella at its thicker complicated base. Longitudinal sections where not central show an outer vesicular Z(5ne the strong vesicle walls curving downward and overlapping, thus formino- by their inner surface the so-called inner wall of the theca. Within this are the vertical, parallel, cut edges of the septa intersected by dissepiments, or what appear sometimes to be upward-arching tabulfe. In a section through the columella the septa are not seen, only the upcurvino- tabulse, cut by the linear columella. Formation and locality : Madison limestone, Crowfoot Ridge, Gallatin MON XXXII, PT II .33 514 GEOLOGY OF THE YELLOWSTOiSE NATIONAL PARK. Range, bed 28 ; J. P. Iddings and W. H. Weed. Head of Gallatin River, west of Three River Peak; Arnold Hague. CLISIOPHYLLUM Dana, 1846. Clisiophyllum teres n. sp. PI. LXVII, figs. 2a, 2K 2c, 2(1. Corallnm of medium size, tapering, slightly curved, and often laterally compressed; but little marked b}- constrictions and irregularities of growth. Length from 75 to 100 mm.; diameter of about 25 mm. There are fifty- three septa of the first order; secondaiy se]Dta short and coalescing with the primary ones. Columella small, complex, composed of radiating and concentric plates. The primary septa extend to the center and are there connected with the columella, about which they twist. Dissepimental tissue present in moderate abundance. Fossula well marked, situated on the convex side, bisected by the fossular septum. This description is not taken from any one specimen, but is the result of observations made on somewhat fragmentary material from several localities. The specimen figured is a somewhat undersized individual, from the summit of Three River Peak, referred to this species. A section taken where the diameter is only 7.5 mm. shows thirtj^-two (primary) septa, which are thick and straight, joining the columella, like radii drawn from the center of a circle, and not twisting around it, as they do later. The columella is large, apparently solid, showing a diametric line of greater density in the direction of the fossular septum. Fossula large. Dissepi- ments numerous and rather regularly disposed, but not enough to suggest tabulae, which appear to be absent. No secondarj- septa have j'et made tlieir appearance. A section taken near the distal extremity, where the diameter is about 14 mm., shows a difterent condition. It appears to intersect a basin- shaped tabula, or perhaps the floor of the calyce, for we see the appearance of a strong inner wall, which is evidently traversed obliquely by the plane of the section. It is decidedly eccentric, being only about 2.5 mm. from the peripher}^ at the fossula and twice as far at the opposite diameter. This tabula is apparently dissepimental in its nature, and not an inner wall, because it does not begin at the bottom of the theca, because it is seen in section to be strongly divergent, and because it depends for its expression LOWKK CAUBONIFHUOIS KOSSILS. , 5] 5 upoa tlic primary septa, between wliiili it is renewed at each inten-al. 1^lie l)riiiiary sejjta are nu.iv iiiinicrous iiere, and the peripheral portidu, like tlie tloor of the ealyce, is dense with stereophisma ; but within the second wall tlie>- 1)econie suddenly extremely thin, sweepinoductus parvus Meek and Wortbeu. Shell very small, somewhat wider than long. Surface ornamented by fine, even, radiating strife, which sometimes exhibit a tendency to become confluent, as in P. costatus. Ventral valve deeply arched, making considerably more than a semi- circle ; front view subquadrate, with nearly parallel sides and slightly curved upper outline. About the beak are a few deep concentric wrinkles, and the entire surface is crossed by fine concentric lines. Occasional spines of comparatively large size are scattered over the surface, especially near the anterior margin, on the heavier compound plications when present. ' King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 265, PI. V, figs. 9-12. LOWER CAKBONIFEKOUS FOSSILS. 537 The onlv dorsal valvo observed is tliat figured. It is nearly flat at first, and geniculate, with well-marked, somewhat pointed ears. The material from the Yellowstone National Park seems to be identical with the form identified, described, and figured by White as Productus parvus (loc. cit.). Compared with Meek and Worthen's figures of that species, P. parvi- fonnis is seen to be uniformly smaller, narrower in proportion to the width, more deeply arched, and more elongate. It seems like a miniature form of P. (jnllatinensis, with which I have at one locality found it associated, and of which, although no intermediate forms have been observed, I am almost disposed to regard it as a variety. Formation and locality: Madison limestone, Crowfoot Ridg'e, Gallatin Range, top of bed 25 ; J. P. Iddings and G. M. Wright. Same, bed 30, bed 31 ; J. P. Iddings and W. H. Weed. South of Forellen Peak, Teton Range; S. L. Penfield. Mountain Spring, Nevada. CAMAROPHORIA King, 1846. Camarophoria ringens Swallow. PL LXIX, figs. 1«, lb, Ic. RhynchoneUa ringens Swallow, 18G0 : Trans. St. Louis Acad. Sci., Vol. I, p. 653. Keyea, 1895: Geol. Surv. Missouri, Vol. V, Pt. II, p. 102. Camarophoria ringens Hall and Clarke, 1893 : Pal. iSew York, Vol. VIII, Pt. II, p. 214. RhynchoneUa (sp.) Keyes, 1895: Geol. Surv. Missouri, Vol. I, Pt.II, PL XLI, figs. 8, 11. There is a little doubt that the form under discussion is identical with that described by Swallow under the name Bhynchonella ringens. His was a large shell (length, 1.90 inches; breadth, 1.43 inches; thickness, 0.99 inch), triangular in outline, marked by about fourteen large plications, eight of which were in a broad shallow sinus. More recently Keyes (loc. cit.) cites the species and says there are twelve plications. The material from the Yellowstone National Park is scanty. Shell large, acuminate-ovate. Dorsal valve flat on top, bending abruptly at the sides and at the front. Ventral valve shallow. Beak long, sharp, not much incurved, apparently pierced by a triangular or oval foramen, without deltidial covering. The surface is marked by twelve or fourteen large but somewhat lax, rounded plications, two or three of which on the lateral slopes are not very distinct. Two or three plications are on the fold, 538 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, tliougli the exact number is difficult to ascertain, as that feature is ahnost obsolete. If this is not Bhynchonella ringens of Swallow it must be a new form, for there is no other representative of the genus with which it could be confused. C. suhtrigona Meek and Worthen, the nearest form, is yet con- siderably different. However, if this reference is correct, Swallow's spec- imen may have been abnormal in having so many plications on the fold, as it is certainly a larger and more -nature individual. In any case the stratigraphic value of this species remains imaltered, for I can vouch for the identity of the Yellowstone National Park material with a form from the lower Burlington chert of Louisiana, Missouri, which passes among local collectors as R. ringens. B. ringens was described from the chert beds of the Encrinital limestone of Callaway County. Swallow (loc. cit.) cites the species from the Burling- ton of Callaway and Marion counties, Avhile two forms, illustrated by PI. XLI, tigs. Ha, 8b, and 11 (Geol. Surv. Missouri, Vol. V, Pt. II), prob- ably referable to C. ringens, were found, the one in the Burlington hmestone, the other in the Kinderhook shales. Formation and locality: Madison limestone. Crowfoot Ridge, Gallatin Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, bed 28; J. P. Iddings and W. H. Weed. Keokuk age, Callaway County, Missouri. Burlington age, Callaway and Marion counties, Missouri. Kinderhook shales, Missouri. CAMAROTCECHIA Hall, 1893. The following species occur in the lower divisions of the Madison limestone. They have been referred to Hall and Clarke's genus, Camaro- toechia, although the generic characters have not been ascertained in detail. Yet a process of exclusion makes it very probable that this refer- ence is correct. All the shells have a strong median septum in the dorsal valve, while the ventral valve is aseptate, but with two converging dental larainpe in the beak. These characters, together with their geologic position, form, natiu-e of fold and sinus, plications, etc., throw out most of the other genera and subgenera into which the Rhynchonelloid type has been divided. LOWER CAKBONIFEUOUS FOSSILS. 539 Camarotcec'hia hekrickana n. sp. PI. LXIX, figs. LV(, 2b, 2r. Ventral \iilvt' rather isliallow, most prominent a little behind the mid- dle, flattened in front and at the sides. Outline nearly that of a square. Sinus shallow, beginning near the middle of the shell; marked by two strong- plications, on either side of which are tive or six others slightly finer. Dorsal valve considerably wider than long, sectorifoi-m, more gibbous than the ventral; sides reflexed. Fold not very high, marked by three strong angular plications. On either side are five plications, the more lateral two smaller than the others. This species occurs in about the same beds as C. metallica, but is sel- dom associated with it at the same locahty. It is readily distinguished fi'oni C. metallica by its somewhat large size, less strong fold and sinus, and coarser and less numerous plications. Of these, C. metallica has live on the fold and eight on either side, while G. Jierrickana has but three on the fold and five on each side. Th's species has not been observed with the two valves in conjunction, but it seems to have been a much less inflated form. It is possible that this species might correctly be referred to some one of the numerous Rhynchonellids described from the Marshall group by "VVinchell. I have studied his descriptions with care, but none cover the characters of this form sufficiently closely to warrant an identification in default of both illustrations^ and identified material. Length of a single ventral valve, 10.6 mm.; width, 12 mm. Length of a separate dorsal valve, 8.5 nun.; width, 10.5 mm. This same form, or one probably only A^arietally distinct from it, is found at Pellas, Marion County, Iowa. Formation and locality: Madison limestone, limestone bluff north of Little Sunlight Creek, Absaroka Range, 600 feet above the stream; Arnold Hague. Divide between Grallatin River and Panther Creek, Gallatin Range; amphitheater east of Bannock Peak, Gallatin Range, bed 28; W. H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 26, upper part of bed 27, bed 28; J. P. Iddings and W. H. Weed. North end of Teton Range, north of Owl Creek; W. H. Weed. Chouteau limestone, Pellas, Marion County, Iowa. 540 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Camarotcechia metallica White. PI. LXIX, flgs. 3a, 3ft, 3c, 3d, 3e. Bhynchotiella metalHca White, 1874: Wheeler's Expl. aud Surv. W. lOOth Merid., Prelim. Kept., p. 20. White, 1875: Ibid., Fiual Kept., A^ol. IV, p. 129, PI. X, figs. 10«, lOd. Bhy7ivhonella pustulosn (f) Hall and Whitfield, 1877: King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 257, PI. IV, ligs, 12-14. This species was described by White from Carboniferous (Upper Car- boniferous "?) rocks. It was found associated, with Hemipronites creiiistria and Spirifer cameratiis. My material occurs in the lower beds of the Madi- son limestone, whose fauna is regarded as closely related to that of the Kinderhook period. As far as is shown by a careful comparison with the type specimen, this Waverly form is identical with White's species, and were the latter of more nearly the same age I should consider the reference unquestionable. As has been said, BhynchoneUa metallica was described from Old Potosi mine, and H. crenistria and S. cameratus are cited from the same locality. Spirifer cameratus is closely related to S. striatus, and has sometimes been mistaken for it, while almost any Lower Carboniferous Orthothetes or Derbya might pass as Hemipronites crenistria. Therefore, it is not impossi- ble that B. metallica was derived from lower strata than White supposed. It is also more than probable that B. metallica is another representative of the genus Camarotcechia, which fact is not without some stratigraphic bearing, as Camarotcechia is not known in Upper Carboniferous rocks, nor indeed as yet above the Waverly. The form here under discussion is the same as that described and figured as B. pustulosa (f) by Hall and Whitfield, in King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 257, PI. IV, figs. 12-14, Avhere it is cited from Waverly rocks. The material from Yellowstone National Park, though scanty from any one place, the localities being numerous, aggregates a number of specimens which agree with one another and exactly with B. pustulosa (f) Hall and Whitfield; but all are without the punctate shell structure characteristic of true Bliynclwpora pustulosa. C. metallica is also much smaller than mature B. pustulosa., with thinner, sharper, and finer plications. These, as stated by Hall and Whitfield, are more numei'ous than in jR. pustulosa, and five of them instead of four (as in the latter) regularly surmount the fold. LOWER CAKBONiFEEOUS FOSSILS. 541 This same shell is found in the Chouteau limestone of Cooper County, Missouri, and at the base of the Lower Carboniferous at Providence Land- ing, Missouri, and at BlaclcAvater Bridge, Saline Comity, Missouri Formation and locality : Madis.on limestone. Hunter Peak, Absaroka Rano-e : Arnold Hay-ue. Limestone bluff north of Little Sunhght Creek, Absaroka Range; Arnold Hague. East side of Gallatin River, west of Electric Peak; divide between Gallatin River and Panther Creek, Gallatin Range; amphitheatre east of Bannock Peak, Gallatin Range, bed 28; W. H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 25 ; J. P. Idduigs and G. M. Wright. Same, bed 26 ; J. P. Iddings and W. H. Weed. South of Forellen Peak, Teton Range ; S. L. Penfield. Northwest slope of same ; S. L. Penfield. South slope of Quadrant Mountain, Gallatin Range ; north of Bighorn Pass, Gallatin Range; Crowfoot Ridge, Gallatin Range, bed 24; A. C. Gill. Same, top of bed 24; J. P. Iddings. Head of Conant Creek, Teton Range; W. H. Weed. North of Owl Creek, northeast slope of Teton Range; W. H. Weed. Upper Carboniferous, Lincoln County, Nevada. Waverly age, Wasatch Range, Utah. Chouteau limestone. Cooper County, Missouri; Providence Landing, Missouri; Blackwatei- Bridge, Saline County, Missouri. Camarotcechia SAPPHO Hall (!). Rhynclionella sappho Hall, 1860: Thirteenth Kept. New York State Cab. Nat. Hist., p. 87. Herrick, 1888: Bull. Deuisoii University, Vol. Ill, p. 40, PL V, tig. 1; PI. Vll, fig. 23. Herrick, 1895: Geol. Ohio, Vol. VII, PI. XXI, fig. 1. Ehynchonella (meiiocesma), sappho Hall 1867: Pal. New York, Vol. IV., p. 340, PI. LIV, figs. 33-43. Camarotcechia sappho Hall and Clarke, 1893 : Pal. New York, Vol. VIII, Pt. II, p. 192. PL LVII, figs. 10-14. The specimen which represents this type is larger than any in the collection referred to the genus Camarotcechia. When perfect it must have measured 16 mm. in length by 21.5 mm. in width. It is a rather flat, explanate shell, resembling in this respect C. herrickana rather than the other forms represented in the Yellowstone National Park. The lateral slopes are nearly straight or slightly concave, and extend about half the entire length of the shell, where they are met by the deeply bowed anterior margin. The fold is not high, biit can be traced to the rostral region. It is traversed by six small, rounded plications, and about seven others are to 542 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. be found on each of the sides. In every respect this very closely resembles Hall's species, although onl}' a provisional reference is possible, owing to insufficient material. C. sapplio first makes its appearance in beds of the Mareellus period, but is known to extend up into the upper Waverly (Herrick, 1888, loc. cit., p. 40). Formation and locality : Madison limestone, Liinestone bluff south side of Soda Bixtte Creek, northwest of Abiathar Peak, Absaroka Range ; J. P. Iddings. Mareellus to Waverly, Leroy, Greneseo, and York, New York ; Licking County, Ohio. Camarotcechia camarifera Winchell (?). Bhynchonella camarifera Winchell (A.), 1862 : Proc. Acad. Nat. Sci. Philadelphia, p. 408. This species is represented in a somewhat fragmentary manner, and the material is too poor for illustration. It resembles G. herrickana, but at the same time seems to be specifically distinct from it. Shape ovate ; length equal to or slightly exceeding the width ; convexity jnoderate. Sides straight, meeting at the beak in something less than a right angle; front deeply rounded. Plications rounded, four on the fold and thi-ee in the sinus, with five or six on the sides. The plications are nearly straight and not verj- divergent, which makes the shell look longer than it really is. It can be distinguished from C. herrickana by the somewhat different arrangement of plications on fold and sides. The proportions of the shell are also different. The plications are slightly finer, less angular, and not so strongly outcurved at their extremities. The nearest described species which I have found is C. camarifera of Winchell. Length, 10 mm.; width, 9.5 ram. Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin Range, bed 26, bed 28, bed 30; J. P. Iddings and W. H. Weed. Marshall group. Point aux Barques, Michigan. Camarotcechia sp. PI. LXIX, figs. 4a, 46. This species is represented by a single specimen, which seems to be distinct from any type occurring in the collection from the Yellowstone National Park. It was found at the limestone bluff on the south side of LOVVKH CxVUBONlFEROUS FOSSILS. 543 of Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range, a locality wliioli has already t'nrnished several new species, and seems to possess a somewhat distinct local fauna. Caniarofa'chia sp. consists of a single dorsal valve. The shape is slightly itval, length and width about equal; cui'vature of the outline regu- lar, and not angular where the anterior margin meets the lateral slopes. Extremel}' gibbous, the thickness of the valve being more than half the length or width. Fold not very high, but defined to the -sncinity of the beaks. It is marked by five rounded plications, and a like number are to be found on the two sides. This form seems to be related to C. orbicularis, of Chemung age. Formation and locality: Madison limestone, limestone bluff south side of Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. LIORHYNCHUS Hall, 1860. LlORHYNCHUS HAGUEI n. sp. PI. LXIX, figs. 5a, 5b. Shell rather large, tumid. Ventral valve fiat in effect ; subquadrate in outline ; beak strongly incurved ; fold deep. Thus the anterior and posterior angles of the quadi-ate shell are strongly flexed in one direction, while the lateral angles are prominently elevated. Dorsal valve very rotund ; fold high ; sides strongly recurved. The surface is smooth (?), sometimes show- ing varices of growth. Fold and sinus alone plicate. Strife on the sides of the shell entirely obsolete. There are five plications on the fold, neither sharp nor strong. The central three are slightly larger than the lateral ones, which are not defined on the outer side, but lie in the regular curva- ture of the shell. Four nearly obsolete plications in the sinus. The general appearance of the shell suggests the genus Pugnax, but a reference to that type is impossible by reason of internal structures. A section across both valves near the beak shows that the dorsal valve is provided with a well-developed median septum, and that the ventral valve has two converging laminar plates in the rostral region. Liorhynchus Jiaguei is very close to L. greenianum Ulrich, of Keokuk (?) age, from New Albany, Indiana, but the latter has three coarse plications 544 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK, on the fold, while the former regularly has five fine ones. L. haguei also resembles to a certain extent L. kelloggi of the Hamilton group, but it is more gibbous, with a higher fold, while the latter has, as a rule, six to ten plications on fold and sinus, with five or six faint lateral plications. Comparison can also be made with Liorhynchus (Pugnaxf) striatocostatum Meek and Worthen, which has tlu-ee or four plications on the fold and two or thi-ee nearly obsolete ones on either side. The fold is lower, broader, and more quadi-ate, and the plications surmounting it are much coarser, than in L. haguei, which has the lateral plications either entirely lacking or more indistinct. The latter appears also to be without the fine striate surface ornamentation of Meek and Worthen's species. Formation and locality : Madison limestone. Crowfoot Ridge, Gallatin Range; cherty limestone, top of bed 24; A. C. Gill. DIELASMA King, 18.59. DiELASMA UTAH Hall and Whitfield. PI. LXIX, figs. 6a, 6b, 6c. Terebratula utah Hall and Whitfield, 1877 : King's Geol. Expl. 40tli Par., Vol. IV, p. 258, PI. IV, fig. 18. The type of this species is a dorsal valve, with a pentagonal outline and a punctate shell. The rectilinear outline is not constant, however, for, on a block of limestone from the same locality containing other type mate- rial (Athyris planosulcata f), is a second specimen whose outline is regularly cuiwed. The material from the Yellowstone National Park agrees with the above so perfectly in general form, proportion, size, etc., that I am confident both belong to the same species. Although it has not been possible to determine the internal charac- ters of this form, it has been referred to the genus Dielasma because of its geological position, punctate shell, and characteristic shape of the ventral valve. Dielasma utah very closely resembles D. formosum Hall, which occurs in' the Mississippi Valley, in strata of Keokuk age; but D. utah is found in the lower beds of the Madison limestones. LOWER CAHBONIFEKOUS FOSSILS, 545 l)i('l. utah will prove synonymous with I). hiirHiif/- tonense White, of the same geologic horizon, but the scanty material of the former species, joined to the very inadequate description of the latter, ren- ders it impossible to determine this point. Specimens of D. hiirliufiioiicnse White from the Cuyahoga shale as exposed at various points in Summit and Medina counties can not be distinguished from I), nfali by any characters that I have been able to discover. Formation and locality: Madison limestone, limestone bluff north of Little Sunlight Creek, Absaroka Range, 600 feet above the stream ; Arnold Hague. East side of Gallatin River, west of Electric Peak ; Crow- foot Ridge, Gallatin Range, bed 28 ; J. P. Iddings and W. H. Weed. Lower Cai'boniferous, Cottonwood Divide, Wasatch Range, Utah. SPIRIFERINA d'Orbigny, 1828. Spiriferina solidirostris White. PI. LXXI, fig. 10«. Spirifer solidirostris White, 1800: Jour. Boston Soc. iSTat. Hist., Vol. VII, p. 232. Spiriferina solidirostris White, 1862: Proc. Boston Soc. ISTat. Hist., Vol. IX, p. 24. A. Winchell, 1865: Proc. Acad. Nat. Sci. Philadelphia, p. 120. This is not a common species in the Yellowstone National Park. It has been observed at a number of localities, but is represented by only one or two specimens at each. These correspond so entirely with S. solidirostris, as far as characters are indicated, that I refer them very confidently to White's species. The area, shape of shell, number and character of plications, and surface ornamentation are exactly as White has described them. The lai-gest specimen, a ventral valve of unusual size, measured 2L5 mm. in width by 12.5 mm. in length; but the one figured (PI. LXXI, fig. lOffl), which measures 15 ram. in width by 12 mm. in length, is perhaps nearer the average. 1 Hall and Clarke, 1895: Pal. Now York, Vol. VIII, Pt. II, PI. LXXXI, figs. 27, 28. -S. A. Miller, 1892 (for 1891) : Seventueuth Rept. State Geologist Indiana, p. 687, PI. XIII, figs. 3, 4. MON XXXir, PT IT 35 546 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The ideutitications of this species are usually iucorrect, the current type of specimens differing- markedly from the original description, which is appended below. f same; summit of Three River Peak, Gallatin Range; J. P. Iddings. South slope of Quadrant Mountain, Gallatin Range: A. C. Gill. South base of same; J. P. Iddings. North of Bighorn Pass, Gallatin Range ; Crowfoot Ridge, Gallatin Range, bed 24 ; A.C.Gill. Bighorn Pass, Gallatin Range ; J. P. Iddings. HeadofConant Creek, Teton Range; north end of Teton Range, north of Owl Creek; east side of Lamar Valley, mouth of Soda Butte Creek, Absaroka Range; W. H. Weed. Limestone bluff south side of Soda Butte Creek, north- west of Abiathar Peak, Absaroka Range; J. P. Iddings. North side of north fork of Mill Creek, Snowy Range; J. P. Iddings and Louis V. Pirsson. Waverly age, Cu5'ahoga Falls, Richfield, Lodi, Bagdad, etc., Ohio; Black Hills, Dakota; Wasatch Range, Utah; Mountain Sjn'iug, Nevada. Spirifek centronatus var. semifurcatus n. var. PL LXX, fig. ia. This form is related to S. centronatus and to S. mcsicosfalis, standing about midwav between them. It seems to me to be sufficiently out of the rang-e of ordinary variations of S. centronatus to be described as a distinct variety. It is of the imbrex type, semielliptieal in outline, fold and sinus strongly expressed ; surface ornamented with regular imbricating growth lines and strong radiating ribs. Of the latter there are ten or eleven upon tlie wings and two somewhat larger ones upon the median fold. These, however, show a constant tendency to bifurcate, wliich often results in tlie formation of four plications ; but the median furrow of the fold is stronger than the two others. Length of the dorsal valve is 30.5 nun. transversely; longitudinally, 12. .5 mm. The dorsal shown by PI. LXX, fig. 4a, can be almost exactly mated in size, in shape, and in the number, size and distribution of the plications bv specimens of S. mcsicostaUs. This, however, is rather small for mesicostalis, and I have not observed, in a large series of this species, any tendency toward bifurcation in the t^vo plications on the fold. Compared with S. 550 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. hiplicatus var. semifiircatus, S. centronatus has somewhat smaller and more numerous plications, and the fold, which is perhaps not quite so elevated, is surmounted by four or more equal radii. Formation and locality: Madison limestone, Hunter Peak, Absaroka Range ; T. A. Jaggar. Near summit of ridge, west end of Hunter Peak, Absaroka Range ; Arnold Hague. Crowfoot Ridge, Grallatin Range, top of bed 26 ; J. P. Iddings and W. H. Weed. Under Quartzite Ridge, north side of Burnt Fork. Spirifeb subattenuatus Hall. Spirifer snbattenuatus (by mistake, Spirifer suhmucronata) Hall, 1858: Geol. Surv. Iowa, Vol. I, Pt. II, p. 504, PI. IV, tigs. 3a-3c. Spirifer suhatienuuia Wiucliell (A.), 1SG2: Proc. Acad. Nat. Sci., Philadelphia, p. 4C5, Whiteaves, 1891: Coutributions to Canadian Palieoutology, Vol. I, p. 223. Shell rather small, semicircular, alar angles somewhat rounded to sharp. On either side of the fold and sinus there are eight to ten comparatively large radiating ribs, which are crossed by strong concentric imbricating ridges. Very variable in the number of plications on fold and .sinus. One dorsal valve shows a low fold with two strong radii equal to those on the wings. Another specimen has a rather high fold with a very faint median furrow. One ventral valve, on the other hand, shows a sharp median ridge in the rather deep sinus, while still another has the sinus simple for over half its length, when suddenly four low plications, somewhat smaller than the rest, appear in it. Length of this last specimen, 10.5 mm.; width, 15 mm. Another example is considerably larger than this. The form in question seems to be closely allied to 8. centronatus, from some varieties of which it is not widely separated. It also bears some resemblance to .S'. strifjostis Meek and S. an/entarins Meek, to the latter in point of size, to the former in the plications of fold and sinus. S. arrjentarius and S.strk/osiis are both described from Devonian strata; so is S. subaffenu- atiis, but it is known to occur in the Waverly also. The material studied is unsatisfactory. Formation and locality: IMadison limestone, Stinkingwater Valley, below mouth of the canyon, Absaroka Range; Arnold Hague. Chemung age, Independence and BuflPalo, Iowa; Rock Island, Illinois; Naples, New York; Athabasca River, Canada. Marshall group. Point aux Barques, LOWER CARBONIFEROUS FOS8ILS. . 551 Spiriker marionensis Shuiruinl (?) Spirifer marionensis Sliumard, 1855: Geol. Kept. Missouri, p. 203, PI. 0, figs. Sa-.Sc. Hall, 1858: Geol. Surv. Iowa, Vol. I, Pt. II, p. 501, PI. VI, figs. l«-lc. Hall and Clarke, 189.-): Pal. New York, Vol. VIII, Pt. II, PI. XXXI, fig. lo. iSpiri/tra marioncn.siti Wiuchell (A.), 1870: Proc. Am. Phil. Soc, Vol. XI, p. 2.52. Hall, 1883: Second Ann. Kept. New York State Geologist, PI. LVI, fig. 15. Herrick, 1888: Hull. Denison University, Vol. Ill, p. 43, PI. VI, tigs. 2-4; PI. VII, tig. 11; Vol. IV, p. 2(!, PI. II, tig. 2. This form is found only at the head of Couant Creek, Teton Range. The material, which is much crushed and broken, so far as ascertained, can well be referred to Shumard's species. It is much larg-er and more coarsely plicate than S. centronatus, and much resembles S. striatns of this report, except that the surface is crossed by numerous lamellose concentric strise, whereas the other is smooth. A satisfactory identification is rendered impossible bv the character of the material. Formation and locality: Madison limestone, head of Conant Creek, Teton Range; W. H. Weed. White Mountain, Absaroka Range, just below Quadrant quartzite ; T. A. Jaggar. Chouteau age, Louisiana and Hannibal, Missouri; Portsmouth and Sciotoville, Ohio. Spikifer striatus var. madisonensis n. var. PI. LXX, figs. 2«, 2&, 2e, 2d. This form in general appearance resembles *S'. striatus Martin, of the Mountain limestone of vai'ious European localities. It does not attain so large a size as is often seen among specimens of S. striatus, and the strise are coarser and less numerous than in some of the forms figured by Davidson. The material under discussion approaches most closely to certain specimens from Cork, Ireland, with which it has been compared, but certain differences obtain which are worthy of at least varietal distinction. The area in S. striatus var. madisonensis is hig-her, even in specimens of considerably smaller size; the ventral beak more overhanging, and the foramen higher in proportion to its width. The outline shape of both types is nearly the same, likewise the number and size of the striae. The fold is somewhat higher in the Irish form, and considerably more angular. The strise bifurcate in the immediate vicinity of the beak, and often again 552 GEOLOGY OF THE YELLOWSTOiSiE ^^ATIONAL PARK. near tlie anterior margin. In the variety inadisonensis the stria? bifurcate near the anterior margin, but can be traced backward to then- origin at the beak without bifurcation. In neither form are the striaj interrupted by imbricating lamellae. Hall and AVhittield distinguish two types among the forms from Utah, which tliey refer to S. striatus. The one which is lower in the stratigraphic series is said to be transversely elongated, while the higher one is about as long as wide, and has finer, more angular, and more fasciculate strife. Their material is so crushed that it is impossible to institute a satisfactoi'v comparison, Ijut if 5. striatus var. madisouensis is identical with either of these, it must be with the former (lower) type. It ditfers distinctlv from the form figured on PI. Y, figs. 13, 14 (loc. cit.), which is somewhat larger; the area, instead of being nearly straight and vertical, is deeply curved, at first nearly horizontal, then resurgent; the fold is sudden, high, and thin. Spirifer striatus var. madisonensis, when mature, can be readily distin- guished from S. centronatus, with which it is associated. It is much larger, the fold and sinus less defined, plications more numerous, but less sharp, and not covered with the imbricating concentric lamellfe which well- preserved surfaces of S. centronatus show. The largest specimen, an incomiDlete ventral valve, measures 55 mm. in breadth. Another shell measures 55 mm. in breadth by 35 mm. in length, which is perhaps near the average. Young specimens, however, are broader in proportion to their length, and can scarcely be distinguished in shape from S. centronatus of the same size. Formation and locality: Madison limestone, Stinkingwater Valley, below mouth of the canyon, Aljsaroka Range; Arnold Hague. Crowfoot Ridge, Gallatin Range, cherty limestone, top of bed 24; A. C. Grill. Spirifer sp. PI. LXX, fig. la. This form is known only from an incomplete dorsal valve, but it is so striking that it seems worthy of some notice. It is very transverse, the width being 51 mm. and the length 16.5 mm. Shape triangular: trun- cate in front; wings acutely angular, mucronate (?). The fold is unde- fined and scarcely at all raised above the general curvature of the shell, surmounted by four or fi\-e bifurcated plications. On either side are found LOWER CARBONIFEROUS FOSSILS. 553 about twenty other plications, which (on the cast) gradually become finer and more obsolete until they disappear and the extreme alar portion is smooth. I know of no type with which this can aptly be compared except S.forbesi, of the Burlington group. Formation and locality: Madison limestone, east slope of Survey Peak, Teton Range; S. L. Penfield. Spirifer sp. A solitary specimen, not referable to any of the forms yet recognized in the Yellowstone National Park. It is a large shell, probably when complete not less than 63.5 nun. wide by 44.5 nun. long; a ventral valve. There is a broad, shallow sinus, which, together Avith the wings, appears to be covered by comparatively fine, obscure, radiating striae. The entire rostral cavity is filled Avitli sliell deposit, as in S. pJemis, of the Burlington. Externally this form approaches Syringothyris ; the beak is erect and the whole shell has what may be called a heraiconical shape; but it is developmentally not a true species of that genus. Formation and locality: Madison limestone. Snake River Valle}', west of Two Ocean Plateau; W. H. Weed. MARTINIA McCoy, 1844. Martinia rostrata n. sp. PI. LXX, figs. 5rt, 5t, 5c, 5d, 5e, 5/', 5g. Athyris planosulcata Hall aud Whitfield, 1877 (pars) : Kiug's U. S. Geol. Exi>l. 40tb Par., Vol. IV, p. 257, PI. IV, tig. 10. Shell large, obese, lozenge-shaped; when young, wider than long; when old, length and width about equal. Ventral valve productiform ; beak prominent, incurved over a moderate-sized area. Foramen large, open. Hinge line half or three-fourths the Avhole width of the shell. Surface smooth; mai'ked by a shallow sinus extending to the extremity of the beak, whei'e it is defined; less marked below and accompanied by a flattening of the whole valve. Dorsal valve rounded behind, converging in front in somewhat straight lines, whose junction is anticipated by the truncation of a very low fold. Beak prominent, but not produced. Transverse curva- ture gentle and even, or sometimes formed by the two planes of an obtuse dihedral angle, whose edge is the median line. Highest point is at the umbo. 554 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, Mature specimens can scarcely be mistaken for anytliing else in the same beds. The smooth surface and area with triangular foramen would suffice to disting'uish even young shells from C. crassicardinalis, which they most resemble, but when these characters are obscured the prominent beak and mesial sulcus of the ventral valve are diagnostic. There is some simi- larity with Spirifer (Martinia) rjlaher Martin, to which I believe this type to have been usually referred. The produced and overhanging beak and large area of M. rostrata are well-marked specific characters. The fold and sinus of M. r/Jahra are stronger than the same features of 31. rostrata, where, in fact, they are but slightly developed, and often exhibit a tendency to bifurcate, manifested by a median sulcus and ridge of more or less depth, never seen in the latter. The synonymy of this form includes, so far as I am aware, besides S. glaber, of various authors, only Atliyris planosuJcata {f) Hall and Whitfield (non Phillips), figured in King's U. S. Expl. 40th Par., Vol. IV, p. 257, PI. IV, fig. 10, which appears to be a young specimen of M. rostrata. Widtli of large specimen, ventral valve, 38 mm.; length, 35.5 mm. Width of medium-sized specimen, ventral valve, 29 mm.; length, 25.5 mm. Width of large specimen, dorsal valve, 51 mm.; length, 34.5 nnn. Width of me- dium-sized specimen, dorsal valve, 29 mm.; length, 23.5 mm. Formation and locality: Madison limestone, east side of Gallatin River, west of Electric Peak; G. M. Wright Amphitheater west of Bannock Peak, Gallatin Range, bed 26; W. H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, lower part of bed 27, bed 31; J. P. Iddings and W. H. Weed. South .side of Gallatin Valley, bed 32; J. P. Iddings. West of Antler Peak, Gallatin Range; A. C. Gill. South slope of peak west of Antler Peak, Gallatin Range; sunmiit of Three River Peak, Gallatin Range; J. P. Iddings. South slope of Quadrant Mountain, Gallatin Range; north of Bighorn Pass, Gal- latin Range; A. C. Gill. North of Owl Creek, northeast slope of Teton Rano-e; W. H. Weed. Limestone Ijluff" south side of Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. LOWER CARBONIFEROUS FOSSILS. 555 RETICULARIA McCoy, 1844. Reticularia cooperensis Swallow. PI. LXX, figs. 9a, 9fc, 9c. Spirifera cooperensis Swallow, 18G(): Trans. St. Louis Acad. Sci., Vol. I, p. 643. Keyes, 1895: Geol. Surv. Missouri, Vol. V, Pt. II, p. 78. Spiri/er hirtus White and Whitfield, 1862: Proc. Boston Soc. Nat. Hist., Vol. VIII, p. 293. 1 Winchell (A.), 186r.: Proc. Acad. Nat. Sci. Philadelphia, p. 119. Hall and Clarke, 1895: Pal. New York, Vol. VIII, Pt. II, PI. XXXVIII, fig. 14 (? PI. LXXXIV, tigs. 36, 37). ^Spiri/er coo2)erensis^leek and Wortheu, 1866: Geol. Surv. Illinois, Vol. II, p. 155, PI. XIV, flg. 5. The specimens here referred to R. cooperensis Swallow have been compared with material from the Chouteau limestone of Cooper County, Missouri, where Swallow's types were found. The iinusually perfect agree- ment exhibited in the two forms leaves no doubt of their specific identity. The same form occurs in the Waverly at Richfield, Ohio. Although Spirifer cooperensis Meek and Worthen is retained in the synonymy of this species, I believe they were dealing with a distinct though similar form. It is only about half the size of mature B. cooperensis, and has a distinct fold with three or four plications on either side, more as in B. peculiaris Shumard. In fact, it seems highly probable that they were dealing with the shell described by lialP from the same (Goniatite) beds, three years previously, as Spirifer semipUcatus. On account of differences mentioned above, I believe this constitutes a distinct specific type, although Hall may have included in his description some of Swallow's species. Meek and Worthen seem to be in error when they state that Swallow refers to his species "obscure, radiating plications" (Meek and Worthen, loc. cit, p. 156). He does, indeed, speak of "punctate and plicate folds" and "concentric folds marked with small pits and short longitudinal plica- tions," but this had reference to the delicate longitudinal flutings of the laminfe, due to the spines or their bases (a character shown in all the speci- mens examined) rather than to the large radiating folds shown in 3Ieek and Worthen's figure. 'Thirteenth Rept. New York State Cab. Xat. Hist., p. 111. 556 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, Spirifer hirtus, from the same beds and the same region as B. cooper- ensis, may ahnost certainly be placed in the synonj^my of the latter species. Foi-mation and locality": Madison limestone, east side of Gallatin River, west of Electric Peak; Upper Gallatin Valley, west of Bighorn Pass; Arnold Hague. Amphitheater west of Bannock Peak, Gallatin Range, bed 26; W. H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, top of bed 26, top of bed 27, bed 28, bed 31; J. P. Iddings and W. H. Weed. South of Forellen Peak, Teton Range; S. L. Penfield. South slope of peak west of Antler Peak, Gallatin Range; J. P. Iddings. North of Bighorn Pass, Gallatin Range; A. C. Gill. Head of Conant Creek, Teton Range; W. H. Weed. Chouteau age, Chouteau Springs, Missouri; Rockford, Indiana; Burling- ton, Iowa; Hickman County, Tennessee; Richfield, Bagdad, etc., Ohio. Reticularia cooperensis var. . PL LXX, figs. C«, Gh, 6c. Spirifera setigera Hall and Wbitfleld, 1877: King's U. S. Geol. Expl. 40tli Par., Vol. IV, p. 270, PI. V, figs. 17, 18. This form is once again as large as R. cooperensis, of which, for the present, I regard it as a variety, but I am not in a position to designate any other character on which a difterentiation can be made. The single specimen found in the collection stands out so strikingly from the material referred to B. cooperensis that it is significant of further diff'erence, but the specimen is so exfoliated and crushed that a detailed comparison, which might bring out constant important contrasts in surface ornamentation, etc., is impossible. As far as the limited material permits me to judge, the same form occurs in the Eureka district and at Dry Canyon, Utah, where it has uniformly been identified as R. setigera Hall, of the Chester limestone, which it strongly resembles. However, in the Yellowstone National Park it is in the lower part of the Carboniferous series, associated with Waverly forms {R. cooperensis, etc.). A comparison with specimens of R. setigera from Chester, Illinois, shows that the Waverly form is of about the same size, but more transverse, beak less incurved, area higher and larger. As has been said, a comparison of the surface ornamentation of the two forms is not possible. LOWER CARBONIFEROUS FOSSILS. 557 Compared witli tlu' Hnrliiifrton t'oriii, It. coopcrens'is var. is smaller, less transverse; fold and sinus less pronounced; area proportionally not so broad. The specimen iigured is from the Eureka district, Nevada. The original shape and pi'oportions are better maintained. Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 25; J. P. Iddings and C M. Wright. Lower Carbon- iferous, Eureka district, Nevada; Dry Canyon, Utah.. Reticularia (?) PECULiARis Sliumard. PI. LXX, figs. 8fl, Sh. Spirifer ? peciiliaris Shuinard, 1S5.5: Geol. Rept. Missouri, i>. 202, PL 0, figs. 7a, 7h. Spirifem {Maitinia) peculiaris White, 1S75: Wheeler's Expl. Surv. W. 100th MericL, Vol. IV, p. «0, PI. V, tigs. 7a, 7b. This species is so rare in the Yellowstone National Park, and its preservation is so unsatisfactory, that any less striking form could scarcely be identified. It can be distinguished from B. suhrotundata by its larger and less numerous plications, of which there are only six or seven on either wing, while the fold and sinus are simple. B. peadiaris is found in the yellow sandstone at Burlington, Iowa, and in the brown limestone of Chouteau age at various places in Missouri. I am not confident that this is con-ectly referred to Eeticulnria. Exfo- liated specimens from the Chouteau limestone appear to have possessed a finely laraellose-spinose surface. Formation and locality: Madison Hmestone, summit of Three River Peak, Gallatin Range; J. P. Iddings. East side of Lamar Valley, mouth of Soda Butte Creek, Absaroka Range; W. H. Weed. Kinderhook age. Cooper County, Missouri; Mountain Spring, Nevada. ReTICULAEIA (?) SUBROTUNDATA Hall. PL LXX, figs. 7rt, 7h. Spirif era suhrotundata Hall, 1858: Geol. Surv. Iowa, Vol. I, Pt. II, p. 521, PI. VII, fig. 8. Keyes, 1895: Geol. Surv. Missouri, Vol. V, p. 78. I have this species from a single locality beyond the confines of the Yellowstone National Park, but associated with a fauna clearly identical with that of the Madison limestone. 558 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK. The ventral valve is strongly arched in an antero-lateral direction, somewhat flattened transversely, with a broad, shallow sinus which can be traced quite to the beak, losing distinctness as it grows broader. Beak high, strongh^ incurved. Area triangular and not well defined. Foramen large and higli. Surface marked by about twenty-six fine, low plications, about six of which lie in the sinus, and with about ten on either wing. The shell is superficially marked by iimumerable fine pits, much resembling the punctation in the genus Spiriferina, but this character is restricted to a thin outer layer, beneath which the shell substance is fibrous and irapunc- tate. This appearance is probably secondary, resulting from an originally S})inose exterior, which, with the general character of the species, elongate shape and obsolescent plications, distinguishes it from any representative of the genus Spiriferina, and seems to denote an alliance witli Reticularia. As regards its specific position, a comparison with typical Spbifcra subrotundata Hall, from the yellow sandstone of Burlington, Iowa, leads me to believe that it is identical with that species. It. subrotundata is in many ways comjjarable to B. jyecidiaris, but the character of the plications aff"ords an easy basis for discrimination. B. sub- rotundata has finer and more numerous plications, of which six or more are in the fold and sinus, while in R. peculiaris the fold and sinus are undivided. The same form occurs in the lower Burlington of Pike County, Mis- souri, and seems to have been usually identified as B,. peculiaris. Formation and locality: Madison limestone, Little Belt Mountains, east side of Belt Creek, 5 nfiles above IMonarch, Montana; W. H. Weed. Lower Burlington chert, Pike County, Missouri. SYRINGOTHYRIS A. Winchell, 1863. Syringothyris cakteri Hall. ri. LXXI, figs. 1«, 1/a Ic. iSpirifer carteri Hall, 1857: Tenth Aun. Rept. New York State Cab. Nat. Hist., p. 170. (partim) Meek, 1875: Pal. Ohio, Vol. II, p. 285 (not liis figures = S. texta Hall). Spirifer (Cyrlia!') hannibalensis Swallow, 1860: Trans. St. Louis Acad. Sci., \'ol. I, p. 647. Syringothyris typa Winchell, 1863: Proc. Acad. Nat. Sci. Philadelphia, p. 7. Winchell, 1870: Proc. Am. Phil. Soc, Vol. XI, p. 252. Hall and Clarke, 1893: Pal. New York, Vol. VIII. Pt. II, p. 48, tig. 40. Hall and Clarke, 1895: PaL New York, Vol. VIII, Pt. II, PI. XXVI, tigs. 6, 7, 10; PI. XXVII, figs. 1-3. LOWER CARBONIFEKOUS FOSSILS. 559 Spiri/cf citinjidatKii iMeek, ISOf): i'roc. Acad. Nut. Sui. riiihulelpliiii. \ol. X VII. j). 275. Meek, 1867: Am. Jour. Sci., Vol. XLVII (2), p. 407. Spiri/ercunpidalii.sf Meek, 1S77: U. S. Geol. Expl. Jdtli I'ar., \'ol. IV, p. S7, PI. Ill, figs. II, llri (lion Martin). Sijriitf/otlii/ris cii.spi(h(ti(s Walcott, 1884: Hon. U. S. (leol. Surv., ^'ol. VIII, Pal. Eureka District, p. 219 (iion Martin). Uerrick, 1888 (paitiui) : Bull. Denison Univ., Vol. III, p. 41, PI. I, lis-. 7; PI. II. tig. 17 (not PI. V, figs. 4-7 = S. herrk-l-i). Si/riiu/othi/ris carfcri Scliuchert, ISiJO: Nintji Ann. Rept. New York State Geologist, p. 30. Keyes, 1895: Geol. Surv. Missouri, \'ol. V, Pt. II, p. 87, PI. XL, fig. 10. i'^iniiii/oilu/ris haunihalensis Hall aiid Clarke, 189.5: Pal. New York, Vol. VIII, Pt. II, PI. XXV, tigs. 33-35. I have adopted for this species the synonymy composed by Schuehert,^ who has given tlie specific limitations of these forms more detailed study than any other investigator. The material from the Yellowstone National Park includes only four specimens, one of which is the external cast of a dorsal valve, shown on PI. LXXI, fig. la; the others are three ventral valves, exfoliated so as to be almost internal casts. These specimens agree well with Hall's description and with Meek's" figures of Spirifer cuspidaias (f) which are here reproduced for reference. The dorsal cast shows the peculiar "textile" surface ornamentation of the genus, and the shell substance, where preserved, gives evidence of being punctate. Therefore, although the char- acteristic structures of foramen and beak have not been observed, reference to the genus and to the species under the genus seems to be justified It should be noticed that one of the ventral valves above referred to has every character of the specimen figured by White as Sijringothijris extenuatus (Wheeler's Rept. U. S. Geogr. Surv. W. lOOth Merid., Vol. IV, 1877, p. 88, PI. V, figs. h, 6c. Shell moderately gibbous, small, circular. Surface smooth, except for a few growth-lines. Ventral valve nearly circular, but for the beak, which is rather large and strongly incurved over the other valve, completely concealing the foramen, which appears only where broken back through the rostral shell. Dorsal valve circular in outline, moderately curved; beak somewhat prominent by reason of a slight flattening on either side. The dorsal valve has an indistinct fold and the ventral valve an insignificant sinus, which are perceptible only by a sinuosity in their anterior margins. Length of a medium-sized specimen, 15 mm.; breadth, 14.5 mm.; thick- ness, 9 mm. Length of a somewhat smaller individual, 12.5 mm.; breadth, 11.5 mm.; thickness, 7.5 mm. Were it not that S. tmsatchensis is an Upper Carboniferous form, while this one is found in the lower beds of the Lower Carboniferous, I would have unhesitatingly referred it to White's species. The great anterior thickening of the shell, which appears to individualize the latter type, is due to old age, and can not be considered a specific character. Otherwise, if occurring in the same beds, the two forms could scarcely be distinguished. Seminula humilis also approaches Spirigera formosa and Sj). euzona, both of Swallow. These forms, however, are marked by a high fold and corre- sponding deep sinus, while Sp. formosa is said to have a punctate shell, and radiating striae when exfoliated (fibrous shell structure?). These characters are decisive in separating Swallow's species from the one in question. Formation and locality: Madison -limestone, Hunter Peak, Absaroka Range; T. A. Jaggar. Crowfoot Ridge, Gallatin Range, lower and upper part of bed 27, bed 28, bed 31 ; J. P. Iddings and W. H. Weed. Stinking- water Valley, below mouth of the canyon, Absaroka Range; Arnold. 566 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Hague. West of Antler Peak, Gallatin Range; A. C. Gill. Summit of peak west of same; cherty belt, Bighorn Pass, Gallatin Range; Crowfoot Ridge, Gallatin Range, top of bed 24; J. P. Iddings. Head of Conant Creek, Teton Range; W. H. Weed. SeMINULA -IMMATURA n. Sp. PI. LXXI, figs. 5a, 5b, 5c, 5<1. Shell rather small, ovate, gibbous. Length somewhat exceeding the widtli. Dorsal valve full, highest at the umbo, without a fold, but slightly emarginated in front; beak small, inflated, deeply incm-ved. Ventral valve oval, beak small, incurved so as to conceal the true foramen. There is a shallow sinus, which, however, is perceptible only near the anterior margin, forming there an upturned projecting lip to fill in the emargination of the opposite valve, and producing a sinviousity in their line of union. Length, 18.5 mm.; width, 15 mm.; thickness, 12.5 mm. Stratigraphically this is the lowest of the Seminulas obtained in the Yellowstone National Park, of which S. madisonensis is the highest. The obsolete fold and sinus, the regular, deeply arched valves, the evenly rounded, ovate shape, the tumid dorsal umbo and incurved beak, and the small resupinate ventral beak are all characteristic, and sharply differ- entiate it from the latter. Compared with S. humilis, it is considerably larger, more tumid; ventral beak smaller and narrower; beak of the dorsal valve larger, more inflated and incurved. Formation and locality: Madison limestone, west of Antler Peak, Gal- latin Range; A. C. Gill. CLIOTHYRIS King, 1850. This genus (or subgenus) is practically coextensive with the species CI roissyi Ldveill^, as the latter at present stands. Partly because the character of the surface ornamentation renders it difficult to secure well- pi-eserved specimens, the discrimination of species in this group, if indeed it has been systematically attempted, has not, I believe, proved successful. The Athyris roissyi question has thus become too complicated through the prolonged sedimentation of cliothyroid forms to admit of its ready solution. That it is desirable to subdivide this group is obvious; that it will LOWKR CARBONIFEROUS FOSSILS. 567 be possible to effect, this scientificall}- by the use of constant characters seems probable. Just what characters will assume such iini)ort, a detailed critical study of the genus will develop. Therefore, I have ventured to recognize certain tyiles in the Yellowstone National Park collections which I feel confident to be distinct from CI. roissiji of Leveill^. Whether these will ultimately prove tenable or be synonymic with other names from different horizons, future investigations will disclose. Cliothyris crassicardinalis White. PI. LXXI, fig. 8«. Athyris crassicardinalis White, 1860: Jour. Boston Soc. Nat. Hist., Vol. VII, p. 229. This species is referred to the genus Cliothyris on the streng-th of a clause in the original desciiption, Avhicli states that "occasional specimens show fringes of considerable length" proceeding from the squamose growth- lines. This, in conjunction with the shape, which is not markedly wider than it is long, seems to make this reference secure. On the other hand, not having had access to specimens from the type locality, and as the species has never been figured, I can consider my identification as only provisional. In the Yellowstone National Park tbe type here called CI. crassicardi- nalis ranges from the bottom to the top of the Madison limestone. It is seen to be a rather small, nearly circular shell, slightly wider than long, lenticular. Fold and sinus indicated only by a slight emargination of the anterior outline. Beaks small and pointed, that of the ventral valve being usually incurved so as to conceal the foramen. The surface is covered with numerous imbricating lamellose expansions, which under good preservation are seen to be subdivided into long spines. The large specimen figured on PI. LXXI, fig. 8a, measures 15 mm. in width by 14 mm. in length, but the average size seems to be somewhat less than this. This form is perhaps identical with the one figured in Mon. U. S. Geol. Surv., Vol. VIII, PI. XVIII, fig. 5, under the name of Athijris hirsuta. It is often extremely difficult in practice to separate CI. crassicardinalis from other forms found in the same beds — that is, when one or both are ill preserved in one way or another. Exfoliated specimens might easily be referred to the allied genera Athyris or Seminula. On the other hand, where single valves occur embedded in limestone, from which they break exfoliated and with the convex side upward, concealing the area, it is very 568 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. difficult to distinguish even ventral valves from the genera Reticularia and Martinia. It is only by a careful system of comparison of the poor with more perfect specimens that the proper affinities can be ascertained. The greatest difficulty is experienced in the case of Semmida Immilis, especially when the material is scanty and poorly preserved. Unfortunately, this is the usual condition. The characteristic surface ornamentation renders the genus Cliothyris peculiarly liable to exfoliation. Usually the spines have been broken away, their base giving the lamellae a scalloped appearance. When the shell is entirely gone, casts of the interior show only a few heavy growth-lines. When exfoliation has obliterated sur- face characters, reliance must be placed upon other peculiarities in distin- guishing CI. crassicardinalis from Semhiula Immilis. The shell of the former is less convex and the beaks are more attenuate. These characters do not always afford satisfactory results; yet I am unable to designate others. The two species occur together at several localities, notably from the upper part of bed 27, Crowfoot Ridge, Gallatin Range, but it so happens that they are there especially well preserved and then- distinctive characters shown in the clearest manner. Where the area is concealed, exfoliated specimens might well be taken for the young of Martinia rostrata or the reverse, but the latter will be seen to have a more prominent beak, and to be provided on the ventral valve with a shallow but perceptible sinus reaching to the extremity of the beak. Reticularia cooperensis is more transverse and the ventral valve more elevated. Formation and locality: Madison limestone, limestone bluff north of Little Sunlight Creek, Absaroka Range, 600 feet above the stream; Arnold Hague. Upper Gallatin Valley; divide between Gallatin River and Panther Creek, Gallatin Range; east face of Antler Peak, Gallatin Range; W H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, upper part of bed 27, bed 28, bed 29, bed 31 ; J. P. Iddings and W. H. Weed. Summit of peak west of Antler Peak, Gallatin Range ; south slope of same ; summit of Three River Peak, Gallatin Range ; south base of Quadrant Mountain, Gallatin range; cherty belt. Bighorn Pass, Gallatin Range; J. P. Iddings. Crowfoot Ridge, Gallatin Range, bed 24; A.C.Gill. Northof Owl Creek, northeast slope of Teton Range; W. H. Weed. Kinderhook age, Burlington, Iowa. LOWER OAltBONIFEKUUS FOSSILS. 569 Cliothyris crassicaedinalis, var. nana. ii. var. Pi; LXXI, (ig. 9rt. The fonn here refeired to is a rare one, and I am in doubt whether to consider it only young or dwarfed specimens of CI. crassicardinalis, a true variety of the same, or a distinct species. Its occurrence is restricted to two or three locahties, where it is not uncommon to find familiar types represented by unusually small indiAaduals. It has not been possible to ascei'taiu whether this shell is a true Athyris (sensu stricto) or belongs to the genus Cliothyris, though the circularity of its outline favors the latter reference. The shell is very small, nearly circular in shape, moderately convex. Beaks small, surface ornamented by numerous close, regular, imbricating, concentric lamellae. It occurs in a limestone and is always more or less exfoliated. There is no fold or sinus, but both valves have a mesial flatten- ing, which in some shells is quite marked. In size, shape, and general appearance this form is very close to specimens of CI. hirsuta from Spergeu Hill, Indiana. Length, about 0.30 inch ; width, nearly the same. Formation and locality : Madison limestone, east side of Gallatin River, west of Electric Peak; Crowfoot Ridge, Grallatin Range, top of bed 25; G. M. Wright. Cliothyris roissyi Walcott (non Ldveilld). Athyris royssii Walcott, 1884: Mon. U. S. Geol. Surv., Vol. VIII, p. 280, PI. XVIII, flgs. 9, 9ft. I have referred to this species a single large Athyroid which, though so exfoliated as to appear almost smooth, yet bears so strong a resemblance to the specimen referred by Walcott to CI. roissyi (loc. cit.) that I can not but believe them identical. There is, liowever, one striking difference, namely, in the size of the ventral beak, that in my collection being of medium size, the other extremely minute. But as both specimens are more or less crushed, it seems that this is only an appearance due to relative dis- placement of the two valves. The generic position of the form figured by Walcott, which shows very clearly the overlapping spinose lamellae characteristic of Cliothyris, is 570 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. beyond all question. Not so the specimens figured by Meek/ and doubt- full)^ referred by him to Leveille's species. In comparing this form with the one under discussion, I find it different not only from it but also from the European type. The shell is large, thick, transversely elliptical; fold but slightly defined, sinus broad and shallow, Avith a sharp median sulcus; surface lamellose with thick layers, which, on the best-preserved surfaces, •show no trace of having been produced into spines. The ventral beak is rather large, not strongly incurved, and instead of being furnished with a round pedicle aperture, as shown in the figure, a careful study of the rostral portion discloses that this appearance is due to a fracture which has also partially removed the shell covering the arch of the beak, and that below the point where the pedicle opening is indicated in the figure there is the anom- alous character of an open triangular delthyriuni. These facts are developed from a study of the type material itself, which in the figured specimen alone preserves the ventral beak entire, or nearly so. As the form seems to be distinct from anything yet described from the same horizon, I propose for it the name Atliyris mira. The specific identity of CI. roissyi Walcott with Leveille's species I hold to be doubtful. That form as figured by its author is smaller (34.5 mm. in width by 22.5 mm. in length) and more deeply folded, the two depressions defining the fold being so deep and triangular as to give the shell a trilobate appear- ance. The fold is surmounted by a faint sulcus ("?), resulting in a slight emargination of the anterior border. Beak not incurved, so that the open round foramen is a noticeable character. The surface is marked b}" not very numerous but strong lamellar expansions, whose ragged edges suggest that they may have been the origin of the characteristic spinose orna- mentation of the genus Cliothyris. In the specimens from the Yellowstone National Park and the Eureka district the fold and sinus are scarcely discernible. The latter has a small, sharp beak, whose deep incurvature completely conceals the foramen. That from the Yellowstone National Park shows an indefinable aperture, partly beneath the beak, partly broken through it. This contradiction is doubtless due to the same displacement which makes the beak of one specimen seem so small, that of the other comparatively so large. ' 1877. King'8 U. S. Geol. Expl., 40th Par., Vol. IV, PI. IX, figs. 3, 3o, 3S. LOWER CARBONIFEROUS FOSSILS. 571 ForiiKition and locality : Madison limestone, Crowfoot Ridg'e, Gallatin Range, bed "JS; J. P. Iddinjrs and W. H. Weed. Same, top of bed 24; J. P. Iddings. Keokuk to Kaskaskia; Europe; Mississippi Valley; White Pine and Eureka districts, Nevada; Salt Lake City, etc., Utah; Lake Valley mining district, etc., New Mexico; Lake County, Colorado; Guatemala; Bonijardin and Itaituba, Brazil. CONOCARDIUM Bronn, 1835. CoNOCARDiuM puLCHELLUM White and Whitfield (?) PI. LXVI, fig-. 14rt. Conocardium pulchelbim White and Whitfield, 1S62: Proc. Boston Soc. Nat. Hist., Vol. VIII, p. 299. In the absence of identified material I am not sure that the reference to White and Whitfield's species is correct, for I have but a single specimen, so that it is impossible to determine the range and normal expression of the shell; while C. pulchellum has not been figured, at least by its authors; and a description unaccompanied by illustrations, especially in this genus, is almost sure to be unsatisfactory. My shell is small, not very convex. Truncation of the anterior margin slightly concave, nearly the same length as the straight hinge line, which it meets at an obtuse angle. Posterior cardinal angle rounded. Ventral margin sloping and curving from the posterior angle to the anterior trunca- tion. Posterior wing somewhat flattened and concentrically rugose. Sur- face otherwise marked by about twenty-five radiating striae, which are strong and abrupt, leaving between them spaces greater than their own diameter. Length along the hinge line, 6.-5 mm.; greatest diameter (from posterior cadinal angle to the junction of the ventral margin with the anterior truncation), 12.5 mm. This species seems to have some points of resemblance with C. napo- leonense Winchell, but it is nearer White and Whitfield's form. C. A. White' has proposed the name Conocardium semiplenum for a form from the same region as that under consideration. It belongs likewise to the same type of shell, as comparisons are made with C. trigonale Hall, which C. pulchellum also resembles. It is not improbable that he may have ■ U. S. Geol. Surv. W. 100th Meridian, Vol. IV, 1877, p. 94. 572 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. had in hand the same form with which I am deaUng, but his descriptive remarks are too general to render the species identifiable. Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin Range, bed 24; A. C. Gill. Kinderhook age, BurUngton, Iowa. NATICOPSIS McCoy, 1844. Naticopsis (?) sp. PI. LXVI, fig. 13a. There is only one specimen of this gastropod, an internal cast in a siliceous matrix. The peritreme is incomplete and there is no telling to what extent the lower whorls are broken dwa)'. Specific identification is therefore out of the question. It appears to belong to the genus Naticopsis. Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 24; J. P. Iddings. LOXONEMA Philhps, 1841. LOXONEMA (?) sp. PL LXVI, fig. 9a. This species consists of the cast of a rather large elongate gastropod shell, probably belonging to the genus Loxonema. The specimen consists of four whorls and part of a fifth, and is very gradually tapering. It some- what resembles L. tenuiUneaium Swallow, of the Chouteau limestone, but the sides converge less rapidly and the peripheral outline of each whorl is much flattened. The shell must have been very thin, for the convolutions are now almost in contact. Length of the imperfect specimen, 27 mm.; width at the base, 12.5 mm.; width at the top, 7.5 mm. Formation and locality: Madison limestone. Crowfoot Ridge, Gallatin Range, top of bed 26; J. P. Iddings and W. H. Weed. LOWER OAKBONIFEROUS FOSSILS. 573 STRAPAROLLUS Montfort, 1810. Straparollus utahensis Hall and Whitfield. PI. LXVI, figs. lOa, 10b, 10c. Uvomphalus [Straparollus) utahensis Hall and Wliitlield, 1877: King's U. S. Geol. Expl. 40tli Par., Vol. IV, p. Ii59, PI. IV, flg.s. 20-L'3, This genus is represented in the collection from eight or ten localities, but the specimens are in so poor condition, being worn or broken, that a specific identification was a matter of difficulty. The beds from which the material was derived are mostly the lower strata of the Madison lime- stone, but some specimens, indistinguishable from the others in their present imperfect condition, occur near the very top of the same formation. It was evident at first sight that the Yellowstone National Park form was close to Etiomphalus luxus White, and Eii. utahensis Hall and Whitfield. After a careful comparison of the thi-ee types the balance of the evidence seemed to favor an identification with Eu. utahensis, and a section through one of the specimens justified the conclusion. It will be remembered that the two species just mentioned are both from the Rocky Mountain region, occurring in Waverly rocks, and often found at the same locality. Eu. luxus is somewhat smaller than Eu. {Straparollus) utahensis. The whorls are flattened on top, with a slight distal carination. In S. utahensis, however, there is a strong carination on the summit of each whorl, from which the sides slope away nearly plane, one toward the center, the other toward the periphery. This proved to be the case with the specimen sectioned, but it is not at all improbable that some of the other smaller specimens may belong to Eu. luxus. The shell of S. utahensis is thin, but thickened on top and on the two sides to form the carinations (PI. LXVI, fig. 10c). The outer side of each whorl as well as the top is carinated, and the shell on the inner side is also considerably thickened, but indented to receive the carina of the preceding whorl. The interior cross section, therefore, is circular or elliplical, and all distinguishing characters are lost when the shell is reduced to a cast. This species should be compared with Euomphalns ohtusus Hall (Geol. Surv. Iowa, Vol. I, Pt. II, p. 623), which was described from the Oolitic limestone of Burlington, Iowa. 574 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Formation and locality : Madison limestone, east side of Gallatin River, west of Electric Peak; divide between Gallatin River and Panther Creek, Gallatin Range; summit of Antler Peak, Gallatin Rang-e; amphitheater east of Bannock Peak, Gallatin Range, bed 30; W. H. Weed. Crowfoot Ridge, Gallatin Range, top of bed 26, lower part of bed 27, bed 28, bed 31; J. P. Iddings and W. H. Weed. Waverly age. Dry Canyon, Oquirrh Mountains; Ogden and Logan canyons, Wasatch Range, Utah. PLAT YC ERAS Conrad, 1840. This genus is represented by specimens which are rather scarce numerically and as to size much below the average. Taken as a whole, they are closely similar to the group of Waverly Platycerata figured by Keyes in Geol. Surv. Missouri, Vol. V, PI. LIII, figs la-Id, 2-8, 9a, db. In a genus Avhere the species var)^ so enormously within themselves — where, in fact, it may almost be said that there are no species — my material is much too scanty and fragmentary to show the range of specific variation and afford the concept of a specific type. Accordingly, no elaborate effort has been made to identify the material with existing species, much less to propose new names, and it has seemed best to describe each form without using specific appellations. Form A. This form is found on Crowfoot Ridge, Gallatin Range, from the top of bed 24. It is small and loosely coiled. The apex is wanting, but the whole specimen appears to have completed little more than half a turn. The apical portion is twisted slightly to the left (looking at the anterior peripheral face), and the base expands rapidly, but unsymmetrically, flaring a little more on the side toward which the apex is turned — the left. There is a broad carination on the front face, delimited by the two shallow grooves. Aperture subcircular. This form appears to be close to P. cornuforme,^ W^inchell, but that shell is said to be planorboid, while in this the apex is distinctly turned to the left. It also resembles P. vomerium ' of the same author in size and in the nature of the carination. Both these species are of Waverly age. 'Winchell, 1863: Proc. Acad. Nat. Sci. Philadelphia, pp. 18, 19; and Keyes, loc. cit., PI. LIII, figs. 3a, 3i>. LOWER CARBONIFEKOUS FOSSILS. 575 Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 24; J. P. Iddings. Form B. Shell very small, not spirally turned; of a conical or pyramidal shape, much inclined. The front is edged or sharply rounded; the back, under the apex, is flat, meeting the right side, which is more inflated than the left, at an angle. The angle at which the posterior face meets the left side is ti'uncated. Peritreme subquadrate. Formation and locality: Madison limestone, north of Bighorn Pass, Gallatin Range; A. C. Gill. Form C. Larger than either of the two already described, yet not very large; much flattened transversely, very rapidly expanding. The right-hand face of the fossil is somewhat flat; more inflated on the other side. Very abruptly rounded in front and behind. But slightly inclined, so that a line let fall from the apex onto the posterior extremity of the peritreme would be nearly perpendicular to the plane of the base. Formation and locality: Madison limestone, north of Bighorn Pass, Gallatin Range; A. C. Gill. Form D. PL LXVI, figs. 12a, 126, 12c. Small, gradually expanding and closely inrolledfor about one volution; then very rapidly expanding for about half a volution, which is highly inflated and not in contact with the involved portion. The latter is minute and turned to the left. The peritreme is broken, but appeal's to have been subquadrate. The sinistral side of the large whorl (that toward which the involved apex turns) is somewhat flattened; the anterior end is sharply rounded. Another angular turn, sinistro-posterior in direction, would bring this subplanate face to the original one at an acute angle were not their junction truncated or broadly rounded (f). Height about two-thirds the antero-posterior diameter. A line fi'om the most posterior point of the peritreme tangent to the involutions would be about perpendicular to the plane of the base. 576 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. This form, though considerably smaller, is closely similar to the speci- men identified by Keyes as Capulus paralius Winchell, and figui-ed on PI. LIII, fig. \d, of the work cited. The largest of these forms is about 9 mm. in height, with a maxi- mum basal measurement of 12.5 mm. Formation and locality : Madison limestone, east side of Gallatin River, west of Electric Peak; south slope of Quadrant Mountain, Gallatin Range; A. C. Gill Form E. PI. LXVI, figs, lla, 116, lie, 11(1. Shell rather small, though larger compared with the other forms in this collection. Very rapidly expanding. Laterally compressed, being flatter on the sinistral side, away from Avhich the small coil is turned. Dextral side more inflated; dorsum sharp, almost carinate. Shell marked by concentric growth-lines, sinuous, following the shape of the peritreme. Peritreme oval in outline. This should be compared with P. nehrascense Meek,^ and more espe- cially with Capulus paralius Winchell, as figured by Keyes (loc. cit., PI. LIII, figs. \h, Ic), Avhich is perhaps not identical with Winchell's type, shown by fig. la of the same plate. Formation and locality : Madison limestone, east side of Gallatin River, west of Electric Peak. CRUSTACEA. PROETUS Steininger, 1830. Proetus peroccidens Hall and Whitfield. PI. LXXI, figs. 14a, 146. Proetus peroccidens Hall and Whitfield, 1877 : King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 262, PI. IV, figs. 28-32. This species is represented in the Yellowstone National Park collec- tions by three cephalic shields (without the free cheeks), which are in exact agreement with the descnption and figures of P. 2)eroccidens. Each of the three heads was found at a separate locality, but one of them occurs on the ' White, 1877: Wheeler's U. S. Geogr. Surv. W. 100th Merid., Vol. IV, p. 159, PI. XII, figs. 5o-5d. LOWEU CAKBONIFEKOUS FOSSILS. 577 same block of limestone which carries the pyg-idium referred to P. loganensis. They are without surface ornamentation. The occipital rinj^' is nairow and not strong-ly marked. The glabella is moderately high, reaches nearly to the anterior margin, evenly rounded in front, about once and a half as long as wide, sides parallel the greater distance, but expanding suddenly behind. Marked by three or four pairs of transverse furrows. Of these only the posterior one is well defined, and it is bent backward at its inner end so as to be almost continuous with the occipital furrow. Frontal border narrow, thick, elevated. Greatest width of the anterior portion of the head, as limited by the suture line, just equal to the length of the glabella. The suture lines contract gradually, but round out strongly for the palpe- bral lobe, the most convex portion of which is not more than oue-fourth the length of the head, forward from the posterior edge. Formation and locality: Madison limestone, east side of Gallatin River, west of Electric Peak; G. M. Wright. Crowfoot Ridge, Gallatin Range, bed 31; J P. Iddings and W. H. Weed. East slope of Survey Peak, Teton Range; S. L. Penfield. Waverly age, Ogden and Logan canyons, Wasatch Range, and Dry Canyon, Oquirrh Mountains, Utah. Proetus loganeksis Hall and Whitfield. PI. LXXI, fig. 15a. Proetus loganensis Hall and Whitfield, 1877: King's U. S. Geol. Expl. 40th Par., Vol IV, p. 264, PI. IV, fig. 33. The identification of this species rests upon a single pygidium which, but for being considerably smaller in size, is exactly identical with that figured as the type of P. loganensis. The surface is without ornamentation. The axial lobe is high, marked by eleven annulations including the termi- nal ones. The lateral lobes have nine annulations each, which extend down upon the border and become obsolete upon the margin near the edge of the shell. It occurs associated with P. peroccidens. Proetus peroccidens and P. Joganensis, both of Hall and Whitfield, rest upon three structural units — a small unornamented pygidium, a laro-e pygidium with more annulations, ornamented with pustules or nodes, and a head with free cheeks more nearly corresponding in size with the larger pygidia, but destitute of the ornamentation which characterizes them. The MON XXXII, PT II 37 578 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. heads and larger pygidia were referred by the author to P. peroccidens, and the small type of pygidiuni was described as P. lof/aiiensis. In the Yellowstone National Park collections no pygidia of the type of P. peroccidens (the unornamented form) have been observed, but the large heads have been identified as P. peroccidens, and the small pygidia as P. loganensis. As the pygidium and a lai'ge head occur associated at the same locality, even on the same slab of limestone, there is some presump- tive evidence that they should be referred to the same s})ecific type, espe- cially as there is only one kind of head and one kind of pygidium known from the Park. The fact that both portions are without ornamentation supports this view. The disparity in size, especially when viewed in connection with a similar condition of affairs in Utah, is opposed to it. One of three hj-potheses seems probable. Both species (and the pygidia show that they are two) may have had unornamented cephalic shields, similar in detail and size; or, since it is now known that the two species occur in the same beds. Hall and Whitfield may have been in error in referring the cephalon from Dry Canyon to the associated pygidia; or, the smooth, plain heads do not belong to the smooth pygidia with which they are associated in the Yellowstone National Park, but (what is not intrinsicallv improbable) to the ornamented nodose ])ygidia with whicb they occur at Dry Canyon, as Hall and Whitfield have suggested. More evidence will be necessary before the point involved in this uncertainty can be ascertained. Formation and locality: Madison limestone. Crowfoot Ridge, Gallatin Range, bed 31; J. P. Iddings and W. H. Weed. Waverly age, Logan Canyon, Wasatch Range, Utah. PLATE LXVI. 579 PLATE LXVI. Page, Fig. 1. Atrypa reticularis 502 a. Type usually found in Yellowstone National Park ; after Walcott. h. Lateral view of same ; after Walcott. Devonian, Eureka district, Nevada. c. View of another specimen ; after Meek. (f) Middle Devonian, Piuon station, White Pine district, Nevada. Fig. 2. Atrypa missoiiriensis 502 a. Rostral view of a small individual, of a type common in Yellowstone National Park ; after Walcott. b. Ventral aspect of same ; after Walcott. Devonian, Lone Mountain, Nevada. c. Dorsal view of another specimen ; after Meek. Middle Devonian, Pinon station. White Pine district, Nevada. Fig. 3. Spirifer engelmanni 504 a. An anterior view ; after Meek. 6. Cardin.al view, showing area and foramen ; after Meek. c. Side view of same; after Meek. d. Dorsal view of same ; after Meek. Middle Devonian, Nevada. Fig. 4. Athyris rittata var. triplicala n. var 504 a. Lateral view of type specimen. h. Dorsal view of same, c. Anterior view of same. Three Forks limestone, south side of Soda Butte Creek, northwest of Abiathar Peak, Absaroka Range. Fig. 5. Pleurotomaria isaacsi (.') .' 505 a. Specimen doubtfully ideutilied with Hall and Whitfield's species. b. Side view of same. Three Forks limestone, Wall Canyon, Clark Fork Valley. Fig. 6. Loxonema delicalum u. sp 506 a. View of type specimen, enlarged. Three Forks limestone, south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range. Fig. 7. Platystoma minutum n. sp 506 a. Apical view of type specimen, enlarged. b. Lateral aspect of same, enlarged. Three Forks limestone, south side of Soda Butte Creek, northeast of Abiathar Peak, Absaroka Range. Fig. 8. Favosites sp 501 a. Silicifled example, showing size of corallites and character of tabulation. Three Forks limestone, north side of Soda Butte Creek, Absaroka Range. Fig. 9. Loxonema (?) sp 572 a. Lateral view of an internal oast. Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 26. 580 U. S. GEOLOGICAL SURVEY MONOGRAPH XXXII PART II PL. LXVI la Ic 2a i'b 2c ^ 3a 3b -J lb 5a 3c 3d 4a 4b 4c lOc 14a I Ic I la I lb |-*'T-'»T-!^,. '^i ^ lOa I 3a ii»^ L 12b 12c DEVONIAN AND LOWER CARBONIFEROUS THREE FORKS AND MADISON LIMESTONES THE HELIOTYPE PRINTING CO.. BOSTON DESCRIPTION OF PLATE LX VI— Continued. 581 Fig. 10. Strapavoltus iitahcnsiH 573 a. Apical view of a small specimen ; after Hall and WhittieM. b. Apical view of a larfjer, somewhat exfoliated speiimeu; after Hall and Whitfield. Waverly age, Dry C'aiivou. Utah. c. Section through a specimen from Yellowstone National Park. Madison limestone, east side of (Jallatiu Kiver, wost of Electric Peak. Fia. 11. Platj/ceras, form K 576 a. Lateral view of a small example attached to an exfoliated hase of riafjicriiiun si/mmelriius. b. Posterior view of same. c. Same seen from above. d. Side view of a larger specimen. Madison limestone, divide between Gallatin River and Panther Creek, Gallatin Range. Fig. 12. Platyceras, form i) 575 a. View of specimen resting on its base, as seen from above, enlarged. 6. Side view of same. c. Posterior view of same. Madison limestone, south base of Quadrant Mountain, Gallatin Range. Fig. 13. A^aticopsis (f) sp 572 a. Internal cast of a specimen from the lower part of the Madison limestone. Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 24. Fig. 14. Conocardium piilchelliivi (?) , 571 a. View of the only specimen found, enlarged. Madison limestone, Crowfoot Ridge, Gallatin Range, bed 21. PLATE LXVII 583 PLATE LXVII. Page. Fig. 1. Menophylliivi (?) excavatnm ii. sp "H a. View of a typical example of this species. Madison limestone, Crowfoot Ridge, Gallatin Range, lower part of bed 27. h. Longitudinal section of another specimen, showing, hut not completely, the depth of the calyce. Madison limestone, Crowfoot Ridge, Gallatin Range, bed 31. c. Transverse section of another specimen taken through the calyce, showing septa of two orders slightly developed. Madi.son limestone. Crowfoot Ridge, Gallatin Range, lower part of bed 27. d. Transverse section of the same specimen, taken a little lower down. Indications of the fossula and the commencement of the fossular wall can be seen. Septa of the second order are not shown in the drawing, but appear in the original section as small projecting points. e. Anotlier section of the same, still more proximal. The large fossula is well developed; the fossular wall and aborted fossular septum are well shown. Septa of the second order are represented by low ridges, two of which, not shown in the figure, are found on either.side of tlie fossular septum. /. Transverse section through another specimen referred to this species. The fossular septum here is extended clear through the fossula to the opposite wall, bisect- ing it, and the whole is much thickened by stereoplasma. Madison limestone, Crowfoot Ridge, Gallatin Range, bed 31. Fig. 2. CUsiophtjllum teres n.sp 51* a. Transverse section showing fossula, columella, and tabula (?). The latter is not adequately represented in point of continuance and distinctness. Secondary septa, not shown in the figure, can be seen in the original, x 2. h. Another section a little more proximal than the above, and showing much the same characters, x 2. c. Another section still more proximal, from the same specimen. The figure shows a somewhat too great development of dissepimental tissue, x 2. . ■A 4c w 6b 6a 6b 6c lOa m I 2a r\ ;:':: .??^1 7a 7b 7c 9a 9b tr. ■'^mti ^m 4d lOb ^H; i r : : la v.i^s^B^ 5b %:^m 8a 8b I Ic 12b LOWER CARBONIFEROUS- MADISON LIMESTONE THE HEUIOTYPE PRtNTlNG CO.. BOSTON DESOKIPTION OF I'LATE LXVIII— CONTINUED. 587 I'agft Fig. 8. Productella cooperensis 528 (I. Lateral view of a specimen ideutilied as Productella cooperenstH. b. Anterior view of 8:ime. c. A dorsal valve associateil with the above and referred to the same species. Madison liniestoiie, Crowfoot Ridge, Gallatin Range, top of bed 24. Fig. 9. Productella cooperensis 528 a. A dorsal valve of a type common in Yellowstone National Park. 6. Ventral valve of the samr species. Madison limestone. Crowfoot Ridge, Gallatin Range, top of bed 25. Fig. 10. Productella uli/era u. sp 530 <(. A dorsal valve of a common size and shape. 6. Outline view of a highly vaulted ventral valve. c. A very auriculate ventral valve. Madison limestone, limestone bluft" south side of Soda Butte Creek, northwest of Abiathar Peak, Abearoka Range. Fig. 11. Prodticius yallatinenaia n. sp. (See also fig. 7) 533 a. Ventral view of the type specimen, ft. Anterior view of same. c. Posterior view of same. d. Side view of same. Madison limestone, divide between Gallatin River and Panther Creek, Gallatin Range. Fig. 12. Eumetria verneuiliana 560 a. Dorsal view of a somewhat crushed specimen of a type common in Yellowstone National Park, x 2. ft. Side view of same, x 2. Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 25. PLATE LXIX. 589 PLATE LXIX. Page. Fig. 1. Caviarophoria ringens 537 a. Ventral view of a large specimen. Madison limestone, Crowfoot Ridge, Gallatin Range, tup of bed 25. b. Dorsal view of a smaller specimen. c. Side view of same. Madison limestone, Crowfoot Ridge, Gallatin Range, bed 28. Fig. 2. CamarotaecHa keirickana n. sp 539 a. (by mistake left unnumbered on plate) Ventral valve, slightly enlarged. Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 25. b. Dorsal valve, similarly enlarged. c. Anterior view of same. Madison limestone, divide between Gallatin River and Panther Creek, Gallatin Range. Fig. 3. Camarotmchia metalUca 540 a. Dorsal view of a specimen identified by Hall and Whitfield as BhynclioneUa piistii- losa (?); after Hall and Whitfield. Waverly age. Dry Canyon, Utah. S. Dorsal view of a large specimen from Yellowstone National Park. Madison limestone, divide between Gallatin River and Panther Creek, Gallatin Range. c. Anterior view of a smaller a specimen from Yellowstone National Park. d. Side view of same. e. Dorsal view of same. Madison limestone, northwest slope of Forellen Peak, Teton Range. Fig. 4. CamarotcecMa sp 542 a. Dorsal valve, x 2. ft. Front view of same, x 2. Madison limestone, limestone bluff south side of loda Butte Creek, northwest of Abiathar Peak, Absaroka Range. Fig. 5. Liorhynchus hagiiei n. sp 543 a. Dorsal view of type specimen, ft. Lateral view of same. Madison limestone. Crowfoot Ridge, Gallatin Range, cherty limestone, top of bed 24. Fig. 6. Dielasma ntah 544 a. Dorsal view of an imperfect example. 6. Side view of same. Madison limestone, Crowfoot Ridge, Gallatin Range, bod 28. c. Ventral view of type specimen : after Hall and Whitfield. Waverly age, Cottonwood divide, Wasatch Range, Utah. Fig. 7. Prodiictiis scabriculus 531 a. Side view of a ventral valve from the Madison limestone, ft. Posterior view of same. c. Outline of same, looked at from above. d. Surface ornamentation, enlarged. Madison limestone. Crowfoot Ridge, Gallatin Range, toil of bed 25. 590 U. S. QEOLOOICAL SURVEY MONOGRAPH XXXII PART II PU. LXIX la 6b 6a LOWER CARBONIFEROUS- MADISON LIMESTONE THE HELIOTVPE PHiNTINO CO., BOSTON IM':SCRIPTION OF PLATE LXIX— Continued. 591 Paga l''io. 8. rroditcliis semireticulalua 535 a. Ventral valve, posterior view. b. Lateral aspect of same. c. Outline as seen from above. Madison liiuestone, Crowfoot Ridge, Gallatin Range, lower part of bed 27. (I. Dorsal valve of same species. Madison limestone, head of Couaut Creek, Teton Range. Fig. 9. Product ns laricosta 534 o. Ventral valve of a specimen from Utah, restored; after Hall and Whitfield. Waverly age, Dry Canyon, Utah. ' 6. A ventral valve from the Madison limestone, flat and immature iu expression. Madison limestone. Crowfoot Ridge, Gall.atin Range, top of bed 25. c. Lateral outline of a ventral valve of the usual type. Madison limestone, Crowfoot Ridge, Gallatin Range, lower part of bed 27. PLATE LXX. 593 MON XXXII, PT II 38 PLATE LXX. Page. Fig. 1. Spirifer sp 552 ((. View oi au unidentified dorsal valve. Madison limestone, east slope of Survey Peak, Teton Range. Fig. 2. Spirifer striatus var. madisonenais n. var 551 a. Dorsal view of a large specimen. 6. Side view of same. Madison limestone. Crowfoot Ridge, Gallatin Range, top of bed 24. 0. Dorsal view of a somewhat smaller specimen. d. Side view of same. Madison limestone, Crowfoot Ridge, Gallatin Range, ciierty limestone, top of bed 24. Fig. 3. Spirifer eentrovalns 547 a. Ventral valve of a characteristic form; after White. Waverly age. Mountain Spring, Old Mormon road, Nevada. b. A. characteristic dorsal valve; after Hall and Whitfield. Waverly age. Dry Canyon, Utah. c. Another type, probably no more than varietally distinct from Spirifer centronaiut, described by Hall and Whitfield -as Spirifa- albapineiisis ; after Hall and Whitfield. Waverly age, Logan Canyon, Utah. d. A young specimen of the general type of Spirifer albapinensis, referable to Spiri- fer centronatus; after Hall and Whitfield. Waverly age, Dry Canyon, Utah. Fig. 4. Spirifer centronatus var. semifurcatus n. var 549 a. A dorsal valve of this type in which the incipient bifurcation of the two plications surmounting the fold is less apparent than usu.al. Madison limestone, Crowfoot Ridge, Gallatin Range, top of bed 26. Fig. 5. Martinia rontrata n. sp 553 a. Ventral view of a rather young specimen. b. Outline of the same, viewed from one side. Madison limestone, east side of Gallatin Rive'-, west of Electric Peak. 0. Ventral view of au old specimen. d. Lateral outline of same, showing the elevated iiud produced beak. Madison limestone. e. A large dorsal valve, referred to this species. /. Front view of same in outline. M.idison limestone, Crowfoot Ridge, Gallatin Range, top of bed 25. g. A very young ventral valve, described by Hall and Whitfield as Athyris planosui- cata (f ). After Hall and Whitfield. Waverly age, Logan Canyon, Utah. Fig. 6. Seticularia coopcrensis var 556 a. An exfoliated but otherwise perfect ventral valve. The heavy concentric lines are due to growth. Between these lie finer striie, the bases of the characteristic spinulose fimbriations, b. Lateral outline of same. c. Posterior view of same. Eureka district, Nevada, Lower Carboniferous. 594 U. S. GEOLOGICAL SURVEY MONOGRAPH XXXn PART II PL. LXX 6c 3a 3c m ^ 7b p 9c LOWER CARBONIFEROUS -MADISON LIMESTONE THE HEUIOTVPE PRINTING CO.. BOSTON DESCKIPTION OF PLATE LXX— Continued. 595 Paga FlQ. 7. /{etioularia (f) subrotundala 557 a. View of a veutral valve. b. Side view of same. Madison limestone, near Monarch, Montana. Fig. 8. lieticularia (?) peculiaria 557 a. Ventral valve, identified by White with Shuinard's species; after White. 6. Side view of same; alter White. Waverly age, Mountain Spring, Old Mormon road, Nevada. Fig. 9. Eeticularia cooperensis 555 a. A dorsal valve, identified as R. cooperensis, Madison limestone. Crowfoot Ridge, Gallatin Range, top of bed 26. b. A ventrnl valve from another locality. c. Side outline of same. Madison limestone. Crowfoot Ridge, Gallatin Range, upper part of bed 27. PLATE LXXI. 597 PLATE LXXI. Page. Fig. 1. Sijringothyrii carteri 558 a. Dorsal valve of a specimen from yellowstone National Park, drawn from au impression of a natural mold. Madison limestone, limestone bluff soutb side of Soda Butte Creek, nortliTvest of Abiatliar Peak, Absaroka Range. b. Anterior view oif an entire example of the same species ; after Meek ; figured by that author as Spirifer (Syringothxjris) cuspidatus. c. Cardinal view of same, showing high area and foramen, and, within the latter, the transverse septum and internal tube; likewise after Meek. Lower Carboniferous ( ?), White Pine district, Nevada. Fig. 2. Seminula tnadisonensis n. sp 563 a. Dorsal view of type specimen. h. Side view of same. c. Interior of a ventral valve, showing hinge teeth, pedicle cavity, and posterior and anterior adductors. Madison limestone, head of Conaut Creek, Teton Range. Fig. 3. Seminula madisonensis va,T.pu8SiUa u. var 564 a. A''entral valve of type specimen, showing shape, enlarged, ft. Lateral view of same. Madison limestone. Crowfoot Ridge, Gallatin Range, bed 28. Fig. 4. Seminula subtilita 564 fl. Dorsal view of a characteristic specimen from the type locality, for comparison with Seminula madisonensis. h. Side view of same, c. Anterior view of same. Upper Carboniferous, near Weston, on the Missouri River. Fig. 5. Seminula immatura n. sp 566 a. Dorsal view of a specimen with the ventral beak broken, ft. Side view of same. c. Dorsal view of another specimen which is somewhat crushed. d. Side view of same. Madison limestone, west of Antler Peak, Gallatin Range. Fig. 6. Seminula humilis n. Bip 565 a. Dorsal view of a rather large specimen. 6. Side view of same. c. Dorsal view of a smaller specimen from the same locality. Madison limestone, Crowfoot Ridge, Gallatin Range, upper part of bed 27. Fig. 7. Athyris lamellosa 561 a. Ventral view of a badly exfoliated specimen. Madison limestone, Yellowstone National Park. Fig. 8. Cliothyris crassicardinalis 567 a. Dorsal view of a specimen showing the usual characters of size and shape, but almost completely exfoliated. Madison limestone, north of Owl Creek, northeast slope of Teton Range. 598 U. S. GEOLOGICAL SURVEY MONOGRAPH XXXII PART II PL. LXXI 3a .lb y/ X 7a Sa 5b 8a w,^ Ic 9a 13a 6c I 4a 14b 8 I 5a 13b 13c 2c 2b 2a ^ ^§; 6a 6b vm 10^ 12a LOWER CARBONIFEROUS- MADISON LIMESTONE THE MELIOTYPE PRINTING CO.. BOSTON DESCRIPTION OF PLATE LXXI— Continued. 599 Fig. 9. Cliothyris craxeUaidinalis var. nana n. var 569 a. Ventral view of a somewhat exfoliated specimen, which is regarded as varietally distinct from the above. Madison liraestoue, Crowfoot Ridge, Gallatin Range, top of bed 25. FlO. 10. Spiri/eriiia solidirostria 545 a. Ventral valve ch.iracteristio of this species. Madison limestone, amphitheater east of Bannock Peak, Gallatin Range, bed 28. Kid. 11. HolaatercUa wrvjhti var. ame.ricana n. var 508 a. View of an isolated spicule raagnitied about twenty diameters. Madison limestone, divide between Gallatin Valley and Panther Creek, near Big- horn Pass, Gallatin Range, bed 24. Fn;. 12. Endothyra baileyi 507 a. An example from Spergen Hill, Indiana, of a not unusual size, x 12. 6. Another, smaller specimen from the same locality, x 12. Warsaw group, .Spergen Hill, Indiana. Fig. 13. Endothi/ra baileyi var. jyarva n. var 507 (I, b. Two specimens of the ordinary character, from the Madison limestone, x 12. c. A small specimeu from the Madison limestone, x 12. Madison limestone. White Mouutain, Absaroka Range. Fig. 14. Proetiis peroccidens 576 a, b. Glabella and free cheek of the kind occurring in the Madison limestone; after Hall and Whitfield. Waverly age, Dry Canyon, Utah. Fig. 15. Proeiua loyamnsis 577 a. Pygidium of a type associated with the above in the Madison limestone; after H.all and Whitfield. Waverly age, Logan Canyon. CHAPTER XIII MESOZOIC FOSSILS. By T. W. Stanton. The Mesozoic fossils obtained iu and near the Yellowstone National Park and submitted to me for study include 78 species of invertebrates, of which 31 are Cretaceous, 46 are Jurassic, and 1 is from beds of supposed Triassic age. The number of species from a single horizon is not large enough to be dignified with the designation "fauna," excepting, perhaps, in one or two cases; yet the study of these fossils and the comparisons made with known horizons have led to some general results that are worthy of brief discussion. The subject will be treated by geological horizons, and after reviewing the general considerations an annotated list of the species with descriptions of new forms will be given. TRIASSIC. The Teton formation, of supposed Triassic age, yielded a few speci- mens of a Lingula at a locality on the summit of Quadrant Peak. This fossil resembles Lingula hrevirostris M. and H., from the Jurassic of the Black Hills, but in the absence of other fossils it should be given little weight in determining the age of the beds. Linguloid shells are so slightly differentiated that it would not be safe to distinguish, by them alone, even between Paleozoic and Mesozoic. The determination of the age of this formation must, for the present at least, rest on the evidence of stratigraphy and lithology. The paleontologist can only say that the underlying beds yield Carboniferous fossils, while the overlying formation has a well- developed Jurassic fauna. 600 MESOZOIC FOSSILS. 601 The only marine Triassic fossils that have been found in the Rocky Mountain region are from the Lower Trias, Ijeneath the "Red Beds" in southeastern Idaho^ The very few fossils that have been obtained from the Red Beds farther south (in New Mexico and southern Colorado) seem to be of fresh-water origin. In California and Nevada, however, marine Triassic beds are well devel- oped, and have yielded a varied fauna which is as yet mostly undescribed. JURASSIC. The Jurassic fossils form much the largest and most important part of the Mesozoic collection. The fauna is not large, but most of the species are abundantly represented, and in number of species it compares favorably with the Jurassic of other parts of the Rocky Mountain region. The col- lections are from many localities in two general areas — one, which yielded the most fossils, in the northwest corner of the Park, on the headwaters of Gardiner and Gallatin rivers and near the Yellowstone ; the other on the slopes of Sheridan Peak and farther southwest of Snake River. The fossils from all these localities evidently belong to a single fauna, though two zones are recognizable, distinguished more by lithological differences than by faunal peculiarities. The upper zone of arenaceous limestone has yielded an abundance of RhynchoneUa gnathojjJiora, B. myrina, Ostrea strigilecula, Camptonectes pertenuistriatus, C.bellistriatus, and a few other forms. Most of these also occur in the underlying calcareous clays and marly limestones associated with many other species, of which the most abundant are Pleuromya siibcompressa, PJioladomya kingi, and Gryphcea cal- ceola var. nehrascensis. The same fauna is represented in the beds just beyond the northern limits of the Park, at Cinnabar Mountain, where fossils that are included in the present report were obtained by Dr. A. C. Peale in 1872. These were identified and some of the species named by Prof. F. B. Meek,- but it was not until 1880 that they were illustrated and more fully described by Dr. C. A. White.^ Still earlier Captain Raynolds had brought back Gnj- phcea calceola var. nehrascensis and a few other fossils of this horizon from ' See White, Triassic fossils of soutlieasterii Idaho : Anu. Rept. U. S. Geol. Surv. Terr, for 1878, pp. 105-118. ''Ann. Rept. U. S. Geol. Surv. Terr, for 1872, pp. 471-474. ^Idern for 1878, pp. 143-153, Pis. XXXVIl and XXXVIU. 602 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Wind River Valley, and they were described by Meek and Hay den/ who had previously^ announced the discovery of Jurassic fossils from the Black Hills. These Black Hills fossils are fully described and illustrated in the Paleontology of the Upper Missouri. Subsequent geological explorations and surveys have shown that the marine Jurassic is widely distributed in South Dakota, Wyoming, Montana, Idaho, and Utah, and have made con- siderable additions to the fauna that have been described by White,^ Hall and Whitfield/ Meek" and Whitfield.® All of these authors seem to have assumed that the fossils they described belonged to a single fauna. At least they made no attempt to recognize distinct horizons in the Jurassic. The meagerness of the fauna — usually only a few species having been obtained at any one locality — was perhaps sufficient reason for not making attempts of this kind. Prof Alpheus Hyatt's recent comprehensive studies of the earlier Mesozoic faunas of the United States, and especially of Cali- fornia, where all the greater divisions of the Jura are developed, have led him to express the opinion that both tlie Upper Jura (Callovian or Oxford- ian) and the Middle Jura (Oolite) are represented in the Rocky Mountain region.' In the former he places the Jurassic of the Black Hills, and of Red Buttes and Aurora, Wyoming, with probably some localities in Utah. Of the Middle Jura he says: "The Oolite certainly seems to have been found by Dr. Peale near the lower canyon of the Yellowstone in Montana, and out of the few fossils from Utah described by Dr. White some are closely similar to those of the inferior Oolite at Mount Jura." It has already been stated that this collection of Dr. Peale's belongs to the same horizon that is represented in the Park. It contained the fol- lowing species: Ostrea strigilecula. Trigoiiia montanaensis. Gryphaja planocoiivexa. Astarte meeki. Camptonectes platessiformis. Cypricardia baguei. Pinna kingi. Pleuromya subcompressa. Gervillia montanaensis. PLoladomya kingi. Morliola subimbricata. Goniomya montanaensis. Trigonia americaua. 'Proc. Acad. Nat. Sei. Phila., 1861, p. 437, and Paleontology of the Upper Missouri, 1865, pp. 74 and 80. = Proc. Acad. Nat. Sci. Phila., 1858, pp. 46, 49-59. 3U. S. Geog. and Geol. Expl. West of 100th Meridian, Vol. IV, Pt. 1, 1875. ' are probably all from one horizon. According to the various reports published, as well as personal observation in both the northern and southern parts of the Territory, the fossiliferous zone is a calcareous bed near the base of the local Jurassic sections. In Weber Canyon it has yielded Cucnlltea liaguei, Pkiiromya suhcompressa, Pentacrinus asteriscus, and a few other forms; in Thistle Canyon the pecuhar Lyosoma poivelll was obtained, and in a collec- tion made by Mr. Robert Forrester on San Rafael River I have recoo-nized Irigonia amerkana and Pholadomya Jcingi, all of which occur in the Park. For these reasons I regard all of the fossiliferous Jurassic beds now known in Utah as belonging to the same horizon that is so well represented in the Yellowstone National Park. The question still remains whether the Jurassic of the Black Hills belongs to a higher horizon. There are some facts in favor of the opinion that the Jurassic fossils of the two regions may not be contemporaneous. For example, a number of the most abundant species in the Yellowstone National Park region, such as Pleuromya suhcompressa, Pholadomija kingi, and Cypricardia haguel, have not been reported from the Black Hills. The Yellowstone species of Trigonia, Modiola, and Gervillia are also distinct. Pseudomonotis (Eumicrotis) curta, which is one of the most abundant species in the Black Hills, is represented in the Park collection by a single doubtful specimen. No example of Cardioceras cordiforme has been found in the Yellowstone National Park, and several other common Black Hills forms are either absent or rare there. On the other hand, there is a considerable list of species common to the two regions, among which may be mentioned: Pentacrinus asteriscus. Camptonectes bellistriatus. Ehyuchouella niyrina. Cami)tonectes platessiformis. Ehyncbonella gnathophora. Avicula wyomingensis. Ostrea strigilecula. Belemnites densus. Gryphsea calcepla var. nebrascensis.' 'The Black Hills specimens of this species are all small. 604 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Many of the species that are considered distinct are closely related. It should be remembered, also, that we know only fragments of the fauna that must have existed at that time if it approached in size those that are now living. Whitfield records only 43 species from all the Black Hills country, and we now have about the same number from the Yellowstone region. If more exhaustive collections were made in both districts, it is probable that the list of common species would be considerably increased, but even as the record stands it shows rather close relationship of faunas. Possibly the lowest Jurassic beds in the Yellowstone region may be slightly older than the lowest in the Black Hills, but the difference in age can not be great — not great enough, as it seems to me, to put them in different divi- sions of the Jura. Throughout all the Rocky Mountain region, wherever marine Jurassic strata are found they are only a few hundred feet in thick- ness and they rest directly on the Triassic "Red Beds" or on older forma- tions. It does not seem possible that Upper Jurassic marine beds could have been deposited in the Black Hills and Wyoming without leaving any traces in the Yellowstone, Montana, and Utah — that is, the stratigraphic relations and the geographic distribution of the marine Jurassic of the Rocky Mountain region are in favor of the idea that all of these deposits were made contemporaneously in a single sea. CRETACEOUS. Dakota (?) formation. — Thc collectlou sliows that sevcral horizons of the Cretaceous are represented in the Park. The lowest of these, according to the geologists, is a thin bed of limestone, not far above the local base of the Cretaceous section, that is filled with fresh-water gastropods and a few Unios. This fauna at once suggests a comparison with the fresh-water forms {Lio'placodes veterniis and Viviparus gUli) from beds of supposed Jurassic age overlying the marine Jura in Wind River Valley, Wyoming, but these forms are not represented in the Park collections. The few species obtained do not show their generic characters very distinctly; still it is evident that they are not closely related to the fresh- water Bear River fauna of southwestern Wyoming nor to the few fresh-water forms known from the Dakota of Nebraska, both of which seem to hold about the same stratigi-aphic position as this bed. There is one other possibility, and that is that the Lower Cretaceous Kootanie formation is MESOZOIC FOSSILS. 605 represented here. It has been recognized by means of its fossil plants at Great Falls, Montana, and in the Black Hills, but its fresh-water mollusks are almost entirely unknown, and the few that have been seen are entirely different from these. All that can now be said concerning the age of these fossils is that they come from a bed that is conveniently referred to the Dakota on account of its stratigraphic position. I have named three of the most common forms of gastropods from this bed, so that they may be definitely referred to, although they are rather obscure and unsatisfactory species. Colorado formation. — The marine Cretaceous beds on Snake River one-fourth to one-half mile above the mouth of Sickle Creek may be directly correlated with the upper part of the Colorado formation as it is developed on the Mis- souri River near Fort Benton. The locality near Sickle Creek has yielded: Inoceramus uudabundus M. and H. Inoceramus flaccidus White. Inoceramus umbonatus M. and H. Baculites asper Mort. (?) Inoceramus acuteplicatus n. sp. Scaphites ventricosus M. and H. All of these, except the third and fourth, occur together in the upper part of the so-called Fort Benton shales on the Missouri, and associated with them are Inoceramus exogyroides M. and H., I. defonnis Meek, I. temii- rostris M. and H., Veniella morfoni M. and H., and Phohidomya papyracea M. and H., and a few undescribed species. This well-characterized zone was included in the Fort Benton shales by Meek and Hayden when they gave that name to the "No. 2" of their Cretaceous section, and they regarded all these dark shales near Fort Benton as the equivalent of the shales underlying the Niobrara limestone in Nebraska, Kansas, Colorado, and elsewhere. The fact is, however, that the Niobrara also is represented by shales in this upper Missouri region, and the fossils indicate that this zone is really the equivalent of the upper portion of the Niobrara. The evidence for this statement rests on the occurrence of several of the above species in the Niobrara limestone and overlying shales of Colorado and in the equivalent Austin limestone of Texas, and also on the absence of all these species except Veniella morfoni from beds lower than the Niobrara in the same region and elsewhere. In Colorado Inoceramus deformis is the most characteristic species of the Nio- brara limestone. Recently Mr. Gr. K. Gilbert has collected Inoceramus umbonatus from shales in the Niobrara above the limestone near Pueblo, 606 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Colorado, and it is probable that the type of I. flaccidus canie from about the same horizon. I. umbonatus and /. exogyroides are reported from the Austin limestone of Texas, and Baculites asper (?) occurs in the same formation. The European I. involutus, which is very closely related to, if not identi- cal with, I. uiubonatus, is also confined to the Emscher Mergel, according to Schliiter, which appears to be the homotaxial equivalent of the Niobrara. The fact that within the Colorado formation experience has shown the various species of luoceramus to be good guide fossils for the different zones gives this evidence of a few species greater weight than it would have otherwise. The name Colorado formation has come into general use for the combined equivalents of the Fort Benton and Niobrara, and it is a very convenient term, especially in the regions where the lithological differences are not clearly marked. A fragment referable to Scaphites ventricosus, obtained on the southeast spur of Electric Peak, makes it probable that the shales there also belong to the iipper part of the Colorado formation. The same horizon is repre- sented at Cinnabar Mountain, just north of the Park, though no Cretaceous fossils from that place are included in these collections. Professor Meek examined fossils obtained there in 1872 and listed^ Scaphites ventricosiis, Baculites asper (f), and undetermined species of Tlu-acia, Trigonia, Inoceramus, and Ostrea. There are two other localities in the northern part of the Pai-k, on Fan Creek and the north branch of Gardiner River, that have yielded an abundance of Ostrea anomioides, a species that occurs in the Colorado formation at several localities in Montana. Montana formation. — Thc Fort Picn'e aud Fox Hills divisious of the Meek and Hayden section are frequently combined under the name Montana formation for reasons similar to those that caused the union of the Fort Benton and Niobrara. In the western part of the Rocky Mountain Cre- taceous area it is often difficult to draw a sharp line between even these two broader divisions. The lower part of the section is distinctively Colorado and the upper part distinctively Montana, but there is frequently a doubtful zone in which the faunas are more or less blended. This is especially true in northern Utah, at Coalville, and in western Wyoming, where both the 'Ann. Kept. U. S. Geol. Sutw Terr, for 1872, p. 475. Ml<:SOZOIC FOSSILS. 607 Colorado and Montana formations contain several heavy beds of sandstone with closely related littoral faunas.^ It is evident that the seashore remained in that region throughout nearly all of Upper Cretaceous time, giving the shallow waters and sandy bottom favorable to the continuance of the littoral fauna that was early established there. The Colorado formation is easily recognized in these sections by the occurrence of a number of widely dis- tributed characteristic species, but for some unexplained reason very few of the species that characterize the Montana formation farther east and north occur there. This phase of the Cretaceous is well developed on Hams Fork, in western Wyoming, and it extends northward from there nearly to the southern boundary of the Park, for it is well represented in the collection from a sandstone on Glade Creek and at other localities near Snake River in the same region. Fossils are abundant, but only about 20 species were obtained. Judging from the fauna, the horizon is not very far from that of the Colorado shales near Sickle Creek — probably a little above them — and it is provisionally referred to the lower part of the Montana formation. Several of the species occur at Coalville, Utah, and in south- western Wyoming, and some of them there range down into the Colorado formation. More thorough collecting from all the Cretaceous beds exposed in the Yellowstone National Park, and a little farther north and east, will probably give both phases of the Upper Cretaceous faunas in one section and enable us to assign these sandstones to a more definite place in the standard Upper Cretaceous section. In the following list of species references are usually given only to the first description and to publications in which the species is figured. For fuller references consult Boyle's Catalogue of American Mesozoic Invertebrates: Bull. U. S. Geol. Surv. No. 102. ' See, for a fuller discnssion of this subject, The Colorado formation autl its iu vertebrate fauua: Bull. U. S. Geol. Surv. No. 106, pp. 37-46. 608 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. ANNOTATED LIST OF SPECIES, WITH DESCRIPTION OF NEW FORMS. TRIASSIC (?) SPECIES. LINGULA sp. undet. A few specimens of Lingula from beds on the summit of Quadrant Peak, supposed to be of Triassic age, closely resemble the Jurassic Lingula brevirostris M. and H. from the Black Hills. JURASSIC SPECIES. ECHINODERMATA. Pentacrinus asteriscus Meek and Hayden. Pentacrinus asteriscus Meek and Bayden, 1855: P roc. Acad. Nat. Sci. Phila., p. 49. White, 187.5: Geogr. aud Geol. Surv. W. lOOtb Meridian, Vol. IV, Pt. I, p. 162, PI. XIII, figs. 6a, b. Clark, 1893: Bull. U. S. Geol. Surv. No. 97, p. 26, PI. Ill, figs. 2a-d. Pentacrinites asteriscus Meek and Hayden, 1865: Palfeont. Upper Missouri, p. 67, PI. Ill, figs. 2a, b, and fig. in text. Whitfield, 1880: Geol. Black Hills Dakota, p. 345, PI. Ill, figs. 1, 2. Pentacrinus whitei Clark, 1893: Bull. U. S. Geol. Surv. No. 97, PI. Ill, figs. 4a^fl. This species, which is known only from portions of the columns, occurs in collections from divide between Fawn Creek and Gallatin Valley, from the slopes of Mount Sheridan, and from west of Snake River, north of Berry Creek. The joints of the columns vary in diameter, in thickness, and in the depth of the reentrant angles, but they do not vary more in these respects than do the different portions of the stem in a single individual of a recent Pentacrinus. The joints of the upper part of the column are always thinner, more distinctly star-shaped, and differ in all other details from those of the lower portion. The name P. wUtei was proposed by Prof W. B. Clark for large, thin joints with deep reentrant angles, but the author of the species informs me that he has abandoned the name for reasons similar to those just given, and in a forthcoming monograph of the Mesozoic Echinodermata, of the United States he will refer all the known American Jurassic Pentacrini to P. asteriscus. MESOZOIC FOSSILS. 609 ECHINOIDEA. Frag^nientarv casts of one or more species of e(;liiuoi(ls were obtained nt-ar the lower canyon of the YeUowstone River and at a hicaHty north of Berry Creek, a tributary of Snake River. Tliey are doubtless new species, but they are not sufficiently well preserved for generic determination, and we must therefore wait for additional and better material. BRACHIOPODA. Rhynchonell.v myrina Hall and Whitfield. Rhynchonella myrina Hall and Whitfield, 1877: U. S. Geol. Expl. 40tli Parallel, Vol. IV, Pt. II, p. 284, PI. VII, figs. 1-5. Whitfield, 1880 : (ieol. Black Hills Dakota, p. 347, PI. Ill, fig. 6, not fig. 7. The tj'pe of this species is a finely plicate shell with aljout eight plica- tions in the median sinus. In Prof R. P. Whitfield's later publication he has united with it the much more coarsely plicate forms, with only three or foiu- plications in the median sinus, that have usually been referred to R. (jnathophora. As the numerous specimens in the present collection do not show the intermediate varieties of form and sculpture, I prefer to treat them as distinct species. Typical B. myrina occurs at a number of localities in the northwest corner of the Park and near Snake River southwest of it, in the hard arenaceous limestone. Rhynchonella gnathophora Meek. PI. LXXII, figs. 1-4. Bhynchonella gnathophora Meek, 1804: Geol. Surv. California, PaliTBOiit., Vol. I, p. 39, PI. VIII, figs. la-/. Rhynchonella ijnathophora 1 Hall and Whitfield, 1877: U. S. Geol. Expl. 40th Parallel, Vol. IV, Pt. II, p. 284, PI. VII, fig. (J. Rhynchonella myrina (H. and W.) Wliitfield, 1880: Geol. Black Hills Dakota, p. 347, PI. Ill, fig. 7, not fig. 6. Rhynchonella sp. Meek and Hayden, 1865: Pahtont. Upper Missouri, p. 71, PI. Ill, fig. 4. The specimens referred to this species have nearl}' the same outlines as i?. myrina, but they are somewhat more capacious and mucli more coarsely plicate. The type of R. myrina has thirty ])lications on each valve, with MON XXXII, PT II 39 610 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. eight in the mediau sinus, while the phcations on these shells vary from fourteen to twenty, with three or four in the median sinus, three being much the more common number. A few specimens have only two. I have not seen Meek's types from the Jurassic of California, but specimens from the Mormon sandstone near Taylorsville (probably Meek's original locality) have been kindly loaned by Professor Hyatt for com- parison. These are larger than any of the Utah or Yellowstone specimens, and none of them has less than four plications in the median sinus, but in all other respects they agree quite closely. All the figured specimens from the Black Hills and Rocky Mountain region above referred to have been examined, and I have no doul)t of their specific identity. In Yellowstone National Park, where the species is very abundant in the upper zone of the Jurassic and occasionally occurs in the underlying shales, the specimens are usually small, many of them being no larger than the one from the Black Hills figured by Meek and Hayden. It is known from northwestern Colorado and from the Uinta Moun- tains, Utah, and it occurs in the Park near the northern and Lake heads of Fawn Creek; on south slope of ridge south of Gray Mountain; south side of Fan Creek Pass; on saddle at head of Fawn Creek, northeast of Monu- ment Peak, in beds 100 feet above principal fossiliferous horizon of Jurassic; in saddle west of south head of Gardiner; 4 miles north of second crossing of Snake River, at 7,500 feet elevation; on hill northeast of Moimt Everts; on ridge south base of northwest slope of Flat Mountain; at Mammoth Hot Springs, on main terrace. PELECYPODA. OSTREA STRIGILECULA "White. Ostrea strigilecula White, 1875 : U. S. Geog. aud GeoL Surv. W. 100th Mericliau, Vol. IV, Pt. I, p. 163, PI. XIII, tigs. 3a-d. 1884 : Fourth Auu. Kept. U. S. Geo!. Surv., p. 281t, PI. XXXV, figs. 0-11. Whitfield, 1880: Geol. Bhick Hills Dakota, p. 348, PL III, figs. 8-12. Specimens referable to this small and somewhat obscure species were collected from almost every locality with BJnjnchonelhi rjimtJi02Jhora aud on northeast spur of peak west of mouth, of Coulter Creek; west end of ridge southeast of Mink Creek; Mount Sheridan; lower limestone on Fawn Creek plateau; east end of northeast spm- from Signal Peak; saddle in rido-e west of south head of Gardiner. MKSOZOIC FOSSILS. 611 OsTKEA ENGELMANNI Meek. Ostrea enfielmamii Meek, 18G0: Proc. Acad. Nat. Sci. Pliihi., p. .Sll. 1870: Simpson's Kept, Expl. (heat Basin, Utah, p. 355, PI. Ill, fig. «. Meek and Uaydeu, 1865: Paliiont. Upper Missouri, p. 73, flgs. A, P>. Wliite, 1881: Fourth Anu. lle])t. U. S. (ieoL Surv., p. 289, PI. XXXIV, tigs. 3, 1. A few frag-ments and imnuiture specimens of this species were obtained near the head of drainage of northeast valley of Fan Creek and top of hill 3 miles southeast of Gravel Peak. Gbyph.^-:a planoconvexa Whitfield. PI. LXXII, tigs. II and 10. Grypluvajilanoconvera, 'Whit^eM 1876: Ludlow's Kept. Keconnaissance from Carroll, Montana, to Yellowstone Park, p. 142, PI. II, tigs. 9 and 10. Shell of medium size, subcircular in outline; attached valve moderately convex with rather [)rominent lieak, and in most specimens with an obscure shallow furrow which separates a rather broad triangular lobe from the body of the shell; upper valve varying from nearly flat to deeply concave; surface marked onl}' by lines of growth and irregular concentric undula- tions. The cartilage pit is verj' broad and shallow. An average specimen measures 57 mm. in length, 50 mm. in height, and 27 mm. in thickness of the two valves united. This form was mentioned by MeeP as "Gryphsea, a small species of the form of G. dUatataP It also rese}nbles some varieties of the Upper Cretaceous 6^. vesicularis and Ostrea pat'nia. Whitfield's type, from the Bridger Mountains, Montana, is somewhat more convex than any of our specimens, and the figure does not show any furrow or lobe, but I have no doubt that it is the same variable species. The specimens figured are from near lower canyon of Yellowstone River, collected by Dr. A. C. Peale, and ridge southwest of second crossing- of Snake River, collected by Mr. W. H. Weed. It was also obtained on north slope of ridge north of Gray Mountain; on divide at head of Fawn Creek; ridge west of south branch of headwaters of Gardiner, and near Snake River 3 miles west of mouth of Coulter Creek. ' Ann. Rept. U. S. Geol. Surv. Terr, for 1872, p. 472. 612 GEOLOGY OF THE YELL0WST02^'E NATIONAL PARK. GrypHxEa calceola var. nebrascensis Meek and Hayden. PI, LXXII, figs. 5-7. Gryphcea calceola var. nebrascensis Meek and Hayden, 1861: Proc. Acad. Nat. Sci. Phila., p. •IST. 1805: PaLtont, Upper Missouri, p. 74, PI. Ill, flgs. la-e and figs. A-E on p. 75. Whitfield, 1880: Geol. Black Hills Dakota, p. 349, PI. Ill, figs. 13-10. White, 1884: Fourth Ann. Ptept. U. S. Geol. Surv., p. 290, PI. XXXV, figs. 1-5. This is one of the most abundant species in the lower fossiliferoiis zone of the Yellowstone National Park Jurassic, occurring in the collection from south slope of ridge south of Gray ]\Iountain ; south end of northeast spur of Signal Peak; east side of Fan Creek Pass; head of north fork of Fawn Creek; saddle in ridge west of south branch headAvaters of Gardiner; summit of wagon road between Sentinel Bi;tte and Terrace Mountain, 1 mile from head of Swan Lake Valley; hills west of Snake Eiver, 4 miles south of second crossing; on north side of old road to Mammoth Hot Springs, and slopes of Mount Sheridan. The species was originally described from the Wind River Mountains and from the Black Hills, though the specimens from the latter locality are all very small. Similar small specimens, however, are very abundant in the Park collections. Lima cinnabarensis n. sp. PI. LXXII, fig. 8. Shell small, obliquely elongate oval in rcssa, Fholmlomijii l'ni. A single specimen from ridge northwest of second crossing of Snake MESOZOIC FOaSlLS. 619 River. The type came from Spring- Canyon and lower canyon of the Yel- lowstone, Montana. Trigonia elegantissima Meek. PI. LXXIII, fin. 2. Trigonia elefjantinsima Meek, 1873: Ann. Kept. U. S. Geol. Surv. Terr, for 1872, p. 474. Shell small, subtrigonal in outline, moderately convex, with prominent, acute, recurved beaks; posterior umbonal ridge prominent, ang-ular, and curved; anterior end brfjadly rounded; posterior end subangular V)elow at the extremity of the umbonal ridge and forming a convex slope to the beak above; escutcheon not distinctly marked; posterior area depressed and bearing numerous equal, fine, radiating lines; remainder of surface with regular, closely arranged, small concentric ribs that show a tendency to bend downward toward the front. Length of figured specimen, 21 mm.; height, l-t mm.; convexity of single valve, 4 mm. This species is closely related to T. americana, from which it differs in outline, and more especially in having much smaller and more numerous concentric ribs. In specimens of T. americana no larger than the type of this species the spaces between the ribs are at least a millimeter wide. Meek's original description, given in a footnote to the Hst of fossils from Devils Slide, Cinnabar Mountain, Montana, is as follows: "A small species of tlie type of T. costata, but having the concentric or horizontal costje on the sides of the valves very delicate, closely arranged, and but slightly larger than the radiating ones on the posterior dorsal region, or corselet. The valves are rather compressed, about one-fourth longer than wide, and have the posterior umbonal slopes acutely angular." A single valve corresponding to this description, but not labeled, is in the original collection from Cinnabar Mountain studied by Meek, and this is probably his type. The specimen figured was collected at the same place by Mr W. H. Weed. Trigonia montanaensis Meek. Trigoma montannensis Meek, 1873: Ann. Kept. U. S. Geol. Surv. Terr, for 1872, p. 472. White, 1880: Idem for 1878, p. 247, PI. XXXVIII, fig. 2a. The types are from the locality near the lower canyon of the Yellow- stone. A few specimens were obtained 1 mile from Swan Lake Valley, 620 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK. north of old road to Mammoth Hct Springs; Cinnabar Mountain; saddle in rid"-e west of south branch of Gardiner River; south sloi^e of ridg-e south of Gray Mountain, and east end of northeast s})ur from Signal Peak. ASTARTE MEEKI n. Sp. PL LXXIJI, figs. 3-5. Shell of medium size, subcircular in outline, moderately convex ; beaks prominent, median in position ; dorsal margin descending rajndly from the beaks, with a convex curve behind and slightly excavated in front; anterior, posterior, and ^-entral margins forming a regular curve ;' surface marked by numerous fine, regular, concentric costse. Margin crenulate within. One of the types, an average-sized specimen, has the following dimen- sions: Length, l(i mm.; height, 14 nun.; convexity of single valve, about 3 mm. The largest specimen in the collection is 23 mm. in length and 20 mm. in height. Associated with these there are several more elongated shells, one of which is figured, that I was at first inclined to regard as a distinct species, but it is probable that the difference ii> form is due to dis- tortion by pressure. Compared with Astarte pachardi White this species is proportionally somewhat more elongate, less convex, and the concentric sculpture is much finer and more regular. The species was first noticed by Meek, who men- tioned it as "Astarte (?)" in a list of Jurassic fossils collected by Dr. Peale near the lower canyon of the Yellowstone.^ It occurs in the collections from head of Gardiner, Sentinel Butte, Cinnabar Mountain, west side of Snake River north of Berry Creek. Astarte sp. Another species of Astarte is represented by fragmentary specimens which show the specific features fairly well, Ixit as they are not sufficient for a good illustration the species has not been named. It is a very elongate form, with strong, regular, concentric ridges. In its younger stages, as shown by the lines of growth, it is a short subtriangular form, but later it rapidly increases in length and the posterior end becomes obliquely truncate. It occurs on the divide at head of Fawn Creek, Sentinel Butte, Cinnabar Mountain, and near lower canyon of Yellowstone River. lAnu. Kept. U. S. Oeol. Surv. Terr, for 1872, p. 472. MESOZOIG FOSSILS. 621 TaNCREDIA ? KNOWLTONr 11. sp. PI. LXXIII, (iff. (i. Shell small, obliquely snbovate in outline; beaks prominent, sub- median; (lor.sal margin behind the beaks descending- rapidly to the broadly rounded posterior end, which is most i)r. 474. ■ Biil. Geo). Soc. Am., Vol. \. p. 418. MESOZOIC FOSSILS, 625 ill ridg-o west of south branch head of Gardiner; head of Fawn Creek north- east of Mouuineut Peak, Cinnabar Mountain. I'lIULADOMYA INjEQUIPLICATA 11. SJl. PI. LXXIV, fig. 4, Ct'. PhoJadomija multilineata Gabb, 18(59: Am. Jour. Coucbology, Vol. V, p. 10, PI. V, fig. <>. Shell small, ventricose, elongate suboval in outline, with prominent approximate beaks situated near the anterior end; anterior and ventral mar- gins forming a nearly regular curve, which is most prominent a little behind the middle; posterior end rounded, slightly subtruncate above; surface marked b}' about twenty radiating costse that vary both in size and in dis- tance from each other and cover the whole valve, excepting a very small space in front and a larger one in the postero-dorsal region. Length, 39 mm.; height, 31 mm.; convexity of both valves, 24 mm. Pholadomya multilineata, which is associated with P. mvadana, seems to be about as closely related to this species as P. nevadana is to P. Ungi. P. multilineata is larger than P. incequipUcata, has more numerous costae (about thirty, according to Gabb), and is more angular at the posterior end, besides differing somewhat in other details of outline. Only a few specimens were collected on divide between Fawn Creek and Gallatin Valley, where it is associated with P. Ungi. HOMOMYA GALLATINENSIS 11. Sp. PI. LXXIV, figs. 6 and 7. Shell of medium size, oblong subcylindrical ; beaks rather prominent, incurved, approximate, and situated near the anterior end of the shell; dorsal margin in front of the beaks declining rapidly to the broadly rounded anterior end, which passes by a gentle curve into the nearly straight dorsal margin. Surface marked by lines of growth and irregular concentric undulations. The posterior end gapes slightly. Length, 85 mm.; height, 42 mm.; convexity of both valves, 36 mm. This species apparently belongs to the subgenus Homomya as detined in Zittel's Handbuch der Palseontologie, but Fischer does not recognize the group and divides the species that have been referred to it between Arcomya and Pleuromya. The specimens from Yellowstone National Park do not MON XXXII, PT II 40 626 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. show the structure of the hinge nor other details of the interior that are used as generic characters. The type is from the divide between Fawn Creek and Gallatin Valley. The species is represented by nine other examples from Fan Creek Pass, head of Gardiner ; saddle in ridge west of south branch of head of Gar- diner; head of Fawn Creek northeast of Monument Peak, and Cinnabar Mountain. Pleuromya subcompressa Meek. P]. LXXIY, figs. 8-11. Myacites {Pleuromya) subcompressa Meek, 1873: Anu. Rept. IT. S. Geol. Sarv. Terr. for 1872, p. 472. 1877: U. S. Geol. Expl. 40tli Parallel, Yol. lY, Pt. I, p. 136, PI. XII, figs. 6, 6a. Myacites subcompressus (Meek) White, 1880 : Anu. Rept. U. S. Geol. Surv.Terr. for 1878, p. 151, PI. XXXYIII, figs, 5a-e. This most abundant species, which was originally described from Weber Canyon, Utah, is represented by several hundred specimens, from everj' Jurassic locality in the Park region at which fossils were collected from the lower argillaceous limestone and shale. Almost every specimen is more or less distorted, and everj^ variation in form is seen that a thin-shelled elongate species can be made to assume when embedded in soft strata and subjected to pressure. In addition to these accidental distortions, it is evi- dent that the species is naturally quite variable in both form and sculpture, some individuals being nearly smooth while others are marked by rather strong concentric plications. Extreme variations approach the plicate ' Pleuromya iveherensis Meek on the one hand and the nearly smooth elongate Pleuromya newtoni Whitfield on the other. The extent and directions of vari- ation are fairly well shown by Wliite's figures above cited, though some of these forms are slightly modified b)^ pressure. Single specimens representing three or four extreme varieties could be selected that if taken alone might be regarded as distinct species, but when the attempt is made to classify the entire large collection coming from practically one horizon and a limited area, it is found that none of the dis- tinctions will hold good. The specimens figured show some of the principal variations in form, and were selected from those apparently least modified by accidental dis- tortion. They are from Fan Creek Pass, divide between Fawn Creek and MESOZOIO FOSSILS. 627 Gallatin Valley, hills west of Snake River 4 miles south of second crossing, and Cinnabar Mountain. The general custom ^f recent authors is followed in using the name Pleuromya instead of Myacites. Thracia weedi n. sp. PI. LXXV. figs. 1-3. Shell of medium size, thin, compressed, elongate, subelliptical in out- line; beaks rather prominent, submedian; dorsal margin sloping rather rapidly and almost equally before and behind the beaks; anterior end broadly rounded, most prominent below; posterior end subtruucate; ventral margin slightly convex, somewhat sinuous toward the posterior end; poste- rior umbonal ridge narrow and sharply defined; surface marked by irreg- ular concentric undulations and by numerous fine lines of growth. The specimens selected for illustration, which are of average size, have the following dimensions, respectively: Length. Height. Convexity of both valves. mvi. 29 26 34 mm. 19 18 20 mm. 4 5 5 All the examples in the collection have suffered more or less accidental compression and distortion in the rocks, so that they show considerable vari- ation in outline, and probably on account of this compression they do not show the posterior gape that they should have if they really belong to the genus Thracia. The species diff'ers too much in outline and proportions from tlie two forms of Thracia (?) described from the Jurassic of the Black Hills to require detailed comparison. The types are from stream bed west of Little Quadi-ant Mountain and from saddle in ridge west of south head of Gardiner River. Other specimens were collected at head of Fawn Creek, northeast of Monument Peak. 628 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Thbacia? montanaensis (Meek)'? PL LXXIII, fig. 10. Gorimya montanaensis Meek, 1873 : Ann. Rept. U. S. GeoL Surv. Terr, for 1872, p. 474. Shell small, subquadrate in outline, convex, with prominent beak situ- ated a little in advance of the middle; dorsal margin nearly straight, declining slightly on each side of the beak; anterior end broadly rounded, forming almost a right angle with the dorsal margin above, and uniting with the convex ventral mai-gin below by a regular curve; posterior end obliquely truncate; posterior umbonal ridge subangular and accompanied by a narrow depressed area or groove ; surface marked by lines of growth. Length, 17 mm.; height, 14 ram.; convexity of single valve, 4 mm. The above description is drawn from a single valve from "Devils Slide, Cinnabar Mountain, Yellow^stoue River," which may be the original type named by Meek in the report above referred to, though it was not labeled by him. It was named in a list of fossils from this locality, with a footnote saying that "This is very similar to some varieties of C. glabra Agassiz, but it is a smaller, proportionately shorter, and more convex shell, with the anterior margins just in front of the beak more excavated." Anatina (Cercomya) punctata n. sp. PI. LXXIV, fig 5. Shell of medium size, not so slender as the typical forms of the sub- genus; beak prominent, somewhat in advance of the middle of the shell, directed backward; dorsal margin almost straight and descending slightly in front of the beaks, concave behind; anterior end broadly rounded, sub- angular above; posterior end much more narrow and rounded, ventral margin slightly sinuous; surface of the shell divided into two distinct areas by a narrow well-defined groove that descends almost vertically' from the beak to the ventral margin; anterior area marked by broad concentric ridges and sulcations and by very fine lines of growth, the latter continuing over the posterior area; middle third of the posterior area slightly more convex and prominent than the rest and bearing about nine distinct granu- lar radiating lines. In addition to this sculpture, which is seen on internal casts, a mold of the exterior of the shell shows that the entire surface bears radiating lines of minute tubercles, which are most prominent on the posterior MESOZOIO FOSSILS. 629 area, and give the punctate appearance that suggested the specific name, though it can liardly be considered a specific character, since it is common in this and related genera. The species is represented by three imperfect A^alves from the divide between Fawn Creek and GaUatiu Valley, south slope of ridge south of Gray Mountain, and west side of Snake River north of Berry Creek. The specimen figured, which is from the second locality mentioned, measures 39 mm. in length and 19 nun. in height. In the well-defined radiating lines of the posterior area this species resembles the Upper Cretaceous forms to which Conrad gave the name Anatimya. Anatina (Cercomya) sp. Another species of this genus is represented by a single specimen from the east side of Fan Creek Pass, which is too imperfect for illustration and full description. It is much larger than A. punctata, measuring 76 mm. in length, and it differs from that species in the outline of the anterior end and in the entire absence of radiating lines on the posterior area. GASTROPODA. Neritina wyomingensis n. sp. PI. LXXV, figs. 4 and 5. Shell small, consisting of about two and a half or three rapidly increasing volutions ; spire very low and inconspicuous ; last whorl slightly shouldered and forming about nine-tenths of the visible bulk of the shell ; surface smooth, with rather distinct lines of growth near the aperture, which has the thin sharp outer lip and straight inner lip with broad flat- tened columella characteristic of the genus. The inner lip is smooth, or nearly so, but the specimens are not in condition to show whether it bears minute denticulations. Height of the type, 6 mm.; greatest breadth, 6 J mm. This species has a superficial resemblance to Neritina? pTiaseolaris "White from the Jurassic of Utah, but, besides slight ditferences in form, the columella in that species is not flattened and the inner lip is not straight, so that it has been referred to Lyosoma. The only other described American Jurassic Neritina is N. nebraseensis 630 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. M. and H., which is much larger and more slender in form, differing in all its details from this species, which is somewhat similar in form and size to Neritina xyisum Meek from the Upper Cretaceous of Utah. The type was collected by Prof. A. C. Gill about 3 miles southeast of Gravel Peak. Lysoma powelli White. Neritina poioelli White, 1876: Geol. Uinta Mountains, p. 110. Lyosoma powelli White, ISSO: Ann. Rept. U. S. Geol. Sarv. Terr, for 1878, p. 153, PI. XXXVllI, figs. 6a-d. One well-preserved specimen was obtained on saddle at head of Fawn Creek, northeast of Monument Peak, and another on ridge south of Mammoth Hot Springs, on main terrace. The species has not before been reported from any locality excepting at the mouth of Thistle Creek, Spanish Fork Canyon, Utah. Both Zittel and Fischer are inclined to make Lyosoma a synonym of Otostoma d'Archiac, an Upper Cretaceous subgenus of Nerita, but Lyosoma really has the thin inner lip without any callus or flattening of the columella, while the Cretaceous form has been shown to have the characteristics of Neritina in these respects. TUKRITELLA Sp. A single small specimen from 3 miles southeast of Gravel Peak has the form of this genus, but is insufficient for specific description. It con- sists of six flattened whorls with channeled sutures. NaticaI sp. A naticoid form is represented by imperfect internal casts from Fan Creek Pass, saddle west of south head of Gardiner, head of Fawn Creek northeast of Monument Peak, and near Sentinel Butte. It is probably undescribed, being very much larger than Natica 1 lelia Hall and Whitfield, which is the only described naticoid shell from the Jurassic of this western interior region. CEPHALOPODA. OppeliaI sp. Ammonites are rare in the Yellowstone National Park collection, and the few that were obtained are too fragmentary and badly preserved for accurate classification. One species is represented by, two flattened specimens, about 3 inches MESOZOIC FOSSILS. 631 in diameter, from the divide between Fawn Creek and Gallatin Valley. This is a nearly smooth, discoid, involute form, with narrow umbilicus and rounded abdomen. The outer two-thirds of the body whorl appears to have been entirely smooth. On the other third the abdomen is crossed by small ribs, giving it almost a dentate outline; and on earlier stages these ribs are relatively longer and more prominent, passing nearly halfway across the flanks of the shell. In general form and sculpture this species resembles Oppelia suhpUcatella Vacek,^ from the Oolitic of Cap San Vigilio. The septa are not preserved. Fragments of larger individuals that may belong to the same species were obtained on Fan Creek Pass, saddle in ridge west of south head of Gardiner, and from Cinnabar Mountain. They are less compressed than the specimens above described, but with the material at hand it is impos- sible to determine whether this difference is due to accidental distortion. Some of the fragments show strong plications on the abdomen. A large specimen, 8 inches in diameter, from limestone on ridge south of Sheridan Peak, appears to be related to the forms above mentioned, though it is somewhat more involute, and is so much weathered that all the surface characters and the iiner subdivisions of the septa have disappeared. The specimen is septate throughout. The septa appear not to have been very complex and the lateral saddles are very broad. It is possible that this specimen should be referred to Ammonites henryi M. and H., which it some- what resembles both in general form and in the septa. Perisphinctes sp. Collections obtained by Dr. Peale near the lower canyon of the Yellowstone contain fragments of two species of Ammonites that probably belong to Perisphinctes, judging from the sculpture. Fragments of one of these species were also obtained on saddle in ridge west of south head of Gardiner River. Belemnites densus Meek and Hayden. Belemnites densus Meek and Hayden, 1858: Proc. Acad. ^at. Sci. Phila., p. 58. 1865: PalJEont. Upper Missouri, p. 126, PI. IV, figs. lOa-c; PI. V, figs. la-i. Meek, 1876 : Simpson's Kept. Expl. Great Basin, Utah, p. 358, PL III; figs. 4a, b. Whit- field, 1880: GeoL Black Hills Dakota, p. 381, PL VI, figs. 15-19. This species, which is abundant in the Jurassic of the Black Hills and ' AbhancU. K.-k. geol. Reiclisaustalt, Vol. XII, p. 82, PI. XI, figs. 1-5, 1886. 632 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. various localities in Wyoming, is represented in the Yellowstone National Park collection by only a few specimens, from saddle in ridge west of south head of Gardiner; west of Snake River 4 miles south of second crossing and 3 miles south of mouth of Glade Creek. CRETACEOUS SPECIES. DAKOTA (1) FORMATION.' PELECYPODA. Unio sp. undet. Several casts of a small species of Unio were collected with the gastro- pods named below in Three Forks Valley, Montana, and on Fawn Creek Plateau. The species is doubtless new, but the material is insufficient for description. GASTROPODA. GONIOBASIS! PEALEI U. Sp. PI. LXXV, fig. 6. Shell small, slender, CiOngate, consisting of about eight convex whorls; apex of spire acute; upper third of each whorl slightly flattened, so tliat it is most prominent below the middle; suture hnear, deeply impressed; surface nearly smooth, being marked only by fine lines of growth, and on some specimens by faint indications of spiral lines. The full form of the aperture is not shoAvn on any of the specimens, but it appears to have been suboval and slightly produced in front. Shell apparently not umbilicated. Length of an average specimen with eight whorls, 14 mm.; breadth of body whorl, 7 mm. This species is very doubtfully referred to Goniobasis, though it seems to be related to G. gracilenta Meek, from the Judith River beds. In general aspect and in the form of the whorls it resembles some recent species of Pomatiopsis, but the form of the aperture and the absence of an umbilicus separate it from that genus. The specimen figured was collected by Dr. A. C. Peale in Three Forks ' See remarks on pp. 604-605. MESOZOIC FOSSILS. 633 Valley, Montana Other examples were obtained in the Gallatin Range anil at several points in the northwestern part of Yellowstone National Park from fresh-water beds of the Cretaceous section of that region. GONIOBASIS? INCREBESCENS n. sp. PI. LXXV, fig. 7. Shell of about the same length as the preceding, but more robust in form, consisting of only about five rapidly increasing convex whorls; surface nearly smooth, with fine lines of growth ; other features, as far as known, the same as in G.? pealei. Length of an average specimen, 13 mm.; breadth of body whorl, 7.5 mm. Nearly all the specimens are in the form of imperfect internal casts retaining portions of the shell, but of course not showing the generic features fully. It seems to be related to G^.? pealei. The type is from the same horizon as the preceding on Fawn Creek, and it occm-s in this bed at several localities in that resrion. Amnicola? ceetacea n. sp. PI. LXXV, fig. 8. • Shell small, conical, consisting of four or five rapidly increasing con- vex whorls; suture deeply impressed; surface marked only by lines of gi-owth; aperture oval. Height, 9 mm.; breadth of last whorl, 6 mm. Occui's with the preceding species on Fawn Creek. COLORADO FORMATION. PELECYPODA. OsTREA ANOMioiDEs Meek. Ostrea anomioides Meek, 1873 : Ann. Kept. TJ. S. Geol. Surv. Terr, for 1872, p. 488. White, 1S80: Idem for 1878, p. 10, PI. XI, figs. 4«, 6. 1884: Fourth Aim. Kept. U. S. Geol. Surv., p. 291, PI. XXXIX, figs. 4 aud 5, Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 55, PI. I, figs. 5 and 6. This species, which was originally described from the Missouri River below Gallatin, Montana, is abundant in sandy shales near the base of 634 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. the Colorado formation on ridg-e north of north head of Gardiner and on north side of Fan Creek. Inoceramus umbonatus Meek and Hayden. Inoceramus umbonaius 'Meeli. and Hayden, 1858: Proc. Acad. Nat. Sci. Pliila., p. 50. Meek, 1876: U. S. Geol. Surv. Terr., Vol. IX, p. 44, PI. Ill, figs, la, b, c; PI. IV, figs. 1«, b and 2«, h. Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 81, PL XVIII, figs. 1 and 2. One specimen was collected on north bank of Snake River one-fourth mile above the mouth of Sickle Creek. The species is abundant in the shales of the upper part of the Colorado formation on the Missouri River below Fort Benton, Montana, and it has recently been collected by Mr. G. K. Gilbert in the Niobrara shales near Rocky Ford on the Arkansas River below Pueblo, Colorado. It also occurs in the Austin limestone of Texas. Inoceramus undabundus Meek and Hayden. Inoceramus undahuiidus Meek and Hayden, 1862: Proc. Acad. Nat. Sci. Phila., p. 26. Meek, 1876 : U. S. Geol. Surv. Terr., Vol. IX, p. 60, PI. Ill, figs. 2a, b. Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 84, PI. XVI, figs. 1 and 2. Occurs Avith the preceding at the locality on Snake River, and also on the Missouri below Fort Benton. Inoceramus flaccidus White. Inoceramus flaccidus White, 1876: U. S. Geog. and Geol. Surv. W. lOOtli Meridian, Vol. IV, p. 178, PI. XVI, figs, la and h. Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 80, PI. XIII, fig. 1. Occurs with the preceding, and at the same horizon, one-fourth mile farther up Snake River. It has hitherto been found only in the Niobrara shales near Pueblo, Colorado. Inoceramus acuteplicatus n. sp. PI. LXXV, figs. 9 and 10, and PI. LXXVI, fig. 1. Shell large, moderately convex, elongate, with the height much greater than the length; hinge line rather short, oblique to the longer axis of the shell; beak prominent, acute, near the anterior end of the hinge line; anterior side gently convex, posterior nearly straight ; base broadly rounded, with a tendency to angulation at the junction with the sides; surface marked MESOZOIC FOSSILS. 635 by lines of growth and by i-egiilar, naiTOw, elevated, concentric ridges that are about one-third as wide as the interspaces. These ridges are somewhat stronger on the anterior half of the shell than on the posterior, and in very large specimens they tend to become obsolete, making the basal portion of the shell nearly smooth. The above description is drawn mainly from a large right valve (PI. LXXVI, fig. 1) from the Sickle Creek locality. The specimens associ- ated with it and having the same general form and sculpture are all much smaller. These are not distinguishable from specimens from sandstone believed to belong to a higher horizon on Glade Creek. There are small left valves in the collection from both localities, and one of those from Grlade Creek is figured. It is proportionally more convex than the right valve, and the beak is more prominent and more curved. The concentric ridges are very prominent on the convex median region, and fade out toward the borders. The largest type specimen measures 201 mm. in its longest diameter, and 135 mm. at rifflit ang-les to that line. This species is related to I. fragilis and I. altus, all tkree belonging to the typical section of Inoceramus. It difi"ers from both of them in being more strongly plicate, in its shorter, slightly more oblique hinge line, and in other details of outline. Locality and position: On Snake River one-fourth mile above the mouth of Sickle Creek, associated with /. umhonatus, Scaphites ventricosus, etc., in sandy shales of the upper part of the Colorado formation, and near the mouth of Glade Creek in a sandstone supposed to belong to a higher horizon. CoRBULA suBTRiGONALis Meek and Hayden. Corbula subtrigonalis Meek and Hayden, 1856: Proc. Acad. Nat. Sci. Phila., p. 116. White, 1880: Ann. Eept. U. S. Geol. Surv. Terr, for 1878, p. 80, PI. XXV, figs. 6a-/. White, 1883 : Third Ann. Eept. U. S. Geol. Surv., p. 442, PI. XIX, figs. 10-13. Stanton, 1894 : Bull. U. S. Geol. Surv. No. 106, p. 123, PL XXVII, figs. 7 and 8. This species and its variety perundata were obtained in black shales supposed to belong to the Colorado formation near Electric Peak and on the Cone head of Gardiner River. These forms were originally described from the Laramie, but they are known to range as low as the Colorado formation in southwestern Wyoming. 636 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. CEPHALOPODA. Baculites asper Morton? Baculites asper Morton, 1834: Synopsis Org. Eem. Cret. Gr., p. 43, PI. I, figs. 12 and 13; PL XIII, fig. 2. Stanton, 1891: Bull. U. S. Geol. Surv. No. 106, p. 167, PI. XXXVI, figs. 4 and 5. Occurs with Inoceranms aciitepUcatus, etc., at the locahty one-fourth mile above the mouth of Sickle Creek, and is abundant associated with the same fauna on the Missouri River below Fort Benton, in the upper part of the Colorado formation. It is also found at Cinnabar Mountain. ScAPHiTES VENTRicosus Meek and Hayden. Scaphites ventricosus Meek and Hayden, 1862: Proc. Acad. Nat. Sci. Phila., p. 22. Meek, 1876: U. S. Geol. Surv. Terr., Vol. IX, p. 425, PI. VI, figs. 7a, h, and 8a, b. Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 186, PI. XLIV, figs. 8-10; PI. XLV, fig. 1. Several specimens from the localities above mentioned on Snake River, and a fragment believed to belong to this species from the black shales of Electric Peak. It occurs well preserved at Cinnabar Mountain just north of the Park, and with the preceding species below Fort Benton. MONTANA FORMATION.! BRACHIOPODA. LiNGULA suBSPATULATA Hall and Meek. Lingula subspatulata Hall and Meek, 1854: Mem. Am. Acad. Arts and Sci., Vol. V, p. 380, PI. I, figs. 2rt, h. White, 1876: U. S. Geog. and Geol. Surv. W. 100th Meridian, Vol. IV, p. 169, PI. XV, fig. 4a. Two specimens from sandstone overlying bituminous shale on Rattle- snake Creek, probably same horizon as the remainder of the species mentioned below. ' See pp. 606-607 for remarks on the horizon of the following species. MKSOZOIO FOSSILS. 637 PELECYPODA. OsTREA soLENiscus Meek. Ostrea soleniscus Meek, 1871: Proc. Am. Philos. Soc, Vol. XI, p. 435. White, 1880: Ann. Kept. U . S. Geol. Surv. Terr, for 1878, p. 9, PI. XI, figs. 2a, b. 1884 : Fourth Ann. Kept. U. S. Geol. Surv., p. 300, PI. XLII, fig. 1. Stanton, 1894: Bull. U. S. Geol. Surv. No. lOG, p. 56, PI. II, fig. 1; PL III, figs. 1 and 2. This species is abundant in both the Colorado and Montana formations at Coalville, Utah, and in southwestern Wyoming. It was obtained near the second crossing of Snake River, just south of the Park. Ostrea sp.. A small species related to 0. peUucida M. and H. occurs at the same locality with the preceding. Anomia sp. A small species resembling A. i)ropatoris White is represented by several casts from Glade Creek, Lizard Creek, and near second crossing of Snake River. Avicula nebrascana Evans and Shumard. A vicula nebrascana Evans and Shumard, 1857 : Trans. Acad. Sci. St. Louis, Vol. I, jj. 38. Pteria {Oxytoma) nebrascana [E. and S.) Meek, 1870: Eept. U. S. Geol. Surv. Terr., Vol. IX, p. 34, PI. XVI, fig. 3fl, b; PI. XXVIII, fig. 11. Whitfield, 1880: Geol. Black Hills Dakota, p. 385, PI. VII, fig. 4. Several specimens from the locality near the mouth of Grlade Creek. It is a widely distributed species in the Fort Pierre shales of the Montana formation. Avicula lingu^formis Evans and Shumard. Avicula linguceformis Evans and Shumard, 1854: Proc. Acad. Nat. Sci. Phila., p. 153. Pteria Zm^M»/brwm (E. and S.) Meek, 1876: Eept. U. S. Geol. Surv. Terr., Vol. IX, p. 32, PI. XVI, figs. l(t-d. Whitfield, 1880 : Geol. Black Hills Dakota, p. 384, PI. VII, figs. 2 and 3. This species occurs with the preceding on Grlade Creek and has about the same geographic and vertical range. Inoceramus acuteplicatus n. sp. Numerous small specimens referred to this species from locality near the mouth of Glade Creek. (See description on page 634.) 638 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Aeca sp. A single imperfect specimen, probably of an undescribed species, from the locality near the second crossing of Snake River. NucuLA sp. A cast near mouth of Glade Creek. Cardium paupeeculum Meek. Cardium pmiperculum Meek, 1871: Ann. Rept. U. S. Geol. Surv. Terr, for 1870, p. 306. White, 1879: Idem for 1877, p. 291, PI. IX, fig. 3a. Stanton, 1894: Bull. U. S. Geol. Surv. No. 106, p. 99, PI. XXII, figs. 9-12. Cardium subcurtum Meek, 1873: Ann. Rept. U. S. Geol. Surv. Terr, for 1872, p. 476. 1877 : U. S. Geol. Expl. 40th Parallel, Vol. IV, Pt. I, p. 152, PI. XV, fig. 3a. This is the most abmidant species in the sandstones near Glade Creek, near second crossing of Snake River, and on Lizard Creek. It is common in the Colorado formation at Coalville, Utah; in south- western Wyoming, and in Huerfano Park, southern Colorado. In these localities it is not known to range as high as the Montana formation. Baroda wyomingensis Meek. Tapes wyomingensis Meek, 1871 : Ann. Rept. U. S. Geol. Surv. Terr, for 1870, p. 310. Baroda wyomingensis Meek, 1873: Idem for 1872, p. 493. White, 1879: Idem for 1877, p. 293, PI. X, figs. 3a, h. A single specimen from Glade Creek. It is possible that this species belongs to Conrad's genus Legumen, described from the Cretaceous of Ripley, Mississippi. I have elsewhere* expressed the opinion that Baroda is probably a synonym of Legumen, which is a prior name. DoNAX cuneata Stanton. DoNAx(?) OBLONGA Stauton. Both these species occur on a single hand specimen from near the second crossing of the Snake River. The type of D. cuneata was collected in sandstone of the Colorado formation at Old Bear River City, southwestern Wyoming,^ and D. oblonga came from the same hoi'izon at Coalville, Utah. D. cuneata occurs also in the Montana formation of the Coalville section. 'Bull. U. S. Geol. Surv. No. 106, p. 107. ^i^em, p. 110, PI. XXV, fig. 1. MESOZOIC FOSSILS. 639 Mactra warrenana Meek and Hayden. Mactra warrenana Meek and Hayden, 185G : Proc. Acad. Nat. Sci. Phila., p. 271. Mactra (Gymhophoraf) warrenam (M. and H.) Meek, 187C: Eept. U. S. Geol. Surv. Terr., Vol. IX, p. 208, PI. XXX, figs. 7a-<^>terile frond small, apparently deltoid in outline, deeply pinnatifid into short, rounded, obtuse pinnre, which are perfectly entire or are cut into few large, coarse teeth; nervation as in the living 0. sensihllls. This fine little species is represented by a dozen or more specimens, the best of which are figured. They are all apparently- fragments, and consequently it is impossible to make out the real shape of the frond with any certainty. One of the most perfect specimens (fig. 13) is about 3.5 cm. long, and i-epresents the upper portion of a frond or possibly pinnule, if it is a large compound frond. The larger fragment (fig. 15) is 4.5 cm. lono- and about 4 cm. broad, but it is broken at both ends and there is no means of determining how long it was originally. Fig. 12 at first sight seems to be entirely diflPerent from the others, but on comparing it with fig. 14 the only dift'erence observable is that one is cut into a few coarse teeth and the other is entire. The nervation seems to be the same in all and to be identical with that of the living sensitive fern. Regarding this interesting species, I am somewhat uncertain as to the shape of the frond, and less so as to the genus to which it belongs. Two of the inost perfect forms (figs. 11, 13) seem to have come from the upper portion of a frond similar in general shape to the sterile frond of Onodea semiUlis; but, on the other han,s. 1, 2, 1878. A siuju-le specimen. Habitat: Top of Mount Everts, west face; collected by Greorge M. Wright, July 7, 188.5. Andromeda grayana Heer. Andromeda grayana Heer: FL Foss. Alaska, p. 34, PL VIII, fig. 5. Lesquereux: Tert. Fl., p. 234, PL XL, fig. 4. Knowlton: Bull. U. S. GeoL Surv. No. 105, p. 56. Habitat: Mount Everts, near the summit of the west end; collected by F. H. Knowlton, July 27, 1888. Teapa! microphylla Lx. PL LXXVIl, figs. 3, 4. Trapaf microphylla Lx.: Tert. FL, p. 295, PL LXI, figs. 16-17a. Ward: Types Lara- mie FL, p. 64, PL XXVIII, figs. 2-5. This is undoubtedly the same species as that figured by Lesquereux from Point of Rocks, Wyoming, and by Ward from Burns Ranch, on the lower Yellowstone. It shows more the habit of the specimen figured by Ward, but has the general nervation of all the specimens referred to this species. In fig. 15ffl of Tertiary Flora the leaflets are petioled, while in fig. 15 they are clearly similar to Professor Ward's examples. These curious but well-marked leaves can not possibly belong to the genus Trapa as we now understand it, but as I am at present absolutely unable to suggest any other afiinity, I can do nothing but leave their correct determination to be settled by future workers. Habitat: North of Piny on Peak, on Wolverine Creek; collected by Arnold Hague, August 10, 1887. 662 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. DiosPYRos STENOSEPALA Heer. Biospyros stenosepala Heer. Lesquereux : Fifth Ann, Kept. U. S. Geol. and Geog. Surv. Terr., p. 296, 1871 (1872). Habitat: "Divide between the source of Snake River and the southern shore of Yellowstone Lake." Fraxinus denticulata Heer. PL LXXVIII, fig. C. Fraxinus denticulata Heer: Fl. Foss. Arct., Vol. I, p. 118, PL XVI,fig.4; PL XLVII, fig. 2. Lesqnereux : Tert. FL, p. 228, PL XL, figs. 1, 2. Several well-preserved specimens that are referred with certainty. Besides these there are several other well-preserved examples, of which the one figured is perhaps the best, that are somewhat larger than the types, but still appear to belong with them. The nervation is obscure, but the shape and toothed margin are quite similar. Habitat: Mount Everts, near summit of the west end; collected by F. H. Knowlton, July 27, 1888. Viburnum rotundifolium Ix. PL LXXVII, tig, 10; PI. LXXVIIL figs. 2, 8, 9. Tihurmim rotundifolium Lx.: Tert. FL, p. 225, PL XXXVIL fig. 12; PL XXXVIII, fig. 10; PLLXI, fig.22. There is considerable difference in size among the specimens, but they seem to belong together, and to approach quite closely to Lesquereux's species. The small leaf shown in fig. 9, for instance, is certainly the same as the plant figured by Lesquereux (loc. cit., PI. LXI, fig. 22), while fig. 8 is like fig. 10, PI. XXXVin (loc. cit.). Habitat: North of Piny on Peak, on Wolverine Creek; collected by Arnold Hague, August 10, 1887. FOSSIL FLORA. 663 Table showing geological distribution of Laramie plants. TellowstoDP National Park. Outside. 1 > o 6 1 > > . 5 i. It J" 1 i a; d Q > 3 a -a 1 '3 & ■s 1 p £ X X Anemia subcretacea (Sap.) Gard. and Ett. X X X xf X X Setiuoia reiclienhachi (Gein.) Heer X X X X X X X X X X X X X X X X X X X X X X X X X X ! X 1 8 7 3 5 5 i It 2 1 a Very doubtful. DISCTTSSIOK OF LARAMIE FLORA. It will be observed that there are only three localities within the Yellowstone National Park that have afforded Laramie plants, viz : Near the summit of Mount Everts, the valley of Wolverine Creek, and the more or less doubtful locality known as "divide between the source of Snake River and the southern part of the Yellowstone Lake." It has not been possible to relocate the latter place, but as it is in a region in which Laramie strata are known to occur, and several of the species represented have since been found in Laramie strata outside, it is assumed to be correct. 664 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. This flora embraces only 18 species, of which number 8 are confiuecl to the Mount Everts locahty, 7 to Wolverine Creek, and 3 to the above- mentioned doubtful locality. Of the 8 species found at Mount Everts, 1 (Pliragmites falcata) is described as new, and 2 species {Quercus eUisiana and Bomheijopsls i)lat- anoides) have never before been found outside of the so-called Bozeman Laramie. The 2 species regarded as doubtful (Mijrica holanderi and M(d(tpoenna weediana) depend on a single fragment each and are obviously of no value in determining the age. They are found normally in much higher horizons Of the 3 remaining species. Sequoia reichenhachi lias been found in the Livingston beds, but is also found in the true Laramie, and abundantly in still older strata. Andromeda grayana and Fraxiniis denticidata have been found in both Laramie and Livingston beds in the Bozeman area. The evidence of the fossil plants confirms that derived from the study of the stratigraphy, namely, that the beds near the summit of Mount Everts are of Laramie age. Of the 7 species from Wolverine Creek, 3 — Asplenium hagiiei, Onoclea minima, and Paliurus minimus — are described as new. The first of these does not appear to have any very close relatives in North America, but apparently finds its nearest analogue in certain species from the Creta- ceous of Greenland. Onoclea minima, on the other hand, is very close indeed to a fern from Point of Rocks, Wyoming, that has been described under the manuscript name of Woodwardia crenata. The Wyoming plant depends on two or three small fragments, which, as pointed out under the diagnosis of Onoclea, are hardly sufficient to properly characterize it. It is quite possi- ble that when new material shall be obtained these two plants will be found identical. Paliurus minimus is perhaps nearest to P. sizyphoides from Black Buttes, Wyoming, and Erie, Colorado. The 4 remaining species are distributed as follows : Sequoia langsdorfii is represented by 1 small branch- let, and the identification is probably correct, as it is an easily recognized species. It has a wide geological and geographical distribution, being especially abundant in the lower Fort Union beds. Paliurus minimus is doubtfully identified in this material. As stated above, it is a true Lara- mie species. Viburnum rotundifolium is also a Laramie species. It has never before been found outside of the type locality, which is Point of FOSSIL FLORA. 605 Rocks and lilack liuttes, ^yy<)lniIlli•. The most interestiuf,'- species is Trapa? mkroplnjUa. It is rej)reseutetl by several perfectly characteristic specimens. This species was first described from Point of Rocks, Wyoming, and was found later by Professor Ward in lowest Fort Union beds, near the mouth of the Yellowstone River. The Wolverine Creek specimens approach closest to Professor Ward's specimens. Professor Ward is of the ojiinion that these lower beds represent the Laramie, since the plants in them differ from those in the undoubted Fort Union beds. The three species from the divide between Snake River and the southern part of YelloAvstone Lake are of little value in determining- the age. Geonomifes schimperi has never been found in any other locality, and Diospi/ros stenosepala is very doubtful indeed. It has not since been col- lected, and the specimen on which Lesquereux based his determination can not now be found. The only remaining species. Anemia suhcretacea or Gymnogramma haydenU of Lesquereux, has a wide distribution, having been found in the Laramie, Denver, and Eocene. DESCRIPTION OF FOSSIL PLANTS FROM THE TERTIARY OF THE YELLOWSTONE NATIONAL PARK. PLANTS, EXCLUSIVE OF FOSSIL WOOD. FILICES. WOODWARDIA PREAREOLATA n. sp. PL LXXIX, flg. 1, Frond pinnate; pinna? alternate, lanceolate, with slightly undulate margins, connate at their bases, forming a broad wing on the rachis; nerva- tion strongly reticulated, consisting of one or two rows of long lacunar next to the main rachis and along the secondary rachis, and the remainder forming large polygonal, slightly elongated, meshes. Unfortunately the specimen figured represents the only example found. It is far from perfect, being only a segment from the middle of a frond, and consequently no idea can be gained of the outline of the whole frond. The segment of the main rachis is 8 cm. long. The pinnje are regularly Qid6 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. alternate — that is, are the same distance apart. They are at least 6 cm. in length and 2 cm. in width. The fnll length and form of the apex could not be determined. The nervation is well shown in the figure. This species is undoubtedly very closely related to the living Woocl- wardia areolata (L.) Moore — so closely, in fact, that it is hardly possible to separate them satisfactorily. The pinna?, are alternate, of the same shape, and have identical nervation in both. The only difference is that the margir s of the pinnjB are entire in the fossil and more or less serrate in the living species. It is possible that more material of the fossil form would show differences in this respect and bring them absolutely together. This new fossil species much resembles Onoclea sensibilis fossilis New- berry, from the Fort Union group, but it differs in having strictly alternate pinuffi that are as far apart as it is possible to be. The pinnje are also without lobes of any kind, being only slightly undulated. The nervation differs slightly in producing more elongated areolae in 0. sensibilis fossilis. In nervation W. preareolata resembles W. latiloba Lx.,^ from the Den- ver group, but differs markedly in having the pinnae unlobed. Habitat: Northeast side of Crescent Hill, opposite small pond; col- lected by F. H. Knowlton and G. E. Culver, August 2, 1888. AsPLENIUiM IDDINGSI U. Sp. PI. LXXIX, figs. 2,3; PI. LXXX, figs. 9,10. Frond large, at least twice pinnate; main rachis thick, slightly zigzag; pinna; alternate, remote, standing at an angle of 30° to 45°, long-lanceolate, tapering to a rather slender apex, rachis strong, often abruptly curved upward, cut into numerous alternate, oblong, obtusely-acuminate pinnules with upward-turning points; nervation of pinnules simple, consisting of a slender inidnerve and about 9 pairs of unforked, close, parallel branches, which are slightly arched forward in passing to the borders; sori oblong, nearer the margin than the midnerve. This fine species is represented by a large number of well-preserved specimens. It appears to have been a very large fern, possibly several times pinnate, but none of the specimens show the larger connections. The largest rachis with pinnae attached is 4 mm. thick, but on the same stone, and 'Teit. I-l., p. 54, PI. Ill, figs. 1, la. FOSSIL FLORA. 667 evidently of the same species, are stems or vachises fully S mm. thick. There is some evidence to indicate that they were combined into a very large frond, but it is not conclusive. The longest example is about 20 cm. long and spreads about 9 cm. The longest pinna (PI. LXXX, fig. 9) is preserved for 9 cm. and still lacks the terminal portion. The pinnse vary in width from 10 to 24 mm., depending upon the portion taken. The pimafe are cut into oblong acuminate pinnules, the sinus some- times extending to within one-third of their length of the base, but usually to about half the length. Pinnules with a slender midnerve and 7 to 10, usually 9, pairs of close, unforked nerves. The lower nerves of adjoining pinnules unite at a low angle and pass upward and end in the sinus. Fruit dots were observed only on one small fragment (PI. LXXIX, fig. 2). Tliey are obscure, but as nearly as can be made out they are oblong and near the margin of the pinnules. Unfortunately none of the larger specimens are fruiting, but apparently they all belong to the same species. I do not recall any fossil species to which this seems to be allied. A number that have been described resemble it, but none closely enough to constitute specific similarit}'. I have named this species in honor of Prof. Joseph P. Iddings, of the University of Chicago, who pointed out the locality which afi"orded the best specimens. Habitat: Yellowstone River, above mouth of Hellroaring Creek (figs. 3, 10); bank of Yellowstone, one-half mile below mouth of Elk Creek, base of bluff (figs. 2, 9); collected by F. H. Knowlton from Fossil Forest Ridge, bed No. 6, "Platanus bed," August, 1888. One specimen collected by Lester F. Ward and F H. Knowlton, August, 1887. ASPLENIUM MAGNUM n. Sp. PI. LXXIX, figs. 5-8, Sa. Frond simple, pinnatifid, sometimes nearly pinnate below, long lance- olate in outline, from a regular obtusely wedge-shaped base, and extending into a long slender apex; cut into numerous, mainly alternate, ovate, sharp- pointed lobes, those at the base being sometimes cut nearly to the rachis, those above less and less until the apex is nearly entire; nervation of the 668 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. lobes or pinnules consisting of a strong niidnerve passing to the tip, and 6 or 8 pairs of alternate once-forked lateral nerves; fruit dots not seen. This large and striking species is the most abundant fern found in the Park. It is represented in the collection by fully 40 specimens, all from one locality. The largest example (fig. 7) is 17.5 cm. long and 2.5 cm. broad, and still lacks the terminal portion. It has a stipe 8 mm. long and 2 mm. thick. Fig. 5 is 16 cm. long and 23 mm. broad, and lacks both base and apex. Some of the fronds must have been fully 25 cm. long. This species is well characterized. It has a thick grooved rachis (1mm.) and a short thick stipe. The lobes or pinnules are irregularly ovate, sepa- rated usually to the middle by a sharp sinus, and having a sharp upward- pointing apex. The nervation consists of a strong midnerve ending in the apex and about 7 pairs of alternate forked branches. As in the former species, the lower nerves of adjacent lobes unite and pass upward to the sinus. Occasionally there may be an unforked nerve, but it is the exception. This species is associated in the same beds with A. iddingsi and much resembles it, differing, however, in having apparently simple fronds that are uniformly larger than the pinuse of the former species, and in having the nervation of the lol^es always forking (see fig. 8 and 8a). It difi'ers further in having a short stipe and in having" the upper portion nearly or quite entire. The correctness of tliis generic reference is of course a matter of more or less doubt, as no fruiting specimens have been found, but the fern appears to be allied generically at least to A. iddingsi. It is certainly a well-marked species for geological purposes. Habitat: Yellowstone River, one-half mile below mouth of Elk Creek, Yellowstone National Park, at base of bluff; collected by F. H. Knowltou, August, 1888. AsPLENiuM ergsumI (Lx.) Kn. PI. LXXX, fig. 6. Asplenium efosum (Lx.) Ku.: Bull. U. S. Geol. Surv. No. 152, p. 45, 1898. Pteris erom Lx.: Tert. Fl., p. 53, PI. lY, fig. 8. This appears to be the same as described by Lesquereux, but is obscure and difficult to make out. None of the specimens are complete, and all have the nervation very poorly preserved. The margin seems more erose than FOSSIL FLORA. 069 tlie type, and the nerves may not foi'k. It is possible that it is a new species, but until better material can be obtained T have preferred to retain the specimens under this species. Habitat: Yellowstone River, one-half mile below mouth of Elk Creek; collected by F. H. Knowlton, August 13, 1888 (fig. 6). Yellowstone River, wall of canyon above mouth of Hellroaring Creek; collected by W. H. Weed, October 13, 1887. ASPLENIUM REMOTIDENS n. sp. PI. LXXX, fig. 7. Pinna3 large, coriaceous, broadly lanceolate, taper pointed, obtuse and unequal sided at base; margin with few remote sharp teeth; midvein strong; lateral veins at an angle of about 45°, simple or forking once some distance above the midvein; sori not seen. The very perfect example figured is the only specimen obtained. It is 11 cm. in length and 2.5 cm. broad. It is broadly lanceolate with a slender tapering apex and obtuse unequal-sided base. The nervation is very obscure. It is probable that all of the lateral veins fork, but it was not possible to make this out, and the figure shows many as unforked. The ones that are made out to have the fork show it some distance above their base. This species is very closely allied to, if not indeed identical with, Asplenium erosum (Lx.) Ku.,^ from the Denver formation of Colorado. It has exactly the same shape, but differs in having few remote teeth, and in the branching of the veins. In A. erosum the veins fork at the base and occa- sionally above the middle. In any case the species are very close together and may be combined at any time if future material from the Yellowstone National Park shows variation in the characters now relied upon for their separation. Habitat: Yellowstone River, one-half mile below mouth of Elk Creek, at base of bluff; collected by F. H. Knowlton, August, 1888. Dkyopteris weeuii n. sp. PI. LXXX, fig. 8; PL LXXXI, fig. 2. Frond twice pinnate; pinnse probably lanceolate in outline; pinnules ' Under Pteria eroea Lx., Tert. Fl., p. 53, PI. IV, fig. 8; Cret. and Tert. Fl., p. 121, PI. XIX, fig. 1. 670 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. opposite or subopposite, nearly at right angles to the rachis, long'-lanceolate, rather abruptly acuminate, cut to within a ver3" short distance of the rachis; nervation simple, consisting of a strong straight midvein and numerous (about 20) pairs of opposite, parallel, unbranched, lateral nerves; fruit dots small, round, on the backs of the nerves midway between the midvein and the margin. This beautiful species is represented by several specimens, the best of which is shown in iig. 8. The pinnules are opposite or subopposite. They are long, slender, and pointing upwaixl. The nervation is very regular, consisting of the strong midvein and 18 to 20 or more pairs of opposite parallel veins. The fruit dots are distinct, though small, and borne on the veins midway between the midvein and margin. This species is closely allied to Lastrea r/oldiana (Lx.) Kn.,' from the Denver beds of Grolden, Colorado. It does not so closely resemble the figure given by Lesquereux as it does certain forms that have been referred to it in my forthcoming monograph of the Laramie and allied formations. The type of the species is described by Lesquereux as having 5 to 7 pairs of nerves, while the forms that I have referred to it have 10 pairs, with no other apparent difiPerence. Bryopterls tveedii, as stated, has 18 to 20 or more pairs. The pinnules are from 10 to 16 mm. long and about 5 mm. broad, whereas those of L. goldiana are only 7 to 9 mm. long and 3 or 4 mm. broad. From this it is clear that these two species are quite closely related, and possibly a larger series of specimens might show them to be identical, but for the present it is best to regard them as different. I have named this species in honor of Mr. Walter Harvey Weed, by whom the first specimens were collected. Habitat: Yellowstone River, breccia in wall of canyon above mouth of Hellroaring Creek (PI. LXXXI, fig. 2); collected by Walter Harvey Weed, October 13, 1887. Cliff on Yellowstone River (left hand), short distance above mouth of Hellroaring Creek (PI. LXXX, fig. 8) ; collected by F. H. Knowlton, August 10, 1888. 'This was first called Aapidium yoldianum by Lesquereux (Seventh Ann. Kept., 1873 p. 393), but was later cbauged to Laeirea {Gomoplvri:,) ijoldiana (cf. Tert. Fl., p. 56, PI. IV, tig. 13). lOSSlL FLORA. 671 Drvoptekis XANTHOLITHENSE U. sp. PI, LXXXI, lig. 1. Frond pinnate?; piniife lanceolate; pinnules opposite, lanceolate-deltoid, obtuse, cut to within one-third of their length of the base, much arched ui)\vard at the point; nervation simple, consisting of well-marked midvein and 9 or 10 pairs of opposite, parallel, unbranched lateral veins; sori large, round, on the backs of the veins at about one-third of their length from the midvein. Of this well-marked species the single specimen figured was the only one found. It is not preserved entire, the fragment being about 5 cm. in length. There is therefore no means of knowing whether or not it was simple or compound. The portions of the pinnae preserved are of the same Avidth throughout, showing that they probably came from the middle por- tion. The pinnules are opposite and arise at an angle of 30° or 40"^ from the rachis. They are lanceolate-deltoid in shape, and about 12 mm. long and 5 nun. broad, being much arched upward at the extremity. The fruit dots are large, round, aud placed on the backs of the veins near the mid- vein. This species is allied to Dryopteris iveedii, from which it clearly differs in having much shorter, arching pinnules, only 9 or 10 pairs of nerves, and larsrer fruit dots which are nearer the midvein. The nervation is the same in character, but differs, as stated, in number of pairs of veins. From Lastrea goldiana this species differs in much the same manner. It has more arching pinnules, and is quite different in general appearance. The number of pairs of nerves is, however, about the same ; all of which goes to show that these three species are closely related. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 6, "Platanus bed;" collected by Lester F. Ward and F. H. Knowlton, August 19, 1887. DeVAI.LIaI MONTANA 11. Sp. PI. LXXIX, fig. 4. Frond thin, twice pinnate, possibly more compounded; rachis strong; pinnae alternate, lanceolate, ending in a sharp, hair-like point; cut into 5 672 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. or 6 lobes or pinnules, the sinuses toward the base going nearly to the secondary rachis, more entire near the apex; lower pinnules or divisions 2 or 3 toothed, all, but especially the terminal pinnules, ending in long, slender, outward-pointing teeth; nervation simple, consisting of a strong- secondary rachis with rather delicate nerves pointing to the pinnules; the nerves near the base two or three times branching, the branches entering the teeth; nerves near the extremity unbranched. The small fragment figured represents all that was found of this species. It is only about 30 mm. long and 25 mm. broad, the pinnae being 17 mm. in length and approximately 10 mm in width. Notwithstanding the smallness of the fragment, there is enough to show that it differs markedly from any other form in the Park flora. I am quite at loss, however, to indicate its generic affinities. I have placed it under Devallia tentatively, and can only hope that subsequent material will serve to fix more satisfactorily its position. Habitat: Fossil Fore.st Ridge, Yellowstone National Park, bed No. 3, "Magnolia bed;" collected by Lester F. Ward and F. H. Knowlton, August 16-19, 1887. Lygodiuji kaulfusii Heer. PI. LXXX, figs. 1-3. Lycjodium neuropter aides Lx.: Tert. Fl., p. Gl, PI. V, tigs. 4-7; PI. VI, fig. 1. According to Gardner,^ the Lygodium neuropteroides of Lesquereux is absolutely identical with L. haulfusii of Heer. Lesquereux was shown specimens of the true L. kaiilfasii from the British Eocene and pronounced them "positively identical" with his species from the Green River group and later formations. A glance at Gardner's^ figures shows that it is impos- sible to separate the American specimens. This species was found at two localities in the Yellowstone National Park, namely, on the Yellowstone River below the mouth of Elk Creek, and on the north bank of the Lamar River between Cache and Calfee creeks. The specimens from below Elk Creek are in hard, rather coarse- grained rock at the base of the section. They are very large, having lobes 1 Brit. Eoo. Fl., Pt. 1, Filices, p. 47. *0p. cit., PI. VII, figs. 1, 3-8 ; PI. X, fig. 11. FOSSIL FLORA. 673 8 em. long' and 2 cm. broail, and A'ery much resemble a figure of this species given by Newberry, ' from the Pacific coast. The specimens from the Lamar River ai"e much slendei'er, being 7 cm. long and less than 1 cm. broad. Some of them, as fig. 2, are very small and delicate. In nervation the specimens from both localities agree perfectly, as they do with European specimens. Habitat: Yellowstone River, one-half mile below mouth of Elk Creek, at base of section; collected by F. H. Knowlton, August 13, 1888. North bank of Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August 21, 1888. OSMUNDA AFFINIS Lx. PI. LXXX, figs. 4, 5. Omiunda affinis Lx.: Tert. Fl., p. (iO, PI. IV, fiR. 1. The Park collection contains specimens of several detached pinnules that it seems necessary to refer to this species. They are about the same size as Lesquereux's type specimen, but are better, in that they show the bases of the pinnules. Li the collection of Denver group plants recently worked up there are a number of specimens of this species, some of which are very fine. One in particular, which has been figured for the forthcoming monograph of the Laramie and allied formations, is very large and perfect. It has a long zigzag rachis with numerous sessile pinnules alternately attached. They have a distinctly heart-shaped base, a slightly undulate margin, and a tapering but obtuse apex. In all these particulars, as well as in nervation, the Park specimens agree. The latter are a little shorter than the Denver specimens, and one is a trifle broader, but the differences are unessential. There is no knowing the part of the frond from which they came, and this may readily account for discrepancies. Habitat: Southeast side of hill north of Lost Creek, Yellowstone National Park, bed No. 1, about 6,5.50 feet altitude; collected by F. H. Knowlton, August 5, 1888. ipiates.Pl.LXII, fig. 1. [Ined.] MON XXXII, PT II 43 674 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. EQUISETACEJ;. Equisetum haguei n. sp. PI. LXXXI, flgs. 3. 4. Stem simple, striate, articulate; articulations rather long; sheaths short; teeth long, appressed, sharp-pointed. This species is represented by numerous fragments, many of which, however, show the sheaths. The stem is from 4 to 6 mm. broad and the articulations are 5 to 6 cm. in length. It is plainly striate, with usually 9 ribs. The sheaths, which are darker in color than the stem, are 6 or 7 mm. in length and are provided with closely appressed, very sharp-pointed teeth, about 3 mm. long. If there are 8 or 9 ribs now visible in the flattened stems, it seems safe to assume, inasmuch as they were cylindrical, that they have 16 or 18 ribs, and an equal number of teeth. It was at first supposed that these specimens could be referred to E. limosuni L. [see following species],^ as identified by Lesquereux from mate- rial collected by Hayden from basaltic rocks near the Yellowstone Lake ; but an examination of the type specimen preserved in the United States National Museum (No. 41) shows that they can not be the same. Lesque- reux's specimen has only 4 or 5 ribs \'isible, making, as he says, about 10 for the entire diameter, while this has 16 to 18, and possibly as many as 20. The segments of the stem are only about 1 cm. in length in Lesquereux's specimen and 6 or 7 cm. in the one under discussion. The sheaths are also longer and the teeth sharper in E. haguei. Among living species this seems to approach closely to E. Jimosum L.; more closely, in fact, than does the specimen referred to E. Umosum by Lesquereux. I have named this species in honor of Mr. Arnold Hague, who pointed out the locality where it was found. Habitat: Southeastern end of hill north of Lost Creek, Yellowstone National Park, bed No. 5; collected by F. H. Knowlton, 1888. 'Fifth Aun. Kept. U. S. Geol. and Geog. Surv. Terr., 1871 (1872), p. 299; Tert. PI., p. 69, PI. VI, tig. 5. « FOSSIL FLOKA. 675 Equisetum LESQUKKEUXII Kll. Eqiiisetinii Ivsquereu.rii Kn.: Bull. U. S. (leol. Siirv. No. 15li, j). !)4, 1898. Equisetum limonum Limi. Lescinereiix : Fifth Aim. Rept. U. S. Geol. and Geog. Surv. Terr., 1871 (1872), p. 29!); Tert. Fl., p. (!9, PI. VI, tig. 5. As already stated under E. hcujuei, the type specimen of this species is in the United States National Museum (No. 41). Tlie figure given in Tert. Fl. (PI. VI, fig. ,5) is much more perfect than the specimen proves to be. The figure shows 7 ribs and the same number of teeth, which would make at least 14 ribs for the whole stem. The specimen shows only 4 or 5 ribs, and the sheaths and teeth are very obscure. As it seems very unlikely that it should belong to the living species, I have ventured to change it, and have named it in honor of Professor Lesquereux. Habitat: "Near Yellowstone Lake, among basaltic rocks." Equisetum canaliculatum n. sp. PI. LXXXI, figs. 6, 7. Stem large, about 50-ribbed; articulate; articulation long; sheath obscure, but apparently short; teeth numerous, short-appressed, sharp- pointed. This species is represented by the two fragments figured and a number of other doabtful ones, which are hardly enough to properly characterize the species; but they seem to differ from all described species likely to occur in this region, and I have ventured to give them a new name. More perfect material may bring out the relationship. The longest stem (fig. 6) is about 6 cm. in length, and the broadest on that piece of material is 13 mm. The other specimen (fig. 7) is 5 cm. long and 21 mm. broad. The ribs are distinct, yet not specially strong. They number, as nearly as can be made out, about 25 on a side, or approximately 50 for the entire diameter. The length of the segments can not be made out. The sheath is also obscure. It maj^ be that fig. 6 repre- sents a single sheath; if so, it is long, but the other specimen gives slight evidence of having a short sheath. The teeth are short and appressed and end in slender points. As near as can be made out, there are about 25 teeth in view, or something like 50 for the whole stem. 676 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The two stems shown in the upper part of fig. 6 show a distinct line of tubercles about the slight constriction. They probably represent the lower portions of the stems. Habitat: Yancey Fossil Forest, beds near the upright stumps (fig. 6); collected by F. H. Knowlton, August 28, 1888. End of Specimen Ridge, opposite Junction Butte, near large upright stumps; collected by Lester F. Ward and E. C. Alderson, August 25, 1887. Yellowstone River, one-half mile below Elk Creek, at base of bluff"; collected by F. H. Knowlton, August 27, 1888. Cliff" west of Fossil Forest Ridge; collected by Ward and Knowlton, August 15, 1887, Equisetum deciduum n. sp. PI. LXXXI, fig. 5. Stems large, many-ribbed, articulate, sheathed; sheaths short, without teeth. This form is represented by several specimens, all very fragmentary and obscure. It has the stem 15 ram. in diameter, and the sheath 14 mm. in length. The diaphragm is clearly shown in 2 specimens, and appears to have been thick. The sheath is close and without teeth, which probably iuidcates relationship of this species with living species, such as E. hiemale, E. robustmn, etc., having deciduous teeth. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, base of bluff' (fig. 5); collected by F. H. Knowlton, August 27, 1888. Fossil Forest Ridge, bed No. 6, "Platanus bed;" collected by Ward and Knowlton, August 19, 1887. CONIFER^}. PiNUS GRACILISTROBUS n sp. PI. LXXX, fig. 12. Cone lanceolate, about 12 mm. in diameter and about 45 mm. long (neither base nor apex preserved); scales in 7 or 8 rows, regularly rhomboidal in shape, about 6 mm. in transverse and about 5 mm. in vertical dimension; scales umbouate, with usually 3 slight projections on the lower angle. The specimen figured is the only one found of this specie^. At first FOSSIL FLORA. 677 sight it seems hardly possible to have so long and narrow a cone with so large scales, but this cone is preserved entire — that is, it has been pressed Hat, and b}' turning it around the entire series of scales may be made out. It is now pressed into an elliptical shape, with a long diameter of aboiit 12 mm. and a short diameter of about 5 nun. Its length, as already stated, is approximately 45 mm. I have not been able to find any fossil species with which this can be compared. There are a number having scales of much the same shape, but none with the same sized cone. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 7, "Castaneabed;" collected by Lester F. Ward and F. H. Knowltou, August 16-20, 1887. PiNUS PREMURRAYANA n. sp. PJ. LXXXII, tig. 5. Cone narrowiv ovate-conical, rounded at base and gradually narrowed above to a very obtuse and rounded apex; scales thick, regularly rhom- boidal, transversely wrinkled, each provided with a rounded blunt umbo, or possibly with a short, stovit spine. This species is represented by the single specimen figured, and is the most perfectly preserved cone I have ever seen, being preserved entire, with little or no distortion. It is about 8 cm. in length. It is broadest at base, where it is about 2.5 cm. in diameter, from which point it tapers gradually to the apex, where it is about 1 cm. in diameter. The scales are very tightly closed, showing that with little doubt the cone was serotinous. They are quite regularly rhomboidal, being about 10 mm. long and 6 mm. high, and appear to have been transversely wrinkled. The tip is thick, raised, and was provided, in all probability, with a short, stout spine. In seeking the probable atfinities of this cone, a number of interesting problems are presented, first of which is the state of maturity. It is, of course, a well-known fact that all cones are tightly closed after fertilization and until the seeds are matured. In the majority of cases the scales open for the discharge of the ripe seeds, yet in a number of species they remain closed, or practically so, for many years. The seeds of these serotinous cones may retain their vitality for years — a provision for the continuance of the species. Whether the cone under consideration is immature, and has the scales 678 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. closed on this account, or is a strictly serotinous form, is a difficult matter to decide. On the whole it seems probable that it was nearly or quite mature, and should be placed among those with normally closed scales. The next question is, What is the age of this cone? — that is, is it a cone of a recent species or does it represent an extinct form? The phe- nomena are so active in the Park at the present time that it is perhaps possible for a cone of this kind to be replaced with silica within a com- paratively short space of time. It however came from a part of the Park where the hot-spi-ings phenomena have ceased for a long period, and this lends color to the idea that it is not of very recent origin. The probability is, therefore, that it represents an extinct rather than a living species. This cone clearly belongs to the pitch pines and not to the soft or white pines, and in determining its affinities this latter group must be excluded. At the present time there are 3 species of pines growing in the Yellow- stone National Park, as follows: Pinus scopulorum, P.JiexUis, and P. contorta miirraj/ana. Of these, P. flexiUs belongs to the white pines and the others to the so-called pitch pines, and of these the last, or P. contorta murrayana, is by far the most abundant. I have shown this cone to a number of botanists familiar with the present ilora, and there seems to be much diversity of opinion as to its probable relationship. Mr. F. V. Coville, botanist of the Department of Agriculture, inclines to regard it as allied to an immature cone of P. scojm- lorum, but a careful comparison fails to sustain this view. Mr. George B. Sudworth, dendrologist of the Department of Agriculture, regards it as most closely allied to P. contorta murrayana, the lodge-pole pine, and I have so considered it. It is of approximately the same shape as mature cones of this species, but is longer and rather narrower. It is not improbable, as suggested by Mr. Sudworth, that it represents a form which was the imme- diate ancestor of P. contorta murrayana, and I have given it the tentative name of premurrayana. Habitat: East of the Yellowstone Lake, Yellowstone National Park. Collected by members of the Yellowstone National Park division of the United States Geological Survey. Pinus sp. Cone lanceolate?, about 16 mm. in diameter, length of part preserved 18 mm.; scales 5 rows in part preserved, probably about 10 or 12 in FOSSIL FLORA. 679 whole cone, approxinuitoly square (or, better, rhomboidal), 5 inm. in each direction; each scale marked by a distinct umbo, and with a prominent ridge along the lower pai-t. The specimen described is also the only one observed. It is possible that it may be the same as P. gracilistrohus, as it comes from the same beds, but it is nearly twice the size, and differs sliglitly in the character of the scales and their markings. Neither the base nor the apex is preserved, and it is therefore impos- sible to know the length, but there is a slight indication that the part preserved is near the upper end, as it is slightly narrowed. This may, however, be due to the poor state of preservation. As stated under P. gracilistrohus, it is hardly worth while to attempt working out affinities with such imperfect material. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 7, "Castanea bed;" collected by Lester F. Ward and F. H. Knowlton, August 16-20, 1887. PiNUS MACROLKPIS n. Sp. PI. LXXX, fig. 11. Scales thick, spatulate, rounded above, slender below, with a raised margin or rim. The mere fragment figured represents all that was found of this species. It consists of portions of 9 scales, arranged in 4 spiral rows. They are broadly spatulate, being rounded above and narrow below. The largest one is 13 mm. in length, 6 mm. broad in the upper portion, and about 3 mm. in the lower portion. The scales were thick and have a strong raised rim. There is every evidence that this was a large cone, but it is so frag- mentary that nothing can be made out but the few scales. It is useless to attempt to work out affinities, except that it was probably a white pine. Habitat: Cliff west of Fossil Forest Ridge, Yellowstone National Park; collected by Lester F. Ward and F. H. Knowlton, August 15, 1887. PiNUS WARDII n. sp. Leaves linear, long, apparently in twos, ribbed, not terete. There are a considerable number of fragmentary specimens that seem in all probability to belong to this genus. They are slender, needle-like 680 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. leaves, about 1 mm. broad and at least 8 cm. in length. They appear to have been ribbed, or at least not terete in cross section. In no case has the point or base of the leaves been observed, but from the fact that two leaves seem to be found side by side, it seems quite probable that they were arranged in twos, as in the living Pinus edtilis Engel., P. contorta Dough, etc. These leaves have a more or less close resemblance to certain described species, but they are too indistinct and poorly characterized to make any comparison valuable. Habitat: Fossil Forest Ridge, Yellowstone liTational Park, bed No. 4, "Aralia bed;" altitude about 8,175 feet; collected by Lester F. Ward and F. H. Knowlton, August 20, 1887. Pinus iddingsi n. sp. PI. LXXXII, figs. S, 9. Leaves linear, very long, teretish, ribbed, in bundles of three, sheath obscure, but apparently short. The collection contains a number of needle-shaped leaves that without doubt belong to Pinus. They are about 2 mm. broad and at least 13 cm. long, but none are preserved entire. They appear to be associated m threes, and in one case (see fig. 8) the upper portion of a sheath is preserved with three leaves arising out of it. As near as can be made out, the leaves are round on one side and flat and channeled on the other. I have named this species in honor of Prof Joseph P. Iddings, the collector. Habitat: Andesitic breccia near gulch northwest of peak west of Dun- raven; collected by Joseph P. Iddings, September 12, 1883. Taxites olkiki Heer. PI. LXXXII, figs. 1,4, 5. Several specimens of this fine species were found. They agree closely with the figures given by Heer^ of specimens from Atanekerdluk, Greenland. Habitat: Walls of the canyon of Yellowstone River above mouth of Hellroaring Creek, Yellowstone National Park; collected by W^alter Harvey Weed, October 13, 1887. (Field No., 2961.) 'Fl. Fos8. Arct., Vol. I, p. 95, PI. I, figs. 21-24c. FOSSIL FLORA. 681 Sequoia couttsi/j: Hoer. The material which I incline to refer to this species was found at only one locality within the Park, namely, the northeast side of Crescent Hill. It was abundant and fairly well preserved. It consists of masses of slender branches with short acute appressed leaves, in some cases with recurving or at least spreading- tips. In a number of cases the male aments were pre- served. The}- are on short, slender branches covered with short scales. The aments are made up of few small, irregular scales. There is undoubtedly much confusion in regard to this species. Ac- cording to Gardner,' much of the material referred to by Heer and others, from Greenland especially, should be relegated to another species, which he proposed to call S. whijmperi. Gardner is also of the opinion that por- tions of the foliage have by various authors been separated as Glyptostrohus ungeri. These, as he points out, are usually associated with Sequoia cones, and are "never accompanied by any trace of the persistent and very distinct cones of Glyptostrobus." I believe this to be true, and conse- quently I would refer to Sequoia couttsice the numerous specimens figured by Lesquereux as Glyptostrohus tmgeri,^ from the Green River group of Florissant, Colorado. I am also of the opinion that the specimens from the Fort Union group, at the mouth of the Yellowstone, described by Newberry^ under the name of Glyptostrobus europmis Brongt., should be placed under Sequoia couttsice. I have never seen any of these specimens, however, and base tliis conclusion on the figures. I have seen a number of specimens from near the same place, collected in later years, and they seem to bear out this conclusion. Some of the luaterial from the so-called Laramie of Canada also appears to be properly referable to this species. The whole subject needs thorough revision, with specimens at hand from all localities, and until this can be had no determinations can be regarded as final. Habitat: Northeast side of Crescent Hill, opposite small pond, Yellow- stone National Park; collected by F. H. Knowlton, August 2, 1888. ' Monog. Brit. Eoc. Fl., Vol. II, Pt. I, GymnospermiP, p. 39. 2 Cret. and Tert. Fl., p. 139, PI. XXII, figs. l-6o. 3 See Cret. ami Tert., PI., XI, figs. 6-8. 682 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. Sequoia langsdorfii (Brongt.) Heer. PI. LXXXII, tig. 2. Sequoia langsdorfii (Brongt.) Heer.: Fl. Tert. Helv., Vol. I, p. 54, PL XX, fig. 2; PL XXI, fig. i. This is by far the most abundant and widely distributed conifer found in the Yellowstone National Park, with the possible exception of Sequoia magnifica, known only from the internal structure. It occurs in many places and in a variety of forms — that is to say, the branchlets and leaves are of various sizes, showing that they have come from many individuals and from different parts of the tree. They are not of the same size and char- acter as specimens from the Fort Union group near the mouth of the Yel- lowstone,^ being rather smaller and not so spreading, but they are very much like the typical leaves figured by Heer^ from Greenland. In all cases, however, the attachment of the leaves appears to be characteristic of this species. In one exceptional case tlie cellular structure of the leaf could be made out. This agreed perfectly with one given by Heer (loc. cit., fig. 21). In one or two cases male aments were observed which much resemble those figured by Heer (loc. cit., fig. 19). Habitat: Fossil Forest Ridge, beds Nos. 4, 6, and 7; collected by Lester F. Ward and F. H. Knowltou, August 16-20, 1887. Clift^ west of Fossil Forest Ridge, altitude about 7,900 feet; collected by Lester F. Ward and F. H. Knowlton, August 15, 18s7. East bank of Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August 21, 1888. Southeast side of hill above Lost Creek, bed No. 1; collected by F. H. Knowlton, August 9, 1888. Yancey fossil trees; collected by F. H. Knowlton, August, 1888. South end" of Crescent Hill, about 300 feet above main wagon road, bed 6 feet below "Piatanus bed;" collected by F. H. Knowlton, August 9, 1888. Northeast side of Crescent Hill, opposite pond; collected by F. H. Knowlton, August 2, 1888. Yellowstone below mouth of Elk Creek, bottom of bluff; collected by F. H. Knowlton, August 29, 1888. Also obtained by Mr. Arnold Hague (September 4, 1897) from 'Cf. Newberry: 111. Cret. .ind Tert. Fl., PI. XI, fig. 4. :F1. Foss. Arct., Vol. I, PI. II, figs. 2-22. FOSSIL FLORA. 683 the south side of Rtiiikiiigwater Valley, at a high bluff east of the mouth of Crag Creek, Wyoming. Sequoia, cones of. _ PI. LXXXI, fig. 8; PI, LXXXII, figs. 6, 7. .The specimens figui'ed are fairly representative of these organisms. They are quite fragmentary, yet appear to be cones. They are found in the same beds with Sequoia langsdorfil, but not in actual connection with that species, and I have preferred to keep them distinct, at least for the present. Habitat: Fossil Foi-est, beds Nos. 5 and 6; collected by Lester F. Ward and F. H. Kuowlton, August, 1887. TYPHACE^. PhRAGMITES? LATISSIMA n. Sp. PI. LXXXIII, fig. 5. Leaf very broad ; stri?e fine, close together. The fragment iigured represents all that has been collected of this form. It is, of course, quite insufficient for proper diagnosis, yet it seems to be different from anything hitherto described from that region. It is certainly quite unlike anything found in the Yellowstone National Park. It must have been a very large leaf, for the fragment is over 3 cm. broad, and it was probably a thick leaf. The stri?e are very fine, straight, and close together. It differs in size and fineness of stride from P. alaskana, to which it seems to be most nearly related. I have given it a new name with great reluctance, for it is too frag- mentary to found a new species on, but for the present it va^j remain as above. Habitat: Northeast side of Crescent Hill, Yellowstone National Pai'k; collected by F. H. Knowlton and G. E. Culver, August, 1888. SPARGANIACEiE. Sparganium stygium Heer. Sparganium stygium Heer. Of. Ward : Types of the Laramie Fl., p. 18, PI. Ill, figs. 6, 7. These specimens do not agree in all particulars either with those figured 684 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. by Professor Ward or with the tj^pes as shown by Heer, They are quite obscure, but in all probability they are identical with Heer's form. Habitat : Yellowstone River, one-half mile below the mouth of Elk Creek, Yellowstone National Park ; collected by F. H. Knowlton, August, 1888. CYPERACEJl. Cyperacites angustior (A1. Br.) Schimper. Cyperacites angustior (Al. Br.) Scliimp. : PaL veg. VoL II, p. 414, 1870. Cyperites angustior AL Br. Lesquereux: Aim. Rept. U, S. GeoL aud Geog. Surv. Terr., 1872 (1873), p. 403. This species was identified by Lesquereux, but the material can not now be found. Habitat: "Elk Creek, near Yellowstone River; collected by A. C. Peale, Joseph Savage, and 0. C. Sloane." Cyperacites oiganteus n. sp. PI. LXXXII, flg. 10. Leaves large, thick, with strong midvein and numerous close nerves. This species, although fragmentary, is represented by several leaves and stems. The largest is 1 8 cm. in leng-th and about 7 mm. in width. It has a well-defined midnerve or vein and numerous close veins. It was evidently of very firm texture. Habitat : Yellowstone River, one-half mile below mouth of Elk Creek, at base of bluft'; collected by F. H. Knowlton, August, 1888 Cyperacites"? sp. PI. LXXXIII. flg. i. This fragment is all of this species, whatever it may be, that has thus far been found. It was at least 2.5 cm broad and had a well-marked keel. The veins are strong, about 1 mm. apart, with a fine intermediate vein. There is altogether too little of it to venture a specific description or determination. Habitat: CHflf west of Fossil Forest Ridge; collected by Ward and Knowlton, August 15, .1887. FOSSIL FLORA. 685 Cypekacites? sp. PI. LXXXIII, fig. 6. Tlie frae ftocondary, and somewhat in tlie teeth. The nerves are also eraspedodrome in I'.firen-iopsis. It is really too traf Fossil Forest Kidge; collected by Ward and Knowlton, August 15, 1887. Salix varians Heer. PI. LXXXV, fig. 3. Saliv varians Heer: FI. Tert. Helv., Vol. II, PI. LXV, figs. 1-3, 6-16. The exami)le figured certainly belongs to this species. It is the same shape, but a little larger, and has the same erose-dentate margin and the same midrib and general nervation. Habitat: Lamar River, between Cache and Calfee creeks; collected by Knowlton and Culver, August 27, 1888. Salix angusta A1. Br. Salix angusta Al. Br. Lesquereur: Tert. FL, p. IGS, PI. XXII, figs. 4, 5; Cret. aud Tert. FL, pp. 157, 247, PL LV, fig. 6. This species, originally described by Heer from the Swiss Tertiary, has been found by Lesquereux in the Green River group at Florissant, Colorado, and in the Miocene of Oregon. A number of doubtful fragments were reported from Spring Canyon in the Bozemau coal field, but they are too fragmentary to be of an}- value. Habitat: Lamar River, between Cache and Calfee creeks; doubtful fragments; collected by F. H. Knowlton, August, 1888; also specimens No. 1967 of Hague's Park collection. Saux lavateri Heer. Salix lavateri Heer: FL Tert. Helv., Vol. II, p. 28, PL LXVI, figs. 1-12; FL Foss. Alask., PL II, tig. 10. Lesquereux: Proc. U. S. Nat. Mus., Vol. XI, 1888, p. 35. Habitat: South end Crescent Hill, bed 25 feet above "Platanus bed;" collected by F. H. Knowlton, August, 1888. 698 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Salix elongata 1 0. Web. SdUx elongata O. Web. Lesquereux: Tert. Fl., p. 169, PI. XXII, figs. 6, 7. A sing-le quite well preserved specimen that seems to belong to this species. The nei'vation, however, is not well preserved, but as nearly as can he nia;le out it may be referred to this form. Habitat: Fossil Forest, lower stratum. No. 1221 of Hag'ue's Yellow- stone National Park collection; collected by Arnold Hague, September 24, 1884. BETULACEvE. Betula iddingsi n. sp. PI. LXXXVI, figs. 4, o. Leaves membranaceous, ovate,' slightly unequal-sided, rather abruptly rounded to the base, more prolonged above ; margin regularly toothed from near the base, teeth slightly unequal, a little hooked; nervation pinnate and craspedodrome ; midrib well marked, straight; secondaries about 10 pairs, mainly alternate, occasionally opposite, arising at an angle of about 45°, straight or nearly so, terminating in the larger teeth, often with forks near the margin, all of which enter the other teeth; nervilles obscure, but apparently percurrent and at right angles to the secondaries; finer nerva- tion not preserved. This species is represented b)^ 3 very perfect leaves, nil of which are preserved on the same piece of matrix The most perfect one figured is 8 cm. in length and 4.5 cm. wide, while the other is about 8 cm. long and less than 4 cm. wide. The petiole belonging to this specimen is 7 mm. in length. This species somewhat resembles a number of described forms, as, for example, Betula stevensoni Lx.,^ from Carbon, Wyoming, from which it diff'ers somewhat in shape, numbej* of pairs of secondaries, and in the more regularly serrate margin. Betula eUiptica Sap., as identified by Lesquereux^ from John Day Valley, Oregon, is perhaps closer, yet this differs in having only 6 or 7 pairs of secondaries and also in the teeth. Betula parce-dentata Lx., from the same locality, has the same kind of teeth, but diff'ers in size. 'Tert. Fl., p. 139, PI. XVHI, figs. 1-5. -Cret. and Tert. Fl., p. 242, PI. LI, fig. 6. FOSSIL FLORA. 699 IVsidi's tlu'se, lu'ltinjiing- to tlie frenus Ik'tula, tliero nro a nuinl)er of otluTS more or less resi'nil)ling this leaf; e. <■'., Alntts cdrpinohlcs Lx.,' from Hridgo Creek, Oreg'on, and Celastrus ovatus Ward, from the Fort Union grou}) of .Montana. Amon lobes. As already stated, the leaf is ol)srurely ()l)l(»iig in g'eneral outline, beinp: sli1)0, all separated l)y broad, ntunded sinuses; midrib very thick below and to the middle of the leaf, from which ])oint it raj)idly diminishes to the apex; secondaries nnmeroiis, alternate, at angle of 30° to 45°, about 4 in each lobe, except the small central lobe, the njjper ones passing- to tlie apex of the lobe, the other curving near the margin below it; short secondaries pass up to and arch along above the sinuses, occasionally in the upper part forking and passing on both sides; nervilles strong, percurrent, nearly at right angles to the secondaries; finer nervation not preserved. The specimen figvxred is the only one obtained of this remarkable and highly cliaracteristic leaf. It is not ]jerfect, yet it appears to represent practically all of the leaf. The part preserved is 14 cm. long and 9.5 cm. broad between the upper lobes. It was probably at least 17 cm. in length, and if tliere were 7 lobes it was of course nmcli larg-er. It was probably 12 to 14 cm. broad between the lower lobes. The width at the middle sinus is a little less than 3 cm. It is strongly 5-lobed, and, following the analogy of Artocarpus lessigiana (Lx.) Kn., may have been 7-lobed. There is, however, no evidence that it had more than 5 lobes. The lower lobe is 5.5 cm. wide at a distance of 1.5 cm. from the midrib, while the upj^er lateral lobe is fully 6 cm. wide at the same distance from the midrib. The extreme length of the ujjper lobe is less than 5 cm., the apex being curved around and up. The secondaries, as pointed out in the diagnosis, are about 4 in number in each lobe. They are about 1 cm. apart, the upper one only entering the apex of the lobe. The only trace of the finer nervation consists of a few strictly percurrent nervilles. I am in doubt as to the proper generic reference of this leaf. When it was collected in the field, the conclusion was hastily formed that it was an oak, but the nervation is not at all that of this genus. It seems to have rather a moraceous character, but I have not been entirely successful in finding affinities. It has some resemblance to species of Ficus, but on the whole approaches closest to Artocarpus. Compared with living species it is of the A. incisa type, yet of course difi'ers in marked peculiarities, having, for example, only five instead of many lobes. Among fossil species this undoubt- edly approaches A. lessigiana (Lx.) Kn.,^ found in the Laramie and Denver formations of Colorado, Wyoming, etc. The Yellowstone leaf has much the ' Science, Vol. XXI, p. 24. 718 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. shape and thick iiiidril) of the other, but difters essentially in having- 3 or 4 secondaries instead of 1 in each lobe. It is, however, a leaf suf- ficiently well characterized to permit it to be readily recognized, and if material is hereafter found that will throw additional light on its affinities, it can be easily transferred to its proper genus. For the present it may remain under Artocarpus. Habitat: Yellowstone River, one-half mile below moutli of Elk Creek; collected by F. H. Knowlton, August, 1888. magnoliacej:. Magnolia californica ? Lx. Magnolia californica Lx. : Foss. PI. Aurif. Gravels, Meiu. Mus. Comp. Zool., Vol. VI, No. 2, 1878, p. 25, PI. VI, figs. 5-7. A single specimen, of which only the upper part is preserved. It has, so far as can be made out, the shape and nervation of this species, but it is so much broken that its positive identification is not possible. Habitat: Fossil Forest Ridge; Hague's No. 1960. Magnolia spectabilis n. sp. PI. XCIII, figs. 1,2. Leaves very thick, coriaceous; broadly elliptical-lanceolate in outline, with regularly rounded base and rather abrupt obtusely acuminate apex; margin perfectl}^ entire, not undulate; midrib thick, straight; secondaries about 18 or 20 pairs, alternate, regular and j^arallel or slightly irregular on emergence from the midi-ib, becoming parallel above; secondaries either forking near the margin or arching along and joining the one next above in a series of loops, with a series of smaller loops outside; intermediate secondaries usually numerous, sometimes passing nearly to the junction of the primary ones, or becoming lost at one-half or two-thirds of the distance from midrib to margin, irregular and not parallel to other secondaries; nervilles numerous, irregular, broken, approximately at right angles to the secondaries; finer nervation beautifully preserved, forming strongly marked quadrangular areolae. This fine species is represented by a large number of well-preserved specimens. The larger leaves are fully 20 cm. long and 7 or 8 cm. wide, FOSSIL FLORA. 719 and some of the smaller ones 12 or 15 cm. long and 4 to 6 cm. wide. The leaves are thick and leathery, and evidently belonged to an evergreen species. It is altogether probable that the leaves obtained by Mr. W. H. Holmes in 1878 from Amethyst Mountain and identified by Lesquereux as MafjnoUa lanceolata Lx.,' really belong to this species. As nearly as can be made out from Holmes's description of the locality," it is the same as that which afibrded the specimens under discussion. But a careful comparison of these lumierous leaves with the figures given by Lesquereux, as well as with specimens from the Auriferous gravels, makes it certain that they can not belong to M. lanceolata. Magnolia spectabilis differs in being broader, more I'ouuded at base, with secondaries more curved and with numerous inter- mediate secondaries. A still greater point of difference is in the texture of the leaf. Of M. lanceolata, Lesquereux says:^ "This leaf is not coriaceous, rather of a thin substance," while M. spectahilis is thick and distinctly coria- ceous or leathery. The finer nervation is not preserved in M. lanceolata, so it is not possible to compare that point. From further evidence it appears that these identical specimens were again submitted to Lesquereux in 1887, and he then identified them with M. inr/lcfieldi Heer,* a species that he has also reported from Lassen County, California, Green River group, etc. It is certainly much more closely related to this than to M. lanceolata, as maybe seen from Heer's figures^ and specimens identified with it from California. It is of the same shape and size as M. spectahilis and is described as being coriaceous, but it differs somewhat in having the secondaries more scattered, apex irregular, etc. The finer nervation also differs. They are undoubtedly close, but seem to be sufficiently distinct for specific separation. Among living s]3ecies the affinity of 31. spectahilis is unquestionably with M. grandiflora L., or M. fostida Sargent, as it is now called. The size, outline, texture, and nervation are practically the same. According to Sargent,** the direct ancestor of Magnolia foetida Avas 'Mem. Mus. Comp. Zool., Vol. VI, p. 24, PI. VI, fig. 4. ^Twelfth Ann. Kept. U. S. Geol. and Geog. Surv. Terr , 1878 (1883), Pt. 11, ji. 49. 'Loc. cit., p. 24. iirc(l l)y Pntfcssor Ward as tliis .s|)(H-i(.'.s from Carbon, "Wyoniino-. ]\[or(' iiiatcrial will l)e in'ccssarv Ijeforc its status can be fixed with oertaiiitv. llal)itat: Yellowstone River, half a mile below mouth of Elk Creek, foot of bluff: eolleeted by F. H. Knowlton, August, 1888. LaURUS PKRDITA 11. SJ). I'l. XCIV, fig.s. 1-5. Leaves coriaceous, broadly lanceolate, wedg-e-shaped at base, obtusely acuminate at apex; margins entire, Ixit very slightly undulate; petiole short, stout; midril) thick, straiglu; secondaries 7 or 8 pairs, alternate, camptodrome, arising, at an angle of 40° or 45° and curving upward and archmg along near the margin and forming numerous broad loops or bows; nervilles numerous, irregular, mainly forked, ajjproximately at right angles to the midrib; finer nervation not preserved. The collection contains a number of specimens of this species, none of them, however, quite perfect. They are about 15 cm. long and about 4.5 cm. ])road. The 5 specimens figured show well the character of the species. They are broadly lanceolate, with a regularly narrow-ed base and apparently a rather obtuse a}iex. The secondaries are about 7 pairs, which arch much upward and along the l^orders. The nervilles are numerous, mainly at right angles to the midrib, and irregular and often broken. This species has some resemblance to Laiinis grandis Lx.,^ from the Auriferous gravels of California, differing in being smaller, narrower, and not so obtuse at apex. The resemblance is close enough, however, to make it reasonably certain that the 2 species are quite closely related. Persea pseudo-caroKneitsis Lx.,2from Table Mountain, California, is some- what similar, but difi'ers in being broader, more obtuse, and in having finer nei'vation. Habitat: Hill above Yanceys and near the standing fossil trees; col- lected by F. H. Knowlton, August 28, 1888. Near same locality; collected by George M. Wright, September 24, 1885. 'Cret. and Tert. Fl., p. 251. PI. LVIII, figs. 1, 3. ^Mein. Mus. Comp. Zoiil., Vol. VI, No. 1, p. 19, PI. VII, figs. 1, 2. 724 GEOLOGY OF THE YELLOWSTONE NATIONAL PAKK. LaURUS MONTANA 11. Sp. PI. XCV, fig. 2. Leaves larg-e, evidently coriaceous, elliptical-lanceolate, narrowed grad- ually (!) to the petiole and (?) uj^ward to an acuminate apex (!), slightly unequal-sided in the U2:)per part ; margin entii'e; midrib thin, straight; second- aries 5 or 6 ]5airs, alternate, the lower at a A^ery acute angle, upper ones slightly less so, all, but especially the lower ones, with numerous branches on the outside, which join and form broad loops just inside the margin; nervilles strong, percurrent, approximately at right angles to the secondaries; ultimate nervation not [)reserved. The leaf by which this fine species is represented unfortunately lacks both base and apex, but is otherwise well preserved." It is 10 cm. long as now preserved, and was, when entire, probably at least 14 cm. in length. The width is 5.3 cm. As stated, it is a little (3 inm.) wider on one side of the midrib than the other, making it slightly unequal-sided. The nerva- tion is peculiar, c(insisting of about 5 pairs of secondai-ies, of which the lower, on the narrower side of the leaf, l)egins well toward the base and passes up to the middle of tlie Ijlade, with numerous branches on the out- side at right angles to the midrib. The lower secondary on the broad side of the leaf is ver}' thin and short, and anastomoses with a branch from the lower portion of the second secondary. This latter is strong, and passes above the middle of the leaf, and has only 4 or 5 branches on the outside, all being at an acute angle with the midrib. The other second- aries have 1 or more branches on outside, and also a number of strong nervilles. This species appears to be related to some of the forms figured by Lesquereux as Laiirus grandis,^ from California, and may possibly be an anomalous form of this species. It is larger, more rounded, slightly unequal- sided, and has quite different nervation. It also resembles L. califonuca Lx.,^ from the same place. Habitat: Yellowstone River, one-half mile below mouth of Elk Creek, base of liluff; collected by F. H. Knowlton, August, 1888. 'Cret. and Tert. Fl., PI. LVIII, fig. 3. 'Op. rit., PI. LVIII, tig. 8. FOSSIL FLOKA. 725 Laurus princeps Heer. PI. XCV, (ig. .}. Ltiiinis 2)nnceps Heer. Lesqixereux : Cret. and Tert. Fl., p. 2.")1, PI. LVIII, fig. 2. Till' tine leaf shown in the plate iis absolutely perfect. It has the same size, shape, and nervation as tig. 2 of Lesquereux's plate (loc. cit.). Habitat: Yellowstone River, one-half mile below month of Elk Creek, base of blntt'; collected by F. H. Knowlton, Aug-nst, 1888. Laurus californica Lx. Laurus californica Lx.: Ciet. and Tert. Fl., p. 250, PI. LYII, fig. 3; PI. LYIII, figs. 0-8. Habitat: Fossil Forest Ridge, beds Nos. 3, 5, and G; Specimen Ridge, Fossil Forest, opposite Slough Creek; collected by Ward and Knowlton, August, 1887. Northeast side of Crescent Hill, opposite small pond, altitude 7,500 feet; collected August 2, 1888, by F. H. Knowlton and G. E. Culver. Laurus grandis Lx PI. XCIII, fig. 3; PL XCV, fig. 1. Laurus grandis Lx. : Cret. aud Tert. FL, p. 251, PL LVIII, figs. 1,3. Habitat: Fossil Forest Ridge, beds Nos. 3, .5, aud 7; collected by Ward and Knowlton, August, 1887. Specimen Ridge, Fossil Forest, head of Crystal Creek; collected by Ward and Alderson, August 25, 1887. Hill above Lost Creek; collected by George M. Wright, September 24, 1885. Perse A pseudo-carolinensis Lx. PL XCV, fig. 4. Persea pseudo-carolinensis Lx. : Auriferous Gravels of California, Mem. Mus. Comp. ZooL, Vol. VI, No. 1, p. 19, PI. VII, figs. 1, 2. The specimen figured, which is the best one found, agrees closely with the figure of this species given by Lesquereux (loc. cit., fig. 1). Habitat: Specimen Ridge, Fossil Forest, head of Crystal Creek; col- lected by Ward and Knowlton, August 25, 1887. East bank of Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August 21, 1888. 726 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, !MaLAPOENNA LAMARENSIS 11. sp. PI. XOIII, figs. 4, 5; PI. XCVI, fig. 5. Leaves thick, coriaceous, ovate-oblong, tapering downward to a long wedge-shaped base and upward to an acuminate or obtusely acuminate apex; margin entire; midrib thick, straight; nervation pinnate, consisting of 2 pairs of" opposite thick ribs or secondaries, of wdiich the lower pair arise near the base and pass up for nearly lialf the length of the blade, while the other arise some distance up and pass nearly or quite to the apex ; several pairs of small secondaries arise from the michib in the extreme upper part of the blade; ribs with occasional branches on the outside; ner\nlles apparently percurreut. This species is represented by several specimens, 3 of the best of which are figured. Unfortunately none of the specimens are perfect. The larger and best-preserved specimen has 9 cm. retained, and must have been 11 or 12 cm. in length when complete. This specimen is 4 cm. wide. Another example has 7 cm. of the ujiper portion preserved and is about 4.5 cm. wide. The small one figured is not quite 4 cm. in length and about 1.5 cm. in width. Among living species 21. Jamaren.sls very much resembles Tetranthera (Litsea) dealhata R. Br., from Australia, and also approaches Litsea glauca Seib., from Japan — that is, it approaches these living species closely enough t(^ make it certain that the generic reference is correct. Among the fossil species, Tetyaidhya prcecursoria Lx.,^ from the Bad Lands of Dakota, is quite suggestive. This species is somewhat obovate instead of ovate-oblong, and has about 4 pairs of secondaries, which do not differ in size as they do in M. lamarensis. Habitat: East 1)ank of Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August 21, 1888. Yellowstone River, one- half mile below mouth of Elk' Creek; collected by F. H. Kjiowlton, August 27, 1888. Litsea cuneata n. sp. PI. XCII, figs. 2-4. Leaf membranaceous, broadly lanceolate, wedge-shaped at base and narrowed in about the same manner at apex; midrib very thick, straight; ' Cret. and Tert. Fl., p. 228, PI. XLVIII, fig. 2. FOSSIL FLORA. 727 st'coiidiirics at ;i very acutt' iinj;-l(', crnsjjcdodrome, alteninto, lowor pair tliiniu'st, those above niiu-li tliicker, lininchino- on the outside, branches at an acute angle, craspedodronie; intermediate secondaries several, generally lost in the space l)etween the secondaries; nervilles strong-, at various angles, mainly percurrent; finer nervation irregular. No perfect example of this species has been found, thc^ fragments figured being all that we have to represent it. The specimen showing the wedge-shaped base is only 5 cm. long, ])ut was probably 10 or 12 cm. in length when perfect. It is 4 cm. wide. The larger of the others is the wedge-shaped apical portion, and is 6 cm. long, with the jwobability of its ha\-ing been at least 12 cm. long. The small specimen was probably hardly more than 8 or 9 cm. in length when perfect. The upper portion appears to have more numerous secondaries than the lower jDart. They are also branched on the outside. Habitat: Yellowstone Eiver, 1 mile below the mouth of Elk Creek; collected by F. H. Kuowlton, August, 1 888. CiNNAMOiiuM spp:ctaj5ile Hecr. n. xciY, tig. (i. Cinnamomum spectahile Heer: Fl. Tert. tielv.. Vol. 11, p. 91, PI. XCVI, figs. 1-8. The leaf figured, whicli appears to be the only one obtained, differs slightly from the figures of the European form to which it is referred. The lower pair of secondaries, for example, are nearer the base of the leaf than in the figures given Ijy Heer, l)ut, granting the slight difterences, I have hesitated to make it a new species. Habitat: Tower Creek, Yellowstone National Park; collected by Arnold Hague (field No., 103G), August 16, 1883. PLATANACE.E. Platanus guillelm.e Gopp. PI. XGVI, tig. 1; PI. XCVII, fig. 5. This species is very abundant, being represented by over 125 more or less perfect specimens. Some of these — as, for example, the one figured are particularly perfect. They differ somewhat in size, the average being about 7 or 8 cm. broad between the lobes and 8 or 9 cm. in leno-th An occasional one is 14 cm. broad and about the same leng-th. 728 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Tliese leaves agree well with the usual description and ligures of this sjiecies, especially as given by Lesquereux^ from Carbon, Wyoming. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 1, the lowest bed, rare; bed No. 5, rare; bed No. 6, the " Platanus bed," most abundant locality, over 75 speciinens noted; bed No. 7, rare; collected by Lester F. Ward and F. H. Knowlton, August, 1887. Ea.st end of Fossil Forest Mountain, middle bed, 775 feet above valley beloAv; specimens rare; collected by Ward and Knowlton, August 13 and 22, 1887. Specimen Ridge, opposite Slough Creek, I'are; collected b}' Ward and Knowlton, August, 1887. Hague's Yellowstone National Park collections (field No., 1960), Fossil Forest section, very abundant; collected by G. M. Wright and Walter H. Weed, September 20, 1885. Hague's YelloAvstone National Park col- lections (field No., 1217), Fossil Forest section, upper stratum; collected by Arnold Hague, September 24, 1884. Hague's Yellowstone National Park collections (field No., 1219), rare; collected by Arnold Hague, September 24, 1884. South end of Crescent Hill, 6 feet lielow "Platanus bed;" collected by F. H. Knowlton, August 9, 1888. Platanus Montana n. sp. PI. XC'VI, figs. 2, 3. Leaves membranaceous, somewhat roughened, rounded-oblong in shape, decurrent on the petiole, rounded above or acuminate, possibly slightly 3-y)ointed ; margiu simplj- undulate toothed ; nervation obscui'ely palmate ; petiole stout ; midril) thick, straight ; secondaries several (about 6) pairs, the k)west some distance above the Ijase of the Ijlade, emerging at an angle of about SC^, passing nearly straight to the border and ending in a small marginal tooth, with several branches on the outside approximately at right angles to the midrib and ending in marginal teeth; second pair of secondaries strong, arising at an angle of 45°, nuich arching upward and ending either in the margiu or possibly in short lobes, with several strong forking branches on the outside, the terminations ending in the teeth ; other secondaries also occasionalh' forked on the outside; nervilles strong, occasion- ally pereurreut, but mainly forked or broken; finer nervation quadrangular. This species is based on a number of more or less fragmentary leaves, tlie best of which are figured. Tlie most perfect specimen is 12 cm. 'Tert. Fl., p. 183, PI. XXV, figs. 1-3. FOSSIL FLOKA. 729 loiiji' iiiid altdut 10 vu\. hrojid. It was |irol)al)ly, when living-, at least If) cm. long-. The marked feature of this leaf is that it is not strictly palmately nerved, having-, as pointed out in the diag-nosis, the 2 lower j)airs of secondaries with branches on the outside which end in tlie niaro-iual teeth Otlierwise it is hardly to be disting-uished from Philanus rmjnoldsii Newby., as iig-ured by Lesquerenx' from the Denver, beds of Golden, Colorado. This species was described by Newberry- as having the margin doubly serrate, but a number of specimens refen-ed to it by Lesquereux have the margin undulate, dentate, or even entire. Newberry's type had 3 lobes or points in the upper portion, while certain of Lesquereux's specimens ^vere rounded and entire above. The smaller leaves from the lower Yellowstone described by Professor Ward under the name of Grewiopsis popuUfoJiu,^ especially fig. 4 of his plate, approach the leaves under discussion. These, as he has already pointed out, are suggestive of P. raynoldsU. They can hardly belong to Grewiopsis. Whether the leaves from the Yellowstone National Park should be regarded as new to science or referred to Plotanus raynoldsU is an open question. They agree closely enough in size, shape, and marginal dentition, but differ in the nervation. It is possible that this character may be of sufficient importance to keep them distinct, and also to exclude them from the genus Platanus, but for the present at least, and until better material can be obtained, they may remain as above. Habitat: East slope of high hill about three-fourths of a mile south from Yanceys; collected by George M. Wright, September 4, 1885. LEdlTMINOSiE. Acacia macrosperma n. sp. PI. XCVIII, fig. 8. Legume large, more than 8 cm. long and 2.2 cm. wide, broad linear, possibly constricted, -with obtuse, regularly rounded end; apparently sur- rounded by a wing 5 nun. broad; seeds numerous, large, oblono-, 10 mm long, 6 mm. broad. ' Tert. Fl,, PI. XXVI, fig. 4 ; PI. XXVII, figs. 1-3. ' ■^ Later Ext. Fl., p. 69; 111. Cret. .and Tert., PI. XVIII. » Types of the Laramie Fl., p. 90, PI. XL, figs. 3-5. 730 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. This species appears quite unlike any species Ijefore found in America, but is not greatly unlike A DiicrojihijUa Heer from the Swiss Tertiary. The latter species is not quite as broad as A. macrosperma, and has not the end preserved. The seeds are about the same size in both. Habitat: Fossil Forest Ridge, bed No. 7, "Castanea bed;" collected l)y Ward and Knowlton, August 16-20, 1887. Acacia lamarensis n. sp. PL XOVllI, tig. (i. Legume linear, broad, more than 7 cm. long, and 1.7 cm. Inroad; end pointed; apparently with marginal wing 2 or 3 mm. wide; seeds oval, 10 nun. long, 8 nun. wide. This may jjossibly be the same as A. macrosperma, but it appears to differ essentially in being narrower and in having an acuminate instead of an obtuse termination. The apparent wing and the seeds are much the same in bt)th. Habitat: Lamar River, between Cache and Calfee creeks; collected by Knowlton and Culver, xlugust 21, 1888. Acacia, wardii n. sp. PL XGVIII, tig. 7. Legume narrow, linear, constricted, (3 cm. long, 9 mm. wide in the broadest portion and 5 mm. wide at the constricted point; point of attach- ment reduced to a slight extension, opposite extremity with a decided curved beak; seeds apparently present, but obscure. This species differs markedly from the others just described, and also, so far as I know, from any heretofore found. Haljitat: Fossil Forest Ridge, bed No. 4, "Aralia bed;" collected by Ward and Knowlton, August 16-20, 1887. Leguminosites lesquereuxiana Kn. PI. LXXXIX, tig. 4. Leiiiiminosites lesquereuxiana Kn.: Bull. U. S. Geol. Surv. No. l.")2, 131, 1898, Leiiuminosites vassioides Lx.: Tert. Fl., p. 300, PI. LIX, tigs. l-i. Habitat: Northeast side of Crescent Hill opposite small jjond; col- lected by F. H. KnoAvlton and G. E. Culver, August 2, 1888. FOSSIL FLORA. 731 LeGUMINOSITES LAMAREXSIS 11. sp. PL LXXXIX, figs. 5, 6. Leaflets thin, <)l)loiiji'-laii('e()l-, pcrt'i^etly strai<>-ht; seeoudaries about 0 pairs, alternate, at an angle of 45°, slightly curving upward; remainder of nerva- tion not retained. This little leaflet is 6 cm. in length and 17 mm. in width. It is very regularl}- rounded, almost truncate at base, and apparently regularly nar- rowed above into an acuminate apex. The petiole, if there was one, is not jireserved. The secondaries are alternate and camjjtodrome, and about 8 or 9 pairs. The nearest related species is Legmninosites lesqiiereuxiana,^ from the Green River beds of Green River, Wyoming, and also Spring Canyon, Montana. This differs in being larger, broader, and more oblong-ovate than the one under discussion. The relationship is evidently close, and perhaps more material would show closer aflfinity than I have recognized. This species also resembles some of the species of Leguminosites from the Tertiary of Switzerland, as, for example, L. j)roserinn(B Heei-.^ There can be no question as to the correctness of the refei'ence to this genus. Habitat: East bank of Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August, 1888. ANACARDIACE.E. Rhus mixta? Lx. Rims mixta Lx. : Mem. Mus. Comp. Zool., Vol. VI, No. 2, p. 30, PI. IX, fig. 13. A single small and somewhat fragmentary specimen. It resembles the smaller of the two specimens figured by Lesquereux. Habitat: East bank of Lamar River, between Cache^and Calfee creeks; collected by F. H. Knowlton, August 21, 1888. 'Tert. Fl., p. 300, PI. LIX, egs. 1-4. ^Tl. Tert. Helv., Vol. Ill, PI. CXXXVIII, figs. 50-55. 732 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. CELASTRACE^. Celastrus culveri n. sp. PI. XCVII, flg. 4. Leaves membranaceous, ovate-lanceolate, apparently rather abruptly rounded at the base, but gradually narrowed above to an obtuseh' acuminate apex; inarg-hi with rather remote, small, sharp, outward-pointing teeth; midrib thick below, much thinner above; secondaries about 10 pairs, alter- nate at an angle of 35° or more, much curved upward, camptodrome very near the margin, with branches outside entering the small, weak teeth; intermediate secondaries occasional, thin, disappearing before reaching half the distance to the margin; nervilles percurrent; finer nervation obscure. This species is represented b}- 2 well-preserved leaves, both, unfor- tunately, representing the upper portion only. The longest specimen is 10 cm. in length, which is probably not far from its original full length. It is a little over 5 cm. broad at a point which seems to be some distance below the middle. Judging from the contour near the base, it seems prob- able that it was either truncate or, possibly, heart-shaped at base. The teeth of the margin are peculiar, being scattered, small, sharp, and outward pointing. This species appears to find its nearest relative in some described fi-om the Fort Union group along the lower Yellowstone. Thus it resembles Celastrus curvinervis Ward^ in shape and nervation, but difters considerably in size and wholly in the teeth. Celastrus ovatus Ward'- has somewhat the same shape, but difters considerably in nervation and in the teeth. Several of the other species described by Professor Ward^ also resemble this in one or more particulars, but none closely enough for specific identity. I take pleasure in naming this fine species in honor of Prof. G. E. Culver, who assisted in collecting at this place. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, top of bluff; collected by F. H. Knowlton and G. E. Culver, August, 1888. 'Types of the Laramie Fl., p. 82, PI. XXXVI, figs. 3, 4. ^Op. cit., p. 81, PI. XXXVI, tig. 1. 30p. cit., Pl.XXXV. FOSSIL FLORA. * 733 Celastrus in^quahs n. sp. PI. XCVIII, fig. 3. Leaf of firm texture, ellii)tieiil-()bov;ito in outline, stronolymorj)hum Ward : Types of tbe Laramie FL, p. 84, PL XXXVIII, figs. 1-7. The fine specimen figured is referred with some doubt to this species. It has much the same shape, serration, and type of nervation as jE. jyoly- FOSSIL FLOHA. 735 morphum, but differs in being imich lai-ficer and in liaving more nunierdiis and c'l(»ser secondaries. It is undoubtedly close to this sj)ecies, and rather than make it a new species I have referred it to this. Habitat: Yancey Fossil Forest, near the standing trunks; collected by F. H. Knowlton, August, 1H8.S. ACERACE^. Acer vivarium n. sp. PI. XCVIII, tig. 4. Leaf membranaceous, palmately 3-lobed, narrowed below to a wedge- shaped base, sinuses rounded, middle lobe lanceolate-acuminate, as long or longer than the body of the blade below the sinuses; lateral lobes at an acute angle (points not preserved); margins remotely toothed with small, sharp, upward-pointing teeth; midrib, or central rib, strong, straight, slightly stronger than the lateral ribs, wdiich arise from the midrib just above the base of the blade at an angle of about 70^ and pass up straight to the points of the lateral lobes or curve slightly outward; lateral ribs with several pairs of secondar}- branches, those on the outside beginning just above the base of the blade and passing straight or with a slight upward cui've to or entering the teeth; secondaries on the upper or inside, beginning- below the sinus, which the lowest one enters, the others probably entering the teeth; middle lobe with about 6 pairs of alternate second- aries arising at an angle of 70° or 75°, and passing' up nearlj' straight, to end in the teeth or fork just belo^^' the teeth, one branch entering and the other going upward near the margin to the one abo\-e; ner^dlles numerous, mainly percurrent; finer nervation beautifully preserved, forming quad- rangular areolae. The example figured is the only one observed of this species. It is about 10 cm. long and 6 cm. broad. The central lobe is about 5 cm. long and a little more than 2 cm. wide. The lateral lobes appear to have been about 2 cm. wide and of an unknown length. This leaf belongs to the Acer trilobatum group, so many forms of which were described by Heer from the Swiss Tertiary. In shape it is most like A. trUohatimi productwn,^ but differs in having only very small, sharp teeth. It is 1 Fl. Tert., Helv., Vol. Ill, PI. CXV, figs. 6-12. 736 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. also somewhat like A. trilohatam ir'wuspidatnm Heer, as figured by Professor Ward from the Fort Union ^ gi'oup, differing in being much more wedge- shaped at base, and in the angle of the lateral ribs and secondaries. Habitat: Fossil Forest Ridge, bed No. 3, "Magnolia bed;" collected by Ward and Knowltou, August, 1887. Acer, fruit of PL XOVIII, fig. 5. The collection coutaiias several of these fruits, the best of which is figured. While they are very definite and clearly belong to Acer, they are not usually regarded as being sufficiently distinctive' for specific reference. A number have been figured and named also, but I have preferred not to name these. They may possibly belong to the preceding species, but of this there is no proof. Habitat: Crescent Hill above Yanceys; collected by W. H. Weed, September 28, 1885. SAPINDACEiE. Sapindus affinis Newby. PL CII, figs. 1-3. Sapindus affinis Newby, : Later Extinct Floras, p. .31; IlL Cret. aud Tert. PL, PL XXV, fig. i. The material upon which this determination is based is amjjle, as it consists of fully 100 specimens, all more or less well preserved. These sjiecimens differ so much in size that it was at first thought that at least 2 species must be represented, but after a careful study it has been found impossible to draw any satisfactory line between them. There are all gradations of size from the little slender leaflets, hardly 4 cm. long, to the large ones, fully 10 cm. long. In the only published figures of this species by Newberry the nerva- tion is not shown, but the National Museum contains the original New- berry material, and on studying this it is found that the nervation agrees perfectly with the specimens from the Yellowstone National Park. It may • Types of the Laramie Fl., PI. XXIX, fig. 3. FOSSIL FLORA. 737 also 1)0 noted that Newberry's material does not show the leaflets as peti- oled, but in the description of S. dj/inis he says, "leaflets * * * sessile or short-petioled." Many of the detached leaflets in his material, named in his handwritnig, are distinctly short-petioled, in which particular the Park specimens ao;i-ee. Some have, it is true, very short petioles, yet all seem to have them. In only two cases have leaflets been found in this collection attached to the rachis, and these have both been flg-ured. Habitat: Yellowstone Kiver, one-half mile below the mouth of Elk Creek; found throughout the section, and most abundant at the bottom; collected by F. H. Kuowlton, August, 1888. ? Sapindus alatus Ward. Sajnndus alatus Ward: Types of the Laramie FL, p. 6S, PI. XXXI, figs. 3 4. This specimen is the only one that I venture to refer to this species. It was found in the same beds with the abundant .S*. affinis Newby., and possibly may be an abnormal or unusual leaflet of that species. It is, how- ever, more regular, and has the thick or winged petiole of S. alatus. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, Yellowstone National Park; top of bluff, 300 feet above the river; collected by F. H. Knowlton, August, 1888. Sapindus grandifoliolus Ward. PI. XCIX, tigs. 1, 2; PI. CII, flg. 4. Sapindus (jrandifoliQlus Ward: Types of the Laramie FI., p. 67, P] XXX flffs 3-5- PI. XXXI, tigs. 1-2. Several small doubtful leaves are referred to this species. One in particular has some resemblance to leaves of Juglans rugosa Lx., but seems to be closer to the Sapindus grandiJoUolus of Ward. Habitat: Fossil Forest Eidge, bed No. 6, "Platanus bed;" collected by Ward and Knowlton, August, 1887. Also found on the south side of Stinkingwater Valley, on a high blufl" east of mouth of Crag Creek, col- lected by F; P. King for Arnold Hague, September 4, 1897. MON XXXII, PT II 47 738 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. SaPINDUS GRANDIFOLIOLDIDES 11. sp. PI. C, fig. 2. Leaflets large, of firm texture, ovate-lanceolate, unequal-sided, rounded at base to a Avell-marked winged petiole, apex acute, slightly falcate; midrib of moderate strength, straight; secondaries about 7 or 8 pairs, strongly alternate^ emerging at a low angle and soon curving up and ijassins- aloiiff near the border; the secondaries on the narrower side of the leaflet emerge at a greater angle (30'^ to 45°) than on the opposite side; finer nervation not preserved. The specimen figured is absolutely perfect so far as outline and principal nervation go. It is just 10 em. long and 3.7 cm. wide in the broadest portion, which is a little below the middle. The margin is slightly undulate, almost toothed in one part. This species so closely resembles Sap'mdiis (jrandifoJioJus WaitP from the Fort Union group, that I have named \i grandifoUohkJes. It difters, however, from the latter in lieiiig more markedly iiijequilateral and in having a winged petiole. It also has fewer secondaries than S. (jrandifoUolus. This species is also related to S. oUusifoUus Lx.,^ found in the Fort Union group. From this it differs in having half the number of second- aries and a A\-inged petiole, otherwise being much the same. Professor Ward's S. (dati(S^ from the same place as S. grandifoUolus has a winged petiole, but difters in being much smaller and in having a broken, loose nervation. It is possible, however, that if more material could be obtained it could be referred to one or the other of these evidently related forms. Habitat: Northeast side of hill above Lost Creek, bed No. 1, collected by F. H. Knowlton, August 8, 1888. Sapindus wardii 11. sp. PI. XCVIII, figs. 1, 2; PI. XCIX. tig. ,5. Leaflet coriaceous, broadl)' lanceolate, rounded wedge-shaped at base, with long acuminate falcate apex; margin perfectlj" entire; midrib thick. ' Types of the Laramie Fl., p. 67, PI. XXX, figs. 3-5 (1887). = Cret. aud Tert. Fl., p. 23.5, PI. XLVIII, figs. 5-7 (1883). 30p. cit., p. 68, PI. XXXI. fig. 3, 4 (1887). FOSSIL FLORA. 739 passiiifi' tliroui-li tlu' middle of tlu- l)lii(le; st'C'oiularies about 8 pairs, alter- nate, strongly eainptodrome, i'oriuiiig- broad loops at a marked distance from the margin, occasionally with a series of smaller loops outside; inter- mediate secondaries occasional; nervilles few, percurrent; finer nervation forming- large quadrangular meshes. The specimens figured are the only ones observed of this species. The best preserved is a little over 10 cm. in length and 4 cm. broad. It is marked by the Lmg, slender, and falcate apex, and the peculiar looped secondaries, which are joined tar inside the margin. One side of the basal portion of the leaflet is missing, but from the direction of the secondaries it is probable that it was somewhat unequal-sided. Fig. 1, PI. XOVIII, Avhich lacks both base and apex, must have been at least 13 cm. in length, and was probably longer. The other (fig. 2, PL XCVIII) was about the size of the best-preserved example. These leaflets very closely resemble Fraxinus affinis Newby.,^ from Bridge Creek, Oregon. This has the same type of nervation, but is much smaller, very slightly unequal-sided, and with more numerous and more regular looped secondaries. The finer nervation is identical in each. There is some doubt as to the correctness of the reference of New- berry's leaf to the genus Fraxinus. This much resembles the genus Sapindus and may possibly belong to it. Sapindus gramUfoUolm Ward^ from the Fort Union group, for example, has much resemblance in general character to these leaves. It would seem that they should all be'' in the same genus. However, the leaflet under consideration is undoubtedly closely allied to what Ward has called Sapindus, and for the present they may remain there. I have named this characteristic species in honor of Prof Lester F. Ward, who was present when it Avas collected. Habitat: Fossil Forest Ridge, bed No. 5; collected bv Lester F. Ward and F. H. Knowlton, August 16-19, 1887. Yellowstone River, one-half mde below mouth of Elk Creek; collected by F. H. Knowlton, Auo-ust 1888. " ' = ' ' U. S. Nat. Mus., Vol. V, 1882, p. 510; Plates (ined), PI. XLIX, fig. 3. = Types of tbe Laramie Fl., p. 67, PI. XXX, figs. 4, 5. 740 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. RHAMNACE.E. Rhamnus rectinervis Heer. Rhatnnus rectinerris Heer: Fl. Tert. Helv., Vol. Ill, p. SO, PI. CXXV, figs. 2, 6. Les- quereux: Tert. Fl., p. 279, PI. LII, flgs. 12-15. This species was first detected in the Park by Lesquerevix,^ and the present collection contains a number of specimens that may be similarly referred. They are all entire, in which respect they resemble fig. 14 of Lesquereux's plate (loc. cit.). Habitat: Fossil Forest Ridge, bed No. 3, "Magnoha bed;" bed No. 7, "Castanea bed;" collected by Ward and Knowlton, August, 1887. Paliurus colombi Heer. PI. CI, tig. 7. Paliurus colombi Heer. Lesquereux: Tert. Fl., p. 273, PI. L, flgs. 13-17 (1878). The little specimen figured appears to be the only one obtained in the area under discussion. It is of the same size and shape as many of the figures of this species, but seems to difi"er slightly in having 2 strong sec- ondaries on one side of the midrib! It, however, approaches certain of the figures given by Heer" of arctic examples of this species. Habitat: Head of Tower Creek; collected by W. H. Weed, Septem- ber 25, 1885. ZlZYPHUS SERRULATA Ward. PI. (JI, figs. 4, 5. Ziziiphus serrulata Ward : Types of the Laramie Fl., p. 73, PI. XXXIII, figs. 3, 4 (1887). The two figm-ed examples agree very closely with the figures given by Professor Ward. They both have teeth well marked, and tlms agree with fig. 4 (loc. cit.). . They are not quite so well preserved as the types, and do not show the finer nervation, but there can be no doubt as to their identity. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, top of bluff; collected by F. H. Knowlton, August, 1888. I Hayden's Anu. Rept., 1878, Pt. II, p. 49. ■^ Fl. Foss Arct., Vol. I, PI. XIX, tig. 3. FOSSIL FLORA. 741 yiTA(;p].E. CiSSUS HAGUEI U. sp. PI. GI, fifi'. 2. Leaf membranaceous, qiia(lrau<>ular-ovate, truncate or jjossibly slig-litly heart-shaped at base and acuminate at apex, Lateral h)bes sliort, ol)tuse; margin toothed, the teeth ki\v, obtuse or somewhat acute; nervation pahnate, midrib thin, iierfectly straight, hiteral ribs of same strength as midrib, arising at an angle of 45°, passing directly to and terminating in the obtuse lateral lobes; ribs with 4 or 5 branches on the outside, which terminate in marginal teeth; secondaries about 4 pairs, alternate, at same angle as the ribs and terminating in the teeth; nervilles thin, sparse, percurrent or often broken. This fine leaf is 8.5 cm. long, 5.2 cm. broad between the loljes and 6.5 cm. broad in the widest part, which is onh^ a short distance above the base. In outline it is what may be called quadrangular-ovate — that is, between ovate and square. It is palmately 3-ribbed, the lateral ribs being at an angle of about 45° and of the same strength as the midrib. They pass straight to and terminate in the sliort lateral lobes, and have 4 or 5 out- side branches which also terminate in the marginal teeth. The relation of this species is undoubtedly with Cisms ^mrroticefoUa Lx.,^ from the Green River group. This latter species differs in being relatively longer, without especiallj' marked lateral lobes, with larger, more obtuse teeth, and unforked outer branches of the lateral ribs. There are also more secondaries in the upper part of the leaf. These, however, are but slight differences, and are possibly only such as might be expected in individual variation. But as only one example has been found in the Yellowstone National Park, thei'e is no means of knowing what maybe allowed for individual variation, so I have preferred to keep them separate. I take pleasure in naming this species in honor of JMr. Arnold Hague, who collected it. Habitat: Fossil Forest Ridge, middle stratum; collected by Arnold Hague, September 24, 1884. ' Tert. Fl., p. 239, PI. XLII, fig. 1. 742 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. sterclliacej:. Pterospermites haguei n. sp. PI. XOIX, flg. 4. Leaf of finn texture, broadly oblong in outline, slightly iiifequilateral, truncate at base, obtusely pointed at apex; margin, except at base, irregu- larly serrate, the teeth small, sharp, upward pointing; midrib strong, flexuose; secondaries 6 pairs, alternate, at an angle of about 45°, flexuose, craspedodrome, or subcamptodrome, with branches outside entering the teeth; lower pair of secondaries forming a series of broad loops; nei'villes strong, mainly broken; finer nervation not preserved. The figured specimen of this species is 11 cm. long and nearly 7 cm. broad. As stated, it is quite regularly broad-oblong in shape, with sparsely toothed margins except near the base. The lower pair of secondaries form a series of broad loops, while the upper ones are mainly craspedodrome. This species is evidently quite closely related to P. minor Ward^ from the Fort Union group near the mouth of the Yellowstone. Fig. 2 (loo. cit.) is especially like this species, but differs in being hardly half the size and in being markedly heart-shaped at the base. It perhaps should be referred to this species except for the fact that the other 2 leaves included by Professor Ward are so very difi'erent that they can hardly be allied to the one under discussion. Habitat: Fossil Forest Ridge; collected by Arnold Hague (No. 1219). CKEDNERIACE.E. Credneria? pachyphylla n. sp. PI. CI, tig. 0. Leaf large, thick, round-ovate, rounded and truncate or very slightly hpart-shaped at base, abruptly acuminate at apex; margin apparently coarsely sinuate-toothed; petiole long (4.5 cm.), thick (4 mm.); midrib thick, passing to the apex; secondaries 6 or 7 pairs, the 3 lower pairs (of which the very lowest is slender and near the margin) opposite and arising from almost the same })oint at the base of the blade, others alternate, all 1 Types of the Laramie Fl., p. 95, PI. XLII, fig. 1-3. FOSSIL FLORA. 743 seemingly craspedddroine, occasionally In-aiicliino- iicnr the margin; finer nervation not preserved. The specimen figured is the only one that has lieen found. It is 14 cm. long without the petiole, which is -il) cm. in length. Both sides of the leaf are destroyed, but it was probably about 10 cm. wide. Habitat : Yellowstone River, one-half mile below mouth of Elk Creek, bluff about 40 feet above the river ; collected by F. H. Knowlton, August 27, 1888. TILIACEiE, TlLI.\ POPULIFOLIA Lx. TiU<( populi/olia Lx.: Cret. and Tert. Fl., p. 179, PI. XXXIV, figs. S, 9. A single large, fairly well preserved .specimen is all that has been found of this species It is referred with very little doubt to Lesquereux's species, which was before known only from Florissant, Colorado. It is a little less heart-shaped at base than fig. 8 (loc. cit.) of Lesquereux's plate, but in the discu-ssion of this species Lesquereux describes it as "round or subcordate at base." The teeth are of precisely the same character, being only slightly smaller. The thick petiole and fine palmate nervation are identical, as is the other secondary nervation. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, top of bluff; collected by F. H. Knowlton, August 27, 1888. GrEWIOPSIS ■? ALDERSONI n. sp. Leaves of .firm texture, broadly obovate, truncate or slightly heart- shaped at base, obtusely acuminate above; margin entire at base, slightly undulate-toothed above; midrib thick, straight; nervation pinnate; second- ai'ies about 6. pairs, alternate, at an angle of 4.5°, caniptodrome; lowest pair subopposite, ari.sing some distance above the base of the blade, with 3 or 4 tertiary branches from the outside which are camptodrome and arch well inside the margin; upper secondaries occasionally forked near the margin; nervilles strong, percurrent. I refer several specimens to this somewhat doubtful species. Neither of them are perfect, but as far as can be made out the average length appears to have been about 9 cm. and the width about 6 cm. It is doubtful if these leaves belong to the genus Grewiopsis, but at 744 GEOLOGY OF THE YELLOWSTONE NATIONAL PAllK. present I am unable to suggest a closer affinity. They have the same size, shape, and approximately the same nervation as G. platanifoJia Ward,^ from the Fort Union group, differing, however, in not having a toothed margin. Professor Ward writes that the specimen upon which his species was founded is quite obscure, and it is possible that they may really be nearer alike than appears from the drawings. Additional material is needed to tix their status. I have ventured to call this a new species, and have named it in honor of Mr. E. C Alderson, who accompanied the expedition on which it Avas obtained and assisted in making the collections. Habitat: Specimen Ridge, opposite mouth of Slough Creek and near head of Crystal Ci'eek; collected by Ward and Knowlton, August, 1887. ARALIACE/E. Aralia wkightii n. sp. PL 01, tig. 1. Leaf firm, coriaceous, narrow in general outline, palmately 3 (possi bly 5) lobed; central lobe largest, long, ovate-lanceolate, slender-pointed; lateral lobes slender-lanceolate, half the length of the central lobe; all margins perfectly entire ; basal portion of leaf unknown ; primary nervation palmate; middle lobe with a pair of opposite nerves nearly at right angles to the midrib, which pass to the sinus, those above with about 10 jiairs of alternate camptodrome secondaries, which are much curved upward and arched along near the margin; intermediate secondaries occasional; lateral lobes with a sti'ong midrib and about 8 pairs of alternate or subopposite much-arched camptodrome secondaries; finer nervation consisting of very fine quadi-angular areolation. This very peculiar species is unfortunately represented by only the fragmentary leaf figured. Tlie basal portion is entirely destroyed and it is therefore impossible to determine whether there were 5 or only 3 lobes. There is some evidence in favor of its having been 5-lobed. The sinuses separating the lobes are somewhat rounded. The central lobe is very much the larger. From the sinus it has 6 cm. preserved and must have been 8 cm. or more in length when entire. In the broadest part. > Types of the Laramie Fl., p. 89, PI. XL, fig. 1. FOSSIL FLORA. 745 wliicli is al)out one-fouith of its loiigtli fn)in the sinus, it is 2.5 cm. broad. The hiteral htbes are about 3.5 cm. long, not enlarged upward. At base they are 1 cm. l)road, from whicli point the}- taper gradually to a slender acuminate apex. The nervation has been described in the diagnosis, and may also be clearly made out from tlie e.xcellent fio-ure. It is hardly possible to compare this species with described forms, from the fact that it is so fragmentary that the i)erfect form can not be made out. The characters of the larger middle lobe and the ^-ery much smaller lateral lobes seem to be so marked that it is strongl)- separated from any described species. Aralia angustiloha Lx.,' from the Chalk Bluffs of Cali- fornia, i)erliaps is closest to this species, yet it differs markedly. It will be necessary to wait for additional inaterial before its exact character can be made out. I have named this species in honor of Mr. George M. AVright, one of the collectors of this and many other valuable specimeias in the Yellowstone National Park. Habitat: Fossil Forest (No. 22c of section); collected by "Wright and Weed, September 20, 1885. Aralia notata Lx. PL C, tig. 1. Aralia notata Lx.: Tert. FL, p. 237, PI. XXXIX, figs. 2-4. Ward: Types of the Laramie FL, p. (iO, PL XXVII, fig. 1. Flatanus duhia Lx. : Hayiieu's Auu. Kept. 1873 (1874), p. 40G. The collection?, contain about 50 .specimens that evidently belong to this species. None of them are absolutely perfect, yet the general character can be made out. They come from three localities, one of wliich, the Yellowstone below Elk Creek, was given as a type locality by Lesquereux." There appears to have been a tendency among later writers to regard this as the same as Newberry's PJatanus nohilis^ from the Fort Union group, which indeed it much resembles. They were both very large species, not often preserved entire, but they seem to differ essentially. On this point Lesquereux says: "This species (A. xotata) seems very closely allied to 'Mem. Mus. Comp. Zocil., Vol. VI, No. 2, PI. V, figs. 4, 5. ''Tert.Fl., p. 237. ^L.iter Extinct Flora, p. 67. 746 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. Platamts nobUls Xewby.; I should not hesitate to consider it as identical, but for the cliaracter of the lateral nerves, which are described by the author as straight, and terminating in the teeth of the margin. In this species the borders are entire and the lateral nerves camptodrome. The difference may be merely casual, for one of the specimens from Troublesome Creek has the close secondarj^ veins camptodrome along the borders of the inner side of the lobes, while on the outer side the borders are obscurely cut by a few sjnall teeth, into which the veins enter as craspedodrome. C)ther speci- mens, thus of Elk and Yellow creeks,^ have the characters of F. nobilis." It would thus ajDpear that Lesquereux himself inclined to regard the Park specimens as being referable to Platanus nohUis, Ijut in the 50 or more specimens that I have studied from this place I have not found one showing the teeth and craspedodrome nervation of P. nohilis. They all have the distincth' camptodrome nerves, as shown in Lesquereux's figures. I have therefore decided to keep theni under Aralia. The further question of the correctness of this generic reference, or rather of the relation of thin Ayalia iiotafa to the genus Platanus, will not now betaken up. Janko has said" that Platanus nobilis "non est Platanus," while on the other hand Professor Ward has suggested^ that several of the so-called species of Aralia may have to be united into a group, under the name of Protoplatanus, representing the ancestors of Platanus. A small specimen of this species, obtained by Prof J. P. Iddings from a gulch north- east of the peak west of Dunraven, is exceptionally well preserved, at least as regards the finer nervation. This is very regularl)^ square, being only about 0.25 mm. in size. The leaf appears to have been rather thick, possibly coriaceous. No other specimen that I have seen has this finer nervation so well preserved. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 7, "Castanea bed", about 25 specimens; collected by Lester F. Ward and F. H. Knowhon, August 16-20, 1887. Southeast end of hill above (north) Lost Creek, bed No. 4, 2 leaves; collected by F. H. Knowlton, Au<>ust 8, 1SS8. Yellowstone River, one-half mile below mouth of Elk ' Probably Elk Creek on Yellowstone River, F. H. K. 'Abstammuiifj; il. Platanen, Englers bot. Jahrb., Vol. XI, 1889, p. 456. ■T.v|)is of the Laramie Fl., j). 63. FOSSIL FLOKA. 747 Creek, top of bluff; collected by F. IT Knowltoii, Au<>-ust27, 1888. Ande- sitic breccia, near <>-ulcli northwest of peak west of Dunraven; collected by J. P. Idding-s, September 12, 18S3. Also found on Overlook Mountain, in breccia, at an altitude of 10,070 feet; (collected by Arnold Haf>-ue, Aug-ust 6, 1897. Southern spur of Chaos Mountain, at an altitude of 10,100 feet; collected by Arnold Hague, August 11, 1897. South side of Stinkingwater Valley, on high bluff east of mouth of Crag Creek; collected by Arnold Hague, September 4, 1807. Aralia serkulata n. sp. PI. CI, fig. 3. Leaf apparentl}' subcoriaceous, palmately 3-lobed, middle lobe longest, ovate, obtuse; lateral lobes short, pointing upward; borders sharply serru- late, with small, sharp, upward-pointing teeth; secondaries numerous, close, alternate, at an angle of 25° to 40°, curving upward and entering the teeth, or sometimes camptotli'ome with outside branches to the teeth, usually 1 tooth between the 2 entered by two contiguous secondaries, which is sup- plied with a branch from the middle of a percurrent nerville, which crosses just below it; nervilles numerous, mainly percurrent and approximately at right angles to the secondaries; finer nervation quadrangular. This fine and apparently characteristic species depends upon the single example figured. It lacks the entire lower portion of the leaf, but 2 lobes are entirely preserved, and a large portion of the other. The central lobe is 4.5 cm. long to the sinus, and the lateral one about 1 cm. higher than the sinus. The distance between the lateral lobes is 8.5 cm. This species has exactly the same size and shape as many of the 3-lobed specimens of Aralia notata Lx.,^ foimd in the same beds. The main difference is in the sharply serrate margins, the teeth extend- ing even down to and through the sinus, and in the secondaries or branches from them entering the teeth. Occasionally, as indicated under the diag- nosis, some of the secondaries are camptodrome, as all are in ^1. notata, with outside branches passing to the teeth. These species are evidently closely related and may possibly be the same, although probably not, for in 100 specimens of A. notata not one was found that possessed these teeth. As pointed out under the discussion of Aralia notata (see ante, p. 745), >Cf. Lesquereux, Tert. Fl., PI. XXXIX, figs. 2, 3. Ward; Types of Laramie Fl., PI. XXVII,fig. 1. 748 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. there was some tendency to refer it to Platanus nobilis Newby., which is sometimes slightly toothed. The teeth of the species under discussion are distinctly aralioid, and not at all like those of P. vohilis. Aralia serrulata is distantly related to A. digitata Ward/ from the Fort Union beds. This latter sjjecies is 3-lobed, or, more often, 5-lobed, with the lobes enlarged upward, and serrate with shallow teeth only near the apex. A. macroi)liyUa Newby.,' from the Green River group of Wyoming, has the lobes serrate, but the teeth are large, coarse, and often scattered, and, moreover, the leaf is twice the size of this and always S-lolied. A number of species of Aralia have been described from California, but none of them agree Avith A. serrulata. Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, top of bluff; collected by F. H. Knowlton, August, 1888. Aealia whitneyi Lx. PI. XCIX, fig. 3. Aralia whitneyi Lx. : Foss. PI. Aurif. Gravels, Mem. Mus. Comp. Zool., Vol. VI., No. li, 1878, p. 20, PL V, fig. 1. Haydeu's Aun. Rept. 1878, Pt. II, p. W. This fine species was described b}^ Lesquereux from the Auriferous gravels of Chalk Blutf, Nevada County, California, and was also recognized by him in material collected by Mr. W. H. Holmes on Fossil Forest Ridge' in 1878. The specimens here referred to this species come from probably the same locality as that wliich afforded Holmes material. They are, with one exception, larger leaves than described in the type. None of the specimens are perfect, and hence it is difficult to determine the exact size, but they must have been 15 to 20 cm. long and probably broader. The small specimen mentioned is referred with some hesitation to this species. It is only about 9 cm. broad and 7 cm. long, but otherwise hardly differs. Habitat: Fossil Forest Ridge, Yellowstone National Park, bed No. 4, "Ai-alia bed," small leaf only; bed No. 7, "Platanus bed;" Specimen Ridge, Fossil Forest, opposite Slough Creek, and near head of Crystal Creek, "Platanus bed;" several large fine leaves. I Types of the Laramie Fl., p. 62, PI. XXVIII, fig. 1. = Proc. U. S. Nat. Mus., 1882, p. 513; Plates (iueil.), PI. LXVII, fig. 1; PI. LXVIII, fig. 1. 'Cf. Haydeu's Anu. Kept., 1878, Pt. II, p. 79. FOSSIL FLORA. 741) Aralia sp. This tViifjinent is the only one of this type oljserveil, and is too ixior to admit of satisfactory identification or characterization if it be new. It consists of a portion of what appears to be the central lol)e and 2 lateral lol)es of a 3-lobed form. The sinnses are rounded and the middle lobe is enlaro-ed above, with the marf^-ins entire. A secondary nerve passes up to the sinuses, and the lobe has about 5 or 6 pairs of alternate much arched camptodrome secondaries. It is quite unlike any other form observed, so far as can be made out. Habitat: Hague's Yellowstone Park collection, Fossil Forest section. No. 22c; collected by Wright and Weed, September 20, 1885 (field No., 1959). CORNACEiE. CoKNUS Newberryi Hollick. PI. cm, fig. 6. Cormis Newberryi Hollick, in Knowltou: Bull. U. S. Geol. Surv. No. 152, p. 77, 1898. Cornus acuminata Newby : Later Extinct Floras, etc., Ann. Lye. Nat. Hist. New York, Vol. IX, 1868, p. 71; 111. Cret. and Tert. PL, PI. XX, figs. 2-4; Plates (ined), PI. XXXVII, figs. 2-4. Represented by a number of well-preserved leaves, agreeing well with NewbeiTy's figures and description. Habitat: Yellowstone River, one-half mile and also 1 mile below mouth of Elk Creek, at top of bluff; collected by F. H. Knowlton. Also found on south side of Stinkingwater Valley on high bluff east of the mouth of Crag Creek; collected by Arnold Hague, September 4, 1897. Cornus wrightii n. sp. PI. cm, figs. 4, 5. Leaves of firm texture, elliptical-lanceolate, nan-owed below and apparently slightly decurrent, rather obtuse at apex; margin perfectly entire; midrib rather. thin, slightly flexuose; secondaries 4 or 5 pairs, lower pair opposite, others alternate, at various angles, curving along the margin and in the upper part, turning by a broad bow to the apex; nervilles few, approximately at right angles to the midrib; finer nervation not preserved. 750 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Several specimeus of this interesting species are known. The most perfect one is figured, and is 7 cm. in length, and yet lacks a small portion of both base and apex. It is a little more than 2.5 cm. broad. It is quite regularly elliptical-lanceolate in shape, with a rounded, rather obtuse apex and a more narrowed base. The secondaries appear to be luiiformly of 4 pairs, those in the upper portion of the leaf arching around and entering the point. This species has some resemblance to tlie preceding species, which differs, however, in being much larger and in having an acuminate apex and numerous (8 or 9) secondaries. They can not be identical. It differs from Cornus ovalis Lx.,^ from Table Mountain, California, in shape and nervation, this species being oval, with obtuse base and apex. Among living species this has considerable afiinity with G. imniculata I'Her., especially with cei'tain of the narrow-leaved forms. I have named this species in honor of Mr. George M. Wriglit, one of the collectors. Habitat: Fossil Forest section, Hague's Yellowstone Park collection, No. 22c of section; collected by Wright and Weed, September 20, 1885. ERICACEiE. AeCTOSTAPHYLOS ELLIPTICA U. Sp. PI. XCVII, lig. 2. Leaf very thick, leathery; elliptical in shape, obtuse above, slightly wedge-shaped at base; midrib thick, slightly flexous; secondaries about 5 pairs, alternate, lower ones short, at a low angle, upper ones at an angle of about 45°, soon curving upward and arching about near the margin to join the one next above; nervilles strong, percurrent; finer nervation obsolete. This fine little leaf is almost perfect. It is 4.5 cm. in length and 1 8 mm. in width. The petiole is about 3 mm. long and is ver}' thick, as is the flexuous midrib. The secondaries are also strong, the upper ones arching and joining in the upper part of the leaf This leaf is very thick, showing that it was of firm, leathery texture. It is e\'idently related to the bearberry {Arctostaphjlos uva-ursi) in shape, ' Mem. MuB. Comp. Zool., Vol. VI, No. 1, p. 23, PI. VI, tigs. 1, 2. FOSSIL FLORA. 751 texture of the leaf, and nervation. Tt ditfers in l)Hin- form and in having- coarse nervation. It has also a short petiole. Habitat: Yellowstone Uiver, one-half mile helow mouth of Elk Creek; collected by F. II. Knowlton. EBEXACE.E. DiOSPYROS HKACHYSEPALA Al. Br. J)iosp!/ri)s hrachysepala Al. Br. Ward: Types of the Laramie Fl., p. 104, PI. XLIX, figs. 1, -2. A tinely preserved leaf, almost identically the same as Ward's fig. 2, except that the secondaries are a little closer together. Habitat: Fossil Forest Ridge, bed No. 4, "Araliabed;" collected b}' Ward and Knowlton, August, 1887. DlOSPYRO.'^ LAMARENSIS n. sp. PI. XCV, tigs, o, 6; PL XCVI, tig. 4. Leaf membranaceous, regularly elliptical or ovate-elliptical, equally rounded at base and apex, or slightly broader at base; petiole not preserved, apparently with a slight wing; midrib thin, straight; secondaries 7 or 8 pairs, alternate, thin, camptodrome, arising at an angle of 45° or 50°, pass- ing straight toward the borders, near which they arch and join by loops to the secondary next above; intermediate secondaries occasional, thin, usually joining the secondary next below; finer nervation consisting of numerous irregular nervilles, jiroducing irregularly quadrangular areola?. This species is about 5 cm. long and a little more than 3 cm. wide, and is quite regularly elliptical in shape. As stated, the petiole is not preserved, but judging from the base of the blade it seems probable that it Avas slightly winged. The lower pair of secondaries arise from the very base of the blade and are very thin; the others are all alternate and camptodrome. One of the other leaves figured is approximately of the same shape, but has slightly more indication of having had a winged petiole. It is rounded at base and has a loose nervation, as in the other. This species is closely related and possiblj- identical with Diospyros ".opeana Lx.,^ from Florissant, Colorado. This latter sjjecies differs in being 'Tert. Fl., p. 232, PI. XL, fig. 11; Cret. .-inil Tert. Fl., p. 175, PI. XXXIV, fig. 3. 752 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. more or less distinctly wedge-sliaped at base, and is obovate rather than elliptical in shape. The nervation is similar in both. I), lamarensis is also like certain leaves of B. hrachysepala Al. Br., from Florissant and the Fort Union group of Montana.^ The leavesj from the Fort Union group are rather larger, and have the secondaries at a different angle and are without the peculiar finer nervation. It seems best, however, to keep them distinct, at least for the present. Hal^tat: Lamar River, between Cache and Calfee creeks; collected by F. H. Knowlton, August, 1888. Fossil Forest; collected by Arnold Hague, September 24, 1884. DiOSPYKOS HAGUEI n. Sp. PI. G, flg. 3. Leaf coriaceous, elhptical, entire, obtuse at apex and base; petiole tliick; midrib thick, flexuose; secondaries about 6 pairs, alternate, very irregular, the pair at the base of the blade thin, vanishing near the margin, next pair strongest, passing to the upper part, camptodrome, branching on the outside and forming broad loops well inside the margin; upper secondaries smaller, camptodrome, forming broad loops; nervilles sparse, strong, percurrent ; finer nervation obsolete. This species rests on the tine, nearly perfect leaf figured. It is 7 cm. long, including the petiole, which is 1 4 nmi. long and 2 nun thick. The blade is nearly regularly elliptical in shape and 3.3 cm. broad. The nerva- tion is peculiar, as may be drawn from the description and figure. All of the secondaries except the lower pair are camptodrome, forming by union Avith the one next above a series of broad loops some distance inside the margin. This type of nervation is peculiar and is clearly that of Diospyros. It approaches quite closely to certain small-leaved forms of D. virginiana L. Among fossil forms it somewhat resembles Diospyros ohtusa Ward,^ from Sevenmile Creek, Montana, in the Fort Union group. The latter species is of approximately the same size and shape, but differs in the details of nervation. It is, however, quite close. I have named this species in honor of Mr. Arnold Hague, of the United States Geological Survey. 'Cf. Lesquereux Cret. ami Tert. Fl., PI. XXXIV, fig. 1, 2; Ward, Types of the Laramie Fl., PI. XLIX, fig. 1,2. ■ Types of the I.aramie Fl., p. 105, PI. XLIX, fig. 5. FOSSIL FLORA, 753 Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, base of blut!"; collected by F. H. Ivuowlton, Augu.st, 1888. OLEACEiE. — Fraxinus WKiGHTii n. sp. PL XC, fig. 4. Leaflet small, membranaceous in texture, oblong in outline, unequal- sided, wedge-shaped at base, obtuse at apex; margin with few irregular scarcely pointed teeth; midrib strong, slightly flexuose; secondaries about 7 pairs, alternate, at various angles, flexuose, camptodrome or subcras- pedodrome, mostly arching and joining by bows some distance inside the margin, sometimes entering the teeth, and usually with outside branches to the minute, often obtuse, teeth; nervilles numerous, irregular, all forked or broken ; finer nervation producing irregular quadrangular meshes. The specimen figured, which was the only one found, is 4 em. long and 2.2 cm. wide. It is decidedly inasquilateral, with a wedge-shaped base, and undulate-toothed margin. The nervation is camptodrome, with the secondaries arched and joined by broad bows well inside the margin, or occasionally with a secondary entering a tooth, thus becoming craspedo- drome. The finer nervation is beautifully preserved, producing very irregularly quadrangular jneshes The relation of this species is undoubtedly with Fraxinus heerii Lx.,^ from Florissant, Colorado. Lesquereux's species differs in being much larger and narrower, with merely undulate margin. The nervation is strictly camptodrome, but otherwise identical. I have named the species in honor of Mr. George M. Wright, by whom it was collected. Habitat: Yellowstone River, below Elk Creek, top of bluff"; collected by Greorge M. Wright, September 9, 1885., Phyllites crassikolia n. sp. PI. CII, fig. 5; PI. cm, fig. 1. Leaves very large, thick, apparently radely oval or orbicular in out- line ; base rounded or slightly heart-shaped, upper portion rounded (?); margin • Cret. and Tert. Fl., p. 169, PI. XXXIII, figs. 5, 6. HON XXXII, PT II 48 754 GEOLOGY OF THE YELLOWSTONE NATIONAL PAlfK. entire or undulate ; petiole usually ver}' thick (7 mm. in diameter) ; midrib thick (5 mm.), straight, splitting above into 2 equal branches; secondaries thick, straight, alternate or subopposite, often forking, craspedodrome or subcamptodrome, the secondaries or their branches united by broad loops with branches from the outside to the margin; nervilles very numerous, strong, mainly percurrent, yet often forked or broken; finer nervation, pro- ducing large, mahdy irregular, quadrangular areolse. This species is based on a number of fragments that are insufficient to show the true character. Two of the largest are figured, showing what is assumed to be the base and upper portions. The largest is 13 cm. long and about 10 cm. wide, but this could have been only a fragment of the original size. This specimen (fig. 6 of PI. CII) is peculiar in that the midrib splits in the upper ])ortion into 2 equal branches, both of which are again branched on the outside. This leaf appears also to have been 2-lobed at the apex, all of which may be abnormal and due to an injurj^ to the midrib. The nervation in the uj)j)er portion quite markedly camptodrome. The lower portion that I have assumed to belong to this species has an exceedingly thick i)etiole, of which only a fragment is preserved, and also a thick midril). They appear so different that it seems hardly probable that they can be identical, but rather than multiply unsatisfactory species they may remain as above until additional material can be obtained. None of the margin except the very base is preserved. On account of the fragmentary nature of these leaves, I am unable to determine with satisfaction the proper genus to which they should be referred. In this uncertaint}' I have placed them provisionally under Phyllites. Habitat: Cliff on west end of Fossil Forest Ridge; Fossil Forest Ridge, near head of Crystal Creek, various beds; collected by Ward and Knowl- ton, August, 1887, and by W. H. Weed, September 20, 1885. Carpouthes orseus Lx. Carpolithes ossem Lx.: Ann. Kept. U. S. Geol. and Geo^-. Surv. Terr., 404, 1872 (1873). A very doubtful species, of wliich the type is lost and the species not since obtained. Habitat: "Elk Creek, near Yellowstone River; A. C Peale, Joseph Savage, and O. C. Sloane." l-'OSSIL FLORA. 755 CaKPITES I'EOUNCULATUS 11. sp PI. cm, fig. 3. Fruit round, apparently 4 or 5 celled; pedicel sliort, tliick. This fragmentary fruit is hardly worthy of description, for it nun' he so deformed by pressure that it can not be recognized again. Among the described fruits of this heterogeneous class C. viburni Lx.,' from Black Buttes, Wyoming, is perhaps closest, but proljablv the resem- blance is onlv superficial Habitat: Yellowstone River, one-half mile below the mouth of Elk Creek, top of bluif (with Ulmus fruits); collected by F. H. Kuowlton, August, 1888. FOSSIL FORESTS. The fossil forests of the Yellowstone National Park are, be3"ond question, the most remarkable of their kind that have thus far been dis- covered in any part of the world. Isolated jiieces or stumps of fossil wood are of common occun-euce, being found in almost all quarters of the globe, from near the point farthest north that was reached b}' the Greely Ai'ctic Expedition to southern South America ; from Spitzbergen and Nova Zembla to South Africa and Australia, and geologically from the Devonian to beds in process of formation at the present da}'. lu many localities there are aggregations of logs and stumps that are worthy to be dignified by the name of fossil forests; as, for example, in Chalcedony Park, near Holbrook, Arizona; near Calistogu, California, and in the vicinit}- of Cairo, Egypt. But in all of these places, so far as known, all or most of the trunks are prostrated and lie scattered about in the greatest confusion. In some cases there is evidence that the logs Avere transported by currents before being fos- silized. The fossil forests of the Yellowstone National Park and vicinity, on the other hand, are not only more extensive in area, but the trees are almost all standing upright in the exact positions in which the}' grew originallv. Many of these trunks, standing on the slopes and steeper hillsides, rise to a height of 20 or 30 feet, and are covered with lichens and blackened and discolored by frost and rain. At a short distance it is hard to distinguish them fi'om the near-by living relatives. The following account bv Prof 'Tert. Fl., p. 305, PI. LX, fig. 26. 756 GEOLOGY OF THE YELLOVVSTOXE NATIONAL PARK. W. H. Holmes, the discoverer of these fossil forests, shows the impression first made by the siglit of them : As we ride up the trail that meauders the smooth river bottom, we have but to turu our attention to the cliU's ou the right hand to discover a multitude of the bleached trunks of the ancient forests. In the steeper middle portion of the moun- tain face, rows of upright trunks stand out on the ledges like the columns of a ruined temple. On the more gentle slopes, farther down, but where it is still too steep to support vegetation, save a few pines, the petrified trunks fairly cover the surface, and were at first supposed by us to be the shattered remains of a recent forest.' Fossil trees or fragments of wood of gi'eater or less size are found in many parts of the Park, hut their distribution is mainly confined to the northern and northeastern portions. The forests of standing trees are all found in the vicinity of the Lamar River, the most striking being exposed on the slopes and cliffs of Amethyst Mountain and Specimen Ridge. Nearly all of these forests are easily accessible from the well-traveled road between the Mammoth Hot Springs and the town of Cooke, Montana. As the visitor enters the area drained by the Lamar River and by the smaller streams running into the Yellowstone below the Grand Canyon, evidences of proximity to the fossil forests are soon at hand. In the bed "of every stream pieces of wood, often of considerable size, may be found. These pieces have in many cases been carried miles from their original source by the torrents incident to the melting of the snows in spring. In this way the pieces of wood have become rounded and worn and at remote distances are changed into smooth, rounded pebbles. The first forest to be visited is near Yanceys, and is known as Yanceys Fossil Forest. It is located about 1 mile south of the hotel, on the middle slope of a hill that rises about 1,000 feet above the little valley. It is reached by an easy trail, and as one approaches, a number of trunks are observed standing upright among the stumps and trunks of living trees, and so much resembling them that a near view is necessary to convince the visitor that they are really fossil trunks. Only two rise to a considerable height above the surface. The larger one is about 15 feet high and 13 feet in circumference; the other is a little smaller. The roots are not exposed, so that it is impossible to determine the position of the part in view. Its original length can not, of course, be ascei'tained. It is also impossible to ' U. S. Geol. and Geog. Survey of the Terr., Hayden's Twelfth Anuiial Report, 1878 (1883), p. 48. FOSSIL FLOKA. 757 determine the original (liain(;ter, as the bark is in no case preserved. The standing trees are both conifers, and belong to the genus Cupressinoxylon. Above these standing trunks many others are visible, but the disinte- grating forces of nature keep them at about the same level as that of the surrounding rock, from the fact that they tend to break up easily into small fragments. Some of these trunks rise only a few inches, while others ai-e nearly covered by the shifting debris. They vary in size from 1 to 4 feet in diameter, and are so perfectly preserved that the annual rings can be easily counted. The internal structiu'e is also in most cases nearly as perfect as though the tree were living. The cells still retain their delicate markings, and often their perfect form. There are numerous fossil leaves found in the rocks about the bases of these trees, but none apparently corresponding to the ti-unks; that is, the trunks are all coniferous, while the leaves are dicotyledonous; but from the nature of the case a coniferous trunk is much more readily preserved than a dicotyledonous one. The next forest that claims attention is the one mentioned by Mr. Holmes, and is the one most frequently visited by observers. It is known locally as the Fossil Forest, and is exposed on the northern slope of Amethyst Mountain, opposite the mouth of Soda Butte Creek. The trunks may be easily seen from the road along the Lamar River and quite a mile away. They stand upright — as Holmes has said, like the pillars of some ancient temple — and a closer view shows that there is a succession of these forests, one above the other, through the entire 2,000 feet of this mountain. That is to say, in early Tertiary time a magnificent forest flourished in this region, which was buried under the dtjbris ejected from volcanoes of greater or less size that are supposed to have existed in this vicinity. The trees were suiTounded by silica-charged waters and were turned to stone. The area on which they gi'ew was probably undergoing a very gradual submergence and the trees were slowly entombed. This is shown by the fact that the trees are in an upright position and were not broken by the incoming- material which covered them. After the first forest was entombed, quiet was restored for a sufficient length of time for a second forest to grow above it. Then volcanic acti^dty was renewed, and the second forest was buried and silicified as the first had been. This process was repeated until 2,000 feet of volcanic material had 758 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. been accumulated ami not fewer than fifteen forests were entombed. Then the volcanoes ceased their activity and final quiet was restored. Probably an upward tendency was given to the area, but it must have been very gradual and not attended by the distortion which so frequently accompanies mountain l^uilding. The disintegrating action of frost and rain immediately set in aiid has carved out this mountain, in the heart of which may be read the story of its origin. In the foothills and several hundred feet above the valley there is a per- pendicular wall of breccia, which in some places attains a height of nearly 100 feet. The fossil trunks may be seen in this wall in many places, all of them standing upright in the positions in which they grew. Their upright position proves that if there have been changes of level they have been gradual and in the same plane, as otherwise the trunks would be variously inclined. Some of these trunks, which are from 2 to 4 feet in diameter and 20 to 40 feet in height, are so far weathered out of the rock as to appear just ready to fall, while others are only slightly exposed. Niches mark the places from which others have already fallen, and the foot of the cliff is piled high with fragments of various sizes. Above this cliff the fossil trunks appear in great numbers and in regular succession. As they are perfectly silicified the)'^ are more resistant than the surrounding matrix, and consequently stand out above it. In most cases they are only a few inches above the surface, but occasionally one rises as high as 5 or 6 feet. The largest trunk observed in the Park is found in this locality. It is a little over 10 feet in diameter, which includes a portion of the bark. It is very much broken down, especially in the interior, a condition which very probably prevailed before fossilization. It projects about 6 feet above the surface. The most remarkable of all the forests, however, is located on the west- ern end of Specimen Ridge, about 1 mile southeast of Junction Butte and opposite the mouth of Slough Creek. It was first brought to the notice, of the scientific world by Mr. E. C. Alderson and the writer, who discovered it in August, 1887. It is found on the higher portion of the ridge, and is several acres in extent. The trees are exposed at various heights on a verjr steep hillside, and the remarkable feature is that most of them project well above the surface. FOSSIL FLOKA. ' 759 One of the largest and best-preserved trees stands at the very summit of the slope. It is 26 i feet in circumfereuce without the bark, and i-ises about 12 feet in heig-ht. The portion of this huge trunk preserved is the base, and below ground it becomes somewhat enlarged and passes into the roots, which are as large as the trunks of ordinary trees. The roots are embedded in the solid rock, as shown in the figure (see PI. CIV). This trunk is a true Sequoia, and is so closely allied to the modern redwood (^Sequoia sempervirens) of California as to be hardly distinguishable from it. It would be interesting to learn the height this tree attained, l)ut it seems safe to assume, from what we know of its living representative, that it must have been -more than a hundred feet high. Just below the large trunk, on the steep hillside, are two more stand- ing trees (see PI. CVI), which we may imagine to have formed the doorposts of the "ancient temple" of which Holmes speaks. They stand about 20 feet apart and rise about 25 feet in height. They are both about 2 feet in diameter and are also without the bark. In other parts of the area there are standing trees which attain a height of 12 to 20 feet They are all under 2 feet in diameter. In a few cases the bark is also preserved. It is hardly ever more than 3 inches in thickness. Scattered about over the area are a great many trunks that rise only a few inches above the surface. These vary in diameter from 2 to 5 feet. They are often hollow in the center and have the cavity lined with brilliant amethyst crystals. • One of the larger trees appears to have been prostrated before it was fossilized (see PI. CVIII). It is about 4 feet in diameter and is exposed for a length of 40 feet. There is nothing to indicate the portion of the trunk in its relation to roots and branches, but neither shows on the exposed part. There is no appreciable diminution in diameter, and consequently it must have been a very tall trunk. The matrix about the bases of these trees, as well as those in the Fossil Forest, contains numerous impressions of leaves, branches, and fruits. In the Fossil Forest there are at least 6 horizons at which plant remains occur. These are separated by a few inches, or in some cases by many feet. In the forest last described, which may be called the Junction Butte Forest, there are only 2 or 3 plant horizons. 760 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Most of the trunks in all three of the described forests are coniferous, but occasionally a dicotyledonous trunk is found, showing that the forest was to some extent a mixed one. It is of course more than probable that the leaves found in the matrix about the bases of the trees were at one time attached to them, but as the}^ have never been found in association, it is manifestly impossible to correlate them. The next fossil forest in rank of size is, perhaps, the one found on Cache Creek, about 7 miles above its mouth. It is exposed on the south bank oi the creek, and covers several acres. The trunks are scattered from bottom to top of the slopes, through a height of probably 800 feet Most of the trunks are upright, although there is only now and then one projecting more than 2 or 3 feet above the surface. The largest one observed was 6 feet in height and about 4 feet in diameter. While most of the trunks appear to the naked eye to be coniferous, there are a number that are obviously dicotyledonous. It is certain, however, that the conifers were the predominant element in this as in the other fossil forests. The slopes of The Thunderer, the mountain so prominently in view from Soda Butte on the south, have also numerous fossil trunks. They are mainly upright, but onlj" a very few are more than 2 feet above the surface. There were no remarkably large trunks observed, the average diameter being less than 2 feet. Mount Norris, which is hardly to be separated from The Thunderer, has a fossil forest of small extent. The trees are of about the same size and characteristics as those on the larger mountain. Forests of greater or less extent, composed mainly of upright trunks, are exposed on Baronett Peak, Bison Peak, Abiathar Peak, Crescent Hill, and Miller Creek. In fact, there is hardly a square mile of the area of this northeastern portion of the Park without its fossil forest — scattered trunks or erratic fragments. The vast area to the east of the Yellowstone Lake has never been explored thoroughly from the paleobotanical side, but enough is known to be certain of the presence of more or less fossil wood. The stream beds contain occasional fragments, which is a sufficient indication that trunks of trees must be near at hand. FOSSIL FLOUA. 761 DESCRIPTION OF 8PKC1ES. Sequoia iMAgnifica n. sp. Pis. CIV, OV, CX, GXI, CXVII, figs. 1-6. Diagnosis. — Truuks ot'tc'U of great size, 6 to 10 feet in diameter, 30 feet high as now preserved, bark when present 5 or 6 inches in thickness; annual rings very distinct, 2 to 3 nun, broad; fall wood reduced to narrow bands of 3 to If) rows of thick-walled cells; cells of spring and summer wood large, hexagonal or often elongated; resin tubes numerous, composed of short cells; medullary rays numerous, of a single series or occasionally with a partial double series of superimposed cells; wood cells with one or two rows of small circular pits. Transverse section. — In tliis scctiou (Pls. CX, CXI) the structure appears beautifully preserved. The rings are rather narrow, being only 2 or 3 mm. broad, or often only 1 mm. They are verj' sharply deraarked, even to the naked eye. Under the microscope the rings are found to consist of a band of thick- walled cells that is never more than 15 rows of cells deep and often is reduced to 2 or 3 rows. The cells composing the spring and summer wood are of uniform size and inclined to be hexagonal in shape. Those of the fall wood are, of course, compressed. The resin cells are numerous and may be readily distinguished by the dark contents. They occiu* mainly in the spring and summer wood. The medullary rays seen in this section are long, straight, and sepa- rated by usually about 3 rows of wood cells. Radial section. — Tliis scctiou (PI. CXVI, figs. 2-3) Is the least satisfactory of all. The wood cells show well under the microscope, but their mai'kings are very obscure. By prolonged search it is made out that the pits are in 1 row, or sometimes 2 parallel rows. They are small, as far as can be made out, and are too obscure for satisfactory measurement. The rays are composed of long, unmarked cells. Tangential section. — This scctiou (Scc PI. CXYI, fig. 1) is Very satisfactory. The wood cells are long and unmarked. The resin ducts are numerous, but scattered, the cells being twice or three times as long as wide. In many cases they are filled with or contain masses of dark material, repre- senting the resin now turned to a carbonaceous mass. 762 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. The meduUaiy rays are composed of 1, or in some cases of a par- tially double, series of 2 to about 25 superimposed cells. They are large and quite thick walled. The average number of cells iu each ray is about 12. This species is closely related to the living Sequoia sempervirens Endl., more closely than any other fossil species with which I am familiar. They are hardly to be separated by any well-defined characters. The living- wood has the same clearly marked annual rings^ resin cells, partially double rays, and pits on the wood cells. The medullary rays in the living wood are provided with numerous round pores or markings. These seem to be absent from the fossil specimens, but, as already related under the diagnosis, the fossil is not well preserved in the radial section and they may have been present there when it was living. The dimensions of the various elements are much the same in the living' and fossil specimens, thus leaving no doubt as to their close affinity. In size of trunks these species are also similar. The largest trunks observed in the Yellowstone National Park belong to S. magnlfica. They range in size from 4 to 10 feet in diameter, one of the largest being shown on PI. CV. This is 26J feet in circumference and stands upright on the hillside. It is 12 feet high, and I'epresents the base of the trunk, as the large roots are well preserved. Their height is of course unknown, but one was fortunately prostrated before fossilization (PI. CVIII), and is 40 feet long, with no apparent diminution in diameter. It is altogether likely that they may have been equal in height to some of the living representatives. I have thought best to give this fossil species a name different from that of the living tree, notwithstanding the fact that they are evidently so closely related. The fossil comes from a locality remote geographically from the living redwood, and, moreover, from a horizon that, although com- paratively recent, is so ancient as to make it extremely improbable that the type has actually been living for so long a period. There can, however, he no doubt that the living redwood is the direct descendant of this remarkable tree that was once so abundant in the Yellowstone National Park. Habitat: Specimen Ridge, Fossil Forest at head of Crystal Creek, Fossil Forest on Cache Creek, etc.; collected by F. H. Knowlton, August, 1887-August, 1888. FOSSIL FLORA. 763 PiTYOXYLON ALDERSONI U. sp. Pis. CVr, CXII, CXIII, CXVIII, tigs. S, i; PI. OXIX, fig. 2. Diagnosis. — Tvuiiks of Ijirye size, 3 to 5 feet in diameter; annual rings very distinct, often 8 or 9 mm. broad, very sharply demarked; resin ducts numerous, large, scattered, occurring in late summer and fall wood; wood cells long, with a single irregular row of medium-sized pits; medullary rays in a single series, or occasionally with divided cells; rays from 2 to 25 cells high, the average being about 10 or 12 cells. Transverse section. — The anuual Hugs are very distinct, being plainly dis- cernible to the naked eye. Some of the broadest rings are fully 9 mm. wide, and none are less than 6 mm. The demarcation between fall and spring wood is very pronounced (see fig. 4 of PI. CXVIII and 2 of PI. CXIX), the cells of fall being small, compressed, and thick-walled, while those of the early spring v\'ood are very large, and, of course, thin-walled. The cells of the spring and summer wood continue for a width of 5 mm., but little, if any, diminished in size. Then they become slightly smaller and thicker-walled and pass gradually into the fall wood. The resin ducts ai'e very large. They are not found in the summer wood, but occur irregularly in the early fall and late fall wood. The medullary I'ays, as observed in this section, are straight and separated by from 3 to 8 or 10 rows of wood cells. The individual cells are apparently long. Radial section. — Notwitlistaudiug the fact that the wood seems to be per- fectly preserved, it does not reveal the structure well in this section. The wood cells are seen to be sharp-pointed where they join. They are, of course, broad in the spring and summer wood, and very narrow and thick- walled in the fall wood. It is very difficult to make out the pits, but in exceptionally well preserved portions a few may be faintly seen. They are scattered, but in a single series. They are so obscure that no satis- factory measurements can be made. The medullary rays in this section are long, thick-walled, and without markiiigs, so far as can be made out. Tangential section. — Tlils sectiou is Very plain. The medullary rays are numerous and in a single series, although occasionally a ray may be observed in which there are 2 series of cells for a short distance. In such cases the 764 GEOLOGY OF THE YELLOWSTONE jSTATIONAL PARK. cells are always smaller than the ordinary ray cells. The number of cells making up each ray ranges from 2 to 30 or more, but the average number is about 8 to 15. The rays in which there is a resin duct are rather rare. The duct is large, taking up all the width of the ray. The remainder of the ray is 3 rows of cells high in the middle and is reduced to 1 at the extremities. The wood cells show clearly in this section. They are not provided with pits or other markings. Habitat: Specimen Ridge, Fossil Forest, near head of Crystal Creek; collected by F. H. Knowlton, August, 1887. Yancey Fossil Forest; col- lected by F. H. Knowlton, August, 1887. PiTYOXYLON AMETHYSTINUM 11. Sp.^ Pis. GVII, GVIII, OXIV, CXV, CXVIII, figs. 1, 2. Diagnosis. — Truiiks of siuall or medium size ; annual rings sharply demarked, 3 to 8 mm. broad; resin ducts numerous, scattered, but mainly ill fall wood; wood cells long, sharp-pointed, provided with a single row of scattered, small, somewhat irregular pits; medullary rays numerous, in a single series of '2 to 12 cells, the average being about 5 or 6. Transverse section. — Mucli likc tlic precodiiig spccles, exccpt that the rings are narrower, the cells of spring and summer wood are smaller, and the late fall cells have thinner walls. The resin ducts are also much the same, being in general only a little smaller. A few are found in the summer wood, but most of them are in the fall wood. The rays are not nearly so numerous as in the last species. They are often separated by as many as 25 rows of wood cells. Radial section. — TliB radial section of nearly all woods from the Yellow- stone National Park is more or less obscure. The one under consideration is no exception to this rule, and it is only after considerable search that the pits can be determined. They are hi a single row (see PI. CXVIII, fig. 1) ' In 1888 Dr. .1. Felix, of Berlin, visited, and collected fossil wood in, the Yellowstone National Park. The results of his work were published in Zeitschrift der Ueutschen geologischen Gesellschaft, for 1896. He described six species of fossil wood, of wliieh number I have recognized four. The following two species were not tignred, and as the locality whence they came is more or less in doubt I have not included them in the systematic enumeration. They are as follows : Piti/oxylon faUax and Cupressinoxyton eulreton. They may be identical with certain of the species I have described, bnt of this I am uncertain. FOSSIL FLORA. 7G5 ami lire rather small. They are so obscure that it is impossible to make trustworthy uieasurements. The uiedullary rays, as seen in this section, are composed of long-, thin- walled cells, and so fur as can be determined the}' are without pits or other markinys. Tangential section. — This soctiou (I'l. CXVIII, fig. 2) sliows the structuro very plainl}". The medullary rays are abundant and always in a single series, except the large compound ones. The number of cells in each ray varies fi'om 2 to 10 or 12, the average number being about 6. The com- pound rays inclosing the resin ducts are rather small, with three rows of cells in the middle portion. No markings can be made out on the wood cells in this section. This species is very closely allied to the one preceding, and should perhaps be referred to it. The main points of difference are the following: Narrower annual rings; smaller resin ducts, that are occasionally found in tlie summer wood; smaller wood cells throughout; smaller and shorter compound medullary rays; ordinary rays always in a single series of 2 to 12 cells (average 6) instead of from 2 to 30 or more (average 12). Habitat: Specimen Ridge, Fossil Forrest, near head of Crystal Creek; collected by F. H. Knowlton, August, 1887. Laurinoxylox pulchrum n. sp. Pis. CXVI, CXIX, figs. 3-5; PI. CXX, fig. 1. Transverse section. — Auuual Hug vcry distluct to the naked eye, 2 to 4 mm. broad. The demarcation between the rings results from 10 or 12 layers of thicker- walled cells, representing the late fall wood, and from the greater abundance of ducts in the immediately following spring wood. The wood cells are small and arranged in serial rows except in the vicinity of the ducts, where they are somewhat irregular (see fig. 1 of PI. CXX). Surrounding the ducts, and sometimes filling the remainder of the space between rays, the cells are larger and not so completely seriated. The ordinary wood cells are about 0.01 mm. in diameter, and those near the ducts 0.015 or 0.02 mm. There is an occasional row of the larg-e-sized wood cells along a ray, as in fig. 1 of PI. CXX. The ducts are very plainly shown in this section. At least half of them are single and nearly or quite circular in section. Of the remainder, 766 GEOLOGY OF THE YELLOWSTONE NATIONAL PAHK. most are double, while occasionally there are 3 iu a row or series, and exceptionally as many as 4. The number in a square millimeter is only from 4 to 6. The smallest of the single ducts range in diameter from 0.03 to 0.06 mm. The largest observed are 0.21 mm. in long diameter and 0.16 mm. iu short diameter. The largest double duct — that is, when there are two tog-ether — is 0.31 mm. The largest of the series of 3 is 0.36 mm., and the largest of the few in series of 4 is 0.44 mm. The average diameter of large and small ducts is probably about 0.12 mm. The medullary rays are 1 to 3 cells wide, and run irregularly among the ducts. They are about 0.01 nun. broad. Radial section. — The wood cells are long, slender, and apparently sharp- pointed. There is evidence also that some of these are divided up into short cells by square divisions. The medullary rays forn:i plates of short, rather thin-walled cells. They are from 0.02 to 0.04 mm. in diameter and from 0.05 to 0 09 mm. in length. They do not appear to be marked, yet there is some evidence that there were minute j)its; but the specimens are not well enough preserved to be cei'tain of this. The ducts shown in longitudinal section (PI. CXIX, fig. 3) are very pronounced. The individual cells are from 0 10 to 0.20 mm., or some- times more, in length. The walls ere covered with small round pits, which occasionally pass into regular scalariform markings (see figs. 4 and 5 of PI. CXIX.) Each duct is surrounded by a mass of tissue from 2 to 6 or 8 layers of cells thick, of which mention was made under the discussion of the transverse section. The individual cells of this sheath are of about the same size and appearance as the large cells of the medullary rays. Tangential section. — The fiuc pliotomicrograpliic reproductions of this section (PI. CXVI) give a far better idea of the structure than any desci'iption can. The medullary rays, it will be observed, are very numerous (about 3 to each square millimeter). They are from 1 to, exceptionally, 4 layers of cells broad and about 12 layers high, the extremes being 5 and 20. This plate shows admirably the ducts and related tissue. The one in the center of the plate shows well the manner of division, although the magnification is hardly sufficient to show the pits or markings. This species is one of the handsomest with which I am familiar. It has affinities with a number of described forms, as, for example, Laurus FOSSIL FLOHA. 767 triseriata Caspary,' from the Tertiary of Prussia. From this it differs in the arrangement of (luets and in rays, and somewhat in the markings. It is also evidently allied to the two forms from the Tertiary of Arkansas, Laurinoxi/loii hnmnen Kn.^ and L. h'Sfjiwreiwiaiia Kn.^ The genus Laurus was evidently abundant in this flora, and it is to be expected that the trunks would be occasionally preserved. It is of course probable that this wood may belong to a species that has also been described from the leaves, but there is manifestly no means of connecting them. Habitat: Specimen Ridge Forest, near head of Crystal Creek, Yellow- stone National Park, a prostrate log; collected by F. H. Knowlton. August 25, 1887. Perseoxylon akomaticum Felix. Perseo,rylon aromaticum Felix: Untersucbiiag liber fossile Holzer, v. Stiick: Zeitsclir. d. Deutscli. geol. Gesell., Jahr. 1806, p. 254, 1S!)(J. Laurinoxylon aromaticum Felix : Die Holzopole Unganis, p. 27, PI. I, tig. 7 ; II, fig. 7, 9. This species was detected by Felix in his visit to tlie Yellowstone National Park in 1888. I did not meet with it. Habitat: Vicinity of Yanceys, Yelhiwstone National Park. Collected by J. Felix, 1888. Plataninium haydeni Felix. PI. OXX, flgs. 3-5. Plataninium haydeni Felix: Uutersuchung ilber fossile Holzer, v. Stiick: Zeitsclir. d. Deutsch. geol. Gesell. Jabr. 1890, p. 251, 1890. Transv;rse section. — The aunual Hugs are faint, yet they niay be seen with the naked eye. I'hey are about 2 mm. broad. The medullary rays are very distinct in the weathered specimen. Under the microscope the structure is shown to be well preserved. The wood cells ai'e not arranged 'in radial rows, but are quite irregularly placed. They are large (0.01 to 0.03 mm.) and angular, being 3 to 6 sided by compression. ' Einige fuss. HiJlzer Pronssens: Abhaudl. z. geol Specialk. v. Prens.sen u. Thiiriugischen Staateu, 1889, p. 60, PI. XI, figs. 6-lL'; PI. XII, tigs. 1-5. = Fossil' woods and lignites of Arkausas: Aim. Kept. Geol. Survey Arkansas, 1889, Vol. II, p. 256, PI. IX, figs. 8-9; PI. X, figs. 1,2; PL X, fig. 4. 30p. cit., p. 258, PI. X, flgs. 3,4; PI. XI, flgs. 3,4. 768 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. The ducts (PI. CXX, fig. 4) are veiy numerous. They occupy at least one-third of the area, exclusive of the rays. They are almost always single, although often placed clo.se together, especially in the beginning of the spi'ing wood. They are uniformly oblong in shape. In the spring wood the average size is 0.09 mm. in long and 0.06 mm. in short diameter. In tlie fall wood they are from 0.03 to 0.06 mm. in long and 0.025 to 0.05 mm. in short diameter. The annual ring consists of a layer of slightly thicker Avood cells, but it is mainly distinguished by the abruptly larger ducts in the spring wood (see fig. 4 of PI. CXX). The medullary vays are very abundant as seen in this section. They are from 1 to 10 or 15 cells broad. Fully 30 per cent of the ai-ea is covered by the medullary rays. The ra3^s uniforndy contain a black car- bonaceous substance, these making them stand out in bold relief Radial section. — Tlic uiost promiuent feature in this section (PI. CXX, fig. 5) is the medullary rays. They form high plates of usually short cells with black carbonaceous contents. The ducts are also prominent, and appear to be marked with scalai'iform thickenings; but as they are quite obscure, this is not positive. Tangential section. — Tho structure of this sectiou is very clearly revealed under the microscope. The medullary rays are very numerous. They range from 1 to 10 or 15 laj^ers of cells broad and more than 100 high. The cells are round, thin-walled, and usually or not at all compressed. They take up, as already stated, fully 30 per cent of the space. In some cases the rays are 0.5 mm. long and 0.35 ram. broad (cf. fig. 3 of PI. CXX). The wood cells are long and sharp-pointed. So far as can be made out, there are few if any square divisions of the cells. The ducts, of course, show well in this section, but the markings, if present, are now obscure. This species is quite closely related to the living Platanus occidentalis L., the common sycamore or plane tree. The living wood shows the indis- tinct annual ring, the in-egular wood cells, and numerous medullary rays almost identical with the fossil wood. There are certain minor points of diff'erence, such as markings on the rays, lignification of the ducts, etc., but they are certainly close enough to make their generic identity reasonably •sure. FOSSIL FLORA. 739 The fact that IMatamis leaves are very al)umhnit in the beds surroimd- ino- the fossil trunks makes it extremely i)rol)al)le that the generic reference is correct. It is of course also ])rol)able that some of the leaves belong to the wood here described as different, but as they have never been fmuid attached, it is manifestly unsafe to assume that there was ever organic union. A number of fossil species have been described from various 2:>arts of the world; none, however, from North America. The general agreement between these and the one under consideration is close, but the siDecific differences are marked in certain cases. One of the nearest forms is PManus klehsii Gasp.,' from the Tertiary of Prussia. It differs in important minor characters, as does P. borealis Casp.,^ from the same place. The two species described by Felix, Plafamnunn porosim Felix and P. regulare Felix, have only general resemblance. In the original MS., which was submitted in March, 1896, I had of course given this another specific name, and it may still prove to be different froni the P. liaijclem of Felix. Unfortunately Felix has not figured his species, and it is difficult, from a mere technical description, to be entirely certahi of their identity. It is reasonably certain, however, that they are identical, and I have so regarded them. Habitat: Specimen Ridge Forest, near head of Crystal Creek, Yellow- stone National Park. From a trunk 6 inches in diameter and about 1 foot in height; collected by F. H. Knowlton, August 25, 1887. Rhamnacinium radiatum Felix. PI. CXVIII, flgs. 6, 7; P]. CXIX, fig. 1. RhamnacinmmradiatmnYeli^-. UntersuchuugiiberfossileHoIzer: Zeitscbr d Deutsch geol. (iesell., Jahr. 1896, p. 252, PI. VI, fig. 3, 1896. Tran.ver=esectic„._Annual ring broad (7 mm.), very indistinct, consisting ol only 1 or 2 rows of slightly thickened wood cells and rather abrupt presence of numerous large ducts in succeeding spring wood. Ducts very numerous, in radial rows. A few of the ducts are single, hxu mainly they are contiguous, with ^Jo^(Mn^a series. The usual number is 3 or = 0p. cit.,Pl. IX, figs. 1-11. MON XXXII, PT II 49 770 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. four. The ducts occupy uearly oue-half of the area, thu& producing an open, soft wood. The longest series of ducts, embracing 10, is 0.50 nun. in length. Series of 4 or 5 having a length of 0.30 nun. are common. The small single ducts are 0.05 to 0.07 mm. in long and 0.04 to 0.05 mm. in short diameter. The average short diameter of all ducts is about 0.07 or 0.08 mm. The wood cells are arranged in distinct radial rows. They are rather large and thin-walled, also showing that the wood was a soft, porous one. The medullary rays in this section are rather numerous. They are 2 or sometimes 3 cells wide, and the cells are short and thin-walled. Radial section. — The ducts appear especially numerous in this section. The marking on the walls is rather obscure, but they seem to be uniformly provided with minute pits. The rays form high plates of short, thin-walled cells, apparently with small circular or oblong pitlike markings. The wood cells are very long. They have sharji-pointed extremities and thin walls. Tangential section. — Tliis sectiou Is xevj cliaracteristic, the most prominent feature being, of course, the cut-off ends of the medullary rays. The rays are ^'arious, being 2 or rarely 3 or 4 layers of cells wide. The number of vertical rows is very indefinite, being rarely less than 10 or more than 30. The cells are rectangular, being often twice as long as wide. Some of the cells in the middle of the ray are more or less irregular in shape. All are very thin-walled. The wood cells are the same as in the radial section. The ducts are also prominent. The}- liave oblique partitions and the walls are provided with round pits. The markings on the walls are not different from those to be observed in the radial sectiou, but they happen to l)e better preserved. In my original MS. this form was described under the new generic name of Populoxylon, from its undoubted close resemblance to wood of living Populus. It is with some hesitation that I transfer it to Felix's species, for they do not agree in every particular. On the whole, however, it is more than probable that they are the same, and I have so regarded them The generic diagnosis, based uptm the wood from the Park only. FOSSIL FLOKA. 771 may be drawn up as follows: Annual rin<4- present, ])ut faintly deniarked; wood cells long-, narrow, sharp-pointed, thin-walled; ducts very numerous, occu})vinf>" about one-half of the area, in radial rows of from 2 to 10, pitted, the pits small, round; medullary rays numerous, of short, thin-walled cells, rectangular or irregular in transverse section, arranged in 2 to some- times 4 vertical rows of approximately 10 to 30 cells each. Habitat: Specimen Ridge, near head of Cr3-stal Creek, Yellowstone National Park; collected by F. H. Knowlton, August 22, 1,S87. QUERCINIUM LAMARENSE n. Sp. PI. CXVni, fig. 5; PL OXX, fig-. 2; PI. CXXI, figs. 1, 2. Transverse section. — Auuual riug preseiit, but vcry falut ; consisting of but 1 or 2 rows of thickened cells. In the succeeding- spring wood the ducts are much larger, thus making the ring visible to the naked eye. Ducts numerous, scattered, most abundant in spring and summer wood; all single — that is, not contiguous. They are almost perfectly circular, being very slightly elongated radially. They are large, though not remarkably so for the genus; the larger ones ranging in diameter from 0.16 to 0.23 mm., the smaller being about 0.20 mm. The very smallest ducts are 0.05 mm. in diameter, and the more common of the small ones are 0.10 or 0.12 mm. in diameter. None of the ducts are arranged in notable radial rows. The wood cells are in distinct radial rows, and are large and thick- walled. In most the lumen is nearly obliterated. The average size of the wood cells is 0.02 mm. The medullary rays are neither very numerous nor conspicuous. They are mainly only 1 cell broad, with au occasional wide one of 20 or more cells, as will be described under the tangential section. Some of the single- celled rays pass for a considerable distance among the ducts, but by far the larger number lie between two ducts (see fig. 1 of PI. CXXI). Radial section. — The ouly scctious available in this direction were, unfor- tunately, from poorly preserved portions of the specimen, and do not show the structure clearly. The wood cells, so far as can be made out, are ver}* long, and, as shown by the transverse section, have thick walls The rays 772 GEOLOGY OF THE YELLOWSTONE :N^ATI0NAL PAEK. form high phites of cells, the exact length of which can not be determined with satisfaction. If there were markings on the rays they can not be seen; neither can the markings on the ducts be observed. Tangential section. — Tlus scctlon sliows much better under the microscope than the radial one. The rays are found to be of two distinct kinds: The most numerous are only 1 cell broad and from 10 to 25 cells high, the individual cells being thin-walled and oblong in shape. At scattered intervals are veiy broad rays composed of 10 to 20 rows of cells and extending for long distances through the section (see fig. 2 of PI. CXXI). These broad rays are often somewhat cut by wood cells passing diagonally through them (see fig. 2 of PI. CXXI). This does not, however, interfere with the ray as a whole, which is clearly demarked from the small rays of a single series of superimposed cells. The individual cells of the large rays are nearly circular in cross section, or more or less 6-sided by mutual pressure. They are also thin-walled. Associated with the small rays is usually a layer or two of short-celled tissue or series of parenchymatous cells. Except for there being shorter cells they are not to be distinguished from the ordinary wood cells. The ducts show clearly enoiigh in this section, but they are not well enough preserved to permit the markings on the walls to be made out. It would seem that the walls were pitted, but this is largely surmised. A considerable luimber of species of Quercinium,^ or oak wood, in a fossil state, have been described from various parts of the world. Wood of this kind is readily distinguished by the large isolated ducts and the two kinds of medullary rays. The species under consideration resembles a number of described forms, but they are all from the Old World, and are readily distinguished from it. This species is closely allied to Quercinium hnowltoni Felix, and may possibly be the same, but as Felix's species is not fully illustrated it is difficult to be positive. Q. lamarensc seems to differ in the shape and size of the large ducts, but it will need a careful comparison of the sections to be positive. For the present, at least, they may remain distinct. Habitat: Specimen Ridge, Yellowstone National Park; specimen from ' Fifteen species and varieties. FOSSIL FLORA. i iO an uprifi'lit trunk, 4 feet in diiunoter; colloctt'd hy F. H. Knowlton, Auj^ust 22, 1887 QrERCINIUJI KNOWLTONI FcHx. Qtiereinium hnoirltoni Felix: IJndersuchiuig iiberfossile Hillzer: Zeitsclir. d. Doutsdi. gftol. (icsell., Jahr. IS'.H!, ii. 250, PI. VI, tig. li, ISDU. As .stated under tlie jtreceding species, these 2 forms may be identi- cal, but in absence of" full drawings of Q. hioivltonl it seems best to regard them as distinct. The size and sha])e of the ducts certainh' dift'er greatlv. Habitat: Amethyst Mountain, Yellowstone National Park; collected by J. Felix in 1888. BIOLOGICAL OOIVSIDERATIOX OF THE TEKTIARY FLORA. The Tertiary flora of the Yellowstone National Park possesses great biological interest. It is a rich flora, and on comparing- it with the living flora it liecomes apparent that great climatic changes must have taken place since the close of the Miocene period to have made these modifications in plant life possible. The fossil flora embraces about 1,50 forms that have been distributed among 33 natural families. Following is a list of these families, with the number of species or forms referred to each:'' Species. Filices 10 Equisetaccw 4 Conifera' 13 1 1 4 1 1 Typhacecv Sparganiace.T Cyperacew Smilacew Miisacea' Juglandacea; 8 Myricacea- 3 Salicacew 10 Betidacew 2 Fagace* 15 Ulmacea! 5 Urticacew 10 Magaoliace;i? 5 Laurace;ii 12 Species. I'latanaceiB 3 Le{/mninos(v 5 Aiiacardiaeea' 1 Celastracea^ 4 Aceracea' 2 Sapindace;* 5 lihamnacew 4 Vitaceai l Sterculiacert' 1 Credneriaceie 1 Tiliaceit 2 Araliacea' G Gornacew 2 JEricacccv 1 Ebenacew .<• 3 01eace;e l Phyllites, Cariiites 3 ' The orders that are also found in the present flora are printed in italics. 774 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK, The .excellent Flora of the Yellowstone National Park/ by Mr. Frank TAveedy, has been made the basis of all comparisons between the fossil and livino- floras. According to Tweedy, the present flora embraces 69 natural families, 273 genera, and 657 species. The fossil flora embraces 33 families, 63 genera, and 148 species. The living flora has, therefore, 4 genera to each order and 2.4 species to each genus, while the fossil flora has not quite 2 genera to each family and 2.3 species to each genus. The relative proportion between the families, genera, and species is shown to be approxi- mately the same in the Tertiary and the living floras. A still further comparison shows tliat there are a fraction more than twice as many living as fossil families, 4.3 times as many living genera, and 4.6 times as many species. On con\paring the families in the two floras, it is found that 19 of the 33 fossil families are not represented in the living flora. In the list of families above given the ones not italicized are the families not repre- sented at the present time. It will be seen that such important families as the Juglandaceffi, Fagacese, Ulmaceai, Magnoliacea;, Lauracea?, Platanacea?, Anacardiacea?, Celastracefc, Vitacete, Sterculiaceai, Tiliaeea;, Araliacese, Ebenacea;, and Oleacese are not represented in the present flora. In other words, there are no walnuts, beeches, oaks, chestnuts, elms, magnolias, sycamores, simiacs, grapes, lindens, aralias, persimmons, or ashes at the present day. The absence of such important trees and shrubs produces a profound modification of the floral surroundings. The dominant element in the living flora consists of the abundant coniferous forests; yet only 8 species are represented, and of these only 5 are at all common, and 65 per cent of the wliole coniferous growth is made up of 1 species. The fossil flora is represented by 13 species, or nearly twice as many as the living. Among them was a magnificent Sequoia that was closely allied to the living Sequoia sempervirem of the Pacific coast. It had trunks 10 feet in diameter and probably of vast height. There were also 2 well-marked species of Sequoia, known from the leaves, and a number of supposed Sequoia cones. The pines were also abundant, no fewer than 8 species having been detected. The deciduous-leaved trees and shrubs of the Yellowstone National Park are conspicuously few in numbers. There are 2 species of Betula, 2 1 WashiiigtdD, 1886, pp. 1-78. FOSSIL FLORA. 775 of Alims, 7 of Salix. 2 of I'opulus, 1 of Acer, 4 of Vacciniuni, 5 of tlie order Caprifoliacea', 2 of Conuux'a>, 2 of the Koaaceje, etc. Perhaps the most conspicuous tree is the quaking aspen {Populus trenmloides). The Cottonwood (I'.aH(fmtifoUa) is rare, being found only ah)ng Caclie Creek. Several of the willows are abundant, as is also the common birc.li (lirfiila (jlandulom), and the June berry (AiiiclanrJiicr almfolia). The other shruljs are rare, or are confined to few localities. The fossil flora, on the other hand, was especially rich in deciduous leaved vegetation. Thus the Juglandacese was represented by 5 species of Juglans and 4 species of Hicoria (Carya), a number of which were very abundant. The g'enus Populus was especially rich, there being no fewer than 7 species. Certain of these, as Populus speciosa, P. (Japhnogemides, and P. f/landidifcra, were in great aliundance, and the stratum in which they occur consists of a perfect mat of these leaves. Something like 100 examples of 1 s])ecies were obtained. Another striking feature was the presence of numerous magnificent magnolias. Of these, 4 species have been described from the leaves and 1 from the thick petals of the flower. The species described as Magnolia spectaUlis is represented by a great number of leaves in a fine state of preservation. It appears to be more closely related to the living M. gran- dijiora (M. fmtida of later authors) than any one previously described. The sycamores were also an important element in this flora. Of the 2 species described from the leaves and 1 from the wood, the one known as Platanus gmlklmce was especially abundant. It is found in nearly all the Tertiary beds in the Park and is represented in the collections by nearly 200 examples. The species described as Plataninium hagdeni is based upon a trunk or branch 6 inches in diameter. It is most closely related to the living Platanus occidentaUs. Another important group is formed by 4 species of Aralia. Of these, AraUa notata was evidently one of the most abundant and imposing trees of the whole flora. The collections contain over 100 examples, none of which are entire, however, as some of the leaves must have been fully 3 feet in length and more than 2 feet in width. A small leaf and one of medium size are figured on the plates. Aralia tvliitnegi, a species common to the Auriferous gravels of California, had striking 5 to 7 lobed leaves, often 1 foot in length. This species was not so abundant, judging from 776 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. the fossil remains, as the former species, but it was apparently quite widely distril^uted. The other species had smaller 3 or 5 lobed leaves. The family Lauracese was strongly represented by 5 genera, 11 species, and a large number of examples. The genus Laurus, which is now exclu- sively an Old World group, was represented by 6 well-marked species. The genera Malapoenna or Litsea and Cinnamomum, other Old World forms, were both represented, the former by 2 and the latter by 1 species. The genus Persea, an extensive Old World genus, with species also in tropical America and the southern United States, was represented by 1 species, which is closely related to a small tree now living in the South. Another large and important group, now entirely uni'epresented in the Park, is the Fagaceae, embracing- 2 species of Fagus, 1 of Castanea, 1 1 of Quercus, and 1 of Drj^ophyllum. The Fagus here described is a lieautiful, characteristic leaf and was evidently rare, as only a few examples were obtained. The Castanea, on the other hand, was very abundant and widely distributed within the Park. The leaves are large, and as handsome and striking as are the leaves of the living species. The oaks, however, were abundant in species and usually in individuals, and all but 3 proved to be new to science. Perhaps the most marked are Qnercus ycmcei/i, Q. ciili-eri, and Q. (/yossideiitatn. The family UrticacefE, which is represented in the living flora by a single rare herb (XJrtka (fraciUs), was represented during Tertiary times by some 10 species of Ficus and a single more or less doubtful species of Artocarpus. Several of the figures are represented by a large number of specimens — as, for example, Ficus densifoUa — but most of them were rare, at least as evidenced by the fossil remains. It is of great interest to learn, how- ever, that tliev were once present in a region that has long since ceased to support them. The curious leaf referred provisionally to Artocarpus is also of much interest as indicating the possible presence of the bread-fruit trees in this portion of the American Continent. Two unmistakable species of Artocarpus have already been detected, 1 from the Laramie and Denver beds of Colorado, and the other from the Auriferous gravels of California and the Miocene of Oregon. It is therefore not improljable that this t}'pe was in existence in the Yellowstone National Park during the early Tertiary. The family Leguininosa?, now represented b}' a host of small herbaceous plants, was then represented by 3 species of Acacia and 2 of Legu- FOSSIL FLORA. 777 minosites, but the fossil forms are not jjsirticularly satisfactory. The forms rcfcn-ed to Acacia consist of well-defined pods and are somewhat con- ventionally I'eji'arded as representing the modern Acacia. No leaves were obtained that coidd with satisfaction be held as representing- the foliage of these pod-bearing shrubs or trees. The 2 species of Leguminosites are supposed to represent leaflets of some leguminous plant, but beyond this it is not possible to venture. The only remaining group of deciduous-leaved jdants of any magni- tude is tlie Sapindaceai, with 5 species of Sapindus. One of these, Sapiiuhis (ij/ii/is, is perhaps the most abundant form found among the Tertiar}' plants. The small characteristic leaflets are found in the greatest profusion. The other species were less abundant. The other forms that require mention are: Ulmus, 4 species; Acer, at least 2 species; Celasti-us, 3 species, and Rharanus, Paliurus, Zizyphus, Cissus, Pterospermites, Tilia, and Rhus, with a single species each. Tlie vascular cryptogams appear to have been a more prominent feature of the flora during Tertiary times than at present. Of the 2 families present, the Filices and Equisetacese, the former is represented by 10 and the latter by 4 species, while the living flora has but 6 ferns and 4 horse- tails, all rare. The ferns were evidently abundant. They belong to 6 genera, and are represented in several cases by a large number of specimens. The largest genus is Asplenium, with 4 species. The species described as Asplenium magnum is one of the largest and finest forms that has been detected out- . side of the Carboniferous. Asplenium idd'mgsl is also a large, well-marked species. The genus Dryopteris, the old Aspidium, is represented by 2 species, both of which are rather rare. They are, however, botli fruiting, a condition of uncommon occurrence among fossil forms. There is also a beautiful Woodwardia, quite closely allied to a species now living in the eastern United States, and fine examples of the widely distributed climbing fern {Lygodium kaulfusii). The only living North American species (L. pahnatum) is found from Massachusetts and New York south to Kentucky and Florida, and is generally rare throughout its range. The other ferns are an Osmunda and a delicate form referred provisionally to the genus Devallia. The genus Equisetum, although represented by 4 more or less satisfac- 778 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. tory species, was not abundant or particularly important. The most abun- dant form {E. Inif/Kci) is small and has much the appeai'ance of the living' E. Vnuosum. The largest form (E. microclontuni) is very rare. It was al)(»ut 3 cm. in diameter. From A\diat has been presented, it is obvious that the present flora of the Yellowstone National Park has comparatively little relation to the Tertiary flora, and can not be considered as the descendant of it. It is also clear that the climatic conditions must have greatly changed. The Ter- tiary fl(>r;i appears to have originated to the south, while the i)resent flora is evidently of more northern origin. The climate during Tertiary time, as made out by the vegetation, was a temperate or subtemperate one, not unlike that of Virg'inia at the present time, and the presence of the numerous species of Ficus would indicate that it even bordered on subtropical. The condi- tions, however, that permitted the growth of this seemingly subtropical vege- tation may have been ditferent from the conditions now necessary for the growth of these plants. Thus, the genus Dicksonia is at present a tropical or subtropical genus, yet at least 1 species is distributed well into the tem- perate region. If a series of beds should be discovered in which there were a large number of Dicksonias, it might be supposed to indicate tropical or subtroincal conditions; yet, as a matter of fact, these species may at that time all have been so constituted as to grow in a temperate land, and the genus as a whole may have become tropical in recent times. Following out this general line of argument, it may be said that while the Tertiary vegetation of the Yellowstone National Park would, from our present standard, be regarded as indicating a temperate or possibly warmer climate, the actual conditions then prevailing may have been quite different. It is certain, however, that the conditions were very diff'erent from those now j)revailing. Tahl( sliiiiciiHi till' iliftrihiilinii of Ihe Tciliarji phdili of llif YiUoirHlove National Park. 779 s. S^M SO Species. IJistrilmtion in Tin- I'ark. r)istril)iitiipn mitside. Fort Union (Eocene). = i^'S CD J5 o Woodwardia jireareolat:! n. sp .. Aspleniiim indingsi n. sp Aspleninm magnur i n. sp AspK'niam crosum (Lx.) Asplenium remotideiis n. sp Dryopteris wcedii u.sp Dryopteris xantbolitheusis n. sp Devallia ? montana n. sp Lygodium kaiilfusii Heer?* , Osmimda affinis Lx Equisetum liaguei n. sp Eqiiisctum Icsiiuereuxi ii. sp Eqiusetum caualiculatum n. ap... Eqnisptum deciduum n. sp Piuus gracilistrobus u. sp Pinuspremurrayaiia Pinus macrolopis n. sp Pinus sp so Pinus wardii n.sp Pinus iddingai n.}} Taxites olriki Heer Sequoia couttsife Heer Sequoia langsdorfii (Brgt.) Heer.. Sequoia, cones of Phragmites? latissima n. sp Sparganium stygiuni Heer , Cyperacites angustior Al. Br. d Cyperacites giganteus n. sp CyperacJtes sp Cyperacites sp Sniilax laniarensis n. sp Musophyilum complicatnm Lx Juglans ealifornica Lx Juglans rngosa Lx a The numbers refer to tbe beds in wbirb the plants were found. & Cherry Creek, Oregon. I Interraediftte (Miocene). a f^ ai ) W Lamar Flora (Miocene). fes fsS •i|-l ta'r t-' « 3"g-' ^ « * s ta a 12. 13. 4.6,7 X 5,0 6 I 6 1... 15. a < I I c Kare. (i Miocene; Elk Creek; Lx. 780 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table showhif/ the dislrihiition of the Tertiary plants of the Yellowstone National Park — Continued. Species. Distributiou in the Park. Fort T'niim (Eocene). III . =- i -J^ ^ ; o I > 0) , O a o!p P.: « SS 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. ^5. 56. 57. 58. 59. 60. 61. 02. 63. 04. 65. 66. 67. 68. •I X Juglana schimperi Lx Jny,laus LuiriloUa n.sp — Juglaus cresceuti.i ii. sp . - . Hiroria antiquii (Newby.) . Hicoria eresoeutia ii. sp — Hicona culveri n. sj) ^ly rica scottii Lx ' X Myrica wardii n. sp -- — Myrica lamareusis n.sp ' — Populus glandalifera Heer X Populus speciosa ^'avd X TopuUis xautliolitbensie n.sp X Populus dapbnogenoides "Ward, .i X Populus balsamoidesGiippt -- Populus .' vivaria n.sp Salix varians Heer Salix angusta Al. Br Salix lavateri Heer Salix elongata? O. Web Betula iddiijgsi n..sp Corylus macquarryi Heer , Fagus antipolii Heer Fagus undulatan. sp Castanea pulebella n. sp Quereua grosideutata n.sp Quercus consirailis ? Xewby . . . Quereus.' niaguifolia n. sp Quercus furcinervis araericana Quercus Tveedii n. sp Quercus sp Quercus olafseni Heer QuercuB yam-eyi n. 3p Quercus culveri n. sp Quercus heaperia 11. ap a The number.^ refer to the beds in wbich tbi^ plants were found. oi n ff fl CS t>^ O § ^ y c >^ •^ dO ^ o a o M O Ph 1 Intermediate (Miocene). .: p^ 3) o i^" o ^ T t4 -« O ;ph H ifc< w i ta 4. I s. Lamar Flora (Miocene). 11. L. S. X M.S. X 5 M.S.6 13. ■Distribution out.side. 'X! X? 16. £ a 17. 18. X X X? X? X x» . X b Mioi-eiie of Alaska. FOSSIL FLORA. Jgl Table ahqii-imj the dintrihiition of the rirtiuiy ptanta of the yellowntom: yutiomil /'aii— Continued. Distribution In the Park. Fort UiiiiUl (Koceiit;). Species. Dryopliyllum longipetiolatum n. sp 70. 71. 72. 73. 74, 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. Ulmua pseudo-iulva .' Lx . . . TJlmus minima ? "Ward Ulnius rljamnifolia.' Ward . I'lniits, fruits of Planera longifolia Lx ITii'us di'iormata n. sp Ficusungeri Lx Ficns sp Ficiis shastensis ? Lx Ficus sordida Lx ■..., Ficus densi folia n. .sj) Ficus liaguei u. sp -.5 -=8 s g II Intcrni(>diatu (Miocene). ^ O -? 3 1. 2. 3 O ,&< Lamar Flora (Miocene). 6. 7. 8. X Ficus tiliiFfolia? Al. Br Ficus asiminitfolia Lx Artocarpus.' quercoidos u. sp. ilagiiolia califoriiica Lx 86. Magnolia spoctabilis n. sp 87. Magnolia micropliyila n. sp ... 88. Magnolia culveri u. sp 89. Magnolia? poUardin.sp 90. Laurus priraigenia .' I'ng 91. Laurus perdita u. sp 92. Laurus montana n. sp 93. Laurus priiiceits Heer 94. LauruB californica Lx 95. Laurus grandis Lx 06. Persea pseudo-carolinensis Lx 97. Malapoenna lamarensisn. sp.. 98. Malapoonna cuneatau.sp 99. Cinnanionium spectabilia Heer 100. Platanus guillelmai Gopp , a Tlu> numbers refer to the beds in J ifeO S2 4^ O Distribution outside. M.S. X M.S. 3 3 3,5,6 3,5,7 ,v? 1.5,6,7 X which tlic plants were found IG. 17 18. X ? D. L. X I 782 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Table showiiiii the disiribiition of the Tertiai-y plants of the Yelloivstoiie Xational ParA'— Continued. Species. 101 102. 103. 104. 105. 106. 107. 108. 100. 110. 111. 112. 113. 114. 115. ]'6. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. Platanus nioutana u. sp Acacia macroapernia li. 8p Acacia lamareusis n. ap Acacia -n^ardii u. sp '.-. Legnmiii()3ite.s cassioides Lx... Lt'guminoaiteslamareusisu. sp. Kbiis mixta ?Lx Distribution in thi* I'ark. Fort T'uion (Eocene). ^ o ^^ "e S £ o S^ - ,; a? M .- c- ^ >H 1'^ im a s 5 o 9 2 S 5 K 00 ' ft Celastru3 cnlveri ii. sp Celastrus injequalis ii. sp Celasti'iis ellipticus u. sp E1,T 0(1 end roil poly morpli urn AVard , Acer vivariniii u. sp Acer, fruit of j Sapindus afiinis Xewby Sapiudus alatus.' Ward Sapiudiis grandifoliolns \^iard6. Sapiudus graiidifolioloides n. ap. Sapindiis vanlii u. sp , Kharanus reetiner\ is Lx Paliurus colouibi Heer Zizyphus serrulatus Ward Cissus hagiiei n. sp Pterospermites hagnei n. sp Credueria .' pachyphylla n. sp Tilia popnlifolia Lx Grewiopsis? aldersoni n. sp Aralia wrightii u. sp.. Aralia notata Lx Aralia serrulatan. sp Aralia wliitueyi Lx Aralia sp Conius newberryi Holliclv Cornus wrightii d. sp a The numbers reler to tiie beds in wliich the plants were found. Intermediate (Miocene). K W 8. 9. .. Lar.iar Flora (Miocene). Distribution outside. -4^ • . • !S to I 2 rS^S 'ts 5 -^.S § ■a -^ ■= Sura ^ p=( :5 5 3,7 M.S.X 13. 14. > 3 S 1 16. ,17. 18. X D.L X h Also ou the Thumlerer. FOSSIL FLORA. 783 Table b/ioici'ii;/ thr tlUtiibittion of tin: Terl'uirn jilaiitu of the Yilluiixtoiic National Park — Cuutiuued. MK Distributiui iu the V ark. Distributiou outside. Fort I'nio K-eut')- Iiitenui'diato (Mioceue). Lamar Flora (Miocene). til a 1 o c '> O g 1 Species. o s « ® = c c c = C ■S O «! - = £ c 1 3. 03 r s CS t- 2 1 o 4. § c 6 u o 03 lU 1 1 S t-i .2 a:* o o >s p V. es o 11 g O 1 a £ 1 O 1 o c_ o j 5 o 1 s c 09 £ o •3 5 ti a ii |l En o ^ Si o 1 3 1 O - * n P. i to n o '3 1 a 3 g s a O ,5 '5 'Z > to 1 1. 2. 5. G. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. i 18. X . _ 4 X! X? X? X -> 1 138. Ffiisiuus wri"htii n. sp X 139. Pbyllites craasitblia n. sp X X X V i 142. Sequoia magnitica u.ey.h 1 X X 145. Lauriiioxylou pulcbellum u. ap.. X 146. Perseosylim aroinaticum Felix. ::::.;;;:: 148, Rhamnacinium radiatuui Felix . 149. Quercinium laniarense ii. sp 1 150. Quercinium kuowltoni Felix X? aThu numbers refer lo the beds iu which the plants were fouud. b Up Cache Creek. GEOLOGICAIi COXSIDKRATIOX OF THE TERTIARY FEORA. Naturally the geological aspects of this fossil flora are considered as of paramount importance, for it was to ascertain the liearing of the plants on the question of geological age that this investigation was undertaken. As I have already pointed out under the section devoted to the biological asjjects of the flora (p. 775), a A'ery large jjroportion of the plants were found to be iiew to science, and therefore could have onlj' limited value in determining the age, but enough previously described forms were lecog- uized to warrant certain deductions. It is the purpose to set these con- clusions forth in this section. 784 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Tlie first plants brouglit back from this portion of the YelloAvstore National Park by the early Hayden survey parties were submitted to Prof. Leo Lesquereux, and although few in number the specimens and species were nevertheless sufficient to afford some indication of their age. Pro- fessor Lesquereux regarded the plants from Elk Creek and vicinity as indicating an Eocene age, and those from the well-known Fossil Forest on the west side of the Lamar Valley as closely allied to those of the Aurif- erous gravels of California. It is a pleasure to state that this adumbration has been abundantly confirmed by the results of more searching study of a larger amount of material, but at the time this was outlined the facts were so few that the suggestions were not regarded as conclusions, and as it was before any careful detailed geological work had been done, these now clearly defined horizons came to be grouped together under the somewhat non- committal term Volcanic Tertiary. Although the geology of the region has been fully discussed by Mr. Arnold Hague in Part I of this monograph, it seems necessary, for the satis- factory understanding of the problems requiring solution, to set forth briefly the geological features characterizing this portion of the Park which have a direct bearing upon the remarkable flora found. In the first place, all the material constituting the beds in which the Tertiary plants are embedded is of volcanic origin. According to the geol- ogists, this material may be divided into two distinct periods of volcanic eruption, which may be distinguished by their mineral composition. The older series of these la^'as has been designated as the early acid breccias and flows, and the younger as the early basic breccias and flows. Both these series of rocks carry plant remains. In general the matrix in which the plants are preserved is a fine-grained ash, probably deposited as a mud flow, with all the appearance of stratification and other indications of water-laid deposits. Occasionally the material is much coarser and has the appearance of breccias mixed with fine sediments. The acid rocks are usually light in color — yellow, lavender, or gray — while the basic rocks, which carry more iron, are darker in color — frequently some shade of green or dark brown, passing over into black. In some instances, as might be expected with fine water-laid beds, the deposits in both series of lavas closely resemble one another, while the great mass of lava of the two bodies may be readily distinguished. The acid breccias, the oldest of the FOSSIL FLORA. 785 lava flows, rest in many places upon the upturned eflj^es of Arcliean and Paleozoic locks. In most instances the basic breccias either rest directly upon the acid rocks or else the underlying rocks are not exposed. The acid breccias are found on both banks of tlie Yellowstone River near the mouth of Elk Creek, and near the junction of the Yellowstone River with Hellroaring- Creek, as well as on Crescent Hill and near the head of 'l\)wer C^reek. In the neighborhood of Lost Creek, and on the northern end of S]iecinien Ridge, along the drainage of Crystal Creek, the basic breccias are known to lie directly upon the acid breccias. In these localities the floj-a has a character distinctly its own, and bears evidence of being younger than the flora from the acid breccias. The basic series of rocks is typified at the Fossil Forest, and also at the cliff a. short distance to the south and east of the Fossil Forest. They occur also on the east bank of Lamar River, between Cache and Calfee creeks. All of these localities are char- acterized by their plant remains, and the following determinations of age are fully wan-anted. The table of distribution of Tertiary plants in the Yellowstone National Park has been prepared for the pmpose of showing in a graphic manner the distribution of the various plants within the limits of the Park and the affinities of those having an outside distribution. From this it appears that the Tertiary flora consists of 150 more or less satisfactory species. Of this number, 81 species, or over 50 per cent, are here described for the first time. New species can not, of course, have the value in determining age that previously described forms have, but when their general facies as well as close affinities are taken into account, they also become of positive value. On eliminating the 81 new species, together with 8 forms not specifically named, there remain 61 species upon which we must depend in the deter- mination of the ages of the various strata in which they are contained. A further examination of the table brings out the fact that this flora may be naturally divided into 3 more or less distinct subfloras or stages. These three divisions are the older or acid series, the intermediate series, and the basic or younger series. The first division (acid) has a flora of 79 species; the second (intermediate) a flora of 30 species, and the third (basic) a flora of 70 species. It further appears that 23 species or forms are common to two or more of the divisions. MON XXXII, PT II 50 78(5 GEOLOGY OF THE YELL0WST02TE KATIO:jfAL PARK. The floi'a of the older or acid series will be first considered. Of the 79 species, 42 are either new to science or not specifically named, leaving 37 species having a distribution beyond the limits of the Park. Following is a list of these species: Aspleuium erosum (Lx.). Uliiius rbauinifolia Ward, Lygodiuiii kaulfusii (Heer). Ficus uugeri Lx. Taxites olriki Heer. Ficus asiminrefolia Lx. Sequoia couttsite Heer. Laurus primigenia ? Uiig. Sequoia laiigsdorfii (Brgt.) Heer. Laurus priuceps Lx. Sparganium stygium Heer. Laurus californica Lx. Cyperat'ites angustior AI. Bi-. Laurus grandis Lx. Musopbyllura tomplicatum Lx. Ciunamoinuin spectabilis Heer. Juglans rugosa Lx. Plataiius guilleliuiii Gopp. Juglans schimperi Lx. Legnminosites cassioides Lx. Myiica scottii Lx. Sapiudus aflim's Lx. Populus glandulifera Heer. Sapiudus alatus Ward. Populus speciosa Ward. Sapiudus grandifolius Ward. I'opulus dapbnogeuoides Ward. I'aliurus colouibi Heer. Salix lavateri Heer. Zizypbus serrulatus Ward. Fagus autipofii Heer. Tilia populifolia Lx. Quercus consimilis Newby. Aralia notata Lx. Quercus olafseni Heer. Cornus uewberryi Rollick. These 37 species have the following distribution: Five are found in the coal-bearing Laramie, 5 in the Denver and Livingston, 17, or nearly 50 per cent, in the Fort Union, 9 in the Green River group, and 11 in the Aurifer- ous gravels of California. Of the species common to the acid rocks and the Laramie at Denver and Livingston beds, not one is found exclusively in these beds, but they are such species as Sequoia langsdorfii, Juglans rugosa, Platanus guillelmce, and Juglans schimperi, which enjoy a wide geological and geographical distribution. The Fort Union element in this flora is a very important one ; in fact, it may be called the dominant element. It includes at least 12 species that have never before been found outside of the type locality. Among these are Sparganium stygium, Populus speciosa, Populus daphnogenoides, Uhnus minima, Ulmus rhamnifolia, Sapiudus affinis, Sapindus grandifoliolus, and Cornus newberryi. Some of these are represented by as many as 200 indi- viduals, showing that they existed in great abundance, as they are also known to have existed at the mouth of the Yellowstone. This abundance FOSSIL FLORA. 787 also makes their determination certain. Several other species, having a wider distribution, are very abundant in these beds, such as Aralia notafci, which is represented by more than 100 specimens, and Sequoia lanf/sdorjii, which has a wide distribution, but is most abundant in this country in the Fort Union beds. Sequoia couttsice, having a somewhat wide range, is also very abundant in the beds under consideration and the Fort Union. Besides these are a number of species that can not be mistaken, as Zizyphus serrulatus, Taxites olriki, etc. One species, Asplenhim erosum, has been found in both Lai-araie and Denver strata in Colorado. It is represented by only 2 or 3 small and more or less doubtful examples from the Yellowstone below Elk Creek. JiKjhms rugosa is a species of wide distribution and therefore of compara- tively little value stratigraphically. It is found from the Laramie to the Miocene, but is rare in the acid beds within the Park. Quercus olafseni has been found in the Laramie, but its determination in the Park depends on a single doubtful fragment from the vicinity of Elk Creek. The species that have also been found in the Green River beds are comparatively unimportant. Lygodium kaulfusii is, in this country, a typical Green River species. It is rare in the acid series, but abundant in the basic series along the Lamar River. Musophyllum complicatwn has never before been reported outside of the Green River beds. Fkus ungeri and Tilia 2>o])uUfolia are typical Green River plants, but are represented here by one or two examples each. The species found in the Auriferous gravels are the only ones remaining to be considered. Of the 11 species, Juglans rugosa, Quercus hreweri, Salix lavateri, and Quercus olafseni are open to doubt, as they are represented by- only one or two fragments each. Ficus asimin'KpfoUa likewise depends upon a single leaf, but it is a well-preserved one, and the determination is probably correct. Aralia notata, another of the species, is very rare, if really found at all, in the Auriferous gi-avels. The three remaining species are rela- tively abundant, and there is little question as to the correctness of their determination. The species whose distribution lies beyond the limits of the Park having been passed in review, it will be of interest to note the obvious affinities of certain of the more important new forms. Thus, Asplenium remotidens is closely related to A. erosum^ and Dryopteris weedii and D. xantho- 788 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. Utliensis to Lastrea goMlanum, both of wliicli are abundant in the Denver beds of Colorado. Juglans crescentia is related to J. nigella, as identified by Professor Ward in the Fort Union group. The beautiful new Populus xanthoUthensis is very close to P. genatrix of Newberry, from the Fort Union group. Betula iddingsi is obviously related to B. prisca; Quercus yanceyi to Q. laimfolia; Platanus montana to P. raynoldsii; Celastrus ctdveri to C. ovatns and C. curvinervis ; and Sapindus grandifolioloides to S. grandi- foUohis, all of the Foi-t Union group. From this evidence it appears that the flora of the eai-ly acid breccias in the Yellowstone National Park finds its closest affinity with the flora of the Fort Union group, and it is unhesitatingly referred to that age. The relation of this flora to that of the Laramie is unimportant, being confined to less than half a dozen species. Its relationship to the Denver and Green River floras is naturally closer, but it forms only a small element of these, as also with the flora of the Auriferous gravels of California. The relation, as based on total number of species, is unimportant, but in the upper beds it beffins to show a transition. It will be next in order to consider the intermediate flora. As already stated, this embraces 30 species, of which number 16 are confined to these beds and 14 are distributed outside, either in the acid or basic series or beyond the limits of the Park. A further analysis brings ovit the fact that of the 16 species peculiar to these beds 13 are regarded as being new to science, and of the 14 species found beyond the limits of these beds 5 are new to science. This makes a total of 18 species that are regarded as new, leaving 12 species having a distribution without the Park. Following is a complete list of these 12 species: Osmunda afifinis Lx. Laiirus grandis Lx. Sequoia langsdorfli (Brgt.) Heer. Platanus guillelmse Gopp. Juglans rugosa Lx. Elseodeudron polymorpbum Ward. Ulmus minima Ward. Sapindus affinis Lx, Ficus tilijefolia Al. Br. Aralia notata Lx. Laurus californica Lx. Aralia wbitneyi Lx. Four of the species above enumerated (Sequoia langsdorjii, Juglans rugosa, Platanus guillelmce, and Aralia notata) have a wide distribution, being found from the Laramie to -the Upper Miocene, and are therefore of com- paratively little value. One" of the remaining (Osmunda affinis) is found in FOSSIL FLORA. 739 the Denver beds; 3 are confined to the Fort Union, and 6 species are found in the Auriferous gravels of CaHfornia. Of the 5 new species found in other beds, 2 are common to the ohler or acid series and 3 to the younger or basic series. It therefore becomes apparent that this flora, although reasonably distinct, finds its greatest affinity with the younger or basic series. This is shown by the species connnon to the intermediate series and the Auriferous gravels and by the new species connnon to the basic series. This is not especially pronounced, and could hardly be made out for the intermediate flora as a whole, were it not for certain species that come from rocks that are directly succeeded by the basic rocks. For these reasons it was at first supposed that a part of the localities represented belonged to the lower and a part to the upper beds, but by combining several of these this intermediate flora was worked out. But, as stated above, the rocks of this series that are known to be the lowest bear a flora nearest to that of the acid rocks, and the rocks known to be higher hold plants most neariy related to those of the upper or younger beds. It now remains to consider the flora of the basic breccias and its relationships. The typical locality for this flora is the Fossil Forest and vicinity, including the locality on the east side of the Lamar River, between Cache and Calfee creeks. This flora, as a whole, embraces 70 species or forms, distributed as follows: 38 species new to science, 3 forms not spe- cifically named, and 29 species having a distribution beyond the limits of the Park. Following is a list of the species having an outside distribution: Lygodium kaulfusii Heer. Ficus sordida Lx. Sequoia langsdorfli (Brgt.) Heer. Ficus asiminiefolia Lx. Juglans californica Lx. Magnolia calif.irnica Lx. Juglans rugosa Lx. Laurus californica Lx. Hicoriaantiqua(Newby.)Kn. Laurus primigenia? Ung. Populus balsamoides Gopp. Laurus grandis Lx. Saiix variaus Heer. ' Persca pseudo-carolinensis Lx. ; Sahx angusta Al. Br. Platanus guillelma3 Gopp. Sahx elongata Heer. ruus mixta Lx. Corylus macquarryi (Forbes) Heer. EL-eodendron polymorphum Ward. Quercus furciuervis americaua Kn. Sapiudus graudifolius Ward. Ulmus pseudo-fulva Lx. Ehamnus rectinervis Lx. Planera lougifolia Lx. Aralia notata Lx. Ficus shastensis ? Lx. Aralia whitneyi Lx. 790 GEOLOGY OF THE YELLOWSTONE NATTONAL PARK. Of these 29 species, only 4 have been found in the true Laramie. These ^re Juglans rugosa, Flatanas guillelmcB, Bhamnus redinervis, and Diospyros brachysepala, the last open to doubt. All of these species have a wide ver- tical range and are consequently of little value in indicating age. The affinities of this flora with that of the Laramie may therefore be regarded as unimportant. The relationship of this flora with the Fort Union, Denver, and Green River groups is also relatively unimportant. There are 7 species found in each of these groups, but none are confined to the Denver, and only 1 to the Green River, and 3 to the Fort Union. The rest are of wide geograph- ical and geological distribution. The relationship of the flora of the basic rocks is clearly with that of the Auriferous gravels of California, for no fewer than 17 of the 29 species are common to the two localities, and 12 of the s^jecies are exclusively con- fined to them. These are such important species as Aralia tvMtneyi, Persea pseudo-car olinensis, Laurus californica, Laurus grandis, Magnolia californica, Ficm sordida, Juglans californica, Rhus mixta, etc. Most of these are present in numbers in the Park flora, and there can therefore be no question as to the correctness of their identification. Besides the species above enumerated that have actually been found common to the two localities, the numerous new species are in many cases unmistakably related to species known only from the Auriferous gravels. Thus, Magnolia culveri is close to M. californica, and Magnolia spectabilis is so close to M. lanceolata that Lesquereux so identified it. Other examples might be given, but they are unnecessary. The preponderance of evidence points to the similarity of age between the flora of the basic series and that of the Auriferous gravels of California. The fixing of the exact age of the Auriferous gravels is not a difficult matter. They were at first supposed to be Lower Pliocene in age, but the latest evidence, derived from a more or less complete restudy of the abundant flora, together with a thorough investiga- tion of the stratigraphy, makes it reasonabl}^ certain that it is really Upper Miocene. This is the view taken in the present instance, and this flora in the Yellowstone National Pai-k is referred to the Upper Miocene: Asplenium idclingsii n. sp. Magnolia? pollardi u. sp. Lygodium kaulfusii. Laurus primigenia? Ung. Equisetum caualiculatum n. sp. Laurus californica Lx. FOSSIL FLORA. 791 Equisetum ilecidmini n. sj). Sequoia laugsdorUi (Bigt.) Ueer. Juglans rugosa Lx. Juglans crescentia n. sp. Castanea pulcbella n. sp. Ficiis clensifolia u. sp. Ficus asimiuffifolia Lx. Laurus gI•andi^s Lx. Litsea lamarensis n. sp. Platanus guillelma; Giipp. ELTodeudron polymorphum Ward. Sapiiidus graiidifoliolus Ward. Sapindus wardii n. sp. Aralia notata Lx. Some of these species, as Lygodium kaulfusii, Castanea pulchella, Laurus grandis, Platanus guillelmce, Sapindus grandifoUolus, and Aralia notata, are important well-marked species that have weight in showing the close relationships between the floras of the two series; but, on the other hand, the perfect distinctness of the beds is shown by the fact that there are some 40 species that are confined to each horizon. It will not, therefore, be difficult in future to determine the horizons of the various plant-bearing beds within the Yellowstone National Park. In order to show how remarkably distinct these three floras are, it will be necessary only to consider the species in common between them. As already stated, only 23 forms out of the total of 147 forms are common to two or more of the series of beds. It will not be necessary to present a complete list of these species in common. The numerical results show that 8 forms only are common to the three beds, 2 to the acid and intermediate, and 3 to the intermediate and basic, and, finally, that 10 are common to the acid and basic. When these facts are presented in connection with the total flora of each series, the diff"erences become even more marked. Thus, the lower or acid series, with a flora of 79 species, has only 20 species common to the others. Of these, 8 are common to all three beds, 2 to it and the interme- diate beds, and 10 to it and the upper or basic beds. The intermediate beds, with a flora of 30 species, have 13 species in common with the others. Of these, 8, as above stated, are common to all three, 2 to intermediate and acid, and 3 to intermediate and basic. The basic or j^ounger beds, with a flora of 70 species, have 20 species common to the others. Of these, it is hardly necessary to repeat, 8 are common to all three, 3 to it and interme- diate, and 10 to it and acid. These 3 floras are, therefore, shown to be markedly distinct, and it will not be difficult to distinguish them in future. PLATE LXXVII. 793 PLATE LXXVTI. Page. Figs. 1, 2. Asple.vium haguei u. sp. Wolverine Creek 655 3, 4. Trapa ? MiCROPH YLLA Lx. Wolverine Creek 661 5. Sequoia LANGSDORFii? (Brgt.) Heer. Wolverine Creek 657 6. QUERCUS ELLisiANA Lx. Mount Everts 659 7-9. Paliurus minimus n. sp. Wolverine Creek 659 10. Viburnum ROTUNDIFOLIUM Lx. Wolverine Creek 662 11-15. Onoclea MiNi.MA u. sp. Wolverine Creek 656 794 U. 8. 0£OUXUGAL SURVEY MONOORAPri XXXII PART II PL. LXXVII - ■••« ^ 1 i 1 1 1 ! ..1 1 ,-. 1, ' ■ 1 \ ■■ J \ LARAMIE FORMATION. PLATE LXXVIII. 795 PLATE LXXVTII. Pajie. Fig. 1. DoMBEYOPSis PLATANOiDE.s Lx. ilouut Evcrts 661 2. ViBUKN'UM ROTUNDIFOLIUM Lx. Wolverine Creek 662 3. Paliurus zizYPHOiDEs? Lx. Wolverine- Creek 660 4. Myrica bolanderi? Lx. Mount Everts 658 5. Phragmites falcata n. sp. Mouut Everts - 658 6. Fraxinus DENTICULATA Lx. Mouut Everts 662 7. Phyllites sp. Mount Everts 662 8,9. Viburnum rotundifolium Lx. Wolverine Creek 662 796 U. 8. OEOLOOICAL SURVEY MONOORAPH XXXII PART II PL. LXXVIIt LARAMIE FORMATION. PLATE LXXTX. 797 PLATE LXXIX. Page. Fia. 1. WoomvARDiA PHEAREOLATA n.sp. Crescent Hill 665 2,3. Asi'LENiUM IDDINGSI D.sp. Yellowstone River below Elk Creek 666 4. Devallia? MONTANA u.sp. Fossil Forest 671 5-8. ASPLENIUM MAGNUM 11. sp. Yellowstone River below Elk Creek 667 8a. Eularged piumiles of tig. 8 667 798 U. 8. OEOLOGICAC SURVEY HONOORAPM XXXII PART M PL. LXXIX PLATE LXXX. 799 PLATE LXXX. Page. Figs. 1,2. Lygoditm kailfusii Heer. I.amav Kiver 672 3. Lygodilm kaulfusii, fruit. Lamar Kiver 672 4,5. OsMUNDA AFFiNis Lx. Hill above Lost Creek 673 6. AsPLENiUM EROSUM? (Lx.) Kn. Yellowstone River below Elk Creek 668 7. Asi'LEXiUM RE.MOTIDENS n. sp. Yellowstone River below Elk Creek 669 8. Dryopteris WEEDii n. sp. Yellowstone River below Elk Creek 669 9,10. ASPLENIUM iDDiNGSin. sp. Yellowstoiie Rlver below Elk Creek 666 11. Pixus MACROLEPis n. sp. Fossil Forest 679 12. PiNUS GRACILISTROBUS n. sp. Fossil Forest 676 800 U. 8. OEOLOUICAL SURVCV MONOOKAPH xxxri PAHr II PL. LXXX TERTIARY. PLATE LXXXI. 801 MON XXXII, PX II 51 PLATE LXXXI. Page. I'lG. 1. DiiYOi'TERis ZANTiiOLiTUENSi; n. sp. Fossil Forest 671 2. Dryopteris webdii n. sp. Yellowstone Kiver lielow Elk Creek 669 3, 4. Eqiisetum haguei ii. sp. Hill above Lost Creek 674 5. Equisetum deciduum 11. sp. Yellowstone Kiver below Elk Creek 676 0. Equisetum caxaliculatum ii. sp. Yanceys Fossil Forest 675 7. Equisetum canaliculatum u. sji. Specimen Riclse 675 8. Sequoia sp. Fo.ssil Forest 683 9. Magnolia? POLLARDi n.sp. Fossil Forest Ridge 721 10. Magnolia? POLLARDi n. sp. Yellowstone Elver below Elk Creek 721 802 U. a. GEOLOGICAL SURVEY MONOCRAPH XXXIl PART II FL. LXXXI ,T- ^ r / , \ '^ i"~% 10 TERTIARY. PLATE LXXXII. 803 PLATE LX XXII Page. Fig. 1. Taxiths oi.riki Heer 680 2. Sequoia LAXGSDORrii (Brgt.) Heer 682 3. Taxites olriki? Hoer 680 4. Taxites olri ki Heer. Yellowstone River below Elk Creek 680 5. PiNUS PREMOKRAYANA 11. sp. East of Yellowstone Lake 677 6, 7. Sequoia sp. Fossil Forest 683 8,9. PiNUS IDDINGSI u. sp. West of Duuraven 680 10. Cypebacites GiGANTEUS n. sp. Yellowstone Eiver bclow Elk Creek 684 804 U. 9. CEOLOOICAL SURVEV MONOGRAPH XXXII PAHT » PL. LXXXII PLATE LXXXIII. 805 PLATE L XX XII I. Page. Fig. 1. MusopnYLLUM complicatum Lx. Crescent Hill 686 2,3. JUGLANs LAURIFOLIA n. sp. Vanceys Fossll Fotest 688 4. Cyperacites sp. Fossil Forest 684 5. Phragmites? LATissiMA n. sp. Crescent Hill 683 6. Cyperacite.s? sp. Crescent Hill 6S5 7. HicoRiA cuLVERi u. sp. YellowBtone Eiver below Elk Creek 691 806 U. 8. OEOLOGICAL 8URVEV MONOGRAPH Xxxll PAHT II PL. LXXXIK ">, K n 'S I ::l ' < 3 TERTIARY. PLATE LXXXIV. 807 PLATE LXXXIV. Page. Fiu. 1. PopuLUS GLANDTiLiFEHA Heer. Yellowstone River bplow Elk Creek 694 2. PoPULUs DAPHNOGENOIDES Ward. Yellowstone River below Elk Creek 69n 3. PoPULUS SPECiosA Ward. Yellowstone River below Elk Creek 694 4. Myrica WARDii u. sp. Fossil Forest 692 5. Myhica lamarensis u. sp. Lamar River 693 6. Myrica scottii Lx. Yellowstone River below Elk Creek 692 7. HicoRiA CRESCENTIA n. sp. Crescent Hill 690 8. JuGLANs CRESCENTIA D. sp. Crescent Hill 689 U. S. GEOLOGICAL SURVEY MONOGRAPH XXXII PART II PL. LXXXIV TERTIARY. PLATE LXXXV. 809 PLATE LXXXV. Page. Figs. 1,2. Popuu-s xamtholithensis ii. sp. Yellowstoue River below Elk Creek 695 3. Salix variaxs Heer. Lamar River 697 i, 5. Fagi'.s UNDULATA u. sp. Yellowstone River below Elk Creek 700 810 U. 8. oeOLOaiCAL 6URVEY MONOGHAHM XXXH PART II PL. LXXXV TERTIARY. PLATE LXXXVI. 811 PLATE LXXXVI. Page. Fig. 1. PoPULUs liALSAMOiDES? Gtipp. Fossil Forest 696 2. PopULUsf VIVARIA u. sp. Fossil Forest 696 3. CORYLUS MACQUARRYi Heer. Fossil Forest 699 4,5. Betula iDDiNGsi n. sp. Yellowstone River below Elk Creek 698 6-8. Castanea rui.CHELLA n. sp. Fossil Forest 702 812 U. 6. OEOLOOtCAL SuRVCY MONOGRAPH XXAII PART I) I'L. LXXXVl TERTIARY, PLATE LXXXYII. 813 PLATE LXXXVII. Page. Figs. 1-3. Cast.\nea puixhell.v u. sj). Fossil Forest 702 4. QuiiKcrs WEEDii u. sp. Fossil Forest 705 5. QuERcrs CULVERI n. sp. Yello-nstoue River l)elow Elk Creek 708 6. QuERCls coxsiMiLis? Newby. Yello-n-stone River below Elk Creek 704 7. QuERCUS GHOSSIUENTATA n. sp. Fossil Forest - 704 814 0. «. GEOLOGICAL SURVEY MONOGRAPH XXXII PM-T It PL. LXXXVtl PLATE LXXXVIII. 815 PLATE LXXXVIII. Page. Fig. 1. QUERCUS? magnifolia n. sp. Yellowstone Rivur below Elk Creek 70-1 2. Ulmus PSEUDO-FULVA? Lx. Laiuiir River 711 3,4. Ulmus, KUUITS. Yellowstone River below Elk Creek 712 5. QUERCUS FURCiNERVis AMKRiCAXA Kn. Fossil Fovest 705 6, 7. DRYOPH YLLUM LONGIPETIOLATUM U. sp 710 816 U. S. OfOLOOtCAL 8URVCV MONOGRAPH XXXII PAHT tl PL. LXXXVIII PLATE LXXXIX. 817 MON XXXII, PT II 52 PLATE LXXXIX Page. FlO. 1. FiCUS DEXSIFOLIA n. sp 714 2. QuERCUS YANL'Evi u. sp. Yunceys Fossil Forest 707 3. Ficus sp. Yellowstone Eiver below Elk Creek 713 4. Leguminosites lesqleiuexiana Kn. Crescent Hill 730 5,6. Legumixosites i.amakensis n. sp. Lamar Eiver 731 7. Quehcvs sp. Yellowstone River below Elk Creek 707 818 U, 0. UEOkOaiCAL SURREY MONOailAPH XXXK PAFIT II PL. LXXXIX TERTIARY. PLATE XC. 819 PLATE XC. Page. Figs. 1,2. Ficus densifolia n. sp 7U 3. Ficus haguei n. sp. Fossil Forest lio 4. Fraxinus WRiGHTii n. sp 753 820 U. 6, OeOLOlilCAL SURVEY MONOGRAPH XXXII PART PI PL. XC TERTIARY. PLATE XCI. 821 PLATE XCI. Fig. 1. Ficus densifoi.ia u. sp 714 2. Ficus deformata n. sp. Yellowstone River below Elk Creek 712 3. Ficus ungeri Lx. Yellowstone River below Elk Creek 713 4,5. Laueus primigenia? Ung 722 822 u. 9. oEOLooicA. suflvev MONOGHAPH XXXII PA.IT II PL. XCI PLATE XCII. 823 PLATE XCII. Page. Fig. 1. Artocarpus? quercoides n. sp. Yellowstone. River Vielow Elk Creek 716 2-4. Malapoenna cuneata n. sp ''^t! 5. Magnolia culvbri u. sp. Lamar River ^... "20 824 U. 8. QEOLOGICAL SUhVCV MONOQRAPH XXXII PART II PL, XCII TERTIARY. PLATE XCIII. 825 PLATE XCIII. P«ge. Figs. 1,2. Magnolia spectabilis n. sp. Fossil Forest 718 3. LAunus GRAXDis Lx. .Specimen Ridge 725 4,5. Malapoenn'a LAMAREXSis n. sp. Lamar Eiver 726 826 U. S. GEOLOGICAL SURVEY MONOuHAPM XXXM PAHf II PL. XCIII PLATE XCIV. 827 PLATE XCIV. Figs. 1-6. Laurus perdita n. sp. Near Yaneeys Fossil Forest 723 6. ClNNAMOMUM SPECTABILE Heer. Tower Creek 727 828 u. 8. aeoLObicAL sunvEv MONOGRAPH XXXtl PAHT U PL. XCIV PLATE XCV. 829 PLATE XCV. Page. Fig. 1. LAunus GRANDis Lx. Specimen Ridge 725 2. Laurus MONTANA n. sj). Yellowstone River below Elk Creek 724 3. Laurus puinceps Heer. Yellowstone River below Elk Creek 725 4. PeRSEA rSEUDO-CAROLINEXSIS Lx 725 5,6. DiosPYRos LAMARENSIS n. sp. Specimen Ridge 751 830 U. 0. OeOkOCICAL fURVEV MONOGRAPH XXXII PADT H PC. KCV TERTIARY, PLATE XCVI 831 PLATE XCVI. Page. Fig. 1. Platanus guillelm^ Gopp. Fossil Forest 727 2,3. Platanus MONTANA n. sp. Hill above Lost Creek 728 4. DiosPYROS LAMARENsis D. sp. Lamar River 751 5. Malapoknna LA.MARENSIS u. sp. Lamar Kiver .• 726 832 U. 6. OCOLOaiCAL SURVEV MONOf^flAPH XXXII PART II PL. XCVl PLATE XCVII. MON XXXII, PT II .J3 833 PLATE XCVII. Page. Fig. 1. El.eodendron roLYMOUPiiUM AVanl. Yancey Fossil Forest 734 2. Arctostaphylos elliptica u. sp. Yellowstoue River beli)W Elk Creek 750 3. Celastrus ELLiPTicus 11. 8p. Yellowstone River below Elk Creek 734 4. Celastrus culveri n. ap. Yellowstone River below Elk Creek 732 5. Platani'S Gl'iLLBLM.E Giipp. Yellowstoue Kiver below Elk Creek 727 834 U. 8. OEOLOGlCAL SURVCV MONOOHAPH XXKll PART II PL. XCVli TERTIARY. PLATE XCVIII. 835 PLATE XCVIII. Page. Fios.1.2. SAriNDis WAUDii 11. sp. Yellowstone River below Elk Creek 738 3. C'Ei.A.sTRCs iN.Eyu.\ns u. sp. Yellowstoue Eiver below Elk Creek 733 4. Acer viVAUiuM n. sp. Fossil Forest 735 5. ACEH, ERiiT. Crescent Hill -• ■ ^^'' 6. Acacia lamarensis n. sp. Lamar River 730 7. Acacia wardii n. sp. Fossil Forest.. 730 8. Acacia macrosperma u. sp. Fossil Forest 729 83U U. «. OEOLOCICAU ftUflVEV MONOGRAPH XXXir PART II PL. XCVIII PLATE XCIX. 837 PLATE XCIX. Page. Fig. 1. Sapindus gkaxdifoliolu.s? Ward 737 2. Sapixdus grandifoliolus Ward 737 3. Arali A wniTNEYi Lx. Fossil Forest Kidge 748 4. rTEROSPEKMiTES HAGUEi n. sp. FossU Forest Ridge 742 5. Sapindu.s wardii d. sp. Fossil Forest 738 S38 U. a. OEOLOCiCAL 8URVEV MONOGRAPH XXXII PART II PL. XCIX PLATE C. 830 PLATE C. Pnge. Fig. 1. Aralia notata Lx. Yellowstone River below Elk Creek 745 2. Sai'indus grandifolioloides n. sp. Hill above Lost Creek 738 3. DlosPYROS HAGUEi u. sp. Yellowstoue River below Elk Creek 752 840 PLATE CI. 841 PLATE CI. Page. Fig. 1. Akali V whightii n. sp. Fossil Forest 744 2. CissiTEs iiAGUKl II. sp. Fossil Forest 741 3. AUALIA SKRRULATA n. sp. Vellovrstouo River Ijelow Elk Creek 747 4,5. Zizynius SERRULATA Ward. Yellowstone River below Elk Creek 740 6. Credneuia? pachyphylla n. sp. Yellowstone River below Elk Creek 742 7. Pai.iurus colombi Heer. Head of Tower Creek 740 842 U. 8. GEOLOQlCAL 8URV(V MONOflRAPM XXXir PART ll PL. Cl TERTIARY. PLATE CII. 843 platp: cii. Page. Figs. 1-3. Sapindus afkinis Newby. Yellowstone River below Elk Creek 736 4. Sapindus GRANDiFOLioLus? AVaiil. Yellowstone River below Elk Creek 737 5. Phyllites CRASSiFOLiA u. sp. Fossil Forest 753 844 U. 6. GEOLOGICAL 8URVEV fclONOOnAPH XXXII PART II PL. Clt PLATE cm. 845 PLATE cm. I'agp. Fig. 1. Phyi.lites ckassifolia ii. sp. Speciiiieu Ridge Forest 753 2. PnYLLiTES sp. Yellowstone Kiver below Elk Creek 753 3. Caepites pedunculatus u. sp. Yellowstone River below Elk Creek 755 4,5. CORNUS WRiGHTii 11. Sp. Fossil Foiest 749 6. CoRxis XEWBERKYi Hollick. Y'ellowstonc River below Elk Creek 749 846 J. 8. QEOLOOICAL fiURVfV PLATE CIV 347 PLATE CIV. iSE(JUOIA MAGXII'ICA II. sp. 848 Page. 671 U. d. OEOLO:>1CAL SURVEY MONOGRAPH XXXll PART II PL. CIV SEQUOIA MAGNIFICA. PLATE CV. 849 MON XXXII, PT II 54 PLATE CV. Sequoia MAGNiFiCA n. sp. 850 Page. 761 U. 8. GlcOLOCICAL SURVEV 1 MONOGRAPH XXXll PART II PL. CV .V / Jb. l i t - -^^^^y "'- ^^^^^1 I |B jL ^^^S^^^ ^ fll^^^F HHyl^B ^^^^i^diflH^Mw^lt^^^^^^^H ^^^^^^^H mp^ " 'M^^E^g^^^^^^^^^H M ^^^■I^^^^^^^^^^H I^^Bg^-;;'^;;^.': "^ ■-';>:-;:'^^?-'.;y>'^.;*;< ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^1 SEQUOIA MAGNIFICA. PLATE CVI. 851 PLATE CVI. Page. PiTYOXYLON ALDERSOM 11. 8p 763 852 U. ft. CEOLOO'CAL 8URVEV MONOGRAPH XXXII PART II PL. C«l PITYOXYLON ALDERSONI. PLATE CVII. 853 PLATE CVII. PlTYOXYLON AMETUYSTINUM n. Sp 854 Page. 764 U. 6. OEOLOGtCAL 8URVEV MONOGRAPH XXXll PART II PL. CVII ^v^MM|||HHH| &• '^^^^^^^^^^^^^B * 1 ^V^v ■ lit . •V. s ^P>' ■k:4^" 1 H^ii - ^^B ^sM^ ^k- t .*i- Vi ^B • • ^B'^ i ^ - ■ • -■ ■ ^ -.■^ ^^^p^Pi^H 1 ]: ^ ' ^ h. 'm ^-' ^ «^ii- . ~ i PITYOXYLON AMETHYSTINUM. PLATE CVIII. 855 PLATE CVIII. Pttj;e PlTYOXYLON AMETHYSTINUM U. Bp '''-* 856 PLATE CIX. 857 PLATE CIX. Page. PiTYOXYLON ALDERSONI n. Sp 763 858 PLATE ex. PLATE ex. Sequoia m agxifica n . sp Transverse section through annual ring. Magnitieii 100 lUameteis. 860 Page. 761 U. 8. OEOLOOICAi. NUHvf. MONOr.RAPM XXXll PART l< PI. CX SEQUOIA MAGNIFICA. PLATE CXI. 861 PLATE CXI. Page. SeQVOI A MAGNIFICA U. 8p 7G1 Transverse section through one annual and two smaller rings of growth. Magnified 100 diameters. 862 U. 8. OEOLOGICAL 8UnvEY MONOGRAPH XXXII PART II PL CX SEQUOIA MAGNIFICA. PLATE CXII. 863 PLATE CXII. Page. PriYOXYLOX ALDERSONI U. sp 763 Transverse section in summer wood, showing large resin passage. Magnified 100 diameters. 864 U. 8. OEOLOOICAL SUnvfY MONnr.MAPH yxxw part li PL. Cxil PITYOXYLON ALDERSONl, PLATE GXIII. 865 MON XXXII, PT II 55 PLATE CXIII. Page. PlTYOXYLON ALDEKSONI 11. Sp _ 753 Loiirritudiiial tauiiential section. Maguified 100 diauieters. 866 U. S. GEOLOGICAL SUflVF II PL. CXIII PITYOXYLON ALOERSONI, PLATE GXIV. 867 PLATE CXIV. Page. PiTYOXYLON AMETIIYSTIXUM 11. SJ> 764 Transverse section passing nearly tliroiigli one aimual ring. Multiplied 100 diameters. SG8 U. 8. GEOLOGICAL SURVEv MONOGRAPH >i<"H PART II PL CXIV PITYOXYLON AMETHYSTINUM. PLATE CXV. 869 PLATE CXV. Page. PlTVOXYLOX AMUTIIYSTINTM 11. sp "64 Transverse section tlaougli lall and spriug- wood, and showing large resin duet. Magnified 100 diameters. 870 U. 8. QEOLOCICAL SURV£ lOIRAPH XXMI fiVHT II PL CK PITYOXYLON AMETHYSTINUM. PLATE CXVI. 871 PLATE CXVI. Page. LaUI!INOXYI,ON PULCHRUM U. 81) '"^ Longitmliual tangential section, showing woiiil cells, medullary rays, and large duct. Magnilied 100 diameters. U. a. OEOLOaiML auRVEV MONOGRAPH XXXII PART II PL. CXVI LAURINOXYLON PULCHRUM. PLATE CXVII. 873 PLATE CXVII. Figs. 1-5. Seqtoia ji.vgxikica n. sp 1. Tangential section X ilO di.amcterg. .Shows AVdod cells, uicdnllary rays, and resin tube of short sutiare-walled cells. 2. Radial section X 00 diameters. Shows wood cells, with a single series of pits, long uieduU.ary rays, and resin tnlie with dark contents. 3. Radial section X 00 diametei-s. Shows wood C(dls in vicinity of annu.al ring, .sm.all pits in one or two rows, and niednllary rays. 4. Radial section x 00 diameters. Shows annual ring, with fall and spring cells and medullary rays. 5. Tangential section X 00 diameters. Shows wood cells, medullary rays, and resin tuhe with dark contents. .874 Pago. 761 0. 8. QtOLOGlCAi. SUHVfv MONOGRAPH KXXIt PART II PL. CXVll 11 1 1 ■' IJfi _ — i 0 G o o o o 1 ■ — ■ — ■ . • SEQUOIA MAGNIFICA PLATE CXVIII. 875 PLATE C XVI II. Page. Fiiis.1,2. PiTYOXYLOS AMETiiYSTiNTM II. sj)- Specimen Kidge 764 3,4. PiTYOXVLON ALDEKsoNi 11. sp. Speciuieu Ridge 763 5. QuERciNiUM LAMAUEXSi; n. sp. Spcciuien Eidge 771 6,7. Rhamnacinium radiatum Felix. Speciuien Ridiie 769 1. Radial section X 90 diameters. Shows wood cells with single row nt' pits, and spring and fall wood; also medullary rays. 2. Tangential section X 90 diameters. Shows the long wood cells and sliort medullary rays. 3. Radial section X 00 diameters. Shows wood cells with a single row of pits. 4. Transverse section through annual ring, x 00 diameters. 5. Transverse section x 320 diameters. Shows the fall and spring wood. 6. Transverse section X 90 diameters. Shows medullary rays of short cells, thin-walled wood cells, and scries of ducts. 7. Tangential section X 90 diameters. Shows wood cells, medullary rays, and dotted ducts. 876 U. S. QEOLOOICAL SU MONOGRAPH XXXII PART II PL. CXVlll 0 o - 0 1 o 1 1 \ 1 _ \ ■- \ 1 1 1 1 \ 1 PLATE CXIX 877 PLATE ex IX. Page. Fid.l. RiiA.MNAClxiUM RADIATUM Felix. Specimen Kidge 769 '2. PrrvoxYi.ox ALDERSOXI n. sp. Specimen Ridge 763 3-5. Lai'RIXOXYlon I'ULCHKUM u. sp. Fossil Forest 7(i5 1. Radial section x 90 diameters, showing wood cells, medullary rays ot' short cells, and large ducts. 2. Trausverse section x 320 diameters, passing through an annual ring. 3. Radial section X 90 diameters, showing narrow wood cells, large plate of medullary rays of short cells, and large dotted ducts. 4. Radial section of reolariforiii iluct X 320 diameters. 0. Radial section of dotted duct X 320 diameters. »78 U. 8. GEOLOGICAL SURVEY MONOI.ftAPH XX^II PAHT II PL. CXIX uxtoa 5 n TTTTT r-/ i r / 'n PLATE CXX. 879 PLATE CXX. Page. Fk;. 1. Laurinoxvlox pulchrum ii. sj). Fossil Forest 765 2. QuERcixiUM i.AMAREXSE 11. sj). Speciiueu Ridge 771 3-5. Pi,atax'in'u':m iiaydeni Felix. Specimen Ridge 7157 1. Transverse sectiiiii x 90 diameters, sliciwing wood cells of two kinds, luednllary riiys, and large ducts. 2. Transverse section X 320 diameters, tlirougb duet. 3. Tangential section x 90 diameters, showing wood cells, scalaril'orm ducts, and very large medullary rays. 4. Transverse section x 90 diameters, showing short-celled medullary rays with black cell contents, wood cells in vicinity of annual ring, and numerous large ducts. 5. Radial section x 90 diameters, showing narrow wood cells, numerous ducts, and short- celled medullary rays. 880 U. * QfOLOOICAL ttUHVtV MONOGRAPH XXXll PART ll PL. CXX TERTIARY. PLATE CXXI. MON XXXII, PT H ,")6 881 PLATE CXXI. Page. Figs. 1,2. Qiercixiu.m la.viarenseii.si). Speeiiiien Ridge 771 3,4. Smilax i.AMABENSis 11. sp. Lauiiir River : 785 1. Trausverse section x 90 diameters, sliowing thick-walled wood cells, immense ducts, and usnnlly single-celleil medullary rays. 2. Tangential section x 90 diameters, showing wood cells, and large and small medullary rays. 882 U. S. GEOLOGICAL SURVCV inONOORAPH XX.'-.W PART II PL. Cxx INDEX. NumbLTs in iVa'ii- are those nf pajjes on which ilkistrationa (plates or fijjures) appear; numbers in black-fucrcl typo are thoHO of ]>ii»res on wliich fossils are dpscribed iu detail. ^V. ra;; 057 AbietitesdubiusLi. es.p Absaroka Kange, analyses of rocks of 272 Absarokites, nualyses of 83,329,352 cLnracter and occurrence of 328-339 photomicrographs of 332 Absarokite-sboshouite-banakite rocks, character and occurrence of 326-355 Acacia lamarensis n. sp 730, SSO Acacia macrosperma u. sp 7*29t S36 Acacia microphy Ua Heer ■ 730 Acacia wardii u. sp 730,836 Acambona osagensis Swallow 56U AceraccjT?, description of species of 735-736 Acer, fruit of 736, SSO Acer vivarium n. sp 735-736, S30 Acer trilobatum productum Heer 735 Acer trilobatum tricuspidutum Heer 736 Acrotreta attenuata Meek 449 Acrotreta gemma Billings 449,472 Acrotreta pyxidicula White 449 Acrotreta subconica Meek 449 Actinostroma sp 496-497 Actinocriuus viaticus 488 Agnostus bideus Sleek 455, 474 Aguostus interstrictus White 454-455, 474 Agnostus josephus 455 Agnostus tumidosusH. &. W 455,474 AUanite, occurrence of 402 AInus carpiuoides Ls 699 Alum Creek, obsidian near 388 Analy&es of rocks. 61,65, 70, 81. 83, 116, 163, 260, 261, 263, 272. 325 Amethyst Monutain, fossil forest on 757-753 Ammonites henry i M. and H 631 Ammonites placenta De Kay 640 Amnicola (?) cretacea 633, (/■4.S Auacardiacea?, descriptions of species of 731 Auatiua (Cercomya) punctata n.sp 6'48-6189,'j46' Anatina (Cercomya) sp 629 Andesite, character of 4, 73-82, 122 occurrence of 4, 24 J-246, 314-321 photomicrograph of sao Andesite-porjihyry , characters of 16, 94-97 occurrence of 10. 12, 19, 2i), 21, 24. 42, 43, 45, 46, 47, 52, 59 photomicrographs of OJ, 104 Andesitic breccia, occurrence of 4,56, 270-274 Andromeda grayana Lx 661 Anemia subcrelacea (Sap.) Gard. andEtt 657,058 Auisotrypasp 516-517 Anomia propatoris "White 037 Anomia sp 6^7 Page. Anoiiiites scabriculus Norwood and Pralten 531 Anoniites semireticulatus Martin 535 Antler Peak, features of 20-23 sections at 21, 22 view of S2 Apatite, occurrence of 402 Araliaceai 744 Aralia angustiloba Lx 745 Araliii digitata Ward 748 Aralia macrophylla Xewby 748 Aralia notata Lx 745-747, 840 Aralia serrulata n. sp 747-748, 54J Aralia sp 749 Aralia whitneyi Ls 74S,53S Aralia wrigbtii n. sp 744-745, 847 Area sp G38 Archimedes sp 492, 519-5!^0 Arctostophylos el]i;itica n.sp 750-751, 874 Arctostojibylus uva-ursi (L.) Spreug 750 Arionellus (Bathyurus) texanua Shumard 460 Arionellus levis n.sp 46'i-463,47'5 Arionellus sp. undet 463,475 Arionellus tripunctatus Whitfield 460,461 Artocarpus incisa L 717 Artocarpus lessigiana (Lx.) Kn 717 Artocarpus/ quercoides u. sp 716-718,554 Aspleiiium erosum .' (Lx.) Kn 668-669 Asplenium haguei n. sp 655, 754 Asplenium iddingsi n. sp 666-667,735.500 Asplenium magnum n.sp 667, 068, 798 Asplenium remotidens n. sp 669,500 Astarte meeki n. sp 6^0,644 Astarte packardi 620 Astarte sp 6^0 Athyris angelica 505 Athyris asblaudensis Herrick 502 Athyris claytoni 439 Athyris hirsuta 567 Athyris incrassata White 488, 562, 563 Athyris incrassata Hall (?) 56t2-563 Athyris lamellosa Meek 50I Athyris lamellosa L6veill6 561-56'-}, ^55 Athyris mira 570 Athyris occidentalis 505 Athyris occidentalis var. triplicata 505 A thyris planosulcata ( ? ) Hall and Whitfield . . . 489, 553, 554 Athyris roissyi 566-567 Athyris royssii AValcott 560 Athyris vittata var. triplicata n. var 504-505, 580 Atrypa destjuamata Walcott 502,503 Atrypa reticularis L 481,502, 503.550 883 834 INDEX. Page. Atrypa missourieneis Miller 481, 50!:i-504f 580 Aulopora geometrica n. gp 492, 308-500, 5S4 Avalanclie Peak, dikes and rocks of 305-30G Avicula custa Hall 617 Avioula liiigiiffiiorrais Evans and Shumard 637 Avicula niucronata 610 Avicula nebrascena Evans and Shumard 637 Avicula (Oxytoma) nuicrouata M. and H 616 Avicula (Oxytoma) wyomingensis n. sp 61G-617 Baculites aspcr Morton (h 636 Baldy Mountain, character of rocks at 340, 344 Banakite, analyses of 347 character and occurrence of 347-351 photomicrograph of 300 Bannock Peak, features of 31 section of 32 view of S3 Barlow Peak, features of 192-194 fossils of 193 Baroda wyomingensis Meek 638 Baronett Peak, view of S04 Basalt, analysis of 438 character of 239-240,241-242 intermingling of rhyolite and 430-432 occurrence of 24 1-242, 275-281 , 302-304. 439 photomicrographs of SoO, 430 Basaltpjrphyry, occurrence of 244 Basaltic andesite, occurrence of 296,302-304 Bascom, F., cited 63 Bathyuriscus Meek (?) 466 Bathyuriscus sp. undet 476 Bathyurus conicus Billings 465 Bear Creek, Montana, analysis of rocks from 352 Beaverdam Creek, lavas on 340,342,347,350 Bechler Canyon, rhyolite of 375-377 Belemnites densua M. antl H 631-63''2 Berr." Creek, section of rocks on 153-154 Betulaelliptica Saj) 698 Betula iddingsi n. sp 69S-699, S12 Betulalutea Michx 699 Betula parcedentata Lx 698 Betula prisca Ett 699 Betula stevensoni Lx 698 Betulacete, descriptions of species of 69$-699 Big Game Ridge, descriptive geology of 1G5-202 features of 188-191 Bighorn Pass, features of 24-27 intrusive sheet at 69-72 section at 25-26 Billingsella Hall 450 Billingsella coloradocnsis Shumard 450-431, 470 Billingsella pepina Hall and Clarke 450 Birch Hills, analysis of dacite porphyry of 163 features of 162-164 Bobcat Kidge, rocks of 180-181 Bornemann, J. G., cited 442 Brachiopoda, descriptions of species of. . 502-505, 609-610, 636 Breccia, acid, occurrence and character of 121-127, 219-220. 237. 270-274, 281-296 andesitic, occurrence of 4, 56, 91 basic, occurreuce and character of 220-223, 233-239, 275-281, 296-298 Bridge Creek, rhyolite on 386-387 Briigger, W.C., cited 246 Page. Browne, A. J. Jukes, cited 40 Bryozoa. descriptions of species of 516-576 Buffalo plateau, geology of 2U6-207 Bnusen Peak, intrusive rocks of 86-88 Bysmaiith, definition of 17-18 Cache Creek, fossil forest on 760 Caniaroplioria ringens Swallow 491, 337-338* 500 Camarota-chia flail 338 Camarota'chia camanfera Winchell (') 5J2 Camaroto'chia herrickana n. sp 339, 541. 542, 5yO Camarotfechiametallica White 489,539, 340-341, 590 Camarotcechia orbicularis 543 Camarotcechia sappho Hall 492, 34t*34!8 Camarotttchia sp 34ii-343) 590 Cambrian fossils, descriptions of 440-478 lists of 440-441 plates showing 46S-478 Camptonectes (Agasaiz) Meek 613 Camptonectes beilistriatus Meek 613-614,64:? Camptouectea beilistriatus var distans n. var 614, 643 Camptonectes extenuatus (M. and H.) Hall and Whitfield 613 Camptonectes extenuatus (M. and H.) Whitfield. 614,615,616 Camptonectes pertenuistriatus Hall and Whit- field 614-613,616,6^ Camptonectes platessiformis White 613-616 Capulus paralius Winchell 576 Carboniferous fossils, table showing range of 484-486 Carboniferous and Devonian fossils, descriptions of. 479-559 plates showing 680-598 Cardium pauperculum Meek 638 Cardium shumardi M. and H 621 Cardium subcurtum Meek 638 Carpites pedunculatus n. sp 733, 846 Carya antiquorura Newby 690 Castanea ungeri Heer 701,703 Castanea pulchella n. sp 70S-704, 812, S14 Celastracea*, descriptions of species of 732-73 » Celastrus culveri n.sp 73'-2, '^34 Celaatrus curvinervis Ward 7J2 Celastrus ellipticus n.sp 734,834 Celastrus injequalia n. sp 733,5^6" Celastrus ovatus Ward 699,732 Cephalopoda, descriptions of species of 630-632, 636, 640 Cerithium (?) sp 639 Channel Mountain, features of 196 Chatani, T. M., analyses of rocks by 135,352 Chemical analyses of rocks. See Analyses. Chicken Ridge, topographic and geologic ieatures of. 191-194 Chonetes illinoisensis 526 Chonetes logani Norwood and Pratten 528 Chonetes loganensis Hall and Whitfield 489, 5ri3-5'.i7. 55'; Chonetes ornatus Shumard 3'-27-3'-28, 586 Chrustachofl", C. von, cited 418 Cinnabar Mountain, section of 53-54 Cinnamomum spectabile Heer 7'^'i, 82S Cissus haguei n. sp 741, ^'4,? Cissus parottiie folia Lx 741 Cladopora labiosa 50 1 Cladopora plnguis 501 Cladopora sp 300-30I Cliothyris King 366-367 Cliothy ris cras.sicardioalis W hite 562, 367-368, 59^ INDEX. 885 Page. 1 Cliotliyria craasicnrdinaUa var naua u. var 500, ^i*'' , Cliotliyris birHtitn 569 j Cliolli.vrta obmnxinia 568 Cliotl.yiis roiasyi Leveille 506 j Cliolhyrisroiasyl'Wnlcott 502..5«O-.'J» I ] Clisioptiyllum teres n.sp 514-515, f'S-t Ctplenterata. dest-riptions of species of 50H-516 I Coloradc formation, fossiU of Gu'i-6ii6 d08cri])tions ot fosaila of 6:i3 CoiuiiiDar Clitt, Madison Canyon view of . . SGS Colinnuar structure, plate showing -^36 ConaiJt Creek, character of rhyolite on 377-378 rocks of 161 Conchita rboniboidalis Wilckcns 525 Coniferiu descriptions of species of C70-683 CoDocardiuiu iiaiioU-onense Winchell 571 Conocardiuni pukbellum White and 'WbitfieM 571- 5»2, 5S1 Conocardium semipleniini Conoeardiuiii trigonale Hall Conocephalites hamulus Hall Couocephalltcs wiscouensis Hall Couocephalus antiqnatus. 571 r.71 4tl 401 456 Corbula subtrigonalis M. and H W35 Corbulua subtrigonalis var. perundata 635 Conmya glabra Agaasiz 628 Cornace.'e 740 Corn us acuminata Newby "*9 | Corn us newberryi Hollick 749 Corn us ovalis Ls 750 Cornus paniculata L'Oer 730 Cornus wrightiin, sp 749-750. 54/; Corylus raacquarryi (Forbes) Beer 699, S12 Cottonwood Creek, Montana, analysis of rock from.. 352 Coulter Creek, rocks of 179-180 : Coulter Veak. rocks of 318-319 j Crags (The) features of 3-5 , Cranilall Basin, acid breccia of 237 ' basalt flows of 239-240 basic breccia of 238 dissected volcano of 245-268 j estentof erosion in 232-233 ' intrusive rocks of 240-259 | lavatiowsof 238-239 j map showing dissected volcano of -216 Craudall volcano, analyses of rocks of 290-267 Crania levis Keyes 520-5iJ 1 , 5S6 Crania niodesta 520 Cianiapermiana 520 Crania rowJeyi 520 Credneria' pachyphyllan. sp 74!J, 54^ Credneriacere 742-743 Crepicephalus Owen 459-4t»0 Crepicephalns iowenais 459, 460 Crepicephalus (Loganellus) raaculoaus 405 Crepicephalus (Loganellus) montanensis 460 Crepicephalus onustis 400 Crepicephalus texanus Sbumard 460, 460-461, 47S Crepicephalus wisconensis 459,461 Cretaceous fossils, occurrence of 604-607 description of 632-640 Crimson Peak, rocks ot 158 Cross, Whitman, cited 17 Crowfoot Ridge, features of 3, 5, 6. 27-30 fossils of 495-196 Paleozoic section at 6-8. ,? Crustacea, descriptions of species of 576-578 Page, Ciystala in rliyolile, forma of growth of 410-410 CuVuUea haguei Meek 618,^44 Cupreswintixylon i-utroton Felix 764 Cyat hophyllum ca-.spitosum Goldfnaa ( f) 481, 500 Cyperacitesgiganteus n. sp 684, 504 Cyperacites sp 684, 6S5, Sor, Cyperaccir. descriptions of species of 684-085 Cypricardia batbimica d'Orbigny 023-024 Cypricardia ( 0 baguei n.sp &'i3-G'24., Gt4 Cypriua cinnabarensis n. sp — 6'21-ti'^t2, r44 Cyprina ( 0 iddingsi n. sp 6*-2S, G44 D. Dacite, oc :urrences of 172-173, 288-290 photomicriigrapLs of 104, ISO Dacite-porphyry, analyses of 05, 163 character of 64-69,84-85,86-88 photomicrograph of ('- Dakot a conglomerate, occurrence of 48, 49 Dakota formation, fossils of 604-605, 632 Dakota limestone, occurrence of 49 Dana, J. D., cited 245,491 Darwin, Charles, cited 82 Daubree, A., cited 418 Derbyakeokuk Hall (?) 491,492,524-5*^5 Devallia? montana n.sp 671-673, 793 Devonian fossils, descriptions of 496-507 table showing 483 Devonian and Carboniferous fossils, descriptions of. 479-599 plates showing uSO-oOS Dicellocephalua latifrons Sbumard 461-462 Dicellomus Hall 446 Dicellomus nana 440,465 Dicellomus nanus M. and H 446,447 Dicellon.us politus 446,465 Dielasma burlingtonense White 545 Dielasma forraosum Hall 544 Dielasma rowleyi Hall and Clarke 545 Dielasma Utah Hall and Whitfield 489, 544-545, 550 Dike rocks, characters of 94-97, 128-133 grades of cry stullization of 107-108, 113-114 variation iu mineral composition of 105-113 Dikes, occurrence of 10,24,224-231 features of 224-231.240-259,304-321 Diospyros bracbysepala Al. Br 751 Diospy ros copeana ix 75 1 Diospyros haguei n. sp 752, 753,540 Diospyros lamaren.sis n. sp 751-753, SS0,S33 Diospyros obtusa Ward 752 Diospyros stenosepala Heer 663 Diospyros virginiana L 752 Diorite, character of 97-103 mineral composition of 109-113 occurrence of 252-256 photomicrographs of 104, 2o0 views of specimens of 100 Diorite-porpbyry, occurrence of 242-240,252-256 photomicrographs of 104,344 view of specimen of 100 Dombeyopsis iilatanoidea Lx 661, 706 Dome (The), features of 12-13 zone of contact between intruded sheet and coun- try rocks near. 68 Donax cuneata Stanton 638 Donas ( .') oblonga Stanton 638 Dosinia jurasaica Whitfield 622 886 INDEX. Page. Pryophyllum aqnamanim Ward 711 Uryophyllum longiiietiulatum n. sp 710* SIG Dryophylluni subtalcalum Lx 711 Dryopteris weeilii n. sp 669-670, SOJ Dryo])teri.-» sautbolitbeusc n. sp 671* S0:2 E. Eagle Peak, view of 296 Eakins, L. G., chemical analyses of rocks made by.. 135 260-261, 325, 329, 3-40, 347, 352 Ebenacese 751 Echo Peak, analysis of rocks of G5 banding in rocks of 67-C8 view of 6S Ecbinoidea, descriptions of species of 609 Ecliinodcrniata, descriptions of species of 515-516,608 Edwards and Haime. cited 498 Electric Peak, analyses of intrusive rocks of 115-121 chemical correlation of rocks of Sepulchre Mountain with those of 142-148 comparison of rocks from Sepulchre Mountain and 138-148 diagram showing molecular variation of rocks at. 119 diagram showing variation in silica percentages of rocks at 117 features of 50-55, 89-92 geologic map of OG grades of crystallization of rocks of 107 igneous rocks of 89-148 intrusive rocks of 92-121 location and altitude of I mineral and chemical composition of intrusive rocks of 105-121 notable intrusive sheet at 82-84 order of eruption of rocks at 140 porphyries at 94-97 quartz-mica-diorite-porphy ry at 103- ] 05 sections at 50-51.53-54 stock rocks and apophyses at 97-103 views of - 90 Elieodcndron polymorphum "Ward 734-735, 5<34 Ellis formation, I'ussils of 174, 176 Ellis sandstone, fossils of 197 Eudothyra haileyi 590 Endothyra bailey i var parva n. var 492, 507, 590 Eudothyra howmani 507 Endothyra lobata 507 E(iuisitacea-, descriptions of species of 674-676 Equisetum canaliculatum n. ap 675, G16,S03 Equisetumdeciduum n.sp G7O,S0-2 Equisetum haguei n. sp 674, 302 Equisetum hiemale 676 Equisetum lesquereuxii Kn 675 Equisetum limosum L 674, 675 Equisetum robnatum 676 Ericacea? 750 Eridopora (?) sp 517 Etna (Mount), profile of ^32 Eumetria altirostris White 560 Eumetria vera 560 Eumetria verneuiliana Hall 491, 493, 560-561 , 5S7 Eumetria verneuiliana Whitfield 560 Eumicrotiscurta (Hall) ileek and Hayden 617 Euomphalus luxus White 489, 573 Euomphaliis (StraparoUus) ophirensis 489 Euomphalus (StraparoUus) utahensis Hall and Whit- field 489,573 Fagaceae, descriptions of species of. , Fagus antipofii Abich Fagus atlantica Ung , Fagus castanea?folia tJng Fagus dentata Gopp , Fagus feroniai Ung Fagus ferrugioea Ait Page. 700-702 700 701 701 700,701 701 700 Fagus undulata n. sp 700-703, 703. SI ) Fails River Pasin, basalt in 435 rhyoUte in 377-379 Fan Creek, rocks on and near 43-44,45,46,47,48, 58 sections on and near 48, 58 Fan Pass, rocks of 49 section at 49 Fan (The), features of 45-50 Favosites sp 501,580 Fawn Creek, rocks on 43 Fawn Creek Valley, features of 39-40 section in 38 Fawn Pass, formations exposed near 42-43 rocks near 43 Feldspar raicrolitcs, photomicrograph showing 433 Feldspar needles, photomicrograph showing 414 Fenestella Lonsdale 518-519 Filices, descriptions of species of 665-673 Ficus asiminje folia Lx 713, 716 Ficus deformata n.sp 712-713.5^5 Ficus densifolia n.sp 714-715, S1S,S20,S23 Ficus haguei n.sp 715-716,5^0 Ficus shortensis? Lx 714 Ficus sordida Lx 714 Ficus sp 713,515 Ficus tilia-folia? Al. Br 716 Ficus ungeriLx 713,520 Flat Mountain, rocks and fossils of 196-197 Flora, fossil, description of 651-882 plates showing 704-8S2 Forellen Peak, rocks of 158-159 Forests, fossil 755-760 Fort Ellis, Montana, analysis of rocks from 352 Fraxinus affinia Newby 739 Fraxinus denticulata Heer 66^, 798 Fraxinus heerii Lx 753 Fraxinus wrightii n. sp 753, 8S0 Friedel and Sarasin, cited 418 Gr. Gabbro, occurrence of 246-252 photomicrograph of 250 Gabbro-porphyry, occurrence of 242, 246-252 Gallatin fault, course of 30 Gallatin Mountains, descriptive geology of 1-59 extrusive rocks west and southwest of 137-138 geologic cross sections of 1-3 intrusive rocks of 60-85 map of 56 panoramic view of IS Gallatin River, geology of region north of 41-50 laccolithic mass on 84-85 section near 58 Gallatin Valley, features of 27-30 Gardiner River, rocks near 45 Gastropoda, descriptions of species of 505- 507, 629-630; 632-633. 639 Geikie,A.,andTealt, J.J. H.,cited 67 (leonomites schiraperi Lx 658 INDEX. 887 Page. Gerrilliiv inoiitanaensia Meek 617 Gervillin Kp 61 T Gibbon liivt-r. rliyolite of 366-367 Gilbert, G.K., cited 17 Gill. A.C..ackiiowI*MlK»'nu*nt3 to 18^ Girty. (i. H., ncUnowltMlj^inents to 441 dt'scriptions i»l' Devonian and Cnrbonifcrows fos- sils hy 479-509 Glass, character of 40:i plobulitic 406-408 raicrolitic 408-410 rliy clitic 406 Glyptoatvobus ungeri Hear 681 Gneiss, ticcurrenceof 4, Iti, 2(J Goniobasis gracilcnta Meek 632 Goniobasis ( .') increbescens n. sp 633, *>-i>' Goiiiobasis { 0 pealei n. sp 63*2-63.3. 04S Grand Canyon of the Tellowstone, rocks of 389-390 Granite, view of specimen of 100 Granitic aplite, photoiuicro^^raphs of 250 Gravel Peak, features of 188-190 Gray Peak, rocks of 42-43, 73-82 section near 46 Grewiopsia aldersoui n. sp 743-744 Grewiopsis idatanifolia VTard 744 Grewiopsis populifolia Ward 729 Grizzly Teak, dikes and rocks of 306-307, 308, 310 Grypba*a calceola var. nebrascensis Meek and Hay- den 61'^, 64:? Gryphsea dilatata 611 Gryphit'a plaiioconvexa Whitfield 611, (j'4^ Gryph;va vesicularis Oil Glyptostrubus curopa'ua (Brongt.) Heer 681 Gynjiiogramnia haydenii Lx 657 Gyrodes depressi Meek 639 Gyrodes petrosa 639 Hague, Arnold, letter of transmittal by xiii ; cited 220, 331 ' Haguia, description of 42'.£ , Haguia sphrerica, n.sp , 44!d-443, 474 Haldatdu Lys, C.N. A.de, cited 418 I Hall. James 446 ! Hall and Whitfield, cited 487.498,499,526 | Hemipronitescreuistriata 540 [ Herrick, C. L., cited 493 I Hicoria antifiuorum (Xewby) Kn 690 , Hicoria crescentia,u. sp 690-69 1 , SOS Hicoria culveri n.sp G9t~G9*i,S06 I Hicoria ovata (Mill.) Britten 692 ' Hillebrand, W. F., analyses by 354 I Hinde, G. J. , ci ted 442 Hornblende-mica-audesites, occurrence of 290-291 Holasterella wrighti var. americana n. var HOS* 599 Holmes, W.H., cited 14.31,221,357,651-652,756 Homomya galiatinensis n.sp ^*ZS-G'2^^ G4G Hoodoo Basin, features of 223 view of 233 Hoodoo Mountain, dikes of 224 dike rocks of 348 Honiblende-audcsite, occurrence of 4, 291 Hornblende-andesite-porpbyrj-, analyses of 81 occurrence of 77-80 Hornblende-mica-andesite-porpbyry, analyses of 61,81 character of GO-64. 7;i-77 occurrence of 256-258 Page. Hornblende-pyroxone-andeBito, occurrence of 258-259, 291-204.300-301 Hornbleudepyroxeueandesitepori>byry, occurrence of 80 Hoyt Peak, dikes and rocks of 306-307 Huckleberry Mountain, dacito of 172-173 descriptive geology of 165-202 detailed geology of 170-173 rbyolito of 172 1 1 urricane Me.sa, di Ues of 225-229 nature of, volcanic rocks of 340, 346 view of - 226 Hurricane Ridge, view of SS6 Hustedia triangularis Miller 560 Hyatt, A., cited 602 Hyolithes primordialia 454, 466, 4r4 Hyolithes (Theca) primordialis Hall 454 Iddiugs, J, P., cited 17, 89, 261, 292, 333, 360 Iddings and Pentield, cited 380 Igneous rocks of Absaroka Range and Two Ocean Plateau 269-325 Ilex undulata Lx 658 Indian Creek, intrusive sheet north of 68 section at 21 Indian Creek laccolith, features of 10, 13-16, 60-64 mode of origin of 9 Index Peak, view of 213 Inoceramus acuteplicattis n, sp 634-635, 637, 648,650 Inoceramus alt us 635 Inoceramus flaccid ua White 634 Inoceramus fragilis 635 Inoceramu.s umbonatus Meek and Hay den 634 Inoceramus undabundus Meek and Hayden 634 Intrusive flows, Crandall Basin 240-259 Intrusive rocks, analyses of 426 Iphidea Billings 447 Iphidea bella 448 Iphidea ctelata 448 Iphidea labradorica 448 Iphidea ornatella 443 Iphidea paunula White 448 Iphidea prospectensis 448 Iphidea sculptilis Meek 447-448, 449, 46S Iphidea sp. undet 449, 463 Iris Falls, rhj-olite at 376 lahawooa Canyon, analysis of rocks from 329 dike rocks of 349 J. Joseph Peak, igneous m ass of 73-82 rocks of 43, 44 section at 47 Juratrias fossils 197 Judd,J.W.,citert 243,245 Jukes-Browne, A. J., cited 40 Juglandacea^, descriptions of species of 687-693 Juglans californica Lx 6*i7 Juglans crescentia, n. sp 6S9-690, SOS Juglana denticulata Heer 689 Juglans egregiaLx 688 Juglans laurifolia n.sp 688-689, S06 Juglans nigella Ung 691 ■Tuglans rugosa Lx 687-688 Juglans schimperi Lx 688-689 888 INDEX. Page. Jurassic fossils, occurrence of 174, 1 76 description of 601-604, 608-632 K. Kersantite, analyses of 70 characters of 69-72 Kinderbook fossils, list of 490 Jiing, Clarence, cited 82 KnowltoD, F. H., acknowlotlgments to 183 Kuch.R.. cited 409 Ivuntze, Otto, cited 652 Kutorginaniiniitissima II. & W 447 Kutorgina sculptilis Meek 447 L. Laccolitb, definition of 17 Lamar Valley, rocks of 207-208 Lamination and banding, occurrence of 424-425 Lampropbyric rocks, occurrence of 259 Laiamie tlora, discussion of 663-665 table sbowing distribution of 663 LastreagoldianaLx 670 Lanracea?, descriptions of species of 722-729 Laurinoxylon arouiaticura Felix 767 Laurinoxylonbrauneri Kn 766 Laurinoxylon Icsquereuxiana Ku 767 Laurinoxylon piilcbrum n. sp 765, 767, 575, 87S. SSO Laurus californica Lx 724, 725 Laurus grandis Lx 723,724, 7«5^A'i'C, 530 Laurus montana n. sp 724, 630 Laurus perdita n.sp 723. 82S Laurus primizenja (?) Ung 722-723, 5^;J Laurus princeps Heer 725, SSO Laurus triseriata Gasp 766-767 Lava, rbyolitic, occurrence of 4, 5 Lava flows, Crandall Basin 238-230 Leguniinosa?. description of species of 729-730 Leguminosites cassioides Lx 730 Leguminoaites lamareusis n.sp 731, SIS Leguminosites lesquereuxianaKn 730, SIS Leguminosites proserpinaj Heer 731 Leptiena rbomboidalis Wilckons 488, 489, 492, 525 LeptsnatenuistriataHall 525 Lesquereux, L., fossil plants determined by 651 Leucite-banakite, analyses of 347 Limestone, dikes in 24 Limacinnabarensis n. sp 612-613, 642 Lindgren, W., cited 353 Liugula brevirostris M. and H 608 Lingula sp. undet. 608 Lingula subspatulata Hall and Meek 636 Lingulepis Hall 443-444 Liorhyncbus greenian\im niricb 503 Liorbyucbus bagut'i n.sp 543-544, 5.9t) Liorhyncbus Kelloggi 544 Liostracus parvus u.np 463-464, 475 Liorhyncbus (Pugnax?) striatocostatum M. and W. 544 Lithoidal rhyolite, views of 304 Lithoiditt', character of 364-365 Litbopbysfe, characters of 416-422 diagrams of ■^" views of 364 Lithostrotionsp 513-514 Litseacnneata u. sp 726-727, S24 Litsea weediana Kn 659 Page. Little Quadrant Mountain, features of 36-39 sections of beds at 36, 37, 38 Little Sunlight Creek, fossils from 481 Lower Carboniferous fossils, table showing range of. 484-486 descriptions of 507 -578 Lower Geyser Basin, rhyolite of 369-372.374-375 Loxonema delicatum n. sp 506, 5S0 Loxonema tenuilineatum Swallow 572 Loxonema ( ? ) sp 572, 5S0 Lygodium kaulfusii Heer 672-673,500 Lygodium neuropteroides Lx 672 Lyosoma powelli White 630 ]vr. Mactra arenaria Meek (?) 639 Mactra (Cymbopbora?) warrenana (M. and H.) Meek 639 Mactra (Trigonella?) arenaria Meek 610 Mactra warrenana Meek and Hayden 639 Madison limestone, fossils of 487-488, 490, 491 table showing zoological groups < f 495 Madison Plateau, rhyolite of 367-369 Madison Range, features of eastern flank of 57-59 Madison Kiver, rhyolite of 366-367 Magnetite, occurrence of 400-401 Magnolia acuminata L 721 Magnolia californica (?) Lx 718, 721 Magnolia culveri n.sp 720-721, 5i?4 Magnolia foitida Sarg 719 Magnolia grandifloraL 719 Magnolia inglefeldi Heer 719, 720 Magnolia lanceolataLx 719 Magnolia micropbylla n. sp 720 Magnolia poUardi n.sp 721, 50i Magnolia spectabilis n.sp 718-720,5-''6 Magnoliacere, descriptions of species of 718-722 Malopoenna lamarensis n. sp 726, Si?6". 55^ Malapoenna weediana ( ?) Kn 639 Mammuth Hot Springs, character of rhyolites at 357-359 Martinia rostrata n. sp ^ 489, 553-554, 568, 504 Mauna Kea, profile of 2:)2 Meek, F.B., cited 482,487,489,494,611,619 Melville, W. H., chemical analyses by 115, 261, 347. 354 Meuophyllnm ( ? ) excavatum 511-512, ;'54 Menopbyllum tenuimarginatum 5U Merrill, G. P. cited 351 analyses by 352 Mesozuic fossils, descriptions of 600-640 plates showing 641~6C0 Meunier, Stanislas, cited 418 Mica-dacite-porpbyry, Bunsen Peak, analysis of 87 Miea-gneiss, occurrence of 4 Michelinia placenta White 489, 510, 5S4 Michelina sp 489 Microgranular structure, occurrence of 422-423 Micrograpbic pbenocrysts, photomicrographs show- ing 414 Micromita Meek 447 Middle Creek, dikes on and near 224,312-314 Minette, analysis of 70 Mink Creek, rocks and fossils of 199-200 Modiola subimbricata Meek 617-618 Modiola (Vulsella) subimbricata Meek 617 Montana, character of absarokites from 351-355 Montana formation. fns.sils of 606-6ii7 description of fossils of 636-640 iNi)i:x. 889 Page Muuzoiitte, pliotoinicrngrapha of '2f>(i Mount Doane, amleait*' of 315 Muiiut Kina prolilo ut '2si Mount Kverts. intruMvo rocks of 85-80 ihyolilo of 358 Mount Hancock, tVatnresof UtO-191 Mount Holmis, analysis of rocks of 05 featurts of by snialith of 16-20, 64-09 view of hysniatolitli of ^S view of uiountaina north of 4 zone of contact between iutriuled sheet and country rock lu-ar 08, 69 Mount Langfonl, dike at 312 Mount Norris, fossil (orust on -*- TOU Mount Norris and The Thunderer, view of 2J? Mount ScUurz. rocks of 310-318 Mount Stevenson, rocks of y 15-316 Mount Vesuvius, profile of '232 Mugge, O. , cited 390 Musaceee, descriptions of species of 080-687 Musophyllum complicatum Lx OSG-OSiyv^'j Myacites (Pleuromya) subconipressaMeek 626 Myacites subcompressus (Meek) White 626 Myrica bauksijefolia Ung 693 Myrica bolanderi ( ') Ls. tt5S-659, 70r. Myrica fallax Lx 093 Myrica lamarensis n sp 693, ^'f*5 Myrica polyraon)ha ScUinip 692 Myrica scottii Lx G9*Z-,S0S Myrica torreyi Lx 692 Myrica wardii n. sp 69*^-693, SOS Myricacea?, descriptions of species of 69*-i-693 Natica(?) sp 630 Naticopsis ( ') sp !i7'2y5Sl Katural bridge. Bridge Creek, rhj'olite at 386-387 views of 3S6 Neritina nebraacensis M.and H 629-6JU Neritina { 0 phaseolaris AVhite 629 Keritina pisum Meek G30 Neritina powelli White 630 Neritina wyoraingensis n. sp «'i9-630, C4.5 Nucula -sp OliS O. Obolella Hall 446 Obolella chromatica 446 Obolella nana M. and H 447 Obolella polita 446 Obolus Eichwald 443-444 Obohis (Lingulella) desideratus Walcott 445-446, •J6\< Obolus (Lingulella) ferruginous 445 Obolus (Lingulella) granvillensis 445 Obolns (Lingulella) manticulus 445 Obolus (Lingulella) perattenuatus 441 Obolus (Lingulella) rotundatus 445 Obolus ( Lmgulepia) acuminatus 443, 444 Obolns (Lingulepis) acuminatus, var. meeki Wal cott ^ 44, 46H Obolus ( Lingulepis) pinniformis 443 Obsidian Cliff, rhyolite of 359-3tJ6 views of SCO OleaceiB ^ 7 53 Onoclea minima u. sp 656-657, 7.i-i Onoclea sensibilis fossilis Newby 050, 006 Page. Opbitic ami related basalts, occurrence of 430-439 Oppelia ( 0 ap 630-631 Oppelia subplicatclla Vacek 031 Orthis coloradi>ensis Sliuniard 45U Ortlns crenistriata 524 Ortbis Kuok uk 524 Orthis niiclielina 521 Ortbis pi'pina Hall 450 Orthis {.') rt'iunicha 451-45*2, 470,472 Orthis (') sandbergi 45*2-453, -/70 Orthothetesina'qualisHall 489, 5*2*2-5*24, oSO Orthothctcs lutiatna 523. r.SG Orthoihetes sp 5*24 Usniunda atlinis Lx 673, SOO Osprey Falls, basalt at 434 Ostrca auomioide!^ Meek 50, 633-634 Ostrea engelmanni Meek 611 Ostrea patina OH Ostrea pellucida M . and H 037 Ostrea soleniscus Meek 637 Ostiea sp .- 637 Ostrea strigilecula White 61 0 Outlet Canyon, topographic and geologic features of. 194-196 view of 204 Owen. D. D., cited 459 P. Pachyphyllura bouchardi 499, 500 Pachyphyllum devoniense 499,500 Pacliypbyllum solitarium 499 Pachyphyllum sp 497-500 Pachyphyllum woodmani 498, 499 Pacitic Creek, rocks and fossils of 198-199 Paleozoic fossils, descriptions of 440-599 Paliurus colombi Heer 060, 740, S43 Paliurus minimus n. sp 659-660 Paliurus zizyphoides Lx 660, 700 Panther Creek, structure of mountains south of 9-JO Peale, A. C, cited 439 ibssils collected by GDI , 602 Pebble Creek, rocks of 21I Pecten bellistriata Meek (J13 Pelecypoda, descriptions of species of. . . 010, 632, 633-035, 637 Pentacrinus asteriscus Meek and Hayden 60S Pentacrinus whitei (jUS Perisphinctes sp 631 Perlite, views of specimens of 370 Persea pseudo-carolinenais Lx 723, 7^25, .SJO Perseoxylon aromaticum Felix 767 Phenocrysts, development ol" 2G0-2C8 Pholadomya ina?(iuiplicata n. sp 6*25, G4G Pholadomya kingi Meek 6*24-625, 6'4'j Pholadomya multilineata Gabb 625 Pholadomya nevadana Gabb 624 Pbragmites alaskana Heer 658 Phragmites falcata n. sp 65N, 706 Pbragmites ( ') latissinia u. sp GS'-i.SOG Phyllites crossifolia n. sp 753-754, rS'^J S4G Phyllites osseus Lx 754 Pliylliles sp ■^oo Pinna kmgi Meek 61S Pin us contorta Dougl 680 Pinus contorta murrayana 078 Pinus edulis Engelm 680 Pinus Hexilis 678 Pinus gracilistrobua n. sp 611,676,500 890 INDEX. Page. Pinna iddingsi n. sp GSO,S04 Pinus niacrolepia n.ap G79,S00 Piniis piTniunayana n. sp G77-G7S.S04 Pimm scopulonim ^~^ Pinus sp «r8-67» Pinus Wardii n.ap tt? »-680 Pinyon Peak, features of 184-188 Pirsson, L. V., analyses by ^54 rited 241 Pitcbstone Plateau, rhyolitc of 379-381 Pityosylon aldersoni n. sp 763-764, S52, 8G4, SGfi, 873 Pityoxylon amelbystinuui n. sp. ? 64-765, S;*^, S;32 Productus newbcrryi var. annoaus 536 Productus parviforniis n.sp 488,533,536-537,586 Productus parvus M. and W 488 Productus parvus Wbite 488, 537 Productus papulata 532 Productus scabriculus Martin 531-533,550 Productus semireticulatus Martin . . 489. 533, 535-536, 591 Proetus loganensis Hall and Wbitfield.. 489, 577-578, 5£>P Proetufl peroccidens Hall and Wbittield 489 576-577,577,578,559 Prospect Peak, analysis of basalt from 438 Protocaidia sbumardi M. and H 6^1 Protozoa, descriptions of species of 507 Pseudobrookite, occurrence of 401-402 PseudomoRotis curta (Hall) / 617 Pseudomonotis (Euiuicrotis) curta Hall 617 Pteria mucronata.M.and H 616 Pteria (Osytoma) munsteri (Brown) M. and H 616 Ptf^ria (Oxytoma) nebrascana (E. and S. ) Meek 637 Pteris erosa Lx 668 Ptcrosperniites haguei n. sp 742, 838 Ptiloporasp 517-518 Ptychoparia antiquata Salter sp 456-457, 458, 478 Ptychoparia (?) diademata 460-461, 462,476 Ptycboparia eryon Hall 458 Ptycboparia (Eulonia) affinia Walcott 457, 473 Ptycboparia Uanocnsis Walcott ( ?) i 458, 476 Ptychoparia (Loncbocepbalus) liamulus Owen, 461 Ptycboparia (Loncbocepbalus) wisconsensis Owen. 461- 462 Ptycboparia penfiebli n. sp 456, 478 I'tycboparia sp. undet 458, 476 Ptycboparia ( 0 sp. undet 458, 476 Ptychoparia striata 460 Ptycboparia teucer 458 Ptycboparia wisconsensis 476 I'ugiunculus primordialis Hall 454 Pumice, occurrence of 403-406 Pyroxene, cbaracter of pbenocrysts of 399-400 Pyroxene-andesite, occurrence of 294-295, 301-302 photomicrographs of ISO Py roxene-andesite-porpbyry, Mount Everts 85-86 Pyrula (?) sp 639 Q. Quadrant formati4in, comparison of sections of 41 Quadrant Mountain, rocks of 33-35 section of 34-35 Quartz, characters of pbenocrysts of 395-398 Quartz-banakite, analyses of 347 photomicrographs of S50 Quart z-mica-diorite, occurrence of 252-256 Quartz-mica-diorite-porphyry, characters of 103-105 Quartzite, occ urrence of 7, 8, 33, 34, 47, 48 Querciuium knowltoni Felix 772,773 Quercin um lamarcnse u. sp.. -, 771-773,876,880,883 Quercus boweuiana Lx 710 Quercug breweri Lx 704 Quercus consimilis ? Newby 704, 314 Quercua culveri n. sp 708, 709, 8J4 Quercus drymc.ja Ung 703 Quercus laurifoliu Newby 708 Quercus ellisiana Lx 659, 794 Quercua furcioervis americaua Kn 705, 816 INDEX. 891 Page. Qiiercna furc-inprvis Rossm 705 (^urrcns gniulaiidica Ucer 706 (^utTciia j;;rosHiiU*iitatii ii. sp 704, S14 Quercu8 lieaperia n. ap 709-7 1 <> Quert'iis / inflgiiifoliii n. sp 7D4-705,,S'i(; Quercus olafpeni Ileer 707 QiierciiM prinuiUca Willd "09 Querruss- 707, SIS Quercua vibiirnitblia Lx 700 Qnorcua weodii n. sp 705-706, 5n Quercus yanceyi n. sp 707-708, SJS Red Creek, rocks od 175 Red Mountains, rhyolite of 381-382 Reissanil Stiibel. cited 29J,400-41(t Eeticularia cooiierensis Swallow 489, 555-556* 568, 59.'5 Reticularia coopcrenais var 556-557, 594 Eeticularia { ?) poculiaris Sliuniard 488, 557, 558, 595 Reticularia aetigera Hall 556 Retieularia (?) subrotundata Hall 557-55S, 595 Eetzia (?) circularis Miller 560 Retzia ( ? ) plicata Miller 560 Retzia popeana Swallow 560 Retzia radialis Walcott 560 Retzia vera Hall 560 Retzia verueuili Hall 5G0 Ehaninacere, deacriptiona of species of 740 Klianinacinium radiatnm Felix 769-77 1 , S70, S7S Rbamuusrectinervia Heer 740 Rliipidouu'Ua michelina Leveille S-Zl Rhus bendirei Lx 691 Rhynclionella camarif era "Winchell 542 Rbyncbonella guatbopbora Meek 609-6 1 0, 642 Rbyncbonella metallica White 491, 540 Rbyncbonella myrina Hall and Whitfield 600 Rbyncbonella pustulosa (?) 489 Rbyncbonella pustuloaa ( i) Halland Wbitfield.. 489. 540, 590 Rbyncbonella ringeua Swallow 537- 538 Rbyncbonella sappbo Hall 541 Rbyncbonella (Stenocesma) sappbo Hall 541 Rbyncbopborapuatulosa 540 Rbyolitea, analyses of 420 cbaraoter and occurrence of 356-4:12 cbaracters of groundmass of 402-410 intermingling of basalt and 430--432 microscopical cbaracters of 393-416 occurrence of 4, 5, 172 variations in composition of 427-429 views of 364 Rbyolite felsite, analyses of - 65 Rbyolitic glasses, photomicrograpbs of 406 Roth, J ., cited 70, 146 Rnssell, I. C, cited 18 S. Sabal major (?)Ung 658 Saddle Mountain, rbyolite of .-... 392 Salicaceie, descriptions of epecies of 694-6^8 Salix angusta Al. Br 697 Salix lavateri Heer 697 Salix varians Heer 697. siO Sanidine, character of pbenocrysts of 398-399 Sapindua affinis New by 736,737 Sapindus alatua ? Ward 7 .'57 Sapindacea;, descriptions of apeciea of 736-739 Page. Sapindus grandifolioloides n. sp 7.1?*,.S'4f? Sapintlus grandii'olioIuH Ward 7.'l7,iVH Sapinclua obtuaifoliua Lx 7:'8 Sapindus ward ii n. sp 738, 739, 830, SSS Scapbiocrhnis sp 516 Scaphites cf. ventricosus M. and H 640 Scapliites veutricosii» Meek and Hayden 636 Schists, occurrence of 4, 11-12 Schucbert, Charles, acknowledgments to ^80 Seminula b nmilia n. sp 565-566, 568. 5US Seminula immatura n.sp 566, 59S Seminula nindisonensia n. sp 41*2, 563-564, 5U3 Seminula madiaonensis var. perailla 564-565, 5uS Seminula qiiadrata *4fl2 Seminula subtilita 4i 2 564, .W5 Seminula wasatcheusis 5(55 Sepulchre Mountain, analyses of rocks of 261 character of lava at 340,341 chemical analyses of rocks of i: 5-137 chemical correlation of rocks of Electric Peak with those of 142-HS comparison of rocks from Electric Peak and 13-<-M8 diagram showing mplecular variations of rocka at 136 dike rocks of 128-i:i3 general features of 8J-92 grades of crystallization of eruptive rocks of 131-133 igneous rocks of 89-148 mineral anina} L 686 Smilax rotuudi folia L 686 Snake River, section in hills near 156 Snake River gorge, geology of 173-1 75 coals of 176 Snake River fault, features of 197-198 Snake River hot springs, features of 177-^88 view of 175 Snowy Mountain, section at 206 Snowy Range, sedimentary rocks of 205-206 topography and geology of southern end of 20 1-244 South end hills of Gallatin Range, features of 10-11 Siilenopleura ( ? ) weedi 464-465, -175 Soda Butte Creek, rocks of 210-21 1 Soda Butte Valley, geology of 212-214 sections in 212,213-214 Sparganiaceje, descriptiona of species of 683-6H4 Sparganiura stygium Heer 683-681 Specimen Ridge, fossil forest at 758 lava at 341 Spherulitea in obsidian, character of 362-364 figures showing sections of 413 forms of 411-416 views of 370, 410, 414. 422 892 INDEX. Page. Shales, occurrence of 8, 15 Shoshonite, analyses of 83, 340 character and occurrence of 339-347 photomicrographs of 344 Silica percentages, rocks of Electric Peak 116-118 Slou;ih Creek, topography ami geoloj;y of valley of. 208-210 Spirifer albapinensis ^89, 548, 594 Spirifer argentarius 550 Spirifer ' flicatus 548 Spir'ft" caraeratus 5'*0 Spirifer carter! Hall 558 Spirifer centronata H;h11 and Whitfield 489,547 Spirifer centronatus \Vinchell 488, 489, 540, 347-549, 550, 552, 504 Spirifer centronatus var. semifurcatus 549-550, 594 Spirifer cuspidatus Meek 559 Spirifer (Cyrtia) bannibalensia Swallow 558 Spirifer engelnianui Meek 504, 5S0 Spirifer extenuatus ■^88 Spirifer forhesi 553 Spirifer hirtus White and Whitfeld 555 Spirifer lauiellosus L6veill6 561 Spirifer niarionensis Shumard (?) 551 Spirifer (Martinia) glaber Martin 554 Spirifer (Martinia) peculiaris White 488-557 Spirifer niesicostalis 5J9 Spiiifer(.') peculiaris Shumard 557 Spirifer aetigera -189 Spirifer sp 55'^-553,;'.'>4 Spirifer sp 553 Spirifer striatus White 488 Spirfer striatns var. madisonensis u. var. 488, 55 l-55'j. 694 Spirifer subattennatus Hail 492,550 Spirifer (Syringothyria) cuspidatus 59S Spirifera albapinensis 489 Spirifera cooperensis Swallow 555 Spirifera aetigera K. and W 556 Spirifera subrotundata Hall 557.558 Spiriferinasolidorostris Herrick 546, ^.W Spiriferiua solidorostris White 545-547,5.99 Spirigcra euzona 565 Spirigera formosa 565 Spirigera monticola 488 Spirigera obraasiiua 488 SphenopterisguyottiiLx 655 Square Butte, Montana, analyses of igneous rocks from -■ 354 Stanton, T. W., fossils identified by 193 Stellaria Creek, rocks on 45.46 Stelzner, A., cited 146 Sterculiacete "42 Stinking water Kiver, dike rocks of 347,350 nature of rocks at 34(J, 345 Stock rocks, characters of 97-103 StraparoUus utahensis Hall and Whitfield. . 489, 573-574, 5S1 Streptorliynchus jequivalvis 522 Streptorhynchus equival vis 522 Streptorhynchus ina-qualis 522 Streptorhynchus inflatus 4S9 Streptorbynchua keokuk 524 Strictoporella (?) 518 Strophomera rhomboidalis White 488, 489, 525 Survey Teak, rocks of 159-160 section at 1^0 Sylvan Paaa, dikes and flows near 304-314 Syriugopora aculeatau. sp 509, 5S4 Page. Syringopora surcularia n. sp 510, 5S4 Syringothyris carteri Hall 488, 492, 55N-559, 59S Syringothyria cuspidatua Walcott 559 Syringothyris extenuatus 488,559 Syringothyria ty pa Winchell 558 Tancredia (?) knowltoni n. sp 6iil,6"44 Tapea wyomingensis Meek 638 Taxitis olriki Hess 6SO, S04 Terebratula (Dielasma) burlingtonensis 488 Terebratula gorby i S. A. Miller 545 Terebratula marcyi Shumard 561 Terebratula micbeliua 521 Terebratula Utah Hall and Whitfield 489,544 Tertiary flora, biological consideration of 773-783 description of plants of 665-791 geological consideration of 783-981 table showing distribution of 749 plates showing plants of 79S-SS3 Teton Range, crystalline schists of 152-157 descriptive geology of northern end of 149-164 map of northern end of 150 sedimentary rocks of 150 1 topographic features of 151-152 volcanic rocks of 157, 161-162 I Tetranthera dealbata R. Br 726 I Tetranthera sessiliflora Lx 659 I Theca gregaria 454 I Theca primordialis Hall 454 Theca (Piigiunculus) gregaria M. and H 454 Thracia (0 raontanaensis (Meek) ? 62fti, C44 Thracia weedi n. sp 647, 64S Three Kiver Peak, features of 23-24 rocks of 16 section of 23 view of S4 Thunderer (The) and Mount Xorris, view of 25? Tilia populifolia Lx 743 Tiianiferous iron ore, occurrence of 400-401 Tower Falls, basalt at 434-435 Trachytic rbyolite, occurrence of 321-328 Trapa ? microphylla Lx 661,794 Triaasic fossils 197,600-601,608 Trilobite Point, rocks of 1 1-12 zone of contact between intruded sheet and coun- try rock near 69 Trigonia americana Meek 618-619,619 Trigonia costata 619 Trigonia elegantissima Meek 619, 044 Trigonia montanaensis Meek 619-640 Tuff (andesitic). occurrence of 4 Tutf- breccia, andesitic, occurrence of 56 Turritellaap 630 Two Ocean Pasa, analysis of rocks from 329 character of lava at 340.343 chemical composition of rocks from 329,337 Two Ocean Plateau, rocks of 258-:ii)0 topography and geology of 200-202 Typhacea^, descriptions of species of 683 XJ. Ulmacea*. descriptions of species of 711-712 Ulmus, fruits of tVi^SlO rimus minima? Ward 711 Ulmus paeudo fulva? Lx 71 l,Si6 INDEX. 893 Pago. U!mu» rhaninifulia^ Ward 7 t''-i Vu'io «p. unt 6CI*<£ Upper CteyatT Uitsiii, liiyulitoof 372-374 Urticaceiu. descriptions of wpeoiea of 712-713 V. VesuviuB ( Slonnt). profile of 233 Vildirnuni roluudifoliiim Lx 66!j, 7^*4, W6 Titaccir. descriiitions of Bi»ecie8 of 741 Volcanic rocks of Absaroka Kange and Two Ocean Plateau 269-325 Volselta subimbricata Whit© 617 Walcott, C. D.. descriptions of Canibriau fossils by. 440-478 TVall Canyon, fossils from 480 "Ward. L. F., paleobotanical work by 652 "Waverly group, fossils of 489,491 Weed, W. H.. cited 53, 2ii6 Weed and Pirsson, cited 353 White. C. A., cited 487,498,601 Wbittield, J. E., chemical analyses made by 61, 65, 70, 81, 115, 135, 163, 325, 329, 340, 347 citid 460 Wildcat Peak, descriptive geology of 169-170 Page. Williams, G.H.. cited C3 AViudy Mountain, dikrs of 230 ■Wolverine Creek, rocks of 181-182 flora of 183 Woodwardia areolata (L.) Moore GG6 Woodvviirdia crenata Kn 656 Woodwardia latiloba Lx 657,666 A\'oiMh\ nrdia jircareoliita II. sp s. V. Fifth Annual Report of the United States Geological Survey, 1883-'84, by J. AV. Powell. 1885. 8°. xxxvi, 4t)!l pp. 58 )il. and maps. VI. Sixth Anuual Report of the United States Geological Survey, 1884-85, by J. W. Powell. 1885. 8*^. xxix, 570 pp. 65 pi. and maps. VII. Seventh Annual Report of the United States Geological Survey, 1885-'86, by J. W. Powell. 1888. S'^. XX, 6.56 pp. 71 pi. and maps. VIII. Eighth Anuual Report of the United States Geological Survey, 1886-87, by J. W. Powell. 1889. 8"^. 2 jit. xix, 474, xii p))., 53 pi. and maps; 1 prel. leaf, 475-1063 pp., 54-76 pi. and maps. IX. Ninth Annual Report of the United States Geological Survey, 1887-88, by J. AV. Powell. 1889. 8"^. xiii, 717 pp. 88 pi. and maps. X. Tenth Anuual Report of the United States Geological Survey, 1888-'89, bv J. AV. Powell. 1890. 8°. 2 pt. XV, 774 pp., 98 pi. and maps; viii, 123 pp. XI. Eleventh Annual Report of the United States Geological Survey, 1889-90, by J. AV. Powell. 1891. 8>^. 2 pt. XV, 757 jip., (Hi pi. and maps; ix, 351 pp., 30 pi. and maps. XII. Twelfth Anuual Ri-i)ort of the United States Geological Survey, 1890-'91, by J. AV. Powell. 1891. 8°. 2 pt., xiii, 675 jip., 53 pi. and maps ; xviii, 576 pp., 146 pi. and maps. XIII. Thirteenth Annual Report of the United States Geological Survey, 1891-'92, bv .1. AV. Powell. 1893. 8°. 3 lit. vii, 240 pp., 2 maps; X, 372 pp., 105 pi. and maps; x'i, 486 jip., 77 'pi. and maps. XIV. Fourteenth Annual Report of the United States Geological Survey, 1892-93, bv .1. AA'. Powell. 1893. 8^. 2 j>t. vi, 321 pp., 1 ])1. ; xx, 597 pp., 74 pi. and maps. XA'. Fifteenth Annual Report of the United States Geological Survey, 1893-'94, by J. AA^ Powell. 1895. 8^. xiv, 755 pp., 48 ])1. and nuips. XVI. Sixteenth Annual Report of the United States Geological Survey, 1894-'95, Charles D. W^alcott, Director. 1895. (Part I, 1896.) «°. 4 pt. xxii, 910 pp., 117 pi. and maps; six, 598 pp., 43 pi. and maps; xv, 646 p|)., 23 pi. ; xix, 735 pp., 6 pi. XA^I. Seventeenth Aunual Kepoit of the United States Geological Survey, 1895-'96, Charles D. AA'alcott, Director. 18f6. 8^\ 3 ]it. in 4 vol. xxii, 1076 pp., 67 pi. and majis; xxv, 8(34 pp., 113 pi. and maps; xxiii, 542 pp., 8 pi. and maps; iii, 543-1058 pp., 9-13 pi. XVIII. Eighteenth Aunual Report of the United States Geological Survev, 1896-'97, Charles D. Walcott, Director. 1897. (Parts II and III, 1898. ) 8^. 5 pt. in 6 vol. 1-440 pp., 4 pi. and maps ; i-v, I II ADVERTISEMENT. 1-653 pp., 10.5 pi. an I luaps; i-v, 1-861 pp., 118 pi. ami maps: i-x, 1-756 pp., 102 pi. and maps: i-xii, 1-642 pp., 1 pi. ; 643-1400 pp. XIX. NiueteentU Annual Report of the United States Geological Survey, 1897-'98, Charles U. Walcott, Director. 1898. 8-. 6 pt. iu 7 vol. MONOGRAPHS. ' I. Lake Bonneville, by Grove Karl Gilbert. 1890. 4^^. xx, 438 pp. 51 pi. 1 map. Price $1.50. II. Tertiary History of the Grand Canon District, with Atlas, by Clarence E. Dutton, Capt., U. S. A. 1882. 4°. xiv, 264 pp. 42 pi. and iitlas of 24 sheets folio. Price .$10.00. III. Geology of the Comstock Lode and the Washoe District, with Atlas, by George F. Becker. 1882. 4°. sv, 422 pp. 7 pi. and atlas of 21 sheets folio. Price $11.00. IV. Comstock Mining and Miners, by Eliot Lord. 1883. 4^. xiv, 451 pp. 3 pi. Price $1.50. V. The Cop])er-Beariug Rocks of Lake Superior, by Roland Dner Irving. 1883. 4^. xvi, 464 pp. 151. 29 pi. and maps. Price $1.85. VI. Contributions to the Knowledge of the Older Mesozoic Flora of Virginia, by William Morris Fontaine, 1883. i^. xi, 144 pp. 54 1. .54 pi. Price $1.05. VII. Silver-Lead Deposits of Eureka, Nevada, by Joseph Story Curtis. 1884. 4"^. xiii, 200 pp. 16 pi. Price $1.20. VIII. Paleontology of the Eureka District, by Charles Doolittle Walcott. 1884. 4^. xiii, 298 pp. 241. 24 id. Price' $1.10. IX. Brachlopoda and Lamellibranchiata of the Raritan Clays and Greensand Mails of New Jersey, by Robert P. Whitfield. 1885. 4". xx, 338 pp. 35 pi. 1 map. Price $1.15. X. Dinocerata. A Monograph of an E.Ktinct Order of Gigantic Mammals, by Othniel Charles Marsh. 1886. 4^=. xviii, 243 i)p. 56 1. 56 pi. Price $2.70. XI. Geological History of Lake Lahontan, a (Juateruarj' Lake of Northwestern Nevada, by Israel Cook Russell. 1885. 4"^. xiv, 288 pp. 46 pi. and maps. Price $1.75. XII. Geology and Mining Industry of Leadville, Color.ido, with Atlas, by Samuel Franklin Emuions. 1886. 4'. xxix, 770 pp. 45 id. and atlas of 35 sheets fidio. Price -$8.40. XIII. Geology of the Quicksilver Deposits of tlie Pacific Slope, with Atlas, by George F. Becker. 1888. 4^. xix, 486 pp. 7 pi. and atlas of 14 sheets folio. Price .$2.00. XIV. Fossil Fishes and Fossil Plants of the Triassic Rocks of New Jersey and the Connecticut Valley, by John 8. Newberry. 1888. 4*^. xiv, 152 pp. 26 pi. Price $1.00. XV. The Potomac or Younger Mesozoic Flora, by William Morris Fontaine. 1889. 4"^. xiv, 377 pp. 180 pi. Text and plates bound separately. Price .$2.50. XVI. The Paleozoic Fishes of North America, bj' John Strong Newberry. 1889. 4'^. 340 pp. 53 pi. Price $1.00. XVII. The Flora of the Dakota Group, a Posthumous Work, by Leo' Lesquereux. Edited by F. H. Kuc.wlton. 1891. i^ . 400 pp. 66 pi. Price $1.10. XVIII. Gasteropoda aud Cephalopoda of the Raritan Clays and Greensand Marls of New Jersey, by Robert P. Whitfield. 1891. 4'^. 402 pp. 50 pi. Price $1.00. XIX. The Peuokee Iron-Bearing Series of Northeru Wisconsin and Michigan, by Roland D. Irving .and C. R. Van Hise. 1892. 4^. xix, 534 pp. Price $1.70. XX. Geology of the Eureka District, Nevada, with an Atlas, by Arnold Hague. 1892. 4". xvii, 419 pp. 8 pi. Price $5.25. XXI. The Tertiary Rhynchophorous Coleoptera of the United States, by Samuel Hubbard Soud- der. 1893. 4 . xi, 206]ip." 12 pi. Price 90 cents. XXII. 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Smyth. 1895. 4^. 608 pp. 35 pi. and atlas of 39 sheets folio. Price $5.75. XXIX. Geology of Old Hampshire County, Massachusetts, comprising Franklin, Hampshire, and Hampden Counties, by Benjamin Kendall Emerson. 1898. i"^'. xxi, 790 pp. 35 pi. Price $1.90. XXX. Fossil Medusic, by Charles Doolittle Walcott. 1898. 4^'. ix,201pp. 47 pi. Price $1.50. XXXI. Geology of the Aspen Mining District, Colorado, with Atlas, by Josiah Edward Spurr. 1898. i°. XXXV, 260 pp. 43 pi. and atlas of 30 sheets folio. Price $3.60. III press: XXXII. Geology of the Yellowstone National Park, Part II, Descriptive Geology, Petrography, aud Paleontology, by Arnold Hague, J. P. Iddings, W. Harvey Weed, Charles D. Walcott, G. H. Girty, T. W. Stanton, and 'F. H. Kuowlton. 1899. 4-. xvii, 893 pp. 121 pi. Price . XXXV. The Later Extinct Floras of North America, by John Strong Newberry; edited by Arthur Hollick. 1898. 4'=. xviii, 295 pp. 68 pi. Price $1.25. ADVEKTISEJIENT. Ill In prepaialhn: XXXIII. (ieolofjy of tli« NaiTiigJiiisctt Basin, 1)y N. S. Shaler, .1. H. WooilwoitU. ami Aiij;ii8t 1'. Koei'ste. XXXIV. Tlio Glacial (iravels of Maine and their Associated Deposits, by George II. Stone. XXX\I. Till' Crystal Falls Iron-Iioarinj; District of Michij;an, l)y .1." Morjrau Clcuients and Henry I.loyil Sniytli : witli a C'liapirr on the iStnrgeou Kiver Tongue, liy William .Shirley I'.ayloy. X.\.\\'1I. I'lora of the Lower Coal Measures of Jlissonri. liv David White. XXXVIII. The Illinois (ilacial Lobe, by Frank Leverett. — Flora of the Laramie and Allied Formations, by Frank Hall Knowlton. BULLI'yiTNS. 1. t)u llyiiersthene-Amlesite and on Trieliuie Pyroxene in Augitic Rocks, by WUirman Cross, with a (ieological Sketeli of Uulialo I'eaks, Colorado, by S. V. Emmons. 1«S3. S . i2 pp. 2 pi, Friee 10 eeuts. 2. (iold and Silver Conversion Tables, giving the Coining Values of Troy Ounces of Fine Metal, etc., coni|iuted by Albert Williams, jr, 1>p. I'rice lU cents. 8. 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Price 1.5 cents'. 147. ICartlninakes iu California in 189.j, by Charles 1). Perriue, A.ssistant Astronomer in Charge of Karth(|uako I Ibservations at tlie Lick Dbservatory. 1896. 8 . 23 p]). Trice 5 cents. 1 18. Aualvscsof Kocks. with a Chapter on Anaivtical Jlethods, Laboratory of the United .States Geological .'Guryev, 1880 to 1896, by F. W. Clarke and W. F. Hillebrand. 1897! 8-. 306 pp. Trice 20 cents. 149. Ulbliography and Index of North American Geology, Paleontology, Petrology, and Miner- alogy for the Year 1.^96. by Fred Houghton Weeks. 1.^97. 8^. 152 iip. Price 15 lents. ' 1.50. Tlie Fducational Series of Koclc .Specimens collected and distributed by the United .States Geidogical Siiryey, by .loseph Silas Diller. 180!S. 8-. 398 pp. 47 pi. Price 25 cents. 151. '['he Lower Cretaceous Gryi>haas of the Texas Region, by R. T. Hill and T. Wavlaiid Vaughau. 1898. 8 . 139 jip. 25 pi. Price 15 cents. 152. A Catalogue of tlie Cretaceous and Tertiary Plants of Xortli America, by F. H. Knowlton. 1898. 8'^. 247 pp. Trice 20 cents. 153. A Bibliographic Index ol North American Carboniferous Invertebrates, by Stuart Weller. 1898. S\ 6.53 pp. Trice 35 cents. 1.54. A Gazetteer of Kansas, by Henry Gannett. 1898. 8-^. 246 pp. 6 pi. Price 20 cents. 1.55. Eartlii|uakes in California in 1896 and 1897, by Charles 1). Terrine, Assistant Astronomer in Charge of Earthcjuake Observations at th<' Lick Obseryatory. 18118. 8-. 47 pp. Trice 5 ceuts. 15(5. Bibliogra]iliy and Index of North American (ieology, Paleontology, Petrology, and Miner- alogy for the Y'ear 1897, by Fred Houghton Weeks. 1898. 8"-. 130 PI). Trice 15 cents. /« preparation: 1.57. The Gneisses, Gabbro-Sehists, anution.' Under this law the following ])apers have been issued : 1. Pumping Water lor Irrigation, by Hcrl)ert JI. '' ilson. 1896. 8-. 57 pp. 9 pi. 2. Irrigation near Thceuix, Arizona, by Arthur T. Davis. 1897. 8^. 97 p]i. 31 pi. 3. Sewage Irrigation, by George W. Rafter. 1.^97. 8. 100 jip. 4 ]il. 4. A Recimnoissance in southeastern AVashington, by Israel Cook Russell. 1897. 8 . 5. Irrigation Tractiei- on I he Great Plains, by Elias Brans(U» Cowgill. 1897. S^. 6. Underground Waters of Southwestern Kansas, by Er.-ismus Ha worth. 1897. S-. 7. Seepage Waters of Northern Utah, by Samuel Fortier. 1897. 8-. 50 pp. S\)\. 8. Wimlmills 1or Irrigation, by Edward Charles Murphy. 1897. 8^^. 49 pp. 8 pi. 9. Irrig.ition near Greeley, Colorado, by David lioyd. 1897. 8^. 90 pp. 21 pi. 10. Irrig.ition in Mcsilla V.iUev, New Mexiio. by F. C. Barker. 1898. 8-. 51 ]ip. 11 pi. 11. River Heights for 1896, by' Arthur T. Davis.' 1897. 8-. 100 pp. 12. Water Resources of Southeastern Nebraska, by Nelson H. Darton. 1898. 8-. 55 pp. 21 pi. 13. Irrigation Systems in Texas, by William Ferguson Huts(m. 1898. 8\ 67 pp. 10 id. 14. New Tests of Certain Tumps and Water-Lifts used in Irrigation, by Ozni T. Hood. 1889. 8-^. 91 pp. 1 pi. 15. Operations at River Stations. 1897, Part I. 1898. 8. 100 pp. 16. Operations at River Stations. 1897. Part II. 1898. 8-. 101-200 pp. 17. Irrigation near Bakerslield, California, by C. E. Grunsky. 1898. 8^. 96 pp. 16 pi. 18. Irrigation near Fresno, California, by C.E. (Jrunsky. 1898. 8-. 94 pp. 14 pi. 19. Irrigation near Merced, California, by C. E. Grunskv. 1899. 8*^. 59 pp. U pi. 20. Experiments with Windmills, by T. O. Perry. 1899. 8^. 97 pp. 12 pi. 21. Wells of Northern Indiana, by Frank Leverett. 1899. 8^. 82 pp. 2 pi. 22. Sewage Irrigation, Tart II, bv George W. Rafter. 1899. 8'^. 100 pji. 7 jd. 23. Water-Right Problems of Bighorn iilountains. by Elwood Mead. 1899. 8-. 62 pp. 7 pi. , 96 pp. . 7 pi. 39 pp. 12 pk 65 pp. 12i>l. VIII ADVERTISEMEKT. Ill presK: 24. Water Resources of the State of New ^'ork, Part I, by George W. Rafter. 1899. 8°. 99 pp. 13 pi. 25. Water Resources of the State of New York, Part II, by Cieorge W. Rafter. 1899. 8°. 101-200 pp. 12 pi. 26. Wells of Soutliern Indiana (Contiiiuatiiiu uf Nil. 21), by Frank Leverett. 1899. 8-. 64 pp. Ill preparation: 27. Oi)eratious at River Stations, 1898, Part I. 28. Operations at River Statious, 1898, Part II. 29. Wells anpographic forms. This has led to the projection of an educational series of topographic folios, for use wherever geography is taught in high schools, academies, and colleges Of this series the first folio has been issued, viz : 1. Physiograpliic types, by Henry (iaunett, 1X9S, folio, consisting of the following sheets and 4 pages of descriptiNo text: Fargo (N. Dak.-Mmn.), a region in youth ; Charleston ( W.Va.), a region in maturity ; Caldwell (Kans. ), aregiou in old age; Palmyra (Va. ), a rejuveualcd region ; Mount Shasta, (Cal.), a young volcanic mountain; Eagle (Wis.), moraines; Sun Prairie (Wis. ), drumlins; Donald- sonville (La. ), river Hood plains; Boothbay (Me.), a tiord coast; Atlantic City (N. J.), a barrier-beach coast. GEOLOGIC ATLAS OF THE UNITED STATES. The Geologic Atlas of the United States is the tiual form of publication of the topographic and geologic maps. The atlas is issued in parts, progressively as the surveys are extended, and is designed ultimately to cover the entire country. Under the plan adopted the entire area of the country is divideil into small rectangular districts (designated iiiiadranifUs), bounded by certain meridians aud parallels. The unit of survey is also the unit of publication, and the maps aud descriptions of each rectangular district are issued as a folio of the Geologic Atlas. Kach folio contains topographic, geologic, economic, and structural maps, together with textual descriptions ami explanations, and is designated by the name of a princijial town or of a prominent natural feature within the district. Two forms of issue have been adopted, a "library edition'' and a "Held edition." In both the sheets are bound between heavy paper covers, but the library copies are permanently bound, while the sheets and covers of the field copies are only temporarily wired together. Under the law a copy of each folio is sent to certain public libraries .and educational institu- tions. The remainder are sold at 2.") cents each, except such as contain an unusual amount of matter, whicli are priced accordingly. Prepayment is obligatory. The folios ready for distribution are listed below. No. Xamo of sheet. State. Limiting meridians. Limiting parallels. Area, in aqnaro miles. Price, iu cents. 1 Livingston Montana'- 110°-111° 1 85°-85o 30' 120° 30'-121= 84° 3U'-85° 121f-121° ;10' 850-85° 30' 105°-105° 30' 85° :iO'-86° 106° 45'-107° 15' I 77° 30'-7S° 120= 30'-1-Jlo 82° 30'-8;i° 45°-46° 34° 30'-35° 38° 30'-39o 35° 30'-36o 38° 30'-39° 35°-35° 30' 38° 30'-39° 35°-35° 30' 38° 45'-39° 30°-39o 30' 38=-38° 30' ;i6° :iO'-37° 3,354 980 932 969 932 976 932 975 465 925 938 957 25 25 3 4 5 6 Placerville Kingston Sacramento \ Tennessee Cilifornia Tennessee Californi:i Tenuessee Colcnaiio Tennessee Coluraiio 25 25 25 25 7 Pikes Peak (out of stock) 25 25 n Anthracite-Cresteil liiitte Harpers Ferry Jackson EstillviUe 50 10 11 12 MVest Virginia.. [Maryland California [Virginia Kenlurky Tennessee 25 25 25 ADVERTISEMENT. IX No. Naiiie I'f slu'ot. Frt'derickaburg. Staunton Lnssen l*riik.... Kuoxville MarysviUu Snnirtsvjllo Clevebind PikeviUe ilcMiunville. 23 Noniiiii . Tliree Forks Louduu 24 25 2G 27 28 29 i NerjuliiCitv. If Yellowstone \ tional I'ark, /Alaryliuul 1 Vir;riiiij» I \'ii-y,ini;i iWi'Mf \'ir;;inia. C'alil'oruia iTeuiicflsi-e \North Carolina Calit'oruia California {Alalmiua.- Georgiii . . . Teunt-'ssee Tennessee Tennessee Tomiessee fMarvlaml. \Virginia .. Montana. . Tennessee /Virginia ::;) California . AVyoming 32 33 34 35 36 Pocubontas |\ West Virginia . Morristo wn Tennessee .(Virginia Piedmont ■/Maryland ' ilWest Virginia. (Nevada City. Grass \'alleV. Banner Hill . (Oallatin .. Na- 1 Canyon... 1 Shoshone. [Lake _, Pyramid Peak ; California T^' 11- f Virginia ^''■*^"^^*" \Weit Virginia.. Briceville Tennessee Bnckliannon West Virginia . Gadsden | Alabama Pueblo Colorado Do\mieville California Butte Special 1 Montana Trnckee ! California "Wartbiirg ■ Tennessee Sonora I California Nueces , Texas Bid-well Bar , (.'alifnrnia rr 11 (Virginia T-'™"'^11 '\\Ve»tTirgima.. Boise I Idaho Kicbiuonil , Kentucky Londim , Kenliu-ky Teumile District Special \ Colorado Roseburg i Oi'egou I.iniitiliir iniu'idians 79^-7!P 30' l-21o_122o 830 30'-84'= 121° :!0'-122o 1210-1210 30' 850 30'-86o 84O'30'-»5o 850-860 30' S50 30'-8CO TOO 30'--7o 1110-1120 840-810 30' 810-810 30' 830-830 30' (121 J 00' 25"-121o 03' 45" \rn° 01' 3o"-121o 05' 04" ll20o 57/ 05"-121o 00' '.'S" 120O-120O 30' 790-790 30' 84°-840 30' 80O-80O 30' 860-81)0 30' 1040 30'-105o 1200 30'-121o 1120 29' 30"-112o 36' 42" 1200-120° 30' 840 30'-85o 120O-120O 30' lOOO-lOOO 30' 1210-1210 30' > 810 30'-82o 1I60-11C0 3D' 840-840 30' S40-840 30' 106O 8'-106o 16' 1230-1230 30' Liniitiu^ ]>nrallol8. 380-38O 30' 3SO-38° 30' 40°-41° 35° 30'-36o 390-390 30' 390-390 30' Area, iu square milee. Price, tu cents. 390 13' 390 10' 390 13' 390-390 30' 925 50"-39' 17' 16" 11.05 22"-39o 13' 50" 12.09 50"-39o 17' 16" 11.05 3,412 938 ' 938 3,634 925 925 925 25 25 25 350-350 30' 350 30'-36o 350 30'-36o 975 909 969 25 25 2."> 380-380 30' 938 25 450-460 350 30'-36o 3,354 969 50 25 370-370 30' 951 25 30O-30O 30' 963 25 932 25 38° 30'-39° 932 25 36°-36° 30' 963 ' 25 38° 30'-39o 932 25 340-340 30' 986 ' 25 380-380 30' 938 50 390 30'-4UO 919 25 450 59' 28"-46o 02' 54" 22.80 ; 50 390-390 30' 925 25 36°-363 30' 963 23 37° 30'-38° 944 , 25 29° 30'-30o 1,035 \ 25 390 30'-40o 918 25 370-370 30' 950 25 430 30'-44o 804 1 25 370 30'-38° 944 ' 25 37°-37° 30' 95D 25 390 22' 30"-39° 30' 30" 55 25 430-430 30' 871 , 25 STATISTICAL PAPEK.S. Mineral Resources of tlie United .States [18X2]. hy Albert AVilliauis, jr. 1883. 8-'. xvii, 813 pp. Price 50 cents. Mineral Resources of the Tniteil State.s. 1883 ;iu(l 1SX4, liv Albert Williams, jr. 1885. 8^. xiv, 1016 pp. Price 60 cents. Mineral Resources of the United States, 1885. Division of Mining Statistics and Technologv. 1886. 8". vii, 576 p]). Price 40 cents. Mineral Resources of the United States, 1886, by David T. Day. 1887. 8^. viii, 813 pp. Price (50 cents. Mineral Resources of the United States, 1887, by David T. Day. 1888. 8-. vii, 832 i)p. Price 50 cents. Mineral Resources of the United States, 1888, by David T. Day. 1890. ,8. vii, 652 pp. Price ■ 50 cents. Mineral Resources of the United States, 1889 and 1890, by David T. Day. 1892. S\ viii, 671 pp. Price 50 cents. ilineral Re,sourecs of the United States, 1891, by David T. Day. 1893. 8^. vii, 630 pp. Price 50 cents. Mineral Resources of the United States, 1892, by David T, Day. 1893. 8^. vii, 850 pp. Price 50 cents. Mineral Resources of the United States, 189.3, by David T. Day. 1894. 8-. viii, 810 pp. Price 50 cents. I X ADVERTISEMENT. On March 2, 1893, the following provision was iuclnileil in an act of Congress: ■•I'rovidid. That hereafter the report of the mineral resonrces of the United States shall he issued as a part of the report of the Ilireetor of the Geological yurvej'." In compliance with this legislation the following reports have been published: Mineral Kesonrees of the Tnitcd .States, 1894, David T. Day, Chief of Division. 1895. 8^-. xv, fU6 pp., 23 pi. ; xis, I'.io pp., (i pi. Being Parts III and IV of the Sixteenth Annual Report. Mineral Kesourees of the United States, 189.5, David T. Day, Chief of Division. 1896. 8°. xxiii, i542 pp., 8 pi. and maps; iii, .543-1058 pp., 9-13 pi. Being Part III (in 2 vols.) of the Seventeenth Annual Report. Mineral Resources of the I'uited States, 1896, David T, Day, Chief of Division. 1897. 8". xii, 642 pp.. 1 pi. ; 643-1400 pp. Being Part V (in 2 vols. ) of the Nineteenth Annual Report. Jlineral Resources of the United States, 1897, David T. Day, Chief of Division. 1898. 8°. viii, 651 pp., 11 pi. ; viii, 706 pp. Being Part VI (in 2 vols.) of the Nineteenth Annual Report. The money received from the sale .of the Survey iiul)lieations is dejjosited in the Treasury, and the Secret ary of that Department declines to receive Ijauk i-liecks. (b-afts, or jiostage stamps ; all remit- tances, therefore, must lie by M<)^"^;v order, made payable to the Director of the United States (ieiilogieal Survey, or in currexcv — thi' exact amount. Correspondence relating to the publiciitions of the .Suvvi'y should be adr, U.NlTEi) States Geological Si'KVEY, Wasiiinuton, D. C, Jpi-il, lt<99. Washington, D. C. [Tiiko lIiiH loaf out and paHlo tlm si'|iarati-(l tilU's iijioii tliroe of your cjita- loK"*' t-ards. TIio lirMl. and sfcoud tilloa m-cd no adilition : over the third write thut subject iinilor wliicli you would jdaco the t)0olt in your library.] LIBRARY CATALOGITE SLIPS. TJuited States. Department of the interior. {U. S. tieoloijical Kurveij.) I)i!])art.mcnt of tho interior | — | Moiiosiaplis | of ttio | United Status s'-ologioal .survey | Volume XXXII | Part II | [Seal of tho (lepartnient] | Wasliiiigtoii | government itrinting ofiicci | 1X99 Second title: United States gcologieal survey | Charles D. Waleott, director | — | Geology | of the | Yellowstone national park I — I Part II | Descriptive geology, jietrography, and pale- ontology I by I Arnold Hague, J. P. Id(ling.s, W. H. Weed | and | C. D. Waleott, (!. II. Girty, T. W. Stanton, and F. II. Knowltou | [Vignette] | Washington | government printing office | 1899 4°. xvii,893pp. 121 pi. Hague (Arnold) aiHl others. United States geological survey | Charles D. Waleott, di- rector I — I Geology | of the | Yellowstone national park | — | Part II I Descriptive geology, petrography, and p.aleontology | C by I Arnold Hague, ,J. P. Idiiings, W. H. Weed | ami | C. D. Wal- g cott, G. H. Girty, T. W. Stanton, and F. H. Knowlton | [Vig- ^ uette] I Washington | government printing oflice | 1899 4". xvii, 893 pp. 121 pi. [TTnitko Rtate.s. Departmi'nt o/ Ikr interior. {U. S. f/enlogicai survey.) Monograpb XXXII.] United States geological .survey | Charles D. Waleott, di- rector I — I Geology | of the | Yellowstone national park | — | Part II I Descriptive geology, petrography, and paleontology | by I Arnold Hague, .1. P. Iddings, W. H. Weed | and [ CD. Wal- eott, G. 11. Girty, T. W. Stanton, and F. H. Knowlton | [Vig- nette] I Washington | governincnt printing oDice | lSfl9 4°. xvii, 893 pp. 121 pi. [Uniti-iI) States. lii-jiarlmnit of tin' intniur. {II. S. genioijical eurvry. Monograpb XXXH.] MON XXXII .58