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Vener Dit est ere aby ns oe STretonanaveriiguees sevareserecst@e-os eae bya hee mare iriseckess eeteresre tat Peper ert RA es I OF THE UNIMER SS 1G OF TLLINOUS ala i Ge) op Un34K Z VA em, =, E80 / LIBRARY USE ORLY Digitized by the Internet Archive in 2011 with funding from University of Illinois Urbana-Champaign http://www.archive.org/details/reportofgeologicO1 unit n coi: one | Ue PROFESSIONAL PAPERS OF THE ENGINEER DEPARTMENT, U.S. ARMY. No. 18. REPORT OF THE GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL MADE BY ORDER OF THE SECRETARY OF WAR ACCORDING TO ACTS OF CONGRESS OF MARCH 2, 1867, AND MARCH 3, 1869, UNDER THE DIRECTION OF BRIG. AND BVT. MAJOR GENERAL A. A. HUMPHREYS, CHIEF OF ENGINEERS, BY CLARENCE KING, U. 8. GEOLOGIST.? ote . VOLUME I. ’ x o 7 = F . i ‘ “ Y : oe uM rn 5 fe - ‘ = Sr - - ” sue ‘ - 7s aw - 2 —— a - a Ea 7 4 > 1 * ~ 7 > 5 5 ; f . an | v ~ ' : i : . _ ae J ' =) , a . ae z a 3 a nd _——— .. H } ‘ * ay P as Ke * t = : 1 _ . { a Fes - a a ~ - t = - , * = _ | : ‘ -- os 7 i . a i ‘ ce y 7 1 A SS a — a ‘ i : ' ‘* : 5 if . UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL, CLARENCE KING, GEOLOGIST-IN-CHARGE. SYSTEMATIC GEOLOGY BY CLARENCE KING U. 8S. GEOLOGIST. SUBMITTED TO THE CHIEF OF ENGINEERS AND PUBLISHED BY ORDER OF THE SECRETARY OF WAR UNDER AUTHORITY OF CONGRESS. ILLUSTRATED BY XXVIII PLATES AND XII ANALYTICAL GEOLOGICAL MAPS, AND ACCOMPANIED BY A GEOLOGICAL AND TOPOGRAPHICAL ATLAS. P WASHINGTON: GOVERNMENT PRINTING OFFIOK. 1878. V-VI ey Me { 4 “a A ke Ve) Géiorer LABr En On CONDENS: ENTRODUOTORY LETTER ..2-s.-ceeeeeo alot iets ote c/a, wialecwawy MIOCENE TERTIARY..-.-...... aye clare erento sey ee iererere IPETOCENE DER DIAR? a eis eeleeieie ceciceere samara ss RECAPITULATION OF TERTIARY LAKES..........- QUATERNARY .....- erhecesee Spe odes Bt etaiora Sai arcane PROPYLIDES se. +e Son oo ecRaocuosade Seteieieleket tee TASNID ESTEE Sprereteyyoyereteistelere Siajeiselsucerereiee eistaiesisvens Sere TRACHYTES..... ei ayowrsin Blele ciety akeree ye Serotiteicine a cle:s REYOLITES! <2. 1c scieciee = waroeteramererets etepenee ey eia.tic ESAS TAME DS Says tet melt iter siecloteronersiats Bese tantarate hess ae CORRELATION AND SUCCESSION OF TERTIARY VOL- CANIC Rocks FUusIoN, GENESIS, AND CLASSIFICATION OF VOL- CANIC Rocks wI4\> VIII TABLE OF CONTENTS. Page. APPENDIX BY J. T. GARDNER ON GEODETICAL AND TOPOGRAPHICAL . MR PHODS er ereretetereterecshe le eiaiatetetereratclars cieiaiarciaraioteseremieteie reine mya is eravaletere aie che stare 762 1 G00) 0), CoRR Pace aan Wi eletar. e eee yer ee mG e HONS Ee AA AOE Teil TABLES OF CHEMICAL ANALYSES. I. ARCHZAN METAMORPHIC ROCKS...... -. -- Raver bale ae eels mm aeiee oer inhl TEAR CHATAN PE RUPTEVE) GRANTDES ccc ceteciciecin creas cieleleiciaeieioieislsleleaielotele 111 III. DEsiccATION-PRODUCTS OF LAKE BONNEVILLE........ elseistee eaeioeiee 502 EV SALINE AND HOT-SPRING ERODUOTS jes scl «soi isteinleleveleliviay= sole) aleletsic lalate 503 V. DESICCATION-PRODUCTS OF LAKE LAHONTAN ....-....2.--.ceesee- ee 528 VI. A.-B. SEDIMENTARY ROCKS, LIMESTONES......---. -- 2+ eeee sees ceee ee 543 VII. A.-B. SEDIMENTARY ROCKS, QUARTZITES AND SANDSTONES.........-. 543 VIII. PROPYLITES AND QUARTZ-PROPYLITES........--2- +200 e---00 eee eee 560 EX. ANDESITES AND DAGITNS seem ec cerecce ctelecccesiciee sa elcee eee eee ame OX CAN = SS RAC He IGS epee rete terete er seat telco alot ae : ; ‘ 2 z = . 4 A . — i ; . - ' | _ 1, - ; i } = j i - £ i ¥ ] 1 ’ SS CHAPTER II. ARCH AAN. SEctTion I.—ARCHAAN EXPOSURES.—COLORADO RANGE—MEDICINE Bow RANGE— PARK RANGE—UINTA RANGE—WAHSATCH RANGE—SALT LAKE ISLANDS AND PROMONTORY—RAFT RIVER MOUNTAINS—DESERT GRANITE RANGE—GOOSE CREEK HILLS—OMBE RANGE—GOSIUTE RANGE—PEOQUOP RANGE—WACHOE MouNTAINS—KINSLEY DISTRICT—FRANKLIN BUTTES—HUMBOLDT RANGE— CoRTEZ RANGE—WAH-WEAH MOUNTAINS—SEETOYA RANGE—TOYABE RANGE— SHOSHONE RANGE—AUGUSTA MOUNTAINS—FISH CREEK MOUNTAINS—HAVAL- LAH RANGE— PAH-UTE RANGE— WEST HUMBOLDT RANGE — MONTEZUMA RANGE—PAH-TSON MOUNTAINS —PAH-SUPP MOUNTAINS—GRANITE RANGE— TRUCKEE RANGE—LAKE RANGE—PEAVINE MOUNTAIN—CALIFORNIA BORDER. SECTION II.—CORRELATION OF ARCHAAN Rocks.—METAMORPHIO Rocks— GRANITES. SECTION III.—GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. SECTION [V.—PRE-CAMBRIAN TOPOGRAPHY. SECTION I. ARCHAAN EXPOSURES. Throughout the Cordilleran system in the western United States there is observed the usual distinct nonconformity between Archzean and subse- quent formations. At intervals over the whole mountainous area west of the 100th meridian, masses of gneiss or crystalline schists, with their asso- ciated marbles, dolomites, and quartzites, and eruptive bodies of granites, porphyries, gabbros, &c., are found to underlie more recent strata. These Archzean bodies are made to outcrop in three modes: First, the summits of Archzean mountain chains whose original elevation above the surrounding topography lifted them, if not over the level of sub- 15 16 SYSTEMATIC GEOLOGY. sequent ocean surfaces, at least above the plane of all subsequent deposition of detrital material. In spite of the powerfull:; accidented surfaces of Ar- cheean areas, and of the distinct and lofty chains whose existence I shall in the following pages endeavor to demonstrate, these primitive summits are the rarest of Archzean outcrops. That they should exist at all is rather to be wondered at, when we remember that a series of later rocks extending from the earliest Cambrian to the present period, and amounting in extreme cases to probably not less than 40,000 feet, has been superposed upon them, and that the region as a whole has been repeatedly subjected to some of the severest mechanical disturbances of which we have any knowledge. Yet such uncovered primitive summits do exist. Secondly, a type of occurrence due to local uplift or faulting, of less importance in a geographical sense than the last group. Archsean rocks are, indeed, here and there thrust through their younger covering; but these are limited blocks, the results of some severe local disturbance, crowded up to the surface or left upon the face of prominent fault walls, and although more frequent than original island summits, they constitute but a small part of the total exposure. Thirdly, the predominating type of outcrop is a result of erosion either upon the axial areas of later elevated mountain chains, or along their flanks, or in those deep river canons of which the system of the Colorado offers the strongest example. At present we have no conclusive proof of metamorphism of Paleozoic strata to so extreme a point as to endanger a mistake between the resultant rocks and those of Archean age. So far, unless in California, the Palzeozoic sedimentary series have only yielded limestones, quartzites, and slates, whose observed alteration-products do not in the least resemble Archzean forms. Perplexities like those in the Appalachian system are not yet brought to light; and the Archzean rocks themselves, as now known, present but a limited number of species. As a general result of this wide-spread petrological simplicity of areas, and the comparatively unaltered condition of Palzozoic formations, the relations between the two are exceedingly plain. Details of the buried and partially exhumed Archzan continent must ARCHASAN EXPOSURES. 17 be accumulated very slowly; but there is still ample room in the remaining unexplored regions of the Cordilleras to find new features and perhaps to present many exceptions to the general laws which the writer is about to deduce from present data. Cororavo Rancr.—That part of Colorado Range lying within the limits of the Fortieth Parallel Exploration, as shown upon Map L, is comprised between latitudes 40° 15’ and 42°. At the northern extremity of the map the range consists of low rolling hills, having a breadth from east to west of about fourteen miles. This width is maintained, with slight varia- tions, down to the region of the railroad, where the range rapidly widens upon its west side, until at the southern line of the map it has reached 35 miles. North of the railroad, the physical characteristics are quite uni- form, the range consisting of a moderately rolling upland, with but few prominent summits, the drainage divide being carried very near the western edge. Streams which for the most part flow eastward have carved out shallow, rocky valleys. The whole uplift is little more than a rolling pla- teau, of which the greatest elevations are in the neighborhood of 2,500 feet above the plains at the east base. The highest summits are a little north of Cheyenne Pass, on the west side of the range, about in the latitude of Laramie City, where the broad, undulating crest reaches the altitude of 9,077 feet. Northward, as far as the upper streams of the Chugwater, the average elevation of the plateau is between 7,500 and 8,000 feet, with peaks reaching 8,600 feet. Thence the plateau country falls off, but rises again in rugged, granite hills, just beyond the limit of the map. South of the rail- road, where the pass-summit reaches 8,242 feet, the line of greatest ele- vation, as well as the watershed, deviates from the meridional line in a southwesterly direction, continuing about 45 miles to Clark’s Peak, a high summit, which belongs more properly to Medicine Bow Range. ‘This divi- ding summit is a broad, gneiss plateau of rolling, forest-covered surface, unrelieved by any high peaks, and unaccidented by any deep canons. The eastward slope, drained by the various forks of the Cache la Poudre, partakes of this same undulating character as far southward as Monitor Peak, latitude 40° 45’. From this point a decided change in the configura- tion of the range takes place. Between the waters of the Cache la Poudre 2K 18 SYSTEMATIC GEOLOGY. and the Big Thompson, a lofty, confused group of peaks, rising constantly to the south, occupies the whole broad area between the Great Plains and the North Park. Hague’s Peak, latitude about 40° 30’, having an alti- tude of 13,832 feet, is the centre of a considerable area of drainage, from which flow northward the South or Main Fork of the Cache la Poudre, and southward and eastward, in deep canons, the Big Thompson. [rom Hague’s Peak, bold spurs slope to the south and southeast, down to the level of a picturesque basin in the mountains, known as Estes’ Park. The country also slopes westward into a depressed region, and rises again at Mount Richthofen. South of Estes’ Park, and south of the limit of the map, the summit culminates in Long’s Peak. In the northern part of the range, and indeed as far south as the head of the North Fork of the Cache la Poudre, 500 feet is the usual depth for canons, and in consequence they offer but shallow exposures of Archzean rocks; while south of that point, corresponding to the greatly increased ele- vation of the peaks and general magnitude of the topographical features, the canons also increase in depth, until between Monitor and Comanche peaks there is a depression of 3,500 feet, with an equal one on the upper waters of the Big Thompson, and the average drainage valleys of this region are not less than 800 feet between walls. Consequently it is in this part of the range that the best exposures of the Archzean rocks may be obtained. Regarding the Archzean exposure as one, it will be observed, by refer- ring to Map I, that owing to differences of upheaval, of original overlap, and of erosion, the relation between Archzean and later series varies from a contact at the lowest horizon of the Paleeozoie up to the most recent of Pli- ocene conglomerates. For about 36 miles on the east side of the range, beginning at the southern limit of the map, the contact-line is between the red strata of the Triassic series and the Archean. From that point, for about 40 miles northward, it is chiefly between Archzean and lower Palxeozoic, which throughout this whole distance have a steep easterly dip; thence northward to the extremity of the range the Tertiaries some- times overlie and entirely obscure the edges of the upturned Paleozoic and Mesozoic series, bringing the Pliocene conglomerates directly in con- ARCHAIAN EXPOSURES. 19 tact with the Archean. In this northern part, heavy promontory-like masses of the Archean jut eastward from the main trend of the east base, throwing the upturned stratifeed rocks into sharp, complicated curves ; the dip of these sedimentary beds varying from about 16° in the south, to a vertical position along the northern slopes, and in some rare instances a reverse dip. On the other hand, the western limit of the northern half of the Archzean exposure is observed to be in contact with the lower part of the Palzeozoic series, which for the upper 55 or 60 miles of the map dip gently westward, with slight local disturbances. South of the railroad, at Harney’s Station, the Triassic series have advanced eastward, and overlap, obscuring the Carboniferous, and the trend of the line of contact between the Trias and the Archzean is to the southeast, occupying a position on the flanks of the southwest divide before described. From the region of Long’s Peak Medicine Bow range deviates from the north-and-south trend of the Colorado body, in a direction about north 30° west, extending 100 miles to Elk Mountain, after which it plunges beneath the Cretaceous formations of the Platte Plain. For about 30 miles from Long’s Peak it is essentially so united with Colorado Range as to be geographically inseparable ; but from Clark’s Peak to Elk Mountain it pre- serves a direction and a character quite its own. It varies in width from about 12 miles opposite the middle of North Park to 80 miles in the region of Marble Peak. Northwest of Clark’s Peak a high rugged ridge is maintained for 8 or 10 miles, but it then falls off to a low rolling pass, utilized by the road from Laramie River to North Park. he lead- ing characteristics of the country from Clark’s Peak northward are not unlike those of the northern part of Colorado Range. In passing north- ward the range gradually rises to a culminating point about latitude 41° 20’, known as Medicine Peak, which reaches an altitude of 12,231 feet; but even here there is little of the rugged character usual at such heights, the canons all exhibiting comparatively broad and gentle flanks. Still farther northwest, in the region of Cherokee Butte, the later sedimentary rocks on both sides of the peak approach within two miles of each other, and the mass of Elk Mountain, a semicircular Archzean body, is entirely surrounded by later stratified rocks. The broad angle between Colorado 20 SYSTEMATIC GEOLOGY. and Medicine Bow ranges is occupied by Laramie Plains, which con- sist chiefly of gently inclined Cretaceous strata, abutting nonconformably against the sloping foot-hills of the Archzan mass of Medicine Bow and overlying, along the eastern side of Laramie Plains, the Jurassic, ‘Triassic, and Paleozoic, which dip at gentle angles from Colorado Range. The west side of Medicine Bow Range sinks into the valley of the North Platte, whose great expansion south of latitude 40° 50’ is known as North Park. . With the exception of a fragment of Carboniferous and a few miles of Triassic, Jurassic, and lower Cretaceous strata, the whole western margin of Medicine Bow Range is covered with but slightly disturbed Tertiary beds. Near the southern extremity of the map the sedimentary margin of the range, as well as the edge of the Archiean core, is overflowed by a mass of rhyolite. It is therefore essentially an irregular, elongated body of Archaean rocks, having its flanks submerged beneath gently inclined Cretaceous and Tertiary series, with a few outcrops of the Paleozoic and the Mesozoic strata appearing at intervals under the more recent sedimentary series. West of North Park, and west also of the valley of the North Platte, lies the northern extremity of a bold wall of Archzean rocks, which extends southward for many miles and forms the western boundary of the series of Colorado parks. To this elevation Mr. James T. Gardner has applied the name of Park Range. About 70 miles of its northern end are embraced within Map I. ‘Topographically it may be considered as a north- and-south range as far north as Pelham Peak, from which point the main mass has a northwest trend approximately parallel to Medicine Bow Range. With the exception of a narrow strip of Triassic and Jurassic strata in the northern part of North Park, and a little Cretaceous against the middle of North Park, the whole eastern margin of this great Archean body is formed by overlying Tertiaries of North Park and Platte Valley. On the west, however, it is chiefly margined by Cretaceous beds, which in one or two places give way to unimportant outcrops of the Jura, and in the region of Hentz’s Peak to considerable outbursts of trachyte. Out of the rolling Cretaceous plains which lie west of the valley of the Platte, in the region of Fort Steele, is lifted a dome-like exposure of older rocks, consisting of the whole stratified series, from the middle Cretaceous down to the Silurian, ARCHASAN EXPOSURES. Pil with a long, narrow outcrop of Archean core in the centre. Although it is remote from either of the main ranges and quite detached from all other Ar- chzean masses, there seems little doubt that this exposure is really a part of the submerged continuation of Park Range, separated from the main mass in the same manner as Elk Mountain is separated from the body of Medicine Bow Range. The central ridge of Park Range varies from 11,000 to nearly 12,000 feet high, its loftiest peak reaching 11,976 feet. North of Mount Zirkel the summits are less elevated, and at the extreme north- western end the greatest altitude is reached in Grand Encampment Moun- tain, 11,063 feet. These three Archzean bodies—Colorado, Medicine Bow, and Park ranges—should be considered as a single chain, whose varied folds - and greatly diversified structure represent the top of a broad Archzean sys- tem; for the separating depressions—North Park, Platte Valley, and Lar- amie Plains—are really but the unimportant shallow basins in the Archeean topography in which the later material has been laid down, That the granitoid and erystalline-schist cores of these ranges are truly Archean in age, is indicated not alone by their characteristic pet- rological facies, but also by the fact that several actual contacts are exposed between the crystalline rocks and either the Potsdam sandstone or a series of conformably underlying slaty rocks presumably Cambrian. These exposed points of contact lie to the north and south of the area of Map IL, but have been visited and studied by the writer, to make sure of their relation. With regard to the Archzan core of Colorado Range within our limits, independently of the relics of superposed strata, it may be said in general to consist of a broad central anticlinal, having along its axial summit a very flat arch, the dip increasing rapidly as the rocks recede from the axis. Considered in longitudinal elevation, the former crest which must have marked the summit of this Archzean fold was neither a horizon- tal line nor a simple inclined one, but possessed several prominent sags or saddle-like depressions; so that the ideal axis of the range, viewed longitudinally, was a deeply undulating line. Furthermore, from longitu- dinal pressure it was also deflected in plan into considerable horizontal sinuosities, and consequently the sides of the anticlinal were alternately thrown into broad convex folds (upon which the strata were brought into 22 SYSTEMATIC GEOLOGY. a state of strain), and recurved in broad reéntrant bays in which the beds were severely crumpled in secondary folds or confusedly dislocated. Added to these disturbances, was a third series of effects resulting from forces that tended to warp the anticlinal, which introduced an irregular shearing, and complicated not only the main fold but the secondaries. As a result, there is one broad central fold with numerous parallel subordinate axes, whose corrugations probably do not penetrate deeply into the strata. It is assumed that all this dynamic action took place after the crystal- lization and consolidation of the rocks themselves—in other words, after they had attained their present phase of metamorphism and crystallization. Subsequently to this system of compound folding, and still before the Cam- brian age, a wide-spread erosion teok place, rounding off and smoothing down the general forms; but it was absolutely powerless to produce sharp canons, or other abrupt features, and had the effect rather to reduce than to heighten the topographical effects of the folding and faulting. Before proceeding to localize any observations within this Archzean body, it will be well to give a condensed sketch of the sequence of the rocks involved in this range. It would be difficult to find a corresponding area in any Archaean country of greater petrological simplicity and unity. The chief rocks are granites and granitoid gneisses, with a few subordinate mica-schists, and in the uppermost or gneissic members a few limited sheets of hornblendic gneiss, the main series being composed of quartz, orthoclase, and mica (chiefly biotite), with a slight admixture of triclinic feldspar. The lowest exposures in the heart of the anticlinal consist of massive pearly and reddish-gray granites, composed almost entirely of quartz and ortho- clase, with a small but variable percentage of mica and a few minute crys- tals of triclinic feldspar, mostly oligoclase. These granites, exposed where erosion has deeply carved away the axial region of the range, or has cut profoundly into an especially disturbed portion of the flanks of the anti- clinal, are remarkably uniform in appearance, and are only varied in the amount of crumbling and decomposition which they show, in the propor- tion of mica, or in the ordinary variability in the size of the quartz and feldspar particles. The latter, either simple or twinned orthoclases, vary from an inch and a half to a size invisible to the naked eye. This granite, ARCHAAN EXPOSURES. 93 which is a characteristic aplite, never presents a true bedding, but ap- proaches a tabular formation as the mica increases. Followed over consid- erable distances, its texture and color are found to change constantly, and in the more crumbling parts, where the granite “malady” has acted most deeply, are found large spheroidal masses of more enduring texture, which have resisted disintegration, and remain either single or in confused heaps. Directly succeeding this formation, and with no apparent unconformity, is a series of more noticeably red granites, showing a distinct bedding which defines their structural relations to the anticlinal. This latter series is com- posed, like the former, of quartz and orthoclase, in this case usually quite red, and mica rather more abundant than in the earlier group, which shows a constant tendency toward a gneissic arrangement of particles. There are no signs of the granite malady; on the contrary, the rock breaks with a sharp angular fracture and shows no effects of rapid disintegration. As in the earlier reddish pearl-colored variety, mica is often wanting, and indeed this member throughout its lower beds may be called a true aplitic granite. At its upper limits only does mica become a prominent mineral, and here it passes by a series of irregular but gentle gradations into true mica- gneisses. Owing to the innumerable faults and complicated folding upon the flanks of the range in the region chiefly occupied by the mica-gneisses, it is impossible, without very extended labor, to arrive at their thickness. There cannot be less than 12,000 or 18,000 feet of them, and there may be twice that amount. From the lowest exposures to the highest, there is a gradual passing from the structureless granitic form through simple broadly bedded gran- ites—which even in the field, without close examination, appear to possess no parallel structure, but upon close following are seen to shade through a general tabular bedding—up to a zone occasionally interrupted by true gneiss beds, which become more and more frequent until the bedded granites are entirely excluded from the series, and thereafter for a great thickness there appear only dark mica-gneisses; these, however, present a very great variety. South of the line of the Fortieth Parallel work, in the region of Ralston and Coal creeks, the late Mr. Archibald R. Marvine, of the United States Geological and Geographical Survey of the Territo- 24 SYSTEMATIC GEOLOGY. ries, brought to light an overlying group of quartzitic, ferruginous schists and quartzites, whose probable equivalents will be described in a later part of this chapter, in localities farther to the west. Equally with the gneisses and mica-schists, the above-described granites are held to be of metamor- phic origin. Of truly eruptive rocks, there are unmistakably intrusive granites, powerful outbursts of gabbro, and dikes of felsitic porphyry, the latter enclosing within the microfelsitic groundmass a varying proportion of crystals of quartz, triclinic feldspar, and lepidolite. It was not within the scope or time of this exploration to cover ground with enough minuteness to map out boundaries of the various members of this series, and the above generalized sketch of the structure and sequence of rocks in our section of Colorado Range is only offered as a tentative explanation whose leading outlines may be relied on, but whose details will of necessity be found subject to slight modifications. The central or oldest body of granite is well exposed on the railroad from a little east of Buford Station westward to about two miles down the west slope from Sherman. It is here characterized in color by a pinkish orthoclase, and is noticeable for its extreme disintegration. To the north and south of the road, rising above the gravelly plateau country, are seen several bold outcropping groups of the hard spheroidal nuclei before men- tioned. Some of these forms reach 40 or 50 feet in diameter. Skull Rocks and Tower Rock are well known examples in the immediate vicinity of the railroad. The trend of this mass of granite is a little to the east of north, and so far as is now known it passes out upon the east side of the range. In other words, the axis of the modern range was slightly diagonal to the Archean fold. Passing southward from Sherman, the harder outcrops rise above the disintegrated material for a few miles, when there seems to be a gradual change in the character of the granite, which becomes harder, the feldspars larger and whiter, rather more mica makes its appearance, and the whole body seems to trend off to the southwest, probably parallel to the water- shed. In the broader part of the range, at the head of the South or Main Fork of the Cache la Poudre, the sharply folded rocks of Medicine Bow ARCHASAN EXPOSURES. 2a Range make contact with those of Colorado Range in a complex manner. The whole country, to the uppermost limits of the timber growth, is ob- secured by forests and glacial débris; but it seems quite clear that the older Colorado granite here passes under the Medicine Bow series and does not reappear at least as far south as Long’s Peak. If it reappears at all in that latitude, it must be to the west and below the red granites of Estes’ Park. The projecting mass in the northern part of the range, in the region of the Chugwater, which advances like a promontory into the eastern plains, seems to belong to the central and older mass of granite. If this slight chain of observations is correct, and it seems to be essen- tially so, the axis of the Archean fold is deflected westward from the merid- ian about 20°, from the northern limits of the map down nearly to Long’s Peak, where it turns into the line of the meridian and continues southward on that strike for many miles. The second series, or the bedded granites, as before mentioned, possess several distinctive features in contrast with the older family, and many features in common. Like the older rocks, they are distinctly aplitie for the most part, but at their upper limit, by the rapid accession of mica, they pass into distinct mica-gneiss. They are more compact, more massive, show more bedding, and in weathering result in less distinctly rounded forms. The granite malady does not seem to have affected them, and there are none of those regions of fine granite gravel, with harder nuclei outcropping. In general, they are of deeper colors, dark reddish grays and reds prevailing. On the railroad they are well shown _at Granite Canon, and may be traced thence north and south, the northward extension disappearing beneath overlying Carboniferous limestones at the head of the North Fork of Crow Creek. Southward along the range they reappear at intervals, the red granite of Estes’ Park and the lower Big Thompson offering well known examples. Besides biotite, these granites contain a second dark mica, which Zirkel identifies under the microscope as lepidomelane. A similar belt of granite bounds the west side of the older or central mass, appearing a few miles northwest of Sherman, and extending thence north along the west side of the range, disappearing in the region of the Sybille beneath westerly dipping beds of pearl-gray eneiss and black hornblendic schist. The same characteristics are observ- 26 SYSTEMATIC GEOLOGY. able in this mass of flanking granite as in its companion formation upon the east of the range, as typified at Granite Canon. It is, perhaps, even more distinctly aplitic on the west than on the east. Passing southward, it crosses the railroad a few miles west of Sherman, and continues southwest- erly for an unknown distance. West of the head of Fish Creek and Sports- man’s Creek a similar red bedded granite is observed, which is probably the identical mass. About the head of the Main Fork of Cache la Poudre, overlying some obscure granite bodies, are found heavy masses of dark eneiss, which cannot be identified with any rocks lying to the north, but may be related either to the gneissic rocks of Medicine Bow Range, to be here- after mentioned, or to those dark mica-gneisses which are developed farther south on Colorado Range, in the region of Clear Creek. A peculiar dark red granite is seen on the railroad at Dale Creek bridge, which in some re- spects is a little different from any other in the range. It is of an intensely deep-red color, and contains broad, tabular crystals of red orthoclase; gray quartz, which seems to occupy a very subordinate position in crystallization, being chiefly wedged into the interstices between the orthoclase crystals. Like the Granite Canon rock, it contains lepidomelane. Under the micro- scope, Zirkel observed small triclinic feldspars. The bedded granite of Long’s Peak is remarkable in a general way for the predominance of twinned crystals of orthoclase, very much elongated in the direction of the bedding. These strata have a dip of from 5° to 8° to the east. The directly under- lying formation is of a distinctly bedded, coarse-grained, pinkish granite, much like that of Granite Canon, and is probably of the same horizon. The gentle slope of these easterly dipping beds carries the formation down along the waters of the Saint Vrain’s and Big Thompson nearly into con- tact with the overlying Trias. Near the modern rocks a gray granite, apparently the same as at Long’s Peak, reappears. Southward over the Long’s Peak rock are piled up the enormous series of gneisses, best shown on Clear Creek. Exposures on the upper Sybille, and those seen along the eastern base of the mountains in the region of Signal Peak, seem to be the representatives of the lowest members of this vast granitic series, the greater breadth and altitude of the range to the south retaining all the members of the fold, while to the north, owing to the gradual depression of ARCHAZAN EXPOSURES. 2 the range and the constant encroachment of overlapping sedimentary rocks upon both sides, only the lower or core members are exposed. Aside from the above-mentioned rocks which constitute the members of this great fold, there is a most interesting feature in the occurrence of an immense mass of ilmenite, near the east base of the range, just north of Chugwater Creek, about a mile and a half abeve where it flows out upon the plains. It has an irregular oval plan, with a sharp definition from the enclosing granite, and rises in a bold boss about 600 feet above the bed of the stream. Masses of granite invade the ilmenite for a short distance, and in their turn protuberances of iron are nearly enveloped in surround- ing granite. The main mass is perhaps a quarter of a mile long, having a trend a little west of north, terminating quite abruptly to the north, but extending eastward, and followed by a train of irregular subordinate out- crops for about two miles toward Pebble Creek. In the vicinity of Horse Creek are smaller deposits, described by Mr. Hague in Volume II. Some normal magnetite and small amounts of hematite accompany the main body of ilmenite. In all these exposures titanic acid enters as a varying but usually very important component, ranging from 20 to 50 per cent. Graphite in impure thin beds, mixed with a bronzy decomposed iron pyrites, is found in the later granitoid rocks of the west side of Laramie Hills, and elsewhere through Colorado Range, in small, scattered occur- rences. In eruptive rocks our section of the Archean range under consideration is decidedly poor. The most important is the group of gabbros, found to the east of Iron (ilmenite) Mountain, and on Chugwater and Horse creeks, all within a narrow geographical area, where they come to the surface through granites and form low rough domes. It is essentially a bluish-gray labradorite, with a little finely disseminated hypersthene. A yellowish- white mica and some fine rounded grains of magnetite and ilmenite are also included with the mass. This association of graphite, ilmenite, and gabbro in the granitoid rocks of Laramie Hills, first observed in the West by Arnold Hague, will be commented on later in this chapter, Besides these there are distinetly intrusive granites and felsitie por- 28 SYSTEMATIC GEOLOGY. phyries which occur along the southern line of our work and still farther south in the range. The porphyries are a microfelsitic groundmass composed of orthoclase (as shown by analysis), quartz, and a little triclinic feldspar. In this are enclosed rounded grains and rudely dihexahedral crystals of quartz, both covered with an opaque coating of fine feldspathic material, crystals of feld- spar (orthoclase as far as determined), and more rarely a white mica, doubt- less muscovite. Porphyry dikes appear usually not far from the middle or axial part of the range, and are found to trend either a little west of north or at right angles to that strike. The intrusive granites are for the most part combinations of quartz, orthoclase in slender tables and twinned crystals, and, curiously enough, muscovite instead of biotite. Triclinic feldspars, though uncommon, are occasionally present. Mepicine Bow Ranecr.—Viewed as a whole, the Medicine Bow offers more complexity, both of material and structure, than Colorado Range Although impossible to an exploration like this, a minute study of the super- position and flexures of its crystalline beds would furnish most interesting special results. While the data gathered by Mr. Hague seem to point with satisfactory agreement to a general theory of the range, on the other hand its exact relation to the contiguous body of the Colorado is not discovered, nor is it by any means certain that the whole series involved in the Medi- cine Bow is conformable throughout. The materials of the range are composed of gneisses; hornblendic, often dioritic, schists; variable schists made of quartz, mica, and both sys- tems of feldspar, in changing proportions; quartzitic schists; argillites; massively bedded quartzites and limestones which pass into quartzite by the giving out of calcareous matter; and lastly subordinate granites and erup- tive diorites. All the observed positions south of a line joining the mouth of French Creek and Sheep Mountain, with obviously local or superficial exceptions, indicate a northwest strike and southwest dip. North of this line two dis- tinct axes, approximately parallel and trending about north 20° to 25° ARCHAAN EXPOSURES. 29 east, are developed across the range; an anticlinal lying a little west of Medicine Peak, and the companion synclinal occupying a depression between Medicine and Mill peaks. Rocks having a northwesterly dip rise from the Platte valley up to the heights on Upper Brush Creek, pass over the anticlinal, and dip down and east through Medicine Peak, rising again with a westerly dip at Mill Peak ridge. These two transverse axes embrace within their folds the iridescent schists, quartzitic schists, argillites, quartzites, and limestones. Their relation to the older and underlying mica gneisses and various hornblendic schists and dioritic gneisses is apparently that of conformity—at least no nonconformity has been observed; for- ests, débris, and local folds conspiring to mask a relation obscure enough under favorable exposures. Whether conformable or not, there are here two series of rocks. The lowest, which have an enormous development, are the gneisses and hornblendic beds, all characterized by the important pres- ence and the frequent predominance of plagioclase over orthoclase, by the general (though not unexceptional) absence of red color among the feld- spars, the occurrence of silvery white micas in some gneisses, and frequency of beds with the composition of diorite. Above these the schists, quartzites, conglomerates, and limestones of Medicine Peak group form the second series. Neither of these seems to correspond, either mineralogically or in broader characteristics, with any portion of Colorado Range within our field. There is, indeed, an apparent resemblance between the Medicine Peak series and that described by Archibald R. Marvine* at Ralston Creek, but it disappears on close comparison The probable mutual relations of these members of the Archzan is reserved for a later section of this chapter. In the region where this elevated mountain block comes in contact with Colorado Range proper, particularly where a high ridge is developed, culminating in Clark’s Peak and Mount Richthofen, the geological relations of the two ranges are difficult to make out. Forests and glacial dcbris combine to offer serious difficulties to a more lengthened study than our exploration permitted. Topographically, the most noticeable feature is the defined line of ridge * United States Geological and Geographical Survey of Colorado (1873), p. 189. 30 SYSTEMATIC GEOLOGY. and peaks which forms the extreme western boundary of the high mountain area, sharply descending beneath volcanic bodies and upturned stratified formations along the east boundary of North Park. The singular trough- like depression which separates this southernmost group of Medicine Bow Range from the chain of central elevations of the Colorado body is occupied by Cache la Poudre and Laramie rivers, which together define a line of depression parallel with the Clark’s Peak ridge. ast of this lies the anti- clinal of Colorado Range already described. The Clark’s Peak wave, as far as can be seen, consists of another and probably a later series of rocks. Structurally, these two series bear a relation to each other not unravelled by actual observation, but inferred, from their relative position, to be a nonconformity. Along the eastern edge of North Park sedimentary border, with a universally obvious unconformable underlie, is seen a series composed for the most part of steeply dipping gneisses and gneissoid beds, which consti- tute the main west slope of the Clark’s Peak ridge. Unlike the series of the Colorado, they contain, besides quartz, orthoclase, and biotite gneisses, a predominance of sheets in which hornblende and plagioclase are prominent if not the chief ingredients. Near the base of the ridge, a few miles north of Clark’s Peak, are conspicuous beds made up of pale pinkish feldspar and bright green hornblende. Besides the predominating orthoclase, distinct small crystals of colorless plagioclase are present. With the exception of this limited belt, the feldspars, of whichever system, contained in these eneisses are usually colorless. A typical gneiss of the region occurs directly west of Clark’s Peak, consisting of biotite, hornblende, quartz, orthoclase, and plagioclase, the latter two nearly white, and a little microscopic apatite. Near the base of the peak occurs a granite not far removed in composition from the orthoclase and quartz aplite of Laramie Hills. Clark’s Peak itself and the ridge in its neighborhood, as well as a broad area to the north, offer a variety of granites. That of Clark’s Peak is quite devoid of any gneissic parallelism of minerals, and is of such uniformity and massive habit as indicate an eruptive origin. It is composed of limpid white quartz, orthoclase, plagioclase, biotite, and apatite. The mineralogi- cal equivalency between this rock and the gneiss lying to the west and down ARCHASAN EXPOSURES. oil the slope will be noticed, and will naturally suggest that the summit rock is only a structureless equivalent of the gneiss, representing a further con- dition of metamorphism. Hornblende in the gneiss, however, offers a per- manent difference. On the summit northwest of Clark’s Peak is observed a dark gray granite, composed of colorless quartz; feldspar, both orthoclase and plagio- clase; and a dark mica present in large proportion, and arranged in paral- lel layers. Three or four miles south of the peak, ina coarse-grained granite which occurs near the foot-hills, carrying large crystals of vitreous oligoclase, Zir- kel detected the presence of zircon in red grains very like those occurring in the zircon syenite of Norway. It is in this southern portion of the range only that true granites are observed. North of this region the defined ridge breaks down into a broad roll- ing plateau heavily covered with forest and soil, over which little of the orographic structure can be learned. Observations along the Laramie, as well as on the edges of the park, indicate a region of varied gneisses, in which dioritic beds are prominent. While several confused folds seem probable, a prevailing dip to the southwest is seen. From the heights above the north- east edge of North Park a specimen was obtained representing a not unfre- quent type, composed of almost blackish-green hornblende, bluish-white, brilliant plagioclase, in slender prisms, often a quarter of an inch long, and a little limpid quartz and biotite, the latter in very subordinate quantity. The northwest strike of these westerly dipping gneisses is often varied by sharp zigzags. Along the northeast region of the park, especially in the foot-hills, gneisses and schists, dipping rather steeply to the west, have their strike arranged en échelon, with the long member trained in a northwest direc- tion, and short, abrupt cross-strikes more nearly in an east-and-west course. Exposures on the east side of the Platte Canon indicate a gencral east- erly dip, at least toward the lower reaches of the river. Between the upper cation and Laramie River but little geology could be obtained; rounded, forest-covered knolls and ridges, showing but few outcrops, alternate with peculiar treeless, grassy glades, which seem to open pathways through the timber quite independently of drainage-lines. Along Bye SYSTEMATIC GEOLOGY. the Laramie valley, however, and northward, near the eastern limit of the Archean body, as far as Sheep Mountain, dips were observed which indi- cate a general westerly slope for the gneisses. Where the North Platte leaves its Archaean canon to debouch upon the broad Tertiary valley, two prominent hills rise upon the left bank: Bennett’s Peak, opposite the confluence of Brush Creek with the Platte, and River Butte, five miles below; the former about 600, the latter 900 feet above the river plain. Both are made up of steep, westerly dipping beds of dioritic gneiss. Upon the hills east of the river, between French and Brush creeks, are sandy mica gneisses striking north 45° to 55° west, with a southwesterly dip, having a parallel arrangement of minerals and a banded appearance. Hornblende does not enter into the composition; transparent, colorless quartz, mica, orthoclase, and plagioclase complete the list of constituents, and make an association rather unusual in this region; plagioclase, when present in important percentage, usually implying a considerable amount of hornblende. In the oldest granite of the Laramie Hills there is indeed a little plagioclase without hornblende, but it is often discoverable by the microscope only, and never plays a réle of importance. Intercalated in the last-named group is a narrow sheet of dark, dioritic material, probably of a common origin with the other crystalline schists, but presenting some of the characteristics of an intrusion. It is a combi- nation of hornblende, plagioclase, and a very little colorless orthoclase. It presents some interest under the microscope, for which the reader is referred to Professor Zirkel’s Volume VI. of this series. North from Brush Creek, mica gneisses with included sheets of horn- blendic schist, usually of dioritic composition, and occasional beds of vitreous quartzite, continue for about fifteen miles. They show many discordant dips, but incline prevailingly to the north. This radical change of position from the rocks farther south and east is due to the development of a strong anticlinal, trending along the range in a northwest direction, roughly per- pendicular to the northeast axis of the Laramie Hills. Gneiss beds, similar to those described on Brush Creek, occur on the crest of Deer Mountain near the head of Cedar Creek. They are rather ARCHAAN EXPOSURES. 33 poor in mica, but are characterized by unusually white clear feldspars and small red garnets. Farther down on the peak are hornblende-piagioclase schists with a variable percentage of orthoclase, showing also under the microscope chlorite, titanite, zircon, and apatite. Hornblende gneisses, which vary greatly in the proportion of quartz, and have a general strike north 40° west, with a southwesterly dip, are observed north of Deer Mountain, making a local exception of the northerly dip observed in this section of the range. A change takes place north of Cedar Mountain, light mica gneisses taking the place of the hornblendic variety which has prevailed along the western margin of the range. An interesting gneiss occurs at Cherokee Butte, an eminence on the narrow Archean isthmus connecting Elk Mountain with the main range. It is hard rock, composed of gray quartz, white and flesh-colored feldspar, both orthoclase and plagioclase, and a little scattered, thin, flaky mica. Zir- kel calls attention to the condition of the quartz, which is made up of small worn and rounded fragments. Directly west of this body is a gray gneiss carrying a little hornblende and microscopic titanite. Nearly half of Elk Mountain, whose detached mass forms the north- ern extremity of the range, is of Palaeozoic and Mesozoic rocks. Archean gneissic beds form the summit and southern portions, however, and unite it with the isthmus of Cherokee Butte. These beds strike from north 45° to north 70° east, and dip to the north and west at high angles, often approach- ing the vertical. Quartz and monoclinic and triclinic feldspars, intimately mingled, are the main constituents, but the gneissic structure is given by a chloritic mineral arranged in fine-grained bands. Where the materials are all very fine, as at the base of the series, the rock wears the aspect of an impure quartzite. Thus far the southern portion of the range and the south and west flanks of its main mass have been briefly described. With the exception of the granites of the Clark’s Peak region, these formations have been seen to consist of a varied body of gneisses, in all of which, with slight exceptions, both systems of feldspar and quartz have been present, with either horn- blende or mica—rarely with both. Dioritie gneisses, closely approaching the minuter characteristics of the 0K 34 SYSTEMATIC GEOLOGY. eruptive diorites, are intercalated conformably in the general series, while in exceptional localities there are masses of a rock of dioritic nature, which are probably true dikes. At Medicine Peak, which reaches 12,231 feet in altitude and is the cul- minating mountain of the range, appears a new geological feature. The peak itself, and the ridge from which it rises, are formed of a heavy body of remarkably white quartzites, approximately 2,000 feet in thickness, strik- ing north 20° to 25° east, and dipping east at a high angle. The zone is irregularly stained a pale reddish hue by thin seams of oxydized iron min- erals. Toward the bottom of the series is a zone of pale bluish quartzite, rather more coarsely grained than the overlying members, and intercalated with sheets of conglomerate holding smooth quartz pebbles in a fine siliceous paste. Cyanite in narrow veins, associated with colorless quartz, is charac- teristic of the quartzite belt. A more prominent and conspicuous feature is the series of diorite dikes cutting the quartzites at nearly right angles with the strike of the strata. The material of these unmistakably eruptive dio- rites is nearly identical with the dioritic schists. South of Medicine Peak, on the head waters of French Creek, con- formably underlying the quartzite series, is a body of argillaceous slates, which have a fine lamination but rather imperfectly developed cleavage in the direction of the strata-planes. A great deal of excessively fine mica is visible under the loupe. A thickness of about 400 feet is assigned to this group of rocks, from the plane of contact with the quartzites down ; whence, becoming rather impure and more quartzitic, they pass abruptly into a series of harder quartzitic argillites enclosing beds of ferruginous, siliceous schists These in turn are underlaid by a more highly crystalline zone of schist, in which the original lamination appears to be for the most part obliterated. Exposed faces are seen to be dotted over with concretionary bunches or knots of fibrous hornblende, much of which is decomposed and coated with a bronze-green, red, and purple material of a peculiar and often brilliant iridescence. Farther down French Creek are silver-white, muscovite, mica slates and quartzose slates, dipping 70° to 75° east and striking north 15° east. Over them appear heavy masses of quartzite, which are doubtless the south- ARCHAAN EXPOSURES. Do ward continuation of the Medicine Peak beds. Still lower in the canon appear the same heavy beds of light mica gneiss characteristic of the south flanks of the range, coming in under the schist zone with apparent con- formity. About ten miles east of Medicine Peak, and separated from it by a rolling timbered upland country, is a strong north-and-south ridge cul- minating in Mill Peak, which reaches an altitude of 10,596 feet. Here a series of quartzites, conglomerates, and schists, doubtless equivalent to Medicine Peak ridge, reappear, but with a reversed position, dipping west and defining the east side of a broad synclinal. The quartzites are more stained and infiltrated with iron oxyd than at Medicine Peak; the conglom- erates also are more important and are somewhat different, being a red, and including large angular cherts and ferruginous quartzite pebbles. The actual summit of Mill Peak is of a light gray and white siliceous lime- stone, resembling a quartzite; indeed, the two rocks, by a varying of siliceous and lime particles deposited together, are made to shade through the intermediate gradations and illustrate a complete but gradual change of sediment. Along the northern foot-hills of the range, and for considerable dis- tances up Cooper and Rock creeks, are exposed dark schists and mica gneisses, the direct equivalents of those along the southern foot-hills. South of Little Laramie River, about Bellevue Peak, similar hornblendic and micaceous crystalline rocks are found, and among other forms white mica gneisses. Amongst them is one noticeable white or silver-gray gneiss, whose constituents are colorless, clear quartz; pearl-colored feldspar, in general very lustrous, but sometimes altered; a little brown mica, both generally disseminated and segregated in bunches and nodules; and minute grains of red garnet. On the northern and eastern slopes of this region occur banded and irregularly bedded rocks, made up of variable per- centages of hornblende and feldspar. Between the above-mentioned leading formations and those noted in the description of Colorado Range, a few common characteristics will have been observed, but noticeable differences prevail. The two ranges are sin- gularly unlike. In the essential construction of the rocks are observed 36 SYSTEMATIC GROLOGY. quartz, orthoclase, plagioclase, hornblende, mica, chlorite, and calcite. This difference is observable also in the general list of accessory products. Small quartz veins traversing the gneisses and hornblendic schists are often observed, particularly in the neighborhood of Brush and Cottonwood creeks, on the western foot-hills. They carry gold in small quantities, magnetite, pyrite, and massive epidote and cyanite. Red and reddish- brown grains of garnet are found, always associated with the light-colored gneisses, as at French Creek and Deer Mountain. Zireon, apatite, and titanite were detected by Zirkel under the microscope. Park Raner.—As an independent body, Park Range has its northern termination within the area of this work. Its eastern flank is sharply bounded by North Park and the North Platte valley; on the west it connects with the elevation of the Elk Head group and an irregular, hilly country about the upper Yampa River. As a range, it ceases a few miles northwest of Grand Encampment Peak. From our southern boundary, as far north as Pelham Peak, it is a distinct meridional ridge, with a sharp slope to North Park, and a broad summit, which was originally a plateau made up of strata gently dipping to the west, but now a mere net-work of plateau ridges, sep- arated from one another by deep glacial canons. Near Pelham Peak the range is abruptly bent round into a northwest trend, which it preserves for about thirty miles, and then plunges down under the Tertiary strata of the lowlands. The Archean body which forms the most important geological feature of the range is bounded on the east by the Tertiaries of North Park and the Platte valley, with the narrow exceptions of a body of basalt out- poured in the region of Rabbit Ears Peak, short stretches of Cretaceous east of Ethel Peak and at the northern entrance to the Park, and a strip of Triassic sandstone exposed against the granitic tongue east of Arapahoe Creek. On the west the upturned Jurassic and Cretaceous rest along the base of the range and border the Archzean series. In the region of Hentz Peak, voleanic outbursts also edge the Archean mass. The crystalline body itself is a single anticlinal fold, of which that portion of the range south of Pelham Peak is the westerly dipping half. The easterly dipping half shows only in the extreme eastern foot-hills and in the projecting spur which lies between Big Creek and North Park. The main body, therefore, is the half ARCHASAN BXPOSURES. 37 of an anticlinal, the other half having suffered a deep downthrow, which has left only traces of the easterly dip. The western-dipping beds present their eroded edges along the steep eastern front of the range, and are seen to incline very gently, gradually rounding to a steep inclination along the western foot-hills. North of Pel- ham Peak the fold has been flexed round into a northwest strike, giving the topographical trend as well as the direction of strike. In this northern por- tion the complete anticlinal is present. In the angle of flexure between the north and northwest trending parts there is much local crumpling and the development of a secondary lateral axis which opens an inclined synclinal from the summit of the range near Pelham Peak in a southwest direction. The meridional part of the main axis indicates a horizontal profile for the original fold, but north of Grand Encampment Peak the axis dips to the northwest, and, aside from the bevelling off by erosion, actually inclines downward and under the overlying 'Tertiaries. The series of Archzean rocks involved in this fold are bedded granitic gneisses of uniform constitution and material, but widely varied arrangement of internal structure, hornblendic schists, and dioritoid rocks, besides limited quartzites. Of Archzean eruptive rocks there are none, unless some obscure dioritic bodies are intrusive, and all the evidence points the other way. A granite occurring in the southern part of the range finds a characteristic expression on the summit of Ethel Peak. It is a rather coarse-grained mix- ture of grayish quartz, red orthoclase, sparsely but rather evenly dissem- inated biotite, and rare triclinic feldspars, the biotite often adhering strongly to the orthoclase faces. While the: rock as a whole shows a broad, distinct bedding, there is no parallelism in the arrangement of individual minerals. On exposure, it crumbles rather readily and breaks with a rough, irregular fracture. It distinctly resembles some of the bedded reddish granites of Colorado Range. Crawley Butte and the long, tongue-like ridge which juts southward from the range bounding the east side of Arapahoe Creek valley, the two being geologically one body, are for the most part composed of a similar red orthoclastic granite. Another tongue-like projecting ridge advances in a southeast direction from Park Range, forming the northwest boundary 38 SYSTEMATIC GEOLOGY. of North Park for a few miles. Here a variety of granites occur; among others, a coarse pegmatite consisting of pellucid or milky-white quartz, large groups of confused, imperfectly crystallized, red orthoclase, masses of bio- tite, and muscovite, the latter mica predominating and occurring in much larger sheets. Great variation is observed in the quantitative proportion and arrangement of the minerals. There are segregations of considerable size, altogether made up of one or the other mineral. One variety is essentially a feldspar rock, with the few grains and crystals of quartz or mica present only as segregated groups, while disseminated through the red orthoclase are irregular veinlets and waving lines of yellowish-green epidote, making a rock equivalent to that described by Frank H. Bradley* from Unaka Range, Blue Ridge chain, between North Carolina and Tennessee. Between Bruin Peak and the Tertiary valley the granites assume a more regular type, composed essentially of quartz and orthoclase, with beds in which either mica or hornblende is present, rarely both. Gneisses are exposed in the same neighborhood. These also are variable as regards the presence and pre- dominance of mica and hornblende, but the latter perhaps exceeds the former in importance. One special rock was found here, composed for the most part of brilliant black or dark-greenish hornblende, although carrying more or less white plagioclase and a very little quartz. It is distinctly bedded, and dips at a high angle a little to the north of east. Hornblende also ap- pears in considerable prominence in the orthoclase-mica gneisses. A final variety of gneiss is almost a mica schist, in which feldspar and quartz are minor constituents, the micas, both biotite and muscovite, arranging their flakes in strictly parallel planes. Zirkel finds especial interest in the micro- scopic examination of this species, as the reader will see by reference to Volume VI. Upon the walls of the glacial catons around Mount Zirkel, as also upon the peak itself, there is a similar association of mica gneisses and hornblendic schists. A distinct bedding may be traced along the canon flanks, gently dipping to the west. By the predominance of one or the other mineral, a black, white, or gray color is given to the individual sheet. Hornblende, combined with orthoclase, plagioclase, and very subordinate quartz, con- *American Journal of Science and Arts, May, 1874; page 519. ARCHASAN EXPOSURES. 39 stitutes the leading type of bed, and the hornblende prisms commonly lie with the bedding-planes. Mica gneisses are present, however, carry- ing always a little hornblende and triclinic feldspar. Feldspar bands, faintly striped with hornblende, zones of pure feldspar, segregations of amphibolite, and sheets of hornblende striped with a little triclinic feldspar and quartz, alternate in every variety of arrangement. The trail up Grand Encampment Creek passes many excellent expo- sures of the Archean series. Near the mouth of the canon is a granitoid gneiss of orthoclase and quartz, with very imperfectly developed bedding. Biotite, instead of the ordinary parallel or banded arrangement, is grouped in large lenticular aggregations, whose longer axes are parallel with the gen- eral structure of the rock. Passing into a crude, coarse granitic form, this same rock distinguishes itself by the development of other segregations of quartz or feldspar not unlike those of Mount Zirkel. Overlying this series is a dark, hornblendice rock, in which white plagioclase crystals are scat- tered at irregular angles, as in a porphyry. Farther up the creek is a granite nearly related to the red orthoclase granite of Colorado Range and those about Ethel Peak of the range now under consideration. In this coarse and variable granite are frequently seen what are usually reserved for the microscope to reveal, namely, fissures in the feldspars filled with quartz, in which are embedded other feldspars as well as quite perfectly developed micas. Flesh-colored orthoclases in these coarse granites often attain a size of four or five inches. The other ex- treme of texture is also sometimes shown in this rock, when it passes into an excessively fine-grained aplitic form, with little or no mica. When present, the mica is apt to show an obscure parallelism. Zirkel demon- strates that the red color of these feldspars is due to oxyd of iron infiltra- tions in the minute fissures of the crystals, and also that the mica is accompanied and sometimes replaced by a strongly dichroitic chloritic mineral. As in the kindred granite of the Colorado, the quartzes are poor in fluid inclusions. On the slopes of the high peak southeast from Encampment Meadow is a series of hornblendic rocks and gneisses presenting the same yaried petrographical habit as at Mount Zirkel. In one of the mica-bearing zones 40 SYSTEMATIC GEOLOGY. of true gneiss are observed red garnets; and so close is the resemblance be- tween the garnetiferous gneisses in all three of these Rocky Mountain ranges as to suggest that they may not improbably represent a common horizon, On the peak are alternating beds in which first plagioclase and then hornblende predominates, with quartz containing in some instances liquid carbonic acid. Upon the summit of Grand Encampment Peak is also a dark-green amphib- olite, quite free from other minerals, but carrying an interstratified bed of an association of rocks to be hereafter noticed white, micaceous quartzite as recurring in Humboldt Range. Gneissic beds having the same variations as have been already described form the whole northwestern part of the range, dipping from the axis northeast and southwest. At the extreme north end of the range, where the northerly dipping Archzean beds plunge down under horizontal Tertia- ries near the mouth of Jack’s Creek Canon, interbedded in a dark, horn- blendic schist, is a bed of pure, dazzlingly white quartz, 50 feet thick, of singular purity, vitreous and only varied by wandering vein-like clouds, which under a high magnifying power were resolved by Zirkel into regions immensely rich in fluid inclusions, partly of water and partly of liquid car- bonic acid. There is also a hornblende, orthoclase-plagioclase rock, with but little quartz; orthoclase, the predominating feldspar, giving it the gen- eral composition of a syenite, which it would undoubtedly be considered but for the certainty of its belonging to the strictly metamorphic series. While planes of bedding and even the ordinary gneissic parallelism of minerals are sometimes wanting, there are seen such infinite variations in the internal arrangement of the crystalline series in these ranges that only the most positive evidence of intrusive origin should be accepted. This syenitic type, a most unusual one, is confidently referred to the gneisses, all of which are here metamorphic products. Not far from the syenitic body of Jack’s Creek are beds which are a crypto-crystalline mixture of dark-green hornblende, with white plagioclase, probably oligoclase, often in long, slender crystals. This again is a rock without appearance of stratification or parallel arrangement of minerals, to all intents a diorite, yet believed to be a member of the series of dioritic gneisses. Dense forests obscure the western flanks of the range; but ARCHAAN EXPOSURES. 4] enough is known to say that the prevailing rocks are hornblendic gneisses dipping rather steeply to the west and southwest. Under the voleanic rocks at the head of Snake River is a red gneissoid rock made up of quartz, orthoclase, plagioclase, and minute flakes of mica, without general bedding or the true schistose structure, yet possessing a banded arrangement of the quartz and mica. Quartz is especially abun- dant, the grains welded together almost in continuous sheets. The ortho- clase is red; plagioclase oceurs in thin, colorless, acicular prisms. The same rock reappears at Camel Peak at the bend of Snake River. At Buck Mountain, near the head of Elk River, is a dioritic rock similar to the one already described on Jack’s Creek, equally free from schistose or gneissic internal structure, equally like the eruptive rocks in habit, but still in all probability metamorphic. The list of essential constituent minerals in the Park Range rocks is even more limited than that of the Colorado or Medicine Bow. It com- prises quartz, orthoclase, plagioclase, biotite, muscovite, hornblende, and epidote. Accessory species are garnet, magnetite, and gold. Under the microscope Zirkel detected, besides these, chlorite and apatite. Epidote as an essential constituent was only seen in the red unakite of Bruin Peak; it appears in a subordinate role in several coarse granites. Garnet of a rasp- berry color occurs in several highly micaceous gneisses, always in rocks with a close family resemblance to mica schist. The garnet grains are commonly as small as a mustard-seed, but occasionally longer, as in the gneiss of the high peak southeast of Encampment Meadow. In the hornblende gneisses of the same peak are numerous microscopic apatites, associated with twinned orthoclase in elongated forms like those on Long’s Peak. Unmistakably eruptive granites, or indeed other forms of intrusive rocks, do not exist in our part of Park Range. An Archean exposure northwest of Rawlings Station is without doubt an outlying dependence of Park Range. As before seen, the gneisses and granites of that ridge dip northwest and downward under the later sedi- mentary formations. Twelve or fourteen miles farther in the same direc- tion, there is a local elevating disturbance at Savory Plateau, where a doming up of the Cretaceous takes place, with quaquaversal dip and an 42 SYSTEMATIC GEOLOGY. exposure of the underlying Jurassic series. No one can doubt the propriety of regarding this occurrence as an effect of the submerged continuation of Park Range. A similar but more important doming takes place at the locality north of Rawlings Butte, involving all the strata from the middle Cretaceous down to the Archean. The truncation of this dome by erosion has laid bare the entire series. Underlying the primordial sandstone is a long, narrow, nucleal mass of a granitoid gneiss, with comparatively distinct bedding, a northerly strike, and a dip of 45° to the west. A northwest valley has been eroded through the dome, doubtless on the line of some important fissure, leaving the best Archaan exposures on the east side of the valley. An interesting exhibition of the grinding power of wind-driven sands is here met with, the more exposed granite surfaces bearing a remarkable polish and grooving. The rock is a close-grained, strongly cohering mixture of quartz, plagio- clase, a little orthoclase, and hornblende, the latter disseminated in light- green fibres through the mass and imparting to it a prevailing greenish color. Strictly speaking, the rock possesses the composition of a quartziferous diorite with a distinctly granitic habitus, and may be regarded as highly quartzose dioritic gneiss. Zirkel points out that the quartzes are rich in fluid inclusions, some of which contain salt cubes and others liquid ear- bonie acid. Uinta Raner.—From the last-described exposures, westward across the whole basin of Green River, as far as Wahsatch Range, within the limits of the Fortieth Parallel Exploration, the entire area is made up of rocks later than Carboniferous, and there is but one outcrop of Archean age. This is a small body near the northern foot-hills of the eastern end of Uinta Range, and directly north of Green River, at the eastern end of Brown’s Park. The exposure is from four to six miles across from north to south, and about seventeen miles east and west. On the south it is bounded by the great sandstone series of the Uinta, except where between Red and Willow creeks the Tertiary of Brown’s Park abuts against it. Along the north it is chiefly bounded by Cretaceous rocks, which are probably brought into contact with it by a fault and a downthrow. A distinct non- conformity between the Archzean body and the Uinta sandstone is observed ARCHAAN EXPOSURES. 43 on the line of contact west from Garnet Canon, and with equal distinctness and more satisfactory exposure north and west from the mouth of Willow Creek Canon. This long, narrow body, having an east-and-west trend, is the only Archean mass for more than 100 miles east or west, and for certainly an equal distance to the north, while to the south none is yet reported within a similar area. Garnet Canon, cut by Red Creek directly through the mass, and giving exposures of over 2,000 feet on either wall, offers the best view of its interior structure. The general plan is that of a flexed anti- clinal, or perhaps a double anticlinal, with converging axes, the fold of the northwestern portion being northwest-and-southeast, and that of the south- ern, northeast-and-southwest. The beds are very sharply uplifted, standing at angles of from 45° to 70°, and showing within the series much abrupt and severe plication. The group consists of pure white quartzites, hornblendic schists, and hydro-mica (paragonite) schists, richly charged with garnet, staurolite, and minute crystals of cyanite. The black, hornblendic beds are essentially an amphibole rock, containing a little quartz and sparing triclinic and ortho- clastic feldspars, the former predominating. Composed as it is almost en- tirely of distinct hornblende prisms, it might be fairly classed as an amphibole rock, and it is clearly to be correlated with that already described at Bruin Peak on Park Range. The association of paragonite with staurolite, garnet, and cyanite recalls many well known Appalachian localities and the classic St. Gothard of the Alps. The association of quartzite with hornblendic beds and cyaniferous schists suggests a resemblance to the series exposed on Medicine Bow Peak, which also carry cyanite; but the staurolitic-parago- nite rocks are entirely wanting in every other locality examined by this survey. In a measure this exposure stands as disconnected petrologically as it does geographically. It is the single instance in the Fortieth Parallel Archean area, aside from chloritic ingredients of certain granitoid rocks, of a hydrous rock; serpentines, steatites, damourite rock, and other hy- drated silicates being altogether absent. Minutely studied, the great white quartzite belt, with its intercalated beds of dark amphibolitie schists, yields the important fact, that while each individual stratum is most persistent in retaining its mineral and chemical 44. SYSTEMATIC GEOLOGY. character when followed longitudinally, adjoining beds may and do differ widely. A clean bed of spotless white quartzite between two dense black sheets of amphibolite preserves its purity even when followed for miles. Whatever, therefore, may have been the cause or mode of metamorphism, the resulting mineral combination was governed absolutely by the chemistry of the original sediment ; nor did the process of change have power to transfer a single atom of a single clement out of the horizon in which it was deposited. Wausatcu Rangr.—The Archean rocks in the explored portion of the Wahsatch are exposed at intervals along the west front of the range for nearly 100 miles, and are composed of granites, garnet rocks, aplitic schists, and a very extended series of gneisses and hornblendic schists, with sub- ordinate quartzites. The manner of their exposure is of very great interest, involving the most extensive dynamic action observed within the limits of the Fortieth Parallel Exploration. The chain of outcrops clearly represents an old Archaean range of bold configuration, which has been buried beneath an enormous accumulation of Palzeozoic and Mesozoic sediments. It was this buried Archean range which controlled the position and direction of the modern Wahsatch Range. After the uplifts took place, and the Paleo- zoic and Mesozoic strata were thrown into their present inclined position, a great longitudinal fault occurred throughout this whole portion of the range, by which the entire western half of the ridge was thrown downward from 3,000 to 40,000 feet, and is now entirely buried beneath the Pliocene and Quaternary formations of the Salt Lake basin. The present abrupt west front of the Wahsatch is the standing face of this great fault, and here the Archean rocks are seen to occupy the core of the range, unconformably underlying the Paleozoic series, and rising to different stratigraphical hori- zons in the overlying series. In the southern portion of Map IIL, in the region of Cottonwood and Little Cottonwood caiions, is exposed an approxi- mately conformable series of 30,000 feet of Paleozoic strata, overlying the granites and schists which there together form a portion of the early Archean surface. The origin and nature of the granites at this point are obscure. ‘There seem to be two distinet types—a granitoid gneiss, having a decided stratification, and an apparently eruptive body, which possesses in wi interesting degree the conoidal structure so prominently developed in the TAH ANGE ) ye ARCHASAN EXPOSURES. 45 granites of the Sierra Nevada. About fifteen miles south of Salt Lake City the Palaeozoic beds are thrown into a broad, semicircular curve, having a con- vexity to the east and a varying dip always away from the centre of this curvature. The ends of the strata of this great flexure advance westward until they approach the region of the great fault, their eroded edges forming the foot-hills of the range. The centre and nucleus of this immense curvature is a body of Archean rock, composed partly of schists, but principally of a great cen- tral mass of granite and granitoid gneiss, having its best exposures in Little Cottonwood Canon and the peaks to the south, and again in the Clayton’s Peak mass, where it rises like an island through the strata of the Lower Coal Measure limestone and the Weber quartzite. Plate I. is a view up among the summits of the Lone Peak mass, showing the rugged region near the head of a deep glacial canon. Although in Clayton’s Peak, and again near the lower end of Little Cottonwood Canon, the rock possesses ail the physical habit of a truly eruptive granite, and although in the Clayton’s Peak region the granite has undoubtedly been a centre of local metamor- phism and of metalization, yet, from the position of the overlying strata, a preponderance of evidence points to the belief that, whether eruptive or not, it is still of Archeean origin; hence its relations with the later stratified series are only those of rigid underlying masses, and the local metamor- phism observed in the limestones near the granites is strictly mechanical, and not to be mistaken for the caustic phenomena of a chemically energetic intrusion. It should be mentioned, however, that it possesses, both in its interior composition and in a peculiar conoidal structure, close affinities with the unmistakably eruptive granite of the Sierra Nevada; and it is quite possible that subsequent study will determine the presence here of two dis- tinct granites, the one having a regular bedding and belonging to the strati- fied Archzean series, the other of conoidal structure and eruptive origin. The main body extends about twelve miles northeasterly, from the trachyte slopes of the Traverse Hills to the head of Little Cottonwood Canon. Its greatest north-and-south expansion is through Lone Peak, a line about eight miles long. South of the mouth of Cottonwood Canon a narrow iso- lated patch of granite appears involved in the Archean schists. The Clay: 46 SYSTEMATIC GEOLOGY. ton’s Peak mass, at the head of Cottonwood Canon, has an east-and-west ex- tent of about three miles, and runs the same distance north-and-south. Near the mouth of Little Cottonwood the granite breaks with a sharp fracture, possessing no bedding-planes and but a few irregular jointings. It consists of quartz, which is seen under the microscope to be remarkably poor in fluid inclusions, orthoclase, a relatively high proportion of plagioclase, biotite, large and brilliant black hornblendes, titanite, and microscopic apatite. For western granites, the titanites are particularly large, not infre- quently reaching one eighth of an inch in length. Passing up Cottonwood Canon, no sharp line of division between the structureless granite and the bedded gneissoid form is observable; but there appear gradually more and more planes having an easterly dip, until finally they approach the regularity of gneiss bed-planes, and the minerals are seen to possess a vague general parallel arrangement. ‘There is no essen- tial change in the mineral composition of the granite in passing from one to the other of these forms. If anything, titanite and hornblende are slightly less frequent in passing up the canon and into the region of bedded gneiss. The granite of Clayton’s Peak, however, has some essential differences. It is dark, very fine-grained, and carries a very large proportion of horn- blende and mica. Under the microscope the titanite crystals, which are present in large number, are seen to be much darker than in the other rocks. The feldspar and quartz, particularly the former, contain many microscopic impurities, chiefly plates of red and black oxyd of iron. The rock is proportionately rich in black magnetite grains, which penetrate the flattened crystals of apatite. The mineralogical differences through all these bodies of granite are indeed slight; changes of texture and arrange- ment produce a decidedly varying petrological effect, but in general they are granites, containing—besides the normal orthoclase, quartz, and biotite— plagioclase, hornblende, titanite, and apatite in high proportion ; all but the apatite being visible to the naked eye. The bodies of granite porphyry shown on the map in the neighbor- hood of Clayton’s Peak are in all probability a dependence of the granite. They are always rich in hornblende and orthoclastic feldspar, which throws them into the class of syenitic granite porphyries. The body which comes ARCHAAN EXPOSURES. AM to the surface in the bottom of Cottonwood Canon, two miles below the bend, is remarkable for the high proportion of pyrites, which has penetrated in fine grains through the quartz and feldspar crystals. A granite-porphyry body adjoining Clayton’s Peak on the north, and forming the divide between the head of Cottonwood Canon and Parley’s Park, is also richly impreg- nated with pyrites. Its groundmass is pale green, from the presence of epidote, here an alteration-product after hornblende, and is rich in plagio- clase. The larger feldspars, which are chiefly orthoclase, have a red color derived from a microscopic dust of iron oxyd. Lying to the west of the granite body of Little Cottonwood Canon, and occupying the extreme foot-hills, is a belt of Archean schists, varying from a mile to two miles in width, and extending from the Traverse Moun- tains north to the mouth of Cottonwood Canon. ‘The general strike of this body is northeast, with a dip of from 45° to 60° to the north and west. From 2,000 to 3,000 feet of schists and quartzites are laid bare. A very good exposure is found in the second small canon south of Cotton- wood, where an estimated thickness of from 2,000 to 2,500 feet of highly metamorphic slates rests directly on the granite. Overlying these is a zone of quartzites, the uppermost members of which are blue, very hard, and schistose. A great deal of local contortion is observed in the strata; in one place they completely surround a small knob of granite, which is probably a submerged portion of the spur running northwest from Twin Peaks. Among the lower horizons is found a green hornblende schist, rich in quartz. It is almost a quartzite, and is thickly penetrated by small bluish-green hornblende prisms, which give the rock its schistose cleavage. There is also a little brown mica. At the mouth of the Little Cottonwood this Ar- chzean zone is represented by about 1,000 feet of quartzites, which extend perhaps half a mile up the canon, making a junction with the granite body. South of the mouth of Little Cottonwood Canon the same quartzites extend down to the trachytes of the Traverse Mountains. In direct contact with the granite at the mouth of Cottonwood Canon is a development of mica schist. On Rhodes’s Spur, at the head of Cottonwood Canon, resting directly upon the granites of Clayton’s Peak, is a curious garnetiferous schist. It 48 SYSTEMATIC GEOLOGY. is a coarse-grained quartz rock penetrated by delicate green fibrous epidote and carrying a very high proportion of brown crystals of garnet, which indeed make up the greater mass of the rock. Zirkel describes the gar- nets as showing under the microscope a peculiar schistiform structure, as if resulting from a continuous aggregation of layers. Besides the garnet and epidote, these rocks show an appreciable amount of specular iron and local concentrations of dark-green fibrous hornblende. Intermediate stages between the hornblende and the epidote are so evident that there can be little doubt that the latter is an alteration-product of the former. There are present in this neighborhood, then, two distinct families of rocks: first, the Archzean, consisting of schists and granites; second, the vast, conformable post-Archzan group of sediments. Wherever observed, the region of contact between the two families displays no marked meta- morphism on the part of the sedimentary series, and within the Archean series no such transitions as would lead to the belief that the granite is only a more highly metamorphic form of the crystalline sedimentary series; on the contrary, the contact is so clearly defined, and the rocks are mineral- ogically so dissimilar, that it is very evident that the granite is either an intrusive mass or else an original boss over which the Archzean sedimentary materials were deposited. While the granite itself bears a very close resem- blance to the Californian eruptive granites, its relation to the flexed Palzeo- zoic strata would indicate that they were bent around a solid body, not that a plastic granite intruded into the bent Paleeozoics. The absence of granite dikes penetrating the immense sedimentary series would strengthen the belief that the granite antedated it. It is also noticeable that the dip and strike of the Archean schists west of the granite body are entirely discordant with the overlying Cambrian series, the former striking northeast and dipping north- west, the latter striking northwest and dipping southeast, this unconforma- bility being preserved up to the contact. Supposing the whole Archzean body to have been thrust upward and eastward when the flexure of the Paleozoic series took place, the present dip of the Archzean schists and quartzites would indicate that before the great Wahsatch uplift they were in a nearly vertical position, flanked to the east by the granite mass. In- trusive dikes do in some instances cut the marbleized limestone, but they ARCILASAN EXPOSURES. 49 are middle-age porphyries, not to be confounded with the Archzean crys- talline rocks. The next Archean body makes its appearance about eight miles north of Salt Lake City, in Sawmill Caton. Here the Paleozoic strata, uncon- formably overlying the Archean, trend diagonally in a northeast direction across the range. Irom the southern line of its outcrop the main mass is composed of an Archzean block extending 20 miles northward, and no doubt occupying the whole body of the ridge, except upon the eastern foot-hills, where it is overlaid by the beds of the Vermilion Creek Eocene group. There seem to be two distinct series within the Archzean mass, the earlier occurring only at the extreme southern end of the exposure, and confined to the spur between Sawmill Canon and that next north. Here is laid bare a small body of intensely metamorphosed material of an ashen-gray color, composed of quartz, orthoclase, and a very little muscovite. It weathers with an excessively rough surface, developing curious waving lines. It appears to have been a body of quartzitic schist, containing a little ortho- clase and mica, which has undergone the most violent compression and crumpling, obliterating entirely the original bedding and leaving only ob- scure traces of short, abrupt, and extremely irregular corrugations. North- ward, this body passes unconformably under the main series of gneisses and schists which form the range in that direction. The regular strike and dip of the gneisses and schists continue close down to the highly corrugated structureless body, but the exact contact was obscured by soil and a dense growth of scrub oaks. From the nature and position of the two bodies there is no doubt that they are actually unconformable, and that the bedded gneisses are the younger group. The later series consists of beds of gneiss, quartzite, and various hornblendic schists, forming a great conformable group which always dips to the west at angles varying from 15° to 40°, and is admirably exposed in the various canons which are cut down the two flanks of the range, and especially also in the transverse cut of the canon of Weber River, where the whole range is severed. The series is characterized by great chemical and usually mineralogical persistence of individual beds for comparatively long distances, and by the absence of any important minor corrugations. 4k 50 SYSTEMATIC GEOLOGY. The group forms a simple monoclinal ridge, dipping to the west at angles increasing from 15° at the south to 25° and 40° farther north in the region of Weber Caion, attaining still higher angles near Ogden. The trend of this series is somewhat sinuous. As developed in the summit rocks, from Sawmill Canon to Farmington Canon, the strike is about north 20° west; but near the head of Farmington Canon the line swerves rapidly to the east, passing to 10° east of north, whichit maintains for four or five miles, and then bends back again to the west, conforming with the strike of the southern portion from north 15° to 20° west. In the axes of these two bends of strike there is a good deal of local flexure and not a little dislocation. North of Farmington Canon, where a deep exposure occurs, there are from 12,000 to 18,000 feet of conformable beds. Down the east slope of the range to the contact with the Eocene, the Archean rocks are still seen dipping to the west. Of course no estimate can be formed as to how much farther down beneath the overlapping Eocene sandstones the conformable Archzean series descends. The lowermost exposed members are of intercalated gneisses and hornblende schists, with minor beds of quartzitic schist carrying more or less feldspar. An interesting type of the coarse gneiss is observed near the head of Farmington Canon. It is composed of large crystalline masses of flesh- colored orthoclase and partially decomposed,earthy brown magnesian mica, with irregular bodies of pure, milky-white quartz. This stratum is interesting as showing the transition from an evenly bedded rock into a structureless one. The original sheets of mica may be readily traced, though at present they all bend into wavy lines through the mass of the bed, or, what is rather less common, mica flakes all arrange themselves on a diagonal to the plane of the bed. Tracing this bed a few miles north from Farmington Cation, the minerals are observed to be less and less disturbed, and finally not a single mica flake deviates from its original parallel position. Such changes as this are frequently observable in gneiss beds; but it has nowhere been the fortune of this Exploration to observe those peculiar rapid transitions from one species of rock to another which are so constantly to be found in descriptions of Archean schists and gneisses. On the contrary, all the observations of this corps tend to prove that there is a remarkable perma- ARCHAAN EXPOSURES. bil nence of chemical make-up within each bed, and that the only changes which take place within a given stratum are through the hydration of some of the contained species, or else mere physical changes in the rela- tive arrangement of the species. A mica schist passing into a hornblendic schist, or a hornblendic schist into a granite, or a gneiss rock into an argil- lite, along the line of their longitudinal extensions, are phenomena which failed to appear on the Fortieth Parallel. It is believed that such observa- tions, not at all infrequent in certain accounts of western geology, betray a talent for fiction which might find a more appropriate field within the domain of romance. While individual beds extend for great distances with- out chemical change, on the other hand in descending or ascending through the series there is the greatest variety of changes, every combination pos- sible to the few mineral constituents being repeatedly illustrated. Over these coarse Farmington gneisses are a series of fine gray gneiss, in which the feldspar and quartz are both white, and the mica muscovite. It is a rock made noteworthy by the presence of freely disseminated minute garnets, which Zirkel has shown under the microscope to be riven in every direction by infinitesimal cracks, and to be more or less altered into chlorite, sometimes attaining the complete pseudomorphism which has been so inter- estingly elaborated by Prof. Raphael Pumpelly in his description of the rocks of Lake Superior. A little higher in the series is another gneiss, still containing a predom- inance of white mica (muscovite), but with a little hornblende. It is also rich in garnets, which likewise show the transition into chlorite. For a full account of the minute method of this pseudomorphism, the reader is referred to the pages on Archzean schists in Volume VI. of this report. Above these is a heavy group of dark-green hornblendic gneisses, rich in feldspar and apatite ; besides which, Zirkel has identified under the microscope a considerable proportion of zircons. They are never large enough to be visible to the naked eye. In the zirconiferous gneisses the hornblende is always more or less fibrous, from dark-green to black, and arranges itself with the broader surfaces of the prisms coincident with the bedding-planes. Quartz and feldspar hold a very variable position in this series, as they do in the hornblendie rocks of Medicine Bow and Park 52 SYSTEMATIC GEOLOGY. ranges. There is every variety here, from a pure amphibole, containing sparse grains of quartz but no feldspar, to beds in which either quartz or feldspar largely predominates, and in which hornblende plays a very insig- nificant part. Apatite is characteristic of those rocks in which mica does not exist. There are no means of closely determining the relative thick- ness of the various types of crystalline schists which repeatedly recur in this body. But it is evident that only the lower members are true gneisses, while by far the greater part represents a varying association of hornblende, feldspar, and quartz. ‘There are narrow zones which may be called quartz- ite, though carrying not a little feldspar, but no large, true zone of pure quartzite. The most noticeable fact is the sequence of richly feldspathic eneisses and mica eneisses containing garnets, the two overlaid by a large series, which is prevalently hornblendic, but carries more or less zircon- iferous beds. This seems to be a very nearly direct repetition of the se- quence in the Rocky Mountain system, and of one which will be described hereafter in Humboldt Range. Four miles north of the canon of Weber River, the Archeean series is lost by passing under beds of the Paleozoic series. Two miles south of the mouth of Ogden Canon it reappears, coming out from under the Cam- brian quartzite, and it is exposed along the western foot-hills of the range in a zone about four miles long by half a mile to a mile wide. On the west it is bounded by the Terrace formation, and along the east it passes uncon- formably under the quartzites of the Cambrian. The rocks of this exposure are an intimate association of dark reddish-gray and dark-red gneisses, in which hornblende largely predominates over mica. Mica is variably present, but never reaches a high proportion, and is sometimes altogether absent. Both orthoclase and plagioclase are present, the latter predom- inating. Quartz occurs freely, sometimes segregating itself into sheets of pellucid grains. Zirkel describes a very interesting arrangement of the mica, seen only under the microscope, as well as the occurrence of apatite and zircon. The interesting method of isolating and determining zirconium in these rocks, as devised by Mr. R. W. Woodward, the chemist of this Ex- ploration, will be found detailed in Volume II.,Chapter III, under the ac- count of Wahsatch Range. His method depends on the insolubility of zircon ARCHASAN EXPOSURES. 53 in hydrofluoric acid. Every variety of structure is noticed in this exposure of hornblende rocks, ranging from distinct lamination, in which the horn- blende crystals are arranged in sheets separated by zones of feldspar and quartz, to a structureless condition in which the rock rich in plagioclase and hornblende might easily pass for an eruptive diorite. As a whole, they have a strike of about north 20° west, with a high dip to the west. Their unconformability with the overlying Cambrian quartzite is well shown along the whole front of the range, from Ogden Cation to Eden Pass. Directly north of Ogden’s Hole, occupying a geological position simi- lar to that of the last-described exposure, unconformably under the Cam- brian quartzite, is another Archean body. At its extreme northern end, four miles south of Brigham City, the Cambrian disappears and the Silurian limestone comes directly in contact withthe Archean. Here also the rocks strike about north 20° west, and dip at a high angle to the southwest. They consist of a series of micaceous and hornblendic gneisses, having rather a granitoid appearance, but for the most part clearly displaying the planes of bedding. A very characteristic hornblende gneiss is collected near the south point of the body, and consists of coarse-grained orthoclase, a compar- atively large amount of plagioclase, quartz, a little brown mica, and much hornblende. Apatite is discovered under the microscope. Among the upper dioritoid beds are some which are decidedly poor in hornblende, but carry well developed microscopical crystals of zircon in considerable frequency. Almost all the lower members of the Ogden Point series are more truly gneissic than the upper ones. It is very clear that the three last-described exposures—the great body forming the range from Ogden Peak south to Sawmill Canon, the narrow body at the mouth of Ogden Canon, and the exposure north of Ogden’s Hole—are all parts of a single series, having a more or less flexed but generally northwest strike, accompanying the general trend of the range, and all dipping conformably to the west. Their contact with the overlying Palzeozoic rocks varies from the Silurian limestone to a horizon 3,000 or 4,000 feet down in the Cambrian quartzites. It is further evident that when the easterly dipping Paleozoic rocks were ina horizontal position, the west- erly dipping Archzean beds would stand at a much higher angle ; and, com- 54 SYSTEMATIC GEOLOGY. paring the points of contact between the Archzan and the Paleozoic, it is clear that the summit profile of the original Archean ridge was eroded into peaks rising at least 4,000 feet above the general outline of the ridge, and that these peaks were not abrupt, but were rather gently rising domes. ArcH&AN oF Satt Lake anp THE PromonTory.—Promontory Range, which projects southward into Salt Lake, has exposed upon its southern extremity a body of slates and quartzites, together with minor hornblendic and mica schists. About five miles south of Promontory Point, on the trend of Promontory Range, lies Frémont’s Island, which may be considered as a part of the same development of Archzean rocks. Still farther south, Ante- lope Island, a body of land twelve or fourteen miles in length by four miles in width, whose longer axis points northwest, seems by its material and posi- tion to be a southward continuation of the same Archzean mass. West of Ogden City, at the landing rocks northwest of the mouth of Weber River, there is also a slight development of westerly dipping Archzean schist. ‘This latter exposure is surrounded by the mud beds of the lower Quaternary desert formation, and is of very slight importance. The two above-men- tioned islands and the southern point of Promontory Range, taken together, represent a body chiefly composed of argillaceous, pyritiferous schists, mica schists, and granitoid gneisses, which, according to the accounts of Stans- bury and the slight notes of our own topographer, appears to dip west on Antelope and Frémont islands, with a general northwest strike; while on the point of the promontory it is much more disturbed, but has, however, a prevalent northeasterly dip, with a northwest strike. The trend of these masses, if continued southward, would carry the body under the western side of Jordan valley. It would seem as if Promontory Range, the two islands, and the Oquirrh represent a range in a measure comparable to the Wahsatch, formed of an Archzean core and an overlying folded Palaeozoic series. Rart River Mountarins.—North of Bovine Station, where the Central Pacific Railroad skirts the northern edge of Salt Lake Desert, rises the southern group of Raft River Mountains, a range which trends north- ward and extends beyond the limits of Map III. In the middle of the ridge, at Citadel Peak, and extending thence along the eastern side of the ARCHASAN EXPOSURES. 55 range for ten or twelve miles, is a triangular exposure of granite, the west and south sides wrapped around and overlaid by limestones, which have been referred to the horizon of the Lower Coal Measures. Quaternary beds skirt the eastern base of the granite, which here forms the foot-hills of the range. The topography is a series of irregular parallel ravines, eroded from west to east. Citadel Peak, the highest summit, reaches 2,500 feet above the level of the desert. The Quaternary of Clear Creek valley pen- etrates the range, isolating a northern mass of granite from the main body, as will be readily seen upon the map. The rock is nearly structureless, the few jointing-planes showing no indications of a parallelism which would sug- gest a gneissoid structure. It has a uniform and medium texture and a pearl- gray color, and is composed of quartz, orthoclase, and mica. The granite malady has taken hold of the surface very generally, and it is covered with crumbling débris. The main spurs and ridges present everywhere smooth, round outlines, with many small, fanciful forms of erosion. Desert Granite Rance.—About 25 miles west of the Cedar Moun- tains, and a few miles south of the southern limit of our Map IIL., is a nar- row ridge extending on a north-and-south trend eight or ten miles, and scarcely more than a mile or a mile and a half in width. From this con- tracted base it rises fully 3,000 feet above the level of the desert. The northern half, where examined, consists exclusively of a variety of granite having < decidedly metamorphic habit, although the bedding-planes were not dis- tinct enough to give a definite idea of the true orographical structure. In general, it is a fine-grained, nearly white mass, sometimes changing into a coarse variety in which the mica plates reach an inch in diameter. The central heights are intersected by veins of a dark-green hornblendie granite, which under the microscope is seen to contain very little unaltered horn- blende, but a dichroitic green chlorite-like mineral, besides considerable dark hexagonal mica, titanite, and apatite. Its quartz and feldspars are rich in fluid inclusions. - - ARCHAAN EXPOSURES. 65 Sacred Pass, the eastern front of the mountain is an abrupt mural face, and is made up of varying masses of granitoid rock possessing always more or less traces of gneissic structure. With local exceptions in what seemed to be northward prolongations of the Frémont’s Pass granite, making up in dome-like masses into the crystalline schists, the whole Archean body of the range is distinctly a bedded series. In Sacred Pass, upper members of the Lower Coal Measures are seen to rest directly and unconformably upon the schists, while to the south, east of Camp Halleck, towers above them a group of high schist peaks. The sudden and commanding lift of these Archean peaks, above the point of contact with the limestone, and the rapid overlap of the uppermost Paleozoic strata concealing lower members of the series, clearly indicate high primitive Archean peaks around which the limestones were deposited. Plate II. shows Lake Marian, a glacial bowl northwest from Overland Ranch in the heart of a group of granite crags, at an altitude of above 10,000 feet. Plate IV. is a look into one of the 2,000-foot glacial troughs wrought out of the rocks of the same region, but on the west slope, back of Camp Halleck. South of Sacred Pass, among the schists, hornblendic varieties and quartzitic schists bearing mica predominate upon the outer flanks of the mountain. In the lowest horizons, as exposed in the deep glacial canons, granitoid gneisses, gradually approaching the structureless form, are ob- served. They vary in their westerly dip from 20° to 40°. The gran- ites before described appear to underlie conformably, and may, upon future study, prove to be only the lowest lying and most extremely meta- morphosed of the series. At the head.waters of the South Fork of the Humboldt, a bold mountain promontory makes out from the range, extend- ing westwardly twelve miles from the summit, and displaying about its base a margin of Devonian and Lower Coal Measure limestones, which are . wrapped around the Archean convexity in the shape of a horseshoe. The mass of the promontory itself is of heavy Archean quartzitic schists, inter- stratified with micaceous and hornblendic beds, hornblende predominating. Both the east wall of the northern part of the mountains, and the deep cafions which are carved down from Mount Bonpland to the western foot of 5K 66 SYSTEMATIC GEOLOGY. the range, offer the best exposure of Archzean rocks. At its base the series is seen to be formed of mica gneisses of a bright-gray color and very great variety of texture and habit, made up of an association of quartz, black and brown micas, and a very variable quantity of orthoclase and plagioclase. Of the whole 8,000 or 10,000 feet, perhaps the lower 5,000 feet are predom- inantly micaceous, a few narrow zones of quartzite lying within the gneiss, but the upper members, while containing a few sheets of typical mica gneiss, are chiefly of hornblendic and dioritic schists, which are interesting on account of the number of minerals they contain. Plagioclase prevails over these hornblendic beds, but both feldspars are always present. Mica, too, frequently occurs, but it is of a dark earthy brown. The predominant hornblende is a dark-greenish black or a pure black. Apatite and titanic iron are very frequent constituents, but are only observable under the microscope. Enclosed between some of the upper beds of gneiss, which are rich in orthoclase and poor in mica, are some sheets of pure amphibole, which are noticeable as containing no other minerals whatever, not even microscopic quartz or feldspar. A very interesting form of gneiss is found on the west slope of the ‘ange, just below Clover Peak. It is a fine-grained, brilliantly gray rock, in which the white particles of quartz and the black micas have a granitoid arrangement; but the rock at large has a distinctly fissile structure, and cleaves easily in sheets of an inch or more in thickness. Besides the hex- agonal biotite, there are frequent plates of a brilliant coppery-bronze ortho- rhombic mica, and the rock is further distinguished under the microscope by containing a great deal of very fine zircon. It is also variably clouded and stained yellow and brown by infiltrated oxyd of iron. The planes which produce the fissile structure are developed by a parallel arrangement of bronzy micas, whereas the solid uncleavable sheets themselves contain biotite and phlogopite, but arranged without any attempt at parallelism. Mica sheets which define the cleavage-planes show a gently undulating surface and many marks of attrition, as if the rock had been subjected to a severe strain and had given way everywhere in a slight interior movement. Throughout the whole formation, with the exception of dioritic gneisses, quartz predominates over the feldspars in quantity. In general there is af VMS it op AG # ARCHAMAN EXPOSURES. 67 more orthoclase than plagioclase when associated in the rock with mica, but in the presence of much hornblende plagioclase takes precedence of orthoclase. These gneisses are particularly instructive as to an interior change, probably due to pressure, which broke up the parallel structure of micas and hornblendes, resulting in a gradual approximation toward the granite form. As a general rule, the more the parallelism of the micas and hornblendes is broken up, the larger individual feldspars, particularly pla- gioclases, are developed. This whole change seems to have been brought about by longitudinal compression of the beds. At present the rock cannot be distinguished, in hand specimens, from a granite, except that there is even yet an indistinct cloudy parallelism of its dark constituents. Between this stage and the true schistose gneiss, in which all micas are strictly parallel and no crystals of quartz or feldspar break through the mica layers, there is every possible transition. The first symptoms of change are observed in a wavy arrangement of the micas. When carried a little farther, these wavy lines are broken and distorted. Feldspar crys- tals and grains of quartz are thrust in, breaking the continuity of the mica lines. Signs of compression are then visible in the squeezing of interstitial quartz and feldspar into a confused mass wholly devoid of parallel arrange- ment. In this condition also it is observable that all the crystalline particles of the rock, notably the micas, are broken into much finer flakes and frag- ments than in the original schisty stage. These changes are often local, and may or may not continue over any considerable longitudinal extent. Such is the variation of the material of the original beds, that while this breaking up of parallelism may occur throughout one bed, the enclosing strata may experience much less interior disturbance. The argillaceous and the more purely quartzitic beds suffer far less of this species of alteration than micé or hornblende beds. The observer is never at a loss to trace the planes of original bedding through these regions of molecular change. One of the most interesting places for observing this phenomenon is on the great gneiss precipices forming the eastern front of the range under Mount Bonpland. As the probable result of a great fault, and partly also from the abrupt carvings of the glacial névés, fine precipices, 1,500 to 1,800 feet in height, are here exposed. As the gneiss beds dip to the west at an 68 SYSTEMATIC GEOLOGY. angle of 15° to 25°, the whole wall is formed of their abruptly cut edges, which are traced in nearly horizontal lines, striping the front of the preci- pice. So well defined are the original beds by the predominance of mica or hornblende, or by the more purely quartzitic nature of some zones, that there is never any difficulty in following a given horizon over long distances. At the same time, the whole series is seen to be clouded in peculiar irregular shadings across the stratification, like an irregular map in different shades of gray. These clouded portions are found to owe their peculiar shade to the greater or less interior disturbance in the mineral particles of the strata. Following the nearly level edges of the series for several miles, they are observed to form gentle up-and-down curves, and always within the concave side of a curve, as would be readily inferred, there is a maximum of interior disturbance of the minerals of a given bed. Simple uniform parallelism was unmistakably the original attitude of all micas. ‘The hornblendes and feldspars lie with their longer prismatic axes in the plane of bedding, and the breaking up of this stage by local longi- tudinal compression has resulted in more or less comminution of individual crystals, besides crowding the fragments into utter disorder. Parallel, vertical, longitudinal fissures, trending with this part of the range, are developed along the summit near Clover Peak and Mount Bon- pland, apparently a series subordinate to and parallel with the great fault which has produced the eastern wall by dropping the eastern half of the range out of view. Erosion has taken advantage of these clefts and fissures in the rock, to produce a remarkable series of pinnacles 50 or 60 feet high, upon some of which are large, rounded, mushroom-like tops formed of beds which have successfully resisted the weathering. Near the summit within the gneiss series, and at one or two horizons far below, the microscope reveals, as an occasional constituent of the rock, crystals of calcite; in some instances there are enough of these to cause it to effervesce under acids. There is usually associated with the calcite a predominating quantity of triclinic feldspar, also rich in lime. At the extreme summit of the gneiss there are several beds of thin, brittle, saccha- roidal quartzite, among which are intercalated apparently very similar beds of highly compact dolomitic limestone of microcrystalline texture. ARCHASAN EXPOSURES. 69 The entire limestone series is here not over 50 or 60 feet in thickness, and the individual beds vary from half an inch to six feet. Intercalated with the dolomites. are gneiss porphyries nearly identical with similarly asso- ciated rocksin Kinsley District. The upper beds pass through transition- beds into the pure quartzite which always contains in its lowest members a little microscopical calcite. The quartzite series, probably about 2,000 feet thick, appears chiefly along the middle and lower altitudes of the western side of the range, and also overlies the gray gneisses of Clover Canon. It is very well developed along the upper waters of Boulder Creek. The Clover Caton quartzites are probably direct equivalents of the great quartzite formation of the western slope, but show some slight characteristic differences, not enough, however, to render a correlation improbable. They are either white or stained a light yellow-brown by infiltrated oxyd of iron. Quartz, which is both milky and translucent, forms the mass. Under the microscope it shows no trace of the original grains of quartz sediment, but is a confused crystalline aggregate. Gar- nets, from the size of a pea down to fine microscopical grains, occur in the lower sheets of the Clover Canon quartzite, together with numerous flakes of white muscovite, which in general are disposed parallel to the bedding of the quartzite. The microscope also reveals fine black plates of horn- blende and minute prisms of actinolite, more or less dislocated The Clover quartzites are distinctly fissile, and split with very smooth faces, upon which are seen a multitude of striations indicating longitudinal motion. The surface of these divisional planes is more or less discolored with iron oxyd and spangled with plates of muscovite. Occasionally, rare and minute _erystals of feldspar rest on these smooth brown bed-faces. This appear- ance of striation is in no way due to the parallel arrangement of the mica, but is evidently the result of a true friction owing to longitudinal motion ; for the strize are traced on the strata surfaces in a variety of directions, indi- cating uneven, irregular, and evidently successive creeping motions. Al- though developed at intervals throughout the whole quartzitic series, these longitudinal movements have been very irregular, and there are consider- able areas which present no evidence of their existence. Observing these 70 SYSTEMATIC GEOLOGY. marks of motion within the quartzites and gneisses, one is irresistibly led to believe that they are contemporaneous and the result of the same forces ; that the effect upon the quartzite is great compression and interior shearing parallel to bedding, while in the gneisses the result is a crumpling within the limits of certain beds, breaking the continuity of the sheets of mica plates, comminution of crystals, and the production of a granitoid rock. Along the western base of the range, in the vicinity of Thompson’s Ranch, the quartzites are duller than those of Clover Canon and grayer in hue, and though they are still characterized by the presence of muscovite, they carry also a little brilliantly black biotite. Evidence of motion is again observed upon the cleavage-surfaces, and here the mica itself is conspicu- ously striated. Plate III. shows a ridge of the quartzites east of Thomp- son’s and near the range summit. Higher on the ridge, above Thompson’s, there is an interesting case of diagonal cleavage, due to the restricted dis- turbance of a local fold in the quartzite. Here the muscovites are all diag- onal to the induced cleavage, but parallel to the original bedding, the brittle character of the material preventing a rearrangement of micas parallel to the newly produced cleavage-planes. ‘Toward the base of the quartzite series the mica is in some instances replaced by chlorite; and where, as is often the case, this mineral reaches a considerable importance in the rock, it may be properly called a chloritie quartzite. A few straggling garnets are observed in the low members of the quartzite, near the horizon of the dolo- mitic limestones. In the rocks here described the reader will have observed a certain general family likeness to those in the main mass of the Wahsatch, in the Farmington region. The association of various mica gneisses and horn- blendic, even dioritic schists, succeeded conformably by quartzites, marks an approximate identity of conditions with the Wahsatch and with Medicine Bow Range. The essential minerals of the range are quartz, orthoclase and plagioclase, biotite, muscovite, chlorite, calcite, dolomite, and hornblende, while the accessory minerals are garnet, zircon, actinolite, phlogopite, titanic iron, and apatite. Cortez Rance.—Among the many isolated mountain blocks which corrugate the surface of Nevada, few have greater geological interest than of ARCHASAN EXPOSURES. 7A Cortez Range. At Granite Canon, directly northwest of Cortez Peak, one of the higher summits of the ridge, a little north of the parallel 40° 15’, appears on the western flanks of the range a solitary mass of granite, surrounded by Tertiary voleanic rocks, which on the north are immense outpourings of buff rhyolite, and on the south high hills of quartz-propylite, culminating in Cortez Peak. Southwest it comes in contact, for a limited distance, with the upturned quartzites which have been referred to the Weber group of the Carboniferous, and on the extreme west its spurs are overlaid by an out- burst of diorite, which comes up in a synclinal of Carboniferous rocks. ‘The longer axis of the granite exposure is with the trend of the range, northeast, and is about five miles long, with an extent of three miles in the opposite direction, making a rude parallelogram, with a sharp point invading the rhyolites. The main mass is a single high spur boldly rising from the Quaternary of Crescent Valley in abrupt slopes of about 4,000 feet. It is a rude pyramid lying between two sharp lateral cations of the range. This granite possesses singularly few divisional lines. It is a remarkably solid mass of a pale cream-color, with shadings of gray and a faint pink. No- where else along the Fortieth Parallel is there an example of such extreme solidity with the absence of all planes of bedding or traces of conoidal structure. It is evidently of eruptive origin, and although no clew to its age beyond the unconformable superposition of the Carboniferous con- glomerates was observed, for reasons to be educed later in the chapter, it is conceived to be Archean. It is composed of salmon-colored orthoclase, frequently in broad crystals, slender white prisms of triclinic feldspar, appar- ently albite, quartz which appears both translucent and of a milky white- ness, long slim prisms of dark-green hornblende, and considerable biotite. Passages of granite which do not seem to be actual veins develop a coarse pegmatite in which the orthoclases reach two inches in length and the masses of quartz an inch. The pegmatite passages are of quite frequent occurrence, but they bear no apparent structural relations to one another. They cloud through the rock in various directions, and shade by perceptible eradations into the ordinary fine-grained variety. Hornblendes here eather in confused aggregations of needles. Besides the biotite, there also occurs an orthorhombic mica, doubtless muscovite. Under the microscope the 72 SYSTEMATIC GEOLOGY. quartz is seen to contain many fluid inclusions. The rock also shows under the microscope a little magnetic iron and some apatite. South of this body, and obscurely occurring within the diorites of Agate Camon, is an insignificant outcrop closely resembling the granite of the Sierra Nevada, and composed of quartz, orthoclase, plagioclase, biotite, a brilliant black hornblende, which is peculiarly cleavable, and macro- scopical titanite. Owing to a considerable alteration in the feldspars, although both are clearly present, it is difficult to decide as to the predomi- nance of plagioclase or orthoclase. Of this decay of feldspar Zirkel says: ‘The product of this decomposition is rather curious. It consists of broader or narrower prismatic, colorless rays, which, either orderless or confused, cross each other like a felt or are heaped together in forms of stars and bunches, presenting beautiful aggregate polarization.” This little mass is entirely surrounded by diorites, and may be a granite dike subsequent to the dioritic outflow. Although classed by Zirkel as a granite, it seems to me quite possible to consider it as an unusually quartzose passage of dio- rite, since nearly all the diorites of the Fortieth Parallel contain, besides the prevalent hornblende and plagioclase, a little quartz, occasional mica, and a small proportion of orthoclase. It is only necessary to increase these to a very slight extent to reach the composition of a granite rich in plagio- clase and hornblende and poor in quartz and orthoclase. Frequently in the great granite fields of the Sierra Nevada are observed passages which are unquestionably mere dependencies, in which plagioclase and hornblende predominate over orthoclase and mica. In such instances the quartz is apt to run low, and the rock, although a true granite, possesses the mineral nature of the abnormally quartziferous and orthoclastic diorite. It seems quite proper, when this same combination is found closely related to a dio- ritic outburst, to consider it rather as a diorite than as a granite, and such the Agate Pass body may well be. But since it has passed under Zirkel’s microscope as granite it is here included with those bodies. South of Cluro Station, on the Central Pacific Railroad, is a group of hills standing out in Crescent Valley and separated from Cortez Range by a broad, shallow, pass. They are composed of a central body of granite invaded by syenites and overlaid on the west by a quartzite, which is referred, for the ARCHAAN EXPOSURES. 73 sake of convenience, to the Weber. The granite body is about five miles long by a mile broad, with a second outcrop near the western end of the hills, where a little dome rises through the horizontal Pliocene strata. ‘The granite is essentially the same as that of Granite Canon, in Cortez Range, lately described. Near the southwestern terminus of Cortez Range stands a very high, bold peak, called by the Indians Tenabo, which signifies “lookout,” a point commanding a very extensive view of middle Nevada. The main body of the range here is composed of a mass of granite which rises from the Quater- nary plain of Crescent Valley, and extends to within 800 or 1,000 feet of the summit, where it is overlaid by a capping of somewhat crystalline lime- stone, which has been referred by Mr. Hague to the Upper Coal Measure series. The overlying lime strata which rest unconformably upon the granite extend down the southern slope of the peak for three or four miles, making an irregular oval body entirely surrounded by granite. It is one of those interesting relics left by erosicn which give a clew to the rela- tive topography of the modern and Archean uplifts, for to that age the Tenabo granite is referred. The pass between Crescent and Grass valleys, which at Shoshone Wells has only an elevation of 1,000 feet above the plain, is also formed of the granite, which in passing westward is seen to be overlaid by the rhyolites of the Railroad Peak group. At its northern limit the granite is again overlaid by the limestones of the north flank of the range, also sup- posed to belong to the Upper Carboniferous. Mill Creek and the lesser streams on the north flank of Mount Tenabo flow through ravines of con- siderable depth, which offer excellent exposures of the granite, here seen to be a very tough rock, difficult of fracture, and with little tendency to dis- integration. It varies very much in texture, from fine to medium grained, and from light to dark gray tones, the latter being due to the variability of the proportion of feldspar and mica. It is composed of rather small trans- lucent grains of quartz, both orthoclase and plagioclase, with dark, partially decomposed biotites. The rock near the western end of the exposure, in the vicinity of the Shoshone Wells, is of a rather lighter color than the main body of Mount Tenabo, but otherwise shows little difference. Between the forks of Upper Mill Creek, under the western slope of Tenabo, 74 SYSTEMATIC GEOLOGY. a mass which comes to the surface as an intrusive body through the granite bears a close resemblance to the dioritoid granite of Agate Pass, already described. It is compact and fine-grained, breaking with difficulty under the hammer, and showing along its fracture a rough, uneven, angular sur- face, and has an almost eryptocrystalline groundmass, composed chiefly of quartz, plagioclase, and fibrous hornblende. Like the Agate Pass rock, however, it contains a considerable proportion of orthoclase and quartz and a little biotite. Titanite, which occurs in the Agate Pass rock, was not observed here. It seems rather to represent an intermediate link between the granite and the diorite, and, like some of the bodies already mentioned in the great granite fields of the Sierra Nevada, may be con- sidered a dioritoid dependence of granite, or simply a granite in which triclinic feldspar and hornblende are present in abnormal quantity; the diagnostic point in such bodies being their association. Wan-wean Movuntains.—Directly south of Cortez Range, and only separated from the foot-hills of Mount Tenabo by the low pass of Gor- don Cut, which connects Grass and Gordon valleys, is a narrow mountain group called the Wah-weah, of which only the northern eight or ten miles lie within our map. On the west side of this group, in latitude 40°, is exposed a small body of granite underlying quartzite. The granite extends about three miles in a north-and-south direction. SeeroyA Ranee.—North of Humboldt River, in longitude 116°, is an irregular range extending from six miles north of Carlin Station to the north- ern limits of the map, a distance of about 45 miles. At Nannie’s Peak, the summit of the range, near the head waters of Susan Creek, is a granite out- crop coming to the surface through limestones of the Lower Coal Measures and brought in contact with a body of peculiar rhyolite. The mass is made up of a series of rude beds, having a strike from north to northwest and a dip of 65° westward, in conformity with the overlying limestone beds, which upon the west and south flanks of the body are wrapped closely around the granite. The bedding-planes of the granite are distinct. The higher peaks of the range are formed of very thick projecting strata of a granite which has all the interior lithological character of the eruptive type. It is composed of quartz containing numerous fluid inclusions, some of which ARCHAAN EXPOSURES. 75 bear salt cubes, distinctly striated plagioclase, which is quite undecomposed, rare apatites, and orthoclase, which slightly predominates over the other feldspar and is not infrequently quite decomposed, showing here and there a distinct zonal structure, resembling sanidins in the trachytic family. Parts of the rock consist of a fine-grained accumulation of small crystal- line particles of quartz and feldspar like the groundmass of a felsite por- phyry. One variety contains little particles of hornblende, which seem to have been formed at the expense of the mica. Both of these granites are entirely free from titanite. That on the eastern slope of the range has a tendency to split into thin slabs, probably from contact with a curious rhyo- lite which once overflowed it and is now found farther down on the spurs. At the southern end of the high peak, in contact with the granite, appears a small body of true granitic porphyry. Farther south, at Maggie Peak, a long, narrow mass of granite porphyry protrudes through the overlying rhyolite, extending six miles in a north-and-south direction, being two miles broad at Maggie Peak. It seems to be an original Archzean summit, lifted above the limits of the rhyolite overflow. The groundmass consists of a fine mixture of quartz and feldspar, in which the crystallization is un- usually good. It contains infrequent clear granules of quartz, which Zirkel found, under the microscope, to be full of liquid inclusions, some of which contain salt cubes, both orthoclase and plagioclase, and an abundance of mica crystals. Apatite, very rare in corresponding German rocks, attains here a remarkable sharpness of crystallization. Green hornblende is occa- sionally found as an accessory mineral. At Maggie Peak itself is a light- gray variety, consisting very largely of a compact, homogeneous ground- mass, containing a very few large feldspar crystals. It is a rock which macroscopically bears a close resemblance to rhyolite, but under the micro- scope the felsitic groundmass has the same structure as the other porphyries, and its quartzes are full of fluid inclusions. ToyaBe Rance.—In latitude 39° 30’, longitude 117°, in the neighbor- hood of the town of Austin, near the western base of Toyabe Range, is a limited body of granite, upon which rest limestones and slates referred to the Carboniferous period, and which is partly environed by flows of rhyolite that evidently at one time entirely submerged the granite, but was eroded off at c 76 SYSTEMATIC GEOLOGY. a later period, leaving traces of its former presence in a peculiar reddened and decomposed condition of the granite surfaces. This decayed condition of the surface is well shown on the divide above Austin. The undecom- posed, normal granite is an even-grained gray variety, consisting of quartz, slightly flesh-colored monoclinic feldspars, and pale-greenish plagioclase in about equal proportion, both very well crystallized, dark-green brilliant hornblende, black biotite in sharply defined hexagonal plates, the last two minerals in about equal proportion, and a plentiful development of titanite, the crystals of which are sometimes one eighth of an inch long. The mass presents no evidence of bedding; on the contrary, it is altogether structure- less, with the exception of innumerable faulting-planes, accompanied by veins of metaliferous quartz and granite dikes. The divide above Austin approaches more nearly to the source of the rhyolitic overflow, and is here penetrated by innumerable fissure-planes. Chemical decomposition has gone on to a great extent, resulting in the complete kaolinization of the feld- spars, which, however, still retain their crystalline outlines. Hornblende, mica, and titanite have disappeared, leaving amorphous earthy spots. The quartz alone seems to have resisted decomposition. It remains unchanged, except by the development of innumerable cracks and the occasional infil- tration of cloudy kaolinic matter. Rare as caustic contact phenomena are, the commonest examples in western America are where granite has been overflowed by volcanic rocks, and the characteristic features in such cases are the development of innumer- able vertical fissures and general infiltration of hydrous sesquioxyds of iron and manganese. In the Fortieth Parallel area there are no such extensive exhibitions as may be seen on the upper Stanislaus River in California. Directly east of Austin, in the Park Mountains, occurs a similar granite, in which the two feldspars are distinctly marked. Hornblende decidedly predominates over the mica, titanite being absent. Here, also, to a certain extent, decomposition has taken place. Passages are exposed in which the feldspars can be no longer distinguished, and the hornblendes appear in light-green, partly decomposed fibres, the mica having almost entirely disappeared. While the interior decomposition of the granite is evidently due to deep-seated causes, such as the penetration of acid vapors ARCHASAN EXPOSURES. V7 and waters through the innumerable cracks and fissures, the peculiar super- ficial crumbling and peroxidation of the iron minerals is doubtless due to the effect of suddenly overpoured molten rhyolites. Suosnone Ranex.—The meridian of 116° 45’ passes through an exposure of granite lying about six miles east of Shoshone Peak. It is a rudely oval body, with the longer axis extended about four miles in the direction of the meridian, and with an east-and-west extent of about three miles. Along the south it is overflowed by a great body of rhyolites which skirts the east base of Shoshone Range for many miles. Otherwise it is surrounded by upturned quartzitic strata, which have been referred to the Weber group of the Coal Measures. The relation with the uptilted strata is somewhat obscure; indeed, it seems to be one of the most difficult geological problems afforded by this region, to decide, in a locality where confusedly tilted strata come in contact with eruptive granites, whether the latter have protruded through the strata in a plastic state, or have been thrust up as an underlying solid point. The configuration of the granite topography of the Archzan surface prior to the deposition of the Paleozoic series, was that of an area of mountain ranges, possessing some very abrupt precipitous walls, sharp, lofty peaks, and broad, low domes. Where these came to be uptilted together with superjacent strata, and afterward exhumed by erosion, which brought to light granite peaks piercing through highly inclined beds, it often becomes absolutely impossible to determine the relation of the two. In the absence of any granitic dikes penetrating the stratified series, or of peculiar local metamorphism, or of general evidence of intrusion, the bodies are usually referred to the old Archzean topography. Only in cases where the granite is actually seen to penetrate either fissures or warped openings in the strata, is it safe to refer it to a later origin than the sedimentary series. This question, as applied to the majority of the granite exposures of Nevada, will be more thoroughly discussed later in the chapter. Structurally the Shoshone granite develops in interesting perfection the broad conoidal bedding after the type of the Sierra Nevada domes. The rock is composed of predominant quartz; orthoclase and plagio- clase in almost equal proportion, biotite, a great deal of easily cleav- 78 SYSTEMATIC GEOLOGY. able black hornblende, and a little microscopic apatite. For uniformly mixed granite there is an unusual discrepancy in the size of the quartz and orthoclase particles. Quartz masses from half to three fourths of an inch in diameter are observed, carrying many enclosed plates of biotite and fluid inclusions. Excellent hexagonal biotite crystals were observed, whose faces are covered with an interesting iridescent tarnish. The color of the plagioclase is a clear white, and it appears in stout crystals resembling albite. The orthoclase shades from white to rusty yellow, owing to micro- scopic infiltrations of iron oxyd. The cation of Reese River severs Shoshone Range into two well marked divisions. The southern portion is a single broad flood of rhyolite, from which, at a few localities, rise isolated outcrops of older rocks. At Ravenswood Peak, certain of the Carboniferous beds, an intrusion of diorite, and small exposures of granite and granite porphyry occur. For eight miles south of that point, the summit is formed of one of these outcropping islands of older rock lifted above the slopes of the rhyolite. It is a narrow meridional mass of granite, about eight miles long and from one to three miles wide, flanked upon either side by narrow zones of steeply dipping schists. This stratified series dips east and west away from the central granite mass, which has rather the appearance of an intrusive core. From their likeness to other known Archean rocks, and for the want of reasons to the contrary, these schists, together with the granite, are referred to the Archean. Parallel divisional planes standing at a very high angle occur with considerable regularity in the granite, giving it almost an appearance of stratification. As the identical granite penetrates the schists in the form of a dike, there seems no doubt that the whole mass is of eruptive origin. It consists of quartz, orthoclase, a few scattered grains which appear to be minute crystals of plagioclase, and white orthorhombic mica—probably muscovite; but there is no hornblende, black mica, or titanite, and very little apatite. The dike which invades the schists is made up of a similar but coarser-grained material, in which there are clearly two feldspars (the predominating one a white or pale salmon-colored, smoothly cleaving ortho- clase) and a few minute prisms of triclinie feldspar, large accumulations of grains of smoky quartz, and irregular bunches of muscovite. ARCHASAN EXPOSURES. 79 There is something unusual and suggestive in the superior coarseness of the mineral components of the dike. Ordinarily, over the area of this Exploration, dike minerals have far greater fineness than those in the parent irruptive mass, due not unfrequently to friction and comminution during intrusion. Perhaps the state of things here is explained by supposing that within the walled and protected dike there was less opportunity for the intercrystalline attrition due to orographical movement than in the larger and more exposed body. The accompanying schists are of two types. One is a very fine-grained compact rock, whose broken faces display a very steely crystalline shim- mer, as from extremely small facets. Yet even the loupe does not discover any crystalline ingredients, the general appearance being that of a fine- grained anamesite; the microscope, however, develops an aggregation of very minute particles of quartz and two micas, biotite and muscovite. Besides these, on the western flank are found series of fine mica schists having the same composition as the more compact rock, except that the constituent particles are larger, and that parallel sheets of minute mica plates produce a bright, irregular reflection of light from the whole sur- face. They may be called spotted mica schists, and are not unlike those described in the neighborhood of the Irish granites by Haughton. ‘These spots, which the microscope made out to be densely compacted grains of mica, are not thick enough to give it the name of ‘“Mnotenschiefer.” It seems probable that the spots represent the features of local metamorphism after the manner described by J. Clifton Ward in his article on the granitic, granitoid, and associated metamorphic rocks of the lake district.* These spotted schists are closely allied to the rocks of the Wright's Canon mass in West Humboldt Range, the main difference being that here the con- stituent particles are finer, and there are interesting bronze passages of schist whose color is derived from infiltrated oxyd of iron. Aveusta Mountaiys.—On the eastern side of the Augusta Mountains, near the northern end of Edward’s Creek Valley, is exposed a small body of granite about two miles in extent, overflowed and surrounded on the north and west by rhyolite, which here forms the dominant rock of the * Part III., Quarterly Journal of the Geological Society, Vol. XXXII, page 1. 80 SYSTEMATIC GEOLOGY. range, and separated from the Quaternary of the valley by a belt of sedi- mentary rocks of Alpine Trias age. Save that the Trias reposes uncon- formably upon it, there is no clew to the age of this granite. Lithologically it belongs with the older eruptive granites, and is composed of grains of varying size of pellucid or slightly smoky quartz, a very large amount of somewhat earthy orthoclase, considerable biotite, a small but varying propor- tion of hornblende, and a very little apatite. Some specimens show the orthoclase of a pale olive-green color, and peculiar strings of crumpled, decomposed mica. The biotite shows an unusual facility for decomposition, so that the exposed and weathered faces of the rock exhibit numerous hex- agonal pits, out of which the products of decomposition have been washed. Fiso Creek Mountains.—Fish Creek Mountains, the northern exten- sion of the Augusta group, are almost entirely formed of rhyolite. - Along the western slope of the northern extremity of the range are a few limited basaltic outflows, and the extreme western base, to the west of Mount Moses, shows a narrow band of granite extending along the foot-hills for about four miles north-and-south, by less than a mile in width. It is overlaid unconformably by Triassic strata. It is a dense, compact rock, composed of quartz, orthoclase, and biotite, with a little plagioclase, and is destitute of structural indications of a metamorphic origin. It is doubtless to be classed with granites in the regions lying to the northwest, which represent a general Archean highland over which the Triassic beds are laid down. Together with the limited exposure at Granite Point, where it is again over- laid by Triassic strata, these granitic foot-hills near Mount Moses represent a portion of an Archzean body which may be largely developed immedi- ately beneath the immense flood of rhyolite now covering the surface of this early range. Havautian Rancr.—A little north of latitude 40° 30’ Havallah Range, in passing northward, bifurcates like a rude letter Y, the most eastern arm trending off about 25 miles in a northeasterly direction, and sinking below the Quaternary plains in the region of Stone House Station. The upper fifteen miles of this arm are composed of a lofty mass of granite, which rises abruptly to its culminating points nearly 4,000 feet above the plain. On its southern edge, at Summit Springs Pass, the granite is overlaid by ARCHAAN EXPOSURES. 81 Alpine Trias strata. The plain of Ragan’s Valley on the west has an alti- tude of 4,500 feet, the highest summit of the granite body reaching 8,150. The topography is decidedly rugged, and it is more minutely varied than the usual exposures of Archeean rocks in Nevada. It is all but certain that even during the deposition of the Trias and the conformable Jura, parts of this range were lifted above the limits of deposition and suffered erosion from a very early period. The broken and serrated outline which char- acterizes the summit of this group renders it essentially different from the neighboring granites. Although not possessed of any distinct planes of bed- ding, this occurrence, in many of its physical aspects, recalls the metamorphic granite bodies described in Colorado Range. It is coarse-grained, ill-com- pacted, and readily disintegrates, leaving irregular-shaped fragments. There seems to be far less uniformity of texture than is usually the case in eruptive granites. The prevailing color is a dull gray. The essential constituents are quartz, orthoclase, plagioclase in brilliant but small crystals, bearing wonder- fully fresh striae, small dark plates of biotite, more or less decomposed, and a little hornblende in small, dark-green crystals. The orthoclase occurs in crystals of various sizes, some of them reaching three inches in length and having broad tabular faces with brilliant lustre. They are usually a bluish, smoky gray, near the ordinary hue of labradorite. Infiltrations of oxyd of iron have penetrated the rock in every direction, leaving a thin ocherous coating on many of the broad faces of the feldspars. Under the microscope Zirkel discovers many points of interest in this rock. Apatite, magnetic iron, and muscovite seem to be accessory minerals. The reader is especially re- ferred to Zirkel’s memoir for a description of the inclusions of the feldspar. He describes the quartz granules as containing three forms of liquid inclu- sions. simple water-bubbles, liquid carbonic acid, and compound bubbles containing both water and carbonic acid. On the east side of the range, a little north of Summit Springs, the main body of granite is penetrated by a narrow dike which has clearly the properties of an intrusive body and bears a close resemblance to the granites of the Sierra Nevada type. The association of intrusive granite bodies with the older forms of Archzean granite is decidedly exceptional over the area of the TFortieth Parallel. In Colorado Range there are indeed some 6 Kk 82 SYSTEMATIC GEOLOGY. instances of bold intrusive masses penetrating the essentially metamorphic granites, and in the case of Mount Clayton and the Little Cottonwood mass, in Wahsatch Range, there is probably a repetition of this association; but it is extremely rare in the country west of the Wahsatch. The granite dike north and east of Summit Springs is a comparatively fine-grained rock, breaking with difficulty under the hammer, and leaving an uneven, angular surface. The constituent minerals have a fresh, unaltered appearance, and in color the rock is of a brilliant gray, of which the irruptive Californian rock may be considered a type. It is composed of quartz, orthoclase, brilliant, pearly plagioclase, biotite, and hornblende, and the microscope detects a very minute proportion of hair-brown titanite. Hornblende and plagioclase rise to considerable importance as principal constituents, almost to the point of shading the rock into those questionable bodies which appear to lie be- tween granite and diorite. Indeed, we have only to increase these constit- uents a little to produce the dioritoid rock of Cortez Range. Biotite is in the form of brilliant, symmetrical, black hexagons. The hornblende is very dark green, and has an extremely fibrous structure, suggestive of the horn- blende belonging to the propylite family. The quartz contains a few salt- bearing fluid inclusions. Dikes of fine-grained diorite, composed of dark-green hornblende and triclinic feldspars, oceur within a few miles of Summit Springs. On the northwest side of Ragan’s Valley, opposite the above-described granite body, is another exposure of the same sort. It is only about ten miles from north to south and four miles east-and-west. As the map indicates, it is partly overlaid by strata of the Alpine Trias period, the east base being wholly bordered by the Quaternary plain of Ragan’s Valley. On the west it is about equally bounded by Quaternary of Rocky Creek, rhyolites which extend southward from Golconda Station, and Alpine Trias of the main Havallah R ange. Though of much lower and less conspicuous topo- graphical configuration than the body to the south, this second mass is, by its petrological nature, closely related to the Summit Springs body, and may be considered as the northern extension of it, merely separated from the main mass by a shallow covering of Quaternary. It is, perhaps, a little less loosely compacted, and is distinguished from the other body by distinet ARCHASAN EXPOSURES. 83 bedding-planes, which have a rather gentle dip toward the west. Near its southern extremity, directly north of Cold Run Creek, the granite is pene- trated by a dike between 20 and 30 feet in width, which stands nearly vertical, striking with the trend of the Havallah. It is a dense, dark-gray rock of high specific gravity, with a fine microcrystalline groundmass, in which crystals of hornblende and occasional segregated groups of mica plates are porphyritically inclosed. Essentially made up of quartz and horn- blende, it is probably another of those singular dioritoid dependencies of granite which are often seen connected with large bodies of that rock. A third granite locality within Havallah Range is exposed upon its west base, between the mouths of Clear Creek Canon and Bardmass’ Pass. Here a strip of granite, nowhere over a mile wide, extends along the extreme foot-hills of the range, sloping under the Quaternary of Grass Valley and flanked upon the east by beds of the Alpine Trias series. Topographically it consists of the points of three main spurs of the range, weathered into rounded and conical hills. As usual, where forms are at all pointed, the granite is of a hard, compact texture and resists weathering most deter- minedly. It is of a dark, warm gray tint, and consists of quartz, orthoclase, brilliant striated plagioclase, a little dark-green hornblende, and a very little mica. In general, it may be characterized as of eruptive habit. Pan-Ute Rance—Pah-Ute Range traverses Map V. from north to south with a remarkably sinuous trend, consisting mainly of a broad con- vex curve thrown to the east, with minor convexities at each end turned westward. It consists essentially of Archzean rocks, granites, and granitoid gneisses, overlaid by the immense conformable series of Trias, Alpine Trias, and Jura; and these in turn are overlaid and deluged at different points by Tertiary volcanic rocks. The granitoid masses in the neighborhood of Tarogqua Peak, in the southern part of the range, have been but little studied. The mass of Granite Mountain is in every way the most im- portant Archean body of our part of the range, and in consequence has received much closer study than the other. Granite Mountain mass is an oval body, touched by the parallel of 40° 15’, having its longer axis of about twelve miles extended in an east-and- west direction, with a shorter diameter of about eight miles. This expo- 84 SYSTEMATIC GEOLOGY. sure is wholly composed of granitoid rocks having a distinct east-and-west strike and standing at very high angles—indeed, approaching the vertical. It is interesting to observe that, while these Archean strikes are altogether in a direction approximating to the east-and-west line, the later sedimentary rocks of the range are all nearly in a north-and-south position. This Archean strike makes itself particularly felt in the lesser topographical structure of the body. As may be seen by a glance at the map, the leading streams near the contact of the granite body with the quartzites to the north have nearly easterly directions. The granitoid rocks which con- stitute this exposure are made up of quartz, orthoclase, and plagioclase, with minute, unimportant additions of mica and hornblende. In short, it is essentially the same aplitic compound as that already described in Colo- rado Range. They are distinctly bedded, but without any observed paral- lelism in the arrangement of the individual minerals. The rock is a light, flesh-colored mass, generally medium grained, and is more or less clouded with stains of infiltrated iron oxyd. Decomposition has gone on to a cer- tain extent in the orthoclase and mica, but the triclinic feldspars, which are probably oligoclase, have retained their original freshness and brilliance. The dark biotite is gathered into minute segregations of broken flakes, and it seems to be far more prevalent in some east-and-west zones than in others. Under the microscope, Zirkel detected liquid carbonie acid in the quartz. Black tourmaline occurs in veins of granite east of the geodetic station on the summit of Granite Mountain; also brown iron garnets asso- ciated with light mica. On the ridge east of the summit of Granite Moun- tain is a narrow band of feldspar porphyry, having an east-and-west strike and lying conformably with the granite zones. It consists of a microgra- nitic groundmass of a brilliant grayish-white, stained here and there by oxyd of iron, and carrying brilliant crystals of feldspar and irregular granules of pellucid quartz. It seems to be referable to the same origin as the granite itself, and is to be classed with the granitoid porphyries of Kinsley Dis- trict and Franklin Buttes. It is an exceptionally fine-grained zone of met- amorphie granite, not an intrusive dike. About fifteen miles to the north, along the east side of the range, is another important exposure of granite. At Granite Mountain the Triassic ARCHAAN EXPOSURES. 85 beds are flexed around the eastern end of the granite mass, but here they bend around the western side, the whole line thus describing a sort of sigmoid curve about the two granite centres. The topography of the Spaulding’s Pass mass is that of lofty conical hills and high rugged spurs, the slopes of which descend to the level of Grass Valley. It is a hard, compact, medium-grained, light-red granite, without the evidences of bed- ding or the variability of zones seen at Granite Mountain. It is probably an eruptive rock, related to the small body at the western base of Havallah Range, directly across Grass Valley. West Humsoipt Rance.—On the west side of West Humboldt Range, about six miles north of Sacramento Canon, is exposed in the body of the range a mass of granite and accompanying crystalline schists. They are well seen in Wright’s Canon and in the two canons next north. The whole exposure is in the form of a broad oval, about four miles in its longer direction of northwest-and-southeast. The southern two thirds are of true eruptive granite, the remainder a variety of crystalline schists. This body is evidently an old Archzean summit, over which the quartzites, argil- lites, and limestone beds of the Alpine Trias were deposited. At the post- Jurassic period of folding of this range the Archean mass was somewhat driven through the strata and slightly shoved to the west, throwing the strata. into sharp curves, the Alpine Trias limestones and quartzites wrapping completely around the north and west sides of the body. In the region of Wright’s Cafion the granite is more or less intersected by jointing- planes, which strike mainly northeast or northwest, standing nearly vertical. At the top of the canon are developed certain broad conoidal bodies, not unlike those of Shoshone Knob, by no means comparable with the Sierra Nevada domes, but still suggesting the true conoidal habit. These two localities and the so-called City of Rocks in Southeast Idaho offer ex- amples of fairly regular cones, which on the whole seem to be the result of a kind of weathering due to a soft and rather decayed exterior. There are none of the characteristic conoidal shells which are developed in so symmetrical a mode throughout the domes of, for instance, the Merced region in the Sierra Nevada. The rock is composed of a very coarse- grained association of colorless and dusky quartz, yellowish and white 86 SYSTEMATIC GEOLOGY. orthoclase, either very little plagioclase or none at all, and two species of mica—a white muscovite chiefly included within the quartz masses, but now and then seattered in minute white spangles through the orthoclase, and a normal proportion of biotite, which is at times a good deal decomposed into a brownish-ereen fibrous condition, suggestive of the transition into chlorite. Black hornblende occurs, but it is segregated into bunches not well dis- seminated through the rock. Neither titanite nor apatite was observed. The contact of the granite with the associated family of schists is very inter- esting; it shows in horizontal plan an irregular, angular intrusion of granite into the schist, with outlying insular masses of schist wholly enclosed within the granite, or promontory-like masses jutting from the schist into the granite. One of these points extends 400 or 500 feet into the gran- itic mass. On the edges of these included bodies of schist, and indeed along the whole contact between granite and schist, there is no tendency toward a passage by gneissoid gradations between the two rocks; the line of demarkation is always sharp and clearly observable. In the vicinity of the schist the granite is penetrated by a great number of structural planes, having a strike partly with the bedding of the schists, as if the part- ings of that rock had somewhat controlled the lines of fissure. There is also another set of joints, with a direction of north 36° west, or approxi- mately at right angles to the schist. A few dikes of granulitic material, containing rare crystals of feldspar and a few raspberry-colored garnets, in- vade the schists. As a whole, the schists strike about north 50° east, and are either vertical or dip at a high angle to the northwest. The lower members of the altered sedimentary rocks are excessively fine-grained mica slates, carrying coarse limpid granules of quartz. It is a Knotenschiefer in which the nodules are aggregated heaps of mica flakes or nuclei of large grains of pellucid quartz, around which the flexible, matted mica scales are bent. The mica appears to be chiefly muscovite, although small flakes of a black variety, probably biotite, are present. An interesting peculiarity of this rock is the minute corrugation of the sheets of mica, which are flexed between the mica and quartz nodules. The whole surface of one of these sheets of felted mica is corrugated in the most minute wrinkles, of which fifty or sixty can be traced in an inch. ARCHASAN EXPOSURES. 87 An irregular decomposition has taken place between the laminz of the rock, resulting in a bright, almost orange-colored oxyd of iron. The lower mica schists are dark silver-gray. Above these occurs a zone of creamy- white or yellow-stained mica schists, made up almost wholly of minute quartz grains and excessively small plates of muscovite, embedded in which, as in the last described lower series, are large grains of limpid quartz, sometimes one fourth of an inch in diameter, and disposed like pebbles in a conglomerate, the mica bending over and enclosing them. In this also the same minute, interesting corrugation bears witness to an internal compres- sion of the whole series. An association of excessively fine muscovite with such large angular fragments of quartz is not found elsewhere in the Forti- eth Parallel area. Passing up in the series, the muscovite gradually gives place to minute quartz grains, but it still contains a few of the large pellu- cid quartz fragments. Here again the internal corrugation is seen upon every fracture-surface, and the rock becomes a quartz schist. These quartz individuals are somewhat difficult to account for. At first glance they might be explained as the small pebbles of a conglomerate whose argilla- ceous matter had passed by metamorphism into muscovite. Such unaltered conglomerates are not unknown in the Rocky Mountain Cretaceous—rocks in which small pebbles are thickly interspersed without the ordinary ar- rangement parallel to the stratification. Another, and doubtless a sounder hypothesis, is the aggregation during metamorphosis of like particles with like, as is seen in the Archzean gneisses of Humboldt Range, where groups of orthoclase form in the midst of a felt of rusty biotite. Montezuma Rance.—In the Montezuma Hills, Archean rocks play : very important role. The range is topographically divided into several groups, separated from each other by considerable depressions and distin- guished by great geological variety. A prominent depression in the region of latitude 40° 30’ severs the range and permits the beds of the Miocene Tertiary to stretch through from valley to valley. North of this pass the range rises to a high granitic summit in Antelope Peak, and dipping away from either flank of this are great masses of rocks which have been referred to the Jurassic period. On the extreme northern and eastern edge it is in contact with the Quaternary beds of the Humboldt plain, and also with a 88 SYSTEMATIC GEOLOGY. limited outflow of basalt which skirts its base. The body lying to the east of Antelope Peak is of rather less extent, though similar in position, being flanked on the west by the slates of the Jurassic series and on the east by the basalt and the Quaternary plain. About its southern point are wrapped the disturbed strata of the Truckee Miocene. South of the pass the range again rises to a lofty ridge characterized by quite complicated topographical forms. It is made up of a middle band of granite, accompanied upon either side by flanking belts of Archean schists. This composite body has an extent of twenty miles in the direction of its trend, by about twelve miles in extreme breadth. The isolated knob of granite rising out of the Humboldt plain west of Lovelock’s Station, called Lovelock’s Knob, may be regarded as a dependence of the main Montezuma granite. So also the several granite outcrops from which erosion has removed the general covering of basalt in the spur west of Granite Point are sub- ordinate parts of the larger block. For a distance of fifty miles, therefore, granite is a frequently recurring feature; and, together with the crystalline schists in the region of Trinity Cafion, it may be said to constitute the core of the range. South of Valley Canon the whole range consists, with but unimportant exceptions, of volcanic outflows which have overwhelmed and submerged all the older rocks. The slight exposures in the vicinity of Lovelock’s Knob and Granite Point are chiefly of a coarse, crumbling granite, very rich in orthoclase, and in rather large, irregular grains of pellucid quartz, together with a sparing quantity of more or less decom- posed biotite The most important Archean exposure is that which culminates in Trinity Peak. Here the granite belt, from twelve to fifteen miles long by four miles broad, occupies the higher portion of the range. It is deeply sculptured by erosion, and the sharp canons lay bare a depth of from 1,200 to 1,500 feet of granite slopes. The general surface shows a great deal of the results of easy disintegration, in the form of granitic gravel which often masks the more solid portions of the rock. At the northern extremity of this body, west of Rye Patch Station, the rock is a uniform fine-grained mass composed of quartz, orthoclase, a little oligoclase, and plentiful mica and hornblende, the latter of a dark-green color and decidedly fibrous crys- ARCHASAN EXPOSURES. 89 tallization. Biotite is present in well developed hexagonal plates, which are usually more or less decomposed and stained an earthy brown. Directly south of this body, and four or five miles northwest of Oreana, in the midst of a broad field of rhyolite, is an isolated hill of granite, which is of interest as forming the country-rock of the Montezuma Mine. Like the granite west of Rye Patch, it consists of quartz, both feldspars, horn- blende, and mica, but, if anything, it is rather more decomposed. It belongs to the decidedly basic granites, and although more siliceous than that of the Wachoe Mountains, approaches it in composition. This whole Trinity body of granite is undoubtedly of eruptive origin, as may be determined from its general habitus and from its penetrating the Archzean schists in well defined dikes. From this granite core the two bodies of Archzean schists dip in con- trary directions, forming a steep anticlinal. The eastern body, well shown in Trinity Canon, has a dip of 60° to the east; that on the west side of the range, directly west of Trinity Peak, dips from 50° to 60° to the west, with a well defined strike of about north 45° east. In these schist bodies there are 4,000 or 5,000 feet of conformable beds of a remarkably uniform appearance. Their color ranges from dark steel-gray to black, with a fine but brilliant lustre on the freshly fractured and cleaved faces. The naked eye is only able to detect a fine microcrystalline mass, but the microscope resolves the body into a compact admixture of quartz, biotite, muscovite, and magnetite. In all the specimens we obtained there is a total absence of both feldspars. Throughout the upper part of Trinity Canon the schists are penetrated in different directions by small granite dikes, petrologically allied to and doubtless depending upon the main, mid- dle mass of granite. The second large body of granite already indicated as lying east of Antelope Peak in that portion of the range north of Indian Pass, so far as our slight geological observations go, appears to be a petrological repeti- tion of the larger body. The two are of medium texture and of a variable light color, being made up of quartz, orthoclase, and large amounts of well developed brilliant hexagonal plates of biotite. It would seem, therefore, that the central body, which is associated with the Archaean schists, differs 90 SYSTEMATIC GEOLOGY. from the other granites of the range in its considerable proportion of horn- blende, while that of Lovelock’s Knob and that of Granite Point seem to be more nearly uniform with the two northern bodies in the low percentage of hornblende and the presence of well developed hexagonal biotite. These bodies are referred to the Archean age simply on petrological evidence. This mode of correlation is dangerous, but a general study of the whole region has strengthened the belief that in the Paleozoic series as a whole there are none of those results of extreme metamorphism which in the Appalachian system are described by some geologists as closely approxi- mating to Archean forms. Pan-tson Mountarns.—From the Quaternary plain west of Indian Pass rises an isolated body of mountains extended about twenty miles a few degrees east of north, and having an extreme width of about eight miles in the middle of the body, near Pahkeah Peak, the highest point of the range. This summit rises about 3,300 or 3,400 feet above the desert plains at its base. The group consists essentially of a small mass of granite and Archzan schists, extend- ing from near the northern limits of the hills southward for ten miles along the west side of the range, rising toward the centre, and occupying the summit in the region of Pahkeah Peak. Eastward, the entire Archsean series is surrounded by outflows of Tertiary volcanic rocks, chiefly rhyolite and basalt. The Archzean nucleus itself consists of three distinct members: crystalline schists closely resembling those already described in Trinity Canon on Montezuma Range; a limited amount of granites; and a subse- quent granite which has broken through the older granite and schists, over- flowing them ina broad field to the north. All the crystalline schists occupy a region from the mouth of Crusoe Canon to the mouth of Frost Canon, with a breadth of about three miles, culminating in Pahkeah Peak. To the unaided eye they closely resemble the fine granular-crystalline condition of the Trinity Canon schists, but under the microscope Zirkel found them to be composed of quartz, biotite, and muscovite, with, in one instance, thin laminze of a third mica, having an oil-green color. As in the Montezuma schists, there is no trace of either feldspar, and no tendency either to a minute schistose arrangement of the beds or to interior parallelism between the constituent minerals. There is, however, a distinct broad bedding, ARCHAAN EXPOSURES. 91 which defines a very high dip and a north-and-south strike. Associated with these is a further development of a fine-grained homogeneous rock, which, though possessing little outward resemblance to the quartz and mica rock, is nevertheless nearly related to it. It occurs near the head of Crusoe Canon, the high ridge southwest of Pahkeah Peak, and has the aspect and fracture of a quartzite, but the microscope shows it to consist of minute crystals of delicate green hornblende and quartz. Feldspars are again totally wanting. The rock appears to be exactly like the other schists, with the substitution of hornblende for mica. In contact with the schist body is a limited exposure of granite, whose original northward extension is wholly unknown, since it is overlaid by a more modern granite, to be described later. Near the head of Crusoe Canon this older granite appears with a surface characterized by great decomposition, resulting in rusty earthy débris, and even the more solid parts of the rock have an extremely friable texture. Quartz, orthoclase, and muscovite form the chief con- stituents. Both this granite and the accompanying schists are more or less inter- sected by dikes, likewise supposed to be of Archean age. One in particular is observed in Crusoe Canon, a very fine-grained, pearly-gray granite, in which are coarse passages of pegmatite, carrying the quartz both in broad irregular masses and fine-grained passages; orthoclase crystals, not infre- quently four inches long, and having the lustrous appearance of pure, unde- composed feldspar; muscovite, lepidolite in thin lamine, brilliant black erystals of tourmaline, and garnet intimately associated with colorless muscovite. Neither biotite nor hornblende is present. Other dikes trav- ersing the schists in the same region possess a very fine-grained association of the same minerals, the tourmaline especially rising to so high a percent- age as to carry the rock into the schérl granites. Whatever may have been the origin of this dike, whether distinctly eruptive, or, as seems to the writer far more probable, the result of hydrothermal secretion, it is an interesting fact that in its body are included noticeable masses of the crys- talline schists, which have either fallen in during the process of forma- tion or in some manner been involved while the rock was in a plastic con- dition. 92 SYSTEMATIC GEOLOGY. ‘Lying to the north of Pahkeah Peak is a stretch of granite extending for four or five miles, which apparently overlies and masks the older granites already described. It is a very fresh, clear, bright-grained stone, with none of the evidences of decomposition and ferric infiltration which characterize the underlying variety. Quartz, orthoclase, a high percentage of plagio- clase, mica and hornblende in variable quantities, and titanite enter into its composition. Under the microscope considerable apatite, specular iron, and occasional bodies of magnetic iron are seen. In the petrographical scale it comes near the basic limits of granite, having of silica 64.02, while there is twice as much soda as potash, which indicates either a predominance of plagioclase or that the orthoclase belongs to that group in which the pro- portion of soda rises to unusual prominence. North of the Pah-tson Mountains, and lying in the gap between Grass Canon and the Kamma group, are three isolated outcrops of granite coming to the surface through the Miocene beds. They are of no interest, except as indicating the northward continuance of the Pah-tson granite, which in the region of Grass Canon is undoubtedly buried beneath the Tertiary voleanic rocks. Finally, it may be said that the entire habitus of both species of granite is distinctly that of an eruptive product bearing no resemblance whatever to those we have classed as metamorphic. Paun-supp Mountarns.—West of the Pah-tson group, and entirely sur- rounded by broad fields of Quaternary, is a very irregularly shaped group, which has been called the Pah-supp Mountains. It consists of a prominent, bold ridge, extending in a well defined line along the eastern margin of the body, and a long, irregular slope to the west, invaded on the north and south by bay-like regions of Quaternary. The main sharp ridge, which has a trend of 15° or 16° east of north, attains an altitude of a little over 3,000 feet above the desert, and is flanked on the eastern foot-hills of its north and south extremities by narrow bands of highly inclined slates and ealeareous shales which have been referred to the Jurassic age. The main body of the range is of a uniform granite, not to be distinguished in its mode of occurrence and general features from the more recent of the granites of the Pah-tson. It consists of quartz, orthoclase, plagioclase, hornblende, and mica, and only differs from the other in the absence here of macro- ARCHAAN EXPOSURES. 93 scopic titanite. Under the microscope Zirkel observed in the quartz a great number of fluid inclusions. The granite is frequently traversed by fine narrow seams of quartz and thin veins of fine-grained, massive feld- spar, varied by a few scattered grains of quartz. ‘Toward the north end of the group, opposite the Kamma Mountains, the granites are more compact and rather lighter colored, owing to the diminished proportion of mica and hornblende. The quartz, too, occurs in rather larger transparent grains. An isolated body of granite lies to the south of this group and establishes a geological connection between it and the Sahwave Mountains. The single specimen brought in from this knob distinctly identifies it with the Pah-supp hornblende-plagioclase-bearing granites. Like the Pah-tson body, and indeed like the neighboring granites of Truckee and Granite ranges, this mass is unmistakably structureless. Granite Raner.—The region in the northwest corner of Map V., representing the limit of our labors in that direction, is occupied by an extensive table-land of basalt known as the Madelin Mesa. Its eastern boundary abuts against a sharp, high ridge of granite which enters the area of the Fortieth Parallel Exploration from the north, and extends south- ward twenty-five miles to the region of Mud Springs and Granite Creek Station. It is a from eight to twelve miles wide, rising at its culminating points to 6,000 feet above the level of the desert Excepting the volcanic rocks which skirt its base upon the east and west, it is wholly com- posed of a single mass of granite, of decidedly uniform texture, and producing, both in the spurs and in the dominating peaks, only rounded and dome-like forms. On the extreme heights northwest from Granite Peak Station, imperfect conoidal structure is developed. From Truckee Range, whose extreme northern point almost comes in contact with the Granite Range body, it is separated by a strip of level desert. This is rather a topographical than a geological separation, because Truckee Range for many miles to the south is itself made up, as will be seen hereafter, of a precisely similar granite. So far as examined, Granite Range consists of a rock having all the features of the neighboring masses of the Truckee, Pah-tson, and Sahwave Mountains. The rock possesses an even, middle- grained texture, breaking quite readily under the hammer. In composition 94. SYSTEMATIC GEOLOGY. it is a mixture of either white or translucent grains of quartz, orthoclase, plagioclase (probably albite), biotite, hornblende, and frequent hair-brown and golden-yellow titanite. Many of the plagioclases have extremely bril- liant surfaces, upon which are traced the characteristic twin striations. As usual in this family of granites, the hornblende and mica are most variable. TruckEE Rance—The Archean exposures of Truckee Range lie wholly to the north of Nache’s Pass. From that depression to its northern extremity in the region of Mud Lakes, the range is nearly a continuous body of granite, with a few limited outcrops of Archean schists and an unimportant mass of Triassic slates, together with a great development of Tertiary volcanic rocks in the region of Nache’s Pass. The Archzean body is composed of schists and of granites representing two periods of forma- tion. First in order will be described the limited occurrence of schists. In the region of Nache’s Peak, directly on the 40th parallel, at the east side of the range, and lying in immediate contact with the main granite body, is a development of Archzean schists which occupy the eastern foot- hills of the range for about nine miles. Among these, one from the summit of Nache’s Peak deserves special mention. To the naked eye it presents the appearance of a fine microcrystalline stone, in which no indi- vidual particles are determinable. Under the microscope it appears as a fine-grained mixture of plagioclase and hornblende with a little quartz. Although without much doubt a metamorphic rock, and essentially a mem- ber of a series of schists, it has exactly the composition of a slightly quartz- iferous diorite. It is indeed mineralogically the counterpart of those dio- ritic gneisses already described in Medicine Bow and Park ranges, as well as in the Wahsatch and Humboldt. But it has this distinction, that its par- ticles are relatively very much finer than those of any of the dioritie schists in the ranges far to the east. South of Nache’s Peak the series seems to be made up of dark mica schists having a decidedly fissile structure, and composed, like the dioritoid rock above mentioned, of exceedingly fine- grained particles. It is essentially made up of minute granules of quartz, with biotite and muscovite. Zones of fine, dark, steely-gray quartzitic schists are also interstratified with the other beds. In some of the banded quartzitic rocks, in which white and nearly black layers repeatedly alter- ARCHAZAN EXPOSURES. 95 nate, the microscope discovers that calcite is present in numerous brilliant crystals. Two or three miles west of Luxor Peak, in the northern part of the range, is exposed a small body of Archzean schists; and again twelve miles to the north the granite is flanked by a narrow belt of schists, a mile and a half wide by six miles long, placed with the strike of the range. Both these unimportant northern exposures are accompanied by outflows of basalt, which mask their dip toward the plains of Mud Lake. Neither out- crop possesses any especial geological interest, except as indicating a con- siderable extension for the schists of the range. It would seem that in many of these western Nevada ranges the structure is that of a simple anticlinal, having a broad, massive granite core with crystalline Archean schists dip- ping away from either flank. Subsequent erosion has removed a great amount of the schists, and the horizontal Tertiary and Quaternary beds have so buried the flanks of the ranges that only small portions of the old schists are visible. Could the horizontal and overlying beds be all removed, there would doubtless be found a great amount of crystalline schists. The litho- logical resemblance is so intimate, and the area over which they are exposed is in reality so limited, that all these detached outcrops of schists may be thrown into one series, which formerly extended over the whole country. Their resemblance is more intimate when correlated by the mechanical con- dition than by their mineral composition. Southeast from Winnemucca Lake is a small body detached from the main granite mass of the range, flanked along the east by strata referred to the Trias, and on the north and south by outflows of rhyolite, the western slope plunging beneath the Quaternary plain. The rock bears the aspect of a readily crumbling metamorphic granite, and is composed chiefly of quartz, flesh-red orthoclase, and a few minute crystals of plagioclase. The only mica is muscovite, and that occurs in so small a percentage, and is so un- evenly disseminated through the rock, as to justify the term “‘aplitic granite.” A further specimen from the same body is made up of quartz, partially decomposed orthoclase and plagioclase—the former much the more abundant of the two—and a little regularly disseminated biotite. The muscovite-bear- ing granite of this body seems to be the older of the two. North of Nache’s Peak, the main range, as well as the accompanying 96 SYSTEMATIC GEOLOGY. body of the Sahwave Mountains with which it is solidly connected, is com- posed, so far as known and wherever we have visited it, of a dioritoid species of granite. It is of a medium grain, varying from a yellowish-gray to a pure bright-gray, and is noteworthy from the rarity of its disconnected divisional planes. It is made up of quartz, orthoclase, plagioclase, biotite, hornblende, and titanite. The microscope, as usual, also shows a few small crystals of apatite. Here, as in the other bodies of this particular type, every mineral component of the rock seems to be nearly uniformly dissem- inated through the mass. As a whole it is a granite characterized by rela- tively very high percentages of hornblende, mica, and plagioclase. The minerals are comparatively fresh and undecomposed, and the plagioclase is more nearly related to albite than to oligoclase. Quartz veins and fine-grained granite dikes traverse the coarser mass of Truckee Range, in many places carrying more or less massive black horn- blende. Hot Springs Butte is a detached continuation of the range just beyond its northern extremity, near the borders of Mud Lake Desert. It is a single knob of granite, of the dioritoid type, rising 1,000 feet above the Quaternary plain. Lakk Raneu.—That portion of Lake Range which lies north of Pyra- mid Lake consists essentially of a central body of granite broken through and surrounded on the south by fields of basalt which slope to the shore of the lake. On its eastern exposure, from near the lake shore to a point four miles north of Pah-Rum Peak, it is overlaid by a series of dark shales, which have been referred to the Jurassic age. Northward, save for a few basaltic interruptions, the granitic mass extends between the two valleys of Mud Lake Desert until it is bounded on the north by a body of gneisses, which it penetrates like a tongue. The Archzean body is about twenty-four miles from north to south, with an extreme width, in the neighborhood of Pyramid Lake, of ten or twelve miles. The granite is of the hornblende-plagioclase type, and does not differ from that so fre- quently occurring in contiguous ranges. In gneisses at the northern end is. observed a singular mineralogical analogy to the associated granite. But they possess a distinctly gneissoid structure, and are distinguished from the near granite by the absence of titanite. They are composed of a ARCHASAN IXPOSURES. 97 very fine-grained mixture of quartz, plagioclase, parallel-arranged mica (probably biotite), and considerable hornblende. The microscope reveals apatite, and also the fact that the quartz granules are very poor in liquid inclusions; two characteristics which would seem to establish a parallelism between the granite and the gneiss. It is, however, quite similar in compo- sition to many of the gneisses already described in the Wahsatch, Humboldt, and Rocky Mountain regions, except that it is very much finer-grained, as are all the metamorphic sedimentary rocks of the Archzean in western Ne- vada. It is essentially a dioritic gneiss, containing considerable quartz and mica. The mineral constituents have a remarkably fresh, brilliant appear- ance, common to nearly all the schists of the neighborhood. Peavine Mountaty.—In the southwest corner of Map VY. is an Archean body, lying a few miles north of Truckee River, and sweeping up from the valley of that stream in bold slopes to the dominant point of Peavine Moun- tain, which has an altitude of 8,217 feet. The body measures a dozen miles from east to west, by about seven miles from north to south. On the north it is entirely surrounded by granite, on the south the inclined strata of the Truckee group of Miocene rest against it, and the eastern end is overflowed by a mass of Tertiary andesite. The whole mountain is built of a series of conformable, highly altered beds, striking from north 50° to 65° east, which consist for the most part of fine-grained quartzite strata, riven in every direction with minute fissures, which are filled with a ferruginous material. The less decomposed parts of the quartzite carry small grains of magnetite and occasionally a little yellowish-green epidote. It is obviously the decomposition of magnetite which produces the iron in- filtration, giving the prevalent yellow color to the body. ‘The felsitie beds contain similar iron seams, and are likewise much discolored by the products of decomposition. In the region of the Bevelhymer Ledge there is an ob- scure occurrence of rock which retains a fresh, undecomposed appearance, made up of dull, opaque orthoclase, some plagioclase, a little hornblende, and mica. It seems to be of eruptive origin and to indicate a sort of con- necting link between syenite and diorite. CauirorniA BorpEr.—F rom Peavine Mountain Pass to State Line Peak, and from the western boundary of the map as far east as Louis’ Valley, ex- 7K 98 SYSTEMATIC GEOLOGY. tends an irregular mass of granite which is topographically varied by wind- ing ridges, the whole being invaded by irregular valleys of Quaternary, which are, in truth, nothing more than the modern material disintegrated from the neighboring granite hills and washed down into basin-like depres- sions. The region has not received sufficient study to make it certain that all the granite is of one type; but as far as observed it seems to consist of quartz, orthoclase, plagioclase, biotite, and hornblende; and in all thin see- tions examined the microscope reveals a plenty of apatite crystals. There are no indications of a metamorphic origin of this general body; on the contrary, it possesses all the appearances of a granitic extrusion, and is no doubt intimately related to the granite mass of the Sierras. On the ridge opposite Spanish Springs Valley occurs an exceedingly fine-grained variety of granite porphyry, in which the individual minerals cannot be recognized by the naked eye. The microscope reveals quartz, orthoclase, beautifully striated plagioclase, biotite, and shattered, imperfect crystals of hornblende. It would seem to be a porphyritic condition of the neighboring granite, differing only by the minuteness of its particles. SiC wo Th. CORRELATION OF ARCOHZAN ROCKS. By referring to Analytical Geological Map L., at the end of this chapter, the reader will observe five Archzean districts where exposures are indicated in the characteristic map-color of that age, namely: the Rocky Mountains, including those portions of Colorado and Park ranges within the limits of this Exploration, as well as the whole Medicine Bow Range; Red Creek region, on the north flank of the eastern end of the Uinta Mountains; the Wahsatch core and neighboring Archean islands; middle Nevada District, comprising the Humboldt Range body, Kinsley District, and Franklin Buttes; and western Nevada District, embracing the schists of Montezuma and Truckee ranges and the quartzite of Peavine Mountain. All other expo- sures of Archzean age are colored as granites. The intention of this dis- tinction is to separate those formations which are of sedimentary origin from the class of eruptive rocks. Two causes prevent the drawing of such a line with entire precision: First, there is a frequent doubt as to the true nature of certain granitoid rocks which are allied on the one hand to eruptive granites by mineralogi- cal constitution as well as by a broad concentric structure, but related on the other hand to a series of gneisses whose bedding and passage into dem- onstrably sedimentary beds mark the granitoid member as only the ex- treme form of a series increasingly metamorphosed in depth. These ques- tionable rocks, where well shown, as in the case of the Laramie Hills, have almost invariably been considered by us to be of metamorphic nature and classed with the series of clastic origin. A second difficulty is encountered where limited bodies of granite are exposed under unaltered sedimentary beds, as throughout Nevada. Such masses, showing no trace of sedimentary origin, and quite disconnected with any crystalline schists or other Archean sedimentary rock, especially where the arrangement of their constituent minerals is after the granitic habit, have been called simply granite, with a general belief that they are of eruptive origin. The further erosion of over- 99 100 SYSTEMATIC GEOLOGY. lying rocks might in many cases reveal such relations with crystalline schists and gneisses as to compel the belief that the granites are metamorphic. Again, among those colored as granite a majority are instances of unmis- takably intrusive origin. The distinction indicated on the map is therefore only approximately true. It is not easy to analyze those subtle appearances which lead the ob- server to incline to one or the other of the two possible modes of origin of a granite outcrop. Parallelism of bedding, and even parallelism of the ar- rangement of minerals, are consistent with the theory of an eruptive origin. Certain passages of gneissoid granite appearing in the great eruptive granite body of the Sierra Nevada show quite as much parallelism of bedding and internal arrangement of minerals as the Rocky Mountain granites to which we have assigned a metamorphic origin; yet the Sierra field, as a whole, is clearly eruptive. But at the same time, in the intimate arrangement of the mineral particles, and in the mode of contact between the various mineral ingredients, there is a certain broad uniformity in all the eruptive granites which produces a characteristic impression upon the eye. On the contrary, the granites which we conceive to have been of metamorphic origin, no matter how simple the mineralogical composition, have always a peculiar variability of arrangement; and even in the ab- sence of any pronounced parallelism, they show the effect of interior compression and irregular mechanical influences. On the one hand, in the eruptive granites there seems to have been a steady expansive force, doubtless due to the heat and elastic fluids, which gave to all the particles a certain independent polarity, while in the metamorphic granites they seem to have been crowded into constantly conflicting positions. As the result of this, the crystalline particles of the metamorphic granites are much less apt to have completed their crystallization, or, if it was com- pleted, they have been crushed and torn asunder and their particles scat- tered, while in the case of the eruptive granites crystallization seems to have been more perfected. The result of this is to give to the eruptive granites something of the uniformity of texture of a volcanic rock, while all the metamorphic granitoid rocks, when once the gneissoid parallelism of min- erals is broken up, have a crushed, irregular, and confused mode of arrange- CORRELATION OF ARCHAIAN ROCKS. 101 ment. Under the microscope especially, there is usually observed a con- siderable difference between the two types, in the amount of dislocation and of intererystalline movement or crushing, the structureless granites often containing perfect hexagons of biotite or completed hornblende, while in the gneissoid granites a defined crystal of one of the less coherent con- stituents rarely if ever appears. Meramorpnic Rocxs—In Colorado Range are two typical series which in all probability are unconformable. The lower, as already shown, consists of gray and pearl-colored aplitic granites with metamorphic facies, overlaid by a red granitoid member, having little parallelism of interior arrangement or evidence of stratification beyond a general tabular bedding, also decidedly aplitic, though carrying rather more mica than the gray variety. Over this lies a third member, very red, with an extremely variable but small amount of mica broadly but distinctly bedded. A simi- lar series is observed in the Black Hills and recurs in Park Range. A small granitoid body in Mill Canon, Wahsatch Range, is referred to this series. The whole group is essentially made of quartz, orthoclase, oligo- clase, very little biotite, rare muscovite and lepidomelane, and extremely little hornblende, with accessory masses made up of labradorite, diallage, ilmenite, graphite, and magnetite. Taken with the dependent development of gabbro, ilmenite, magnetite, and graphite, the resemblance to known Laurentian bodies is so strong that we have little hesitation in referring our series to that age. In this connection the assignment by Dawson of closely similar rocks in Manitoba and British Columbia should be remembered. If, as we suppose, these exposures represent all the metamorphic Lauren- tian within our area, it is a very noticeable fact that limestones, dolomites, quartzites, conglomerates, pyroxene rocks, and the various hydrated Lau- rentian forms are wanting, and that among the irruptive species gabbro and felsitie porphyries only occur. A little chlorite is the only representa- tive of the hydrated minerals. A rude estimate would place the thickness of the series at about 25,000 feet. A second and equally well characterized series of metamorphic rocks is found in the upper horizons of the Medicine Bow, and also in the higher members of Park Range, Red Creek in the Uinta, the Wahsatch and Salt 102 SYSTEMATIO GEOLOGY. Lake islands, and the exposures in the Humboldt Mountains, Franklin Buttes, and Kinsley District. Probably to these localities should be added a portion of the gneiss, schist, and quartzite formation of Colorado Range, south of our map. This series consists of true gneisses, often decidedly granitoid, and made up of quartz, orthoclase, biotite, rare muscovite, and plagioclase, asso- ciated and repeatedly interstratified with mica schists, both of biotite and muscovite, the white mica beds sometimes carrying garnets; hornblendic schists, in places pure amphibolite, and again amphibole and quartz, with either orthoclase alone or plagioclase alone, or the two associated. Some- times the hornblende unites with plagioclase to form a true dioritic gneiss. In several of the hornblende rocks where mica is either absent or plays a. minor role, zircon is present in minute crystals, visible under the microscope only, but freely disseminated through the mass. The above described series is exposed certainly 12,000 or 14,000 feet thick in Wahsatch Range, about the same in Humboldt Range, and probably somewhat less in Park and Medicine Bow ranges; but in the Clear Creek region of Colorado Range it shows not less than 25,000 feet. Conformably overlying this group is a thick development of argillites, siliceous schists (carrying in places a hydrated chloritic mineral, and verging toward the nacreous schists of Canada), jaspery conglomerates with a fine siliceous matrix, iridescent hornblende schists, quartzites more or less rich in minute feldspar crystals and carrying also a variable amount of muscovite and chlorite, and finally white or gray dolomitic marbles. The upper part of the series seems to be variable in the sequence of its members and in thickness. The best exposures occur in the Medicine Bow, where there must be between 3,000 and 4,000 feet. The whole series—gneisses, amphibolites, dioritic gneiss, garnetiferous mica schist, and zirconiferous amphibolite schist, quartzite, and limestone— occurs in the Medicine Bow and Humboldt. The lower or gneiss and am- phibolite schist portion is represented in Park Range, in the Wahsatch, as also probably in the schist zones overlying the granitoid Laurentian part of Colorado Range. At Kinsley District and Frankiin Buttes are observed only the upper CORRELATION OF ARCHASAN ROCKS. 103 limit of the gneiss (here porphyroidal), together with white dolomite; the same association and intercalation as at Mount Bonpland in the neighboring Humboldt Range. The Archeean islands of Salt Lake, which were not especially examined by us, evidently belong to the same series. Argillites are best developed in the Medicine Bow and Salt Lake islands. As a whole, this second series bears more than a superficial resemblance to the Huronian of Canada, and to that age, with some hesitation, it is pro- visionally referred. G. M. Dawson, finding essentially the same two series in the Rocky Mountains, near the 49th parallel, makes the same reference. With the Huronian is classed also the Red Creek exposure of quartzite, dioritic schists, and paragonite rocks, carrying garnet, staurolite, and cya- nite; so also, a limited area of intensely metamorphosed quartzite at Pea- vine Mountain, near the California boundary. Between the rocks thus referred to Laurentian and Huronian ages, there is a characteristic difference in the intensity of metamorphism and obliteration of original structure. The former are essentially granitoid in type, and show lithological changes only when examined over considerable areas, or up and down through a rather wide vertical range. Bedding is wanting, except in the upper members, and even there it is rather of the character of a tabular structure, made up of beds varying from a foot to five feet in breadth, than a true stratification. On the other hand, the sup- posed Huronian zone is always distinctly, often minutely, stratified; and, moreover, a conspicuous feature is the permanence of the mineral charac- ter of beds over considerable distance. Gradual changes are observed in the mechanical condition of single beds. They may be characterized in one place by fine-grained, minute crystallization, in another by the assemblage of very coarse, large particles. Ilere is seen a strict parallelism of the mica or amphibole particles; a little way off, owing to inequalities of pressure and consequent interior mechani- cal rearrangement, the constituent minerals may possess the mode of aggre- gation of a granite or porphyry. Observed over great distances, it is true that changes are detected in the chemical character of a given bed, but here the limit of change ends, and we fail entirely to observe any of those rapid mineralogical fluctuations so frequently noted by some other students of ay aye vey Pr Cordilleran geology. 104 SYSTEMATIC GEOLOGY. As between the different contiguous beds of the series, there is indeed a constant variability shown. Every conceivable permutation possible to quartz, mica, hornblende, orthoclase, and plagioclase seems to be brought out and repeated again and again; but within the limits of a single bed the chemical and generally the mineralogical constitution are rigidly preserved. . Even in the single exception to this, where chloritic matter replaces by pseudomorphosis either garnet or mica, the alteration is strictly confined to the affected bed, never in a single instance clouding off into the bounding strata. Where the stratification is thin, and where irregularly crumpled regions have been eroded, there is often great difficulty in identifying or following 2, given bed, existing surfaces often showing a very gentle bevel of the edges of the members of a series of strata. So in passing from one to another it is many times hard to determine the divisional plane, and hence probably the cause of such expressions as “this mica schist passes rapidly into a syenite,” or ‘this hornblendie schist in a few feet passes by imperceptible gradation into an orthoclase granite.” Whatever changes occur within a given stratum of the crystalline schists, even including the pseudomorphism of hydrated chloritic minerals after anhydrous silicates, are due to a mere mechanical or chemical re- arrangement of particles within the bed, and there is no tendency whatever to break up the chemical constitution of a given stratum, no disposition on the part of a stratum to scatter its minerals up or down into adjacent beds. Instances of this permanence of constitution are constantly seen in single zones of dioritic gneiss or of pure black amphibole rock, lying between white quartzites, without a trace of hornblende one inch from the main bed; or a garnetiferous muscovite gneiss enclosed in a biotite gneiss, never with the least tendency for the garnets to straggle up or down. In the heavy white quartzites of Humboldt Mountain there are garme- tiferous zones and muscovite-bearing zones, but they are rigidly confined to their own horizon. Whatever, therefore, may have been the cause which rendered the original sediments crystalline, it failed to impregnate one zone with the chemical elements of its neighbor. Evidences of metamorphic alter- ation, such as results in other Archean regions in the production of taleose CORRELATION OF ARCHASAN ROCKS. 105 bodies, are almost altogether wanting. A protogenoid granite of limited extent indeed occurs on War Eagle Mountain, Owyhee District, Idaho, and also in immediate contact with mineral veins in Colorado Range; but these are obviously due to the action of very modern causes and are re- stricted so closely to fissured regions as rather to fall under the head of vein phenomena. The appearance, on a microscopic scale, of chlorite after garnet in the beds of the Wahsatch and Humboldt, is paralleled in a large way in Archean schists observed by the writer near the head of Santa Maria River in Arizona, where large garnets, equal in size to those described by Pumpelly on Lake Superior, are changed into a pale-green chloritic mineral. Slaty hematites are seen feebly represented in the schists of Ralston Creek, Colorado Range, under the quartzites. The specular-iron schists which occur in the region of Prescott, Arizona, are wanting in the Fortieth Parallel area. The mechanical disturbances that have taken place within given beds which are simple and comparatively unchanged as to their chemical nature, seem to be worthy of a second mention here. In treating of the Wahsatch and Humboldt, it was said that certain beds show a passage from a parallel arrangement of minerals to a granitoid mode of disposition of particles. In the varying dip, sinuous strike, and deep bellying down of certain folds, there is abundant evidence of irregular mechanical strain. The general shrinkage of beds by superincumbent weight is a phenomenon too well known to need description here, but besides this there is often ample evidence of longitudinal compression. The strata of dioritic eneiss, true gneiss, mica schist, and even so compressible a rock as quartzite, show an interior erumpling, already described in detail, which breaks up the par- allel schistose arrangement of particles and squeezes the minerals into a granitoid irregularity. It is evident that great longitudinal compression, due to the sagging down of a very thick series when brought to bear in a group of beds, does not meet so sharp a resistance as to produce a crushing, or even a very localized effect ; but the strain is relieved by a wide-spread readjustment of particles, after the manner of eranite. 106 SYSTEMATIC GEOLOGY. In the Humboldt gneisses, and conspicuously in the dioritie gneisses at the mouth of Ogden Caron in the Wahsatch, this phenomenon may be most interestingly observed. It should be said that this effect has gone no further in our Huronian rocks than the destruction of parallelism within beds. This being true of rocks which have not been subjected to very intense and complex disturbance, it would seem only necessary to heighten and magnify the action to obliterate the parallel structure through great masses and produce out of bedded rocks, by mechanical means alone, many of those puzzling granitoid forms which by certain subtle, difficultly analyzed appearances, give to the field observer the impression of a meta- morphic origin. How else than by crushing of the constituent particles can we account for those grains of quartz which have upon their periphe- ries the open pits that could only have been formed as the walls of fluid inclusions? The above suggestions are not intended to have a positive application beyond the gentle action described in our supposed Huronian beds, but only to indicate that the precise limit of purely mechanical action on already crystallized schists is at present unknown, and that it may pos- sibly include the comminuted granitoid Laurentian rocks. It would be altogether unsafe to make from the character of the Ar- chean outcrops of the Fortieth Parallel a generalization as to the fundamental rocks of the whole United States Cordilleras. In the wide areas which are still unexamined geologically, there is ample room for a repetition of all the Appalachian phases. At the same time one cannot fail to notice the wide- spread simplicity of petrological forms, the prevalence of granites, granitoid eneisses, and dioritic metamorphic rocks, the paucity of argillites, quartzites, limestones, and zirconiferous and staurolite schists, the infrequence of large bodies of magnetic, specular, or spathic iron, and the complete absence of corundum, chrysolite, serpentine, steatite, pyroxene rocks, the true nacreous schists, and other minor forms observed in the Appalachian system. Without doubt, the most interesting laws which come out of the compari- son of these exposures are, that when considered in depth, from the upper- most limits of our so called Huronian to the lowest Laurentian exposure, there is, first, a regular, steady increase of the intensity of metamorphism, and secondly, a pretty regular increase in the thickness of individual members CORRELATION OF ARCHAZAN ROCKS. 107 of the series. The lowest Laurentian aplitic granitoid bodies of the Laramie Hills are the heaviest beds and the most changed from their original sedi- mentary condition. The higher Huronian group of gneisses, quartzites, con- elomerates, dolomites, and argillites are at once the most thinly bedded and least metamorphosed. Individual beds remain as specialized as the day they were deposited. At the lower exposures of the whole Archean forma- tion well defined crystals are of great rarity; even microscopic apatite, the best presented species, is generally crushed and dislocated; micas are dis- torted, and all feldspars are more or less fragmentary. A marked con- trast is observable at the upper extreme. Here many micas, hornblendes, garnets, and even feldspars are nearly if not quite completed crystals. The exceptions to this are those places already described, where local compression has broken up the original arrangement of the crystalline ingredients. The western Nevada schists are exposed as a series, never over 4,000 or 4,000 feet thick, of rocks whose constituent particles are in a fine state of subdivision. They are largely compounds of quartz, muscovite, and biotite, or quartz and hornblende. Feldspars are rare, and in most cases all the crystalline ingredients are only resolvable under the microscope. Appended to this section is a table of analyses of metamorphic rocks. Granrres.—Leaving out of consideration those forms which are deemed to be of metamorphic origin, the eruptive granites will be seen by reference to the map accompanying this chapter to be, so far as the belt of the Fortieth Parallel is concerned, situated west of longitude 111° 30’, or west of the east base of Wahsatch Range. Nearly every considera- ble mountain body between the Wahsatch and the California line shows in the lower horizons exposures of one or more bodies of granite. A petro- logical comparison of these exposures leads to a classification into four distinct groups. The first type consists of quartz, orthoclase, a few minute and unim- portant crystals of plagioclase, and muscovite, with a small but variable percentage of microscopical apatite. The granites of this type are all west of Reese River, longitude 117°, and in each case are associated with the western Nevada type of Archiean schists, consisting of a very fine micro- 108 SYSTEMATIC GEOLOGY. crystalline combination of quartz, biotite, muscovite, and magnetite, or quartz, hornblende, and magnetite. Muscovite granite occurs at the Ravens- wood Hills in Shoshone Range, and in the Pah-tson Mountains, where it contains pegmatite passages made up of the same minerals as the granite, only on a far larger scale of crystallization. A third outcrop of musco- vite granite is in Truckee Range, in the body southeast of Winnemucca Lake. This last named locality has been but little studied, and is chiefly surrounded by outpourings of Tertiary volcanic rocks, and its relation with other members of the Archzean series is altogether unknown. As to the age of the granites of this type, we have practically no adequate data. At Ravenswood Peak the muscovite granite is intimately involved with the upturned crystalline beds, and is clearly overlaid unconformably by the rocks of the Carboniferous. There is little doubt of its Archaean age, but its reference to that period is only on general lithological grounds. The second type consists of quartz, orthoclase, little plagioclase or none at all, biotite, and microscopic apatite. It is essentially a granite, like type the first, with the substitution of biotite for muscovite. It has a rather wider range than the other, making its first appearance in Ombe Range, west of Salt Lake Desert, and reappearing westward to the Cali- fornia line. It is found in Ombe Range, at Nannie’s Peak in Seetoya Range, at Mount Tenabo in Cortez Range, in the neighboring Wah-weah Mountains, in the granite body of Montezuma Range lying east of Antelope Peak, and finally in the hills southeast of Winnemucca Lake, Truckee Range, where it is associated with the muscovite granite of the first type As in the first type, the microscope always reveals a small but varying pro- portion of minute apatite. The third type consists of quartz, orthoclase, little or no plagioclase, biotite, hornblende, and microscopic apatite. Its distribution is co-extensive with that of the second type. It makes its first appearance in the Goose Creek Mountains, a little east of the 114th meridian, and reappears at. intervals (often in close proximity to the granites of the second type) westward to the 120th meridian. It is developed at Goose Creek; at Granite Cation in Cortez Range; near the head of Susan Creek in Sectoya Range; at Shoshone Knob and the Wood Ranch Canon, both in Shoshone CORRELATION OF ARCHASAN ROCKS. 109 Range ; at Granite Point, Augusta Mountains; in the Havallah; near Spauld- ing’s Pass, Pah-ute Range; at the Montezuma mine, and in Montezuma Range west of Rye Patch Station. It is distinguished from the second type by the presence of hornblende. The fourth type presents the most complex petrological features of any of these families of granite, and consists of quartz, orthoclase, plagioclase, which is often equal in quantity to the orthoclase, and sometimes exceeds it, usually a high percentage of biotite, with an equal proportion of horn- blende, titanite visible to the naked eye, and a high proportion of micro- scopic apatite. The rocks of this group display their minerals usually in a very fresh, undecomposed condition. In general, the rocks differ from those of the third type by the presence of macroscopic titanite, and by the high proportion of plagioclase and hornblende, which sometimes dominate over the orthoclase and biotite, and throw the affinities of the granite toward a diorite. Indeed, there is but little difference between those diorites that are unusually rich in orthoclase, mica, and quartz, and the granites of this type, which have an uncommonly high proportion of hornblende and plagioclase. The presence of titanite is not a distinguishing feature, for some of the diorites possess that mineral in the same proportion as the rocks of this group. So, too, microscopic apatite is common to both rocks. In the previous type the plagioclase always, or nearly always, approaches oligoclase ; in the present type it is often albite. While the granites of this group are perhaps the most prominent as regards geographical distribution of the truly eruptive varieties observed by the writer in the system of the Cordilleras, and while they possess a great uniformity of appearance from the Wahsatch to the Sierra Nevada, it is true that those dependences of diorite which mineralogically approach it are of extremely rare occurrence, and are always so related to dioritic masses as to be clearly recognized as a dioritic variety. There is therefore little danger of ever confounding the granitoid diorite with the extremely dioritic members of the fourth type. This classification, based upon field observations, is interestingly car- ried out by Zirkel, whose microscopic examinations in every way confirm the field arrangement. To his interesting chapter on granites the reader is referred for those minute yet important interior phenomena which char- 110 SYSTEMATIC GEOLOGY. acterize the granites of all these families. The table of analyses of the eruptive granites accompanying this section gives a single instance of the second type, that of Nannie’s Peak ; two of the third type, from Shoshone Knob and Wright’s Cation; and the remainder of the table is devoted to the rocks of the fourth type. Of these latter it is seen that the range of silica embraces the extreme members of the series, that of Agate Pass reaching 75 per cent.; while in the Wachoe granite the silica is only 553 per cent., representing with one exception the most basic granite of which there is any published analysis, and with the one referred to, that of Ar- dara, described in Haughton’s paper on the rocks of Donegal,* it is almost identical in composition, both chemically and mineralogically. In general the granites of the fourth type in Western Nevada are rather basic, the rock of El Capitan in Yosemite Valley furnishing about the normal chem- ical type. When seen in appositions which give a clew to the relative ages of the several types, it is found that they occur in the order given, the muscovite being the oldest, the dioritoid variety the youngest. Passing from muscovite to dioritoid species, the chemical acidity declines to a minimum in the Wachoe occurrence. In denominating these groups of granite as eruptive, it is only intended to indicate that in their relations to the contiguous Archzean schists they have the appearance of intrusive bodies, and that in their interior structure and general mode of occurrence there are none of those evidences of alli- ances to the crystalline schists which are observed in the granitoid gneisses of so many localities, especially in the Rocky Mountain region. In so- called eruptive granites there is neither parallelism of general bedding nor of interior arrangement of the minerals, and the most ordinary phenomenon of structure is the development of conoidal shapes formed of concentric lay- ers varying in thickness from a few inches to 100 feet. This structure, so far as observed, is strictly confined to the hornblende-bearing granites, and never makes its appearance in those of the first and second types. While among the rocks of the Fortieth Parallel this phenomenon of conoids is only obscurely shown, in the great hornblende-plagioclase body * Transactions of the Royal Irish Academy (1859), Vol. XXIIL., p. 608. This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout This is a Page Marker - Please Insert Foldoyt here Page Marker lasert Foldout This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout THs iS Q Page Marker -— Please Insert Foldout here Page Marker Dnsert Fol/doud This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout THIS 1§ A PAGE MAARKER - PLEASE INSERT FOLDOUT HERE PAGE MAARKER INSERT FOLDOUT This 1° 2 “Page Darvker - “Please ] ngsert Yroldout here Page Dia rhe ” ] n§e rt re (deut This is a Page Marker = Please Insert Foldout here Page Marker Insert Foldout | { | TABLLEL, Number of analysis. ~ + 2S) 16 U7 18 19 20 21 22 Locality. |Remarks. 23 Wachoe Mountains ~ Jaring liquid inclusions, orthoclase Il. unaltered plagioclase, large indi- ide and biotite, microscopic apatite, black microlites. Granite Peak, East R sions, orthoclase, much p!agioclase, Mountains ite, and frequent macroscopic titan- apatite. Hills west of Granite Cr in inclusions than granite given Nevada ne same mineral composition. Shoshone Knob, Shosho).... little plagioclase, hornblende, broscopic apatite. Wosemites Valleys HIsCatcusions: orttociasesaibite biotite , apatite. Canon north of Wrigh)nausions, orthoclase, rare plagio- West Humboldt opic apatite, zircon!! Egan Cajon, Egan Ranhsiderable plagioclase, biotite, spar- Nannie’s Peak - - - hlusions, carrying salt cubes, ortho- \ttle biotite, microscopic apatite. Cottonwood Canon, Wahiclusions, orthoclase, much plagio- e, biotite, titanite, apatite. Agate Pass Canon, Cortedich plagioclase, hornblende, rare This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout This is a Page Marker - Please Insert Foldout here Page Marker lasert Foldout This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout This 1S Q Page Marker — Please Insert Fo/dout here Page Marker Insert Foldoud This is a Page Marker - Please Insert Foldout here Page Marker Insert Foldout THIS 1§ AX PAGE MAARKER - PLEASE INSERT FOLDOUT HERE PAGE MAARKER INSERT FOLDOUT 1 hig © 2 "Page Darke "- Please Inge rt re Ideut he Pe )), qe Marker Inge rf Ju (det Page Marker Insert Foldout CORRELATION OF ARCHASAN ROCKS. ila of the Sierra Nevada, which is both geographically and mineralogically the characteristic occurrence of this type of granite, the dome forms assume a most imposing scale and become some of the most prominent topographical features in the granite area. So far as these concentric conoidal shells throw light upon the outbreak of the granite, they seem actually to indicate something like the original form due to violent extrusion of the plastic though not fluid bodies. Although instances of each granitic type are found unconformably underlying the low members of the Paleozoic series, this is not the case with each outerop; many granitic masses are found unconformably under- lying Mesozoic or even Tertiary yoleanic rocks. But there is absolutely no evidence whatever in favor of the belief of granitic extrusions later than the Archean age. With so many mountain ranges deeply fissured and faulted, broken and thrown into all conceivable positions, there would seem to be abundant exposures to find intrusions of granite into the crevices and fault-fissures of the post-Archzean formations, if such existed. None have been discovered in the Fortieth Parallel area. Great simplicity is given to the relation of the two series by the unal- tered and conformable conditions of the whole Paleozoic strata. Intrusions of granite into sedimentary strata other than Archzean crystalline schists, such invasions as are brought io light by Whitney in the Sierra Nevada, where granite invades the highly altered ‘Triassic and Jurassic strata, are wanting. As an instance of how dangerous any attempt to correlate age by petrological features alone really is, may be cited the Jurassic granite of California and the granite of the Cottonwood region on the Wahbsatch, which is unmistakably Archzean. They are positively identical down to the minutest microscopical peculiarity. Very many of the exposures laid down on the map are known to be Archean by position. In the remaining cases there is no proof that they are not Archean. The absence of evidence of disturbance throughout the Paleozoic, or of granitic intrusion anywhere in the post-Archzean forma- tions, strengthens the belief that all the granites and crystalline schists are pre-Cambrian. SHC TrON: ke GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. After so much detail, it would seem only appropriate to convey the impressions I have gained as to the comparative genesis of the crystalline schists and allied granites. Considering as a whole the later series which I have referred to the Huronian, there can be no doubt that they were formed by the development of their various crystalline minerals out of preéxisting sediments, in such a mode that the chemistry of the original individual beds was unchanged. The same conclusion is doubtless true of the older series which are here assumed to be the equivalents of the Lau- rentian. Purely siliceous beds, either those composed of fine material or siliceous conglomerates, have retained their chemical simplicity even where highly basic beds, as of hornblendie gneiss, are interstratified with them. Had there been the slightest tendency toward chemical reaction between the ma- terials of adjoining beds, the highly basic layers would inevitably have com- bined with the contiguous quartz strata and developed minerals of resultant composition. On the other hand, the original forms of the clastic particles of which the beds were sedimented are entirely lost; the interstitial space which must necessarily have separated the irregular-shaped particles of detritus is totally obliterated, and the sole figure of the original sediment- ary particles is now shown in the pebbles of the conglomerates. In zones of simple material, like carbonate of lime or quartz, metamor- phism has been confined to an obliteration of interstitial space and crys- tallization. In beds originally of mixed mineral character, chemical affinity has resulted in the production of various new minerals, identical ultimate composition often failing to produce identical results; as, for instance, in the Huronian schists we find a bed in one place composed of quartz, ortho- clase, and biotite, while in another, the ultimate constitution remaining the same, are developed quartz, orthoclase, iron garnet, and muscovite. Fur- le GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 113 ther, all metasomatic changes observed by us in the Huronian series are in like manner confined to individual heds. The presence of water, carbonic acid, and saturated solutions of salts at the time of crystallization is evidenced by the minute presence of these bodies as inclusions in several of the component minerals of the schists. It would seem, therefore, that we are authorized in assuming an approxi- mately complete knowledge of the chemical materials and their stratified con- dition at the time of crystallization. Pressure and heat being the only known exterior causes which could have codperated to induce the observed compres- sion, chemical combination, and crystallization, the vital question is as to their mode of action. Evidence of excessive heat seems to be wanting, at least of such temperature as could produce the slightest even local liquefaction, for the phenomena of groundmasses and bases which have in variably resulted from crystallization out of liquefied magmas, and which are thoroughly charac- teristic of known eruptive rocks, are altogether wanting among the schists ; so, too, the entire absence of glass inclusions in the component minerals is in a measure conclusive of the absence of molten or glassy passages during crystallization. The behavior and effect of great heat, however, are, as is well known, disturbed and rendered altogether abnormal by the presence of high pressure, as may be seen in the voleanic rocks, where the relative points of fusibility of various minerals, as determined at the earth’s sur- face, are not strictly held to in depth. One of the most common features in many of the rocks known to be eruptive is the envelopment by minerals of high fusibility of those of lower fusibility, and vice versa. If other forces can thus upset so apparently rigid a physical property as the temperature of fusibility, it is perhaps unsafe to argue from the absence of the products of fusion that a degree of heat adequate for lique- faction was absent while the crystalline schists were in process of formation. On the other hand, if post-Archean geology offers any analogy, it is, that in periods of metamorphism and the development of crystalline rocks, the crust has been subjected to the most severe pressure, and it would seem that press- ure, whether exerted downward by the building up of a superincumbent mass on terrestrial radii, or as developed in the tangential strains due to the earth’s shrinkage, has been at least the invariable accompaniment of diagenesis. 8K 114 SYSTEMATIC GEOLOGY. While thus theoretically, in the present stage of knowledge, it is impos- sible to assert that a temperature sufficient to liquefy was absent, it is quite safe to assume that either the temperature was below the degree necessary to melt any single ingredient, or else its effect was annulled by pressure, the fact being that in the formation of the schists there never was fusion, and that many minerals are present in a molecular condition which they are known never to retain if subjected to high temperature; Sheerer, in this connection, having shown the presence in granite of what he terms pyrognomic mineral species, namely, those which under high heat undergo a permanent molecular alteration, but which in granites and schists are in the unaltered state. Thus for all intents and purposes pressure becomes the dominant power in bringing about the condition necessary for the de- veloping of such chemical affinities as will produce the resultant minerals. A considerable degree of heat, with the presence of moisture and alkaline solution, was doubtless essential to the excitation of chemical affinity. In the development of the schists, what was the predominant pressure, and what the mode of action? For reasons which have been expressed before, I am undisturbed in the belief that the crystalline schists are sedi- ments spread out in the bed of the early Archzean ocean, for the most part mechanical, perhaps in some exceptional instances, such as the magnesian silicates, chemical precipitates as contended for by Hunt, or, as seems to me more probable, the results of mechanical separation by washing. I assume that they were the detritus of then existing land masses swept into the oceans and arranged in precisely the manner of subsequent aqueous formations. As beds of heterogeneous sediment, the heat to which they were sub- jected by conduction from the floor on which they were laid down could not have been sufficient, since it permitted the existence of oceans, to induce the chemically inert particles to break up their then existing combinations and begin a new chemical activity. It is only when subjected to enormous pressure from above or increased heat from below that the particles would be forced into new mineral combination. A simple inspection of the prominent crystalline schist and gneiss areas of western America shows, first, that as a whole they are among the thickest GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 115 known bodies of conformable sediments. The geognostic behavior of subse- quent great bodies of conformable sediments may be profitably compared, and their dynamic laws applied to the ancient sediments of the Archean series. Post-Archzean sediments of detrital origin are well known to be thickest nearest the source of supply and to thin out over the more remote portions of the oceans. A section normal to a great sedimented coast region, as in the case of the Appalachian Paleeozoic series or the corresponding series in the Cordilleras of the Fortieth Parallel, shows a great accumulation near the ancient shores and a rapid thinning out toward the middle of the seas. It is difficult to suppose the conditions of deposition to have been otherwise for all detrital materials during Archzean time. A further law in the great conformable sediment of later time has been, that heavily loaded regions sink into the subjacent crust. This subsidence, as is evident from an inspection of sections, is a direct displacement of a part of the underlying floor and a gradual pressing downward of the accu- mulating sediments, by the weight of the continually piling up series. In the case of the conformable Paleozoic series, as exposed in the Wahsatch, where a section of 30,000 feet is displayed, it is evident that before disturbance, and while yet in the horizontal attitude of deposition, the lower Cambrian beds were under the pressure of a column of 30,000 feet of rock, that as marine sediments they were imbued with saline water, and that from mechanical compression and consequent loss of volume there must have been a considerable raising of temperature. A further increment of heat must have been caused by the inevitable rising of the earth’s concentric surfaces of temperature into the mass as it displaced crust and sank into the hotter depths of the earth. Yet with all this there is in the lowest Cambrian beds only the very slightest tendency to the production of crystalline schists. We have no reason to suppose that the thickness of Archzean conformable groups was enough greater than the series just cited to create a downward pressure so superior as by weight alone to bring about the totally dissimilar result of true schist crystallization. Between the two sets of conditions there was one radical difference, namely, the secular cooling of the earth and consequent secular recession of isothermal surfaces. 116 SYSTEMATIC GEOLOGY. Supposing sedimentation, consequent subsidence of a series of beds, and the accompanying displacement of subjacent crust to take place in the same direct ratio of quantity now and in the earlier stages of the earth’s refriger- ation, given beds arriving at the same depth would in Archwan time find themselves raised to a temperature greater than at the same depth to-day, by the actual amount of secular recession of temperature through the whole vast interval of time. The Archean beds might easily find themselves, when pressed into the crust even to a moderate depth, in presence of those conditions essential for the processes of diagenesis. From all the well known synthetic studies of chemical combination under pressure, moderate heat, and alkaline solutions, it would seem that with a considerably hotter condition of the superficial crust of the globe the amount of subsidences known in post-Archean time might be sufficient to ‘arry strata down into a region where chemical activity should begin. If this view of the probable history is correct, fair deductions are, first, that somewhere below the surface, varying with the thermal state of the earth, there will be a horizon with the necessary heat condition and re- quired superincumbent weight to urge the material present into chemical activity; secondly, that with the refrigeration of the globe this horizon will recede deeper and deeper toward the centre of the earth; thirdly, that so long as this horizon is within the depth to which bodies of sediment are brought by displacement of crust and subsidence, so long will crystalline schists continue to be made; fourthly, that when by secular. cooling the. required horizon passes below the possible levels to which strata may be sunk by displace- ment of crust due to accumulation of sediment, then forever afterward there will be no formation of the schists. Supposing no objection to be made to this hypothesis when applied to the gncisses, true schists, quartz- ites, marbles, dolomites, and chrysolites, there still remain to be accounted for the rocks characterized by the presence of hydrated protoxyd minerals and hydrous magnesian silicates. The view of Hunt that they were originally hydrous magnesian sili- eates, of which an example is furnished by the sepiolite of the Paris Basin, is no longer tenable as regards most serpentines and chloritie rocks. Modern microscopic research has proved that these are direct pseudomorphs after GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. Gl anhydrous silicates, such as garnet and chrysolite, every stage of the whole process of pseudomorphism being shown beyond all doubt. Their origin is therefore relegated to the common origin of the anhydrous schists. The discovery in Appalachian schists of great bodies of chrysolitic formation, making an integral part of the crystalline schists, is sufficient answer to the question, Whence came the anhydrous magnesian silicate out of which to make the pseudomorphous serpentine ? Without attempting to examine the validity of Hunt’s claim that the early magnesian silicates are chemical precipitates from the acid ocean of their period, I see no reason to seek for a different origin for the magnesian silicates from that of the commoner aluminous minerals. Olivine-bearing rocks are among the oldest irruptive bodies ; why may not olivine sands, like those now seen on the shores of the Hawaiian Islands, have been then as now accumulated by the mechanical separation of sea currents and subsequently buried by rushes of feldspathic and quartz sands? Be that as it may, the whole tendency of microscopic research is to prove that the hydrous magnesian silicates are plainly pseudomorphic after anhydrous forms, and the problem of genesis, as Hunt very justly remarks in this connection, is, Whence the anhydrous ones? There is little present necessity, it seems to me, for the invocation of aqueous precipitates, when the sea bottom and shores of to-day offer such varied chemical materials which are so obviously detrital. From these considerations, so far as the gneisses and crystalline schists are concerned, I am led to give ina complete adhesion to the hypothesis of diagenesis for the anhydrous silicates and of subsequent pseudomorphism for the hydrous magnesian rocks. My views approximate closely to those of Dana, and, if I rightly comprehend him, of Gumbel, rejecting on the one hand the plutonic hypothesis of Naumann and his followers, and on the other the all but forgotten theory of direct crystallization from solution, as advanced by Delabeche. In the crystalline schists and gneisses are found identically the same anhydrous minerals which characterize the granites. The characteristic features of the schists are, the parallel-bedded arrangement, the strict reten- 118 SYSTEMATIC GEOLOGY. tion of chemical materials in their original zones, and the interealation of beds made of simple materials like quartzites and limestones. Granite possesses the same minerals, and furthermore their microscopical structure and the character of their foreign inclusions are identical. The sole differ- ence seems to be, that granite is often demonstrably a plastic intrusion, and possesses no parallel arrangement of minerals, its various components lying more or less evenly distributed throughout the mass. In the granites and schists alike there is invariably a total absence of the phenomena of base, groundmass, and glass inclusions. The geognostic position of the schists is exactly like the other strata which were deposited horizontally and after- ward disturbed. On the other hand, granite, in an immense majority of cases, is found to be exposed either in the hearts of mountain ranges or in ridges which have been evidently subjected to immense orographical or tangential pressure. When the points of Archean mountain ranges pro- trude through gently inclined and subsequently unaltered strata, as is very often the case, the true orographical relations of the granite cannot be known. It is only when we can observe granite in direct connection with the strata into which it has intruded or out of which it has been made, that the true relations can be seen; and it is safe to say that wherever these intimate relations are observable, the granite occupies a region which has been subjected chiefly to horizontal or circumferential pressure. The fre- quent phenomena of the under-dip of the strata flanking a granite mass, as in the great granite body of the Sierra Nevada, are prominent instances of the intimate relation spoken of. If in such cases an unconformable over- lying and unaltered series were to cover all but the summits of the granite hills, the granite would appear simply as an unconformable underlying body, whose genetic relations are absolutely unknown. Into this category a vast number of granite exposures of the Cordilleras have to be placed. It is an invariable law, then, that where the genetic relations are clearly perceived, eruptive granite is always found in connection with very great horizontal pressure and consequent disturbance. Suppose, now, a deep- lying series of varied sedimentary beds, covered by sufficient superimposed mass to exert a pressure powerful enough to sink them to the necessary thermal horizon for the induction of crystallization in the material of the GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. 119 beds. As long as the attitude of these beds was undisturbed by horizontal compression, the result would be a series of crystalline schists and gneisses. But the moment horizontal or tangential pressure either overcame or disturbed the action of the downward pressure, the horizontal arrangement of these erystallizing materials would be broken up, and their resulting arrange- ment would depend upon the interaction of the two forces. In case the hori- zontal force were the slighter, the result would be simply those corrugated schists which are characteristic of certain regions. Butif the horizontal force suddenly or even gradually overcame the radial pressure of gravitation, the original arrangement of the strata would be broken up and their com- ponent beds crowded into a structureless mass. In that case the tougher and stronger minerals, and those whose crystalline forms were most compact, would suffer the least dislocation, while the long and slender bodies (or those whose crystalline nature developed easy cleavage or fracture) would be torn asunder, and the particles often widely distributed. Granite then would be made out of any sediments or rocky materials of the necessary chemical combination, carried down to the required thermal horizon, whenever tan- gential pressure overcame the effects of the downward thrust of a superin- cumbent mass. If this preéminently mechanical theory of granite be correct, we should find every gradation between the corrugated schists and gneisses and the uniform granites. Supposing the schist beds to be partially formed and in a more or less plastic condition, or even supposing them to be wholly crystalline when the horizontal pressure came to be exerted upon them, it is evident that if the breaking up of horizontal position which I have described took place, the beds would be ruptured and torn asunder, and that certain regions would be converted into a uniform granite, while others retained the traces of the original beds. Accordingly, we find in certain instances long tongue-like masses of crystalline schists mechanically entangled and em- bedded in structureless granite. The case already described in Wright’s Canon is a conspicuous example of this. A further stage of the obliteration of the original bedding would be found in the very great variations of a mass of granite where the materials had not been perfectly commingled, and accordingly in some great granite precipices the homogencous granite in- 120 SYSTEMATIC GEOLOGY. cludes masses having the most extraordinarily irregular form, whose min- eralogical composition is totally different from that of the surrounding mass. There is not another such fine example of this in America as the wall of El Capitan, in the Yosemite Valley, which is a precipice 3,200 feet in height, the result of fracture, so smooth and so near the vertical plane that erosion has scarcely affected the fissure-surface. Upon the face, which in general is of a uniform gray granite, are seen irregular cloud-like masses and rudely lenticular bodies which seem to be made of segrega- tions of certain of the mineral components of the granite. The rock asa whole belongs to our fourth type, and is characterized by a high propor- tion of plagioclase, hornblende, and titanite. The irregular included bodies referred to are in some instances nearly black, and are made up of accumu- lations of brilliant black hornblende and quartz, absolutely without feldspar, and again with quartz in such low proportion that it may be said to be strictly a black amphibole rock, in which quartz is an accidental occurrence. Others of these segregations are of black mica and orthoclase, with a little quartz, to which the greatly predominating biotite gives a generally black appearance. Still others are of an aplitic type, being composed of ortho- clase and quartz. A study of this precipice would convince any observer that, whatever may have been the origin of the body as a whole, uniform commingling has failed to take place, and that the sharply defined inclu- sions are mechanical, not chemical, accidents. Suppose erosion to lay bare a horizontal face of this rock on which should be observed at intervals these various included bodies. A field ob- server, coming upon them and finding their boundaries very sharply de- fined by the enclosing granite, would naturally suppose them to be intrusive masses of different nature, and they would be mapped according to their wineralogical composition. Whereas in this magnificent Capitan section, which lets us into the nature of these deep-lying masses, it is seen that they are mere local dependences of the granite, and they may be regarded as enveloped bodies which for some reason or other have resisted the tendency to become merged in the main granite. Were the chief factor in the genesis of granite to be, as I suppose, tangential, or, as I like to denominate it, orographical pressure, there must GENESIS OF GRANITE AND CRYSTALLINE SCHISTS. Pall of necessity be all the transitions from a uniform homogeneous granite down to those rocks in which radial or gravitation pressure has produced the ordinary bedded schists; and it would seem that such envelopments as are seen upon the front of El Capitan, and also in a less conspicuous way in many of the granites of the Fortieth Parallel, might be considered parts of the original beds, which the accidents of pressure have failed to commingle into a general mass of uniform granite. Finally, this distinction between the action of the forces of gravity and those of tangential compression, as accounting for the characteristic differ- ences between bedded schists and mineralogically identical but structureless granite, is offered, not as a rounded theory, but as an hypothesis which to the mind of the writer best accounts for the present known facts. SECTION LY. PRE-CAMBRIAN TOPOGRAPHY. After the consideration of the mode of occurrence of the Archzean bodies and their petrological correlations, there remains a further and still more interesting feature of the Archean age, namely, the configuration and general relief of the area of the Fortieth Parallel at the close of Archean time and prior to the deposition of the unconformably overly- ing Cambrian beds. I am aided in this interesting enquiry by the relations of the Palsozoic, which, as already repeatedly said, are observed to be conformable from the lowest members of the Cambrian to the top of the Upper Coal Measures. Over the whole distance from the Rocky Mountains to western Nevada, in almost every prominent range, the contact may be observed between the Archzean and the Palzeozoic series. At times Archzean summits are seen to rise above the level of the deposition of the Upper Carboniferous, and the contact is exposed at various points all the way from that horizon down to the lowest exposures of the Cambrian, an extreme range of over 30,000 feet. It is obvious, therefore, that in any single mountain range the exposure of a contact between the Archzean and the Palaeozoic, covering a given number of feet in thickness of Palzozoic strata, represents just that much actual topographical slope of Archean hills. Assuming the deposit-plane of the Upper Coal Measures to have represented a uniform level, this level, closing as it does the great conformable Palzeo- zoic series, forms a datum-surface from which the features of Archean topography may be worked out. Over the Rocky Mountain system as exposed from Rawlings’ Peak to the east base of Colorado Range, the entire Paleeozoic series, from the Cambrian to the Upper Coal Measures inclusive, is not over 1,000 feet in total thickness. Passing westward from this region, a maximum thickness of 32,000 feet is reached in the Wahsatch. In other words, the Paleozoic has thickened from 1,U00 to 32,000 feet between the meridians of 105° and 112°. Now, if the plane of deposition of the uppermost mem- 122 PRE.CAMBRIAN TOPOGRAPHY. 123 ber of the Palsozoic had represented throughout an actual level, the differ- ence of depths of the ocean in which the Paleozoic sediments were laid down would probably be equal to the increase in the thickness of the series. But from all that may be observed of the present mode of deposition in ocean basins, as well as the data obtained from the study of extended exposures of the earlier rocks, it is in no wise probable that a given geolog- ical horizon necessarily represents a level plane of deposition. On the con- trary, over an ocean of greatly varying bottom it would seem that there must of necessity be some tendency on the part of deposited beds to follow the larger depressions of the bottom. The proximity of shores and the force of currents must of necessity greatly vary this law; but it should be at the same time recognized that there is a constant tendency to approach a level. It is true that the Cambrian formation as displayed on the Fortieth Parallel has been very unevenly deposited, and has shown a general ten- dency to fill up the lowest depression with enormously thick accumulations of detrital material. I leave out of consideration the continued deepening of the Palzeozoic ocean bottom, because, although important im an orograph- ical sense, it does not bear upon the question of detailed topography of the ocean bed, the only enquiry here pursued. Rising in the Paleozoic series, a horizon of deposition would represent constantly a nearer approximation to the level; so that at the close of the series it is not at all improbable that the Upper Coal Measures showed no very great deviations from a gen- eral plane. In assuming the top of the Paleozoic as a plane from which to work out the forms of the Archean bottom, it is true that we arrive at mimimum results of the depth of the ocean; we simply obtain the depth of deposit below a fixed surface. The Palzeozoic series represents the material accu- mulated in the bottom of the pre-Triassic ocean, and gives no clew to the real ocean surface of the period. In consequence, the Archaan topography represents only that which was buried under the bottom of the Paleozoic ocean, and leaves us entirely in the dark as to the heights to which the con- tinental and insular bodies rose either above the plane of deposition or above the actual surface of the ocean. When, therefore, I assign to the Archean mountain peaks a height of 30,000 feet, it is obvious that there is to be 124 SYSTEMATIC GEOLOGY. added to this a certain unknown quantity which will give them a still more imposing height. Some vague ideas of the additional altitude of the land masses of the Archean above the plane of deposition may be obtained in the Rocky Mountains and in the country west of Reese River. It is clear that in the case of Park Range there are at present 5,000 feet lifted above the horizon of the Carboniferous contact. This is demonstrated by the overlap of the Trias and Jura, which are shown along the flanks of the range. To this 5,000 feet must be added the elevation which has been removed by erosion—an element that cannot have been unimportant. So, too, west of Battle Mountain, in western Nevada, Archzean land rose above the limits of deposition of the Carboniferous and formed a broad area extending westward into California, over which no Carboniferous has been deposited. Within Nevada there is no evidence that this was in general more than a land mass of moderately rolling topography; and, as will be seen in a later chapter, its area and extent must remain entirely problematical. A few known points were lifted fully 6,000 feet above the lower regions. From the westernmost exposures of the Palaeozoic, it is evident that the series has lost none of its thickness in passing westward from the Wah- satch. On the contrary, those members whose limits are clearly defined in western Nevada are even thicker than in the Wahsatch. It is natural that there against the shore of the continent of Pacifis, the area directly deliver- ing its detrital material to the ocean which covered America, all sediments should be at their maximum; but that they should retain a thickness of 82,000 feet as far east as the Wahsatch, 300 miles from the continent which mainly furnished them, is most surprising. The special configuration of this broad ocean bottom was diversified by enormous mountain ranges, far exceeding in height the elevations of modern chains. The greatest single mountain slopes now exposed in the Fortieth Parallel territory are those in Colorado Range, where the extreme peaks are lifted 9,000 feet above the Great Plains. The highest known slope of the old Archean peaks is shown in the Cotton- wood Cafions of the Wahsatch, where a single, highly inclined, almost precipitous face of 30,000 feet was presented to the west—a mountain wall far exceeding that of any known modern example. At Red Creek, on PRE-CAMBRIAN TOPOGRAPHY. 125 the north base of the Uinta Mountains, the contact between the Uinta sand- stones and the old quartzitic Archeean mountain shows a nearly vertical precipice of not less than 10,000 feet, with some actually overhanging cliffs. Besides these observable and measurable slopes there must have been a considerable amount removed from high summits by erosion, and we have no means of knowing whether the lowest exposure of the Cambrian really represents the base of the series, or whether there may be a still further addition to reach what was the true base of the great Archaean peaks. In the northern part of the Wahsatch the topography was that of broad dome- like peaks with more gently inclined sides; yet their average elevation must have been very great, since they touch the Silurian and Devonian level, and we know the Cambrian to have been at least 15,000 feet thick. The height of this range above its base must therefore have been from 17,000+ feet to 30,000+ feet. In a later chapter will be discussed the influence of these immense underlying ranges upon subsequent mountain folds, and it is expected to show that they have entirely controlled the subsequent topographical features. At the bottom of the map of the Archean exposures, at the close of this chapter, is drawn a section representing the various members of the Paleo- zoic series, starting in the region of the Rocky Mountains at the west base of Park Range, where the whole Palaozoic does not exceed 1,000 feet, and thickening westward to the region of the Wahsatch, where it reaches nearly its greatest expansion. It will be seen that Park Range is given an elevation of 5,000 or 6,000 feet above the level of the Carboniferous, that being its present proven height above the point of Carboniferous contact. In the region of Red Creek is shown the great Archean peak, whose out- crop appears upon the map on the north base of the Uinta. Unfortunately the precipitous face of 10,000 feet is turned toward the south, so that it cannot be shown in an east-and-west section. In this region the outlines given in the section are entirely hypothetical, and are based upon the indi- cations of the east-and-west slope as given at the points of contact between the Archean and the Weber quartzite. Between Park Range and Red Creek there is no Archzean exposure, and the configuration of the bottom is there- fore not known. So too between Red Creek and the Wahsatch it is quite 126 SYSTEMATIC GEOLOGY. unknown. At the Wahsatch is given the immense mass, having its culmi- nation in Clayton’s Peak, which rises nearly to the top of the Weber quartz- ite and sweeps downward to the west beneath the 15,000 feet of conform- able Cambrian. Westward the Archzean masses of Wachoe, Humboldt, and Cortez ranges are seen rising to their proper elevations, as shown by the local sections observed in the field; while between these different mountains are (leep valleys whose bottom strata are afterward upheaved into interme- diate ranges, as for example in Pinon Range, between the Cortez and Hum- boldt Archzean bodies; and finally to the west of Battle Mountain is shown the sweeping up of Archzean land above the level of the Paleozoic series, forming a barrier in that direction. West of the Pinon the lower Cambrian is entirely unobserved, no section penetrating deeply enough in the moun- tain cores to expose it. There is no evidence, however, that it may not exist, under the exposed strata of the Pinon, or anywhere between the Wahsatch and the western limits of the Paleozoic, as thick or even thicker than the Wahsatch development. While, therefore, there is much in this section that is hypothetical, there are still many fixed quantities, such as the great slope at Red Creek, the enormous precipice at the Wahsatch, the towering peaks of the Cortez as lifted above the lower strata of the Pinon, and the depth of Cambrian as shown in the ranges of the desert west of Salt Lake. We are amply war- ranted in assuming the heights thus given for the Archaan mountain bodies, and it is further evident that while much of their elevation is due to origi- nally eroded surfaces, the great mountain wall in the Wahsatch, and also that at Red Creek, can only be the result of faults. It is impossible to suppose a precipice of Archzean schists like that exposed at Red Creek to be the result of other than absolute fracture. Therefore upon the Archzean bottom of the ocean in which the Paleozoic strata were deposited, there were mountain ranges of magnificent proportions, whose flexed beds and faulted precipices show all the orographical phenomena known to modern ranges. ‘Their great importance consists not only in their being features of i the Archeean surface, but in the fact that in them is found the local cause of modern ranges, and that in their nature and origin, as well as in that of subsequent uplifts, is to be studied the deeper and primal cause of moun- tain building. AW AL GEOLOGICAL MAP Oia ANEUE enG al a a ee te Nea a0 us 1) 20 TRIASSIC RED BEDS iia PRE-MESOZOIC pee ine * 7 26 ie ae Oe Mala ONR MENT Wbih IVR IL IIE. — TL. EmSOZOIC EXPOSURES 106" MAP| L. ¥ == = ica B a Ap GHK ts } Iron d d cae i 152) NY ‘ : ry 1° - 7 . om Fy ou + PALMOZOIC EXPOSURES. 155 the axis. The interesting orographic details of this structure will be found fully described in Chapter III, of Volume IL., and their essential features again treated in Chapter VIII. of this volume. A full description of the Paleozoic outcrops of this range would occupy more space than has been allotted to the whole of this volume, and I must content myself with a sufficient number of the great characteristic exposures to constitute a proof of their correlation into a generalized see- tion. In order that these sections may be better understood, I offer here a mere outlined statement of the chief beds, in the order of their super- position. Beginning at the top, we have: 1. Permo-Carboniferous, composed partly of calcareous, partly of Feet. argillaceous, and partly of arenaceous materials, the whole giving evidence of shallow-water origin, and characterized from bottom to top by fossils of Permo-Carboniterous age- - 650 2. Upper Coal Measure, essentially made up of limestones, inter- spersed with a variable amount of siliceous beds, the equiva- lent of the Upper Coal Measure series already described in the Uinta region, characterized by numerous well defined Coal Measurenossilse = a2 - sae = ae ae = 2 iefat- 1, 700 to 2, 100 3. Weber quartzite, a heavy body of quartzitic strata, slightly inter- spersed with greenish-gray slates, and containing, at both limits, unimportant intercalations of limestone. ------ 5, 000 to 6, 000 4. Wahsatch limestone, blue and gray rocks, in the upper part fre- quently rather thinly bedded and interstratified with a few persistent light-colored siliceous beds and quartzites. For the most part the limestones forming this series are compact and heavily bedded, and toward the base very dark-colored and more thinly bedded, with a few siliceous intercalations. Coal Measure fossils are numerous down to 1,600 feet from the base, where occur sub-Carboniferous types, which occupy but a narrow horizon, immediately followed by fossils of the Waverly group, these underlaid by beds containing Devonian forms, the whole making a continuous single body ai? [hinayfiigirs 6 le Ae Se Se eee aoe 7, 000 156 SYSTEMATIC GEOLOGY. 5. Ogden quartzite, generally white, shading off into pale green, Feet. often saccharoidal, more or less associated with greenish clay slates and rare conglomerates..-..---------------- 1, 000 to 1, 500 6. Ute limestone, a dark-blue, compact, fine-grained rock, contain- ing, a short distance below the top, Quebec fossils, which con- tinue nearly to the base of the series. Toward the base the limestone becomes shaly for several hundred feet...- 1,000 to 2, 000 7. Cambrian shales, a bed of variable calcareous and argillaceous slates of varying thickness, containing Primordial fossils... 75 to 600 8. Cambrian quartzite, an immense series of siliceous and arkose POCK Soop PI or RRR ee ao oe oe et pe Ie eft 12, 000 9. Lower Cambrian slates, dark argillites, and intercalated siliceous SC HISES Ue yes we SNe ce ek tak Re Ree eS 800 I purpose briefly to describe two separate sections in Wahsatch Range, which will serve to illustrate the succession of strata and life from the lowest of the Cambrian series to the close of the Paleozoic. The most excellently displayed of these, so far as continuity of outcrop goes, is that shown in the canon of Weber River, from near the mouth of Lost Creek down to Morgan Valley. This section shows only the upper edge of the Cambrian series, never exposing the deepest members. The second sec- tion will be that from the mouth of Big Cottonwood Carion directly across the range to Parley’s Park. As much of this section is on mountain sides and ridges, the absolute continuity of outcrop is often lost under unim- portant masses of débris and accumulations of soil; but the lower portion, namely, the Cambrian, is observed in deep continuous exposures in the canon cut. Besides these two sections, details of the general scheme will be filled up by such additional partial sections as are considered essential to the rounding out of our knowledge of the region. The base of the Weber Canon Paleozoic section is seen in Morgan Valley, a depression parallel with Wahsatch Range at the east base of the Archean mass which forms the main ridge from the region of Ogden nearly down to Salt Lake. Upon the eastern flank of the Archean to the north and south are seen resting the members of the Paleozoic, but directly i _ : _ ; ee wa i 7 ; ; i C 7 oS =f - ' 7 > : tat - = ; - = is ' : 7 . T : : v : 7 7 7 n > - B : we ot AGG? ’ : 7 7 a Mi hal: : ee, 7 A PALZHOZO!IC EXPOSURES. 157 east of Farmington the Paleozoic series is eroded away very deeply, and its former place is overlaid by the nearly horizontal members of the Ver- milion Creek Tertiary, which rests directly, in evident unconformity, upon the Archean. On the eastern side of the valley, however, the Tertiary is chiefly eroded away, and the bold heights of Morgan Peak are entirely made up, from summit to base, of the Palzozoic series. The lower foot- hills, all along the eastern edge of Morgan Valley, are partially composed of the horizontal strata of a very late Pliocene series, and are still further covered up by débris which rolls down from the height to the east. The section observed, from the base upward, is as follows: 1. The lowest visible outcrops of the older rocks are composed of the peculiar cream-colored and pinkish quartzites, overlaid by thin greenish siliceous argillites, very compact and having a splintery fracture. No great thickness of these rocks is exposed, certainly not over 200 or 300 feet, but it is the unmistakable summit of the Cambrian, as will be seen by future com- parison. 2. Conformably overlying this is a body of limestone about 1,100 feet thick, the lower part composed altogether of calcareous shales, very black, and splintery in fracture, while the upper members are of dark and con- tinuous beds of limestone. This zone, too, is much obscured by overlying débris and soil. The outcrops are never continuous for any considerable length, and the extremely limited exposures yield no fossils. But, as will be seen hereafter, it is clearly in the position of the Ute limestone, the great body of the Quebec Silurian horizon. 3. Overlying the limestone and conformable with it, as is seen at one exposure, is a body of white quartzite, containing more or less restricted zones of conglomerate, the average grain of the quartzite being very fine, and the color varying between pure white and grayish green. Like the two previous members of the section, it is chiefly covered by débris and rubbish, with only oceasional outcrops here and there along a line of five or six miles. These have the character of the low lines of cliffs, for the most part buried in soil, the base rarely appearing, while the backs of the strata slope east- ward at an angle of 30° or 40° into the hills, rapidly covered by débris. The thickness is estimated, by the space occupied by these scattering outcrops, 158 SYSTEMATIC GEOLOGY. at 1,200 feet. Up to this point, these three members would be of little value taken by themselves, but their general thickness, lithological character, and sequence are important when hereafter compared with sections of better ex- posure. They occupy the low foot-hills, and their total amount of outerop is rather small. The strike, as shown at several points, varies a little both to the east and to the west of north; the dip is eastward at an angle of about 40°. 4. Directly and conformably overlying the Ogden quartzite comes the great Wahsatch limestone, which shows continuous outcrops for several miles and is thoroughly exposed from summit to base, making a total single series of limestone of 6,500 to 7,000 feet. The most valuable part of the whole Weber section begins with the bottom of this limestone, which rests on a few thin sheets of olive-colored argillites separating it from the Ogden quartzite below. There seems to be no intercalation whatever of limy material at this point. The quartzite comes up sharply to the argillites, which are here not over ten or fifteen feet thick, and give way immediately to impure earthy lime- stones of a very dark color. Thus far, on this section, the lower 1,200 feet of the Wahsatch have not yielded any fossils, but at the height of from 1,200 to 1,400 feet from the bottom of the limestone, in the neighborhood of Weber Station, the hills directly north of the dépét are rich in Coal Measure forms. This point constitutes the entrance to Weber Canon, which is cut in a nearly east-and-west direction transversely to the strike of the strata. The hills on the north side of the river rise to 2,000 and 2,500 feet above the canon bottom, and the Paleozoic strata edges are seen dipping eastwardly at angles from 28° to 45°, the outcrops slanting up the hills and sinking beneath the bed of the canon. At Weber Station the beds, which are about 1,300 feet stratigraphically above the base of the limestone, present their edges clearly to view, and show a varying dip of from 80° to 40°. They are here usually of quite pure limestone, and the strata vary in width from extremely thin sheets to heavy tables. So, too, they vary in their lithological condition, some being highly crystalline, others merely granular, and some even very roughly granular. 'The following forms were collected here: Zaphrentis Stansburyi. Chonetes granulifera. PALHOZOIC EXPOSURES. 159 Productus symmetricus. Martinia lineata. Spirifer opimus. Spiriferina Kentuckensis. Athyris subtilita. Passing up the cajion, the series of limestones continues consecutively, without any interruption, for five or six miles, exposing 5,000 to 6,000 feet in thickness above the dépot. The dip varies from 35°, in extreme cases, to 55°, but the steep dips are extremely local, and are enclosed both above and below by beds of the normal inclination of 40°. About 1,100 feet from the summit of the group, in very pure grayish- blue limestone of dark hue, the following fossils were obtained : Spirifer opimus. Athyris subtilita. Terebratula bovidens. Productus prattenianus. Aulopora sp.? Nearly 800 feet from the top were collected— Terebratula bovidens. Productus prattenianus. Aulopora sp.? Also 500 feet from the top are Terebratula bovidens and Athyris subtilita. About 300 feet from the summit of the series are some extremely dark beds, which emit a feetid odor upon being struck with a hammer, and are intercalated with very impure arenaceous limestones. These contain numerous Spirifer opimus and Athyris subtilita. The limestones at 1,000 feet from the top enclose a series of thinly bedded but heavily blocked quartzites, which contain two or three sheets of small pebbles. These, however, are very thin and localized. The quartzite is more properly indurated sandstone and occupies a belt 150 feet thick. In general, the upper 1,000 or 1,500 feet of this limestone series are made up of thinly bedded rocks, less pure than the strata below, and 160 SYSTEMATIC GEOLOGY. more or less intercalated with siliceous zones. Some of the beds are also considerably argillaceous. It is noticeable that while the massive limestones below are quite uniform in dip, the intercalated region is subject to great local disturbances. It would seem that the limestone beds are able to undergo compression with less contortion than the more siliceous beds. As a conse- quence, the included siliceous zones are wavy, and exhibit extreme irregu- larity of dip, while the limestones enclosing them on both sides maintain an even inclination. Below this upper thousand feet the materials are much more uniformly calcareous, and the siliceous zones are never pure enough to show any distinct sandstone strata. Asa whole, the color of the series is dark. From the Weber dép6t to the summit of the series, therefore, the whole of this immense limestone is characterized by distinct Coal Measure forms, while the lower 1,200 or 1,300 feet have here yielded no fossils. This is no doubt due to the fact that it touches the edges of the foot-hills, and, like the three series described below, is largely covered with débris. Particular attention should be paid to the fact of the contortions and disturbances in the region of sand and quartzitic beds in the upper 1,200 or 1,000 feet of the series, as those phenomena are persistent over considerable areas of the Wahsatch, and will hereafter be described more particularly in some of the partial sections, where their recurrence is marked by most interesting inter- nal plication. The closing members of the Wahsatch group are arenaceous limestones, with a brilliant brick-red color. 5. The passage from the Wahsatch limestone into the Weber quartzite is made in perfect conformity, and, as the beds clearly evidence, with undis- turbed consecutive deposition. Above the reddened and arenaceous sum- mit of the Wahsatch limestone are a few intercalations of siliceous lime- stone. The Weber beds at this point dip about 40° to the east. In this lower zone are sheets of conglomerate, the pebbles of which are usually small and composed of white quartz. The general appearance of the quartzite zone is here that of a coarse, rather gritty sandstone, unevenly compressed into quartzite. The bottom of the series is prevailingly red for about 250 feet, and averages coarser than the material above. Over the red is a very finely laminated white and grayish quartzite, quite uniform in texture, and with only the most sparing enclosures of pebbles. Above this PALZOZOIC EXPOSURES. 161 point the series rapidly decline in dip to an inclination of only 16° to 20° to the east, accompanied by slight undulations. The curve from the steeper to the gentler dip is very gradual, and is unaccompanied by dislocations. There seems to be also a very small amount of local cracking of the strata. This low dip is held for about two miles up the canon, the strata becoming thicker and more heavily bedded, the texture of the quartzites more and more dense, and the conglomerates occurring at less frequent intervals. A mile and a half east from the base of the series there is scarcely any conglomerate at all, and the rock is a true quartzite of whitish or greenish hue, developing on many of its weathered surfaces a peculiar dark brown stain which looks like the oxydation of manganese. At the lower railway tunnel an interesting sharp double curvature is described by the strata. From the easterly dip of 16° they pass under a short shallow synclinal, rising on the reverse dip of about 20° for 100 feet or so, then, curving over an anticlinal, dip again to the east, from which point the easterly dip is maintained at an angle of 50° to57°. There isa small development of lime- stones here, quite black, and sufficiently siliceous to scratch glass, though effervescing under acids. This singular black rock is found to contain 83 per cent. of silica, 5 of organic matter, and 12 of carbonate of lime and magnesia. Above the tunnel are about 1,500 feet of massive quartzites of greenish-white hue, closely resembling the similar rocks at Mount Agassiz. The strike here deviates more and more to the north in ascending the canon. Throughout the whole 5,000 feet of this series no fossils are found. Toward the top are numerous peculiar holes in the rock, which seem like the cavities left by decomposing fossils, but the evidence is too slight to be of value. It is from the characteristic occurrence of this remarkable bed of quartzite at this locality that the name Weber quartzite has been given to the body. It is here essentially a quartzite, although toward the base rather more truly an indurated sandstone. The thickness, which we estimate in this exposure at 5,000 feet, represents the minimum observed section of this series, where both its lower and upper limit can be observed. It likewise represents the most extreme lithological result in the direction of the quartzite; and I am convinced that those two conditions are expressions of a common cause— that rocks made up of siliceous detritus may be compressed to half the 1B ae 1 oy SYSTEMATIC GEOLOGY. thickness of the original deposit in passing from an incoherent sand rock to the strictly crystalline condition of quartzite. 6. Conformably overlying the quartzite is a very heavy bed of much altered gray limestone from 600 to 700 feet thick. The bedding-planes are often entirely obliterated, and the material extremely crystalline, showing traces of great interior disturbance. The lower beds show a true conformity with the underlying quartzite. One or two hundred feet up in the series the alteration of the limestones reaches its maximum, and on the heights to the north of the cation it approaches a white marble. It is riven with cracks in every direction, but shows no trace of the intrusion of foreign chemical agents. South of the canon a few fossils were collected in a badly pre- served condition, but sufficiently distinct to be referred by Prof. Meek with- out hesitation to the Upper Coal Measure forms. One of these is a Sprri- ferina Kentuckensis; the other S. prattenianus. The gradual deviation of the strike from true north-and-south to a little east of north, already mentioned in the Weber quartzites, here reaches a direction of north 15° east. The average colors of these limestones are creamy grays, inclin- ing often to white in the more crystalline portions. A deep ravine which enters the canon from the north cuts diagonally across the upper part of the Upper Coal Measure limestones down into the Weber quartz- ite, and displays their conformable contact very well. Here the lime- stones are still more altered, and may be called a crude marble. The quartz- ites are also more disturbed, and show the effects of intense compression. This region of maximum disturbance and metamorphism is directly in the axis of the change of dip already mentioned as shown below the lower rail- road tunnel. Passing over this curve to the west of the head of the ravine, the limestones are again seen conformable to the diminished dip of the quartzite, inclining at about 16°. On the heights south of the river, where the whole formation passes under the horizontal beds of Eocene conglom- erate, this great bed of limestone is less altered, and shows many strata of pale yellow and drab color, resembling their equivalents, the lower drab limestones of the Upper Coal Measure series of the Uinta. Overlying this main body of 700 feet of limestone is a series of yellow shaly lime- stones 175 feet thick. This rock is extremely brittle, and, owing to the PALASOZOIC EXPOSURES. 163 uneven strain to which it has been subjected, is shivered into pecul- iar splinters, so that the surface of each stratum, instead of being the natural smooth plane of deposition, is a series of minute waves and troughs, like broken wave-marks. This shaly structure is obviously due to uneven pressure. ‘The surfaces of the fragments are not infrequently stained a pale, sulphur yellow. Overlying these calcareous shales, as heretofore quite conformable, is a series of sand and mud rocks, all more or less calcareous, varying in color from chocolate to olive, with red argillaceous sandstones, the whole about 225 feet thick. It has the appearance of a comparatively shallow-water deposit, made of argillaceous material, limestone, and sand, the thickness of individual beds being unusually limited. There are very many beds not over an inch thick On the upper surface of the strata, at several horizons, ripple-marks are preserved with unusual distinctness, and on a scale of fineness not often seen, the distance between the wave and trough being frequently not over an inch or an inchand a half. Alternating dark chocolate and olive-colored shales form the lower 200 feet of this group, while the upper 25 or 30 feet are pretty solid sandstone. Over these, still conformable, are 100 feet of yellow and olive calcareous shales, which are so earthy as usually to decompose, yielding a bad outcrop. Above this is a bed of bluish-gray limestone, rather compact, about 150 feet in thickness. Next come 20 feet of reddish-brown clayey sand, hardly compacted into rock, containing thin stony seams intercalated at intervals in the soft, easily eroded matter. This is immediately followed by 75 feet of a yellowish-gray, brittle, easily decomposed limestone Next above are 100 feet of light-colored, very thinly bedded limestones, that give way to 100 feet more of dark, siliceous, tough limestone, which breaks under the ham- mer with great difficulty, yielding an exceedingly rough, ragged fracture. In this were obtained a few fragments of fossils, made out by Professor Meek to be of the genus Bellerophon; and the highly siliceous character of the bed, closing as it does the Upper Coal Measure series, leads me to correlate it with the siliceous Bellerophon limestones already described in the Uinta. 7. Next above in sequence, and apparently with entire conformity of dip angle, although there are slight indications of erosion upon the surface 164 SYSTEMATIC GEOLOGY. of the siliceous limestone prior to the deposition of the overlying shales, follows a body of-variable shales, thin seams of limestone and mud and sand rocks, the whole being of shallow-water origin and displaying ripple-marks, comprising 620 feet of conformable beds. At three localities in this series were obtained fossils of Permo-Carboniferous facies, including — Aviculopecten McCoyi. Aviculopecten oxidaneus. Aviculopecten n. sp. Schizodus ovata. Myascites Weberensis. Directly above the siliceous limestone, which I consider to be the equivalent of the Bellerophon limestone, are shales carrying beds of argil- laceous sandstone three or four feet in thickness, which vary in color from chocolate to olive, the whole being about 100 feet thick. The olive-colored shales carry the same remarkably preserved ripple-marks as were ob- served below the Bellerophon limestone, but they are far larger than those above described. Above this series of chocolate and olive shales are 200 feet of soft muddy shales, containing thin beds of argillaceous limestone, also ripple-marked, and limited layers of mixed arenaceous and impure limestones. Still above these are 250 feet of buff and gray sandstone, usually made of extremely fine material held together by more or less argillite, and alternating with fine beds of earthy argillaceous shales, the whole capped by a thin siliceous series, almost a quartzite, 70 or 80 feet in thickness. The series of Permo-Carboniferous shales varies in dip from 48° to 60°, rising in some local cases as high as 70°. The capping bed of quartzitic sandstone is directly and conformably succeeded by the red beds of the Trias, which will be found described in the chap- ter on Mesozoic formations. Leaving out of consideration the thickness of beds which at the base are but very obscurely exposed, below the bottom of the Ute limestone (No. 2 of the described series), and counting from the bottom of that lime- stone, we have in this single section to the top of the Permian 16,000 feet of conformable strata, characterized by Permo-Carboniferous fossils in the PALZOZOIC EXPOSURES. 165 upper 620 feet; and in the next 1,600 feet, Coal Measure fossils related to the forms of the Upper Coal Measures, though very scarce and very fragmentary, owing to the physical condition of the rocks, which are highly altered. ‘Then comes the Weber group, made up of 5,000 feet of quartzite, occupying the position of the Middle Coal Measures, underlaid by more than 5,000 feet of Coal Measure limestones, comprising the upper five sevenths of the Wahsatch limestone. From this section we obtained, first, a clear expression of the stratigraphical sequence of the series; sec- ondly, the upper and lower limits of the Coal Measure series, which give for that member here a thickness of about 12,000 feet. Of the 16,000 feet, about 9,100 feet are limestone, 6,200 are of purely siliceous material in the form of sandstones and quartzites, and 700 to 800 feet of argillaceous and arenaceous mud rocks, characterized by more or less calcareous material. It is also noticeable that, with the slight exception of the thin bed of slate which underlies the Wahsatch limestone and separates it from the Ogden quartzite, and a few slightly argillaceous limestones in the upper 1,000 feet of the Wahsatch body, all the shales and argillaceous material are confined to the upper region of the Coal Measures directly under the Bellerophon limestone, and to the Permo-Carboniferous which immediately succeeds it. I will now give a section observed between the mouth of Cottonwood Cation and Parley’s Park, the most extended and instructive stratigraphical exhibition of the Paleozoic series in the Fortieth Parallel area. 1. A glance at Map III. of the geological series will discover a consider- able body of Cambrian occupying the lower half of Big Cottonwood Canon. The same formation is seen to recur upon the south side of the granite ridge which separates the two Cottonwood canons, extending part-way down to the bed of the canon, and again recurring upon the heights northwest of Alta. The deepest section of this body is offered on the lower course of Big Cottonwood Canon, which lies wholly in the Cam- brian for five miles. The strike of the rocks is diagonal to the canon, so that the exposures on the canon walls and in the lateral ravines display both the edges and the backs of the beds, giving an excellent idea of their physical condition. The canon in its zigzags often follows the strike of the rocks for a short distance, and then cuts either perpendicularly or 166 SYSTEMATIC GEOLOGY. obliquely across them. The estimate of the general thickness of the body as exposed here is made by laying down a great number of local observa- tions on the map, and deducing an average dip and strike, to which is applied the transverse distance of the outcrop, and the result gives about 12,000 feet. While an accurate, detailed measurement is probably impos- sible, this estimate is a sufficient approximation to truth for all our purposes. Near the mouth of the canon, to the south of which the Cambrian series overlie the granite and Archean body unconformably, are seen the lower- most members of the series, here formed of a body of dark blue and purple, and dark olive-green, often almost black slates, largely made up of fine- grained and thinly laminated argillites which alternate with zones more or less siliceous, the whole measuring from 800 to 900 feet in thickness These constitute our Lower Cambrian slates. Conformably above them are 8,000 to 9,000 feet of mixed siliceous schists and argillaceous schists, in beds vary- ing from a few inches in thickness to heavy strata eight or ten feet thick. They are prevailingly siliceous, but over a great thickness the alumina pro- portion is high. One of these intermediate forms gave on analysis 60 per cent. of silica, the other constituents being mostly alumina, with a little iron, lime, and alkalies. Above these varying schists are about 3,000 feet of true quartzite, capped by 200 feet of schistose rocks, quite micaceous toward the bottom. Among the beds near the top of Twin Peaks, a high summit south of the canon, is a series of the strata of micaceous quartzite, in which the mica occurs rather sparingly in fine brilliant specks, apparently muscovite. It imparts a decidedly fissile structure to the rock. On the peak next east is found a dark-blue, argillaceous slate, in which there is a considerable development of phlogopite in dark bronze crystals. Throughout the region of Twin Peak schists which directly underlie the highest quartzites of the ‘ambrian, are numerous zones that closely approach mica schist. In the ravines that lead down the northeast side of Twin Peaks these mica-bearing schists, which are not sufficiently charged with the mineral to be called a mica-schist, are observed underlying the upper quartzites. An excellent section of the Cambrian schists is obtained from the mouth of Big Cottonwood Canon, in a northeasterly direction across the spur which divides the waters of Cottonwood Creek from those of Mill Creek. About PALM OZOIC EXPOSURES. 167 the same estimate of thickness is formed from an examination of this ridge, namely, that from the dark bottom slates to the top of the argillaceous slates which cap the body, there is an exposure of about 12,000 feet. Although search was made throughout these schists as carefully as our time would permit, no fossils were obtained, and the reference to Cambrian will be explained later in the chapter. The series consists essentially of four members: the bottom slates, 800 feet; varying siliceous and argillaceous schists containing some mica-bearing zones, 8,000 or 9,000 feet; salmon-colored and white quartzites intercalated with dark schists, 2,500 to 3,000 feet; and the capping schists of 200 feet, which are partly argillaceous and calcareous and partly mica-bearing argil- lites. The dip as shown in Cottonwood Canon is very high, in the region of 60° near the mouth of the canon, declining eastward, so that the higher members of the groups directly under the Silurian limestone in Big Cot- tonwood Canon slope to the east about 45°, while across the ridge just below Alta, in Little Cottonwood Canon, they preserve the steep dip of 60°. The contact between this series and the underlying unconformable mass of granite and Archzean schists is extremely interesting, and from its situation offers remarkable opportunities of studying the early contours of the older rocks. From the mouth of Cottonwood Canon the line of contact rises upon the ridge to the south, forming the divide between the two Cotton- wood canons, and circles across the divide around the base of Twin Peaks, leaving the upper 2,000 feet of the mountain mass Cambrian, and the lower 3,000 feet on the Little Cottonwood side granite. The line of contact is nearly horizontal, and extends back six miles to a little below the town of Alta, successively higher members of the Cambrian series resting against the granite, until at last the ancient series rises into contact with the Silurian limestone, which conformably overlies the Cambrian. This is well shown in the lower section at the bottom of Map III. 2. Next above the Cambrian lie 1,000 feet of Ute limestone, which for the most part is very light-colored, highly crystalline, and characterized by peculiar cloudings of color that extend across the beds. Near the bottom of the series, and at one or two horizons near the top, it is noticeable for contain- ing a large proportion of tremolite, and under the microscope it is seen to 168 SYSTEMATIC GEOLOGY. be highly siliceous, the silica appearing as rounded glassy grains of pellucid quartz. The outcrop extends up the hills on both sides of the canons, and to the south is conspicuous upon the divide, from which it descends into Little Cottonwood and in the valley a little way below Alta exposes a fine precipitous cliff, the result of a fault. Here again are seen the same highly crystalline, almost marble-like condition and the same prevalence of tremolite and silica. Under these circumstances it is not at all remark- able that the bed contains no fossils; but it is unquestionably Silurian, as will be seen later. 3. Above this Ute limestone occurs the white granular body of Ogden quartzite, which is here reduced in thickness to about 800 feet. It may be traced up the hills to the south, and forms an interesting saddle on the ridge-top between the Ute limestone and the bold masses of Wahsatch limestone which directly overlie it. Here are but limited traces of the thin body of greenish argillites that farther south, in the region of Rock Creek, were found on both sides as bounding-beds of the Ogden body. 4. Immediately above this is Wahsatch limestone, which forms the high ridge north of the canon, and is traceable south against the granitic slopes of Mount Clayton. In the whole semicircular sweep which the Wahsatch limestone here describes around the Archeean body are the most interesting changes of molecular condition. The ridge to the north of Big Cottonwood shows a scarcely altered dark limestone, in which the fossils are preserved, while toward the south it becomes white marble, and near Mount Clayton is intersected by numerous dikes of granite-porphyry. The lower beds are pretty sharply defined from the Ogden quartzite; but themselves contain a little granular quartz, which remains upon dissolving the limestone in acids, and is partially rolled, though in general angular. The lower Wahsatch beds in Big Cottonwood Canon are heavy, and owing to the high state of alteration contain no fossils. On the ridge to the south, at the Reed & Benson Mine, about 1,300 feet from the base of the series, were found the following species characteristic of the Waverly: Spirifer Albapinensis. Spirifer centronatus. PALMOZOIC EXPOSURES. 169 Athyris planosulcatus. Athyris Clayton. Euomphalus Utahensis. Terebratula Utahensis. Cryptonella sp.? On a horizon a little above that of the Reed & Benson Mine were obtained the following distinctive Coal Measure forms: Spirifer cameratus. Spirifer planoconvexus. Spirifer sp.? (like disjunctus). Syringopora sp.? Diphyphyllum. And still higher up, about 2,500 feet from the base of the series — Spirifer lineatus. Spirifer sp.? (like disjunctus). Athyris subtilita. Euomphalus sp.? Zaphrentis sp.? (like centralis). On the summit of the ridge above the Flagstaff Mine, a bed of white calcareous quartzite in Wahsatch limestone is full of indistinct cylindrical cavities, the casts of fossils, and frequent Spirifer cameratus. ‘On the heights to the south of the canon are some Z-shaped folds in the upper part of the Wahsatch beds, similar to occurrences which will be described in the Ogden Canon section. On the north side of the cation bottom, in the less altered limestones about 2,000 feet from the top of the series, were obtained — Chonetes granulifera. Productus Nebrascensvs. Productus pertenuis. Productus symmetricus. 170 SYSTEMATIC GEOLOGY. Farther west on the strike, at about the same horizon, were obtained — Productus semireticulatus Spirifer ? Zaphrentis ? Crinoids. From the very uppermost beds directly under the lower members of the Weber quartzite, on the hill-top north of the Big Bend of Cottonwood, were obtained — Productus prattenianus. Productus semireticulatus. 5. Conformably over the Wahsatch limestone is the enormous body of Weber quartzites with shght intercalations of conglomerate, and near the upper limits of the series a few thin, argillaceous schists. In the region of the schists, which cannot be less than 4,000 feet up in the series of quartz- ites, the siliceous beds themselves are interestingly banded like ribbon jasper, a feature which is worth noticing as occurring farther east in the Uinta, but as not observable in the Weber quartzites to the north or west of this point. The area occupied by the Weber at the head of Cottonwood Canon is cumbered with an immense amount of glacial and modern débris obscured by growths of coniferous timber, and in general it is impossible to measure the thickness accurately. Where observed, the dip, like that of the underlying series, approximated to 45°, but occasionally was some- what higher. Judging by the average dip and the area in which only quartzitic strata outcrop, there cannot be here less than 6,000 feet of the Weber formation. This body may be traced to the northwest until its steep edge appears against the foot-hills of Jordan plain. By a general examination of the ridge it becomes clear that it is pure quartzite without important intercalations, except at the bottom, where for several hundred feet. the passage from Wahsatch limestone into quartzite is made by thick intercalations of seven or eight beds of limestone. This feature, unnotice- able to the north, recurs to the south, and is characteristic of the junction of the two formations in this longitude. 6. Continuing from the Big Bend of Cottonwood Caiion in a northwest PALHOZOIC EXPOSURES. 171 direction toward Parley’s Park, the contact of the upper limit of the Weber quartzite with the heavy beds of drab limestone which form the lower por- tion of the Upper Coal Measures, is distinctly observed; but owing to the forest and débris, only a few fossil forms were obtained, and those in a much-weathered, unsatisfactory condition. Yet the character of the lime- stone, and its conformable position directly over the Weber, clearly refer it to the base of the Upper Coal Measure series. A continuous belt of lime- stone, about 1,200 feet thick, is here exposed, of which the upper portion is rather finely stratified and shaly, and bears Bellerophon carbonarius. 7. Directly over this is a series of calcareous shales and ripple-marked argillites with yellow shale rocks, and at the summit of the series a consider- able body of quartzitic sandstone which directly underlies the red Trias. In the mud rocks and in the caleareous shales on the extreme foot-hills of Parley’s Park, in a position about three hundred feet below the ‘Trias, were obtained a Bakevellia, probably parva; a Eumicrotis, probably Hawni; and an Aviculopecten, like parvula. Owing to the amount of forest and débris, it is impossible to be sure that these upper series, which correspond with the Permo-Carboniferous shales of the Weber section, have not been redu- plicated by a fault, for there seem to be, as nearly as can be estimated, about 9U0 feet. The principal points of interest of this section are, first, the deep expo- sure of rocks which we have referred to the Cambrian, lying conformably below the Ute Silurian limestone, affording us the deepest view of the Pal- weozoic beds that we get anywhere upon the Fortieth Parallel; secondly, the absolute stratigraphical parallelism between this and the Weber section ; thirdly, the fact that we obtained, as in the Weber section, Coal Measure fossils down to within about 1,300 feet of the base of the Wahsatch lime- stone, and at that horizon was established by ample evidence the existence of the Waverly group; fourthly, the lithological and faunal identity of the Permo-Carboniferous shales with those of the Weber. Asa whole, the sec- tion is not so continuously exposed and the opportunities for measurements of the thickness of beds are less favorable than in Weber Canon The Wahsatch limestone seems to be thicker than in the Weber, while the Ogden quartzite has diminished from 1,000 to 800 feet © Otherwise a comparison 172 SYSTEMATIC GEOLOGY. of the sections will show an approximate identity. As in the Weber sec- tion, there is absolutely no nonconformity from the base, 30,000 feet up to the very summit. South of Lone Peak the great body of Wahsatch limestone already described in the Cottonwood region completes a semicircle about the granite mass, and then abruptly trends in a southeasterly direction, form- ing the whole range from base to summit. The region is here compli- cated by faults parallel to the strike, as well as transverse, so that an accu- rate measurement of the thickness of the series is impossible. As at the north, Coal Measure fossils characterize the beds to within 1,200 or 1,300 feet of the base of the series. That base is exposed very clearly north of the town of Provo; and along the whole eastern flank of the range back of Provo Peak the limestone is seen to pass by a series of intercalations into Weber quartzite. A remarkably good instance of these intercalations is shown on Tim-pan-o-gos Peak. The peak itself is a narrow ridge trending parallel to the strike of the body, namely, a little west of north, and reaches an elevation of 11,937 feet. It falls abruptly down to the east and west from 3,000 to 5,000 feet, and is composed of approximately horizontal strata of the Wahsatch series. The beds forming the upper part . of the ridge consist of repeated alternations of layers of limestone and limestone shales, with light-colored quartzites and siliceous shales. This intercalated passage into the Weber is clearly recognizable along all this region south of Clayton’s Peak, and represents a much more gradual tran- sition than in the Weber section, where the change from Wahsatch lime- stone up into Weber quartzite is characterized by a sudden break and a few unimportant intercalations. The interbedded zone carries numerous fossils in the limestone members, which in general have been changed into a white calcitic material. Among the species recognized were — Spirifer cameratus. -Athyris subtilita. Productus semireticulatus. Discena sp. ? The mixed zone, varying from 400 to 550 feet, includes about forty intercalations. The well known layer of white vitreous quartzite in the ob + PALA OZOIC EXPOSURES. Lee) upper part of the Wahsatch limestone and a little below the transition-zone is constant here. Plate X. represents the front face of the Wahsatch at Provo Fall; the cascade is here about 600 feet high, tumbling over escarped edges of the Wahsatch limestone group. The following few other illustrations are selected from Wahsatch local- ities, to add data to the general section. On the foot-hills a short distance to the north of Camp Douglas, directly underlying the red Trias limestone, are seen the series of the Permo-Carboniferous and Upper Coal Measures. Here was obtained Aviculopecten Weberensis. Farther south, on the spur between Parley’s and Emigration canons, is a local anticlinal, a minor contortion in the great series of the northerly dipping strata which extend thence to the mouth of Cottonwood Canon. Conformably included within the anticlinal fold of the red Trias sandstones is a small body of the characteristic red beds and clay shales of the Permo-Carboniferous, containing the following: Aviculopecten Weberensis. Aviculopecten curtocardinalis. Aviculopecten MeCoyt. Aviculopecten parvula. Sedgwickia concava. Eumicrotis Hawn. Myalina permiana. Myalina aviculoides. North of Clayton’s Peak, and directly surrounding the eastern side of the body of granite, are seen the heavy beds of the Weber quartzite, here very much iron-stained and showing evidences of severe alteration. The general strike describes a complete curve around the granitic mass of Clay- ton’s Peak, with its convexity toward the east. The rocks east of the peak dip directly east under the Provo trachytes, and make with the westerly dipping quartzites of the Uinta an unquestionable synclinal, through whose faulted axis bodies of trachyte have appeared. About four miles up City Creek Canon, Ute Silurian limestone is 174 SYSTEMATIC GEOLOGY. seen between Cambrian schists and Ogden quartzite. It is here from 1,000 to 1,100 feet in thickness, and at a horizon about 600 feet from the bottom yielded specimens of Dikellocephalus Wahsatchensis, a fossil characteristic in this region of the Quebec age. Upon the high summit of the Wahsatch, east of Centreville, uncon- formably overlying the Archean gneisses, is a body of salmon-colored quartzite, containing large gritty grains of pellucid quartz, and underlaid by a dark, heavy bed of purple quartzite. The salmon-colored quartzite is about 600 feet thick, and is overlaid by a few calcareous shales, which are immediately succeeded by Ute limestone 1,000 feet thick, showing the con- formable transition from Cambrian to Silurian. The Cambrian recurs on Ogden Peak, where heavy quartzitie beds, with an easterly dip of 60°, lie upon the steep edges of Archzean bodies which stand about 75° to the west. Near the top of Ogden Peak the Cambrian is characterized by a well defined bed of compact conglomerate, containing remarkably smooth pebbles of quartz. From this point north for twelve or fifteen miles, looking at the range from the west, the Archean gneisses may be seen to be overlaid by an unconformable body of strata dipping to the east, which represent the edges left by the great fault that has depressed the western half of the range. Of these conformable strata, the uppermost, northeast of Ogden, are Wahsatch limestone, while the lowest exposure is of Cambrian of varying thickness. Here, from the study of the contact between the Cambrian and the Archean, it is clear that the Archeean itself was shaped into rather elevated topographical forms, and that the Cambrian was deposited over them all, submerging the entire ridge. Supposing the uplifted Cambrian back in a horizontal position, the present exposed contacts give an idea of the pre-Cambrian, Archean to- pography, and it is evident here that there were Archean peaks of 3,000 and 4,000 feet, while an examination of the nonconformable contact in the region of Cottonwood Canon shows a steep mountain face of 30,000 feet ; and in the deposition of the Cambrian against these slopes it is evident that there was no tendency on the part of the sediment to conform at all to the ancient surface. Ogden Canon offers an admirable partial section of the Palseozoie. PALMOZOIC EXPOSURES. 175 1. Dioritie gneisses, the prominent feature of the Archzean near the mouth of Ogden Canon, are unconformably overlaid by Cambrian quartzites striking north 30° to 35° west and dipping 60° to 65° eastward. Here are about 1,000 feet of quartzites, overlaid by 100 feet of siliceous and argillaceous shales, which in passing up become decidedly calcareous, showing an evident transition into the overlying Ute limestone. The occur- rence of these argillaceous and calcareous shales here is well shown on the south bank of the cation, and is of importance, since they form the stratum in which the uppermost Primordial forms are found elsewhere. Throughout the lower part of the exposure the quartzite is of uniform lithological habit, and smooth, even bedding. It is exceedingly compact, and the quartz grains which compose it are sometimes visibly rounded. In other words, the orig- inal figure of the grains of sediment has not been entirely obliterated and compressed into a uniform crystalline mass, as is the case with nearly all the Archean quartzites examined by us. The tints are light-gray in the lower horizon, inclining to salmon above, due to oxyd of iron upon the stratum- planes. In the upper part of the series, corresponding to the conglomerate horizon on the top of Ogden Peak, are seen distinct beds of conglomerate, made of evenly worn oval pebbles of gray, red, brown, and white jasper, reaching two or three inches in diameter. Both here and in the conglom- erates which are displayed on the east side of the Wahsatch, under the Ute limestone near Centreville, the pebbles are interesting for the evidence they give of the great pressure to which the quartzites have been exposed. They are often flattened and elongated, and in some cases two pebbles are com- pressed so as to overlap each other. In some instances three or four pebbles are compressed into one solid mass, penetrating each other as if absolutely plastic. Throughout all these distorted and compressed pebbles there is no evidence of cracking. The argillaceous shales, which here, as elsewhere, close the Cambrian series, are exceedingly fine-grained, are of prevailing olive and greenish-gray color, and are identical with the beds from the same horizon which underlie the Ute limestone at Quebec Peak, at the forks of the Muddy. 2. Above these are twenty-five feet of more characteristically calcareous shales that pass up into well defined limestone, which is thicker than to the 176 SYSTEMATIC GEOLOGY. south, reaching 1,200 to 1,500 feet. Tere, on the hill-sides to the south and north of Ogden River, is an excellent consecutive outcrop of the material forming the Ute limestone. As a whole, it is here, as in the region of Cottonwood, distinctly a siliceous limestone, and although formerly burned for lime was found to yield too siliceous a product. About 3800 feet above the base is a well marked zone, twenty or thirty feet thick, of argillites similar to those which mark its separation from the Cambrian. Below these twenty feet of shales the general character of the limestone is more shaly than above. Directly over them is a dark-blue limestone, overlaid by a nearly white series of granular crystalline beds, the upper portion of which is more or less characterized by shales. The only fossils found here were highly altered Stromatopora. 3. The Ogden quartzite, which directly overlies the Ute limestone, has here a thickness of from 1,250 to 1,350 feet. It is pale-reddish or yellowish, and conspicuous for a multiplicity of jointing-planes. Subjected to chem- ical analysis, it yielded 77.79 of silica, the remainder of alumina, lime, and alkalies. About midway in the formation is a thin bed of white marble, above it a thin series of olive-colored, argillaceous shales. 4, From the summit of Ogden Peak to the head of Ogden Canon ex- tend the massive, continuous beds of the Wahsatch limestone, which are displayed particularly on the north wall of the canon in precipitous cliffs 2,000 to 2,500 feet above the level of the river. Immense piles of débris, fully 2,000 feet in height, obscure many of the lower strata. As a whole, the beds are coarsely crystalline, often siliceous, sometimes cherty, and here and there characterized by argillaceous, muddy impurities. About 5,000 feet from the base of the series, and near the top of the canon, we reach the siliceous zone already described in the Weber section, and here occurs a remarkable series of plications. The impure siliceous zones are plicated in the form of the letter Z, the amplitude of the folds being about 500 feet. The beds directly under the siliceous zone, although entirely conformable, show the effect of this crumpling but very slightly, and in the overlying strata this influence gradually dies out, leaving the higher members abso- lutely conformable with the undisturbed region below the siliceous zone. Twelve hundred feet from the base of the limestone here, or practically at PALHOZOIC EXPOSURES. ee F the identical horizon at which the Waverly fossils were obtained at the Reed & Benson Mine, we collected the following: Productus sp. ? Spirifer Albapinensis. Spirifer centronatus. Waverly. Athyris planosulcata. Euomphalus Utahensis. | Streptorhynchus inequalis. i Devonian. Proetus peroccidens. While this series of fossils, as a whole, has an unmistakable Waverly facies, the occurrence of the last two, which are essentially Devonian forms, marks this horizon as the turning-point between the Devonian and the Wa- verly. In this connection it should be mentioned that at about the same horizon in Wahsatch limestone at Rock Creek was obtained Spirifer cen- tronatus, a well defined Waverly species also occurring in the White Pine District at the base of the Waverly. Farther up, directly above the flexed region of the siliceous zones near the head of the canon, was found a new species of Zaphrentis associated with true Lower Coal Measure forms. The horizon of the Waverly is again shown in Logan Cation. Cache Valley is a broad anticlinal formed of the Paleozoic series, from the Cam- brian well up into the Wahsatch limestone. The axis of the synclinal is occupied by horizontal beds, which obscure the uppermost members of the Wahsatch. In the low beds which are exposed near the mouth of the canon, about 1,400 or 1,500 feet above the lowest exposures, at a horizon which must be very closely that of the Waverly, in Ogden Canon, were obtained the following fossils : Chonetes Loganensis. Rhynchonella pustulosa. Euomphalus latus, var. lacus. Spirifer Albapinensis. Spirifera centronata, Proetus peroccidens. Proetus Loganensis. 12 178 SYSTEMATIC GEOLOGY. Higher in the same limestones, in the horizon of the Lower Coal Meas- ures, were obtained a small species of Productus, Zaphrentis Stansburyi, and Lithostrotion. From Copenhagen to Call’s Fort the Cambrian, with the Ute limestone and overlying Ogden quartzite, is seen outcropping very distinctly. The contact between the Cambrian and the Ute limestone slopes down to the plains, and is depressed under the Quaternary directly at Call’s Fort. The quartzite here has a high vitreous lustre, conchoidal fracture, and extremely fine texture; its prevailing colors are decidedly salmon. The strike of the quartzites and limestones is approximately north 20° west, diagonally crossing the range. Here the upper member of the Cambrian directly over- lying the quartzites is a fine-grained argillaceous slate, shading up into cal- careous shales, of the bottom of the Ute limestone. At the base of the latter were obtained — Dikellocephalus Wahsatchensis. Dikellocephalus gothicus. Crepicephalus (Loganellus) quadrans. Lingulepis Ella. Here the limestones generally are considerably thicker than in the sec- tion described in Ogden Canon. We estimate them at about 2,000 feet. From the upper part of the same series, a few miles south, at the head of Box Elder Canon, F’. H. Bradley, in 1871, obtained Halysites catenulata. In this immediate region, therefore, we have obtained Quebec forms near the base of the Ute limestone, and Bradley a form distinguishing the Niagara near the summit of the same member. East of Cache Valley synclinal lies a broad anticlinal, which diverges from the trend of the Wahsatch and strikes a little east of north. The character of this anticlinal is somewhat peculiar, showing a very gentle slope to the east and a much more considerable one to the west. Throughout the whole axial region of the anticlinal is a gently dip- ping series of the Cambrian quartzites, overlaid on both flanks by the out- wardly dipping Ute limestones. ‘To the east the series above that horizon is entirely covered by the Vermilion Creek Eocene Tertiary, while to the west the * United States Geological Survey of Montana, Idaho, Wyoming, and Utah, Hayden, 1872. PALHOZOIC EXPOSURES. 179 exposures in Muddy Canon and Blacksmith’s Fork show the full section from deep in the Cambrian quartzite to the middle and higher members of the Wahsatch limestone. About eight miles to the north of Blacksmith’s Fork Canon the Cambrian quartzites appear with a gentle dip to the west, grad- ually flattening out to the east. Conformably overlying them, and itself conformably overlaid by the Ogden quartzite, is a fine and characteristic exposure of the limestone at Ute Peak, the typical locality from which this body of Silurian limestone has received its name. The peak is on the south side of Muddy Creek, just below the junction of its two important forks, the lofty and abrupt faces of Ute Peak itself forming a wall of the main canon and of the south fork. From the stream’s bed it has an elevation of 2,500 feet of precipitous slope, while toward the west it falls away with the gentler inclination of the higher plateau country. The beds here strike from 15° to 20° west of north, and dip westwardly from 15° to 20°. The relations of the Ute group with the underlying series are well shown. The canon of the south fork has cut through the base of the Silurian limestone, and also through the thin shales which form the uppermost member of the Cambrian, exposing in the bed of the canon the Cambrian quartzites, which gently rise to the east toward the axis of the anticlinal. The canon of the north fork of the Muddy, running at right angles to the strike, cuts through 1,600 to 1,800 feet of the quartzite, forming a narrow, almost impassable gorge, with perpendicular walls. In these quartzites were observed some pecul- iar markings suggesting imperfect borings or the tracks of worms, such as have been ascribed to the genus Scolithus. The shales over the quartz- ites are indurated argillites, slightly calcareous and interlaminated with brown, earthy-colored sandstone, altogether making a group 100 feet in thickness. A Cambrian rock of interest occurs in Beaver Cafion. It is a peculiar smoky-purple quartzite, which is again seen on the east side of the Wahsatch, opposite Centreville. It is of remarkably vitreous lustre, and is a tough, dense rock. The individual grains of quartz, up to the size of a pea, have a peculiar purple dusky hue, the siliceous matrix being made up of an excessively fine eryptocrystalline, almost amorphous quartz, the beds developing a certain schistose structure from partly foliated quartz. Minute flakes of white mica, and fluid inclusions with moving bubbles, are detected 180 SYSTEMATIC GEOLOGY. with the microscope. The Ute limestone is shown upon the slopes of Ute Peak to be very nearly 2,000 feet thick. Although there are numerous passages of pure limestone, the average character of the whole mass is siliceous, while the lower third or quarter is varied by a considerable amount of fine argillaceous material. Besides the general siliceous nature of the whole Ute group here, there are also beds of pure sand, and an immense amount of calciferous sand rock is intercalated at intervals throughout the whole mass. Some fine beds toward the middle of the series develop, on weathering, a remarkably banded structure, due to the variable amount of silica and the organic matter connected with the lime. Calcareous schists and sandy beds decidedly predominate over the pure lime beds. This siliceous character seems to be remarkably persistent over wide areas. About twenty-five feet above the top of the Cambrian argillites, in a bed of calcareous shale, enclosed in dark, dense limestones, are found numerous Entomostracea containing new species of two genera: Dikellocephalus quadraceps. Conocephalites subcoronatus. Two hundred feet higher in the series is a dark, siliceous limestone, some- what cherty, which outcrops on the north side of the peak, bearing an undetermined species of the genus Obolella, and near the summit of the series, about 200 or 250 feet below the bottom of the Ogden quartzite, were found — Euomphalus (Raphistoma) rotuliformis. Euomphalus (Raphistoma) trochiscus. Maclurea minima. On the summit of the ridge, but still somewhat below the Ogden quartzite, were found — Ophileta complanata. Raphistoma acuta. os These characteristic spaces prove that the greater part of the Ute limestone is Quebee. They leave a small portion of the top of the series unaccounted for, and it seems probable from the Halycites which was found near the PAL OZOIC EXPOSURES. 181 summit of the series by Bradley, taken together with the Upper Silurian fossils from the upper part of the Silurian limestone in middle Nevada, that the extreme upper portion of the Ute limestone of the Wahsatch, say from 150 to 200 feet, may be, and most probably is, of Upper Silurian age, while the remainder of the 2,000 feet is clearly Quebec. Box Elder Peak is the culminating point of the promontory-like north end of Wahsatch Range. The limestones that overlie the Ogden quartzite dip to the northeast from 45° to 50°. Well up in the series of limestones were obtained the following : Zaphrentis excentrica. Zaphrentis Stansbury. Cyathophyllum Nevadensis. Lithostrotion Whitneyr. Productus cora. Productus punctatus. Here are exposed about 4,000 feet, not far from two thirds of the entire Wahsatch limestone. Province oF THE GREAT Basty.—From the meridian of 112° to that of 120° extends the Great Basin country, which is characterized by broad valleys of Tertiary and Quaternary, interrupted by fragmentary outcrops of meridional ranges, which often reach a considerable height, and culmi- nate in Humboldt Range at a little over 12,000 feet above sea-level. The country immediately bordering the western base of the Wahsatch, whose lowest depression is occupied by Great Salt Lake, is at an elevation of about 4,200 feet. This nearly level basin extends westward about two degrees to the base of Ombe and Gosiute ranges. Thence for about seventy miles westward the average elevation of the Quaternary valleys rises, until at Ruby Valley it is about 6,000 feet. Still westward the valleys gradually decline to the level of Pyramid Lake, 3,900 feet in altitude. This whole region is ribbed with detached mountain ranges, rudely par- allel and generally of meridional trend; anticlinals, synclinals, and mon- oclinal masses which rise suddenly out of the Tertiary and Quater- nary plains. They are essentially composed of partial exposures of 182 SYSTEMATIC GEOLOGY. Paleozoic rocks, together with unconformable underlying masses of Ar- chean granite and schist, the whole broken through and often masked by extensive flows of Tertiary volcanic rocks. This briefly characterizes the region as far as the meridian of 117° 15’, beyond which to the west no Paleozoic exposures are seen. From that meridian to the Sierra Ne- vada the main geological characteristics are frequent masses of Archean granite and schist and enormously thick developments of rocks of the Alpine Trias and Jurassic ages, together with great outbursts of volcanic rocks. The section of the Great Basin, therefore, which comes within our observation consists of a central mass in the region of Pinon and Humboldt ranges, longitude 115° 45’, where the valleys which skirt the mountain bases are about 6,000 feet high, and depressed regions flanking it to the east and west, one occupied by the basin of Great Salt Lake, and the other by the family of lakes which receive the drainage of Humboldt and Truckee rivers. The entire distance from the base of the Wahsatch, which bounds the basin on the east, to the flanks of the Sierra Nevada, which outline it on the west, is about 425 miles, while the extent of the region characterized by Paleozoic outcrops, namely, from the Wahsatch to the meridian of 117° 15’, is about 275 miles; and this is the province whose geological complexities I am about to attempt unravelling. In this region there are between twenty and thirty considerable mountain masses which rise out of the Quaternary and Tertiary plains, extend a short dis- tance, usually in a north-and-south or northeast-and-southwest trend, and then either abruptly or gradually decline beneath the level of the desert again. In no single one of these ranges is the whole Paleozoic section displayed, and, studied by itself, it would have been excessively difficult to establish a correct sequence for the various members. It is only when com- pared with the full conditions so splendidly displayed in the Weber section of the Wahsatch that we are at all able to decipher these isolated moun- tain blocks. With the exception of Humboldt and Pinon ranges, the con- tinuity of the strata is not very great. Since the whole Palzeozoic is made up of quartzites and limestones, in the absence of characteristic fossils it is sometimes impossible to refer a body of limestone finally. There are many instances where the whole mountain mass consists of a low exposure of PALM OZOIC EXPOSURES. 183 limestones ot no very great thickness, characterized by Coal Measure invertebrates; the fossils offering insufficient evidence to warrant a defi- nite reference either to the Upper or the Lower Coal Measure limestones. In general, the Upper Coal Measure limestone, which in the provinces of the Wahsatch and Uinta was distinguished by the constant intercalation of sandy material throughout its upper horizons, in the province of the Basin is chiefly of limestone, and that often dark and heavily bedded, not litho- logically distinguishable from certain parts of the Wahsatch body ; so that when an isolated body of limestone is met with, whose exposed thick- ness is not too great to be stratigraphically referred to the Upper Coal Measures, and the fossils likewise do not show distinctly to which horizon it should be assigned, we have sometimes been obliged to make an arbi- trary reference simply from the probable connection of the body with neighboring ranges. When we find a body of from 5,000 to 7,000 feet of limestone underlaid by a quartzite and containing Coal Measure fossils in the upper members, we unhesitatingly refer it to the Wahsatch, and this reference has been further strengthened by the discovery, in the lower horizons of the body, of a considerable number of sub-Carboniferous and pure Devonian types, as well as the recurrence of the Waverly horizon, so well developed in the Wahsatch. On the other hand, as will be seen to be not infrequently the case, when a range consists of a body of lime- stone under 2,000 feet in thickness, resting upon the quartzite and carry- ing Coal Measure fossils down to the lowest limestone beds, we have felt entirely secure in referring it to the Upper Coal Measure series and Weber sandstone. In the case of a thick body of limestone carrying the well defined Devonian forms in its lowest members, and directly underlaid by a thin quartzite never exceeding 800 feet, we have recognized it as the bottom of the Wahsatch and the Ogden quartzite. Again, a thin quartzite is seen in some localities capping a body of dark siliceous limestone which carries in its summit members lower Helderberg fossils, and in that case the quartzite was considered to be identical with the Ogden Devonian. No forms at all equivalent to the Permo-Carboniferous fossils have been found, and no rocks at all similar to the shales which enclose them in the Wahsatch have been seen anywhere in our section of the | Great Basin. 184 SYSTEMATIC GEOLOGY. While the Wahsatch section illustrates in its completeness the whole strati- graphical sequence of Paleozoic rocks, paleontological proofs are only furnished in that range from the summit of the Permo-Carboniferous down to the base of the Quebec, at which horizon the fossils collected at Call’s Fort, directly above the Cambrian shales, mark the lowest depth from which organic forms were obtained. In the-Great Basin the lower rocks— Quebee limestone, and shales and quartzites of the Upper Cambrian— are well developed, and here with a stratigraphical sequence equiva- lent to that of the Wahsatch we find abundance of Primordial forms. Therefore, in establishing the complete scheme of the Palzeozoic series, while the Wahsatch furnishes everything but Cambrian life, that life is furnished in the desert ranges in a series which are the undoubted equiva- lents of the basal rocks of the Wahsatch. With these two the section is rendered complete, and is based upon evidence which may be considered to give it a final value. Since the great Paleozoic feature of Wahsatch Range is its remarkable display of continuous sections, in treating of that province I have done little more than describe and fortify these sections. The prov- ince of the Great Basin, on the other hand, is one in which the individual sections are very slight and too innumerable for re-description here. They will be found in Chapters III. and IV., and part of Chapter V., of Volume II. Since the interesting Paleozoic feature of the Great Basin, so far as it applies to this chapter, is the continuance westward of the series as dis- played in the Wahsatch, I conceive that the best method of treatment here is to begin with the lowest strata, and describe the occurrence of each t member in ascending. JI commence, therefore, with the CAMBRIAN AND SILURIAN. Passing over the limited display of quartzites underneath the trachytes of the Traverse Mountains, which from lithological evidence alone have been referred to quartzites of the Cambrian, the first occurrence which merits attention is in Oquirrh Range. By an interesting series of faults near the western edge of this body, in the immediate vicinity of Ophir Canon, the Cambrian quartzites and the thin bed of argillites so often mentioned as capping the series are displaced and brought up to view amidst masses of Wahsatch limestone which form the quaqua- PALAOZOIC EXPOSURES. 185 versal uplift of this region. About one eighth of a mile north of Ophir City is a straight, sheer wall of quartzite 300 or 400 feet high. The material of these siliceous rocks is the reddish salmon quartz that forms the uppermost part of the great body of Cambrian quartzites in the Wahsatch. Over these are about 100 feet of greenish-yellow clays, the equivalent of the argillites of Call’s Fort and the Cottonwood region, which contain the following forms, equivalent to those collected at Call’s Fort and represent- ing the horizon of contact between the Primordial and the Quebec—a hori- zon in Utah always confined to these shales: Ogygia producta. Ogygia parabola. Ogygia n. sp. Lingulepis n. sp. Kutorgina n. sp. Dikellocephalus sp.? Dikellocephalus sp.? The relation of this exposure to the overlying parts of the series is obscure. The next fossils found in the limestones above are of the Wa- verly horizon, which Mr. Emmons, who has examined the region, be- lieves to have been faulted down into contact with these Quebec shales. The chief value of this locality, aside from its relations with the rock above, is in confirming the reference to the Quebec age of the upper part of these shales and fixing the bottom of the Silurian. The western slope of Aqui Range, from Skull Valley up to Bonne- ville Peak, is formed of a continuous exposure of quartzites, making in all a thickness of about 6,000 feet, which have an average dip of 25° to the west, and decline to a much less steep position at Bonneville Peak. The prevailing rock is white and yellowish-white quartzites, with occasional conglomerate beds and limited strata of dark-green argil- lites containing spangles of muscovite on the surface-planes. There is also a dusky purple quartzite with pellucid pebbles, such as have been described from Blacksmith’s Fork and the Wahsatch of the Farming- ton region. The fact of so extended a series of quartzites underlying 186 SYSTEMATIC GEOLOGY. 5,000 or 6,000 feet of limestone is strong evidence in favor of assigning this to the Cambrian. The same quartzite stretches northward along the western side of Aqui Range, up to Grantville Peak, which is the crest of an abrupt anticlinal whose western member dips only about 45°, while the eastern approaches a horizontal position. The exposures at both places are very fine. At Bonneville Peak, particularly, the eastern base presents an almost perpendicular wall 2,000 or 3,000 feet in height. The characteristic feature of the beds on the saddle north of Grantville Peak is the occurrence of the flattened and distorted pebbles of the conglomerate already described in Ogden Canon. In the Schell Creek Mountains, which form the eastern boundary of Steptoe Valley, south of the great flow of rhyolite that overwhelms nearly all the sedimentary rocks in the northern part of the range, at a locality somewhat south of the limits of our map, are seen the heavy quartzites of the Cambrian, and directly over them argillaceous and calcareous shales from which were obtained Crepicephalus (Loganellus) amytus and Lingulepis Mera. This, from its position, capping the great Cambrian quartzite, and containing undoubted Cambrian forms, shows that the dividing-plane between the Cambrian and the Quebec is for this region in the thin shales. Farther westward a great limestone body takes the place of the upper Cambrian quartzite and the shales. In the high ridge east of Egan Canon is displayed a section of Cam- brian rocks resting unconformably upon the granite and overlaid by heavy bodies of limestone. Between the Cambrian and the continuous outerops of limestone is a region variably covered with soil and characterized by infrequence of outcrops. There is ample room for Ute limestone and Ogden quartzite, though their presence is not proved. Here, directly over the granite, are several thousand feet of quartzitic schists, capped by about fifty feet of highly laminated fissile argillites. The character of the quartzites is quite similar to that of the quartzitic schists of the Wahsatch. It is compact, often semi-transparent, frequently quite vitreous, and shows occasional traces of granular structure. Certain beds of dark purple quartzite carry coarse quartz pebbles, others contain flakes of mus- covite, and still others show a considerable development of bronze-colored phlogopite. All the outcrops noted as coming to the surface through the PALHOZOIC EXPOSURES. 187 soil and débris which overlie this Cambrian series show the conformable dip of the limestones to the west. In White Pine Range, the base of Pogonip Ridge at its northern end, shows certain limited outcrops of granite, upon which are only partially exposed bodies of mica schists and black arenaceous and argillaceous shales, overlaid by an undetermined thickness of compact, vitreous, steel-gray quartzites, identical with the Cambrian quartzites hereafter to be described in the Pinon. Their position shows an eastward dip of from 24° to 30°. Rising a little on the range, they are conformably overlaid, although the contact is débris-covered, by a great thickness of dark limestone. The lower limestone beds are highly siliceous, of a steely-black, with blue shades, and varying a good deal in physical characteristics, passing down- ward into rather argillaceous, calcareous shales. Higher in the series it develops a dark-blue color, and is seen to be much banded by zones of arenaceous limestone and occasional seams of pure chert several inches thick. The entire limestone zone is about 4,000 feet thick. From these dark heavy beds were obtained the following fossils, determined by Hall and Whitfield: Crepicephalus (Loganellus) Hague, n. sp. Crepicephalus (Bathyurus) angulatus, n. sp. Crepicephalus (Loganellus) sp. undeterminable. Crepicephalus (Loganellus) sp. undetermined, Conocephalites (Pterocephalus) laticeps, n. sp. Dikellocephalus flabellifer, n. sp. Dikellocephalus quadriceps, n. sp. Ptychaspis pustulosus, n. sp. Ptychaspis n. sp. undescribed. Charicocephalus tumifrons, n. sp. Agnostus communis, n. sp. Lingulepis Mera. Obolella sp. undetermined. These clearly Primordial forms extend up for 2,000 feet into the body of limestone. This is the first indication of an important change between 188 SYSTEMATIC GEOLOGY. the lower Palzeozoic horizons of the Basin and the Wahsatch. We saw that at Call’s Fort, on the western base of the Wahsatch, Quebec forms, although representing the very base of the Quebec and closely allied to the Primor- dial species, were found at the base, or very near the base, of the Ute lime- stone, the lowest limestone of the whole series; and again that Quebec fossils were found within twenty-five feet of the base of the Ute limestone at Ute Peak by the forks of the Muddy. The thin calcareous and argillaceous zone which rests upon the top of the quartzites has here given place to cal- careous sediment expanded to a thickness of 2,000 feet, and merged itself into the Ute limestone. This limestone from the typical locality at Pog- onip Ridge is called the Pogonip limestone, although the upper 2,000 feet are in reality the equivalent of Ute limestone. Near the top of the series, above the horizon from which the foregoing Primordial fossils were obtained, the following Quebec species were collected: Ptychaspis pustulosus, n. sp. Bathyurus Pogonipensis, ni. sp. Orthis Pogonipensis, n. sp. Strophomena Nemia, n. sp. Porambonites obscurus, n. sp. Raphistoma acuta, n. sp. Cyrtolites sinuatus, n. sp. Above these Quebec members of the limestone series of this locality there is a gap occupied by a valley deeply covered with soil, and neither of the uppermost members of the limestone series is seen, nor their contact with the rocks above. All that this locality develops are the Cambrian quartz- ites and schists overlaid by a body of at least 2,000 feet of Primordial lime- stone, which passes up without petrological change into beds of similar limestone characterized by distinct Quebec forms, and the upper continu- ance of the limetones is unknown. At the Eureka Mining District, which is in the body of hills that con- nect Diamond and Pinon ranges, south of Diamond Valley, and a little south of the south line of our map, there is an excellent exposure of the Pogonip limestone with the underlying Cambrian schists and quartzites PALMOZOIC EXPOSURES. 189 The ridge of Prospect Mountain shows the same lithological features as those of Pogonip Ridge, and carries through an enormous thickness of the formation, certainly 2,500 feet, Primordial forms, embracing the following: Crepicephalus (Loganellus) granulosus. Crepicephalus (Loganellus) maculosus. Crepicephalus (Loganellus) nitidus. Crepicephalus (Loganellus) simulator. Crepicephalus (Loganellus) unisulcatus. Dikellocephalus bilobatus. Dikellocephalus multicinctus. Agnostus Neon. Agnostus prolongus. Agnostus tumidosus. Lingulepis Mera. Lingulepis minuta. Obolella discoida. Kutorgina minutissima. Leptena melita. Owing to great disturbance and alteration of the limestones, few fossils were obtained from the upper 1,800 feet of the Pogonip belt; but an Orthis Pogonipensis and a Bathyurus, probably Pogonipensis, were col- lected—enough to prove the occurrence of the Quebec, and thus establish the complete parallelism of horizons with the great Pogonip limestone at White Pine. The Eureka locality, however, is of great geological interest, since conformably over the Pogonip is the Ogden quartzite admirably defined, having a width of about 900 feet, and still conformably over that again the immense Wahsatch limestone. Under the Pogonip are con- formable quartzites of the Cambrian, which, however, were not critically studied. The northern end of that portion of Pinon Range which lies south of Humboldt River culminates at the high point of Raven’s Nest Peak. Here is a fine exhibition of the Cambrian quartzites and schists, with a perfect exposure of their passage upward into the Pogonip limestone, although the 190 SYSTEMATIC GEOLOGY. limestones here have so far failed to yield any fossils. But from evidence of the overlying Ogden quartzite and the Devonian base of the Wahsatch limestones, which are characterized by numerous well defined Upper Held- erberg species, the heavy body of limestone colored as Silurian could not be mistaken for Wahsatch limestone, of which only the lower or Devonian portion is here seen. Pinto Peak, a high tabular quartzite mountain, lies in the axis of an anticlinal, the rocks both to the east and west dipping in con- trary directions, and the whole curve of the anticlinal being clearly seen to the south, where the Devonian quartzite and limestones arch continuously over and form the summit of the ridge. The Cambrian quartzites, as shown at Pinto Peak and at the base of Raven’s Nest Peak, are heavily bedded quartzitic schists, carrying some beds which are highly micaceous, and at the top characterized by occasional thin beds of argillaceous material. The higher quartzites are steel-gray, rather saccharoidal in texture, are slightly calcareous, and superficially resemble the steel-gray limestones above them. For a considerable distance in the upper quartzite zone, say 300 or 400 feet below the contact with the Pogonip, there is not a little calcareous material, the analysis yielding only 76 to 78 per cent of silica, the remainder being carbonate of lime. It is a highly crystalline calcareous quartzite, and passes upward into rather siliceous limestones, which are alternately dark and light. Doubtless if the steep slope of Raven’s Nest Peak were given a more careful examination than our time permitted, Primordial and Quebec fossils would be found. The whole limestone cannot be less than 4,000 feet in thickness, and by its volume and position conformably between the Ogden quartzite and the basal quartzites can be nothing but the Pogonip. The strike of the lime- stones of Raven’s Nest Peak is diagonally across the range at about north 25° east, and they dip from 25° to 35° northwest. Directly south of Dixie Pass the ends of the strata are abruptly cut off by a fault and very deep dislo- cation, and their edges are abrupt and partly masked by an immense overflow of trachyte. The upper members directly under the Ogden quartzite are less siliceous than the beds below, a good deal altered, more highly crystal- line thar the lower strata, and reticulated with innumerable seams of white calcite. The quartzites and schists underneath this body of limestone are exposed downward for not less than 5,000 feet. The conformity between PALZOZOIC EXPOSURES. 191 the deep Cambrian quartzitic schists and the Ute-Pogonip limestone is abso- lutely perfect, as is the contact between the upper members of the Ute- Pogonip and the overlying Ogden. In reference to the line here separating the Cambrian and the Silurian—which is intended to be so drawn as to it should be said that there is an error on the geological map at this point. The line as include the Primordial in the Cambrian, as fixed by Dana drawn here represents the junction of the steel-colored limestones with the underlying steel-colored quartzites. It should be carried 1,600 or 1,806 feet higher, which would have the effect of narrowing the Silurian band on the map and widening the Cambrian. Not enough study was given to this region to prove clearly that the lowermost rocks exposed here are not Ar- chan. There are some gneissoid rocks which differ lithologically from any of the known Cambrian beds, but they were not sufficiently observed to determine their conformity or nonconformity with the quartzites above. Farther south in this range, near Mineral Hill, the Ogden quartzite is well developed about 800 feet in thickness; and conformably underlying it, especially as displayed upon Cave Creek, about three miles south of Mineral Hill, is the top of a body of limestone more or less siliceous, which, from its position under the Ogden, is also referred to the top of the Ute-Pogonip body. The only organic remains found in this devel- opment of limestones are some stems of corals, which, however, are of special interest, as Whitfield determines them to be of the Lower Helder- berg horizon. West of Pinon Range and south of Garden Valley, in the Roberts Peak Mountains, appears a high mass of limestone, flanked on both sides by quartzites, which have been referred to the Ogden. About 3,000 feet of conformable limestones are displayed here, which lithologically repeat the features of Pogonip Ridge. These are dark, more or less siliceous, and intercalated with calcareous shales and thin, cherty beds. ‘The strata incline to the east with a varying strike of northwest-southeast. Along the northern slopes the observed dip was 40° or 50°, here striking north 20° west, while the southeasterly foot-hills gave a dip of but 18° to 24° to the east, and a strike more nearly due north. The upper horizons on both the north and south slopes yield fossils ranging from the Upper members of 192 SYSTEMATIC GEOLOGY the Quebec to the Lower Helderberg, the collection including the fol- lowing: Cladopora sp 2? (resembles C. seriata) Orthis sp.? (resembles O. hybrida). Atrypa reticularis. Atrypa sp.? (resembles A. nodostriata). Ehynchonella sp.? Illenus sp.? All of these but the Rhynchonella have been ascribed by Hall and Whitfield to the Niagara; while the Rhynchonella, which was collected farther up, closely resembles the Rhynchonella found at White’s Ranch, associated with Lower Helderberg forms. North of the Humboldt, in Boulder Creek Valley, near the intersec- tion of the 41st parallel with the meridian of 116° 30’, at a place called White’s Ranch, is an isolated hill of limestone conformably overlaid by a pure, greenish-white quartzite having all the characteristics of the Ogden. The outcrop, as will be seen upon the map, is limited on all sides by the Quaternary of the valley. It is an absolutely isolated hill. The limestones were rather dark, fine-grained, and decidedly siliceous, the beds, for the most part, thin and intersected with siliceous seams, the latter carrying some branching impressions like rootlets. There is a total thickness of about 600 feet of limestones. From these were obtained, in the neighbor- hood of the overlying quartzite, the following Lower Helderberg association of forms: Atrypa reticularis. Pentamerus galeatus. Strophodonta sp.? (like S. punctilifera). Orthis sp.? Trematopora. Celospira. Rhynchonella. Favosites (sp. allied to F’. Helderbergia). Diphyphyllum n. sp. Campophyllum. PALZOZOIC EXPOSURES. 193 This establishes the fact that the uppermost horizon of the Ute-Pogonip limestone body is distinctly Lower Helderberg. Roberts Peak, Eureka, and White Pine form a region along a meridional belt extending north- and-south for seventy miles, by a breadth of about thirty miles, exposing the entire development of Silurian and a part of the Cambrian series. The whole 4,000 feet of limestone consists of three distinct members: 1, the lower 2,000 feet of Primordial; 2, a restricted but as yet unknown amount of the middle of the series, being Quebec; 3, a considerable breadth of Niagara overlying that, with the summit members (underlying the Ogden quartzite) of the Lower Helderberg. 'The line, therefore, which separates the Primordial, or Cambrian, from the Silurian, will in this region come near the middle of the Ute-Pogonip limestone. Ocpen Quartzite.—Humboldt Range, by far the most considerable mountain ridge in central Nevada, consists essentially of a long body of Archean granitoid gneisses and quartzites, unconformably upon which rest strata of the Wahsatch limestone dipping to the east and west, show- ing the range to have been an anticlinal which was folded with its axis running approximately in the line of the old Archean body. The few exposures of the westerly dipping rocks have their plane of contact in the horizon of the Wahsatch limestone, the Ogden being altogether buried; but south of Frémont’s Pass the whole body of the ridge is formed of east- erly dipping strata, 7,000 feet of the Wahsatch limestone underlaid by the quartzites of the Ogden. From Frémont’s Pass to Hastings’s Pass the ex- treme western foot-hills are made up of easterly dipping quartzites, having a close physical resemblance to the Ogden beds of the Pinon. Their hori- zon is determined by their lying conformably at the base of the Wahsatch group. Above the Ute-Pogonip limestone of Raven’s Nest Peak, Pifion Range, and quite conformable with it, lies a body of quartzite 900 to 1,100 feet in thickness. It is of thin, even lamination toward the lower members, and above of rather heavily bedded quartzites, much stained with iron. ‘The material of the rock is extremely fine. It contains no conglomerate, as far as observed, and no coarse, angular, or gritty grains, and shows throughout an extremely fine suberystalline texture. It is traversed by many jointing- 13 kK 194 SYSTEMATIC GEOLOGY. planes striking northwest-and-southeast, or nearly at right angles to the strike of the rock. From the Raven’s Nest region it trends southwest and then curves again to the southeast, skirting the great body of Ute- Pogonip limestone, and about five miles south of Pinto Peak forms the crest of the main anticlinal of the range. ‘Toward the southwest, the west- ern side of the anticlinal is seen dipping under the lower members of the Wahsatch limestone. At Pinon Pass the outcrops are very distinct, and toward the west they pass gradually beneath Devonian limestones. These limestones form here a synclinal whose axis is northwesterly, and rapidly curve up again with an easterly dip, the Ogden quartzite reappear- ing at the western base of the range In other words, from Pinto Pass it curves under the anticlinal, and reappears between the Silurian limestone of Cave Creek and the overlying Devonian limestone. Here, where it is distinctly outlined by the limestones on both sides, it is about 800 feet thick, while north, in the region of Raven’s Nest, it is 900 to 1,100 feet. The exposure in the region of Pony Creek, where the Ogden quartzites arch over and form the cap of the anticlinal, is exceedingly fine, bold hills having been eroded out of the arch. The lithological characteristics of this quartzite throughout the Pinon are similar, except perhaps along the western base, where it has a rather more flinty and vitreous aspect. The quartzite which overlies the Silurian limestone of Roberts Peak is rather obscure, and its contact with the underlying rocks is not shown; so that, while it is probably Ogden, the proof is uncertain. At the small isolated hill which rises to the surface through the Quaternary of Boulder Creek on the line of the 41st parallel, near the meridian of 116° 30’, a body of quartzites has already been described as conformably overlying the limestones which carry Lower Helderberg fossils. This, from its position directly over the top of the Ute limestone, is assigned to the Ogden. At White Pine, where are exposed both Pogonip and Wahsatch lime- stones, there is a gap between the two great bodies—a valley covered with Quaternary débris, in which are seen no outcrops. The whole region, which should be covered by the Ogden quartzite, is masked by detritus and earth, so that its presence or absence at that locality is so far not proven. PALMHOZOIC EXPOSURES. 195 From the undoubted equivalence of the two bodies of limestone to those exposed in the Pinon, and from their relative dip here, there is little doubt that the Ogden does occur underneath the valley earth. As already noted, it recurs in Eureka District in its proper place in the series. Excepting Aqui and Oquirrh ranges, wherever the Ute and the Wahsatch limestone are both exposed, the Ogden is clearly seen. In the Aqui the examination was exceedingly hasty, and the region is complicated by faults, so that its not having been seen is no proof of its absence. On the contrary, we believe it to be there, and have so stated on the map. In the region of Ophir City, in Oquirrh Range, the Ogden is wanting. At that locality is found a small gap between the fossils which represent the Call’s Fort horizon and the Waverly group. In other words, both the Ute limestone and the Ogden quartzite appear to be wanting; but we con- ceive this to be wholly due to complication resulting from faults. Except- ing in these two obscure localities, wherever we have found a section which has exposed both Silurian and Carboniferous beds, the Ute limestone and overlying Ogden quartzite are invariably recognized, and we consider them to be, so far as the Fortieth Parallel region is concerned, of remarkable stratigraphical persistence. At one place in Frémont’s Pass, Humboldt Range, nonconformable contact between the Ogden quartzite and the underlying Archzean may be observed. Otherwise, wherever the Ogden is seen west of the Wahsatch, either the base is not visible or else it is found resting upon the Ute- Pogonip limestone. Limited, then, by the Lower Helderberg fossils below and the Upper Helderberg fossils above, and itself yielding no organic forms, it may be taken, until still further restricted, to represent the Oriskany, Cauda-galli, and Schoharie horizons; and since the Lower Helderberg fossils possess so high a facies, I have considered it right to classify the Ogden quartzite altogether as Devonian. It is not at all impossible that future study may discover sufficient evidence to settle this question finally. Until then, it seems to me, on the whole, most likely to be chiefly Devonian, and it is therefore so placed in our series. Wausatcu Limestone.—North of Salt Lake is a considerable area of limestones, which begin on the west side of Malade Valley, on the northern 196 SYSTEMATIC GEOLOGY. limits of our map, and extend south and west, dipping under Hansel Spring Valley, and then extending still farther southward to form the greater part of Promontory Range. This region shows several synclinal and anticlinal folds, with very gentle dips, but exposes no great thickness of limestones except in the higher part of the Promontory itself. Southwest of the railroad are large bodies of limestone, of prevailing gray color, the lower exposures inclined to dark, almost black beds. The rocks dip at an angle of 38° westward. Extending down the range, they are subject to interesting structural disturbances, and in general expose about 3,800 or 4,000 feet of thickness. Somewhere about 1,200 feet below the top of the series is an included zone of yellowish-brown sandstone, decidedly calcare- ous, intercalated with numerous thin sheets of gray limestone. The lower portion is sharply defined against underlying beds of dark-blue limestone, but on the upper limit, 300 feet up, it passes gradually through shaly beds into the limestone above. The general strike here is north 28° east. From the limestones directly below and directly above this siliceous zone, not far from Antelope Springs, were obtained the following : Productus prattenianus. Spirifer opimus. Athyris subtilita. Streptorhynchus (fragments). While farther south in the range, from limestones of the lower horizon, were obtained many Zaphrentis Stansburyi and Productus semireticulatus. It is assumed that this siliceous zone is equivalent to that described in the Weber section not far from the summit of the series. From the lithological character of the limestones themselves, as well as from the great thickness exposed and the facies of the fossils, this series is referred to the Wahsatch limestone, although neither the underlying nor the overlying quartzite occurs here at all. Considering this line of upheaval in its southern extension, it is evi- dent that I'rémont and Antelope islands are only parts of an Archean body which bears to this line of upheaval the same relation as does the Ar- cheean of the Wahsatch to that range. Southward on the same line are seen PALASOZOIC EXPOSURES. 197 the Paleozoic masses of the Oquirrh and Pelican Hills. Within our map the Pelican Hills present only an unimportant mountain mass, made up of thinly bedded blue limestones with frequently intercalated quartzites, un- doubtedly referable to the uppermost region of the Wahsatch limestone as displayed upon the top of Tim-pan-o-gos. A few imperfect spirifers and crinoids were the only fossils found. The Oquirrh Mountains, on the other hand, offer an important ex- posure of the Palzeozoic series, thrown into complicated structural rela- tions, and about half made up of Wahsatch limestone, the remainder being overlying Uinta quartzite. The peaks rise to a height of 6,000 feet above the plains, and offer splendid exposures. As seen at Dry Canon, the uppermost fossils of the Wahsatch limestone are of sub-Carbo- niferous types, and the vertical range through which fossils of this horizon and of the Waverly extend, is apparently greater than at any other point where the Wahsatch limestone is displayed. Since there is a structural obscurity about the bottom of the limestone, the exact height in the series at which the Waverly fossils are found is not known. From the westerly dipping beds near the mouth of Dry Canon were obtained — Streptorhynchus inflatus. Strophomena rhomboidalis Spirifer Albapinensis. Spirifer centronatus. - Rhynchonella pustulosa. Euomphalus Utahensis. Euomphalus Ophirensis. Michelina sp.? Zaphrentis sp.? In addition to these, from a ridge above and between Dry and East canons, in a fine-grained, dark limestone, Professor Clayton obtained some of these species, and— Proétus peroccidens. Orthis resupinata. Luomphalus latus, var. laxus. 198 SYSTEMATIC GEOLOGY. Twelve hundred feet higher stratigraphically, Professor Clayton found — Trematopora. Fenestella. Polypora. And still higher geologically — Productus levicostus. Productus elegans. Productus semireticulatus. Productus Flemingi, var. Burlingtonensis. Spirifer striatus. Spirifer setiger. Spirifer Leidyi. Athyris subquadrata. From the head of Ophir canon, near the divide, were obtained — Streptorhynchus robusta. Chonetes granulifera. Spirifer opimus. Rhynchonella Osagensis. The crest of the range, between East Canton and North Cafion, shows the remarkable intercalations of quartzites and limestones of the Tim-pan- o-gos horizon, abounding in casts of Productus prattenianus and Spirifer opimus. Although the upper limit of the Wahsatch body is here defined by the Weber quartzite above the Tim-pan-o-gos horizon, the bottom is nowhere definitely shown. It is needless to amplify localities of the sub- Carboniferous or Waverly fossils in the Oquirrh. Suffice it to say that the whole condition described in the Wahsatch—the intercalations of the Tim- pan-o-gos horizon with their characteristic forms, the 5,000 feet of varied Coal Measure forms down to the sub-Carboniferous, and the occurrence of the Waverly level—is here thoroughly displayed. So also are the persist- ent siliceous zones which are near the upper part of the series, but still below the intercalated Tim-pan-o-gos level. Near Black Rock, enclosed in limestones carrying Productus semireticulatus, Productus prattenianus, PALAZOZOIC EXPOSURES. 199 Streptorhynchus crenistrea, Spirifer opimus, Fenestella, Polypora, and Trema- topora, is a peculiar bed of white sandstone made up of rounded grains of limpid quartz differing entirely from the ordinary vitreous beds which are the characteristic intercalations of the Wahsatch. From the very north- western foot-hills of the range were obtained — Chonetes granulifera. Productus Nebrascensis. Productus longispinus. Martinea lineata. Athyris subtilita. A feature of the Wahsatch limestone not recognized by us in Wah- satch Range is the occurrence of beds of black, waxy shales, which are found at one or two horizons: one a small development just below the Waverly horizon, which may possibly correspond to the Devonian shales of White Pine; another appearing at the horizon of the Mono Mine, higher in the series. These shales are made up of black magnesian clay of ex- cessive fineness, which is also strongly charged with limy material. Upon Aqui Range is seen a long, continuous outcrop of heavy beds of limestone, extending from the northern extremity of the range to the south- ern limit of our map. From its thickness and physical character this has been referred to the Wahsatch, although the only recognizable fossil is a Zaphrentis multilamella. Stansbury Island isa sharp, steep anticlinal of dark limestones, dipping about 75° both east and west, with a north-and-south strike. The lime- stones are rich in Zaphrentis Stansburyi and Euomphalus subplanus. Along the eastern base of the island are considerable bodies of quartzite, conform- ably overlying the limestones, but themselves much obscured by soil. They have been referred to the Weber from their extent, but may possibly represent the siliceous beds of the Tim-pan-o-gos horizon. Bordering Great Salt Lake along the western side, and outcropping here and there through the Quaternary and Lower Quaternary beds of the desert, are isolated rocky hills, often rising to a considerable height, and for the most part com- posed of beds of dark, more or less siliceous limestone, capped in places by 200 SYSTEMATIC GEOLOGY. bodies of quartzite and somewhat masked by Tertiary voleanie rocks. Car- rington, Hat, Dolphin, and Gunnison’s islands, Strong’s Knob, and the Lake- side Mountains, with four insular masses to the west and two considerable bodies of the Rocky Hills, together with Cedar Mountain and the little lime- stone buttes to the west, are all referred by us, from such scanty evidence as we could obtain, to the Wahsatch limestone. They are in general dark siliceous limestones, carrying Coal Measure fossils, usually of the species which predominate in the Wahsatch. The evidence on which they are re- ferred will be found in Volume II. For our present purposes they are only of value as indicating the continuity of the sheet to the west. Both the Ibenpah Mountains and the high ridge of Gosiute Range, culminating in Lookout Peak, a summit reaching 9,695 feet, display large masses of Wah- satch limestone. At the latter locality are shown fully 4,000 feet of dark limestone series. Highly altered specimens of Productus, not specifically recognizable, associated with crinoid stems, were the only organic remains found. At the south end of Peoquop Range and its connected body which culminates in Spruce Mountain, is seen a great area of varied limestones, for the most part dark-blue and dark-grayish-blue, and containing several interealations of siliceous and earthy impurities. Near the summit of Spruce Mountain were obtained — Productus costatus. Productus semireticulatus. Productus Nebrascensis. Eumetria punctilifera. From the ridge directly north of the peak and from several other localities were obtained Productus Nebrascensis and Fusilina cylindrica, together with large crinoid stems, pentangular disks, and the delicate form of an undeter- mined Trematopora. From several localities of the lower Peoquop to the east of Spruce Mountain were collected Athyris subtilita and Fusilina cylindrica. Here in the Peoquop are certainly between 3,000 and 4,000 feet of these heavily bedded limestones containing Coal Measure fossils, but the PALZOZOIO EXPOSURES. 201 series is nowhere deeply enough exposed to arrive at the Devonian beds, nor high enough to show the overlying Weber quartzites. North of the Humboldt, in Tucubits Range, Wahsatch limestone is developed on a line extending from Tulasco Peak northwesterly for about twenty-five miles, and in topographical breadth the belt varies from three to four miles. The crest of Tucubits Range is formed of heavy masses of quartzite, referred to the Weber. Beneath these the dark limestones are particularly well exposed in Emigrant Canon and all along the western base of the range, especially at the South Fork of Forellen Creek. The beds have a gentle dip of 20° to 25° northward, while they strike a little west of the trend of the range, and consequently lower and lower limestones are ex- posed in passing southward. Near the mouth of Emigrant Cafion the beds stand at a steep angle, in some cases as high as 45° or 50°, and show ample evidence of local faulting. In a little ravine entering Emigrant Canon from the south is evidence of a northwest-and-southeast fault, of which the up- throw has been upon the eastern side, the eastern beds bending down steeply at the faulting-plane. A short distance above this, and east of the fault, at a point very near the base of the limestone, are exposed beds of calcareous shales several hundred feet thick. Above these are 300 feet of light-gray limestone, overlaid by 100 feet of yellowish calcareous shales, and above these 100 feet of black, thinly laminated, calcareous shales abounding in fossils; above these again 200 feet of dark-gray limestone, followed by the ordinary heavily bedded blue limestone for 1,500 or 1,600 feet. From the black shales above mentioned were obtained the following fossils of the Upper Helderberg horizon : Orthis multistriata. Orthis n. sp. Spirifer Vanuxemi. Atrypa reticularis. Cryptonella (fragment). Crania sp.? The cation slopes above this point are in general too much covered with detritus to afford continuous sections, but from the frequent intervals of limestone outcrops, and the absence of all others, it is clear that there 202 SYSTEMATIC GEOLOGY. ~ are 4,000 or 5,000 feet of consecutive beds showing toward the upper part a high proportion of shales, which are generally of light colors. Near the upper limits of the cafion is an outcrop of 500 feet of calcareous shales, weathering very yellow, and overlaid by light-drab limestones which pass into blue and siliceous limestones, carrying seams of calcite and crystals of pyrites. Conformably above, although the contact is obscured by soil, are seen heavy masses of Weber quartzite, which extend eastward and compose the whole summit and eastern slopes of the range. At the southern edge of the belt, at Tulasco Peak, in a little ravine running northwest from the summit, were obtained several Coal Measure fossils, among which were the following: Spirifer cameratus. Spirifer Kentuckensis Athyris subtilita. Pseudomonotis radialis. Pseudomonotis sp.? Dentalium Meekianum. Chatetes. Fenestella. Trematopora. These beds are almost in contact with the overlying Weber quartzites, and their peculiar position with regard to the rest of the range is probably solvable by a system of faults, some of which have been clearly observed. Their facies is higher than the usual Coal Measure horizons of the Wah- satch limestone, and represents the very uppermost limit in their longitude. The Waverly horizon was not here observed, but it is clear that the Upper Helderberg fossils occur in a horizon not far from the bottom of the Wah- satch limestone, and are overlaid by 5,000 feet which contain at intervals true Coal Measure forms, although the beds closely overlying the Helder- berg, in which we might expect to find both the sub-Carboniferous and the Waverly, are here, so far as our observations go, entirely barren of fossils. In the little fragment of gray siliceous limestone which rests uncon- formably upon the granite of the Wachoe Mountains at Castle Peak, were PALZOZOIC EXPOSURES. 203 found Productus sub-horridus and Athyris Roissyi. Southward, in continua- tion of the same uplift, at the northern extremity of Antelope Hills, two inconsiderable masses of limestone rise above the general field of rhyolite, ~ and show alternation of limestones and siliceous and argillaceous limy shales, characteristic of the upper middle part of the Wahsatch limestone. From the Egan Mountains north of our southern limit, with the excep- tion of a small body of rhyolite which, in the northern end of the range, north of Mahogany Peak, breaks through the limestones, the range is com- posed of the Wahsatch body. At Mahogany Peak were obtained — Productus multistriatus. Productus sub-horridus. Athyris subtilita, var. Roissyt. From Gosiute Peak were obtained Productus punctatus and a fragment of Campophyllum, and still farther down an undeterminable species of Diphyphyllum. The facies of the fossils, and the great thickness of the limestone exposed—not less than 4,000 feet—refer this great ridge un- questionably to the Wahsatch; and although the lower members of the series are not reached, the occurrence of Silurian a little farther to the south in the range suggests the desirableness of further search for the Waverly and Helderberg beds by whoever shall explore south of our limit. The Ruby group, which lies between Egan Range and Ruby Valley, exposes a considerable thickness of heavy drab, cream-colored, and blue limestones, undoubtedly of the same series as Egan Range, although they represent, both lithologically and by their fossil remains, higher members than are seen on thatrange. Among the collection made were the follow- ing Lower Coal Measure forms: Productus multistriatus. Productus semireticulatus. Productus Nevadensis. Spirifer pulchra. Athyris subtilita. Athyris Roissyi. From Frémont’s Pass south to Hastings’s Pass the entire Humboldt 204. SYSTEMATIC GEOLOGY. range is made up of conformable rocks dipping to the east, having about 1,000 feet of quartzite, referred to the Ogden group at the base of the series, and skirting the foot-hills on the western side of the range. Above this, and forming the whole body of the range and its eastern slope, is a superb exposure of Wahsatch limestone, between 6,500 and 7,500 feet in thick- ness. The average dip of this whole body is from 16° to 20° eastward, increasing to the south to as much as 25°. The eastern slope in the region of Ruby Lake is scored by remarkable narrow, deep canons, with abrupt walls, nearly perpendicular, reaching 1,400 or 1,800 feet in height. Plate XI. illustrates one of these sharp cuts in the Wahsatch limestone. At the northern end of the exposure the limestones come directly in contact with the granite and gradually rise to a vertical position, tailing out to the north as a mere narrow blade of beds on edge. On the high peak back of Cave Creek the dip is only 16°; farther south it becomes nearly horizontal, but rises rapidly again north of Hastings’s and east of Fort Ruby, where it reaches an angle of 16° and 20°, inclined to the northeast. While as a whole the ridge is an easterly dipping mass, it will be seen that it describes a slight curve, with convexity to the west, and the extreme ends of the curve dip slightly toward each other. This is only one of those instances of curved strike so frequent in the Basin ridges The Wahsatch group is unmistakably conformable with the quartzites below, and the transition between the two rocks is made in very short distances, without any noticeable intercalation of beds. As they approach each other, the-quartzites become slightly caleare- ous, and the limestones somewhat siliceous, yet the line of demarkation can be easily observed. The lower limestones, for about 1,500 feet, are of light grays and buffs, interrupted by a few dark-blue strata. Above this the bed- ding becomes heavier, the limestones darker, and there are more intercala- tions of shaly material. On the eastern base there is a great deal of unimportant siliceous interstratification, and not a little buff, shaly lime- stone. As a whole, from bottom to top, the 6,000 or 7,000 feet are essentially a limestone, only varied by small proportions of clay and sand. Midway are some beds which are purely dolomitic. One of these saccharoidal magnesian stones, taken from about the middle of the series, was analyzed, and its result will be found in the tables of analyses of stratified rocks. at ot PALMOZOIC EXPOSURES. 205 Scattered through the higher members are fragments of recognizable Coal Measure fossils; but the lower members have yielded only stems of Cyathophylloid corals and a few badly preserved S'pirifers. The only identifiable fossil species obtained are in the horizons of the Coal Measure forms: Chonetes granulifera. Productus Nebrascensis. Fusilina cylindrica. Although faithful search was made at several points through the lower members of the series, no fossils were found, owing to the somewhat altered condition of the strata. Where the main South Fork of Humboldt River flows out from its cafon on the western slope of Humboldt Range, north of Frémont’s Pass, the Archean mass projects westward in a bold prom- ontory. Around its western base is wrapped a series, about 4,000 feet thick, of limestone, overlaid to the north, west, and south by the horizontal Pliocene strata. They describe a crescent-curved strike, and dip normally outward at angles of about 25°. Near the bottom is a slight exposure of conformable quartzite, which is assumed to be the top of the Ogden. The first 1,800 feet are of a prevailing light color, with shades of gray and buff, but mostly covered with earth and débris and yielding no fossils. Above these comes a dense, blue-black limestone, containing the following species : Productus semireticulatus. Productus longispinus. Fusilina cylindrica. Camarophoria. Farther north, in the region of Sacred Pass, the upper members of the series yield— Syringopora multattenuata. Productus costatus. Athyris subtilita. White Pine Mountains, a group culminating about thirty miles south of 206 SYSTEMATIC GEOLOGY. our southern limit, were visited by several members of the Expedition in the prosecution of mining studies. Here is obtained, though not an entire section of the Wahsatch limestone, decidedly the most important one in western Nevada. The base of the series passes under the Quaternary accu- mulation of a mountain valley, and its lower geological boundary is there- fore not determined. Nor is the upper limit of the series obtained, but a body of 5,000 feet is exposed, which near the base has the most interesting lithological sequence of beds, each charged with characteristic fossils illus- trating the complete passage from the Devonian through the Waverly and sub-Carboniferous into the Coal Measures. On Treasure Hill are actually exposed about 1,500 feet of blue limestones, all dipping to the east. The upper 800 feet of these offer conclusive evidence of Devonian age. The species obtained from these Devonian strata have been determined by Hall and Whitfield to range from the Upper Helderberg to the summit of the Chemung. Among them are the following: Cladopora prolifica. Diphyphyllum fasciculum. Acervularia pentagona. Ptychophyllum infundibulum. Naticopsis sp.? Orthoceras Kingii. Strophodonta Canace. Productus subaculeatus. Atrypa reticularis. Rhynchonella Emmonsi. Pentamerus sp.? Spirifera argentaria Cryptonella Rensellaria. Orthis sp.? (resembles O. resupinata). Spirifera sp.? (resembles S. striatus). Paracyclas peroccidens. Bellerophon Neleus. Isoneima sp.? PALMOZOIC EXPOSURES. 207 The section from Babylon Hill included— Syringopora Maclurit ? Smithia Hennahit. Favosites sp.? Atrypa reticularis. Rhynchonella Emmonsi. Pentamerus sp.? Orthoceras sp.? Pterinea sp.? The only forms obtained from Mount Argyle belong to corals. Although they are mostly fragments, Professor Meek has identified the following: Alveolites multiseptatus. Cladopora prolifica. Smithia Hennahii. Dyphyphyllum fasciculum. From the Blue Ridge, in the top of the series, we have — Spirifera Engelmanni. Productus subaculeatus. Pleurotomaria sp.? Above these limestones is a series of calcareous shales, which so far have yielded no fossils. But in the siliceous limestone which directly overlies them were found, upon Telegraph Peak, stems of crinoide and Spirifer Albapinensis, new species of Hall and Whitfield. This specimen here underlies a stratum which clearly belongs to the Genesee slates, al- though in the Wahsatch it ranges up into a higher horizon and is associated with groups of Waverly fossils from Ogden and Logan cafons, which in themselves show certain distinct Devonian forms, yet at the same time present a general Waverly facies. Above this siliceous limestone, in per- fect conformity, is a series of 125 feet of black shales which form a well marked geological horizon at this locality, though they have not been dis- tinctly recognized elsewhere in the Great Basin. It is a peculiar outcrop at 208 SYSTEMATIO GEOLOGY. best, which will bring to the surface and preserve easily weathered shales, and they may well be supposed to exist in the Wahsatch limestone of the neighboring ranges, their narrow outcrops covered with earth or débris. As shown at White Pine, they are divided roughly into two distinct bodies. The lower group is more argillaceous, and the upper more arenaceous; but in general appearance they are strikingly similar, though a sharp division is indicated by the association of species. From the lower were obtained — Leiorhynchus quadricostatus, Hall. Aviculopecten catactus, Meek. Iunulicardium fragosum, Meek. Nuculites triangulatus, H. & W. Goniatites Kingii, H. & W. Orthoceras cessator, H. & W. From the upper beds we obtained — Streptorhynchus sp.? Spirifera sp.? (resembles S. disjuncta). Productus semireticulatus. The occurrence of Leiorhynchus quadricostatus, a form characteristic of the Genesee slates, in the lower member of the black shales, led Hall and Whitfield to regard the horizon as Devonian, while in the upper series the equally marked Spirifera, resembling S. disjuncta, was believed by them to mark the horizon of the sub-Carboniferous. The sandstones which directly overlie these shales contain only vegetable impressions, leaves and stems of Lepidodendron and Cordaites, and casts of crinoidal stems similar to those observed in the siliceous limestones below. Next above this the great body of blue limestone is abundantly furnished with distinct Coal Measure forms : Diphyphyllum subcespitosuar. Zaphrentis sp.% Streptorhynchus crenistria. Productus semireticulatus. Productus prattenianus. PALZOZOIC EXPOSURES. 209 Productus longispinus. Productus sp.? (resembles P. Wortheni). Productus Nebrascensis. Productus costatus. Spirifera camerata. Spirifera Rockymontana. Spirifera planoconvexa. Spiriferina spinosa Athyris subtilita. Athyris sinuata. Eumetria punctulifera. Terebratula sp. ? The value, therefore, of this White Pine section is in its illustration of the complete. passage from Upper Helderberg forms through Genesee into sub-Carboniferous and up into the Coal Measures. It is also seen that the Upper Helderberg has a range of several hundred feet. The same forms that were obtained by Mr. Hague from the Coal Measure limestones of White Pine recur in a cream-colored limestone at Railroad Canon. It is a mere block of the series, dislocated from any traceable connection with either mountain mass, and surrounded on all sides by deep valley Quaternary, or fields of basalt which overflow it toward the west. It yielded the follow- ing forms: Chetetes sp.? Streptorhynchus crassus. Productus semireticulatus. Productus prattenianus. Productus costatus. Spirifera Rockymontana, Spiriferina spinosa. South and west of Pifion Pass, in Pinon Range, lies a synelinal, of which the lowest members upon the western side are Silurian lime- stones. They do not come to the surface on the eastern side; but directly overlying the Ute-Pogonip body at Cave Creek is the Ogden quartzite, 14 k 210 SYSTEMATIC GEOLOGY. as before described, showing an exposure of about 800 feet. This curves under the synclinal and rises again, occupying the summit of Pition Pass. Held in the curve of the anticlinal are seen the lower 2,000 feet of the Wah- satch limestone. There is little intercalation at the region of contact between the Ogden and the overlying limestone, the latter beds resting sharply upon the laminated quartzites. The lower 1,200 feet of the Wahsatch are formed of gray, drab, and buff beds, with only occasional intercalations of the ordinary blackish-blue limestone. It is a very exact repetition of the same portion of the Wahsatch limestone in the neighboring Humboldt Range. From 800 to 1,200 feet up in the series the beds yield abundant Upper Helderberg forms. These limestones, never exposing over 2,500 feet, extend southward along the range as far as the southern limit of our map, forming, south of Fossil Pass, a singular monoclinal ridge, with a dip to the east. The 2,500 feet is a relic of erosion, all the overlying beds having been carried away. Upper Helderberg fossils recur at several points, although in one place there would seem to be a mingling of Upper and Lower Helderberg, but Hall and Whitfield decide that they might all occur in Devonian beds; and this decision is sustained by the presence of Lower Helderberg below the Ogden quartzite. Near Hot Spring Creek the limestones furnish the following forms : Dalmania sp.? (closely resembles D. anchiops from Schoharie group, New York). Edmondia Pinonensis (associated on thesame block with Chonetes and Spirifer). Orthis oblata. Orthis sp.? (resembles O. quadrans). Strophodonta sp. ? Spirifer Pinonensis. Spirifer sp.? (resembles S. arimosa). Atrypa reticularis. Rhynchonella sp.? Several of these species recur near Fossil Pass, on the summit of the range. PALMOZOIC EXPOSURES. 211 Nearly due east from Chimney Station, on the eastern side of the range, were found a few fossils, among them: Zaphrentis sp.? (figured by Prof. Meek). Favosites sp.? Cladopora sp.? Spirifera sp.? Besides these, there were corals not specifically identifiable, but closely related to Upper Helderberg forms. Mr. Engelmann, geologist of Colonel Simpson’s Expedition, obtained from Swallow Canon, in the same range, though south of our work, a col- lection of Devonian fossils, which have been described by Professor Meek. They embrace— Productus subaculeatus. Spirifer Utahensis. Spirifer Engelmann. Spirifer strigosus. Atrypa reticularis. All of these have been found by us in the Wahsatch limestone of White Pine and the northern Pinon. In the southern part of Seetoya Range, rising out of an immense mass of rhyolite, stands Nannie’s Peak, a granitic nucleus, which has a heavy body of Wahsatch limestone dipping from it in every direction; itis a long, oval quaquaversal, with the greatest elongation of granite lying north-and- south. The best section is seen on Coal Creek, where the strike is nearly east-and-west and the rocks dip to the south about 45°, exposing 2,000 feet of limestones, capped by a heavy bed of conglomerate that may possibly represent the base of the Weber. This locality is interesting because, about a mile from the mouth of the creek, and several hundred feet down from the highest exposure of rock, is a bed about fifteen feet in thickness of black carbonaceous material, passing in places into an impure anthracite coal. The section is as follows, beginning at the top: 1. Conglomerate, possibly the base of the Weber..--.------------ asp blueplimtestonos withishalosy f-/.<)2Se02 aoe os Foe eee oe boos ee 100 212 SYSTEMATIC GEOLOGY. Feet 3. Bluish-black, finely divided argillaceous shales .......--.-..--- 150 A Coal seam... 2.cto2 5. leas ste. be ne <6 oe eee er 15 5, -Bittminous shale: = ists 2e-ce-.. oe eee n 50 6. Gap (nosexp0sure)s...jcc 222. eee (se oer ee 100 (. (Blacksshale..: 255222 3c oe Seer eee 10 8. Argillaceous limestone. = 5.22222 222256 eas See ee er 50 9. Yellowish calcareous sliale.s.42a2---2 see eee eee 200 10. Drab siliceous limestone, with shaldce a2 32k se eee eee 200 11. Blue limestone, with seams of white calcite-....-...-.-.--.--- 50 12... Rusty quartzite... <2 3.1 ite Se oe eres ater arte ere 50 3. Compact blue fossiliferous limestone.........-..-.----------- 100 14. Blue limestone and shales 22 =... 52... ee ee ee eee eee eee 200 From below the coal were obtained the following Coal Measure fossils : Productus semireticulatus. Syringopora multatienuata. Cyathophylloid (fragments). Below the canon of the Humboldt, which opens into the valley of Carlin, south of the river the Weber quartzites, which at the mouth of the cafion stand nearly vertical, decline to the east, gradually reaching an angle of about 40°. Quite conformably under them lies the Wahsatch limestone, presenting its edges to the valley, which cuts directly across the strike. In rising the hill the limestones quickly pass under overlying volcanic rocks, and the exposure is confined to the foot-hills immediately bordering the river. Here the limestones are seen to be exceedingly impure, varied with both slaty and sandy material, and to show traces of considerable compression and alteration. Not far from the top (the actual distance could not be determined) are beds of black carbonaceous shales, passing at times into the same impure anthracite which has been opened at Coal Creek. Mining here has also been actually begun on the carbonaceous streak. There are stems of Lepidodendron and obscure vegetable impressions in these shales. Farther down, the limestones are again pure, and contain the well known association of several species of Productus and the ordinary corals of the Coal Measures. PALAOZOIC EXPOSURES. Die Weser Quarrzire.—Wherever in Oquirrh Range its complicated structure exposes the upper limit of Wahsatch limestone, it is seen to pass by a series of interealations of limestone and quartzite, characteristic of the Tim-pan-o-gos horizon, into Weber quartzite. The latter body is ex- posed over fully half of the range, and in the north, at Connor’s Peak, is again overlaid by the limestones of the Upper Coal Measures. The exact thickness exposed cannot possibly be arrived at, owing to the faulted con- dition of the country. It is magnificently shown in the region of Bingham Canon, where is exposed certainly as great a thickness as is seen in the Wahsatch, and probably a much greater one, approximating to the depth of the same series in the Uinta. The Tim-pan-o-gos horizon is finely shown at Soldier Canon. Far more than the limestones, the quartzites are liable to angular, fragmentary disintegration, and the surface of all the quartzite slopes is much more covered and masked by débris than that of the lime- stones; hence the structure-lines are much better made out in the under- lying and overlying limestones. The greatest quartzite display is in the region of Bingham Carion and to the south as far as the mouth of North Canon. The structure throughout this region is subject to extremely sud- den changes, involving great complications and fractures. The general section exposed in Bingham Cation shows a synclinal fold, whose western members are short and abrupt, the axis of the fold being depressed toward the north. Owing to the irregularity of the structure, it is impossible here to arrive at the thickness, but it cannot be less than 6,000 or 7,000 feet. In these quartzites Professor Clayton, nearly always successful in his search for fossils, obtained the following forms: Archaocidaris n. sp. Martinia lineata. Polypora. Crinoid columns. Here is an instance in which distinctly Coal Measure forms are found in Weber quartzite, and where this is seen overlying Wahsatch limestone. The reader will remember, in the Uinta, my mention of the two Coal Measure forms which we found in the débris of the quartzite in the heart 214 SYSTEMATIC GEOLOGY. of that range. There was an instance in which the fossils were obtained in the quartzite underlying the Upper Coal Measure limestones. The Bingham find, which is free from all doubts, lends probability to the fragmentary data of the Uinta. These two occurrences of organic forms in this wonderful body of quartzite add the final link of proof of its age. In the section of Weber Canon the quartzites are seen distinctly enclosed between the two great Coal Measure limestone bodies, without a shadow of doubt as to the position; and now in two localities Coal Measure fossils have been found in the quartzite. After this we conceive there can be no dispute as to the age of this member of the Paleozoic. In the region of Connor’s Peak the synclinal already mentioned at Bingham Canon is again seen, although near the summit of the peak the upper beds only of the Weber quartzite are exposed, overlaid by blue siliceous limestones and soft, earthy lime beds of the Upper Coal Measures, containing poorly preserved specimens of Spirifer and Productus. Important masses of Weber quartzite are seen in Stockton Hills, on the eastern base of Aqui Mountains, in Cedar Mountains, among the Lakeside group, and on Stansbury Island. Otherwise the Salt Lake Basin and the hills which skirt it within the limits of our map are composed of no higher members than the middle portion of the Wahsatch limestone. If the reader will refer to Map IV. of the geological series, he will observe that the southern portion of the lower half is composed of ridges of Wahsatch limestone and rhyolite, surrounded by fields of Quaternary. Northward, however, he will observe that the upper half of the map is char- acterized by a very small occurrence of Wahsatch limestone, and by the prominence of Weber quartzite and overlying Coal Measures, and that only in Tucubits Range is there any considerable occurrence of Wahsatch limestone along the northern part of the map. The Gosiute, Peoquop, and Little Cedar Mountains, the Toano group, Fountain Head Hills, and much of the Tucubits show considerable bodies of Weber quartz- ite. Upon the Tucubits it is seen conformably overlying the enormous development of Wahsatch limestone. On the other hand, in all other ranges—Little Cedar, Peoquop, Ombe, Toano, and Gosiute—the quartzite, the lowest rock, is seen to be overlaid by heavy bodies of gray and blue PALHOZOIC EXPOSURES. 215 limestone, varied with certain argillaceous and sandy zones, and carrying fossils of the Upper Coal Measure series, to the very base, absolutely in con- tact with the quartzite. Such is the faulted and disturbed position, and such the irregularity of the quartzite outcrops, that in this section no correct idea of their thickness can be obtained. On the Tucubits and Fountain Head Hills there cannot be less than 6,000 or 7,000 feet. The other exposures display much less. The quartzites so far do not yield any fossil forms in this region. The point of interest to us is the persistence of this vast bed of quartzite, and the fact of the stratigraphical parallelism with the Weber section. One of the finest exposures of Weber quartzite in this region is that of Pilot Peak, Ombe Range. Directly south of Patterson Pass a body of quartz- ite is seen to rest nonconformably upon the granites of the pass, and to oc- cupy the entire ridge down to Pilot Peak. This body is composed of beds of white quartzite, having rather a complicated structure, evidently sub- jected to great lateral compression, and accompanied with frequent local displacements In general, there is evidence of a synclinal and an anticlinal fold, their axes traced diagonally across the range. Pilot Peak itself is upon the anticlinal, the beds striking north 15° to 20° east, with a dip of 15°, the greater part of the rock mass inclining to the southeast. Along the east- ern face of the mountain is seen a precipitous section of the quartzite edges, displaying about 7,000 feet. Lithologically it presents no very great varia- tion. It is all rather heavily bedded, with distinctly marked divisional planes. Near the southern end of the body it has a prevailing bluish-gray or brownish-gray color, while on Pilot Peak it is pure snowy white, passing down into a deep bluish tinge, the lower beds being more or less feldspathic and interrupted by sheets of conglomerate, whose pebbles are formed of quartzite and jasper, evincing considerable compression and cracking. Here are interposed also a few thin sheets of silver-gray micaceous schists. There is nowhere a finer instance of the method of disintegration of quartzite bodies than is shown on the eastern slope, which is covered with huge cuboidal blocks of débris, indicating the ease with which it was shat- tered by frost. The summit region is characterized by open fissures or rents in the quartzite, with walls 200 or 300 feet deep. Subjected to analy- 216 SYSTEMATIC GEOLOGY. sis, the quartzite of this peak gave 94.93 per cent. of silica, .17 of water, with the remainder of alumina, lime, and the alkalies. At the southern end of this mountain mass the quartzites are conformably overlaid by gray limestones, from which, in close proximity to the quartzites, were obtained Productus punctatus and Spirifer cameratus; this relation serving to fix the age of the quartzite. In Fountain Head Hills is a wide display of quartzitic rocks, which are continuous westward aéross the saddle connecting that body with Tucubits Range, and sweep up to form the crest of the range and its eastern slope. The quartzite, as displayed in Fountain Head Hills, is a great bed of angular quartzitic conglomerate, a feature which to the west of this point is persistent across northern Nevada as far westward as the Paleozoic is known to continue. It is a medium-grained, sugary rock, made up of angular fragments of flints and cherts of various colors, in which black and red invariably predominate. The matrix is a yellowish-brown, iron-stained, saccharoidal quartz, having to the touch a peculiar earthy feeling. Under the microscope it is seen to contain a considerable propor- tion of minute crystals of calcite, the matrix being made up of both erypto- crystalline grains and rounded fragments of quartz. Near its northern end Tucubits Range is formed of beds of quartzite which conformably overlie Wahsatch limestone. Much of the quartzite is curiously banded with a cherty material, showing black and green colors. The whole of this ridge, and the country south of it overlying Tulasco Peak, are much covered with débris and dislocated blocks cf quartzite. Con- tinuous outcrops are never found of sufficient extent to permit a measure- ment of the thickness. South of Tulasco Peak the brecciated quartzites are again seen, full of grains of limpid quartz enclosed in the rough saccharoidal matrix, and singularly resembling certain forms of rhyolite. The brec- ciated quartzites here again contain an enormous amount of cherty frag- ments, brown and black, the matrix being more or less yellow-stained by oxyd of iron. The alumina proportion seems to rise in the brecciated region. At Middle Pass in Gosiute Range the lowest rock displayed is a small mass of granite, which occupies the pass itself. Directly to the north and south it is overlaid by Weber quartzite, which towers into hills 1,500 or PALAOZOIC EXPOSURES. PA ff 2,000 feet in height. Both north and south the quartzites are overlaid by the limestones of the Upper Coal Measures, carrying characteristic fossils nearly down to the contact between the two series, thereby clearly iden- tifying the Weber body. The quartzite here is mainly pure white, with bands showing bluish and gray sheets, with a few thinly bedded regions of almost jet-black jasper. It appears to be made up of two sizes of grains, metamorphosed and condensed into a compact rock. The microscope de- tects thin flakes of mica, sometimes aggregated into layers, and the quartz grains which have not lost their original outlines, although much flattened and compressed, show numerous fluid inclusions. Conglomerate beds appear in the Quartzite near Orford Peak, characterized by coarse sub- rounded pebbles of chert and flint, overlying a heavy mass of yellowish quartzite, the whole having a strike of north 28° to 30° east, dipping at an angle of 30° to the northwest. Overlying the conglomerate is a thin bed of dark, steel-gray quartzite. Upward the series rapidly rises into contact with the conformable limestones, which bear fossils of the Upper Carbon- iferous. River Range, north of Humboldt River, is for the most part made up of a long anticlinal of Weber quartzites, flanked on both sides by Pliocene valleys, and more or less interrupted and limited by bodies of rhyolites. At the extreme southern end, and near the north, occur the overlying lime- stones of the Upper Carboniferous. No very deep exposures of the quartz- ites were obtained in this region, not over 4,000 feet at the utmost. The deepest are seen at Penn Canon, where the structure is that of an anticlinal whose eastern member is almost perpendicular, while the main body of the range is formed of westerly dipping beds, with angles at the centre of the range of 10°, steepening to 25° on the western foot-hills. The lowest ex- posed strata show a considerable thickness of argillaceous schists and quartzites, which are overlaid by conglomerates, generally including a cer- tain proportion of angular cherty fragments, while the most prominent beds of all are the peculiar dark, angular conglomerates already mentioned. In the upper part of the series is an included bed of limestones underlying an upper series of conglomerates, which are apparently always rounded. The conformable overlying Upper Coal Measure limestones carry their charac- 218 SYSTEMATIC GEOLOGY. teristic fossils down to the point of contact, as will be seen when treating of that limestone. In close connection with the group of rhyolites which bounds River Range, are some finely angular conglomerate quartzites, con- taining a great number of grains and cryptocrystalline fragments of limpid quartz and angular chips of black and green chalcedony. Associated with these are peculiar striped felsitic rocks, interbedded with the quartzites, and having the appearance of felsitic tufas, contemporaneous with the Weber quartzite. In Osino Canion, where Humboldt River and the Pacific Railroad cross the end of Elko Range, is exposed a good section of steeply dipping quartz- ites and conglomerates, the latter of the angular chert-bearing member. The general structure is that of an anticlinal fold having a north-and-south strike, the beds being upturned at high angles. Here again the quartzites contain black carbonaceous seams. At Moleen Canon, a mile and a half below the upper mouth, may be seen the contact between the Upper Coal Measure limestones and the Weber quartzites. There is here an apparent nonconformity, the beds of lime- stone having a slighter dip than the quartzites; but this is probably due to a fault which is evidenced on the hills to the north and south. The upper- most observed beds of the Weber are formed of angular cherty conglom- erates, with saccharoidal siliceous cement, which is more or less mixed with feldspar fragments, and, as the microscope shows, with carbonate of lime. These angular conglomerates do not form the uppermost members of the series, and that is an additional argument in favor of an explanation of the discrepancy of angle at the contact by a fault, since the lower or angular conglomerates are brought into contact with the limestones. A further proof that the angular conglomerates are not the uppermost beds is shown at Mo- leen Peak, where the lower and northern foot-hills of the group are formed of Weber quartzite for 1,000 feet up the foot-hill slopes. Here the quartz: ites are of broad, heavy bedding, and of yellow, green, and purple colors, with a coarse texture, resembling that of the upper part of the Weber group on Mount Agassiz, Uinta Range. The quartzites enclose numerous beds of conglomerate of purple and green siliceous pebbles, which are never so angular as those of the lower members. The quartzitic conglomerates = | PALHOZOIC EXPOSURES. 219 are here conformably overlaid by the gray limestones of the Upper Coal Measures, which carry numerous fossils down to within a few feet of the contact with the Weber. As displayed in the upper portion of Seetoya Range, the Weber quartzite, which there conformably overlies about 4,000 feet of Wahsatch limestones, is interesting as illustrating the recurrence here of the Tim-pan- o-gos horizon, namely, the intercalation of upper limestone beds of the Wahsatch with the lower members of the Weber. At this horizon are numerous calcareous slates. Although between the upper limits of the quartzite, as displayed northwest of Seetoya Peak, and the body of rhyo- lites that forms the eastern base of the range, there are a few exposures of a limestone which overlies the Weber, no fossils were obtained, and there is uncertainty whether this is the Upper Coal Measure or the Wahsatch again faulted to the surface. An estimate of the thickness in this region would therefore be liable to serious error. The southern part of the Seetoya group shows an immense mass of Weber quartzites extending as far up as Mount Neva. It is of crystalline texture, containing more or less siliceous argillites, with cherty seams. One particular bed was noticeable for its wavy structure, accompanied with a plentiful inclusion of graphite. At Agate Pass, in Cortez Range, occurs a large body of quartzites with characteristic included angular chert conglomerates, which are only of interest as showing the remarkable persistence and thickness of this peculiar development of the Weber. There is not less than 3,000 feet of coarse, saccharoidal rock, of which the matrix is made up partly of quartz and partly of feldspar grains, with a considerable proportion of microscopical earbon- ate of lime. A singular feature of the rocks is the constant occurrence of small vugs lined with crystals of quartz and calcite. The siliceous pebbles here reach five or six inches in diameter and are partly well worn, rounded, littoral pebbles, and partly sharply angular fragments of similar cherts. The great mass of Shoshone Peak and the western foot-hills of the northern prolongation of Shoshone Range up to the Union Pacific Rail- road, are formed of a great body of quartzites, schists, and quartzitie argil- lites. Their prevailing strike is a little west of true north, with a dip of 35° 220 SYSTEMATIC GEOLOGY. to the east. They ure frequently finely laminated, and at the lower horizon, at the base of the quartzitic series, they pass into blue calcareous bands, with a little pure limestone, supposed to represent the Tim-pan-o-gos hori- zou. Within the lower limestones, near Argenta, in a limy schist, is a bed of carbonaceous shale which in places inclines to anthracite and has been actually mined for coal. The Shoshone mass itself shows an expansion of quartzites of sixteen miles, at right angles to the trend, and extend- ing for twenty miles on the strike-direction, the eastern foot-hills being covered with belts of rhyolite from two to five miles broad. These quartzites have a southerly and easterly, though chiefly easterly, dip The uppermost layers of the quartzite are compact and dark, interbedded with thin sheets of fine, fissile, argillaceous slates, which, after a gradual calcareous transition, are capped with beds of quite pure limestone. These beds yielded no fossils, and the whole series of argillaceous and calcareous rocks nowhere exceeds an exposure of 200 feet in thickness. As there is some uncertainty about the age of these rocks, and as the only clews are given by the bed of impure anthracite near Argenta, and, further, since the actual connection between the coal-bearing rocks of the northern foot-hills and the immense quartzitic exposure near Shoshone Peak cannot be proved to be free from faulting, we content ourselves with referring this to the Weber, on a basis of simple probability. In general, the great Shoshone body cannot be less than 10,000 feet thick, composed for the most part of dark quartzitie schists, with some beds of almost jetty-black chert, a few argillaceous seams, and a rather limited amount of conglomerate carrying the angular pebbles of chert, the whole dipping eastwardly, or from Reese River Valley. On the opposite or western side of the valley rises the isolated mass of Battle Mountain, which, with the exception of a few masses of limestone (one on the summit of Antler Peak, and another bordering the western side of the body), is composed of a similar series of quartzitic schists, which, although much disturbed and of varying angle, has a pretty general dip to the west. These two similar bodies face cach other on the two sides of Reese River Valley, standing in the position of a broad anticlinal. On the Shoshone side the overlying limestones amount to nothing strati- PALHOZOIC EXPOSURES. 221 graphically, and yield no fossils. In Battle Mountain the upper limestones, as exposed at the mouth of Willow Creek, yield Coal Measure forms down very close to their contact with the quartzite, and forms which are more allied to the Upper Coal Measures than to the Wahsatch limestones. For that reason the underlying quartzites, although of prodigious thickness, certainly not less than 10,000 feet, allowing then, even, for considerable reduplication of fault, are, with some doubt, referred to the Weber. This is the most westerly exposure of the series, and also the most western point of Paleozoic outcrop. Beyond this meridian, quite to the Sierra Nevada, the oldest fossiliferous rocks are Trias, which are seen to rest directly, with- out underlying conformable rocks, upon the Archzean. Upper Coat Merasures.—In the region of Great Salt Lake, as dis- played upon the western half of Map HI, there are no known outcrops of the Upper Carboniferous except im the single locality of Connor’s Peak, in the northern part of Oquirrh Range, where have been obtained a few Upper Coal Measure species in beds of gray limestone overlying the enormous thickness of Weber quartzite. Northwest of Salt Lake, and north of the map, is a large province chiefly made up of Weber quartzite, overlaid by limestones of the Upper Coal Measure series They make their appearance at the southern end of the Ombe Mountains, south of Pilot Peak, and at the town of Buel. So far as could be ob- served, they are quite conformable with the Weber quartzites. Among the most important localities, as illustrating the relation of the two series, are the hills both to the north and south of Toano Pass. Directly north of Fairview Peak the quartzites are seen to be conformably overlaid by limestones which dip to the northwest. From a cherty band near the top of the ridge the following Brachiopoda have been recognized— Productus Rogersi. Spirifer pulchra. From the limestones adjoining the cherty band were also obtained — Productus Nebrascensis. Spirifer crassus n. sp. Cascinium. 229 SYSTEMATIC GEOLOGY. Northwest of Montello Station, where the limestones directly overlie the quartzites — Spirifer pulchra and Productus Nebrascensis were collected, thus proving the limestones to belong to the upper series, and not to the Wahsatch. The rocks are largely of calcareous shales, gray and yellow, intercalated with beds of solid blue limestone. Higher in the series they seem to be more uniformly of the bluish-gray rock. Here and there appear a few beds which are exceedingly dark, almost black, the color being due, as the microscope shows, to the presence of carbon. In the group of hills northwest of Toano the limestones are altogether similar, though no fossils were discovered here. The upper limestone mem- bers are in general quite heavily bedded, and more or less seamed with white calcite. There is an intercalated bed of black siliceous limestone, hard enough to seratch glass, but effervescing freely with acids. The micro- scope shows it to be made up of fragments of angular and sub-rounded quartz, calcite, and opaque carbonaceous particles. Low in the series is quite a development of calcareous shales. South of Toano Pass the rocks in the region of Owl Valley and along the western half of the range are formed of easterly dipping Weber quartzite, conformably overlaid by a body of limestone showing not less than 1,500 or 1,600 feet in thick- ness. Near the base of the series, intercalated in the limestone, is a body of quartzite about 250 feet thick. The overlying limestones con- tain indistinct impressions of Spirifer and Productus. South of Middle Pass, at Pine Mountain, the quartzites are again overlaid by a westerly dipping body of limestone, which yielded Spirifer opimus and Athyris subtilita, both forms common to the two bodies of Coal Measure lime- stones. In Peoquop Range, directly south of Peoquop Pass, is a fine exposure of Upper Coal Measure limestones, conformably overlying the Weber. On the western side of the range, they have a dip in general to the west, though directly to the south of the pass they describe a broad curve and reach a northeasterly dip. Immediately above the quartzites the lower beds of limestone yield — PALMOZOIC EXPOSURES. 223 Producius semireticulatus. Spirifer cameratus. Discina sp.? Orford Peak, the high summit southeast of this pass, which reaches an elevation of 7,556 feet, carries upon its crest a body of limestone isolated from the main mass, and probably thrown up by dislocation and not alto- gether eroded off. It is only 150 to 200 feet in thickness, and directly and conformably overlies the Weber quartzite. It contains — Athyris carbonaria. Productus semireticulatus. Productus punctatus. Productus Nebrascensis. Productus longispinus. Spirifer cameratus. Athyris subtilita. Athyris Roissy. Associated with these were corals of the genus Campophyllum. Through- out the limestones of the northern end of the Peoquop are frequent inter- stratifications of cherty material, often carrying nodular concretions of flint and banded strata of exceedingly fine-grained cherts, with narrow bands of chalcedony. When treated with acids, the most siliceous specimens give a slight reaction for carbonate of lime. North of Independence Spring the limestones which extend south from the high mass of Euclid Peak conformably overlie the Weber quartzites and carry in their very lowest beds Productus semireticulatus, and bryozoa belonging to the genus Trematopora. South of Cedar Pass the Little Cedar Mountains are for the most part made up of heavy exposures of Weber quartzite, overlaid on the east by limestones of the Upper Coal Measure series, dipping to the east at angles varying from 10° to 22°, and passing under the shallow Quaternary deposit of the valley to form, with the westerly dipping limestones of the Peoquop, a synclinal. In this limestone were obtained several bryozoa, together with Productus sub-horridus. Insimilar but westerly dipping limestones on the 224 SYSTEMATIC GEOLOGY. western side of the range, still conformably overlying the quartzite, were found — Productus prattenianus. Athyris subtilita. Syringopora multattenuata. Chatetes sp.? On the summit of the ridge, a little north of Albion Peak, a fragment of the lowest beds of the limestone has been spared from the general erosion of the region. The limestone, when subjected to analysis, besides a small proportion of white quartz sand, showed the theoretical composition of dolo- mite. West of this point the region throwing most light on the Upper Coal Measure series is the neighborhood of Moleen Canon. The southern end of River Range, for a distance of twelve or thirteen miles northwest from Moleen Canon, shows the Upper Coal Measure limestones conformably overlying the Weber quartzite. They are composed here of a highly varied series of limestones, often earthy and marly, containing many zones of gray and yellow shales and some hard, heavy beds of black carbona- ceous limestone emitting a foetid odor when struck with the hammer. About four miles north of Moleen Canon were found, in close proximity to the contact-plane between the limestones and underlying Weber quartz- ites, Productus sub-horridus and Athyris subtilita. The Athyris was also ob- tained from the very uppermost members of the limestone, where they pass under the Quaternary of Humboldt Valley, showing a vertical range of about 1,000 feet. South of the river, at Moleen Peak, is a display of lime- stones overlying the Weber quartzite. The whole series has an inclination to the southeast of 5° to 8°. These two masses, the Moleen mass and the southern part of River Range, directly across the valley, have a similar dip, and between them there seems to be insufficient room for the other member of a fold. They are therefore regarded as parallel monoclinal uplifts, the result of dislocation. The conformable contact-plane between the limestones and the Weber quartzite is very distinct, and there are only the slightest intercalations. On the other hand, the upper members of the quartzite, especially the matrix of the conglomerate, contain a great deal of PALAOZOIC EXPOSURES. 995 ra carbonate of lime, and the lower members of the lime series are highly siliceous and more or less argillaceous. From 150 to 200 feet from the bottom were obtained — Productus sub-horridus. Productus symmetricus. About 300 feet higher in horizon — Productus sub-horridus. Athyris subtilita. Spirifer cameratus. Zaphrentis Stansburyi. And from a third horizon a little below the summit of the peak, say 1,200 feet above the quartzite, were obtained — Productus sub-horridus. Productus semireticulatus. Productus prattenianus. Productus symmetricus. Streptorhynchus crassus. Orthis carbonaria. Eumetria punctilifera. The extreme western point to which the Paleozoic series extends in our belt, as already mentioned under the head of ‘Weber Quartzite,” is the group of Battle Mountain. There, with apparent conformity, upon the summit of the great quartzite body on Antler Peak, is a mass of isolated limestones; but a little to the west and south the same strata recur inclined to the westward at dips of about 20°, well displayed upon Willow Creek, where they form a precipitous wall of 1,200 to 1,500 feet of dark-gray limestones, in places somewhat shaly. In the lowest exposures in Willow Canon were found the following Carboniferous forms : Productus semireticulatus, Productus prattenianus. Eumetria punctilifera. Athyris incrassata. 15 kK 226 SYSTEMATIC GEOLOGY. About 100 fect below the summit of the peak, and separated from the last locality by about 1,000 feet of limestone, the following fossils of entirely distinct generic forms were collected : Fusilina cylindrica. Spirifer pulchra. Campophyllum. The Upper Coal Measures, as a whole, over the Great Basin part of the Fortieth Parallel area, are a single body of limestones varying as to chemical purity and mode of stratification, reaching 1,600 or 1,800 feet in thickness. It rests conformably on the Weber quartzite, and in this region is the uppermost member of the Palzozoic series, the Permian never appear- ing west of the Wahsatch. Sh CEO Nhe: RECAPITULATION OF THE PALHOZOIC SERIES. Analytical Geological Map II. accompanying this chapter shows all the Paleozoic exposures within the Fortieth Parallel area. At a glance it will be seen that the Rocky Mountain region has only a very slight development of Paleozoic rocks, and they appear simply as the bordering foot-hills of the Archzan mountain masses. Between the eastern boundary of the work, in the neighborhood of longitude 104° and Wahsatch Range, the greater part of the surface of the country is so deeply covered with Mesozoic and Tertiary rocks that little is seen of the underlying Paleozoics. It is only in the great Uinta uplift that the low-lying rocks make their ap- pearance. It is quite clear, however, that, with the exception of the lofty insular Archean bodies at the east, the Palzeozoic forms a continuous sheet over the whole area beneath the later rocks. On the map accompanying this chapter the Archean and granite exposures are shown for the purpose of illustrating their relation to the Paleozoic series. In Wahsatch Range and in the series of desert ranges which lie to the west as far as longi- tude 117° 30’ there is no considerable mountain body without its exposure of Palzeozoic strata. In nearly all, the Archean rocks also come to the surface, and almost every mountain block is therefore an illus- tration of the relation of nonconformity subsisting between the two great groups. Within the Paleozoic there are no considerable passages of met- amorphism, no tendency to the formation of gneissoid rocks or erystal- line schists, such as are described by some authors in the Appalachian sys- tem. As already mentioned, the Paleozoic series are strictly conform- able, from the lowest Cambrian beds up to the top of the Upper Coal Measure limestones. Between this vast series and the group of shales and argillaceous limestones of Permo-Carboniferous age which close the Paleozoic age, there is little, if any, discrepancy of angle at the locali- 227 228 SYSTEMATIC GEOLOGY. ties observed by us, but there is a slight appearance of nonconformity by erosion. In the Wahsatch region the limestone surface seems to have been acted upon either by marine currents or by shore waves, result- ing in the production of gentle hollows, over which the fine muddy and shaly sediments of the Permo-Carboniferous were deposited with a slight nonconformity. Our observations are too limited to lay much stress upon this very trifling discordance. Below that horizon there is, however, no doubt of a strict parallelism over the whole area surveyed. The most remarkable feature of the section opened up by our labors is the very great thickness of the Paleozoic series from longitude 117° east- ward to and including Wahsatch and Uinta ranges, and the rapid thinning of the series from that longitude eastward to the Rocky Mountain zone. The entire series is not exposed in the most western longitudes. The deepest members of the Cambrian are not uncovered there, but the recognized members from the bottom of the Primordial limestone to the top of the Upper Coal Measures show a thickness even greater than in the Wahsatch section. Providing the Cambrian holds at the extreme west the same great volume that is displayed in Cottonwood Canon of the Wahsatch, the western Nevada section could hardly be less than 40,000 feet conformable. In the Wahsatch it is 32,000 feet. The Uinta only shows an imperfect ex- posure, nowhere reaching the bottom of the Weber quartzite, and the beds of the Rocky Mountain region with us have a maximum of only 1,200 feet. The great accumulations of sediment, therefore, lie between the east end of the Uinta and the western Paleozoic limit in middle Nevada. Between the Wahsatch section and that at the extreme west there are but slight differ- ences either in the character of the individual members of the Paleozoic or in the total thickness. The area of greatest sedimentation seems to have been from longitude 108° 30’ to 117° 30’. Referring to Analytical Geological Map I. accompanying the Archzean chapter, and observing the ideal section at the bottom of the map, the reader will perceive that the bed on which the Paleozoic series have been imposed was by no means a plain; on the contrary, it was a vast mountain system which had suffered submergence, and over which the Paleozoic sediment settled. One feature of importance is the fact that there is little RECAPITULATION OF PALZOZOIC. 229 or no tendency on the part of the sediments of a given horizon to follow the hill-slopes, but in all cases where observed they abut directly against them as if deposited in absolute horizontality. Owing to the very great height of these Archean ranges, reaching in one instance an abrupt cliff slope of 30,000 feet, the earlier sediments, those of the Cambrian and Silurian, must have been deposited chiefly in what were the valleys of the sub- merged Archzan mountain system. The base of the Cambrian is never seen. To the full section, as observed, there is therefore an unknown plus quantity to be added. All the Paleontological lines are drawn in conformity with the New York system, except that under the term Cambrian I include all the rocks from the lowermost Paleozoic exposures up to and including the whole of the Primordial. This is the line as drawn by Dana, the only difference between his system and mine being that, instead of making the Cambrian a part of the Silurian, I follow approximately the English nomenclature, and confine the Silurian to the region above the junction of the Quebec and the Primordial. Naturally the most imperfectly exposed of all the members of the series is the Cambrian group. Thus far, among the reported occurrences of the rocks of this horizon in the Cordilleras, the locality at the mouth of Big Cottonwood Carfion must remain as the finest example and the stratigraphical type. The lowest member—the Cottonwood slates, a group about 800 feet thick, which here rest upon highly metamorphic Archean schists—has thus far yielded no organic forms. Though searched by us with considerable care, it presented no indications of life. The rocks are dark blue, dark pur- ple, dark olive green, and blackish argillites, all highly siliceous, and as a group sharply defined from the light colored quartzitic schists which conform- - ably overlie them. This second group, by far the greatest of the whole Cam- brian series, is a continuous zone of schists which have a prevailing quartz- itic character though varied with a considerable amount of argillaceous mat- ter. It would seem to be the product of a fine-grained arkose formation, simply compressed into dense schists. From 8,000 to 9,000 feet thick, it has a general uniformity of lithological condition from bottom to top, except that in the region of Twin Peaks are some phlogopite schists and siliceous 230 SYSTEMATIC GEOLOGY. zones, carrying considerable muscovite. The phlogopite members recur in the Egan Cafion region The prevailing colors of this member are gray, greenish gray, drab, and pale brown; never dark colors. Conformably over- lying it are 2,500 to 3,000 feet of cream-color and salmon-color and white quartzites, and quartzo-felsites. Occasional sheets of conglomerate are seen in the quartzites not far below the summit of the Cambrian. These as dis- played in Ogden Cafion are of extreme interest. All the pebbles are much flattened, and not unfrequently they are welded together, squeezed into one another, having evidently become plastic when under great pressure. There is not a crack or divisional plane in these welded pebbles. The summit member is a thin series of green siliceous argillites, which are usually not more than 75 or 80 feet thick, and which, in different localities, carry in the lower part of the narrow group, fossils of Primordial types, and in the upper strata basal Quebec forms. In the region of the Wahsatch arid Oquirrh, this little group of argillaceous and sometimes calcareous shales holds the division-planes between Silurian and Cambrian. No organic forms have been found in the enormous quartzite series. In middle Nevada, where again the Cambrian series is displayed, a decided change is found to have occurred. The little shale zone has disappeared, and its place is taken by a body of dark, steel-gray and ashen-gray siliceous limestone, in- tercalated with repeated series of calcareous shales, the entire body of lime- stone being about 4,000 feet thick. The lower 2,000 contain abundant Primordial fossils, and the upper 2,000 Quebec and later Silurian forms to the top of the limestone. This limestone, called from its typical locality, Pogonip, is persistent over a considerable region of western Nevada, and its lower half always carries Primordial fauna. Only the top of the Cam- brian quartzite series is exposed in western Nevada. The true Potsdam sandstone, characteristic of the eastern region, and recurring with remark- able persistence through the Black Hills and parts of the eastern Rocky Mountain system, does not, as such, appear in the middle or western For- tieth Parallel area. Conformably underlying the beds of the Carboniferous limestone series of the Rocky Mountains is the same fine, gritty, red sand- stone which a little north of our map and in the Black Hills carries the Potsdam fossils. It is unmistakably the same stratum extending south- RECAPITULATION OF PALAOZOIC. 231 ward into the region of our work, but with us is quite devoid of fossils. From the Utah and Nevada Cambrian were obtained the following: Lingulepis Mera n. sp. Lingulepis ? minuta un. sp. Obolella discoidea n. sp. Obolella sp.? Kutorgina minutissima n. sp. Paradoxides? Nevadensis, Meek. Conocephalites (Ptychoparia) Kingi, Meek. Conocephalites (Pterocephalus) laticeps n. sp. Crepicephalus (Loganellus) anytus n. sp. Crepicephalus (Loganellus) Haguei n. sp. Crepicephalus (Loganellus) granulosus n. sp. Crepicephalus (Loganellus) maculosus un. sp. Crepicephalus (Loganellus) nitidus n. sp. Crepicephalus (Loganellus) simulator n. sp. Crepicephalus (Loganellus) unisulcatus n. sp. Crepicephalus (Bathyurus ?) angulatus n. sp. Chariocephalus tumifrons n. sp. Ptychaspis pustulosus n. sp. Dikellocephalus bilobatus n. sp. Dikellocephalus flabellifer n sp. Dikellocephalus multicinctus n. sp. Agnostus communis n. sp. Agnostus Neon n. sp. Agnostus prolongus n. sp. Agnostus tumidosus n. sp. In the Wahsatch region, overlying the narrow argillite zone, is a body of limestone varying from 1,000 to 2,000 feet thick, carrying Quebec fossils nearly to its summit. This Ute limestone in passing westward evi- dently merges into the greater Pogonip body, lime sediments having gone farther down into the Cambrian so as to include 2,000 feet of Primordial, which in the Wahsatch is occupied by the salmon-colored and white quartzites. 232 SYSTEMATIC GEOLOGY. The Silurian Ute limestone at its characteristic locality, Ute Peak, is a body about 2,000 feet thick, of gray siliceous limestones and calcareous shales, carrying Quebec fossils to within 60 or 75 feet of its base and within 150 feet of the summit At Ute Peak it is never metamorphosed to any considerable degree, and rarely shows even the most rudimentary form of crystallization. It is essentially an unaltered bed of variable lime and sandy sediment, in which the lime so far prevails as to give to the whole a general caleareous character. This group is persistent through the entire length of the Wahsatch, and is exposed at a great number of points. In the region of Cottonwood, where the strata are thrown into an extraordi- nary semicircular curve around a nucleus of granite, all the members of the Paleozoic are compressed to a very great degree. The Ute limestone is here only 1,000 feet thick and is essentially a bed of much shattered white marble, containing tremolite and fine quartzitic intercalations. In the eighty miles between Ute Peak and the Cottonwood region it is true that there is abundant room for great variation in the actual original volume of sediment. But it is also true that when subjected to extraordinary com- pression, and in passing into the crystalline form, there is a very great shrinkage in all limestones, and it is not at all improbable that the difference of thickness in the two localities named may be due purely to the effects of compression. A similar instance is observed in the limestone of the Laramie Hills. On the west flank, where it lies nearly horizontal and has never been much disturbed, the series is about 1,200 feet thick, while di- rectly across the range, where the limestones are highly crystalline and thrown into vertical position, the maximum thickness is inside of 800 feet. It is therefore probable that over the area of our map there was no very great original variation in the thickness of the Ute limestone. In the Wahsatch region no fossils were obtained from the actual summit of the group, but in the Wind River region, not far removed to the north and east, Comstock, while accompanying the Jones Expedition, observed a limestone comprising 200 feet of beds, carrying Quebec fossils, capped by 150 feet with forms characteristic of the Niagara. In the south- ern Wahsatch the group is too uniformly crystalline to yield fossils. In middle Nevada, however, in the region of White Pine, Eureka, Pinon, RECAPITULATION OF PALAOZOIC. 230 and Roberts Peak ranges, the great Pogonip limestone, whose lower half, as already described, is charged with Primordial fossils, contains in its upper 2,000 feet several Silurian horizons. The Quebec probably there occupies 1,500 feet. From Nevada and Ute Peak in the Wahsatch were obtained the following Quebec species: Lingulepis Ella n. sp. Lingulepis or Lingula sp.? Obolella sp.? Kutorgina sp. undet. Orthis Pogonipensis n. sp. Leptena melita n. sp. Strophomena Nemia n. sp. Porambonites obscurus n. sp. Ethynchonella sp.’ (fragments only). Ophileta complanata, var. nana, Meek. Euomphalus (Raphistoma) rotuliformis, Meek. Euomphalus (Raphistoma) trochiscus, Meek. Raphistoma acuta n. sp. Maclurea minima n. sp. Cyrtolites sinuatus n. sp. Fusispira compacta n. sp. Conocephalites subcoronatus un. sp. Crepicephalus (Loganellus) quadrans n. sp. Dikellocephalus gothicus n. sp. Dikellocephalus quadriceps n. sp. Dikellocephalus Wahsatchensis n. sp. Bathyurus Pogonipensis n. sp. Ceraurus ? sp.? Ogygia paraboloidalis n. sp. Ogygia producta n. sp. At Roberts Peak, about 300 feet from the top of the Pogonip series, were obtained the following Niagara forms : 234 SYSTEMATIC GEOLOGY. Cladopora, sp. (resembles C. seriata, Hall). Orthis (resembling O. hybrida, Dal., but larger). Atrypa reticularis, L. Atrypa (resembles A. nodostriata, Hall). Tilenus sp. undet. The very top of the Pogonip, almost in contact with the basal strata of the Ogden quartzite at Roberts Peak and White’s Ranch, has yielded the following fossils of the Lower Helderberg horizon : Favosites Helderbergia, Hall. Diphyphyllum n. sp.? Campophyllum (impressions only). Crinoidal columns. Small branching Bryozoa, too indistinct for generic determination. Crania sp. undet. Orthis multistriata, Hall. Orthis n. sp. (resembling young 0. oblata, Hall). Strophodonta punctulifera,? Con. (fragments only). = Spirifera Vanuxemi, Hall. Trematospira ? Collospira n. sp. (allied to C. imbricata, Hall). Atrypa reticularis, L. Rhynchonella, sp. undet. Pentamerus galeatus, Dal. (fragments only). Cryptonella sp.? (fragments only). The next overlying member of the series, the Ogden quartzite, is a remarkably persistent and singularly pure sheet of siliceous sediment, which has been in general compacted into a quartzite, and which is spread with remarkable evenness over the whole Palzeozoic area west of and including the Wahsatch. At its typical locality in Ogden Canon, Wahsatch Range, it is 1,200 or 1,400 feet in thickness; at Cottonwood Canon it is compressed to 1,000 feet, and where seen in middle Nevada varies from 8V0 to 900 feet. RECAPITULATION OF PALAOZOIC. 235 When examined under the microscope the individual grains of sediment can always be detected, and among the siliceous granules are crystals of carbonate of lime, a little uniformly distributed carbon, and particles of feldspar. In Ogden Canon it is bounded at the top and bottom by thin developments of greenish-gray argillites, and about the middle of the quartzite is a thin bed of white, slightly siliceous marble. No fossils have ever been found by us in this member. It is referred to the Devonian, because directly underlying it in the top of the Pogonip limestone are Lower Helderberg fossils having marked affinities also with the Upper Helderberg, and at the base of the Wahsatch limestone, directly in contact with the upper beds of the Ogden, occur plentiful Upper Helderberg forms. It therefore occupies the interval between the two Helderberg groups, covering the rocks of the Oriskany, Cauda-Galli, and Schoharie epochs. It is hardly possible, from the physical condition of the bed wherever seen, that any considerable organic forms can ever be found, and it is doubtful whether the precise upper limit of the Upper Silurian will ever be definitely arrived at in the Great Basin. The next member of the series, the great Wahsatch limestone, first appears in the Fortieth Parallel area in the Wahsatch. It is never seen by us east of that range. It is a single body of limestone about 7,000 feet in thickness, and holds its enormous volume with remarkable evenness wher- ever observed over Utah and Nevada. The passage between the Ogden quartzite and the Wahsatch limestone is very abrupt, without any con- siderable intercalations of quartzite and lime. The prevailing type of limestones throughout the whole series is dark and heavily bedded strata. Near the base, in western Nevada, are about 1,000 feet of gray and drab, slightly marly strata, and always about 1,000 feet from the top there is an intermixture of silica, amounting in some cases to distinct beds of sandstone or quartzite 100 feet. thick. In the region of this siliceous zone, which is never more than 1,200 feet from the top of the series, are also frequent earthy impurities, argillaceous and sandy. In the little quartzite intercala- tion alluded to is a quite persistent sheet of conglomerate, the pebbles being made of dark jaspers. At the top of the series its passage into the great Wahsatch quartzite is extremely variable. In Weber Canon the uppermost limestones are brick-red, and there are one or two unimportant intercala- 236 SYSTEMATIC GEOLOGY. tions of red sandstone with the lime beds, but the whole transition is made within 100 fect, and above that horizon stretches the enormous thickness of the Weber quartzite. On the other hand, in the Cottonwood region, more especially in the valley of Provo, on the heights of 'Tim-pan-o-gos Moun- tain, there is a full 1,000 feet of frequently repeated alternations of red- dish-blue limestone and quartzites. The transition, as observed in middle Nevada, is usually abrupt like that of the Ogden region, but north of the Humboldt are seen the Tim-pan-o-gos intercalations. The lower 1,400 feet of this group are distinctly Devonian, yielding fossils of the Upper Helder- berg, Chemung, and Genesee. From the Upper Helderberg were ob- tained — Alveolites multiseptatus, Meek. Cladopora prolifica, H. & W. Acervularia pentagona, Goldf., Meek. Smithia Hennahii Lourd., Meek. Diphyphyllum fasciculum, Meek. Ptychophyllum infundibulum, Meek. Naticopsis sp. undet. Orthoceras Kingii, Meek. From the upper members of the Devonian, ranging from the Upper Helderberg to the Chemung inclusive, were obtained — Favosites polymorpha, Goldf., Meek. Syringopora Macluri? Bill. Smithia Hennahii, Lourd., Meek. Cyathophyllum Palmeri, Meek. Strophodonta Canace, H. & W. Productus subaculeatus, Murch. Spirifera Albapinensis n. sp. Spirifera argentaria, Meek (very closely allied to S. zigzag, Hall). Spirifera Engelmanni, Meek. Atrypa reticularis, L. Rhynchonella Emmonsi n. sp. Pentamerus sp.? Cryptonella sp.? = Renselleria sp.? Meek. RECAPITULATION OF PALZOZOIC. 23% Paracyclas peroccidens n. sp. Pterinea sp.? Pleurotomaria sp. undet. Isoneima, sp.? Bellerophon Neleus n. sp. Orthoceras sp.? In a single instance, at White Pine, the Chemung is overlaid by black shales, the probable equivalent of the Genesee group, from which we col- lected the following: Leiorhynchus quadricostatus, Hall = Rhynch. (Leiorhynchus) papyra- ceous, Meek. Aviculopecten catactus, Meek. Nuculites triangulatus n. sp. Linulicardia fragosa = Posidonomya fragosa, Meek. The Chemung and Genesee beds are immediately followed, at the height of about 1,400 feet from the base of the Wahsatch, by a consider- able thickness, probably 300 or 400 feet, of dark, heavy limestones, car- rying fossils which have a close resemblance to the Waverly group, but which have perhaps a closer affinity with the Devonian. The list consists of the following species: Michelina sp.? Streptorhynchus equivalvis, Hall. Streptorhynchus inflatus, HW. & W. Strophomena rhomboidalis, Whal. Chonetes Loganensis n. sp. Productus sp.? (fragments only). Spirifera centronata, Winch. Spirifera Albapinensis n. sp. Athyris Claytoni n. sp. Athyris planosulcata? Phillips. Rhynchonella pustulosa? White. Terebratula Utah n. sp. Euomphalus (Straparollus) Utahensis n. sp. 238 SYSTEMATIC GEOLOGY. Euomphalus latus var. lavus, White. Euomphalus (Straparollus) Ophirensis n. sp. Proetus peroccidens n. sp. Proetus Loganensis u. sp. Directly above the Waverly, and altogether below a horizon 2,200 feet up in the series, are dark beds containing sub-Carboniferous forms, such as — Zaphrentis excentrica, Meek. Fenestella sp.? Polypora sp.? Glauconome sp.? Orthis resupinata, Mart.? Productus levicostatus, White? Productus semireticulatus, Mart. Productus elegans, N. & P.? Productus Flemingi var. Burlingtonensis, Hall. Spirifera striata, Mart. Spirifera setigera, Hall. Spirifera Keokuk, Hall. Spirifera sp.? (resembles S. imbrex, Hall). Athyris subquadrata, Hall. Sub-Carboniferous fossils are obtained in Oquirrh, Wahsatch, and White Pine ranges. From this horizon the upper 4,500 feet of Wahsatch limestone are char- acterized by abundant Coal Measure fossils. In middle Nevada, at several localities, principally at the Coal Mine Canon of River Range, in the hills south of Carlin Valley, and in the Pancake Mountains, from 500 to 800 feet down in the Wahsatch limestone, were observed one or two zones of carbonaceous material, almost anthracitic. They have been quite exten- sively prospected for coal, and the indications of a considerable coal flora are obtained. Stems of Lepidodendron and fragments of broad fronds have been collected. Up to this horizon from the bottom of the Cambrian, excepting the conglomerate beds, there are no indications whatever of shal- RECAPITULATION OF PALZOZOIC. 239 low water, or of those frequent oscillations of level which mark the corre- ponding horizons in the Appalachian Palzozoic.* The following Coal Measure forms were obtained from the Wahsatch limestone : Syringopora multattenuata, McChes. -.--...--.-----.-------------- 3? dnihostrotion Wreumeyt, Meek: 5252520552 2.6 5522225028 tee. one eo 32 Bophopnyuum proujenum, MeCChes.: 2522... 2.85 -.-eseesss5c-5 =. 1 LGN WAAR ISULLDSUC Ti, EEN RES SRE oe SO ead cd cod es toeaee ace 4 JAF NORAD DON CUGE DT GE, NING) 2a eee aea cia ses oe sicSa class < 6s sane see eee eee 3 Streptorhynchus robusta, H.---.-------- SER Da ET ee ane eae ns 1? Streptorhynchus crassus, Meek & W...-..-:.-2---2 2-22 -----22 4 Meckella striata-costata, Swallow.- =. «2 === Sas52ses-2- ee oe 1 Chonetes' granulifera, Owen 22sec teak 2 ae a ee if Productus longispinus S0We2- 522 +38 Sor ee eee 1 Productus multistriatus, Week .. 2.2. 2.52222 ao see oe te 2 RECAPITULATION OF PALZOZOIC. 243 PV OUUCLUS INCU ASCENSISY Mam mer ee eee =o. 5 2 22. ete eles Se See 2 IPT OOUCIUS PVOMCHIANUSS NOP Me nae s ess on sta ete Se Ly Lay 5) ERODUCTUS SDUNCLAUUS Marie tae oe 228 see 2 See ci Se Le old 2 Producius punctatus var. Rogerst, N. & PB... 2.2.5. .62 eee eee 2 eroductusssemicucuiaius., Marts. 22 2) 2000. seo ook ee ee ee 5 ET OMUCUES: SYMMEMGUSH MIG CHES. As\s's Soc oe te ok. Sons Sieee 2c bes 1 SUNT Cn Gd COMCNALIM MOM. 8 faye See ee OS ei aaa di SHOVEL G OUlonlecdimpetally 9. 8 7 vee. Scns cee hein seam Sais as 1? Spirifera Rockymontana, Marc., sp. opimus, H.......--.---.--. ------ 3 Srrvjerasp, resembles sp. lorbest, I.) a0: 2222s sa5 sees 45 eee 2 SUE CT UNCP IM CNLNCKENS(S GONUMISS ee: se ee ieee ee ee ere eee 1 SPUTISCriNde DULCIT Oe MCG Ks nee Sekt ee eee eee ee eo 4 JW OT UTAES UBD Aais. I EN ge eg e egeEe e e e e 3 MMC Ia PUNCH CVG, OOUM. 2222 2e a2 5 oe os eee es ob cee ee il PANINI SES UULEL ICG n tie letra se Le Poe Sie ee se SoS p58 i 7 PAIL MU MESHICOTSSUB evar tT eetars fe ee RN as eS oe ee aia eRe ere SB 1 LG YUCRONCHOLU LON. Manel: 3 ooo eaea co aces sna ot ee ae ee 1 IACONO Oem NICO Nessa ets toy: ee ae ee Se ee eS 2 1 PNEECUCI OMS [I omens ate Sa emcee or LN Oy oh ge te ps 1 INEECHLONOADCIISIViOLGs SLOVONS —S2 22. 2 Soc) loc.ko2 52 ese ne oa sae 1 ISCOQLOIEKHE a CONCAUGT CO ua” Sm enae ra tai c ee ae 1 icurophorus oplongus, Meeks = 0. 222 fs sete cece se ce nee eeetese 1 ICO USICUN TUS eC OKs te area etek ce Se yet ee ee 1 INCA CICS, ST0e Ce vee iy oN ne ay eR fs RA PTs Pte eek oe 4 a 1 Bellerophon carbonaria, Cox? (broad bands)......-..-.....-.------ 2 EHELONNOW SP. t: (SMOOUNLSP)) elses) wES oe Seed Boo Ue. 2 OrtROCeras: CreUurosinn, CeUNitZ aio <5 oe ce iain ows space eee ee aS 1 -The following is a list of species recognized in the upper beds, but not found below the Weber quartzite : Buslimearcylindyica, PIsCher= ; 150 SOA Ui Be PON meee ees ao ese or eee ee tegveddish-vellowssanstone 202 = erie ei ss ee se In the region of the Big Thompson, where the greatest thickness on the flanks of Colorado Range is exposed, the series consists of heavy beds of coarse and friable pink and brick-red arenaceous material, partly inter- rupted by conglomerates, partly so coarsely gritty as to conceal the trace of bedding, and partly again thickly accumulated strata of brick-red sand- stone, the middle region interrupted by red shales and clays, the whole closed by a series of pinkish, pinkish-gray, and yellowish-gray sandstones, the upper members containing several beds of pink and white gypsum and blue limestone. Taken as a whole, and with the exception of the gypsum and lime- stone beds, which nowhere within our field of observation exceed forty feet in thickness, it is essentially a sandstone series, for both clays and shales are exceedingly arenaceous, and the dominant color is a brick-red for the lower half of the series, and variable lighter reds, pinks, and yel- lowish reds for the upper half. While this division of color holds good in general, it is often varied by extremely brick-red, almost vermilion- colored beds appearing near the top, and light ones intercalated in the region of the heavy red lower strata. The position of the narrow blue limestone beds, as well as that of the gypsums, varies through the upper half of the series. Next to the red color, the most noticeable feature is a remarkably sharp, persistent cross-bedding, developing very fine flow-and- plunge structure with the most remarkable arrow-head sections, which is observed in the upper horizons, where the bedding appears heavy; but never, so far as we have observed, among those beds which come into im- 252 SYSTEMATIC GEOLOGY. mediate contact with the Archean. Zones of conglomerate in general are either confined to the lower members of the series or else to the near neigh- borhood of the Archean. The pebbles are rarely very large in this mate- rial, and are almost all siliceous. Besides the several well defined limestone beds, a few of the horizons of the upper and impure sandstones appear highly calcareous; rocks which in hand specimens would never be supposed to contain lime, giving a brisk effervescence when treated with dilute acid. A typical specimen of the red sandstone taken from the upper members of the Trias, near the entrance to Big Thompson Camon, is a fine-grained, friable rock, deep-red, with a laminated, almost shaly structure. It was subjected to chemical analysis, the results of which will be found in the table of analyses of sedimentary rocks. The analysis shows, besides the siliceous and ferruginous material of the normal sandstones, the presence of an unexpected amount of soluble carbonate, including some dolomite, with an inconsiderable mixture of arenaceous material. It is noteworthy that no sulphates are detected, although the formation immediately in the neigh- borhood bears beds of quite pure gypsum. Below these shaly beds occur deep-red strata, having a coarser grain and no traces of the lamination characteristic of the last-named specimen, which upon being treated with acids gave no indication of the soluble carbonates. Laminated red shales, from a horizon near the top of the Trias on Horse Creek, and interstratified between coarse sandstones, were found on examination to contain an amount of calcareous matter equivalent to that of the Big Thompson, together with a similar amount of dolomite. The narrow beds of limestone already noted occur sharply defined from the enclosing siliceous material. Under the microscope they of course do show a considerable percentage of angular quartz grains, but they are almost wholly of dolomitic limestone. In the region of the Chugwater they occupy a horizon very near the top of the Trias, the lower bed consisting of a some- what cherty material, and the upper of a characteristic bluish-white, sili- ceous dolomitic limestone. These limestone beds, although outcropping at intervals all the way from the Big Thompson to the Chugwater, do not seem to possess any considerable continuity, but occur at or about the same horizon at irregular intervals. The indications are that there were cessa- TRIASSIC. 253 tions of deposition of the siliceous material, and that the calcareous deposits were not in continuous sheets, but were gathered by the oceanic currents into limited areas, which in turn were buried by the succeeding sand-strata. Gypsum deposits characteristic of the red Triassie beds occur chiefly, if not altogether, in the upper half of the series, their irregular, lenticular masses occurring, as do the limestones, at intervals. The gypsum beds vary from two to twenty-five feet in thickness, the heavier masses occurring with a broad bedding, and thinning out from a point of maximum thickness in every direction. The sulphate occurs both massive-granular and highly crystalline, varying in color from a pure, dazzling white to a pinkish shade, according to the amount of ferruginous impurities. In general it appears as a streak of creamy whiteness in the bright red sand-strata, streaked and stained into a variety of pale pinkish and yellowish-pink shades. From the interesting locality at Red Valley, near the northern end of Laramie Hills, a specimen of gypsum gives nearly the characteristic formula, the analysis yielding — Sulphatewotelimene) Met cae ee eae oe ee (komtlal \ISEER Gy OE cola e, Nk AS Re rah ae tA ct ela an 21.21 SPIN EE le opener ey ane, Sere a nee eae 99.32 The Red-beds of Colorado Range have thus far yielded to our search no organic remains, saving obscure pieces of half-petrified, half-carbonized wood, which crumbles on exposure to the air, and displays no characteristic structure. The following are some of the more noticeable localities along the eastern base : Wherever along the eastern base of Colorado Range the strata of the ielined sedimentary series extend for any considerable distance westward toward the heart of the range, they are found to occupy an approximately horizontal position, showing that the rapid change of dip occurs very close to the eastern belt of foot-hill beds. An example of this rule is the recurve around the head of the Chugwater; but at the head of Bush Creek the upper valley, above the region of the Pliocene conglomerates, is occu- pied by a shallow basin of Trias, which rests, almost horizontally, directly upon the granite. The valley surface is entirely made up of the gypsiferous 254 SYSTEMATIC GEOLOGY. upper portion of the Trias, a large part of the basin being covered with irregular outcrops of gypsum. The strongest bed observed is about fifteen feet thick, of clear, pure-white sulphate, only stained by the contact with ferruginous enclosing rocks. Around the Chugwater promontory outcrops a Trias curve, standing at very high angles, with a rapidly varying dip. The beds slope from 61° to 55° on the north-and-south lines, and only 25° where they reach an east-and-west trend. In the region of Lodge-Pole and Horse creeks, where the beds stand at an extremely high angle, they are more compact, fine-grained, often shaly, with a great appearance of argillaceous material, the colors being deep red and reddish yellow. As with the underlying beds and the over- lying Cretaceous in this region of high dip, the whole series is actually thinner than where its inclination-angle is much lower, and this can hardly be due to a local thinning of all the conformable series. It is rather refera- ble to the shrinkage due to unusual disturbance and compression. Whoever has examined the slightly compacted modern sea-sands made up of the débris of marine Pliocene, especially when placed under the microscope at a low power, cannot fail to remember the large amount of interstitial space between the particles of quartz, sand, and sea-shell. It is evident from such observations that rough sandstones can lose fully forty per cent. of their volume without any compression of the quartzy material. In the more compacted sandstones the interstitial space is either entirely made up of infiltrated argillaceous and ferruginous matter, or obliterated by pressure. In the case of the older quartzites, the Cambrian particu- larly, the outline of the original granular quartz may often be traced, flat- tened to a long, lenticular form. In the case of the Archean quartz- ites, the figure of the original particle is altogether lost, and the entire mass shows a confused cryptocrystalline structure. It is not strange, then, that a series of beds exposed along a line of 100 miles, as is the Trias east of Granite Ridge, should suffer very great variations of thick- ness: first, from an irregular depth of original deposit; secondly, from the factor of compression. It is assumed to be a rule that in all cases of extremely high dip the volume of each member of the sedimentary TRIASSIC. 255 series is distinctly less than in cases of low dip; and the physical condi- tion of the rock is itself an evidence of this compression. Accordingly, when the gently dipping Trias sandstones of the Big Thompson region are compared with those near the head of Horse Creek, the dip, thick- uess, and actual petrological compactness are found to vary correspond- ingly. South of Box Elder Canon occurs another instance of a westward-ex- tending overlap of Trias resting directly in a depression of the Archzean in a nearly horizontal position, only dipping from 2° to 4° to the southeast. In direct contact with the granite is a considerable bed of reddish-gray conglomerate, overlaid by massively bedded red sandstones. This bed was nowhere recognized to the north, where it is possible that the Carboniferous always lay between it and the Archean, and the occurrence here is due to the immediate neighborhood of the Archean mass. From the Cache-la-Poudre to the southern edge of our map the forma- tion rapidly thickens and becomes correspondingly looser in texture. The series is defined in outcrop at the upper limit by the persistent, trough-like depression which separates the red Trias from the hard Dakota sandstone. On the Big Thompson the upper part of the Trias is characterized by the presence of several thin sheets of limestone, and in general the transition into the Jura is marked by a calcareous passage-member, mixed with varying sheets of sand, the whole having a thickness of about fifty feet. In this region the gypsum bed is about twenty-five feet thick, of nearly pure white erystalline-granular sulphate, interbedded with dark-red sandstones. The extremely gentle dip of the sedimentary formations on the western flank of the Archean mass of the range, renders the final surface, when beveled off by a uniform erosion, remarkably free from bold outcrops, so that the junction between the underlying grayish-blue limestones of the Upper Carboniferous and the Trias is often only discoverable by the change in the color of the earthy deposit which masks the more solid edges of the beds. Here and there at intervals are the limited escarpments of the red sandstone beds, with their bluff faces toward the range. At Red Buttes, near the Pacific Railroad, are the best exposures of the sandstone to be seen on the western slope. For some distance to the east and north of 256 SYSTEMATIC GEOLOGY. the railway station the sandstones, marls, and clays have been eroded by the local streams, showing cliffs and buttes which reach 100 feet of vertical exposure. The basal sandstones of the series rest directly upon the bluish and yellow Carboniferous limestones. These lowest Triassic beds are here rather pale reddish-yellow, and are characterized by the development of concentric red spots. They are formed of distinctly visible grains of quartz, held together by a calcareous and marly cement. There are several zones of pebbles, and the whole series is prevailingly and characteristically red, up to the very base of the Jurassic. South of the railroad the Triassic beds still maintain their gentle dip, and in the region of the track overlap the Carboniferous and pass into direct contact with the Archean. It is a noticeable fact that the Laramie Hills, or northern part of the range, are separated from the more elevated portion to the south by a depression marked by the northern waters of Cache-la-Poudre Creek, the pass extending across the whole range in a northwest-and-southeast direction. This continuous depression terminates on the western side exactly where the Trias overlaps the Carboniferous, while the eastern end of the depression comes at the head of Box Elder Creek, where also the Trias overlaps the Carboniferous and in a similar manner comes in contact with the Archean. This, to my mind, would suggest a pre-Cambrian displacement here which has depressed the whole northern part of the range, the depression making itself chiefly felt along the eastern base of the northern half. South of the railroad, on the western side, the contact of the Trias with the Archean is rather interesting. It is seen gradually to overlap the gentle inclinations in thin beds, and to abut squarely against the steeper slopes of the Archean. In general, it dips gently away from the Archean, the Trias ridges being defined by the harder beds which have protected from erosion the softer and more shaly portions below; and wherever there are lines of erosion parallel to the contact-line with the Archzean, the steeper or more escarped faces are turned toward the range. Gypsum deposits are well shown north of the Willow Creek and North Park road, where they occur through a thickness of at least 80 or. 100 feet, and are interstratified with dark, intensely red sandstones. TRIASSIC. 257 South of the road are some remarkably eroded forms suggestive of ruined cities. West of Antelope Creek the Trias extends twelve miles to the south of the Wyoming and Colorado boundary, filling a bay-like depression in the Archean body. Here are exposed, along the eastern side of Laramie Valley, 1,200 feet of beds having a very slight dip to the north and west, a high, abrupt wall of nearly 1,000 feet presented toward the plains. Upon the front of this escarped precipice may be seen the interstratified marls and limestones of the Jura, overlying the heavier red gypsiferous beds of the Trias. In contact with the Archean body, the sandstones are of coarse ash-colored materials containing angular fragments and rounded pebbles, with more or less calcareous matter in the cement, followed by a hard, thin, cherty limestone, which passes up into reddish-gray sandstone, and above this the usual beds of coarse red sand, with numerous red clay beds, varyingly shaly, which give a prevailing argillaceous character to a wide zone of the sandstones. Within this red argillaceous series are thin beds of pure clay and white gypsum, the latter varying from two or three inches up to several feet, with one solid body of twenty-two feet enclosed between two series of intensely red, dark, indurated sand-rock. Above this gypsiferous zone occur heavy red sandstones, which pass through yel- lowish friable beds with marly intercalations into the calcareous beds of the conformable Jura. The following section illustrates the chief features of the Triassic series, as displayed here, beginning at the summit: Feet. 1. Yellowish-red sandstone, passing down into fine, deep-red, evenly bedded, strongly coherent sandstone .........-----.--- 375 to 400 2. Argillaceous shales and argillaceous sands, with interstratified layers of fine, pure clay, the whole prevailingly red, with grayish and yellowish-red zones carrying four or five beds of gypsum, one reaching twenty-two feet in thickness; in all..-......-....-- 150 3. Red compact sandstones, beds of varying thickness, some coarser inal SlOvonS) Seba eT a oe Eryn ee ee ee 250 4. Reddish-gray sandstones carrying a bed of cherty limestone four On Nye dteottnick-sthe whole .coo so. c}. 2 ae hie i schencexe eect 175 17 Kk 258 SYSTEMATIC GEOLOGY. Feet. 5. Coarse, friable, ash-colored sandstones of remarkably loose texture, matrix containing more or less calcareous matter, with sheets of pebbles, partly rounded and partly angular cherty masses, together with some fragments of Archzean schists, both horn- blendic and, granitoid: 2260 ae tes ee eee 150 to 200 The Triassic beds are characteristically developed in North Park, especially on the western base of Medicine Bow Range from near the head of Retreat Creek south for sixteen or eighteen miles. The exposure from the base, where they rest unconformably against the Archean, up to the marls and limestones of the Jurassic, is nearly 1,000 feet. At the base are some light-colored sandstones, carrying pebbles, which are usually small, well rounded, and of a siliceous nature, the cement being extremely fine ferruginous sand, which breaks with a rough fracture, allowing the pebbles to drop out at a blow from the hammer. A similar exposure is seen on the western side of the Park, where again it rests unconformably upon the Archean. There is only one point in the Park, and that near the head of the eastern of the three forks of the Platte, where are interposed any Paleozoic beds between the Trias and the Archean. At that point, for a distance of not more than two miles, the conformable underlying Carboniferous limestones are interposed. From the thickness of the overlying Cretaceous which is exposed in this Park it is evident that the basin was very deep, and it is not at all improbable that it is underlaid throughout by the whole series of Paleozoic rocks which are displayed in Colorado Range. At Elk Mountain and Cherokee Butte the belt of conformable strata wrapped around the Archean mass contains the Trias, which here presents very generally the characteristics seen on the eastern base of Laramie Hills. The series is distinctly defined here by the Carboniferous limestones below and the soft, Jurassic shales above. At Cherokee Butte, a little to the south of the trail, the Trias is the uppermost member of the inclined series, and passes directly under the North Park Tertiaries which obscure the Jura. There are about 800 feet in all. The western slope of the Rawlings quaquaversal uplift is marked by concentric monoclinal ridges. The Trias here shows a thickness of about TRIASSIC. 259 700 feet, and at the base is formed of pinkish sandstones of rather fine tex- ture and thinly bedded, the upper portion having more of a massive habit and being a deep Indian red. About half-way up in the series is a bed, only about a foot thick, of greenish-drab lithographic limestone, enclosed in soft clays of variable purple and red. This bed is of interest here, since it recurs with great persistence along the flanks of the Uinta Mountains. The base member of the series is here noticeable for extremely thin joint- ing-planes. Along the western base of Park Range the Cretaceous is usually the lowest rock exposed, overlapping the rest of the conformable series and coming directly in contact with the Archean; but east of Hantz Peak, in a shallow recess of the Archean, and in contact with it, is a limited outcrop of red sandstones which have been referred to the Trias, al- though without any positive evidence. Farther south, near the southern limit of the map, where Moore’s Fork enters the Quaternary valley which lies between the Archzean and the ridge of Dakota sandstone to the west, at the base of the Dakota, are seen the shales and marly limestones of the Jura, underlaid by a long, narrow outcrop of the upper beds of the Trias, which, however, affords no indication of the thickness or general character- istics of the series. Uma Rance.—The Trias outcrops of Uinta Range consist of the edge of the upturned series displayed at four or five points at the northern base of the range, and a much broader and more intricate and extensive expo- sure on the south side, particularly in the eastern half of the range in the region of complicated secondary folds connected with Yampa Plateau. As displayed upon the northern margin of the range, its most eastern de- velopment is shown in the region of Vermilion Creek. The section of Trias- sic beds here laid bare, begins at the top of the series of shales which we have referred to the Permo-Carboniferous, the base portion consisting of red con- glomerate-bearing sandstones which carry a seam of drab limestone. Above these is a body of red sandstones of several hundred feet; then beds of massive buff sandstone varying from 600 to 1,000 feet, and corresponding to the cross-bedded sandstones of Flaming Gorge. Above these are fine white and red sandstones, with some intercalations of clay and shaly mate- 260 SYSTEMATIC GEOLOGY. rials, this member equalling about 100 feet, making a total thickness of Trias of about 2,000 feet. It will be seen that in passing westward from the region of North Park, the Trias has at this point doubled in thickness ; moreover, that the prevailing color is no longer a pure brick-red, but the upper half of the series is a massive light-buff sandstone. These rocks con- tinue north from Vermilion Creek Canon about two miles, and then pass beneath the horizontal series of the Vermilion Creek Tertiary. The Trias is masked along the northern slopes of the range, until, west of Red Creek and west of the mass of Archeean quartzites and schists, it again makes its appearance, faulted down into contact with the Archzan and with the Weber quartzite. Its outcrops from this point west to the cation of Burnt Fork are characterized by remarkable sinuosities, of which the most con- siderable is where Green River cuts its canon into the Uinta Mountains at Flaming Gorge. Here the Trias bends from its cast-and-west course to a northwest course, crossing Flaming Gorge, then turns almost a right angle into a southwest strike for about four miles, after which, at Kingfisher Creek, it resumes the normal strike of approximately east-and-west. In Flaming Gorge Ridge the strike varies from east 50° south to east 50° north. At this point, the Tertiaries having been eroded from the Mesozoic series, the upper limit of the Trias is well marked by the variegated marls of the Jura and beneath by thin shale-beds of the Permian, which are interposed between the base of the sandstone and the summit of the Carboniferous limestone series. As displayed on Flaming Gorge Ridge, the following members are observed, beginning at the top: Feet. 1. Massive, cross-bedded, white and buff sandstone. -...-..-..-- 400 to 450 2. Yellow clayey ‘sandstones. - 22 — <2 eer ce ee eee 50 3. Massive’ yellow sandstones -< -20<- eee *... 400 to 450 4. Red sandstones with white seams, on the whole rather thinly: bedded .2: 2 inc 2 = elem 2 eee er eee 300 to 350 5. Red, heavy-banded sandstones --.-.- .-.----------=--- 400 to 450 6. Greenish and greenish-purple clays.....-.-------------- 200 to 250 West of Flaming Gorge the valley of Sheep Creek follows the soft shales of the Permo-Carboniferous, leaving on the north high escarped walls TRIASSIC. 261 of the Trias. At Dead Man’s Springs the massive sandstones of this north- ern wall have a dip of 50° to the north, and they are further character- ized by extensive deposits of gypsum. West of Sheep Creek the Trias continues to a little west of the valley of Burnt Fork. In the region of Mount Corson, the overlying Eocene and Pliocene beds, rising high on | the slope of the Uinta foot-hills, overlap the Cretaceous and Jura, and come in contact with the Trias. Close to the wooded ridges, far up on Burnt Fork, the upper massive yellowish sandstones of the Trias, locally flecked with red stains of oxyd of iron, are seen conformably underlying the Jura. Here the lower Red-beds, although colored on the map, are obscured by débris. But they are seen underlying the buff sandstones a little farther to the east, at the eastern base of Mount Corson. Still farther west of Burnt Fork they come out from under the Tertiaries in the region of Lime Pass and extend westward for seven or eight miles, showing but imperfect exposures. On the western side of Junction Peak, Little Snake River has eroded a deep valley through the Tertiary strata, exposing the lower members of the Cretaceous, the shales of the Jura, and underneath them the sandstones of the Trias, which rest conformably upon the soft shales of the summit of the Palzozoic. Thus exposed, the beds strike north 45° west, and dip about 45° to the southwest. The eastern edges of Escalante and Yampa plateaus are margined by a broad band of Triassic sandstones, which south of the cafon of Yampa River rapidly shallows in dip and broadens in area of outcrop, occupying a large portion of the southern Yampa Plateau. In the remarkable strike from Kast Mountain to Fox Creek, the upper buff sandstones of the Trias form a conspicuous topographical feature. South of the river the prevail- ing color of the whole Triassic outcrop is of the usual red. On the summit of Yampa Plateau, directly south of the junction of Yampa and Green rivers, is a fragment of the Trias which formerly capped the whole plateau and which has been spared by erosion. To the west of Yampa Plateau, around the two anticlinals of Section Ridge and Split Mountain, the Trias winds in a sigmoid curve, bending to the east around Island Park and resuming its normal westward trend along the southern 262 SYSTEMATIC GEOLOGY. slope of the main body of the Uinta, by Tirakav Plateau. In these won- derfully sharp, complex curves the Trias has developed an amount of flexibility, a power to conform to sharp local bends, which is one of the most surprising orographical features of the region. A fine exposure of Trias is that laid open on Geode Cain, one of the upper forks of Ashley Creek. The first prominent ridge overlying the steeply dipping Bellerophon limestones is formed of a body of coarse, mas- sively bedded, deep-red sandstone escarped toward the north, and having numerous intercalations of saline impregnations, of which common salt is the chief ingredient. To the east of Geode Canon, between the two forks of Ashley Creek, is an exposure of thirty feet of solid white gypsum enclosed in the Trias sandstones and overlaid by red and white clays. Subjected to analysis, the gypsum is found to contain 76.7 sulphate of lime, 21.5 water. As exposed upon the surface, it has the appearance of a massive statuary marble, varied by pinkish and yellow veins. The red sandstones are here capped by harder, compact, yellowish-gray sandstones, above which are pale pink sandstones 300 or 400 feet thick, and above these a gap of 100 feet or more, representing some soft, easily eroded beds, whose outcrop is lost beneath the surface accumulations. The pinkish sandstones are capped by the beds of flaggy red sandstone, and above that is a line of cliffs composed of 200 feet of yellowish sandstone, above which appear the heavy white cross-bedded sandstones about 600 feet thick. The cross-bedding here develops a remarkable section, in which the flow- and-plunge action are found inclined 30° and 40° to the true planes of stratification. Here are altogether exposed about 2,000 to 2,500 feet of Triassic sandstones. Within the Uinta, gypsum has only been observed in this region, and on Sheep Creek, at the northern base of the range. The failure to observe the sulphates cannot be wondered at, when it is remem- bered how much of the Trias is obscured by débris, and that the shales which enclose the gypsum are, more than all other parts of the series, liable to rapid degradation. In the reéntrant synclinal between Split Mountain and the main ridge the Triassic beds range high around the eastward curve, almost to the sum- TRIASSIC. 263 mit of Yampa Plateau, forming a line of curved bluffs with steep escarp- ments always toward the hills, while the backs of the dipping beds form approximately the outer surface of the slopes. At Obelisk Plateau is a portion of the massive cross-bedded sand- stone of the Upper Trias, dipping 29° to the southwest and striking north 65° west. Near the mouth of Antero’s Canon, on the west branch of Ute Fork, the upper cross-bedded sandstones appear prominently on the eastern side of the gateway formed by the mouth of the canon, where are exposed about 1,500 feet of white and brownish sandstones standing at the angle of 70°, with the lower, red strata conformably below them. From Obelisk Plateau as far west as Heber Mountain on the meridian of 111° 5’, the nearly horizontal Uinta Tertiaries extend far up the flanks of the range, often overlapping the whole Mesozoic series and coming in contact with the Upper Coal Measures, but at intervals eroded away, open- ing more or less exposures of Mesozoic rocks. At the heads of Lake Fork, especially in the gateway of the western branch, are exposed about 1,500 feet of Triassic sandstones dipping 380° to 35° south, and striking north 65° to 75° east. Here the uppermost exposures are about 600 feet of light-colored, buff, cross-bedded strata, which are capped by shaly clays assumed to be the bottom of the Jura. Under the cross-bedded series are yellowish-white sandstones, gradually becoming redder with increase of depth. Still farther west, in the cafion of the east branch of the Du Chesne, the following members of the Trias are uncovered: The upper limit is well inarked by a limestone carrying Pentacrinus asteriscus, which is considered to be the base of the Jura. Beneath this appears the white, cross-bedded sandstone, 600 to 700 feet thick, underlaid by 200 feet of yellowish sand- stone; below that, 300 to 500 feet of pinkish-white sandstone, beneath which is the seam of greenish limestone, with some shaly sandstone. This greenish limestone is the one before mentioned, which occurs as far east as the Rawlings uplift, and in future study will doubtless be correlated with a similar limestone sheet observed along the flanks of Colorado Range. Be- neath the horizon of the limestones are 5V0 feet of deep, brick-red sandstone. Between the two bodies, and near the greenish limestone, was found a 264 SYSTEMATIC GEOLOGY. Naticopsis, a new species, having somewhat of a Jurassic aspect. The total exposure here is about 1,900 feet. West of the Du Chesne Fork, along Stanton Creek, are afforded some excellent developments of the massive light buff sandstone, the upper mem- ber of the Trias. This exposure extends nearly to the head of Stanton Creek, the whole valley bottom being on the Triassic beds. West of the head of the creek they are masked by the overlying Tertiaries, which here rise to a great height, and further by the floods of trachyte which over- pour the region for many miles to the north. Below the trachytes at Heber City, however, the foot-hills are formed of broken outcrops of reddish sand- stones striking northwest and dipping at 25° to the southwest. They are undoubtedly the lower red sandstones of the Trias, and are here in the very position which might have been predicted by the known curvature of the underlying strata of the Uinta. North of Kamas Prairie, for many miles up the valley of the Upper Weber, heavy Triassic sandstones are seen dipping to the north. They are well exposed just north of the mouth of the cation, where it emerges from Uinta Range upon Kamas Prairie, and here consist of heavy reddish beds intercalated with some clays and bearing one or two minor sheets of pebbles. In passing upward they are much covered by dcbris, and to the west are masked by the overlying trachytes; but enough could be seen of the upper members to recognize the massive cross-bedded sandstone, which is here redder than to the east, although the distinctive structure is as clear as at any place. At Peoria, a little village just north of the remarkable right-angle made by Weber River at the northern margin of Kamas Prairie, the erosion of the trachytes along the river valley displays the Triassic strata on both sides, overlaid by variegated marls and shales of the Jura. The dip is usually 50° to 60° to the north. There are 700 or 800 feet exposed, the lower members appearing under the tra- chyte. The upper portion, instead of the pale buff or white color charac- teristic of the cross-bedded series east and south of the Uinta, is here of the same bright pinkish tint which is seen at the quarry farther down Weber River below Echo City. The upper members, however, display the intricate cross-bedding which is characteristic of this horizon. Wausatcu Range—In Parley’s Park the foot-hills which border the TRIASSIC. 265 valley on the western side are made of the ordinary Triassic sandstone dipping to the east. = E z : = 7 7 - 7 7 » a : - a : , = rs ~ a : i a ; “ = : - 7” 7 = oe 7 7 7 dee " : - - ; ; ; ‘ a : a 7 - E an | —* = > oat = = ; : | ; 7 -—* - e a 7 i c : , Bo - ¢ 7 ; 7 . : : 7 = - > os, ~ , sal = = =. - = bead ? : 7 7 5 a 7 ce > ~ a F _ : ~ yee a r 4 7 : . a = a : ” ' : er | = = Ae | ; = 1 : : oat - . ’ 2 a) » = . : | -~ — . mn - TRIASSIC Se RED BEDS lias STAR PEAK PRE-MESOZOIC feSOZOIC EXPOSURES } i — = ————EE——E eS iN BATE OFF (AAO C1 fy Gj “a ee, We | o eS eye Lk oh (My Sy Ly ue CRETACEOUS : COLORADO (aesaza FOX ni LARAMIE eS lsat, AEC ty, RECAPITULATION OF MESOZOIC. BLOT Finally, the Laramie, by its own vertebrate remains, is proved to be unmistakably Cretaceous, and the last deposit of that age, and it contains no exclusively fresh-water life. Its plants resemble European Tertiary, but its Dinosaurs are conclusive of Cretaceous age. It was the last of the con- formable marine deposits of middle America. Its latest period of sedimenta- tion was immediately followed by an energetic orographic disturbance, which closed the Mesozoic age. In that orographic action the inter-Amer- ican ocean was obliterated, and the Cretaceous locally thrown into great steep folds. The following deposits over the Green River area were fresh- water lacustrine lowest Eocene strata laid down nonconformably with the Cretaceous, except in accidental localities. This lowest Eocene has its age abundantly proved by vertebrate life, as will appear in the succeeding chapter. CHAPTER YV. CENOZOIC. Section I.—EocENE TERTIARY.—VERMILION OREEK GRouPp—GREEN RIVER Grourp—BrRIDGER Group—UINTA GROUP. Section Il.—M1ocENE TERTIARY.—WHITE RIVER Group—TRUCKEE GROUP. Srorion IfL.—-PLIOcENE TERTIARY.—NIOBRARA Group—NortTH Park GRoUP— HumMBoLpt GRouP—WYOMING CONGLOMERATE. SEcTION LV.—RECAPITULATION OF TERTIARY LAKES. SECTION V.—QUATERNARY.—GENERAL REMARKS— EXTINCT GLACIERS AND CANONS —DLAKES OF THE GLACIAL AGE AND THEIR DESICCATION. SHC TLON L- EOCENE TERTIARY. In the region of the Fortieth Parallel the changes of configuration brought about by orographical movements at the close of the Cretaceous period, resulted in the complete extinction of the American mediterranean sea, which, since the close of the Coal Measure age, had stretched from the Wahsatch to the longitude of eastern Kansas, dividing the east and west areas of American land into two distinct bodies. In Eocene time, so far as we now know, the entire continental area had a free drainage to the sea, with the exception of a long, basin-like depression extending from Wah- satch Range eastward to the meridian of 107° 30’, with a north-and-south extension not yet definitely known. This depression was immediately occu- pied by an early Eocene lake, whose northern portion corresponded with approximate accuracy to the present drainage-basin of Green River. South- 309 360 SYSTEMATIC GEOLOGY. ward it extended through portions of Utah, New Mexico, Colorado, and probably into Arizona. The series of marine Eocene deposits of the Alabama period are placed in a higher horizon than the beds of the Vermilion Creek group, which were the first to be laid down in the interior lake. On the western coast, in the California region, the uppermost members of the ocean Cretaceous are con- formably overlaid by other marine deposits, of which certain members are unmistakably Miocene. For the lower members, those directly contiguous to the Cretaceous summit, the organic remains thus far collected are too indistinet to lead to a firm belief as to their exact age. There are indica- tions of Eocene in the series overlying the Cretaceous of Oregon and Wash- ington Territory. West of the Sierra Nevada, all the series are purely marine, and those of the Alabama and Vicksburg groups, also marine, are the only Eocene found east of Colorado Range. As yet the great Eocene lake, whose main deposits are circumscribed by the boundaries of the basin of Colorado River, is the only one of any considerable geographical area known in the middle Cordillera region. In its earlier stages this lake was coextensive with the rocks of the Vermilion Creek period, the lowest division of the American lacustrine Eocene. The great Eocene formation of this region is divided into four promi- nent groups: 1. Vermilion Creek Group, 5,000 feet thick, lowest Eocene. 2. Green River Group, 2,000 feet thick, middle Eocene. 3. Bridger Group, 2,500 feet thick, upper Eocene. 4. Uinta Group, 500? feet thick, latest Eocene, approaching Miocene. VeERMILION CREEK Groupr.—Between the uppermost members of the Laramie Cretaceous and the lower beds of the Vermilion Creek Eocene, there is but very slight lithological difference. They are both reddish, friable, sandy rocks. After the post-Cretaceous uplift had raised the Rocky Mountain bar- rier to the east, forming the basin of Colorado River, the original bottom of the newly formed lake was made of the uppermost Laramie beds, of which limited portions were left horizontal. When these exceptional localities were subsequently covered by Eocene strata, and the two uplifted together, EBOCENE TERTIARY. 361 they were, so far as angle of position is concerned, conformable. But a total break of organic life is observable between them; and as stated at the close of the Cretaceous section, there is elsewhere a true general noncon- formity between the Laramie and Vermilion Creek groups, amounting in some places to an angle of 90°. Along the eastern limit of the outcrop of the Eocene its beds lie upon nearly horizontal Laramie rocks. The line of demarkation, in the frequent absence of fossils, is always more or less indefinite, and in consequence there may be to the east of our eastern boundary of the Vermilion Creek certain outliers in the general Laramie area which truly belong to the Vermilion Creek; but since we are unable to determine these, we have given a generalized boundary-line. The rocks colored Laramie may be relied on as chiefly of that age, the same being true of the Vermilion Creek group. This doubt only applies to the horizontal region along the railroad and a few miles north and south. The most eastern outcrops recognized by us are in a bay-like recess between Mount Weltha and Navesink Peak, in the Elk Head region. The surface is here composed of coarse red sandstones, interbedded with more or less clays and arenaceous marls of pinkish and creamy colors. Tracing this formation westward, although the surface is in considerable measure made up of decomposed earthy material, yet its character is such as to leave little doubt that the subjacent strata are continuous with the more solid Vermilion Creek beds which are seen to the west. They present little or no difference of angle with the underlying Cretaceous strata at this locality. Along the banks of Little Snake River the series is better displayed, and is seen to consist of coarse gritty sandstones, containing numerous siliceous casts of Melania. There is the same want of definition between the Laramie and Vermilion Creek beds, from the junction of Little Muddy and Snake rivers northward quite to the Pacific Railroad. In the region of the Washakie and Red Desert, and northward as far as the boundary of our map, the country consists of a deposit of more or less decomposed Vermilion Creek strata. Where they retain their original structure, they are seen to be nearly horizontal, and to consist of very easily eroded red clay and sandy beds. 302 SYSTEMATIC GEOLOGY. From a little west of Rawlings Peak, the Vermilion Creek beds occupy the surface westward nearly to Bitter Creek Ridge, the country characterized by irregular barren plains, devoid of the dry water-courses which are features of the region to the south. From the Rawlings Peak uplift, the Laramie Cretaceous strata were described as falling off with rapidly decreasing dip, reaching an almost horizontal position north of the railway, between Washakie and Creston. They pass with no uncon- formity of dip under the eastern edge of the Vermilion Creek series. There is no doubt that in former times the Eocene beds extended con- siderably farther to the east, though it seems improbable that they ever passed over into the valley of the North Platte, certainly not into the depression of Laramie Plain. The exact boundary of the lake, there- fore, in which this lowest Eocene group was laid down cannot be given along the east in the northern portion of our work. South of the parallel of 45°, however, the Cretaceous rocks have a higher dip, and a nonconformity with the overlying Vermilion Creek is clearly seen. Furthermore, in passing eastward the Green River over- laps the Vermilion Creek, and itself comes in contact with the Cretaceous, thus clearly proving that the boundary of the Vermilion Lake was in the neighborhood of Fortification Peak. About six miles east of Washakie Station, Laramie beds are undoubtedly reached, and are recognized in out- crops of a thin bed of sandy argillites of a strong vermilion hue. They are fine-grained and remarkably fissile, splitting into exceedingly thin laminz, which are covered with well preserved impressions of deciduous leaves, and are underlaid by the sandstone carrying coal-seams. Ten miles north- west of this spot they may be again observed, capped by thinly bedded sandstones. In both cases their position is approximately horizontal, the slight observable dip being to the west. This red leaf-bed, characteristic of the upper region of the Laramie series, serves as a basis for the Cretaceous upper limit as colored upon the map. About sixteen miles southwest of Washakie, in the near vicinity of well recognized Laramie beds, in a rather shallow valley, are beds of greenish marls and clays, weathering in the peculiar manner of the Bad Lands, developing smooth, rounded, dome-like forms. Their dip of 5° EOCENE TERTIARY. 363 westward would carry them under the Vermilion Creek beds at Cathedral Bluffs. A little south of this a discrepancy of angle appears between these soft clayey beds and the sandstones of the Laramie, which here rise at an angle of 15° to 20°, dipping northwest and striking northeast. East of Muddy Creek the bases of the Vermilion Creek benches are made up of loosely aggregated sandstones of chocolate, buff, and gray colors, carrying Goniobasis and Viviparus in a yellow sand-bed, which appears to represent the base of the series in this region. On the western borders of Muddy Creek Valley, however, upon the upper edge of the high plateau, are very distinct and characteristic outcrops of the bright pinkish and reddish mix- ture of sands, clays, and marls which form the upper part of the Vermilion Creek series. Their planes of stratification are to be traced by changes of color rather than by abrupt changes of material, or those distinctly marked surfaces which characterize temporary cessation of sedimentation. 'The faces of these bluffs have a peculiar striped, banded appearance, given by local variations of green, white, and almost brick-red colors, alternating through the general pink mass. Wherever these beds are worn away, the sandy particles are most easily transported, and there is invariably a residuum of red clay, which gives the peculiar color to the soil of the country. The best exposures of these upper striped beds are at Washakie Mountain and Cathedral Blufis. The former is a flat-topped ridge, lying about seven miles east of Little Muddy River, and reaching an elevation of 1,500 feet above the surrounding plain, the surface being composed of a remnant of the Pliocene conglomerate, afterward to be described. Washakie Peak affords an admirable point of view for studying the relations of the three different groups of Eocene. A broad expanse is opened westward, of 75 or 100 miles. The Green River series which directly underlies the Pliocene summit of the mountains is seen to describe a rude circle of bluffs having a general dip toward the middle of the Washakie Basin. The line of contact between the Green River and the Vermilion Creek trends a little west of north from Washakie Mountain to Cathedral Bluffs, thence westwardly to Table Rock near Bitter Creek Station, thence southwest to Pine Bluffs, and from there southeast to the Vermilion Blufts ; and upon the southeast the line is approximately that of Little Snake River. 364 SYSTEMATIC GEOLOGY. Outside of this line, which represents the outer boundary of the Green River formation in this basin, are the broad undulating plains of the older Ver- milion Creek Eocene, everywhere dipping under the Green River series. The middle of this Washakie Basin, as shown upon the map, is occupied by a small area, about sixteen by twenty-four miles, of the next higher member, the Bridger group. With the exception of the rocks in the region of Cherokee Ridge, there has been no considerable plication since the depo- sition of these series. The slight dip toward the middle of the basin marks the result of orographic action, and cannot be accounted for from dips of deposition toward the deepest point of the lake. Washakie Mountain itself has a special geological interest, as the upper beds of the Vermilion Creek are here seen to underlie the Green River series, with a distinct nonconformity of 4° or 5°. The importance of this observa- tion will be seen later. Between Washakie Mountain and Barrel Springs, and indeed on as far as Cathedral Bluffs, the division-plane between the Vermilion Creek and the overlying Green River beds may be easily traced by the differences of color and texture of the series. This plane of division is depressed in passing northward as far as Barrel Springs, and again rises as far as Cathedral Bluffs. The whole plain from Washakie Station to Black Butte Station is characterized by earthy deposits resulting from the decomposition of the Vermilion Creek beds, as usual of prevailing red color from the fine Ver- milion Creek clays, which have given the local name of Red Desert to these plains. A few miles west of Washakie are some low bluffs extending toward Red Desert Station, showing some outcrops about the middle of the Ver- milion Creek series. They are thin, reddish, flaggy sandstones about 200 feet thick, underlaid by whitish clays, and have yielded some frag- ments of Eocene mammals, of genera which will be found in the list appended to the account of this group. South of Red Desert Station, the country gradually rises in broad terraces, the first formed of whitish clays overlaid by sand-rocks, the outcrops being traced nearly parallel to the line of the railway. About four miles south of this chain of bluffs is a line of still greater elevations, composed of striped pink, white, and red EOCENE TERTIARY. 365 upper members of the Vermilion Creek. To this line has been given the name of Cathedral Bluffs, owing to the remarkable architectural forms which have been developed by erosion in the soft, casily wrought material. On the northern fronts of these bluffs are exposed about 600 feet of the variegated upper Vermilion beds, overlaid by drab limestones which mark the base of the Green River series. The summit, member of the limestones is a seam about four inches thick of odlites, chiefly silicified, and resulting in a dark-gray chert or chalcedony-like material. The plane of junction between these two Eocene groups is also shown along an irregular line between Cathedral Bluffs and Table Rock, the latter being made up of sandstones and caleareous shales, with slight seams of lignite and several thin beds of a limestone which is characteristic of the base of the Green River series. These limestone beds are almost entirely made up of Melania, Vivi- - parus, and Unio, together with the agatized odlitic bed before mentioned. The beds here, as usual, dip inwardly toward the centre of the basin in a southeasterly direction, at an angle of 4° or 5°. The main body of the Vermilion Creek beds at the north dips only 2$° to 3°. From Table Rock westward and in the region of Black Butte, is a low, open country made up of the disintegrated Vermilion Creek beds, in which appear a few outcrops of the still coherent members of the group. Along the line of contact with the Green River shales, southward as far as Pine Bluffs and even to the old Cherokee Trail, the upper striped part of the Vermilion Creek series is conspicuous. The lower members, as seen at Black Butte, Hallville, and on the upper part of South Bitter Creek, rest with apparent conformity wpon the Laramie Cretaceous, and are only to be distinguished by the change in vertebrate fossils. As is the case between the lower members of the Vermilion Creek and the Laramie, on the east edge of the Washakie Basin the lithological changes are such as to render any stratigraphical division valueless. It is therefore true of both sides of the Washakie hollow, that the Eocene is practically conformable with the Upper Cretaceous. At various points there is a slight appearance of non- conformity by erosion, but this is necessarily somewhat deceptive, and the line is only to be drawn here with real security upon the basis of vertebrate remains which will be mentioned hereafter 366 SYSTEMATIC GEOLOGY. The upper portion of the Vermilion Creek series is observable near Otter Gap on Little Snake River, east of Cherokee Ridge. Here the interstratified red sandstones and clays give their characteristic color to the country, which for the most part is made up of the débris of these beds. Between Otter and Elk gaps, the river follows pretty nearly the plane of junction of the Vermil- ion Creek and Green River groups. In the region of Sunny Point, however, erosion has carried off the Green River series from the immediate hills bordering upon the stream, and there are extensive exposures of the upper part of the Vermilion Creek, of the characteristic color, and, as usual, much disintegrated. The exposure amounts to about 1,000 feet in thickness, and is altogether made up of the reddish-colored part of the series. The contact between the uppermost of these beds and the calcareous lower horizon of the Green River is characteristically observed. The structure in the region of Elk Gap is quite complicated, the underlying ‘series considered to rep- resent the upper portion of the Vermilion Creek dipping 10° to the south and being overlaid by a series of the sandstones carrying at their base a prominent bed of reddish shales which dips 29° to the southwest. The overlying series are referred to the Green River, but it seems possible that they may represent the Bridger, which is seen directly to the northwest. East of the river at Godiva Ridge the top of the Vermilion Creek series is well shown by its contact with the characteristic cherty Gonio- basis bed at the base of the Green River series. Around the whole circle formed by the great Green River body in Washakie Basin, the upper limit of the Vermilion Creek, as we have seen, is quite a defined plane, the variegated and banded red series of the upper Vermilion Creek giving way quite suddenly to the calcareous basal mem- bers of the Green River series, which are often conformable, but in one or two places show distinct nonconformity with the lower series. The broad plains which surround the Green River exposure offer few satisfactory out- crops and no valuable sections of the lower portion of the Vermilion Creek group. Wherever it approaches the nearly conformable underlying Lara- mie, the Cretaceous and Eocene possess great petrological similarity. The deeper members are better shown in the basin of Vermilion Creek, the locality which has given its name to the group. The upper members EOCENE TERTIARY. 367 also are here well shown along the line from Pine Bluffs to Cherokee Trail, and again as forming the lower portion of the Vermilion Bluffs, which bound the basin upon the southeast. Here, as at Washakie Mountain, the uppermost edge of the bluff is formed of unstratified Pliocene conglomerate, below which is a development of 500 or 600 feet of the calcareous Green River series, underlaid by 800 feet of the characteristic Red-beds of the upper Vermilion, which pass downward in the region of Vermilion Creek into gray and drab beds. It is the horizon of these gray and drab basal members, which are elsewhere rich in bones of Coryphodon. At the foot of Vermilion Bluffs the dip is only about 2°, but toward Vermilion Creek it gradually reaches an inclination of 12°. The whole surface of the basin of Vermilion Creek is a region of terrace- like benches, scored and more or less deeply eroded by water-courses, which are now for the most part dry. Throughout the lower part of the basin, especially near the contact with the underlying and nonconformable Lara- mie Cretaceous, are a series of dark-drab and gray gravelly sandstones, which lie approximately horizontal, rising very gently to the east and north. The underlying Laramie Cretaceous dips to the northeast about 25°, the two being utterly unconformable. Attention is especially called to the fact of an angular nonconformity of 25° between the Laramie and the lowest member of the Eocene, the same groups already noted as conformable at Black Butte and east of Washakie. If the geologists who have asserted the conformable passage from the Cretaceous to the Tertiary by a transition series had not confined their observations in the Green River Basin to the region of Bitter Creek and Washakie Basin, the present unreasonable con- troversy would never have arisen. The higher members of the Vermilion series, as exposed on the western flanks of Vermilion Creek valley, are coarse gravelly sandstones, the upper portion of which has the character- istic red color of the formation. Directly north of Diamond Mountain these higher Vermilion Creek beds yielded several bird-bones from a coarse, gritty, buff sandstone. Passing southward, the uppermost members of the group come into nonconformable contact with the Carboniferous limestones. Southeast of Diamond Peak, and along Talamantes Creek, the whole series are seen to pass unconformably over the Cretaceous, Jura, Trias, Permian, 368 SYSTEMATIC GEOLOGY. and upper Carboniferous, coming finally into contact with the Weber quartz- ite of O-wi-yu-kuts Plateau. The meridian of Bishop’s Mountain, a little northeast of Diamond Peak, marks an anticlinal in the Vermilion Creek series. Eastward the whole strata incline gently to the east, to pass under the Green River and Bridger series of the Washakie Basin, and westward beneath the Green River rocks of Tabor Plateau and Quien Hornet Mountain. The entire thickness of the Vermilion Creek series, as displayed in the basin of Vermilion Creek, cannot be less than 4,000 feet. Considered as a whole, the Tertiary field lying east of the meridian of Quien Hornet Mountain is a single broad basin, of which the Vermilion Creek forms the lowest member, and upon the east and north lies conform- ably as to its angle upon the Laramie beds of the Cretaceous, while to the south the discrepancy of angle between those two formations amounts to 25° at Vermilion Creek, and to 3° or 4° near Fortification Peak, in the val- ley of the Yampa. The greater part of the area is covered by easily eroded earthy beds of the Vermilion Creek series, which are characterized by the presence of a considerable number of fresh-water Tertiary genera — Melania, Goniobasis, Viviparus, and Unio, and also by the bones of verte- brates, including Coryphodon. The upper limit is frequently well marked by contact with the lower limy members of the Green River series; but since these two members are nonconformable, the Green River often overlaps and obscures the edges of the Vermilion Creek beds. This is the case between Sunny Point and Ver- milion Bluffs, and also through the whole Tertiary exposure from Godiva Ridge to the White River divide. West of the meridian of Bishop’s Moun- tain the Vermilion Creek beds incline very gently to the west, passing be- neath the irregularly eroded Green River series. Along the immediate base of the Uinta Mountains the later strata are eroded off, leaving a narrow strip of the Vermilion Creek beds extending from the head of Willow Creek westward to the slopes of Mount Corson. Along this line is an admirable opportunity of studying the relations of the Vermilion Creek with the Cretaceous. West of the ford of Green River, about four miles north of Flaming Gorge, the upper Cretaceous sandstones EOCENE TERTIARY. 369 of the Laramie group are seen dipping to the north at very high angles, 25° near the river and increasing westward, until at the gap where Henry’s Fork enters the Quaternary valley north of Camp Stevenson the Laramie sandstones dip 75° or 80° to the north, while the Vermilion Creek beds, distinctly and nonconformably above them, dip only 25°. Continuing still farther west from the gap north of Dead Man’s Springs, the Vermilion Creek beds swing to the south and overlap first the Fox Hill, then the Colorado, and later the Dakota. They are in turn overlaid by the unconformable Bridger series, forming with a Pliocene gravel-cap the mass of Mount Cor- son. The lowest Vermilion Creek member exposed along Henry’s Fork is a coarse conglomerate which underlies some striped red sandstones, the conglomerates dipping 25° to 35° northward. Along the western side of the Bitter Creek uplift and in the valley of Sage Creek the erosion of the calcareous beds of the Green River series has laid bare a narrow belt of the Vermilion Creek lying between the Green River group and the Laramie Cretaceous. The relation with the Laramie sandstones is obscure, owing to the soft and friable nature of both series. North of Uinta Range, to the east and west of where Bear River emerges from the mountains, the foot-hills are deeply overlaid with Ter- tiary sandstones and conglomerates, which, near the mouth of Bear River, have a dip of 8° or 10° from the range. Extending westward along the flank, these conglomerates become more and more important, until directly north of the upper cation of Weber River the mountain wall is composed of excessively coarse conglomerate between 3,000 and 4,000 feet thick. It is almost structureless, and lines of stratification can rarely be perceived. The blocks of which the conglomerate is chiefly formed range from the size of a pea to masses with a weight of several tons. Here and there a comparatively fine-grained bed gives a clew to the dip, and the formation is seen to incline from 4° to 5° northward away from the foot-hills of the range. The rapidity with which these conglomerates grow finer in advancing from the shore along the Uinta is very conspicuous. Of these coarse conglom- erates, perhaps the most remarkable exposure is on a point directly north of the upper Weber Cation, about ten miles south of the 41st parallel. 24 Kk 370 SYSTEMATIC GEOLOGY. This peak is over 11,000 feet high, and marks the greatest altitude which the comparatively undisturbed Tertiaries have been observed to attain. To the north the ridge and peak are scored down by deep canons which well display the graduation of the material from the coarse conglomerate immediately in contact with the older rocks out toward the north, until, near Wahsatch and Evanston, they have become fine-grained, sandy beds, devoid of pebbles. A section displayed on the 111th meridian, from the high peak to Evanston, estimating from the observed dips, indicates a thick- ness of about 4,000 feet of strata; while from Evanston to Croydon, on the Union Pacific Railroad, some distance to the west, certainly 2,000 feet of lower beds are displayed. It is entirely within bounds to assign to the Vermilion Creek of this region a total thickness of 5,000 or 5,500 feet, and it should be borne in mind that this nowhere represents the former summit of the Vermilion Creek series. On the contrary, we can but suppose that a considerable portion of the uppermost beds have been removed, and hence that an unknown amount is to be added to the total thickness of the group. In the region of Aspen Plateau the Vermilion Creek beds are about horizontal, and are, for the most part, alternately of cream-colored and red arenaceous clays, with not infrequently a considerable proportion of marly strata. They have yielded in this vicinity numerous fragments of Coryphodon, which add certainty to the assignment of the rocks of this region that had been already made upon structural and stratigraphical grounds. East of Aspen, both the Vermilion Creek group and the small ex- posure of Green River group pass rapidly under the unconformable Bridger beds, and the eastern flank of Aspen Plateau seems to have been the western limit of deposition of the Bridger beds of the Bridger Basin. At the mouth of Echo Canon the Vermilion Creek conglomerates are seen to contain a large number of rounded pebbles, from extremely fine sizes up to six, eight, and even ten inches in diameter. The latter size, however, is very rare. Passing up in the series, the conglomerate beds are capped by Indian-red sandstones, which expose in Echo Canon fine precipitous fronts, carved down by transverse ravines, which carry off the drainage from the high Tertiary plateau to the north. Between Echo City EOCENE TERTIARY. 301 and the top of this plateau are represented about 3,800 feet of strata, chiefly of these Indian-red sandstones, containing toward the upper limit gray shale-beds, with occasional sheets of fine conglomerate. Directly west of Coalville the Vermilion Creek rocks are seen to rest unconformably upon the northwesterly dipping Cretaceous. This line of discordant contact may be traced southwestward across Weber River, appear- ing on the hill-sides north of Silver Creek. From Echo City along this entire line of contact, even past the north side of Parley’s Park, there is no single instance in which any close observer could possibly assume a con- formity between the Vermilion Creek beds and the underlying Cretaceous. On East Cation Creek the discrepancy rises to 50° or 60°, gradually growing less toward Echo City, until directly south of the mouth of Echo Canon the nonconformity is reduced to about 10°. At Croydon low beds of Ver- milion Creek are seen resting unconformably upon the Fox Hill sandstones of the Cretaceous, the latter dipping 25°, while the Tertiaries never dip over 5°, and are for the most part nearly horizontal. East of the great Cambrian anticlinal of the northern end of the Wahsatch, shown on Map IIL, is a parallel highland, the Bear River Plateau. It is merely an area of elevation that has escaped the extreme erosion which the beds in immediate contact with the Cambrian and Silu- rian rocks of the older uplift have suffered. It varies from two to five miles in width, and on the east overlooks the valley of Bear River and descends by a series of rudely sloping spurs, which are separated by the canons of Woodruff, Randolph, and Saleratus creeks. The beds here are inclined from 1° to 2° to the east, and show a thickness of about 2,500 feet. They have the usual characteristic red color, and are made up of prevailingly coarse arenaceous materials, with occasional strata carrying suf- ficient pebbles to be denominated a loose conglomerate. ‘There are a few beds of nearly pure, white, fine, siliceous sand, which are striped with fine seams of gray argillaceous marl. On the divide between Saleratus and Lost creeks the coarseness of the material increases westward till it shows a perceptible approach to the heavy conglomerates displayed in the Narrows below Croydon and at Echo City. The western edge of Bear River Plateau descends by a rapid declivity, often almost an escarpment, between 2,000 312 SYSTEMATIC GEOLOGY. and 3,000 feet deep to the level of the Silurian and Cambrian rocks. This abrupt, precipitous face is cut by deep canons, the branches of Blacksmith’s Fork and Muddy River. These canons do not cease their cutting action when they reach the harder rocks of the Silurian and Cambrian beds, but have deeply scored through that anticlinal, making gorges 1,800 to 2,000 feet deep in the quartzite. From the peculiar relations of the topography of the Bear River Plateau with the older rocks, it is clear that the Vermilion Creek rocks formerly passed uninterruptedly over the summit of the older anticlinal, that the courses of the streams were determined in the softer Ter- tiary above, and that upon cutting down to the level of the harder under- lying rock they were confined by the Tertiary walls above and obliged to erode in the thus predetermined channel. Afterward, long after the streams had cut deeply into the older rocks, the Tertiaries were in great measure removed. On the western side of Oyster Ridge and west of Concrete Plateau there is an enormous development of red sandstones and clays, with promi- nent belts of conglomerate, the whole increasing in coarseness of sediment as it approaches the Uinta on the south and the Wahsatch on the west. Here is an area about sixty miles from north to south by fifty miles from east to west, which is essentially a plateau of Vermilion Creek beds, in general approximately horizontal, but in the vicinity of the Wahsatch rising to 14°. On the south it abuts without change of angle against the Uinta Mountains, and between Upper Bear and Weber rivers forms an elevated plateau which reaches 11,000 feet, a plateau made up of coarse, irreg- ular strata of red gritty conglomerate material, dipping northward at angles of 3° to 4°. On the flanks of the Uinta, canons have been carved out of these loose, friable strata by the ice action of the glacial period, leaving sharp, deep walls 1,000 to 1,200 feet in height. Between Weber River and Wahsatch Range there is a lofty plateau culminating in an extremely high point, which reaches nearly 11,000 feet. This plateau is cut through by the valley of East Canon Creek, and not less than 4,500 or 5,000 feet of horizontal sandy and conglomerate beds of the Vermilion Creek group are displayed. They are here nearly horizon- tal, but toward Richville, farther down on East Canon Creek, the red sand- EOCENE TERTIARY. ale stones of the group are seen dipping from the Wahsatch at an angle of about 14°. The railway crosses a point of this plateau through a sharp gorge at the Narrows, where the Tertiary conglomerates and sandstones are nearly horizontal and about 2,000 feet thick. In the region of Bear River City and Evanston, the Cretaceous, which stands nearly vertical, has its highest members dipping at an angle of 70°. Here, as at Black Butte, the uppermost beds lying above the heavy white sandstones of the Laramie consist of a variety of thin, sandy shales, having many carbonaceous beds, more or less clays, and thin streaks of coal, the whole carrying enormous numbers of Unio, Corbicula, Corbula, Pyrgulifera, Viviparus, Melampus, &c.; and here the rocks of the Vermilion Creek series are horizontal—in other words, there is an angular discrepancy of 70°. They are characterized by the presence of Melania and Goniobasis, and also by numerous mammalian remains of the typical Eocene genus Coryphodon. At Evanston the highest portions of the Laramie Cretaceous are not exposed, but the sandstones near the summit of the group contain the enormous workable coal-beds of the Rocky Mountain and Wyoming Coal companies. These coal-bearing Laramie beds dip at angles from 16° to 25°, whereas the Vermilion Creek Tertiaries are nearly horizontal over them, and carry remains of the genera Coryphodon and Eohippus, and fishes. In the region of Echo Canon, again, the uppermost members of the Laramie are not displayed, but the distinctive Vermilion Creek beds, which have been traced in absolute continuity from the Coryphodon beds near Evanston, are here seen to overlie unconformably the Cretaceous, the angu- lar discrepancy being 12° to 25°. Near the upper part of the cation, below Castle Rock, they reach their greatest nonconformity in that immediate region, and near Echo City there is a difference of 11°. The continuous series of Vermilion Creek beds, passing westward, overlaps all the Palzeozoic formations, which are conformable with the Cretaceous, and comes directly into contact with the Archzean. Between Bear River and Oyster Ridge is a further extension of this great Vermilion Creek Plateau, abutting nearly horizontally against the highly inclined Cretaceous of the ridge. The broad upper valley of Bear River is excavated from these strata, which occupy the heights to the 374 SYSTEMATIC GEOLOGY. west, and extend thence across Bear River Plateau. Along the eastern side of the Wahsatch, east of Farmington and Keysville—indeed, from Hunts- ville all the way to Parley’s Park—the Vermilion Creek beds rise high upon the flanks of the Wahsatch, the highest portions of the Tertiary being fre- quently higher than the top of the older range. ‘This is true of the whole Bear River Plateau, and true of the Vermilion Creek heights directly north of Parley’s Park. The only exposure of these beds west of the summit ot the Wahsatch is to be found in a small body of hills lying directly north of Salt Lake City, of which Ensign Peak is a prominent point. This is a mass of sandstone and conglomerate, which has been faulted down into its present position. ‘The entire absence of this great series to the west of the Wahsatch would indicate that the range itself formed approximately the shore of the lake, and it is probable that the small detached mass around Ensign Peak was merely a bay of the Tertiary putting into the land which lay to the west. From the outcrops thus broadly sketched, it is clear that a single lake extended from longitude 106° 30’ to 112°, stretching northward probably over the greater part of the Green River Basin and southward to an unknown distance. The rocks of this same group which occur in New Mexico represent a southern continuance of the identical lake, characterized by the same fauna. So far as the area of the Fortieth Parallel goes, these rocks have only been definitely studied in the region east of the Wahsatch and north of the Uinta. South of the latter range, from the heights west of Strawberry Valley eastward across Green River, extends a broad area of Tertiary rocks of great thickness. These have not been sufficiently studied to say definitely to what members of the Eocene they belong. In the region of White River some beds have yielded fossils which, although Eocene, have a more recent facies than those of the highest or Bridger member to the north of the Uinta. They are still lower than the Titanotherium beds which form the base of the Miocene east of the Rocky Mountains. It seems most probable that the immense mass of Tertiary south of the west- ern end of the Uinta, which is shown in the valleys of Du Chesne, Red Fork, and upper Uinta rivers belongs to the Vermilion Creek series. In the absence of more definite information, the whole sweep of the Ter- EOCENE TERTIARY. By 65) tiaries south of the Uinta, with the exception of certain little patches of known Pliocene, has been colored as the Uinta group, whose upper mem- bers near White River have yielded the highest Eocene forms; but there is no doubt whatever that subsequent study will show that the rocks in the angle between the Uinta and the Wahsatch south of the former range are identical with those in the opposite angle north of the Uinta, and that they should be classed with the Vermilion Creek. And the altitudes to which the level Tertiary strata northeast of Strawberry Valley attain, indicate that the level of their deposition was as high as the rocks north of the Uinta. We may expect a full elucidation of the Tertiaries south of the Uinta from the pens of Powell and Gilbert. The thickest exposures of the Vermilion Creek series are in the imme- diate vicinity of the Wahsatch, as shown by the deep valley of East Canon Creek, where is exposed not less than 4,000 feet. The most characteristic exhibition is in the basin of Vermilion Creek, where a fuller section is dis- played. It is made up of a heavy, gritty series at the base, which in the region of Vermilion Creek and north of Evanston is gray, but as displayed at Echo Canon and East Cation Creek is characterized by the presence of enough red sandstones and clays to give it more of a brick or in places a deep pinkish color. The middle members are of finer material and are more intercalated with clays, while the upper part of the series, as shown wher- ever the group comes in contact with the Green River series, is made up of striped and banded sandstones varying from gray to yellow, white, and red, with prevailing red and white tints. As regards the relations of this with the underlying group, it should be repeated that the evidence has finally accumulated so that there can be no longer a doubt where to draw the line between the Cretaceous and the Ter- tiary series. I unhesitatingly say that the bottom of the Vermilion Creek is the base of the Tertiary, and that it rests in essential nonconformity (though locally in accidental conformity) upon the Cretaceous. The Cretaceous members, as we have seen, are inter se strictly con- formable. The uppermost exposures in the near vicinity of the Vermilion Creek beds are along the Bitter Creek uplift, at Evanston, at the eastern end of the O-wi-yu-kuts Plateau, Red Creek, the northern slopes of the 376 SYSTEMATIC GEOLOGY. Uinta, Oyster Ridge, Bear River City, and Echo Canon. Of all these localities, the only one where there is the slightest appearance of conformity of position is in Washakie Basin, where the inclinations of the two forma- tions are practically identical, and the appearance of nonconformity by erosion is wanting. The Cretaceous, as we have seen, is here characterized lithologically by a variation between beds of heavy sandstone, yellowish shales, finely laminated sandstones, dark clayey shales, ashy, laminated clays, and numerous intercalated beds of coal. The organic remains of these upper Cretaceous, as I have shown when describing that formation, are numerous vegetable remains, including the leaves of palms, and mol- lusks of the genera Ostrea, Anomia, Corbicula, Corbula, Cyrena, Goniobasis, and Viviparus; while above these Meek, Bannister, and Cope exhumed a portion of a skeleton of Agathawnus sylvestris, a distinctly Cretaceous Dino- saur. Passing upward, Cope obtained in the immediately overlying series the following list: Clastes ? glaber. Emys megaulax. Emys pachylomus. Emys euthnetus. Trionyx scutumantiquun. Alligator heterodon. Orohippus vasacciensis. All these types are distinctly Tertiary. The following list, partly from Green River Basin, will give the characteristic features of the verte- _brate fauna of the group: VERMILION CREEK GROUP, CARNIVORA. Oxycena lupina, Cope. Oxyena forcipata, Cope. Pachyena ossifraga, Cope. UNGULATA. Phenacodus primevus, Cope. Meniscotherium chamense, Cope. Helaletes singularis, (Cope) Marsh. EOCENE TERTIARY. Sidad. Enohippus tapirinus, (Cope) Marsh. Lohippus angustidens, (Cope) Marsh. Eohippus cuspidatus, (Cope) Marsh. Eohippus validus, Marsh. Eohippus major, Marsh. Eohippus pernix, Marsh. Parahyus vagans, Marsh. Coryphodon hamatus, Marsh. Coryphodon elephantopus, (Cope) Marsh. Coryphodon latidens, (Cope) Marsh. Coryphodon radians, (Cope) Marsh. TILLODONTIA. Dryptodon crassus, Marsh. Esthonya bisulcatus, Cope. Ectoganus gliriformis, Cope. Calamodon simplex, Cope. REPTILIA. Diplocynodus stenops, Cope. Crocodilus grypus, Cope. Crocodilus heterodon, Cope. Trionyx leptomitus, Cope. Trionyx radulus, Cope. Plastomenus corrugatus, Cope. Plastomenus communis, Cope. Dermatemys costilatus, Cope. It will be seen from these facts that I am fully justified, first, in assert- ing general nonconformity between the Laramie and the Vermilion Creek; secondly, that the angular conformity in the region of Washakie Basin is exceptional; thirdly, that the Vermilion Creek fauna is distinctly lowest Eocene. Green River Grovp.—Not only is the middle member of the Eocene series, or the Green River group, unconformable with the rocks of the Ver- milion Creek group, but from certain occurrences in western Utah and 378 SYSTEMATIC GEOLOGY. eastern Nevada it is now known that it overlaps to the westward at least 200 miles. Within the area covered by Vermilion Creek rocks the Green River series rests for the most part unconformably upon the horizontal as well as the highly inclined Vermilion Creek beds. It probably somewhat overlapped the Vermilion Creek rocks toward the east, but the area of the lake in which it was deposited expanded westward to certainly twice the east-and-west dimensions of the lake of the Vermilion Creek period. At first it seemed possible that the exposures of the Green River Eocene, which are observed in western Utah and eastern Nevada from longitude 114° to 116°, might represent a second middle Eocene lake, whose deposits and fauna are identical with the contemporaneous deposits and fauna in the Green River region; but the recent discovery of Tertiary beds near Stockton, west of the Oquirrh Mountains, and the extension from the Oyster Ridge region far to the northwest, or toward the Great Basin country, con- firm the general belief that the detached outcrops between the meridians 114° and 116° are really parts of the sediments of one lake. The way in which the Vermilion Creek beds abut against the eastern flank of the Wahsatch nearly up to its summit, is sufficient warrant for the belief that that range formed the westward barrier for a great amount of the sediments of the early Eocene lake. But when we pass eastward from the immediate neighborhood of Wahsatch Range, it is found that the slightly inclined Vermilion Creek beds rise rapidly in altitude, still maintaining their horizontal position and forming extensive plateaus, which have been more or less eroded, leaving isolated highlands and even mountain peaks, all made of horizontal beds. Such points are the high peak directly northwest of Wanship, and the elevated plateau country north of Croydon, also Bear River Plateau, which lies to the east of the Cambrian anticlinal on the northern portion of our Map III. From an examination of the outcropping edges of these horizontal Vermilion Creek beds, it is clear that if continued westward they would pass over the top of Wahsatch Range; while an ex- amination of the country to the west of the range shows a depressed basin in which, so far, no traces of Vermilion Creek rocks have been discovered. One must therefore believe either that the Vermilion Creek rocks formerly extended over the top of the now exhumed Wahsatch Range and continued EOCENE TERTIARY. 379 to some indefinite distance westward, or else that the Wahsatch formed the barrier to the westward extent of the lake, and that subsequent faults have carried down the region west of the range, while the erosion of the glacial period has degraded the main Wahsatch range, so that it is now below the level of the Eocene plateaus directly to the east. From evidence to be adduced in the chapter which treats of orographical disturbances, it will be seen that unquestionably a series of enormous faults occurred posterior to the deposition of the Vermilion Creek series, which depressed the whole country out as far as middle Nevada, and which permitted the waters of the Eocene lake to flow westward and make a comparatively continuous sheet from the Rawlings uplift at longitude 107° to longitude 116°. Ac- companying this great dislocation, the Vermilion Creek rocks east of the Wahsatch were thrown into a series of more or less abrupt folds. Along the northern slope of the Uinta, in the region of Henry’s Fork, they were uplifted at an angle of 25°, and in general they sagged downward to form two prominent basins, one of which forms the Bridger Basin, the other the basin of Washakie. At the beginning of its existence, then, the middle Eocene lake had for its bottom, from its eastern shore as far west as the Wahsatch, the hori- zontal or upturned beds of the Vermilion Creek, that covered all but the single mass of Uinta Range, which probably formed a great east-and-west island in the lake. That portion of the lake lying west of the Wah- satch occupied a region in which the Carboniferous were the uppermost rocks, a region which had been a continental land-mass since the close of the Carboniferous, and over which no Mesozoic or lowest Eocene strata had been deposited. It was, indeed, the land area from which the materials of the eastern Mesozoic and the main mass of the Vermilion Creek Eocene beds had been furnished; and it must have been, as we may judge from the relations of the slight exposures of western Eocene beds to the older rocks, a comparatively corrugated region characterized by bold ranges of Palseozoie rock, many of which doubtless projected above the level of the middle Eocene lake, creating a complex archipelago. From the character of the Eocene deposit west of the Wahsatch, we may assume that the lake in that region during the latter part of its history 380° SYSTEMATIC GEOLOGY. was comparatively shallow, and that the detritus was largely derived from the islands, partaking of their extremely localized character. On the other hand, the rocks of the Green River Basin of this same period show deeper waters and excessively fine sediments, which might have been transported from a considerable distance, and which doubtless represent material not only from the neighboring Uinta Range, but from a variety of different sources around the whole shore of the lake. The sediments, deposited noncon- formably against the sharp, ridgy chains of the archipelago of the west, show always a sharp nonconformity with the immediately underlying rocks. On the other hand, in the region east of the Wahsatch, a large amount of the Vermilion Creek series was left in a nearly horizontal posi- tion, and the sediments there sank quietly through deep water upon an approximately level bottom, accumulating in strata nearly conformable with the underlying Vermilion Creek rocks. From the manner in which the rocks of the Green River group abut westward against the Vermilion beds, it is evident that there was in the region included between the Wah- satch and Uinta a highland lifted above the lake of the Green River period. Exactly the extent and area of all the islands which rose above the surface of the Green River lake, it is at present impossible to tell. The central and higher parts of the Uinta were out of water, but it seems quite clear that the depressed portions of the eastern end of the range were for the most part submerged. 'The entire Vermilion Creek series, as we have seen, was made up of sandstones and intercalated clays, with more or less conglomerates near the old shores of the lake. This detritus doubtless came partly from the erosion of the siliceous Cretaceous beds which must in great part have formed the shore and islands of Vermilion Lake. But it would seem that about the close of the Vermilion Creek period, erosion must have worked off from the higher summits most of the Mesozoic rocks, and with the beginning of the Green River group have begun its work of degradation upon the calcareous beds of the Carboniferous. The Green River beds are in sharp contrast with those of the earlier Eocene, first, by the extreme fineness of the material, and, secondly, by their calcareous nature. As a whole, east of Wahsatch this group consists of caleareous sands and slightly siliceous limestones, which are overlaid by EOCENE TERTIARY. 381 remarkably fissile calcareous shales, the former abounding in fresh-water mollusks, the latter in the remains of fishes, plants, and insects. The lower member, the impure limestones, probably reaches about 800 feet in thickness, and the thin, fissile, caleareous shales about 1,200 feet, making a total of 2,000 feet for the entire group. To what height they originally reached along the northern flank of the Uinta, is in a great measure unknown. Where the overlying Bridger group overlaps them and abuts against the Coal Measure limestones of the Uinta, as it does from Mount Corson to Concrete Plateau, there is, of course, a certainty that the Green River beds extended no farther to the south; and likewise directly west of Concrete Plateau, where the Bridger comes into actual contact with the Vermilion Creek, it is clear that the Green River beds did not extend in that direction. But in the region of the present valley of Green River they doubtless extended much higher against the flanks of the range, and east of the Uinta saddled across the divide into the valley of White River. Over the Washakie Basin they occupied the greater part of the area, and were there again deposited as fine calcareous sediments. Detached outliers of the Green River series still exist between the Bitter Creek Cretaceous uplift and the Archzan mass at the head of Red Creek, sufficient to show that the sheet of sediment stretched over all that country and connected the Washakie and Bridger basins. The chief present outcrops of the Fortieth Parallel region are: First, a narrow strip east of Oyster Ridge, first observed near Piedmont Station, where it overlies unconformably the Vermilion Creek rocks, and is itself overlaid by the Bridger with heavy Quatenary desert deposits to the east. This narrow zone extends in a northeasterly direction as far as the northern limits of our map, and probably over into the Nevada extension of the Green River lake, the exposure gradually widening to the north, where it covers eight or ten miles. The next, and by far the most characteristic development, is a broad belt extending from the northern edge of the map in a meridional direction down the valley of Green River to the foot-hills of Uinta Range. It is from this typical display in the valley of Green River that the group has derived its name. Farther east the broad area occupying the middle of Washakie 382 SYSTEMATIC GEOLOGY. Basin, and extending over the region from O-wi-yu-kuts Plateau to the White River divide and southward, forms decidedly the most important geo- graphical area of this group within our limits. The most eastern exposures are west of the valley of Little Muddy Creek, in the region of Washakie Mountain, where the variegated upper beds of the Vermilion Creek group, which have a dip of from 4° to 5° westward, are overlaid by the horizontal brown sandstone and blue cal- careous shales and clays of the Green River series. This locality is of special interest as displaying the nonconformity of the two groups at the most eastern exposure of the Green River, and the gradual rise of the Vermilion Creek group passing eastward would indicate that a portion of the earlier group was lifted above the level of the lake of the Green River period, or at least above its plane of deposition. From this point the margin of the Green River formation defines a rude circle through Cathedral Bluffs, Table Rock, Pine Bluffs, Vermilion Bluffs, and Sunny Point, the strata of the series always presenting their edges to the exterior of the area in a more or less important escarpment, but dipping in from every direction, at gentle angles, toward the centre of the basin. In passing from Washakie to Cathedral Bluffs the plane of contact of the Ver- milion Creek and Green River series is depressed toward the north until at Barrel Springs it reaches the lowest point, and then rises again. At Cathedral Bluffs, capping an exposure 600 or 700 feet thick of the upper Vermilion Creek beds, is a layer 100 or 150 feet thick of the impure limestone which forms the base of the Green River group. It is here of concretionary structure, with a dull drab color, carrying more or less sili- ceous matter, and near the top a prominent seam four or five feet thick of odlitic limestone largely metamorphosed into chalcedony. The round grains are from a thirtieth to a tenth of an inch in diameter. They are of more or less concentric structure, showing a cryptocrystalline calcareous cement. They are probably crystallitic and not organic, and may be related to the calcareous spherical sands, examples of which are now found on the beaches of Great Salt Lake. They here contain 74.81 of silica, the remainder being carbonate of lime. Besides this bed there is a prominent chalcedonic stratum made up of casts of Goniobasis. Farther west, at Table Rock, EOCENE TERTIARY. 383 the summit is of calcareous beds with more or less lignite, several of the thin limestone beds being almost entirely composed of Melania, Viviparus, Unio, and other fresh-water shells. The siliceous odlitic bed observed upon ‘athedral Bluffs recurs here. Very characteristic displays of the Green River series are observed at Pine Bluffs, a conspicuous escarpment which offers a commanding view over the valley of South Bitter Creek and the Washakie and Vermilion Creek basins. The upper 400 feet of the escarpment are made up of a highly calcareous buff sandstone, which dips 4° to 5° to the east and strikes a little east of north. Directly beneath the sandstones are white, shaly beds un- derlaid by thin sandstone, all slightly calcareous. At the Springs, where Bitter Creek emerges from the Green River area, about ten miles north of Pine Bluffs, are admirable exposures of the charac- teristic limy beds and shales of remarkably fissile structure, which readily split into flakes almost as thin as a sheet of paper. These are more or less interspersed with carbonaceous and arenaceous beds, the carbonaceous mem- bers especially showing a tendency to whiten on exposure to the air. Con- siderable surfaces of the upper valley of Bitter Creek are covered by white chips of the calcareous and carbonaceous shales, which, by exposure to the air, have acquired this peculiar chalky appearance. The shales at Barrel Springs, another point near the extreme boundary of the Green River area, lying south and east of Cathedral Bluffs, are highly carbonaceous, and, as usual, are intercalated with more or less sandy members. They are rich in leaf-impressions, and among the numerous fresh-water mollusks have been recognized — Unio. Tellinides. Goniobasis tenera. Goniobasis nodulifera. Goniobasis Cartert. In the region of Cherokee Ridge the very slight dip toward the centre of the Washakie Basin, which is observed in all the distinct outcrops of the Green River area, gives way to a local anticlinal where beds of the series are observed dipping 7° northward, the line of Cherokee Ridge marking 384 SYSTEMATIC GEOLOGY. pretty nearly the axis of the anticlinal. The series here consists of drab laminated sandstones, slightly calcareous and abounding in casts of Gonio- basis, the sandstones passing into slightly saccharoidal, creamy-brown lime- stone. The whole northern half of this anticlinal declines at first to 7°, passing unconformably under the overlying Bridger series to the north; but the southern member of the anticlinal, which seems to have been some- what faulted up, declines to the south at angles of from 25° to 30°, marking the highest slope developed in the Green River group. The area enclosed between Vermilion Bluffs, Brown’s Park, the Esca- lante Hills, and Snake River, is one in which the relations of the Tertiary are involved in much obscurity. It is a region which has suffered exten- sive faults and extraordinary erosion, and is for the most part largely cov- ered with deep accumulations of soil. It is certain that at some point in Vermilion Bluffs the Green River strata occupy the surface, and we are unable to observe any break from Vermilion Bluffs southeastward into Brown’s Park. The rocks in Brown’s Park are also in great measure covered by local accumulations of soil. Throughout the southern part of the valley, wherever exposed, the Tertiaries are seen to be approximately horizontal, and to be composed of soft, friable beds. Along the north wall of the valley there is a sharp break, however, and the Tertiary rocks which come to the surface lie immediately against the quartzitic sandstones of the plateau and dip to the south at an angle of 18° to 25°. They are of a rather coarse, gritty char- acter, containing many sheets of fine pebbles, and are prevailingly calca- reous. They are unlike any Tertiary in the region; but from their calca- reous nature, the fact of their being upturned at so high an angle, and their apparent connection with the series which sweeps around the eastern end of O-wi-yu-kuts Plateau, they are assigned by Mr. Emmons to the Green River age. There seems to be a decided difference between the strata which were seen uptilted along the south base of the O-wi-yu-kuts Plateau and the soft, white, friable, horizontal beds of the valley itself, which are seen to extend eastward well toward the divide separating the valley of Vermilion Creek from that of Little Snake River. It is not improbable that there are two distinct members here—the Green River, which is seen inclined along the northern edge of the park, and a more recent horizontal EOCENE TERTIARY. 385 member, assigned to a special group by Powell, which overlies the beds we have referred to the Green River age. The surface of the whole Green River outcrop, both of the Washakie Basin and of the southern area from Vermilion Bluffs southward to the White River divide, is always characterized by a more marly soil, by infre- quent outcrops of solid rock, and by the prevalence, among the few actual exposures, of calcareous members, sandy shales, or thin fissile shales, vary- ingly carbonaceous, and always more or less charged with casts of Gonio- basis, Melania, and Viviparus. Along the whole valley of the Little Snake, at Sunny Point, as well as at Godiva Ridge and Elk Gap, the lower horizon of the Green River group is easily recognized, consisting of calcareous sand- stones and impure limestones, resting, as usual, upon the brilliantly striped beds of the upper Vermilion Creek. At Sunny Point particularly there is a thickness of about 950 feet of Green River, made up as follows: Feet. 1. Coarse brownish sandstone, with intercalated brown calcareous SIME 2 oA as See ee ee ne Be eres ee einer aecarte 100 2. White calcareous shales, with half-inch seams of gypsum and a four-inch seam of agatized Unios.-..-.-------------------- 45 3. Drab, concretionary limestone, with brown sandstone shales.-.. 85 4. White and brown argillaceous shales...-.-------------------- 120 beitusty, arenaceous, shales: --_.... 4-2-8. 24----+=------2----- 100 6. Beds of soft, light-colored, argillaceous and calcareous shales, some of which are impregnated with carbonaceous material and have a light blue color on the weathered surface, contain- ing also small seams of gypsum ..-.----------------------- 400 fee ibitersandstones;and (clays 2) 5282-6 2252-2 100 The relation of the two series at Elk Gap is somewhat perplexing, from the unusual attitude of the rocks. The lower exposure consists of the upper members of the Vermilion Creek group, which dip to the south at an angle of 10°, but are overlaid by a series of somewhat calcareous sand- stone having at the base a prominent red shale, the upper member dipping 29° to the southwest. A short distance down the river both series are found perfectly conformable. In order to account for this position, it is 25 K 386 SYSTEMATIC GEOLOGY. necessary to suppose that, prior to the deposition of the Green River series, a portion of the Vermilion Creek series was faulted up with a considerable northerly dip, and that since the deposition of the Vermilion Creek series nonconformably over this faulted rock, a second disturbance has taken place in this locality which has reversed the dips of both series to south, thus bringing the underlying bed, which formerly had a steeper dip to the north, into the position of a less steep dip to the south. It is notice- able that the line of strike of this steeply southward-dipping Green River series at Elk Gap would carry it directly into the northern edge of Brown’s Park, where beds also assigned by us to the Green River series hold the same position, dipping 25° to the south. It would seem, therefore, that a long line of displacement has occurred here, with a downthrow to the south. Provided the upturned beds in Brown’s Park are, as we suppose, Green River, there is a vertical displacement of 5,000 feet between them and the series of the same horizon north of the Archean mass on Red Creek, the Brown’s Park being the depressed member. Around the base of Godiva Ridge, overlying the variegated beds of the Vermilion Creek series, are the sandy and calcareous lower members of the Green River series, capped by white limy rocks, containing silicified beds made up of casts of Goniobasis, an occurrence, as we have seen, most fre- quent in the lower Green River series. There is apparently a slight non- conformity between the two series here, but it is decidedly less marked than at Elk Gap. Beneath the Wyoming conglomerate on the summit of Vermilion Bluffs is an exposure of 500 or 600 feet of calcareous beds, here largely made up of papery shales of the Green River. Excellent exposures are obtained on Vermilion Creek, below its canon, which is cut through the Carboniferous series. Here the beds are com- posed of a characteristie white, fine-grained, siliceous material, intercalated with coarser, loosely compacted drab sandstones, the latter containing among the siliceous material a great many feldspar and mica particles. Besides these intercalations, certain members of the white silts have a pecu- liar silky lustre, and pass into fine siliceous limestones and calcareous shales. Moreover, not a few of the limestone beds develop concretionary structure, EOCENE TERTIARY. 387 a peculiarity confined, so far as we have seen, among all the Tertiaries, to the Green River group. The White River divide, as before mentioned, is formed of the Lara- mie Cretaceous rocks, which have a sharp northerly pitch of 25°. They are unconformably overlaid by soft calcareous Tertiaries which dip to the north at only 3°, and which stretch uninterruptedly northward, connecting with the caleareous beds of Godiva Ridge. As displayed near the divide, there are about 1,500 feet of these rocks, which are unquestionably but the relic of a wider extension. From the character of the Green River series directly south of the White River divide, where their identification is rendered complete’ by the recurrence of fossils characteristic of the beds in the region of Green River City, there is no doubt that the Green River beds formerly saddled across the whole divide and formed a continuous sheet of sediment far to the south. Beneath the Wyoming conglomerate of Bishop Mountain a thin sheet of the Green River calcareous beds extends to the north and west toward Tabor Plateau, overlying the upper beds of the Vermilion Creek series. On the western side of South Bitter Creek, upon Tabor Plateau, and thence for fifteen or twenty miles northward, the Green River series not only overlies the Vermilion Creek, but overlaps the Laramie and Fox Hill Cretaceous beds, the calcareous Eocene beds having a dip of 4° to the north. From twelve miles above Green River City down to Flaming Gorge, the whole valley of Green River is excavated from the nearly horizontal strata of the Green River series. Between the Cretaceous of the Bitter Creek uplift and the eastward margin of the area of the Green River rocks is a narrow band of the Vermilion Creek rocks, extending from north of the map as far as Sage Creek. Between this series and the Cretaceous rocks, we have described a slight nonconformity ; but between them and the overlying Green River calcareous beds just to the west there seems to be no recognizable angular discrepancy, at least as far south as Sage Creek. From that point southward there is a slight and growing discrepancy, which, north of the northern foot-hills of the Uinta, becomes a perfectly distinct nonconformity. North of Big Horn Ridge, and especially where 388 SYSTEMATIC GEOLOGY. Green River enters the Quaternary valley north of Camp Stevenson, the discrepancy between the two series is also perfectly clear. Perhaps the most characteristic development of the Green River series is to be found in the neighborhood of Green River City, where the Union Pacific Railroad crosses the river. Here, on both sides of the stream, the broad valley is walled in by cliffs and hills formed of the calcareous shales and sandstones of the Green River group, which are displayed for a thick- ness of scarcely less than 2,000 feet. Inarailway-cut on the western bank, the extremely fine paper shales that occur on both sides of the river have yielded numerous fossil fishes, of which the more characteristic forms are enumerated later in the section. Plate XIV. gives an excellent idea of the steep cliff bordering the river immediately north of Green River City. Here the shales are excessively thin and fine-grained. Plate XIII. is a close, detailed view of the same cliff front. The plateau north of the railway and east of Green River Valley is a gently rolling summit. In the immediate vicinity of the railway, rise isolated, tower-like rocks, which possess all the abruptness and hardness of outline of artificial fortifications. The sculpture of the shales along the river banks is also extremely interesting, displaying vertical cuts 300 or 400 feet high, capped by rounded hill-tops, and these in turn by towers. South of the city, on the eastern side of the river, is a remarkable series of hills stretching back four or five miles from the river, appropriately called by Powell the Alcove Ridges, from their singular mode of erosion. The river cliffs are here cut by transverse ravines, bold headlands project- ing against the river bank with almost vertical faces. The exceedingly fine characteristic shaly structure of the upper part of the group is also well shown in Bitter Creek Valley, in a railway cut The plateau to the north of the railway presents to the south and east a bluff from 800 to 1,000 feet high. All these strata dip at gentle, almost imper- ceptible angles to the west toward a middle line of depression, in the Bridger Basin. At a short distance west of Green River the calcareous shales pass, with apparently a slight unconformity, beneath the softer beds of the overlying group. As exposed by the river-cut and the Aleove Ridges, LOCENE TERTIARY. 389 there is no less than 2,000 feet of the series displayed, of which the white and brown paper shales occupy the upper 1,200 feet. Throughout this thickness they are more or less intercalated with arenaceous beds, which at the base of the shale-series rapidly increase in proportion and become more and more calcareous, finally appearing either as marly sandstones or as creamy-white, brittle, fine grained, earthy limestones. Capping the shales, and making the uppermost member of the series in the region of Green River, are displayed about 100 feet of brown-sandstone of massive structure. It forms the heavy, dark-brown cap upon the bluffs in the region of Green River City, where all traces of the original stratification are lost, and the rock presents an appearance of somewhat peculiar local metamorphism. The physical characteristics, especially the compactness, of this upper rock, vary very greatly, and to this fact may be due the circumstance, that ex- ceptional parts of the bed have resisted erosion and protected the softer underlying shales from wearing down, which has resulted in the remarkable turret and bastion forms that characterize the region. Although enormous numbers of individual fossil fishes are obtained from these shales, the number of genera is exceedingly small. The types are closely allied to those of Monte Bolea, in Italy. Fresh-water mollusks which are found in the more compact limestones of the lower portion of the group are chiefly Viviparus and Goniobasis, genera found in both the Vermilion Creek and the overlying Bridger series. There are no brackish- water forms whatever. A considerable amount of the fine calcareous shale- series is heavily charged with bituminous matter, a very large portion of which is volatile. Throughout the region near the railway the shales possess a charac- teristic dip of 3° to 4° to the west, which they retain on the western side of the river. Near the summit of the low, flat ridge between Green River and Black’s Fork, they pass under the thinly bedded drab sandstone which forms the base of the Bridger group. The latter never possesses a dip of more than 2°. The contact of these rocks is well covered with disintegrated soil; but when last seen the Green River beds, before they pass under the Bridger, still retain their dip of 4°. It is therefore probable that the two formations have here a slight nonconformity, a condition 390 SYSTEMATIC GEOLOGY. of things which is rendered more probable by the peculiar overlap of the Bridger in the region of Concrete Plateau. The dip of 4° extends all the way down the river to the lower valley of Henry’s Fork. East of the river this group forms broad terraces which ascend toward the east as far as the meridian of Quien Hornet Mountain, while a short distance to the west of the river they invariably pass under the horizontal Bridger series. With the exception of the anticlinal in the Green River group, already described at Cherokee Ridge, the highest observed dips of this series are along the flanks of the Uinta Mountains. From Quien Hornet Mountain to Green River the caleareous under- lying members of the group dip at 5° to the north, with a slight inclination to the west, unconformably overlying the Vermilion Creek group with a discrepancy of angle of 5° to 12°. Where Green River emerges from its upper valley into the broad, open area above its confluence with Henry's Fork, the limestones which form the base of the Green River series dip 5° to the north, while the underlying sandstones and clayey beds of the upper portion of the Vermilion Creek underlie them at higher angles, usually 8° to 14°. West of Green River the upper shales appear at the bases of the long eastern spurs. From Twin Buttes, and north of Dead Man’s Springs, the valley of Henry’s Fork passes through the Green River formation for four or five miles. Here: is displayed a small lignite bed. The highest inclination recognized in these beds is north of Dead Man’s Springs, where the low ridges, made up of yellow sandstone and the creamy-colored brittle limestone, dip northward from 20° to 25°, carrying, as usual, an infinite number of casts of Gonio- basis. West of Bridger Basin the display of Green River rocks is very limited. As before mentioned, it at first makes its appearance coming out from under the Bridger beds in the vicinity of Piedmont, and thence northward its exposure increases in width, until at the northeastern edge of our map the belt is about thirty-five miles wide, and probably includes the northern limit of the Bridger Basin. South of Piedmont it seems clear that the Bridger group completely overlaps the Green Tiver, coming directly in contact with the Vermilion Creek, which gradually y g! 4 ay EOCENE TERTIARY. 391 rises toward the west, occupying higher and higher positions, till it reaches the elevated plateau made in the angle between Uinta and Wahsatch ranges. This plateau, which received its relative elevation at the close of the Ver- milion Creek period, slopes gradually to the east and again gradually to the north, and the Green River formation abuts against the gently inclined beds of this series, describing a curve northward, and swinging around to the west through northern Utah into Nevada. Near Piedmont the white, impure limestones and thin, calcareous shales have yielded a few fishes sdentical with those found in the shales near Green River City. North- ward they pass across the railway west of Carter’s Station, and are there represented by light, creamy, calcareous beds. Down the valley of Bear River, beyond the northern limits of Map IIL, the rocks of the Green River group have been observed by Dr. Hayden, and north of Oyster Ridge, on Fontanelle Creek, by Professor Cope. The discovery of this group at these two points seems very clearly to warrant the belief that the lake of that period extended westward around the north of Bear River Plateau, connecting with the deposits to the west, which are about to be described. . At the extreme northwestern limits of the Great Salt Lake Desert, at the eastern foot of the prominent group of the Ombe Mountains, out- crops a series of beds which dip at an angle of 45° to the east, with a general north-and-south strike. Their most prominent exposures are about ten miles south of the railway. Although devoid of fossils, they are readily referred by their lithological characteristics to the Green River series, consisting as they do of white and thinly bedded shales, both siliceous and calcareous, equally fissile with those of Green River, and, like them, charged with richly bituminous zones, the latter sometimes reaching the condition of coal and appearing in beds one or two feet in thickness. The material of the coal is a jet black, lustrous mass, which, however, slakes, crumbles, and becomes valueless on exposure to the air. This correlation is not based solely on the resemblance of the beds to those of the distant Green River Basin, but also on identical rocks a little farther west, which are well charged with Green River group fossils. A few miles farther west, and a short distance from Peoquop Range, 392 SYSTEMATIC GEOLOGY. there is a break in the continuity of the great Paleozoic bodies. In this depressed basin, as shown on Map IV., where the Quaternary is not pres- ent, may be seen the upturned edges of rocks of the Green River period, striking about east-and-west, resting unconformably upon the Palzeozoic series on both sides of the gap. They strike a little north of east, and dip both to the north and south, with a varying inclination of from 5° to 20°. They are in general a series of fine carbonaceous shales and marls of a pre- vailing yellow-brown hue, though occasionally passing into blackish beds, where the carbonaceous matter is highly concentrated. The lowest strata are heavy red shales and marls, with a few indurated gray clays as the basal member. Although no organic remains have been found here, they are referred to the Green River period by their exact resemblance to the beds which occur at Elko, a little farther west. A further development of these Green River beds is found in Hunting- ton Valley, extending from Dixie Valley southward. The rocks occur here as a low ridge between the Dixie trachyte hills upon the west and a body of Lower Coal Measure limestones on the east. They consist of creamy calcareous rocks, sandy marls, and fine calcareous shales, con- taining the usual carbonaceous seams, and even thin coal-beds. The eal- careous shales yield fragments of fossil fishes evidently identical with those of Elko, but too nearly obliterated for specific determination. The beds have a dip of 30° to the east, and strike about north 20° east. Here is displayed an interesting relation to the trachytes which have broken through them. A very characteristic member of these Green River shales is found on the eastern base of the River Range, due north of the station of Osino. As in the Dixie group, the characteristic beds are white and creamy brittle limestone, in beds six inches to a foot thick, overlaid by calcareous and arenaceous shales carrying beds of clay from one to two feet thick. The development of carbonaceous material here rises to the importance of coal-beds, of which one is two feet, another five to six feet, another three feet thick, besides which there are many brown beds of carbonaceous material containing a high proportion of volatile hydrocarbons, burning when heated with an intensely bright flame for a short time, and then EOCENE TERTIARY. 393 crumbling into a loose ashy residue. The coals of the true coal-beds are black, lustrous lignites, containing a great many yellow, amber-like grains, and white coatings of sulphate of lime through the cracks and fissures of the coal. Like the Ombe coal, this rapidly slakes and crumbles upon expo- sure to the air, and has little commercial value. Above the coal-seams in the characteristic bituminous shales, which are here highly calcareous, the true paper shales of the formation, are found great numbers of fishes and insects of the identical species occurring at Green River City. From all that may be seen at Dixie and on the flanks of River Range, it is probable that there are 2,500 or 3,000 feet of beds in these exposures. At the coal-mine the dip is 45° to the east, while farther down the ravine it rises to G5°. The same series of beds recurs in Elko Range, east of Elko Station. They here have a strike about due north, and dip 35° to the east, and consist of very thin shales, sometimes calcareous, often sandy, and again dark-brown, with bituminous matter. Fragments of an undeterminable fish were the only fossil discovered by us here. West of Dixie Hills no outcrops of the Eocene have been recognized, and for the present we must consider that Pinon Range was the western boundary of the Green River group. I ought not to close this subject without remarking again that, although I consider the general tendency of the evidence warrants the belief that these western deposits represent truly the extension of the great lake of the Green River period, yet at the same time the absence of outcrops between Ombe Range and Bear River renders it possible that the western group of occurrences may represent an independent lake.* Whatever may have been the climate in the region of the western out- crops, there can have been no change between there and the Bridger Basin. The atmospheric condition must have been practically the same; and since both sets of strata are characteristic of still and deep-water deposition, it is not strange that the species should be the same, even if the lakes themselves had no communication. It is only necessary that they should drain into *Since the above was written, inclined coal-bearing fresh-water Tertiaries have been observed near Stockton, at the base of Oquirrh Range, thus indicating very positively that the group once stretched quite to the base of the Wahsatch. 394 SYSTEMATIC GEOLOGY. the same ocean to account for the identity of species, because the only remains of aquatic fauna besides the fresh-water mollusks have been fishes, certain of which, from their nature, once probably migrated annually to the south and were afterward land-locked. The following are some of the more characteristic fossils of this group: GREEN RIVER GROUP. FISHES. Clupea humilis, Leidy. Clupea alta, Leidy. Clupea pusilla, Cope. Osteoglossum encaustum, Cope. Asineops squamifrons, Cope. Asineops viridensis, Cope. Erismatopterus Rickseckeri, Cope. Heliobatis radians, Marsh. INSECTS. Antherophagus priscus, Scudder. Endiagogus saxatilis, Scudder. Trypodendron impressus, Scudder. Corymbites velatus, Scudder. Bripcer Grour.—The belt of Eocene country studied by this Explo- ration leaves some open questions as to the physical conditions at the close of the period of the Green River rocks. I have shown that at the close of the Vermilion Creek the lake which had formerly extended from the meri- dian of 107° 30’ to the Wahsatch was rather suddenly allowed to expand itself westward to the meridian of 116°, the expansion being caused by the subsidence of the country between the Wahsatch and the meridian of 117°. So isolated are the present outcrops of the Green River rocks which have accumulated in the western portion of the lake, that we have a very slender basis from which to reason as to its conditions. The fauna was identical with that of the Green River Basin, the rocks show a singular likeness to those in the eastern areas We are somewhat at a loss when we proceed to examine the areas and EOCENE TERTIARY. 395 character of the Bridger group or next succeeding member of the Eocene; the main difficulty being to determine whether the few isolated bodies of Bridger rocks represent parts of what was formerly a continuous sheet, or whether at the close of the Green River period the lake limits were immensely con- tracted, and the Bridger series only permitted to accumulate in certain small, detached basins. Much light would be thrown on this were we able to decide finally whether the Green River and Bridger series are conformable with each other; but it so happens that the Bridger beds are usually found in the middle of basins, in nearly horizontal position. These areas of Bridger rocks are surrounded, as a glance at the map will show, by groups of the Green River formation, which pass under the Bridger at angles so slight as to leave it somewhat uncertain whether they are strictly uncon- formable. On this point, however, all the positive evidence is in favor of a true nonconformity. Whatever may have been the conditions in the basin of Green River, it is clear that the western part of the lake, namely, that west of the Wahsatch, never received any sediments of the Bridger period, since it is inconceivable that if they had accumulated in such a large area as the expanded Green River period lake is known to have covered, some fragments should not have escaped both processes of removal and burial which have been active over this area since Eocene times. From the relation of the Green River beds with the high, rocky, mountainous ridges near the 116th meridian, it is evident that there were large areas from which detritus must have been removed during the Bridger age, and there is no reason to suppose that very much less material would have been accumulated than in the basin of Green River, for nearly uniform climatic conditions must have obtained over both regions ; and while 2,000 feet of the sediment of the Bridger period were accumulating in the restricted basin of Green River, there was land-mass enough, which must have yielded a very large, if not indeed an equal amount of sediment over the area of the western part of the lake. The total absence of any Bridger beds may be considered as a strong indication, amounting almost to proof, that there was a great physical change at the close of the Green River age, which gave to the country west of the Wahsatch, drainage either to the sea or into the Green River Basin; in other words, that it was no longer 396 SYSTEMATIC GEOLOGY. a lake west of the Wahsatch. That since the Green River period there has been sufficient mechanical disturbance of the area to bring about the new condition, is evident from the extreme dips of the Green River rocks near the River Range of Nevada, where they reach 60°, and at Cherokee Ridge, in Wyoming, where the southern side of the east-and-west anticlinal dips to the south at angles reaching 25°. If this disturbance took place, as the evidence indicates, immediately at the close of the Green River period, it will sufficiently account for the isolation and limitation of the deposits of the Bridger period. If, however, they succeeded the Green River beds without any orographical changes, we can only account for their absence over the region west of the Wahsatch by supposing that the sediments of the Green River had previously filled up that portion of the lake. In either case, there was no lake during Bridger time west of the Wahsatch. Supposing the Bridger beds of the Washakie and Bridger basins. to have been deposited conformably in the same lake which laid down the Green River series, and to have been uplifted together with the Green River in a post-Bridger upheaval, it is not a little remarkable that erosion should have removed the Bridger from all parts save the middle of these two basins. The few observations which bear upon this point in the way of the dips of the two formations combine to indicate that the movement took place at the close of the Green River period, that the western lake was extin- guished by this upheaval, and that the waters of the period formed a lake of restricted area altogether within the basin of Green River. Even with this supposition, which I conclude to be the most probable until it may be varied by future evidence, there is left the shadow of a doubt whether the three Bridger bodies which appear upon our map—that of the Bridger Basin, the Washakie Basin, and the region east of Vermilion Creek—were parts of a continuous sheet, or whether they themselves were areas of special lakes in the same general basin, isolated from each other, but characterized by great fauna resemblances. A glance at the eastern half of Map II. shows that the middle of the Washakie Basin is occupied by an irregular area of beds of the Bridger period. It has an extension of about twenty-five miles from east to west, by sixteen to twenty from north to south. It is completely surrounded, as rs Ae Reyes + AY pe 1 -3 EOCENE TERTIARY. 397 already described, by the beds of the Green River period, which dip at gentle angles toward the middle of the basin. The inclination is never over 4°, except on the northern side of the Cherokee anticlinal, where it steepens northwestward to 7° and passes with apparent nonconformity under the Bridger series. 'The country around the girdle of Green River rocks is largely covered with soil, and the few outcrops are either creamy lime- stones, calcareous shales, or slightly calcareous sandstones. Immediately in the neighborhood of the junction of the Bridger and Green River groups, the plains are covered with extensive deposits of soil, so that the actual con- tact of the two deposits is rarely seen. From twelve to fourteen miles southwest of the head of Bitter Creek are seen exposures of the soft green clays, marls, and whitish-gray sands of which the upper beds of the Bridger group are made. Pass- ing eastward of Pine Blufis, the country is covered with more or less drifting sand, which forms noticeable trains of dunes. The sand sud- denly gives way to the soft Bridger beds which are intricately eroded into branching ravines. This bad-land country extends southeastward to the mouth of a dry valley north of Cherokee Ridge, and from that point a chain of bluff escarpments extends northeasterly for twelve or four- teen miles. The relations of this sharp wall to the Green River coun- try to the south are obscured by deep accumulations of valley soil; but the nearest approach of the two sets of strata shows the Bridger lying nearly or quite horizontal, the other dipping at 7°. This escarpment is the most remarkable example of the so-called bad- land erosion within the limits of the Fortieth Parallel Exploration. The Bridger beds here rise about 300 feet above the level, dry valley to the south, and present a series of abrupt, nearly vertical faces, worn into innumerable architectural forms, outliers often standing detached from the main wall in bold blocks, which have been wrought into a variety of singu- lar forms by wolian erosion. Plate XV. gives a very fair general view of a portion of the Bad Lands, showing some of the curious buttressed shapes. A few ravines eut their way through the plateau from considerable distances back in the basin. Along the walls of these ravines the same picturesque architectural forms occur, so that a view of the whole front 398 SYSTEMATIC GEOLOGY. of the escarpment, with its salient and reéntrant angles, reminds one of the ruins of a fortified city. Enormous masses project from the main wall, the stratification-lines of creamy, gray, and green sands and marls are traced across their nearly vertical fronts like courses of immense masonry, and every face is scored by innumerable narrow, sharp cuts, which are worn into the soft material from top to bottom of the cliff, offering narrow galleries which give access for a considerable distance into this labyrinth of natural fortresses. At a little distance, these sharp incisions seem like the spaces between series of pillars, and the whole aspect of the region is that of a line of Egyptian structures. Among the most interesting bodies are those of the detached outliers, points of spurs, or isolated bills, which are mere relics of the beds that formerly covered the whole valley. These blocks, often reaching 100 feet in height, rise out of the smooth sur- face of a level plain of clay, and are sculptured into the most remarkable forms, surmounted by domes and ornamented by many buttresses and jutting pinnacles. But perhaps the most astonishing single monument here is the isolated column shown in the frontispiece of this volume. It stands upon a plain of gray earth, which supports a scant growth of desert sage, and rises to a height of fully sixty feet. It could hardly be a more perfect specimen of an isolated monumental form if sculptured by the hand of man. Looking along the perspective of this strange line of escarpments, the uniform buff and gray marls and clays are seen to be interrupted at several elevations by beds of peculiar green earth, which add to the architectural forms the element of variegated courses. Not the least remarkable feature is the fact that the plains skirting the base of these Bad Lands are quite level, there being little or no talus at the bottom of the abrupt slopes of the cliffs. It is easy to see that these exceedingly fine materials, when dis- lodged from their original positions in the beds, would be rapidly carried away by the waters which are concentrated by the ravines and angles of the Bad Lands. The present clay floor at the foot of the cliffs has almost the appearance of the accumulation of a lake, but it is in reality only the detritus levelled by flowing water, a task which the exceedingly fine nature of the material renders comparatively easy, and which is permitted here EOCENE TERTIARY. 399 by the slope of the underlying Green River beds toward the Bad-Land escarpment. These bluffs are extremely rich in the remains of vertebrate fossils. At the base of almost every cliff were observed the bones of Mammalia, and frequent shells of Testudinata. It is not altogether easy to account for the peculiar character of this erosion, resulting as it does in such singular vertical faces and spire-like forms. A glance at the front of these Bad Lands shows at once that very much of the resultant forms must be the effect of rain and wind storms. The small streams which cut down across the escarpment from the interior of the plateau do the work of severing the front into detached blocks; but the final forms of these blocks themselves are probably in great measure given by the effect of rain and zxolian erosion. The material is so exces- sively fine that under the influence of trickling waters it cuts down most easily in vertical lines. A semi-detached block, separated by two lateral ravines, becomes quickly carved into spires and domes, which soon crum- ble down to the level of the plain. Outlying hills or buttes are carved away, leaving narrow, isolated spires, which finally disappear by the same process of erosion. It seems probable that some of the most interesting forms are brought out by a slightly harder stratum near the top of the cliffs, which acts in a measure as a protector of the softer materials, and prevents them from taking the mound-forms that occur when the beds are of equal hardness. As to the thickness of the Bridger series in the Wa- shakie Basin, no precise figure can be arrived at. It probably amounts to less than a thousand feet. A little west of south from Washakie Basin, between Vermilion Bluffs and Elk Gap, is a detached area of soft, easily eroded clays and sands, which, from their position overlying the paper shales of Green River, have been assigned to the Bridger. No organic remains were found here, and the occurrences are of very slight importance. The chief exposure of the Bridger beds is to be found in Bridger Basin, between the meridians of 109° 30’ and 110° 45’, extending from the foot-hills of the Uinta, on the south, northward beyond the limits of our map. As displayed along the base of the Uinta Mountains, it consists of a 400 SYSTEMATIC GEOLOGY. series of soft, sandy, and clayey beds, for the most part covered with soil, or obscured beneath unconformable deposits of Pliocene conglom- erates, and wherever distinctly seen it is found to dip at gentle angles to the north, angles never exceeding 2°, and hence within the probable limit of the original deposition. Thus exposed, there is a body of 50 to 60 miles from east to west, the main axis trending a little east of the meridian. It is bounded on the east, in the region of the meridian of 109° 30’, by the shales of the Green River series, which come upon the surface from a posi- tion beneath the Bridger. On the west, also, it is margined by a narrow line of Green River beds, separating it from the still lower Vermilion Creek group. Throughout the middle of the Bridger Basin it rests in positions of complete horizontality, and throughout its whole extent shows no evi- dence of orographical disturbance, such as could be registered in local changes of angle. The aggregate thickness of the beds of this group is estimated as between 2,200 and 2,500 feet. The material is almost wholly made up of fine sand and clay, arranged in varying proportions, and occasion- ally slightly changed by calcareous admixtures. As between this series, however, and that of the Green River, the notable difference is, that the Bridger is a prominent sand-and-clay forma- tion, while the other, from bottom to top, is essentially characterized by the presence of abundant lime. The strata of the Bridger are also exceed- ingly soft, and are eroded with almost the facility of beds of Quaternary earth. The upper 1,000 feet are nothing more than a soft, sandy clay sedi- ment, varying from drab to pale olive, carrying a few beds of slightly in- durated sandstone and occasional stripes of grayish and greenish marls, and at one or two horizons beds of inconspicuous limestone, which closely re- sembles the arenaceous limes of the Green River group. One of the noticeable features of this group is the vitrification of cer- tain beds. It is not uncommon to observe, along the steep escarpments of the eroded clays and sands, the edge of a hard bed standing out like a shelf, which upon examination proves to be chert or hornstone, sometimes inclining to semi-transparence, in which case they represent chalcedony, or more nearly hyalite. Such sheets are of not infrequent occurrence, but are EOCENE TERTIARY. 401 usually of no great lateral extension. They rarely exceed three or four feet in thickness, and but for their lithological peculiarities would be an en- tirely unimportant member of the series. There are also calcitic and selenitic intercalations, from which erosion removes the superincumbent clays, leaving the surface covered with the rubbish of crystals. In the siliceous hyalitoid strata, innumerable dendritic infiltrations of iron and manganese are observed, whose most highly developed form is the well known moss-agate of the region. ' On the northern limit of the map only the lower members of the Bridger are seen resting upon the Green River beds; but in passing south the country gradually rises, and each successive topographical elevation marks a higher stratigraphical horizon, the formation rising in broad, irregu- lar terraces, bounded by more or less abrupt slopes, and sometimes by bold escarpments of Bad Lands. North of the railway, and for a considerable distance to the south, is an undulating desert almost devoid of vegetation, its surface desolate stretches of arid, ashen-colored sand or clay, without any conspicuous hills. In the region of Church Buttes outliers of the Bridger group con- stitute detached bodies rising above the Plains in the most picturesque forms, eroded in the characteristic bad-land shapes; domed mounds and buttressed blocks remind one of a variety of architectural designs. The color here is grayish drab, with numerous stripes of greenish argillaceous sandstone characteristic of the lower part of the series. Farther to the south a second broad, irregular terrace is seen, whose front, under the name of Grizzly Buttes, presents an escarpment not unlike that already described in Washakie Basin. The forms here are usually soft, rounded outlines, deeply scored with sharp, parallel ravines cut down at short intervals. The extremely steep slopes are weathered into absolute smoothness. The colors are here light-gray and drab, with white and greenish bands; and the perspective of the front of Grizzly Buttes is cer- tainly one of the most remarkable geological views of the region ; not so architectural as the Bad Lands of Washakie Basin, but singularly im- pressive by the infinite variety of peculiar shapes. The deepest exposures of the Bridger series are laid bare in the valley 26 K 402 SYSTEMATIC GEOLOGY. of Henry’s Fork, where, as south of Turtle Bluffs, a thickness of 1,800 to 2,000 feet is exposed. If we are right in assigning to the Wyoming con- elomerate a Pliocene age, it is probable that a very large amount of the upper strata of the Bridger series was eroded prior to the laying down of the Wyoming conglomerate. On the southern slope of Turtle Blufis, and on the north as well, have been found innumerable fossil vertebrates, together with a considerable number of Unio and Planorbis spectabilis. By far the larger amounts of the beds are gray sands and clays, but here and there are prominent calcareous strata. The chemical constitution of a green cal- careous marl upon the southern face of these bluffs will be found in the tables of analyses of sedimentary rocks. A second analysis was made of the light-green band taken from Grizzly Butte, and it was seen under the microscope to consist of fine grains of quartz and black mica and some feldspar, with a permeating cement of green clay. At Mount Corson and Concrete Plateau, and along the prominent conglomerate spur which forms the divide between Henry’s and Smith’s forks, the Bridger series is overlaid by great thicknesses of conglomerate, ranging from 200 to 600 feet in thickness, which may be an upper shore member of the group. With the exception of the Planorbis and Unio beds in the upper mem- bers, the greater part of the molluscan remains of the Bridger series is found in the lower strata. The chief forms are: Unio Haydenii. Planorbis spectabilis. Physa Bridgerensis. Goniobasis tenera. Viviparus paludineformis. Viviparus Wyomingensis. Pupa Leidyi. The chief interest of this formation arises from its remarkable fertility in vertebrate remains of true Eocene type. The following list, though by no means exhaustive, will serve to indicate the character of the Bridger fauna: EOCENE TERTIARY. 403 BRIDGER BEDS. PRIMATES. Lemuravus distans, Marsh. Hyopsodus minusculus, Leidy. Hyopsodus paulus, Leidy. Limnotherium tyrannus, Marsh. Limnotherium elegans, Marsh. CARNIVORA. LTimnofelis ferox, Marsh. Limnocyon riparius, Marsh. Vulpavus palustris, Marsh. Uintacyon edax, Leidy. Sinopa rapax, Leidy. Orocyon latidens, Marsh. Dromocyon vorax, Marsh. INSECTIVORA. Talpavus nitidus, Marsh. Centetodon pulcher, Marsh. Entomacodon angustidens, Marsh. Paleacodon vagus, Marsh. Passalacodon littoralis, Marsh. Paleacodon verus, Leidy. CHENOPTERA. Nyctitherium velox, Marsh. Nyctitherium priscus, Marsh. Nyctilestes serotinus, Marsh. DINOCERATA. Uintatherium robustum, Leidy. Tinoceras anceps, Marsh. Dinoceras mirabile, Marsh. Dinoceras lacustris, Marsh. Dinoceras lucaris, Marsh. Dinoceras laticeps, Marsh. 404. SYSTEMATIC GEOLOGY. UNGULATA. Paleosyops paludosus, Leidy. Hyrachyus agrarius, Leidy. Orohippus agilis, Marsh. Helaletes boops, Marsh. Hyrachyus Bairdianus, Marsh. Homacodon vagans, Marsh. Helohyus lentus, Marsh. RODENTIA. Paramys delicatus, Leidy. Mysops minimus, Leidy. Sciuravus nitidus, Marsh. Tillomys senex, Marsh. Tachymys lucaris, Marsh. Apatemys bellus, Marsh. TILLODONTIA. Anchippodus minor, Marsh. Tillotherium hyracoides, Marsh. Tillotherium fodiens, Marsh. Stylinodon mirus, Marsh. AVES. Bubo leptosteus, Marsh. Aletornis nobilis, Marsh. Aletornis pernix, Marsh. Aletornis venustus, Marsh. Aletornis gracilis, Marsh. Aletornis bellus, Marsh. Unitornis lucaris, Marsh. CHELONIA. Hybemys arenarius, Leidy. Baptemys Wyomingensis, Leidy Bena arenosa, Leidy. Anosteira ornata, Leidy. Trionyx guttatus, Leidy. EOCENE TERTIARY. 405 SAURIA. Glyptosaurus princeps, Marsh. Thinosaurus leptodus, Marsh. Oreosaurus lentus, Marsh. Tgquanawus evilis, Marsh. Saniva ensidens, Leidy. Crocodilus Elliotti, Leidy. Crocodilus brevicollis, Marsh. Limnosaurus ziphodon, Marsh. OPHIDIA. Boavus occidentalis, Marsh. Boavus agilis, Marsh. Boavus brevis, Marsh. Lithophis Sargentii, Marsh. Limnophis crassus, Marsh. PISCES. Amia Newberrianus, Marsh. Amia depressus, Marsh. Amia Uintensis, Leidy. Amia media, Leidy. Lepidosteus glaber, Marsh. Lepidosteus Whitneyi, Marsh. Hypamia elegans, Leidy. Phareodus acutus, Leidy. Pappichthys plicatus, Cope. Rhineastes radulus, Cope. Uinta Grovp.—Of the Tertiaries immediately south of Uinta Range, comparatively little is distinctly known. Flanking all the alluvial valleys of the streams are bluffs and ridges formed of Tertiary strata, the lower members being chiefly rough, gritty conglomerate, passing up into finer- grained sandstones, and at certain points developing creamy, calcareous beds. The strata apparently form an unbroken line from the region of the Wah- satch eastward throughout the length of Uinta Valley, and across Green River into the valley of White River. Near the lower lands of Uinta Valley 406 SYSTEMATIC GEOLOGY. the upper beds are wanting, and on the flanks of the Uinta Mountains, where the upper series is present it is in great measure overlaid by glacial débris and moraines, which generally obscure its occurrence. The verte- brate remains which have been found in the continuation of these beds in White River Valley belong to a period higher than the Bridger series. They even contain some forms closely approaching the lowest Miocene types. But exactly what relation these White River beds bear to the more western members of the Uinta group does not at present appear. There is little doubt that the main western portions around the head of Uinta Valley, the Du Chesne, and the region of Strawberry Valley be- long, as before indicated, to the Vermilion Creek group, and it is not at all impossible that the upper calcareous beds seen along the middle and eastern Uinta may represent fragmentary portions of the Green River series, which have thus far succeeded in resisting erosion. Some of the lowest exposed beds of the region are seen at Wansits Ridge, near the southeastern point, where they repose unconformably upon the Fox Hill sandstones, dipping at angles of from 8° to 10° to the southeast. In passing southward, this com- paratively steep dip declines to a nearly horizontal position. These beds consist of earthy sands and eonglomerates containing many coarsely rounded pebbles of the older rocks of Uinta Range. These pass up into greenish and reddish sandy beds, having many coarse, chocolate-colored sandstone members. A still higher dip is observed in these same rocks along the upper branches of Ute Fork, where an inclination of 25° is sometimes seen. But in approaching the flanks,of the mountains the sandstones are com- pletely overwhelmed by the rubbish of the Glacial Period, and by moraines eight or ten miles long. The same coarse, red sandstones appear near the mouth of Antero’s Creek. A locality of some petrographical interest was noticed between the upper east and west branches of Lake Fork, near the slopes of the older rocks along Uinta Range. Here is displayed a very thick series of yel- low sandstones, rather coarse in texture, developing a concretionary struct- ure, and yielding by erosion peculiar spire-like forms. At the foot of these cliffs the lower members are heavy, reddish beds, the whole exposure of about 600 feet dipping 4° or 5° to the south. Westward from the creek EOCENE TERTIARY. 407 the Tertiary beds are seen occupying the cliffs at a height apparently of 2,000 feet above its bed, the upper members made of coarse conglomerate, resembling those of Pliocene age. In the region of Strawberry Valley the outcrops are still further obscured by an enormous amount of overlying disintegrated soil and a thick growth of forest. Some outcrops of sandstone along the eastern slope of the Wahsatch, of very high dips, were referred to the Cretaceous, but from stratigraphical reasons only. As north of the Uinta, the Tertiary series seem to thicken greatly on approaching the Wah- satch, which is unquestionably to be accounted for by the fact that that range marks the shore of the land-mass against which the earlier Eocene lake was traced; and the lake being very deep near its own shore, the detrital material accumulated more thickly there than to the east. When the Tertiaries south of Uinta Range are carefully unravelled, as they doubt- less will be by Powell and Gilbert, it will probably be found that the most recent Eocene group, as developed in White River Valley, is unconform- able with all the earlier Eocene groups. It is a shallow deposit, of which not over four hundred feet are seen, and in all probability is the sediment of a very restricted post-Bridger lake, wholly south of Uinta Range, and the last member of that remarkable series of Eocene lakes whose great deposits are piled unconformably over one another in the region. To this group alone should the term Uinta be applied. As provisionally used on the Fortieth Parallel Atlas, Uinta group was a term stretched for conven- ience to cover all the Tertiaries south of Uinta Range, of whose true sub- divisions we were ignorant. The following list comprises some of the more important vertebrates of the true Uinta series : UINTA GROUP. Hyopsodus gracilis, Marsh. Diplacodon elatus, Marsh. Epihippus Uintensis, Marsh. Epihippus gracilis, Marsh. Agriocherus pumilus, Marsh. Amynodon advenum, Marsh. SEC TLO Nee MIOCENE TERTIARY. Wuite River Grovup.—Over a vast portion of its area the geological province of the Great Plains has a covering of Pliocene Tertiary beds, varying in thickness from 2,000 feet down to a few hundreds. The streams, which flow from the front of the Rocky Mountains and join the various affluents of the Missouri, have not infrequently cut through this covering of Pliocene and exposed the underlying rocks. In several places it is found that the Pliocene rests unconformably upon beds of upper Cretaceous, which lie either horizontal or in slight undulations. At other points, notably the valleys of Platte River and White River, the wide- spread Pliocene has been found to be directly underlaid by beds of Mio- cene age, characterized by an ample and typical fauna. Along the 41st parallel, at the extreme eastern end of the belt of Fortieth Parallel work, the Pliocene strata have been eroded away, leaving a rudely terraced escarpment, which faces the south, overlooking a nearly level plain com- posed of the beds of the Fox Hill and Laramie Cretaceous. East of the Denver Pacific Railroad and south of the 41st parallel a small development of Miocene beds is seen to be interposed between the Cretaceous and the Pliocene; being in fact an eroded edge of the sheet of Miocene which, over a considerable area of the Plains, underlies the Pliocene. The precise area and boundaries of this Miocene lake cannot yet be definitely assigned. It is clear that the beds brought to light upon North Platte and White rivers, and at the locality just mentioned at Chalk Bluffs, near the Denver Pacific Railroad, belong to the same lake. Messrs. KE. 8. Dana and G. B. Grinnell, in their valuable geological reconnoissance from Carroll, Montana, to the Yellowstone National Park,* have brought to light in the vicinity of Camp Baker, Montana, a further development of Miocene beds, here as elsewhere on the Plains capped by Pliocene, both series containing characteristic fossils. The altitude at which these beds were observed by them, 5,000 feet, induced them to suppose that the rocks they - * Reconnoissance of Capt. William Ludlow, 1875. 408 MIOCENE TERTIARY. 409 examined belonged to an independent lake, shut off from the great Miocene lake of the Plains, the elevation being 2,000 feet greater than that of the beds exposed on White River. But since the small exposure falling within the limits of the Fortieth Parallel Exploration has an altitude of nearly 6,000 feet, and since there is no known barrier which could have separated it from the Miocene rocks upon Platte River, as well as those displayed upon White River, I have felt bound to assume that the Chalk Bluff beds, as well as those displayed farther east, near the northern boundary of Kansas, are a part of a general Miocene lake, the beds of the region having under- gone broad changes of level since the Pliocene period. These Miocene beds evidently pass southward as far as the northern boundary of Kansas, and continue northward into Montana. At the somewhat ambiguous locality of Fort Union, on the Upper Missouri, occur beds bearing molluscan and vertebrate faunz, which corre- late directly with the higher horizons of the Laramie Cretaceous. From later beds at the same place has been collected a rich flora corresponding with great exactness to the Miocene beds of Manitoba, of Greenland, and of northern Europe. It has never been announced whether these two series of beds were conformable. Both horizons have been embraced in the Fort Union group, whereas there is every probability that the rocks at that locality bearing Dinosaurians are Laramie, while the upper distinctly Miocene series is with equal probability to be correlated with the known Miocene of the Plains. At Chalk Bluffs the Laramie Cretaceous and White River Miocene are observed in immediate contact, with but slight angular unconformity. Cretaceous and Miocene fossils occur in close proximity, and in the absence of a clear understanding of the stratigraphy this locality might easily appear as paradoxical as Fort Union. In the Fortieth Parallel Exploration we have, therefore, only a very limited exposure near the edge of the Miocene lake, where it washed the foot-hills of Colorado Range. That the beds extended south over the Cre- taceous area of the Plains, forming the southeast corner of Map L, is un- questionable from the Miocene escarpment. The strata of which the Chalk Bluff escarpment is composed rest unconformably upon the gently dipping sandstones and shales of the Laramie or uppermost group of the Cretaceous. 410 SYSTEMATIC GEOLOGY. The latter group are here nearly horizontal, but if examined over consid- erable areas are found to be thrown into very slight undulations, and toward the western limit of the outcrop to have a perceptible dip to the east. Prior to the deposition of the Miocene beds, the Cretaceous had under- gone a great deal of deep erosion, which left the surface in soft undula- tions of very gentle grade, the details of the surface rarely showing any abrupt topographical forms. The entire escarpment, including the Miocene and Pliocene beds, reaches a height of 700 feet above the Cretaceous plains. The small streams of the Plains have worn numerous narrow ravines down the escarpment, cutting back to a considerable distance, and offering ad- mirable sections in which to observe the character of the beds. Following the escarpment westward, it becomes evident that the Mio- cene deposits abut against the very lowest base of the foot-hills, always limited by the upper Cretaceous rocks, whereas the overlying Pliocene overlaps to the westward, and formerly rose high against the range, as is shown from Box Elder Creek northward to the Chugwater. In other words, the Miocene lake was of much lower level, covered, as far as we now know, a smaller area, and was limited in this region along the east by the gently upturned upper Cretaceous beds. In the limited exposure from Carr Station eastward along the tributaries of Owl and Crow creeks, the Miocene shows a thickness of about 300 feet, the altitude of the uppermost strata being here about 5,800 feet, or fully 2,200 feet higher than the contact between the same beds upon White River. At this locality the separation between the two series is not at all one of angle or of any abrupt change of material. The conglomerate mentioned by Dana and Grinnell to the north as the dividing-line between the strati- graphically conformable Miocene and the Pliocene, is here wanting, and the division is established solely on palzeontological ground. The beds consist of constantly varying thin layers of gray and creamy clays, fine sands, and marls. The latter, in broad white beds, presents so chalky an appearance as to have suggested the name of the region, Chalk Bluffs. There are nu- merous ferruginous layers where the sandy material is cemented by brown earthy iron oxyds, whose more compact outcrop may be traced along the varied forms of the escarpment for several miles MIOCENE TERTIARY. 411 The lower 300 feet are characteristic Miocene, and have yielded nu- merous typical Miocene vertebrate fossils. The following list is made up largely from this locality, but partly from other points of the same horizon, also on the Great Plains : MIOCENE OF THE PLAINS. Laopithecus robustus, Marsh. Drepanodon intrepidus, Leidy. Drepanodon primevus, Leidy. Dinictis felina, Leidy. Amphicyon vetus, Leidy. Amphicyon angustidens, Marsh Hyanodon horridus, Leidy. Hyanodon cruentus, Leidy. Hyanodon crucians, Leidy. Oreodon Culbertsoni, Leidy. Oreodon gracilis, Leidy. Eporeodon major, (Leidy) Marsh. Eporeodon bullatus, (Leidy) Marsh. Merycocherus proprius, Leidy. Agriocherus antiquus, Leidy. Percherus probus, Leidy. Leptocherus spectabilis, Leidy. : Protomeryx Hallii, Leidy. Leptomeryx Evansii, Leidy. Leptauchenia major, Leidy. Poebrotherium Wilsoni, Leidy. Hyopotamus Americanus, Leidy. Lilotherium Mortoni, Leidy. Elotherium superbum, Leidy. Elotherium bathrodon, Marsh. Elotherium crassum, Marsh. Menodus giganteus, Pomel. Brontotherium ingens, Marsh. 412 SYSTEMATIC GEOLOGY. Brontotherium gigas, Marsh. Diconodon montanus, Marsh. Rhinoceros Nebrascensis, Leidy. Rhinoceros occidentalis, Leidy. Mesohippus Bairdi, (Leidy) Marsh. Mesohippus celer, Marsh. Mastodon mirificus, Leidy. Paleolagus Haydeni, Leidy. Ischyromys typus, Leidy. Paleocastor Nebrascensis, Leidy. Eumys elegans, Leidy. Leptictis Haydeni, Leidy. Ictops Dakotensis, Leidy. Meleagris antiquus, Marsh. Truckee Grovup.—Passing westwardly from Colorado Range, the en- tire country, as far west as the western base of Wahsatch Range, is alto- gether free from deposits of the Miocene. The broad area of Tertiary which oceupies North Park and the upper valley of the North Platte is mainly posterior to the period of basaltic eruptions; and from its analogy with deposits in connection with the great basaltic outflows of Idaho, Oregon, and Nevada, it is assumed that these Tertiaries are Pliocene. The Plio- cenes of the Great Plains also bear the same relation to the basalt north of the limits of our work, and there are further strong lithological grounds for referring the limited lacustrine Tertiaries of North Park and the Platte to the Pliocene. The basin of Salt Lake, unlike the country between it and the Great Plains, is at present low enough to have been the receptacle of Miocene beds; but there is every reason to suppose, as will be seen hereafter, that the depression of the Utah Basin took place at a date posterior to the close of the Miocene age, and that during the Miocene period it was, like the country to the east, a land area without considerable lakes The same is true of middle and eastern Nevada, and it is not till we arrive at the meridian of 117° that we again reach strata which may be referred with any degree MIOCENE TERTIARY. 413 of probability to the Miocene age. This longitude marks approximatively the division between the higher plateau country of Nevada and the western Nevada Basin. The valleys of the latter area sink to an altitude of 3,700 feet, while those of the plateau country to the east are 5,000 and 6,000 feet. A line of great geological change has been indicated as existing imme- diately west of the Battle Mountain group and Toyabe Range. The main feature of this change has been already indicated as the complete cessa- tion of Palzeozoic strata, which have continued from far to the east up to this meridian, and the sudden coming in of ranges made of Triassic and Jurassic rocks which continue westward into California. Besides the occur- rence of these rocks of the middle age, there appears with equal sudden- ness, cropping through the immense Quaternary deposits of the valley, and in some instances in the eroded ravines of the rhyolite ranges, a series of upturned sedimentary beds displaying a very great total thickness, prob- ably not less than 4,000 feet, the series being older than the rhyolites, partly older and partly contemporaneous with the trachytes. A large portion of the material of the group is made of trachytie muds, which carry, especially in Oregon, enormous numbers of Miocene fossil mammals. The rocks of the group are limited on the east, within the boundaries of our Exploration, by the 117th meridian, and on the west by the abrupt wall of the Sierra Nevada. Northward they extend through Oregon and pass into Washington Territory, having their greatest development on Crooked River, the John Day, and the Malheur. South of our work they are well known in the valley of Walker River, but beyond that southward I am not aware of their having been observed. An immense upturned series of fresh-water Tertiaries is displayed on a grand scale in the region of Cajon Pass, in southern California. Thus far I am not aware of these having yielded more than uncharacteristic fresh- water mollusks and a few unidentifiable fragments of mammalian bones. In future this is likely to be correlated with the lacustrine Miocene of the north. The rocks of this series, within the limits of Map V., are always found upturned from 10° to 25°, and wherever observed in connection with ba- saltic eruptions they are cut through and overflowed by the basalt. The 414 SYSTEMATIC GEOLOGY. rhyolites also break through and overflow them, while the sub-lacustrine eruptions of the trachytic period are intercalated in the Miocene series. On the eastern half of Map V. the Miocene first appears upon Silver Creek, at the western base of Toyabe Range, in latitude 39° 95’. Here and at Boone Creek, surrounded and overflowed by enormous masses of rhyolites, are some beds inclining from 15° to 20°, composed of light buff and ashy strata, very thinly bedded in some places, and in others made up of broad belts of uniform sediment 30 or 40 feet thick. They are charac- terized here and there by passages of chalcedonic material, which are local silicifications in situ, and in the softer passages by the presence of rolled specimens of fossil vertebrate bones, which are always too imperfect for identification. Under the microscope it is evident that this material is of voleanic origin, consisting of particles of crystalline grains of sanidin, with more or less magnetic iron, hornblende, mica, and a little quartz. There is no direct proof of their Miocene age, but they are referred to the Truckee group from their evident recent nature, and the fact that they immediately antedate the massive rhyolites. Similar rocks, even more conspicuously made up of volcanic materials, are seen in the valley of Reese River to the north and west of Silver Creek, and also around the flanks of Lone Hill Valley, between the Shoshone and Augusta Mountains. Here the middle of the broad depression is occupied by heavy accumulations of Quaternary, which conceal all but a belt of Tertiary rocks, that line the edge of the valley and are immediately overlaid by the massive eruptions of rhyolite which form the greater part of the two bounding ranges. A similar inclined mass of voleanic and sandy sediments lies to the west of the Augusta Mountains, in like relations to the Quater- nary valley and overlying rhyolites. This group again appears near the southern end of Havyallah Range, where a broad mass of basaltic rock has outpoured along the eastern face of the range, burying the greater part of the Miocene beds. Similar unchar- acteristic exposures are seen directly south of Buffalo Peak and east of Lovelock’s Station on the foot-hills of West Humboldt Range. The sedi- ments are here less characteristically volcanic, and seem to be made up partly of volcanic material, but largely of coarse sands and gravels, and MIOCENE TERTIARY. 415 from their immediate contact with the Triassic rocks it is fair to assume that these exposures represent the lower limits of the series, while the soft volcanic beds displayed in the Shoshone and Augusta Mountains are with- out suggestion as to their position in the series. . I have merely mentioned these outcrops, because they are of some local importance, and in general their lithological resemblance and their relative position to the other rocks refer them to the one group. Future work may add the necessary proof of age to these scattered exposures. The most important and characteristic development of this series within our limits is at the Kawsoh Mountains and along the southern extremity of Montezuma Range. The northern and eastern portion of the Kawsoh Mountains and the valley which lies north of them, separating their broken detached group of hills from the end of Montezuma Range, together offer a section of about 2,300 feet of Miocene beds, noting from the top as follows: 1. The upper 1,200 feet consist entirely of drab, mauve, gray, pale-buff, and white stratified trachytic tuff, intermixed with more or less detrital material. The beds are characterized by rapid changes of color and texture, are of very variable coarseness, and have a pre- vailing amount of glassy fragments, as if an enormous amount of the material were the glassy scoria and rapilli of violent and long-con- tinued trachytie eruption. At intervals are beds of pure gray sand with a few seams of slightly marly clay. The microscope shows that this entire series is made up of angular and sub-angular frag- ments, many of them excessively small. There are some singular chalcedonic strata, one to two feet thick, of which the lower stratum-plane is exceedingly rough, resting upon the trachytic tuff and including a great many minute fragments of the volcanic material, the upper surfaces being rudely botryoidal, the protuber- ances reaching the size of an egg. Toward the lower edge of this great series of trachytic tuffs, the upper limits of which are nowhere seen, the proportion of true detrital material—quartz and feldspar sand—becomes rapidly greater until the tuff is underlaid by — 2. Coarse, sandy grits, gray and yellow fragments, partially rounded, jc, partially angular, with a slight proportion of calcitic material. 250 416 SYSTEMATIC GEOLOGY. Feet. 3. Saccharoidal limestone, rich in fresh-water mollusks. .-..-.------ 60 4. Marly grits, yellow and drab, rather coarse. .-..-----...-+.---- 40 5. Fine-grained, friable, buff and gray sandstone, having a peculiarly sharp, ovitty feel 2c< 22122 eee Ce ee 70 6. Variable cray sandstones!) 2222+. 2 eee eee 100 7. A marly erity. 22 12.36 cee eee ete 50 or 60 8.. White and *yellow infusomal silica 22222 9= ee 200 to 250 9. Palagonite tuff, base never seen, 250 feet being maximum exposure, No lower members than the bed of palagonite tuff are observed in the Kawsoh Mountains, or in the southern end of the Montezuma; but in Warm Spring Valley, a small depression in the basaltic hills a few miles north of Hawes’s Station, on Carson River, the palagonites, there remarka- bly well developed, are seen to be underlaid by a light siliceous clayey bed made up of fine silt and comminuted infusoria. It is always far less pure than the white infusorial beds above the palagonites. Here, as every- where, the series has an inclined position, dipping 15° to 20°. Miocene palagonite has only been observed by us in this litthke Warm Spring Valley, at the northeast corner of the Kawsoh, and at the southern point of Montezuma Range. We have nowhere over 250 feet exposed. In the Kawsoh exposure it is rather uniform, made up of yellowish- brown, decomposed-looking material, varyingly mixed with sand, and north- west of Mirage Station, in a little ravine at the foot of the rhyolitic hills, it is a rather coarse breccia, containing decomposed fragments of a somewhat vesicular augitic rock, the binding material in this case being pretty pure palagonite. Microscopic sections of the enclosed fragments of rock show a richly augitic material, in which a considerable glassy base has suffered extreme devitrification. Not only plagioclase but orthoclase is present. In passing from the outside inward, the section of these fragments shows a progressive palagonitic decomposition of the augite. In the region of Hawes’s Station, on Carson River, it is finer-grained, more uniformly yellowish-brown, and consists of a purer palagonitic material. In this case it is free from carbonate of lime. The palagonite of Fossil Hill, at the northern end of Kawsoh Range, when treated with acids, shows MIOCENE TERTIARY. 417 avery feeble effervescence. Our purest type of palagonite, that of Hawes’s Station, has been subjected to analysis, with the following result : Taras) 2 5 Ai Ait ee eee re IROLASSA Ree ee nee eS WVicite Lee tee on ee ere eee ee oe 100.00 50.88 14.37 13.30 6.18 4.14 1.86 0.93 8.34 100.00 For the optical character of this palagonite and its microscopical beha- vior the reader is referred to Vol. VI. of this series. For purposes of com- parison with other distant occurrences of palagonite, I give here three analyses. No. 1 is a palagonite from Iceland, collected between Thing- vellir Lake and the Geyser (Bunsen*). No. 2 is from James Island, Gala- pagos (Bunsen). No. 3 is from Dyampang-Kulon, Java (Prélsst). No. 1. Sill Caleyene Mepaernestan ens Eat oles ee 41, 28 PAV ToUn TYE ea 11. 03 iermiczoxyd) 22) 22cm. Se NSS 2, aiineme meets ee 8.75 IMCS oe er Sitch aire 3 6.49 SKOCGE) S Goees 0. 62 ROtassaMee rte te sees ee 0. 65 Wintenrere te mre sts fois ok. st 17. 36 100. 00 No. 2. 36. 93 11.56 10. 71 7. 95 6.28 0.55 0.78 25. 24 100. 00 No. 3. 37.57 15.18 13. 07 6. 02 5. 58 0. 79 ya W| 19.61 100. 00 The Javan occurrence, described by Junghuhn, like our own, forms stratified deposits in a series of upturned Tertiary rocks. * Poggendorff Annalen, 1857, p. 219. \ « a Comparing our t Neues Jahrbuch far Mineralogie, 1869, p. 434. 27 K 418 SYSTEMATIC GEOLOGY. palagonites with all these others, a remarkable difference may be observed between the silica equivalents, the Nevada specimens carrying about 10 pen cent. more than the others. The Icelandic and Galapagos palagonites, as well as those described by Sartorius von Waltershausen from Etna, are clearly derivable from doleritic eruptions, whereas our Miocene palagonites most certainly antedate all the basaltic period. In the stratified series overlying the palagonite, as before indicated, is a great thickness of purely trachytic tuffs, and from fissures through this stratified series after its complete deposition have outpoured the entire rhy- olite series, and again, still later, the basalts, which are generally unaltered and directly overlie the upturned edges of the palagonite beds, the latter having suffered no inconsiderable erosion prior to the basaltic period. The reference of the palagonite and the accompanying stratified rocks to the Miocene will be accounted for later. For the present it is sufficient to assert that we have no knowledge of any basaltic eruptions until long after the consolidation and subsequent upheaval of the Miocene palagonites. Throughout Nevada, it is true, the basalts precede the visible Pliocene beds, which in many cases rest horizontally against the somewhat eroded flanks of the basaltic hills. — i = cs - * ~ . x QUATERNARY. 493 The mechanical deposits within the area of Lake Bonneville consist, as Gilbert has shown, first, of subaerial gravels washed down by flood and stream, and rolled down steep slopes by rain and wind; secondly, of the finer detrital and precipitated matters which have accumulated on the floor of the lake in strata of sandy, clayey, and calcareous mixture, and which, in the present desiccated age, are exposed, undisturbed beds, the greater part of whose area is uncovered by later subaerial gravels. The subaerial unstratified deposits were continuous or at least recur- rent formations, covering the whole lapse of Quaternary time over the bounding-slopes of the Bonneville area which were not at any time water- covered. It is seen that the gravel series is divided or interrupted by the stratified beds; in other words, that in point of sequence there is, first, a heavy bed of gravel, both rounded and angular, of a maximum exposure (the bottom being concealed) of 200 feet; secondly, the stratified sediments which overlap the earlier gravels; and thirdly, a latest gravel, varying from 75 to 150 feet, which since the last desiccation has been washed down the basin-slopes and over the edges and a considerable area of the surface of the fine Bonneville strata. My observations on-all these points agree in detail with Gilbert’s. By reference to the Geological Atlas accompanying the report, it will be seen that east of the Wahsatch, in the region which during all the Quaternary age had free fluviatile delivery to the sea, the Quaternary is colored in one tint. It consists, besides the irregular coating of soil, the result of chemical and mechanical disintegration of rocks, a feature too incon- spicuous to show on the general geological maps, of river-bottom accumu- lation of no great extension. Although the eastern part of the work touches the Loess deposits of the plains, it merely touches them, and that in their least characteristic region. As I have no considerable light on the question, the Loess is not discussed. West of the Wahsatch the Quaternary is shown in two colors: one, denominated Lower Quaternary, is the great lacustrine formation; the other, or Upper Quaternary, is intended to embrace the sheet of subaerial gravel which is subsequent to the latest desiccation, and hence later in age than the lacustrine Lower Quaternary. The lowest or ante-sedimental 494 SYSTEMATIC GEOLOGY. gravels are not shown on the map, from the fact that they are nearly always covered by the two later divisions. All these were, however, recog- nized in the Bonneville Basin and in that of Lake Lahontan. Geological Maps HI, IV., and V. show in the basin of the two great Quaternary lakes, and elsewhere in the area of lesser extinct contempora- neous lakes in middle Nevada, a wide expanse of the Lower Quaternary or lacustrine beds, and the still greater distribution of the most modern sub- aerial gravels. Avoiding as far as possible the repetition of Gilbert’s reasoning, I yet find it necessary to say here, as he has said before, that the sequence and stratigraphical relations of these three members of the Basin Quaternary, not only for Bonneville, but for the whole Great Basin region, indicate, first, a dry period in which subaerial gravels were washed down into basins; sec- ondly, a filling of the depressions with water, during whose occupation the stratified deposits covered the broad basin-bottoms and considerably over- lapped the earlier subaerial gravels; thirdly, an age of desiccation, in which the lake waters dried out and the Upper Quaternary or most modern sheet of subaerial gravel washed down over the earlier gravels and over the dried surface of the lake beds. There are other considerations, to appear later in this section, which confirm this interesting proof of two desiccation- epochs, and considerably enlarge our conceptions of the history of the period. The Lower Quaternary (Bonneville beds of Gilbert) contains an abun- dant molluscan fauna, of which the following are the most important forms: Limnea desodiosa Pomatiopsis lustrica. Amanicola Cincinnatensis. Succinea lineata. The latest subaerial gravels have yielded a skull of Bison latifrons and fragments of bones, supposed to be reindeer. The evaporation of such a great body of fresh water could only result in the concentration of the soluble salts and the precipitation of those whose chemical nature forbade their continued solution in the increasingly QUATERNARY. 495 strong alkaline water. The uppermost terraces are made of the washed gravel and pebbles of a beach deposit, which in most cases are quite securely cemented together by a calcareous tufa. In places the entire material of the terrace is of more or less porous tufa, in which are enclosed but few rock fragments, sometimes angular and sometimes rounded, in all eases derived from the neighboring hill. A characteristic specimen of this tufa, collected on the main terrace at Redding Springs in Salt Lake Basin, and analyzed by Mr. R. W. Woodward, of this Exploration, is given in the table of chemical products due to the evaporation of Lake Bonne- ville. It is seen to consist essentially of carbonate of lime, with a small percentage of silicic acid (for the most part, doubtless, included sand, but also to a slight extent as combined silica), a low percentage of alu- mina, a trace of sesquioxyd of iron, 34 per cent. of magnesia, a little soda and potash, and a trace of lithia and phosphoric acid, with a constant minute proportion of water. The specific gravity of the tufa is from 2.4 to 2.3. If the reader will refer to the table of the desiccation-products of Lake Lahontan, he will observe that the tufa of that great companion body of fresh water possessed, down to the minutest constituent, precisely the same chemical nature. The tufa of the Lake Bonneville terraces is a fine, compact, grayish- yellow mass. When acting as a cement for the terrace-beach pebbles, it usually occurs in concentric layers enveloping the pebbles, with the inter- stices filled in with a fine granular carbonate. Where it exists in solid cakes, as on the terrace above Redding Springs, it has in great measure the porous texture characteristic of calcareous tufas and travertines. In thin section under the microscope it presents a curious, opaque appearance, and has a light, earthy-gray color, carrying innumerable fine, dust-like particles, which are simply the mechanically entangled silt of the shore. Through the absolutely opaque section are cloudings of transparent material, which, under crossed nicols, are seen to be microcrystalline masses. The indi- vidual crystals are too small to display the color phenomena of calcite, but by the analysis they are unquestionably a fine microcrystalline lime-car- bonate. Considerable passages of the transparent carbonate wander in cloud-like forms through the more opaque material. The latter is doubtless 496 SYSTEMATIC GEOLOGY. opaque simply from the mechanical suspension of minute mineral particles. Organic matter like the roots of water-plants, as well as minute mollusks, is enveloped in the mass. One peculiarity, as seen under the microscope, is the development of concentric circles, which are defined by a banded arrangement of the included foreign particles, or by the spherical arrange- ment of a homogeneous, gray, cloudy material, the origin of whose opacity is unknown, since the highest power of the microscope fails to resolve it. In the table of analyses of this lake is given also the composition of the present water of Salt Lake, which is seen to consist essentially of chloride of sodium, sulphate of soda, sulphate of potash, sulphate of lime, and chloride of magnesium. Among these the chlorides of sodium and magnesium greatly predominate, while the united sulphates of soda, potash, and lime reach about 10 per cent. of the entire solid material. In the analysis it will be seen that Professor Allen has computed all the lime as sulphate. It is a noticeable fact that in such a dense saline solution, one in which the solid matter is approximately 15 per cent. of the entire weight, there are none of the alkaline carbonates which are characteristic elements in the saline lakes farther west. The percentage of sulphate of lime is not too high to remain in solution, even in waters of far less density. Indeed, the analyses of nearly all the European rivers show a higher percentage of sulphate of lime in the entire sum of solid material than do the waters of Salt Lake. The chloride of magnesium, representing one tenth of the entire solid contents of the lake, is present in unusually high proportion. Lithia, though given in the analysis only as a trace, is present in sufficient quantity to give an invari- able reaction in the spectroscope from the contents of a single drop of water. In many respects the present solution in Great Salt Lake differs from that of any other saline lake. The Caspian, a far fresher water, with but six tenths of 1 per cent. of solid material, has its salinity chiefly made up of the chlorides of sodium and magnesium, with the sulphates of magnesia and lime; but there is also an appreciable percentage of bicarbonate of lime and magnesia, elements entirely lacking in Great Salt Lake. The Dead Sea, on the other hand, has a far higher total of saline matter, varying, QUATERNARY. A97T according to different analysts and specimens, from 14.7 to 26.3 per cent. of the whole weight. In the Dead Sea, magnesium chloride is the pre- dominating salt, according to Gmelin and Marchand. In the absence of carbonates, Great Salt Lake resembles the Dead Sea; but in the enormous predominance of chloride of sodium over all other salts, and in the entire absence of carbonates, it is unlike any other large lake the analysis of whose waters has been published. A case of even more exclusively sodium- chloride solution is the small lake of saturated brine which, in the rainy season, overlies a bed of nearly pure chloride of sodium in Osobb Valley, western Nevada, containing only chloride of sodium, with minutest traces of chloride of magnesium and sulphates of the two bases. At the time of the Stansbury expedition, in 1849, the level of Great Salt Lake was about eleven feet lower than at present, and the area of the lake as surveyed by him gives 1,700 square miles. From our survey we esti- mate 2,360 square miles of lake surface, an increase since Stansbury’s work of 660 square miles. The balance between inflowing waters and evapora- tion was about even, showing only slight oscillation from before Stansbury’s time till 1866. From 1866 to the present, a slight climatic oscillation has occurred, by which the influx of waters is in excess of evaporation, and hence the level of the lake has risen about eleven feet, covering a wide expanse of lowland, and making its greatest encroachments westward over the nearly level floor of the desert and northward over Bear River Bay. In conse- quence the solution has been diluted, from a point where, according to the analysis of Dr. L. D. Gale,* the water yielded of solid contents 22.4 per cent., to its present low density. Gale’s analysis is evidently at fault in showing no sulphates of potash and lime. From the analysis of the present water it is evident that the carbonate of lime, almost invariably the predom- inating salt of all heretofore examined rivers, is less soluble in the presence of a strong alkaline solution like the modern Salt Lake than it is in pure fresh water; while the sulphate, nearly always inferior to the carbonate in river waters, is able to remain in solution in the presence of sulphate of soda and the chlorides of sodium and magnesium. In consequence, the car- bonate of lime which is continually poured in by the rivers is promptly pre- *Stansbury’s Exploration and Survey of the Valley of the Great Salt Lake of Utah, 1853, p. 419. 32 K 498 SYSTEMATIC GEOLOGY. cipitated. That these waters also refused to hold in solution the carbonate of lime when they were comparatively fresh, is proved by the important deposits of calcareous tufa upon the upper terrace. Had the waters of the lake at the time that it possessed an outflow been exactly like those of the rivers, it is difficult to see why the carbonate of lime which they introduced should have crystallized out in the form of tufa; but at the time of its greatest expansion the lake no doubt contained a great number of hot springs, swelling the flood with both alkaline and calcareous solutions. In the presence of these salts the carbonate of lime went down; and while the fresher lake contained sufticient carbonate of lime to furnish the material for the tufa terraces, the more concentrated waters of to-day are absolutely free from that salt. The same phenomenon is constantly observed near the mouths of rivers which deliver into the sea, where the carbonate of lime brought down by the fresh streams is deposited in the form of a fine erystal- line precipitate, which is seen in the deltas cementing the sand and gravel of the estuary. While the tufa represents the insoluble and the present lake waters the soluble portions of the contents of Lake Bonneville, there are upon the desert plains in the neighborhood of the lake, residua of evaporation which during the annual rainy season soak down into the Lower Quater- nary beds, and during the dryer months by capillary attraction are drawn to the surface and dry, leaving glistening saline efflorescences, which are of great effect in the peculiar arid landscape. The valley of Deep Creek sends down a small stream bearing the drainage of a valley which in gen- eral is lifted entirely above the level of Lake Bonneville. The creek waters flow out and gradually evaporate over the Quaternary beds At the point of sinking, the ground is more or less covered with a white efflorescence of no great thickness and of variable purity. A specimen collected was ana- lyzed by Mr. Woodward, and the result is given in analysis 24 of the Bonneville table. The insoluble portions are the sand and gravel which are unavoidably collected with so thin an efflorescence. The salt consists essentially of chloride, carbonate, and sulphate of soda and potash; when theoretically combined giving 38.25 of chloride of sodium, 37.09 of carbo- nate and bicarbonate of soda, and 17.54 of sulphate of soda, with 4.71 of QUATERNARY. 499 sulphate of potash. The salt in this basin collected by us is peculiar as containing the only carbonate of soda which we have observed within the area of Lake Bonneville. Analysis No. 25 is of the efflorescence upon the lower Quaternary beds of the Great Desert, between Granite Peak and Cedar Mountain, on the old Overland Stage Road ; and as it occurs in con- siderable thickness, often an inch or an inch and a half, the specimen is remarkably pure, having 97 per cent. of soluble matter. It is essentially a normal chloride of sodium, yielding upon analysis 99.37, with a slight admixture of sulphate of lime, amounting to only about two tenths of one per cent. At the southern extremity of Promontory Range, the Archzean siliceous and argillaceous schists, coming down nearly to the water's edge along the eastern shore, present a cliff nearly 50 feet in height of dark shaly schists, dipping about 25° to the west. The whole cliff is deeply shattered and seamed with interlacing fissure-lines, and the rocks are variably decomposed and coated with a white aluminous efflorescence. Dr. Gale, in the Stansbury report, gives an analysis of this alum, and classifies it as manganiferous.* Prof. J. Lawrence Smith+ also gives an analysis of the same alum, having crystallized it from an aqueous solution. Mr. Woodward’s analysis of the salt collected by us gives sulphate of magnesia 57.07, sulphate of iron .87, sulphate of alumina 37.48, sulphate of potash .37, chloride of sodium 3.04, and excess of sulphuric acid 1.17. It will be seen that this differs from the analyses of Professor Smith and Dr. Gale by the absence of manganese, and the very small percentage of iron, which evidently replaces it. The specimen collected by this Exploration was obtained twenty-two years after the former, and probably there has been a radical change in the character of the salt. The analysis as given by Mr. Woodward makes the mineral a richly magnesian alum, with a little chloride present as an impurity. It is rather a pickeringite than a bosjemanite, which was clearly the salt analyzed by Professor Smith. Copious springs, rich in chloride of sodium, with a little sulphate of soda and sulphate of potash, flow out from under the limestones along the * American Journal of Science and Arts, Vol. XV., 1853, p. 434. tAmerican Journal of Science and Arts, Vol. XVIII., 1854, p. 379. 500 SYSTEMATIC GEOLOGY. eastern base of Promontory Range, and add their salts to the already strong chloride solution of the lake. Upon the old Overland Stage Road, west of River Bed Station, was a stage-house known as Dugway Station. Analysis No 27 is of the salifer- ous strata of the upper Quaternary, taken from two feet below the surface in a ravine near the station. It is essentially a fine but gritty sand deposit, with a soluble salt distribution through the interstices. It only contains about five per cent. of saline matter. The analysis yields 86.33 of chloride of sodium, 1.05 of sulphate of soda, 9.11 of sulphate of lime, 1.9 of sulphate of magnesia, with a small excess of sulphuric acid. The sur- face of the desert, made up of a loose, calcareous, clayey soil, mixed with a good deal of fine sand, was also examined chemically. The result in analysis No. 28 shows that there were but five tenths of 1 per cent of soluble matter, and the main portion of the insoluble is sulphate of lime. A little chloride of sodium and an unimportant amount of sulphate of magnesia make up the soluble part. In other words, from the surface-soil has been leached out the greater part of the soluble salts, while from the strata a few feet below is obtained a sample having eight times as much soluble matter, and that chiefly made up of chloride of sodium and sulphate of magnesia. Along the base of Wahsatch Range, at Salt Lake City and north of Ogden, are important hot springs pouring a large volume of heated waters into the lake drainage. They contain sulphuretted hydrogen, carbonates of lime and magnesia, sulphate of soda, and chloride of sodium, the latter being in all cases much the largest factor. South of Utah Lake the bed of the ancient lake has not been examined by this Exploration. From a qualitative examination of numerous salines, besides those whose quantitative analyses are given in the accompanying table, it seems that the predominant salts of this whole basin are chlorides of sodium and mag- nesium, with sulphates of soda, lime, and potash, the latter always in much less quantity than the chloride salts. The efflorescence at the sink of Deep Creek is the only alkaline carbonate observed; and even if in the localities not visited by us there should be found other sources of alkaline carbonate, they must remain as exceedingly unimportant and exceptional salts in this basin. It is essentially a chloride basin, with the addition of a moderate QUATERNARY. 5Ol amount of sulphate salts. It would seem that the carbonate of lime, which is now brought in by the present drainage, either goes down as a crystal- line precipitate of carbonate, or decomposes some of the sulphates and remains in solution as sulphate of lime, of which the present waters bear .85 solid in 1,000 liquid grammes. Interesting spherical carbonate of lime sands are observed at several points on the beaches and lake bottom, notably near Black Rock on the west shore of Promontory and on Bear River bay. Under the microscope these globular sands are seen to possess a concentric structure, the layers made up of what appeared to be crys- tallites. From the numerous chloride and sulphate springs within this basin, it is clear that, although now the lake is very concentrated, the present constituents have been the predominating ones as far back as we have any chemical clew. While it is well known that in process of time there is a change in the chemical products of springs, yet there is no local reason to suppose that in this case they have been other than chloride and sulphate springs. In the case of Lake Lahontan, as will be shown later, there has been a great chemical change in the character of the salinity, but there is no reason to infer that a parallel change has taken place in the Bonneville area. The desert efflorescences arise from strata which were thoroughly impregnated with the salts of the lake at the time of its desiccation, and which come out upon the surface in the dry months, and during periods of rain are partially drained into the lake and partially soaked back into the strata. To the springs and to the rivers which flow into the lake we must look for the true source of supply of the ingredients of the lake ; and while the prominent salts of the rivers are carbonates and sulphates of lime, those of the thermal springs are chlorides and sulphates of the alkalies. To the rivers, therefore, are due in great measure the tufaceous material and limy sand, while to the springs are probably due the alkaline properties of the lake. The saline zones seen at points in the Pliocene strata, although they never possess a high percentage of soluble matter, are sufficient to indicate periods of desiccation during the Pliocene, or, in other words, oscillations in the dryness of climate quite analogous to the two dry ages shown by the subaerial gravels of the Bonneville area of Utah, which has been the theatre 502 SYSTEMATIC GEOLOGY. of two or more periods of important desiccation, with an accompanying concentration of solutions. A few alkaline incrustations in middle Nevada, outside the limits of the two great Quaternary lakes, are of some interest and are given here in table of chemical analyses No. IV. In the same table are included for convenience some hot-spring products which will not be specially mentioned. Among the more interesting salines, the following may be particularly noticed : Clover Valley, which lies directly east of the highest part of the Hum- boldt Mountains, carries the well known Eagle Lake, and receives the drain- age of a considerable area. Some of the streams which flow from the mountain into this basin sink into the gravelly Quaternary, and always, during the dry, warm season, there is a limited amount of saline efflores- cence at or near their sinks. A specimen collected by us shows an amount soluble in water of 37.8 per cent. Under analysis, it proves to be com- posed of 24.96 of chloride of sodium, 39.04 of carbonate and bicarbonate of soda, and 33.88 of sulphate of soda, with a trifle of sulphate of potash. It will be seen that this mixture of chloride, carbonate, and sulphate is the characteristic mixture of the lakes of western Nevada, and the high per- centage of carbonate already shows a change from the Bonneville area. On the west side of Humboldt Range, in the valley of the North Fork of the Humboldt, near Peko, there is also an alkaline efflorescence which permeates the sandy soil of the flood-plain of the river. This saline matter is a seepage from the alkaliferous strata of the Pliocene which covers a great portion of the country drained by the North Fork of the Humboldt. These sands, as collected, contain 53 per cent. of soluble matter, of which only a small proportion (74 per cent.) is chloride of sodium, while there is the unusually high proportion of 834 per cent. of carbonate and bicar- bonate of soda, with 4.6 per cent. of sulphate of soda and 4.4 per cent. of biborate of soda. These salts, the result of carbonate and borate springs, have impregnated more or less of the Pliocene strata on both sides of the river; but this is the most typical and richest of the carbonate efflorescences of this region. Locii gS | Number of analysis. i) as Sink of Deep Cre\. Great Desert, bety ; and Cedar Mou. 25) 26 | Alum Bay, Utah |7.07 7-01 27 | Dugway Station, 1.71 road, Great Des\; .go below surface. 28 | Surface, Dugway a Fe Si S| Total. 0.04 | 99-65 0.13 100.03 0.87 | 37-48 | 1-17 | 100.00 0.83 | 37-25 | 1-21 | 100.00 0.05 | 99-00 0.58 | 98.97 Loca Number of analysis | 29 | Main Terrace, Re Lake Desert. Loc ‘a Ss Number of analysis. | 30 | Salt Lake water* MgCl Cl Total. Excess. | 858 14.908 -862 | 149.940 TABLE OF CHEMICAL ANALYSES. III—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. DESICCATION-PRODUCTS OF LAKE BONNEVILLE. Saline Effllorescences. < = ina | i a Locality. Analyst. Ca | Mg | Na | Na |] K K} | Cl Cc S ae Total.} Na Cl|Na C+-C] Na§| KS | CaS aia aunce|| Eat. oO 2 = carbonate. vo 24 | Sink of Deep Creek - - - - -|R.W. Woodward 26.47 | 16.50) 2-55] . |} | 23.20 4-91 13-36] 12-05] - -| 99.04} 38-25] 37-09 | 17-54] 4-71 26.39 | 16.37 | 2.51 || - 23-14 5:00 13-36] 11-9r} - «| 98.68) 38.14] 37.17 | 17.37) 4.63 25 | Great Desert, between Granite Rock se 97-00 0.10 39-06 | tr. : 60.31 nee - -| 018] . . | 99-65} 99.37 0.24 and Cedar Mountain, 97-00 0.09 . 39-28 | tr. 5 60.49 60 : +} 0.17] . . |100.03} 99.68 0.22 Al, O; 26 | Alum Bay, Utah - - - - - - “ 26-55 |0.35 x26 19.02] . =| 2.24) 0.2 1.85 Gas - + | 64.96] 0.04 |100.00] 3.04 0.37 A 23 36-55 }0.33| 11-18 | 19.00] . .| 2.16) . .| og 1.86 b 0 + «| 65.41 | 0.06 |t00.00} 3.05 0.65 27 | Dugway Station, Overland stage- ss 4.83]. 3:84] 0-57) - - | 34.56 | tr. 0 | 52-53 0 9 + +| 7-37] 0-214] 99-01] 86.61 mete I-31 9:32 road, Great Desert, Utah, two feet 4.83 |. 3:76 | 0.63] - . | 34.88) tr. | 52-37 & 0 - .| 7-21] 0.12 | 98.97] 86.33 fon 1-05 g.I1 below surface. 28 | Surface, Dugway Station - - - ce 00.50 31.22] 1-84] - «|| 9.54 9-78 bito - - | 45-60] 0.54] 97-44 : 00.50 30-87 | 2.41 - =| 9-20 - {| 10.81 o 9 - . | 45-48] 0.50 | 98.27 . = 1 Thinolite (fseudo-Gay-Lussite). Gy j s bar | Specifi 5h ie. s re: cen 4 5 5 4 “ : 5 pecific aa Locality. Analyst. Si At ¥e Ca | Mg | Na K hi H C | Total. gravity. ie | = 29 | Main Terrace, Redding Spring, Salt | R. W. Woodward | 8.40* | 1.31} tr. | 46.38] 3-54] 0.48] 0.22 ir. PO* tr. | 1-71 | 38.20 | 100.24 | 2.4, 2.3, 2.4 Lake Desert. 8.22* | 1.20] tr. | 46:50)! 3.525) (0.54 || O.22 3 BOF itr. 91.62) |/48:43) coord) eee * Combined (silicic acid and sand. Lake Water. = = ee 3 a ade ( 4 : afl Bee Specific ras 2@ Locality. Analyst. Ca Mg Na K cl 4 B Pp ae Total. ae NalGly | 9 Naish) Ks aS pd fens 6 30 | Salt Lake water* - - - - - -|0,D, Allen- - | +3570 | 6.301 | 66.978 | 2.901 | 83.946 | 8.2115 tr. tr. 18.758 | 149.940 | 2.4,2.5 | 118.628 | 9.321 | *Solid grammes in 1000 grammes’ weight of water. (EEE IE ae | Z vu tali|K Cll K'$|Ca CljCa SMgcl Si |y Total. 99-42 | | CO? | . | 1-94] 0.43 | 100.25 Nigfitgy cr "5, oe fox peo) eas Camo (RC Ab eee eee Les + | 100.21 | | Na } . 0.88 . «| 11-94 6.31) BSN a foie alo. cal 1:53 100.89 | Na aie 0.87 ae 201 5-84] 8-55 | 5 Allg ela oll cetefss || skeresui©) Ip | | aillc 41 Steamboat Springs, Geiger Grade - us 0.80 | 0.14]. 0.0 °. 18 tr. - |92-67| 5-45] . (Incrustation.) A+Fe 2 5 75 ss d Q 7) 5:45), 0.65 | 0.18 0.05, 0.99 0-15 tre - (92-76) 5-47]. . ; At+ie | 42 | Steamboat Springs, Geiger Grade - se 0.72 | 0.41 tr. tr. + |go-11| 7-56) « } (Incrustation.) AL+Fe ; i | 0.53 | 0.33 tr. | tr. | - | 90-42) 7-55 | | ie | ~~ 43 Sediment from Hot Springs, Reese i ui! eH 8.98 r tr. | 238 | River Valley. | et reg: Oh r 0:38 (Incrustation.) + 0.42 | 48.98 0.96 tr. on, | | | 44 Hot Spring, Grass Valley - - - a - | 0.26 | 48.32 3:98 “i li ' 13:9 a He Io (Incrustation.) 5 0.12 |48.26]. . |4.11 =} th): ee T Na C+C} NaS} 21.11 39-04 | 33-88) { 83-57 | ada 4 QUATERNARY. 503 In Diamond Valley, between Diamond and Pinon ranges, is a remark- able exposure of the Lower Quaternary, being the bed of an extinct lake composed of strata of sand and clay of excessively fine material. During the wet season, and at times throughout the whole year, there is still a shallow lake near the northern end of the valley, which is a strong solution of sulphate, carbonate, and chloride, in which, however, the carbonate pre- dominates over the sulphate, and at times equals the chloride. During the drier seasons the whole of this broad alkali flat, for a distance of ten or fifteen miles, is a clean, hard, white sheet of alkaline and calcareous clay, which upon drying receives a glaze like hard-finish, and indeed is almost as hard as the plaster upon a wall. Heavy teams driven across it scarcely leave a wheel-print, and the sun reflects from it as from a marble pavement. In Crescent Valley, between Pinon Range and Shoshone Peak, is an area of wet clay and quicksand, which receives the drainage of several saline springs, and bears upon the surface in the drier portions of the year a variable incrustation of salt. This is almost a pure chloride, with a very little sulphate and carbonate. Owing to the influx of the saline springs, this whole clay is kept in a very soft and plastic condition, and, as there is no outward drainage, the salts accumulate and stand during the moist periods in pools of saturated brine. The salts of nearly all these predomi- nant chloride deposits are used for commercial purposes, chiefly for the chloridizing of silver ores. East of Toyabe Range, in Smoky Valley, there is a prominent depression, formed of Lower Quaternary stratified clays, which receives the drainage of the mountains on both sides, and is a wet, marshy clay- bed during winter, and a hard, smooth, alkali flat during summer. At the northern or lowest portion of this alkaline plain there is a region of reason- ably pure chloride of sodium, which is derived from the evaporation of saline springs that pour their water into the valley. The salt proves to have 90 per cent. of chloride of sodium and a little over 9 per cent. of sulphate of potash. Interesting hot springs occur in the northern part of Ruby Valley, between Frémont’s Pass and the Overland Ranch. They are essentially like the Icelandic geysers, depositing a tufa which is about 90 per cent. 504 SYSTEMATIC GEOLOGY. silicic acid, with small additional percentages of sesquioxyd of iron, lime, soda, and potash. ‘These hot springs, besides depositing a large amount of pure white siliceous geyser tufa, discharge waters carrying more or less of the carbonates of potash and soda, which pass into Ruby Lake, a shallow body of water occupying the trough-like depression of the valley. The lake is predominantly a carbonate one, but it is of such a weak solution that fish are able to live there. All the spring waters of central Nevada, with the few exceptions of those having their origin in granite, are strongly impregnated either with salts of lime or with those of the alkalies. Humboldt and Reese rivers, like almost all modern rivers, carry car- bonate of lime in excess over all other salts, but all the Nevada rivers have also a variable amount of free alkaline carbonates. On entering the brackish lakes at the sinks of these rivers, the carbonate of lime mainly goes down, and the alkaline carbonates, chlorides, and sulphates remain to enrich the saline solution. LAKE LAHONTAN. Already, in the account of the Tertiary, it has been shown that at the close of the Pliocene period the lake which stretched over the present area of the Great Basin suffered disturbance, its two sides subsiding to form two new deep basins. The depression of Lake Bonneville extended from lati- tude 37° 30’ to latitude 42°. The corresponding depression of the west of the Great Basin lying at the east side of the Sierra Nevada extended from latitude 41° 30’ southward to about the same latitude as the southern waters of Lake Bonneville. The general area of the lake was somewhat. less than that of the Utah depression, and its altitude also was a few hun- dred feet lower. As the widest area and deepest depression of Bonneville Lake were under the bold heights of the Wahsatch, so in the depression in western Nevada the greatest depth and the greatest width are opposite a high group of the Sierra. To the western Nevada and California Basin I have given the name of Lake Lahontan, in honor of the French explorer. There is no single large sheet of water like Great Salt Lake in the present desiccated bed of Lake Lahontan, but there are several considerable bodies whose united QUATERNARY. 505 area is about equal to half the present lake surface of the basin of Bonne- ville. Walker, Carson, and Truckee rivers carry the eastward drainage of the Sierra Nevada and flow into the west side of the old Jake basin. The Humboldt enters it from the northeast and flows for over a hundred miles within its former boundaries. A very considerable part of the area of Lake Lahontan was occupied by lofty mountainous islands which rose above the surface to heights often of several thousand feet. The Pah-Ute, Humboldt, Montezuma, Pah-tson, Sahwave, Truckee, and Lake ranges were all gathered as a great group of islands in the middle area of the lake. Southward, the shore-line was noticeable for its long, deep bays, en- tering the land to the east and surrounding complicated, narrow peninsulas. The entire beach line is well defined by a series of terraces, cut, like those of Lake Bonneville, in the steep, rocky slopes of the mountainous shores and islands, or gently excavated along the easy slopes of the inclined Ter- tiaries. Walker, Carson, Humboldt, Winnemucca, and Pyramid lakes, receiving the present influx of water, represent relics which the general desiccation has spared. One of the most interesting of the recent geographical features in this area was the bifurcation of Truckee River on its downward flow. Emerg- ing from Virginia Range, it turns a sharp right angle and flows northward in the valley depression between Virginia and Truckee ranges, the general level of the country declining to the north. The Truckee here flows in the bottom of a sharp cation which it has cut through the horizontal Pliocene beds. Northward these beds are bevelled off, and near the south end of Pyramid Lake the river flows out upon a plain, its banks lined with wan- dering groves of cottonwood trees. At the time of our first visit to this region, in 1867, the river bifurcated; one half flowed into Pyramid Lake, and the other through a river four or five miles long into Winnemucca Lake. At that time the level of Pyramid Lake was 3,890 feet above the sea, and of Winnemucca about 80 feet lower. Later, owing to the disturbance of the balance between influx and evaporation already alluded to as expressing itself in Utah by the rise and expansion of Great Salt Lake, the basin of Pyramid Lake was filled up, and a back water overflowed the former region 5O6 SYSTEMATIC GEOLOGY. of bifurcation, so that now the surplus waters all go down the channel into Winnemucea Lake, and that basin is rapidly filling. Between 1867, the time of my first visit, and 1871, the time of my last visit, the area of Winnemucca Lake had nearly doubled, and it has risen from its old altitude about twenty-two feet, Pyramid Lake in the same time having been raised about nine feet. The outlines as given upon our topographical maps are according to the survey of 1867, and form interest- ing data for future comparison. The regions of the two great Quaternary lakes have this general geo- logical difference: Bonneville was an area of depression as early as the Eocene, but during the Miocene had free drainage to the sea; Lahontan was a land area during the Eocene, but during the Miocene was a lake basin. In the present desiccated period the aspect of the Lahontan area does not differ very greatly from that of Lake Bonneville. It is a series of alkaline clay plains, composed of undisturbed Lower Quaternary beds, the equivalent of the Bonneville clays, surrounded by more or less inclined regions of subaerial gravel between the actual Lower Quaternary level areas and the mountain foot-hills. The mountain ranges, such as the Pah-Ute, Montezuma, and West Humboldt, rise from 3,000 to 6,000 feet above the ancient lake bottom, their rugged sides for the most part bare of any con- spicuous vegetation, carrying upon their upper heights a few scattered piflon and cedar trees. Nowhere reaching to the level of perpetual snow, and in general either of dusky desert colors or displaying the brilliant, variegated tints of the volcanic series, the general aspect of the mountains is of unrelieved barrenness. The clay plains, during the dry summer months, are covered with efflorescences of soluble alkaline salts, which in many instances give the appearance of fields of snow. In particular, the basin of the Carson-Humboldt Sink affords landscapes of the most peculiar type. The various channels of Carson River are mar- gined by bands of intensely green vegetation, sharply hemmed in by the absolutely barren surface of the desert. The plains are either ashen gray or snowy white, and the waters of the lake reflect the colors of the sky or the QUATERNARY. 507 tints of the neighboring mountains. Along the foot-hills is traced with perfect distinctness the old beach-line of the extinct lake, its even, hori- zontal terraces carved into the Tertiary slopes or escarped in the hard vol- canic bluffs. The altitude of the surface of Lake Lahontan was 4,388 feet, or about 800 feet lower than Lake Bonneville. A cursory examination of the country lying north of the lake area indicates that there was no outlet in that direction. South of the great archipelago formed by West Hum- boldt, Montezuma, and Truckee ranges, with their dependencies, was a broad stretch of lake without islands, including the basin which now contains the two saline lakes of Carson River. Along the foot-hills of the Pah-Ute and the hills to the south of Carson River, the old beach- lines are exceedingly well displayed, and, wherever the slope is suffi- ciently gradual, the recession of the water marked, as in the case of Lake Bonneville, numerous terraces, indicating pauses in the general progress of desiccation. South of Walker’s Lake and Gabb’s Valley, the outline of the basin is hypothetical, and is constructed from a few barometrical notes afforded me by Mr. A. D. Wilson. I have never examined the region of a supposed outflow to the south, but a singular topographical feature, known as Forty-Mile Canon, south of the Ralston desert, seemed to me to afford a possible solution of the question of the drainage of the lake. The accounts brought by prospectors of Forty-Mile Canon indicate that its waters formerly flowed southward, and it is not at all impossible that the surplus of Lake Lahontan found exit through that channel and flowed southward along the slope of the continent. The valley of the Great Desert of California from San Gorgonio Pass southward to the Mexican line affords a close parallel to the area of Lake Lahontan It is far lower in altitude, its extreme depth being below the present tide-level. There, however, as on the mountain coasts of Lake Lahontan, the terrace lines are recorded in well defined beaches, and wher- ever the character of the underlying rock was at all calcareous there is an accumulation of tufa which either encrusts the surface in thick beds or acted as a cement for inflowing gravels, forming a shore breccia. As compared with Lake Bonneville, the chief characteristic difference 508 SYSTEMATIC GEOLOGY. in the phenomena of terraces and shore lines is the great abundance in the Lahontan basin of calcareous tufas. Modern subaerial gravels have been in great measure washed down over the calcareous matter, but it frequently exists even on the broad bottom of the lake in thick accumulations— covering areas of several miles with a tufaceous deposit from twenty to sixty feet thick. As will be seen later, this tufa is of very great chem- ical interest, and its mineralogical nature affords a clew to the history of the lake. From its very great importance and its peculiar origin, I have taken the liberty of giving it a lithological name. Since it formed on the shores of the lake, I have called it, from the Greek 7s (shore), Thinolite. During all the Quaternary the high mountains have afforded the loci of disintegration and removal. Aside from the period of great cafion- cutting, the general frost and snow disintegration, and the recurrence of annual storms and floods, have swept down from the mountain flanks and from the canons an enormous amount of sub-angular fragmental mate- rial partly in the condition of fine sands, but largely of coarse gravel, of which the fragments vary in size from a hazel-nut to blocks of sev- eral tons in weight. The thickness of these deposits is nowhere seen, but from the manner in which they build up talus-slopes against the foot-hills of the mountains it is evident that there can not be less than one or two thousand feet in some extreme instances. From every mountain and range foot declines this gentle slope, the larger materials next the mountains, the smaller washed out to greater dis- tances. The uppermost gravels of this series, when traced down into the level desert areas, are seen to overlie the horizontal stratified sands, clays, and marls of the Lower Quaternary, which are an undisturbed for- mation of an unknown depth. In the stream-cuts which have opened extremely modern sections in the subaerial gravels, it is seen that the strati- fied Lower Quaternary overlies a considerable portion of the subaerial gray- els; indicating a former expanse of water during which the lake area encroached upward and outward over the older subaerial gravels, a final recession from its extreme expansion, and a subsequent pouring down of modern subaerial gravels over the exposed surface of the sedimentary beds. This is the same phenomenon which Gilbert has described within the basin QUATERNARY. 509 of Bonneville. It is best shown, over the Lahontan area, in the region of Pyramid Lake and the flanks of Truckee and Lake ranges near their northern ends, where are considerable exposures of the lower and earlier gravels. Near the height of the uppermost terrace the gravels are largely cemented by calcareous tufa, as they are upon the higher terraces at Lake Bonneville; but in passing downward the calcareous deposits are very dif- ferent, the tufa occurring in enormous masses 30 to 60 feet thick, and with little inclusion of foreign rocky fragments. The broad area of Mud Lake Desert, the floor of Gabb’s Valley, and the clay flats surrounding the two Carson lakes are conspicuous examples of the larger exposures of the Lower Quaternary lacustrine clays and sands. As in the Bonneville region, the lower and earlier subaerial gravels show to such a very small extent in the exceptional modern cuts that they could make no feature upon a geological map. Organic life seems to have been much rarer in Lahontan Lake than in Bonneville. A few Planorbis are the only species of Mollusca we have found embedded in the gravels. One or two deep wells have been sunk on the Carson Desert, in the hope of finding a water free from the prevalent alkaline salts, and these display from 80 to 100 feet of Lower Quaternary beds composed chiefly of clay and sand, with far less of the marly or calea- reous matter than may be seen at the Dugway well in Bonneville Basin. A partial examination of the waters and desiccation-products of the La- hontan area has resulted in the discovery of some very interesting chem- ical facts. Among the waters which now enter the basin as rivers or exist in the form of lakes, perhaps the most interesting are those of Pyramid, Hum- boldt, and Soda lakes. Pyramid Lake has a specific gravity of 1.0027; its solid contents com- puted for a thousand grammes of water and expressed in grammes show : Chloride of sodium, 2.8871; carbonate of soda, .5384; sulphate of soda, 2485; carbonate of lime, .0178; besides a little magnesia and carbonic acid. It is essentially a chloride lake, with the presence of carbonates of soda, magnesia, and lime, and a little sulphate of soda. The relative pro- portions of chloride of sodium and sulphate of soda in Pyramid Lake do not greatly differ from the ratio of the same salts in the far denser solution of 510 SYSTEMATIC GEOLOGY. Salt Lake, but the waters differ widely by the presence of carbonates of soda, lime, and magnesia. The high proportion of carbonate of soda, amount- ing to one sixth of the total saline contents, accounts for the presence of the carbonate of lime. It was seen that in the solution of Salt Lake car- bonate of lime did not exist. That salt, as it was delivered by the inflowing rivers, cither suffered double decomposition with the sulphate of soda, remain- ing as sulphate of lime, or, as was evidently true of the greater amount of the carbonate, fell as a precipitate. The possibility of carbonate of lime, even in the small percentage which is present in Pyramid Lake, remaining in solution in the presence of so much chloride of sodium and sulphate of soda, is unquestionably to be accounted for by the presence of carbonate of soda. Humboldt Lake, which is really a mere expansion of Humboldt River, is a water of considerably less salinity than Pyramid Lake, having a specific gravity of 1.0007, with a total amount of saline matter of 88.8 solid in 1,000 liquid grammes. It differs quantitatively from the water of Pyramid Lake by the inferior percentage of chloride of sodium, and qualitatively by the astonishingly high percentage of chloride of potassium, which amounts to nearly one third of the entire saline contents. In the Pyramid Lake water there is an excess of magnesia over the carbonic acid with which to combine it. In the Humboldt Lake water, however, besides the necessary carbonic acid to unite with the magnesia, there is an excess amounting to .0425 of free carbonic acid, and there is also a minute percentage of phos- phorie acid. It is highest in the percentage of carbonates of any water in the basin, with the exception of the Soda Lakes north of Ragtown. Traces of boracie and silicie acid occur in both Pyramid and Humboldt lakes, and their waters also gave, under the spectroscope, a distinct reac- tion for lithia. For a detailed description of the little Soda Lakes lying on the desert north of Ragtown, Nevada, the reader is referred to Chapter V., Vol. II. The water of the larger Soda Lake is of very great interest, since from its dense solution at all the drier periods of the year, when the fluid is concentrated by natural evaporation, the mineral gaylussite crystal- lizes on the edges of the basin and on any bits of organic matter which QUATERNARY. 511 may be floating or lying in the lake. It is a dense water, having, at the time of our examination, in 1,000 liquid grammes, solid contents of 114.449 grammes, and a specific gravity of 1.0975. Although the propor- tion of carbonate of soda to chloride of sodium is not so high in this lake as in the waters of Humboldt Lake, its large carbonate tenure, amount- ing to 29.2482 of carbonate of soda, .0652 of carbonate of magnesia, with a considerable excess of free carbonic acid, makes it the most important carbonate water in the Lahontan area. Of chloride of sodium there are 69.9413 grammes, and of sulphate of soda, 13.7626. Sulphide of sodium is present, amounting to .2384, and sulphate of potash equalling 3.6513. Like the Humboldt water, it has a little combined silica. It is therefore a chloride, carbonate, and sulphate water, in which no lime whatever was detected by the most delicate tests. It is interesting that in a lake which is especially noted for the annual production of fine crystals of gaylussite, there should be no trace of lime in the water. It is evidently true that in the presence of a high proportion of alkaline carbonates every atom of lime which the annual floods wash in from the surrounding calcareous soils is at once seized by the alkaline carbonate, and made up into gaylussite. Prof. O. D. Allen, of Yale, who executed the above analyses, also made a careful examination of the solubilities of Nevada gaylussite in clear water and in weak carbonate solutions. The mineral was readily acted upon in the presence of sulphates and chlorides and a small proportion of carbonate of soda. It retained its integrity only in solutions with a considerable excess of alkaline carbonate. An examina- tion of the evaporated salt is given in the table of analyses No. V. of the desiccation-products of Lake Lahontan. The gaylussite itself yielded 19.19 of lime, 19.95 of soda, 29.55 of fixed carbonic acid, a trace of sulphuric acid, 31.5 of water, and .2 of insoluble residue, which was altogether small particles of sandy material; the water percentage being a little higher and the insoluble residue a little lower than the analysis of Boussingault given in Dana’s Mineralogy. The artificial production of gaylussite by Fritsche, requiring an enormous excess of carbonate of soda, is thoroughly in keeping with the chemical reactions of the Soda Lake water. It is interesting to observe that all the forms which crystallize in 512 SYSTEMATIC GEOLOGY. this lake are thin in the direction of the orthodiagonal, producing short, flat crystals, like Figure 607 in Dana’s Mineralogy. The occurrence of these two lakes is so peculiar and interesting as to demand more than a passing mention. The surface of the country in their neighborhood is about 4,000 feet above the sea-level, and is formed of the level beds of Lower Quaternary strata, here consisting of sandy clays, having a surface which has been modified only by eolian erosion and the slight effect of rains and storms. The two basins lie within an eighth of a mile of each other, and they are almost exactly circular, the larger having a bank varying from 85 to 150 feet in fine perpendicular walls, and a diam- eter of about five eighths of a mile. The smaller lake occupies a similar crater-shaped basin, its banks having a height of from 50 to 70 feet, and at the date of its highest water the diameter is hardly more than one fifth of a mile. In the smaller lake during the drier periods of the year the solution becomes very dense, and a considerable part of the bottom of the lake is laid bare, with a thick incrustation of trona over the exposed portion. Neither basin has an outlet. The larger one is fed by a cool fresh-water spring on the northwestern side, which pours from a gravel stratum just above the lake. The formation of these depressed, funnel-like hollows in the middle of a Quaternary desert, having no out- ward drainage, and only varying in their density according as the humid or the evaporating period advances, is not altogether easy to account for. The presence of much basaltic material on the banks and narrow margin of beach, and the circular, erater-formed depression which the lake occupies, lead us to suspect that during the period of the occupancy of this region by Lake Lahontan, when the Lower Quaternary beds were in process of accumulation, and when there were at least 500 feet of water over the present surface, these crater-like lakes were points of extremely powerful springs, deriving their great activity from volcanic sources. Extremely powerful springs are now observable, coming to the surface from very great depths in the strong alkaline solution of Mono Lake. That water, besides being densely charged with alkaline carbonates, is also charac- terized by the abundant presence of borates, its solution being far denser than any of the considerable lakes of the Lahontan area. Rowing on its surface ft QUATERNARY. 513 in a boat of considerable size, over water of a depth of more than a hun- dred feet, I came upon strong springs of rather fresh water, which rose above the level of the lake in low mounds, and this constant fountain-like pro- jection of fresh waters above the surface was strong enough to deflect the boat from its course. The diameter of some of these cold-water mounds was from 100 to 150 feet. A jet like this evidently necessitates a very powerful pressure of water at the lake-bottom, where the spring emerges from the sandy material of the floor. If from any cause the basin of Mono Lake, which is now covered with fine lacustrine muds, should be exposed by the desiccation of the lake, and the great spring jets cut off from their source of supply, on the horizontal beds which are now accumulating over the bottom would undoubtedly be found crater-like basins similar to those of the alkaline lakes near Ragtown. Plate XXVI. in this volume gives a very correct idea of the general appearance of the larger Ragtown lake, showing the high, steep banks, with the beach-line underneath them and the lower banks on the left. The smaller lake is shown in Plate XXII., Volume II., where the trona fields may be seen on the partially dried lake-bottom. In later pages it will be seen that an enormous amount of alkaline carbonate must formerly have characterized the waters of one period of Lahontan. The origin of these alkaline carbonates is among the most difficult of the chemical prob- lems of the region. That this carbonate was not a result of the organic decomposition of other salts, will become evident from a glance at the enormous quantities involved. Only a very few of the thermal or cold springs of the whole Great Basin country are now delivering carbonated alkalies. The hot springs of Ruby Valley, which deposit a liberal incrus- tation of geyser silica, yield a considerable proportion of carbonate of soda. It is not improbable that the Ragtown lakes, with their dense car- bonate solutions, represent the relics of a once copious source of the salt. Among the efflorescences found upon the desert, that at Magg’s Station on the Truckee desert is nearly pure chloride of sodium, only varied by less than 2 per cent. of sulphate of lime. At Hardin City, however, in the Black Rock region, the efflorescence of the ereat Mud Lake desert yielded in 100 parts, 18.47 of chloride of sodium, 52.10 of carbonate of soda, with 33 K 514 SYSTEMATIC GEOLOGY. 27.55 of sulphate of soda. This is the only instance of a considerable area of efflorescence, in which the alkaline carbonate exceeds the united chlorides and sulphates. At the sink of Quinn’s River the efflorescence contained chiefly sodium chloride, varied only by sulphate of soda and lime. A sim- ilar salt, with a higher proportion of sulphate of lime, occurs as an efflo- rescence through the alkaline earth near Buffalo Station. From the lesser Soda Lake near Ragtown comparatively pure trona is taken, having a com- position of 40.77 of soda, 37.88 of carbonic acid, with a little chlorine and sulphuric acid, and 20 per cent. of water. I have already remarked that the most interesting chemical result of the desiccation of Lake Lahontan was the enormous deposit of thinolite tufa. In the immediate foot-hills of some of the higher ranges, the terraces and slopes, thickly incrusted with a gray coral-like material, are covered over with the most recent subaerial gravels. This is particularly the case along the Osobb Valley, which lies between Augusta and Pah-Ute ranges. So, too, along the slopes south of Carson Lake, on the divide between Jarson and Walker basins, much of the thinolite surface is covered with extremely modern gravelly detritus, but here and there along those slopes, wherever the topography was steep enough to preserve a rocky front, the crusts of gray and whitish tufa are still uncovered. Even along the flat bottom of the desert, at elevations of about 4,000 feet, there are long reefs covered with the tufa, which rises in most peculiar and fantastic forms, stand- ing up often in cylindrical chimneys, having an obscure, partly obliterated tube in the axis. Some of these chimneys are ten and twenty feet in height. For the most part thinolite has an extremely rough, ragged surface, full of intricate interstices, rarely in the region of Carson Lake showing any consid- erable exposure. In the region of Humboldt Lake, on the slopes of Monte- zuma Range, it is nearly overwhelmed with modern débris, but along the rail- road are a few rocky ledges covered with coatings five to ten feet thick of tufa. Single isolated groups of fantastic forms occur southwest of Oreana, rising above the Quaternary plain, which is based upon the horizontal Tertiary of the Humboldt group. Along the slopes of Pah-Ute Range which face the Carson desert are but few traces of thinolite; but on the south foot of "oe ‘- + ' y a = oy ‘ o ‘ : - , ‘ Vics ‘ 5 ‘ . * + 7 . , ae “ 4 We ot A *, : F a s fa. oe : : y as 1 ¢ oan t 7. { i ‘ ‘ 7 44 - ! co QUATERNARY. 515 West Humboldt Range, which directly overlooks Carson Lake, the upper terraces show considerable incrustations, never, however, over five or ten feet in thickness. By far the best general exhibitions of the material are in the neigh- borhood of Pyramid Lake and the valley of the Truckee. Here the steeper slopes of Lake Range and of the northern projection of Virginia Range, where they flank the lake, are thickly coated with pure gray thinolite, which at the uppermost levels carries a considerable amount of angular and sometimes rounded fragments, imbedded as in a conglomerate. Decidedly the most interesting single specimens of thinolite outcrops: are to be seen at the Domes, the Pyramid, and Anahé Island. The Domes particularly are of extreme interest. They are a series of bold spheroidal forms, partly bordering on the east shore of Pyramid Lake opposite the Pyramid, and partly rising as detached, abrupt islands above the surface of the water. They are immense botryoidal masses, always showing more or less of an obscure central opening, as if they were due to spring currents and had been built up like some of the domed mounds of thermal springs. The Domes themselves are from fifty to sixty feet in height, the caleareous material generally of a light-brown and light-gray color. The Pyramid, a remarkable detached island from which the lake takes its name, rises about a mile from the shore, having an extremely narrow base and an alti- tude of about 400 feet. Plate XXIII. shows the thinolite domes and the Pyramid. Almost its entire surface is incrusted with relics of a thinolite coating, which at one time must have covered it uniformly. About three miles from the eastern shore is the bold Anahé island, which reaches 500 feet above the surface. Terrace lines having been observed fully 500 feet above the present water's edge, no doubt this island was formerly entirely covered by the waters of Lake Lahontan. The island is about a mile across, and fully three quarters of its surface are thickly covered with thinolite, or show traces of its former presence where modern erosion may have remoyed it. The incrustations on the steep upper slopes of the island around the central peak are extremely peculiar. They possess a rough botryoidal surface, which has the appearance of being made up of huge mushroom-like forms that overlap each other like roof tiles. When 516 SYSTEMATIC GEOLOGY. closely studied, each special mushroom-like member is seen to have an independent central stem. Plate XXIV. gives a near view of a portion of this singular thinolite surface. The coating is from ten to twenty feet in thickness, and the surface is one of the roughest imaginable geological exhibitions. It is only equalled by the frothy and porous surface of a newly congealed lava-flow. The lower valley of Truckee River is cut through a cation of hori- zontal sands, assumed from their connection with the Humboldt beds to be of Pliocene age. This canon, in continuing northward toward the lake, cuts deeper into the formation, and at last the abrupt banks are over 200 feet in height. Upon the plateau-like summit of the beds, on the edges of both the east and west walls of the cation, thinolite appears in very curious forms. Itoccupies the surface of the Pliocene beds in broad mushroom-like bodies, varying from two to eight feet in diameter, having smooth, round surfaces entirely free from the coral-like openness of structure observed in the great banks where they are incrustations on the inclined rocky surface. The peculiarity of these mushroom-like formations is, that they are gathered together, forming a complete surface of country, touching edge by edge, and that from the middle of these round bodies there is a distinct stem which penetrates the Pliocene sands to a depth of from one to three feet. Besides these, the Pliocene itself is more or less coated with irregular flat sheets of thinolite. The effect upon the edge of the canon wall or upon the edges of the side ravine, where erosion has cut away the supports of the mushrooms and left them overhanging on the brink of the walls, is peculiar in the extreme. Certain limited passages of the Pliocene surface carry these mushrooms, extremely smail, about the ordinary dimensions of the edible fungus. Specimens, with a cen- tral stem, and the whole root phenomena, were submitted to a com- petent botanist, who at once saw in them petrifactions of fungoid growths ; but they are without doubt of a concretionary or crystallitic origin. The lower figure of Plate XXV. gives an idea of these mushroom forms on the edge of a canon, Pliocene strata showing below. It is evident that the thinolite tufa formed after a considerable bevelling of the Pliocene, but before the final cutting of the present Truckee Canon, since the thino- Parallel eol. Expl. 40 fal ) 10S “VAVAUN aMV GInNVaAd aNV'TSI a 7 - ) an 7 oe é . * . * oo 7 a ise . 7 . @ : ? r a : ai a s a * : : 1 - : ¢ 2 a , - 1 st ¥. as i - i . . ; - t ' A ‘ ' - : » v i 7 ‘ fo i be ‘yt ry nm : - - 7 : . - 7 i =. ' < hd oo : ‘ : Day x a : : 7 “nga . ba 7 : : : ’ > 1, Mi + 2 : a te ’ ae ‘ “Sam 7 7 - ' ‘ - ‘ 7 ' A ‘ 5 7 i on - . 7 ‘ 7 ‘ - a i - ‘ r . : si ‘ : 7 = ae 7 = i = wes : Pater ot : o = ; 7 —3 . I » ny a area : a 4 7 7 : ' : ‘2 A n = 7 A 4 7 7 ' ; ; ’ : ia A a is ' \ 1 y ‘ cae 1 * nl ir We a 7 = ' _ . 7 ' _ 7 - ‘ - : : : 7 7 : : , _ 7 y 7 7 ns ' ji 1 ‘ a ft % 7 ' : 4 ‘ A ey 7 ve _ = - ' : + 7 - : 7 i ‘ - = . Pi a ' 5 : , 7 Ht c ‘ wee Pa . ‘ - : ae . a i : : Jt _ ' ‘ - 7 - 7 - 7 ' i ’ Ny a ' iy ' ee : i - uy " - . ¥ 7 7 4 : ‘ te t ' ae ‘ . = QUATERNARY. 5 Lf lite nowhere covers the sides of the cafion, but comes in an even sheet up to the very edge of the walls on both sides. The immediate surface of the rough thinolite coatings on the rocks at Pyramid Lake is very well shown in the upper left-hand detail figure of Plate XXV. The curious, rude, botryoidal surface, with its markings and pits, is seen, and a little within the botryoidal zone may be detected the irregular, imperfect forms of crystals. The left-hand middle figure of the detail plate shows a region of the underlying irregular crystals just under- neath the superficial botryoidal zone. This is composed of an intricate net-work of imperfect octahedrons, varying from an inch to one sixteenth of an inch on the shorter axis, but elongated up to a foot in length. The right-hand upper figure of Plate XXV. gives a better view of these irregular, distorted, long octahedrons, and shows also their manner of interference, and the peculiar branchlets which grow out at angles from the sides of the main crystals. A large number of thin sections from the solid beds of thinolite, from mushrooms of the Truckee valley, from the smooth surface of the Domes, and from a variety of solid thinolite material collected over the Carson and Humboldt desert, when examined under the microscope show distinct translucent crystalline forms, surrounded by a dull opaque gray substance, which, as the sixteenth objective shows, derives its gray color from a cloud of minute foreign particles. The included distinct erystals vary in size from very minute forms to half an inch in diameter, and show numerous angles which, when measured, show close approximation to the angles of gay lussite. I submitted several of the more perfect crystalline forms to Prof. J. D. Dana and Mr. E. 8. Dana. After a very careful examination they con- firmed my reference of the mineral form to gaylussite. Unable to obtain specimens of the “clavos” from Lagunilla, in Maracaibo, I have not been able to compare the elongated nail-form of the octahedrons of that locality with similar bodies here; but the Lahontan forms of the thinolite crystals are unquestionably a peculiar development of the mineral gaylussite. Over a very large part of the thinolite area these imperfect crystals are abun- dant. This is true of all the porous developments of tufa. On the other 518 SYSTEMATIC GEOLOGY. hand, wherever it is smooth and consolidated, thin sections show the inclu- sion of a large number of minute octahedral crystals having the long nail- shape, with others more related to the shorter shapes of the larger Soda Lake. A full examination of a large number of field localities and collected specimens leads me to the belief that the entire thinolite formation, with all its enormous development, its extent of hundreds of miles, its thickness of 20 to 150 feet, was nothing less than a gigantic deposit of gaylussite crystals. Referring now to the table of analyses of desiccation-products of Lake Lahontan, it will be seen that there are three analyses given of the thino- lite—one from the tufa dome on the shore of Pyramid Lake, one from a reef in Carson desert, twelve miles north of Ragtown, and one from the basaltic slopes of Truckee Range just above the mushroom-capped Pliocene strata, where their surfaces of thinolite abut against the foot-hills east of the cation. The included silica, which is chiefly mechanically entangled sands, and not an integral part of the crystalline thinolite, varies from 2.19 per cent. to 7.27 per cent., and the alumina varies correspondingly from 8 per cent. to 24 per cent. The included foreign material is, therefore, siliceous and feldspathic sands. The percentage of magnesia rises in one instance, at the Carson desert, to 4 per cent.; there is always a little soda, a little potash, traces of phosphoric acid, about 1 per cent. of water, and about 90 per cent. of carbonate of lime. The thinolite is, therefore, practically, and leaving out of consideration the mechanical impurities, a pseudomorph of carbonate of lime, after gaylussite. The chemical deductions from this interesting fact are of exceeding importance in the history of Lake Lahontan. In the study of the alkaline desert lakes near Ragtown, we have seen that at the stage of the greatest fullness of water or greatest weakness of solution the gaylussite crystals are redissolved and none are to be seen. On the other hand, at the close of the long evaporating-period of the summer, the waters having very materially diminished and the solution become dense up to the point of erystalliza- tion, gaylussite freely separated out. A spirit-level determination of the highest observed thinolite places it at 470 feet above the 1867 level of Pyramid Lake, whereas the highest # + + \ — . = = 7 ‘ - *. ‘ . - ® . . . . . at QUATERNARY. 519 observed terrace-lines are about 500 feet above the 1867 level of the lake. There were therefore about thirty feet between the highest level of the lake and the highest point at which thinolite formed. From its highest develop- ment there were nearly continuous sheets incrusting the mountain slopes upon both sides of Pyramid Lake down to the water level, and, at the time of the examination in 1867, sailing over the very clear water in the neigh- borhood of the Pyramid, Anahé Island, and the Domes, and also when standing at the top of the Domes and on the Pyramid, it was seen that the thinolite formation extended far beneath the level of the water. It is probable that we saw at least thirty feet of thinolite surface below the water level. The present solution of Pyramid and Winnemucca lakes is so low in saline contents that the mineral gaylussite, which was the original basis of the thinolite, could not by any possibility be formed. Moreover, the present waters are so weak in alkalies that carbonate of lime is still held in solution. It is therefore evident that, at the time of this enormous crys- tallization of gaylussite, the great body of Lake Lahontan, filling up the area of four degrees of latitude in length by three degrees in breadth, with an average depth of 400 or 500 feet, must have been of sufficiently strong carbonated solution for the production of the mineral gaylussite. The experiments on the solubility of this mineral by Professor Allen, already mentioned, and the existing facts of its natural production by the concentration of the carbonated waters of the Ragtown Soda Lake, show that a dense solution of carbonate is essential to the formation of gaylussite. The thinolite itself, a pseudomorph of carbonate of lime after gaylussite, shows at once that the original mineral was formed in the highly car- bonated alkaline solution; the pseudomorph being a subsequent result of the addition of calcareous matter to the solution, the lime replacing the car- bonate of soda of the gaylussite, and transforming it into carbonate of lime. Whether we consider the solution after the formation of gaylussite, or still later after the liberation of carbonate of soda from the gaylussite during the act of pseudomorphism, it is evident that the whole Lahontan basin, up to the level of the highest thinolite, must still have been a concentrated car- bonate solution. When we now realize that the lake has dried away, and 520 SYSTEMATIC GEOLOGY. whatever alkaline tenure it had at the period of desiccation must have been gradually concentrated in the lower residual basins—namely, the present and when we further consider existing lakes within the Lahontan area that the present lakes are so fresh as to permit the healthy life of numerous fishes, including one or two of the Salmonida, it is evident that the present waters do not represent the residual concentration of the great carbo- nate lake To account for the enormous accumulation of saline matter in the orig- inal Lake Lahontan to a sufficient density for the development of gaylussite, it is of course obviously necessary that the lake should have had no outlet; in other words, its waters were constantly concentrating by evaporation, never flooded out by any considerable overflow. The occurrence of such a tremendous formation of alkaline carbonates, to say nothing of the other contents of the lake, necessitates a very long period during which the surface of Lake Lahontan was some distance below its level of outlet. To account for the existing presence of the weak solutions of the residual lakes, it is necessary, after the formation of gaylussite and its pseudomorphism into thinolite, to suppose a flood-period during which the lake had free drainage over its outlet, and which continued long enough to wash out practically the whole saline contents of the great lake. The chemical nature of thinolite, therefore, necessitates, first, a long continued period without drainage to the sea, during which the inflowing waters, derived both from the direct drainage of the tributary rivers and from the carbonate-producing springs of the basin, were enormously concentrated by continued evaporation; secondly, the solution having arrived at the required density, a general development of gaylussite erys- tals incrusting the walls and slopes of Lake Lahontan. Supposing the solution concentrated to the point of the formation of gaylussite, we have no direct means of saying whether the mineral would form over the whole sides and bottom of the basin, or whether it would simply form on the shores as the waters concentrated and the lake shrank by evaporation. The analogy of Ragtown Soda Lake would seem to indicate that gaylussite forms only near the surface, and the arrangement of the tufas over considerable terraces would further seem to warrant the belief that it was a shore product QUATERNARY. 521 marking the gradually retiring water-line. It is, however, chemically quite possible that with a solution of moderately uniform density and of sufficient concentration for the development of crystals, they might form simultaneously over the bottom and sides ; but that seems the less probable hypothesis. A further argument in favor of the thinolite having formed as a shore deposit, is to be found in the occurrence of angular and rounded beach gravels in it at numerous points, although generally the thinolite found upon the immediate bottom of the lake is rather free from included fragments. This, however, would naturally be the case from the remote- ness of these lake-bottom thinolite bodies from any shore line where pebbles could have been washed in among the forming crystals of gaylussite. If the desiccation was carried down, say to the present amount of water within the Lahontan area, the entire surface of the extreme low levels must have been covered by an enormous saline residuum composed of the excess of soluble salts over the amount required for the gaylussite. The present condition of the basin and the freshness of the lakes show that after this period of desiccation came a second flood-period, which raised the level of the lake to its height of overflow and washed out all the soluble salines of the basin. In this process of refilling the lake and diluting the solution, it is evident that there would still be carbonate enough to preserve the gaylussite, because gaylussite had continued to form down to the lowest levels. In the second flood-period which removed the great saline contents, during the process of filling the lake, there must have been either a cessa- tion of the addition of carbonates by springs, or an excess of lime brought in by the rivers. At all events, the process of pseudomorphism occurred before the solution was weak enough to redissolve the gaylussite crystals. When we realize that during the formation of gaylussite as seen in Ragtown Soda Lake there must always be a great excess of carbonate, and all the lime is made into gaylussite, it must be admitted that in the age of pseudomorphism there must have been density of solution sufficient to retain the crystals, and yet lime enough to furnish the material for the pseudomorph. It is rather a delicate chemical question, how the solu- tion ever should have contained lime enough for the pseudomorph, and yet carbonate of soda enough to prevent the re-solution of the gaylus- 522 SYSTEMATIC GEOLOGY. site. In a single alkaline deposit, that of the upper Humboldt Valley, there is a considerable amount, reaching in one instance 12 per cent., of chloride of calcium. Suppose after the formation of gaylussite, the lime, instead of coming in as carbonate by the slow delivery of the rivers, was a hot-spring product in the form of chloride. The chloride of calcium coming into the presence of an excess of carbonate of soda, double decom- position would occur, making carbonate of lime and chloride of sodium, providing the solution were of the requisite density. It would seem that a process of that kind might account for the substitution of carbonate of lime for the carbonate of soda of the gaylussite. However that may be, a second flood-period evidently washed the entire basin free from all soluble saline contents, and maintained it for some time as a pure fresh-water lake. The subsequent desiccation of that lake, starting with a pure, fresh water, and carried down to the present almost complete drying-out of the basin, is the last fact in the history of this lake of which we have any knowl- edge. Weare therefore warranted in assuming, first, a lake having an outlet ; secondly, the sinking of the level of that lake by evaporation below the level of outlet; thirdly, the long continued concentration by evaporation of its saline solution up to the point of the formation of gaylussite; fourthly, the desiccation of this lake and development of the great incrustations of gaylussite crystals, and possibly, though not probably, the formation of the pseudomorph; fifthly, the coming on of a second flood-period which filled the basin to its point of overflow ; sixthly, the maintenance of the lake at its maximum level long enough to wash out the soluble salts completely, and probably, during this period, the formation of the pseudomorph; seventhly, the modern rapid desiccation from the point of maximum fullness down to the present, in which only the few lowest basins contain the meagre residual weakly saline lakes. When we come now to correlate the features of this chemical history with those brought out by the relation of the sediments of Lake Bonne- ville, as clearly shown by the observations of Gilbert* and myself, we find that the reading of the sedimentary deposits shows, first, a period in which the lake basins were dry, and during which subaerial gravels washed down *United States Geographical Surveys West of the One Hundredth Meridian, Vol. II., Geology, Chap. III. QUATERNARY. 523 the slopes far into the heart of the lake basin; secondly, a flood-period in which the lacustrine sediments accumulated over the whole floor of the lake, overlying the lower extension of the earlier subaerial gravels; and, thirdly, the present period of desiccation, in which the waters of the lake have dried out and a second subaerial gravel formation has been washed down its slopes, covering the edges of the lacustrine sedimentary beds. Gilbert, therefore, beginning at the present, shows our period of dryness to be immediately preceded by a period of high humidity, in which Lake Bonneville was filled to the brim, and a period of dryness anterior to the Bonneville Lake. The chemical history of Lake Lahontan, when corre- lated with this, shows not only those three periods, but a period of humidity anterior to Gilbert’s earliest age of dryness. For the clear reading of the chemistry of Lahontan is: our modern period of desiccation corresponding to the period of latest subaerial gravels, as displayed both in the basin of Lahontan and of Bonneville; a period of flood immediately preceding that, during which the saline contents of Lahontan were washed out, and during which Bonneville was filled to its highest terrace; Gilbert's earliest period of dryness, which corresponds to the age of the thinolite desiccation of Lake Lahontan. The appearance of thinolite itself up nearly to the highest terraces of Lahontan shows a period of moisture anterior to Gilbert’s first period of desiccation. Gilbert justly remarks that the Bonneville beds appear as an episode occurring between two periods of aridity. The addition of a still earlier period of humidity to this series of climatic changes could never have been arrived at from the lake sediments alone, since the lacustrine beds of the second humidity-period would naturally cover up and obscure those of the first humidity-period. Could we obtain a section deep enough on the borders of the two lakes, beneath the earliest subaerial gravels which Gilbert and I have ob- served in both basins, there would doubtless be seen still earlier lacustrine beds underlying the bottom of the thinolite. That Lake Lahontan was filled before the formation of the first gay- lussite, is proved by the position of the pseudomorph of that mineral nearly up to the point of outflow. The earliest knowledge, then, we have of these 524 SYSTEMATIC GEOLOGY. lakes is of their being full. When we compare the amount of salinity which was retained within the lake basin in the first period with that which is now observed as the result of the second desiccation-period, it is at once seen that the first lake had an enormous excess of soluble salts over the second lake, since its chemical residua on evaporation contained such a vast amount of carbonate. Making all due allowance for any change in the chemistry of the springs of the basin, which at that time must have yielded an immense amount of the alkaline carbonates, and which now yield very little of the same salts, it will be seen at once that the period of concentration of the first lake, namely, the period at which it was maintained at a high level, though below the point of outlet, must have been enormously longer than in the second age of desiccation, since the residual products of the second period of desiccation are not enough to render even the small existing lakes very saline. We are therefore warranted in assuming for the first age of humidity of the lake an enormously long continuance as compared with the second. The first long-continued period of humidity is probably to be directly correlated with the earliest and greatest Glacier period, and the second period of humidity with the later Reindeer Glacier period. The Quaternary lakes of the Great Basin are therefore of extreme importance in showing one thing—that the two glacial ages, whatever may have been their temperature-conditions, were in themselves each distinctly an age of moisture and that the interglacial period was one of intense dry- ness, equal in its aridity to the present epoch. It is worth while to emphasize the fact that the present is essentially a period of desiccation, as contrasted with the wet periods during which the Quaternary lakes were filled. The Glacial periods, then, must have been far more moist than the climate of to-day. As regards the heat-condition, I have before called attention to the fact that the mean annual temperature over a considerable part of the United States Cordilleras is to-day lower than over the still glaciated portion; that the difference between the gla- ciated and the still colder regions is simply one of relative moisture. Suppose a secular change to occur now, in which the climate of the northern hemisphere should for a time become colder than at present. It is obvious that there would be less evaporation of the oceanic moisture, and QUATERNARY. 525 that the winds which carry that moisture over continental areas would be even drier than at present. Even with the relative humidity which now char- acterizes these winds during a lowering of the temperature, it is extremely doubtful whether glaciers would form. In the presence of greater cold there would be a greater precipitation relative to the moisture of the conti- nental atmosphere; but that atmosphere itself would be correspondingly drier from the diminished supply evaporated from the ocean surface. On the contrary, in a warmer period, the sea-winds blowing over the continent would bring a greater amount of moisture, and there would be, as regards the whole area, a correspondingly greater precipitation; and the cold, high-altitude points or climatic islands of low temperature would still act as powerful condensers and extract from the moister winds more snow than at present. The instructive example of New Zealand affords an illustration of the abundant production of glaciers in a climate of higher mean tempera- ture and greater relative humidity than that of the United States. Late writers on the Great Basin, especially G. K. Gilbert, have called attention to the rise and expansion of Salt Lake. I have already shown that between the period of the Stansbury survey and that of my own there was an increment of 600 square miles in the area of the lake, and a rise of eleven feet. In popular discussions, it has frequently been suggested that the additional cultivation of the desert lands by the system of artificial irri- gation introduced by the Mormons had brought about the change. This hypothesis is too absurd to require detailed refutation. The cycle of moisture which has recorded itself in the increased volume of Salt Lake is also evident in many other localities and in different ways. Mono and Owen’s lakes at the east base of the Sierras show a correspond- ing rise, and, as has been stated before, all the residual lakes in the basin of Lake Lahontan evince the same change. When it is remembered that the moisture-bearing wind, indeed the entire source of aerial moisture for the whole western Cordilleras, is the upper, constantly blowing west-to- east wind, it will be seen that no changes of cultivation of unimportant, isolated agricultural regions could possibly have brought about the general increase of humidity. This increase of the volume of the lakes 526 SYSTEMATIC GEOLOGY. has taken place in the presence of an enormous power of evaporation. Over a very large part of the Great Basin the average climate is so dry that there is a wide permanent difference between the observations of wet and dry bulb thermometers. During the period of maximum evaporation in midsummer and even in November I have recorded differences of 36°. Observations were made by my party with a series of evaporating-pans, which were observed in the shade and in the sun, and by means of a delicate micrometer screw actual hourly and daily evaporations were noted. A half inch a day was not an uncommon result in the dryest period of the year. It becomes a question of great interest to determine whether this recently observed climatic oscillation is within the range of frequent occur- rence, or whether it is a noteworthy departure from the climatic habit of the immediate past. Some light is thrown on this question in the alpine regions of the Sierra Nevada and the higher points of the desert ranges. The phenomena, however, are so much more clearly shown upon the Sierra summit, that I confine myself to that region in discussing this point. Below the line of perpetual snow is a variable, open region of about 1,000 feet in altitude, in which the tree-growth is rather sparse and com- prises only strictly alpine species. Below that point, from Alaska nearly to the Mexican line, is a continuous dense growth of coniferous forest. A very large number of observations on the average age of the timber growth at its upper limits shows a mean of about 250 years. Since the late cycle of increased moisture, the winter accumulation of snow on the Sierra summit is evidently greater than since the earliest growth of the present forest. The barren zone which I have mentioned, between the perpetual snow and the main timber growth, represents a region where the snows accumu- late too thickly for the propagation of the coniferous species, and may be said to express the downward limit of the encroachment of snow for 250 years. In the present climatic change the snow accumulation is greater, and extensive avalanches where the topographical configuration favors, have begun to pour down into the true forest belt and to sweep before their rush considerable areas of mature tree growth An avalanche starting in a high alpine gorge ploughs its way downward, not infrequently mowing down a half mile of adult trees. It is obvious that no such avalanches QUATERNARY. SPAT could possibly have occurred during the germination and growth of this forest. On the summit of the Central Pacific Railroad Pass are a considerable number of well grown coniferous trees. An examination of them during the construction of the Pacific Railroad showed that they were at that time being seriously damaged, and in some cases actually killed, by the drifting snow-crystals borne on the strong west winds during the winter storms, the notch or depression of the pass making a sort of funnel, through which the wind blew with unusual violence, concentrating its freight of sharp snow-crystals, which not only wore away some of the foliage of the trees, but actually cut off the bark from exposed positions and sawed into the wood for several inches. An inspection of the branches thus cut showed that the annual rings had formerly perfected themselves, and that the snow had worn off a considerable portion, often several inches, of the thickness of the wood, leaving a smooth polished surface, displaying the cut edges of the layers of annual growth. From these facts it would appear that the existing climatic oscillation began before the year 1870, and was the first of its kind for over 250 years. The year 1866 is about the date of the increase of Salt Lake. Mono Lake shows a rise in 1864, and the destruc- tive Sierra avalanches began about 1860. Although unimportant in its general results, this oscillation becomes a matter of very great interest from a theoretical point of view. The mechanical and chemical facts which have been observed in the Quaternary phenomena of the Fortieth Parallel show that post-Pliocene time has been marked by a very long period of very great humidity, fol- lowed by a period of intense dryness, which gave way to a second but briefer epoch of humidity, which was rapidly succeeded by the present age of drought. In comparing these climatic phenomena with what we can tell of the Pliocene, the Quaternary appears to have been a much more varied age. In the deposits of the Pliocene there are certain alkaline beds which I have noted, and which seem to me to mark periods of desiccation; but in all the mountain phenomena and in the sediments there are no appearances which could suggest the presence of a considerable glaciation. 528 SYSTEMATIC GEOLOGY. We know from the fauna and flora of the Pliocene that it was a warm age, permitting palms and crocodiles to extend as far north as the British line. The interior of the continent had at least two enormous fresh-water lakes, one covering the area between the meridian of the Wahsatch and that of the Sierra Nevada, the other the province of the Great Plains. To maiutain these great interior lakes it must therefore have been an age of very great humidity. During the Quaternary age most modern mountain topography received its present form. Most, if not all, of the sharp cafions were carved, and the mechanical results of that erosion are seen in the great accu- mulations of subaerial gravel in regions of interior drainage like the Great Basin, and in deposits of unknown thickness classed as Lower Quaternary, which gathered on the beds of the Quaternary lakes. The long carbonate- lake period which followed the first great flood-age of the Quaternary was an age of desiccation even greater than the present, as is proved by the occur- rence of thinolite on the deep bed of Pyramid Lake. In other words, the lakes of that period were practically completely dried. During the long continuance of that earlier drought a very large amount of the Fortieth Parallel area must have been even more devoid of desert vege- tation than at present, and the dry west wind must then have drifted an enor- mous amount of fine sands from west to east. Even now this process is seen in operation at various points in the Cordilleras, where trains of dunes are gradually moving eastward. This is especially observable in the region of the Colorado desert in southern California, where the prevalent west wind sweeps the desert floors clean of their fine loose material and banks zolian sands high up on the west faces of the mountain ranges. If Richthofen’s theory of the olian origin of Loess be finally accepted, the dust deposit which is now the Loess of the Mississippi Basin might readily, as Pum- pelly has shown, have blown from the desiccated regions of the western Cordilleras during the great drought which immediately followed the first great flood or glacial period. Contemporaneous geological action on the area of the Fortieth Par- allel is confined to the slow and extremely limited transportation of mate- rial by the rivers, the feeble xolian transportation, the slow accumulation | ; Nab KeSCarsi a H Total. | = 1.63, 1.97 0.73 100.00 98.12 | fall. 82| 8.57 . + | 100.00 SOs | n30)5} || 0.24 99-06 | + free CO? | 0-99 2-81} 28.93 + « | 100.00 Na | 0.04 99-87 | Na /0-13 99-96 | | 100.00 100.00 eh é S|CaCjMgC|Mg ¢ ) & | B | ‘otal. £281) .o157 3-2365 | TABLE OF CHEMICAL ANALYSES, V.-UNITED STATES GEOLOGICAL EXPLORATION OF DESICCATION-PRODUCTS OF LAKE LAHONTAN. Efflorescences and Lake Salts. THE FORTIETH PARALLEL. NaCl |NaG|Na C+C s a8 : ae oe S| eae i eee 2 | os 25 Locality. Analyst. Bs Fe|/ Ca | Ca|Mg|Mg| Na] Na | KR | Lil] cl © | Sy By Py sey ae < Be Total z* me ee) | eee cee Ji ehe |e. | 45 | Maag’s Station, Truckee Desert -|O.D. Allen - - / | 95-67 wad i | : | 46 } Hardin City- = = - - = - - ws | . || . (eat es eee oa Go }ho9 of |erallis | ao! j - | 18.47 | | i H | | 47 | Sink of Quinn’s River- - - - - Ws | | H 85.27 48 | Buffalo Station - - - - - - - cD per ikealfeie ||sacis | 36:25) mifor87| tr. 42.97) . - 3 6 Gade | tie, 70.81 49 | Gay-Lussite, Soda Lake, Ragtown iS ~ =} =| tg-r9}- -}- -|- =| 79:95] = |. aI). .| tr. 29-55| tr 31-05 | 0.20 99-94 | | 50 | Trona, Soda Lake, Ragtown - - © a 1b | 3 oll So ullu alto 4ilo= oll MGH7GI 0 0.46 37-88) 0.35 20.07 | 0.30 99-83 51 | Salt from Soda Lake, Ragtown - - c agra Wee ieee econ tees . | 40-53 eee |- - | 0:98 36-74] 0-75 | tr. | tr |- -| 19.93] 0.80] 0.22 g9-5r] - 40-57 | 0.97 36-87) o71 | tr. | tr 19-87 | 0.80 | 0.22 99:57] - 52 | Salt from small Soda Lake, Ragtown se me 6 cd eoedle ala. (|s cet ee. tre doe Kee od Pe Raa ine, |) ile, ‘ | I-10 } | 53 | Deposit from Soda Lake, Ragtown | R.W. Woodward | 78.50. .| . .|. . | 2 |e isieg4| oom |. - | 0-20) 10-39) |) 46) Norge eaeo 99:87 0-43 | i | } 1 FESS o allo ollo o | Bolla of yegis| Cogn || > qamiemeel| Certs) | Mets | efOon§|) eum) |ic a |lo | Sp | 99:96 | 0-47 | 54 | Brown’s Station, Humboldt Lake - ff KeBeeS ol) 5 oije allo allo ollattelinopccl) tn, || o Aelia eters 2.48 6.50 11.76 | 6.78) . E S 100.00 49-67 5 : BUEN }0- 0-0. olla 0 | + f+ =| 22.88) ro.5n) tr} .|. - | 30-02 2.48 6.50 11.73 | 6.78) . z + 100.00 49-63 | | | | 55 | Salt, incrusting decomposed Rhyo- rs 4-50/- .| Chiefly Na Cl on surface of specimen). . |: 2 1 lite, Red Hills, West Humboldt. | Ser 2 mee - poses Z pee sol I A be NR Ue Phimolite (Pseudo-Gay-Lussite). eae mee —— — # Pee Sea ee Z °c sd | Analyst & | Ai | we | Ca | Mg | Na ee) | ataent, | Soe ae Woes ies a i g “|| gravity. 22] } 4 renee 2 a ee | faces at ele Be ie a IY | 7 ad | i) Po® a 2 56 | Tufa Dome, Pyramid Lake - - - | R. W. Woodward} 7.27*| 2.14 | tr. |) so3 try) 200s 8-23 90H 8 2-4 POs | | Ggo*} 2-54 || tr. | AGS \ {is ote) | 6 52) 99:81 A . RO# | . 57 | Twelve miles north of Ragtown, BAR| OH { so ft | ++ 44-35 | 100.01 |2-5, 2.5, 2-5 | Carson Desert. Pos 2.19* | 0.82 | { SO3 \ tr. 41-43 | 100.30 oe 6 my | BO® j GEG 58 | Near Wadsworth = - - - - - a 3:01* | 0.89 Shvisos iis Hote pee [oo 2.46, 2.41 z i Pos aH | | 3-10* | 0.86 : | Ree \ tr. 1.40 oe nO || 5 | z = = =: CaaS silicic acid rl cram, Waters. } | a | | Ae Locality. Analyst. Si | Ca | Mg | Na Ce Stienel 5 2 z | i eh : | Free. Le | EMER -02392 59 | Pyramid Wake. = == 25S =» =O: yAlicneeeees erin ee +1292) 4234] -8999) t D: 2) und, || 1.3870}. 5 UN yo Sees | Smo ip co ee |e I 60 | Sodaakes ey) “a +2050) - /.0230| . - |42.838 ; tr. eee” 39-394) 0978 +430. ; : — + 2 . . u . Al ny P Gr } Humboldt Lake - - --- - - , yr : sige +0274) to70 | 2952 0. | | 52-10) 26.08 | | 66.27 | dj 98-49 0-91 98-51 0.85 } 18.15 | 20.88 | 18.15 | 20.84} | | Fi : ce ; ey P . nm > ; 3 7 ft ai a a: ‘| i 5 ~ : ar ; : 1 o ; 2 a 7 i} iz yy ; 1 rt) y r a : 4 t , , i . < : & 3 rm : £ it 7 1 i = i MN ao TAK ES) Os me anf ES S RAS ae aoe 40° : fin (\ 1) fAN Poros 17 “e ly as at } 30° fateeemes { A re heh iS : 39° & >) eg nen oN 50 - | = 4 4 al < MONG VAY if is ~ a z | 38° E | La | | ms Pa ' A a th ba . ° 7 30° ue? 30 us" 30° 20 6! et ee eT te ii et Oe pom fA nee) ce ee ay ee a oS ee een ee ee = ee — STALL 1 13 IRC WO) 1D) eae Be LR U0 FALL ny QUATERNARY. 529 of calcareous precipitates and river sediment in the beds of the present shrunken lakes, the disintegration of mountain tops and formation of angular, high-mountain débris, and the few rare instances of true oro- graphical action, in which the solid rock foundations of the country are absolutely faulted, the most conspicuous example of the latter being the great fault described by Prof. J. D. Whitney* in his account of the Owen’s Valley earthquake of 1872. * Overland Monthly for August and September, 1872. 34K ae Te a Sen ra a : CHAPTER VI. RESUME OF STRATIGRAPHICAL GEOLOGY. It is the purpose of this chapter to present in the briefest possible manner the leading outlines of stratigraphical geology in the area of the Fortieth Parallel. In the foregoing chapters I have given the reader a summary of such facts as seemed to be necessary to a general compre- hension of the sequences and subdivisions of the sedimentary geology. It seems appropriate that the enormous developments of strata which have there been described should be succinctly shown in their broader geograph- ical and historic relations. In the 120,000 feet of sedimentary accumulations the grander divis- ions of Archean or Azoic, Paleozoic, Mesozoic, and Cenozoic are dis- tinctly outlined by divisional periods of marked unconformity. Considered as a whole, there is a noteworthy fullness in the geological column. None of the important stratigraphical time-divisions are wanting except those obscure intermediate deposits which in other countries lie between the base of the Cambrian and the summit of the crystalline Archean series. From the first of Cambrian age to the present every important interval of time is recorded in the abundant gathering of sediments, which are with singular fullness characterized by appropriate and typical life-forms As in all other geological fields, the most important interruption of the continuity of deposit was at the close of the Archzean age, and the most striking difference between any two successive groups of rocks is that which characterizes the relations of the Archean and the Paleozoic. With 581 5 5 2 SYSTEMATIC GEOLOGY. the exception of a few slates of supposed Huronian age, which the micro- scope shows to be richly charged with crystallites, all the non-eruptive Archean rocks have passed from the original condition of detrital beds into sheets or bodies of distinctly crystallized material. Not only are the Archzan exposures of such frequency over the For- tieth Parallel area as to insure a moderately complete knowledge of strati- graphical sequence and materials of the period, but also, owing to the rela- tions which have been described with the overlying Paleozoic, I am able to reconstruct with considerable accuracy the topographical configuration of the Archzean surface. Supposing all the post-Archzan rocks to be removed, and considering what we now know of the whole area at the close of the Archean age, the first prominent fact is, that coextensive with the greater part of the Cordilleras—that is, from longitude 104° westward as far as the Archean exposures extend—was a great Archean mountain system built up of at least two sets of nonconformable strata, referred to Lauren- tian and Huronian; the lower and older composed of granitoid gneisses chiefly made up of quartz and orthoclase, but carrying a little mica, sparing triclinic feldspars, and chlorite pseudomorphous after garnet and mica. Over these, whether with actual conformity or not is undetermined, lies an enormous series of mica gneisses rich in quartz and biotite, orthoclase ordinarily exceeding plagioclase. The earlier aplitic gneisses and the later mica gneisses expose about 25,000 feet each of conformable beds. A third group, nonconformable with the earliest aplitic series, the rela- tions with the intermediate mica-gneiss series being unknown, consists of mica and hornblende schists passing upward into slates, quartzites, lime- stones, and dolomites. In the mica schists biotite predominates, and is usually associated with an excess of orthoclase over plagioclase. When muscovite replaces biotite it is frequently accompanied by garnet. The hornblendic schists are gen- erally characterized by the presence of zircon, and, as a rule, carry plagioclase in excess of orthoclase. Interstratified with the quartzites are beds of smooth, rounded conglomerates, sheets of dioritic (horn- blende-plagioclase) schists, and in one or two instances hydromica (para- gonite) rocks associated with kyanite and staurolitie schists. The lime- STRATIGRAPHICAL RESUME. 533 stones, prominently dolomitic, are usually intercalated with mica gneisses, or overlie the oldest quartzites. The mica gneisses, which form the lowest part of the third group, so closely resemble the highest mica gneisses of the second group, that, although they are never exposed in conjunction, it is supposed that they are one and the same series, and that groups No. 2 and No. 3 are conformable, making, therefore, but two conformable series, the lower granitoid beds and the upper composite group, as described. The geographical range of the lower series is confined to the country between the 104th meridian and the Wahsatch. The upper series appears to extend over nearly the whole Fortieth Parallel area. West of the Wahsatch the folded, crumpled, dislocated masses of these sedimentary Archean groups are invaded by plastic, structureless granites of four litho- logical types, for whose petrological characteristics the reader is referred to the second section of Chapter II. and to Volume VI. Upon grounds set forth in Section IV. of Chapter I. it is clear that the general topography prior to the deposition of the earliest Cambrian rocks was that of a great mountain system, displaying lofty ranges made of crumpled strata, enormous precipices, a result of mechanical dislocation, and, finally, a type of high mountain sculpture of such broad, smooth forms as to warrant the belief that subaerial erosion had never earved and furrowed the mountain flanks with the sharp ravines characteristic of modern mountain topography. East of the Rocky Mountains, in the geological province of the Great Plains, there are no Archzan outcrops; and when we consider the comparative thinness of the later sedimentary beds superposed over that region, the absence of outcropping Archean masses piercing through the later sedi- ments is excellent proof that over that area Archean mountain ranges did not exist. This is important as defining the Archean Cordilleras within the limits of the modern Cordilleras, or, as is a more strictly correct view, the ancient Archean Cordilleras have determined not only the general area but much of the local detailed structure cf the modern Cordilleras. The topographical features of the present terrestrial surface are far less grand than the Archean orography. The great Archwan precipices brought to light in Uinta and Wahsatch ranges are absolutely unpar- uleled in the topography of to-day. That prior to Cambrian time this 534 SYSTEMATIC GEOLOGY. mountain system was a land area, is clear from the absence of interpolated sets of strata between the finished crystalline mountains and the uncon- formable Cambrian sediments. In the modern dislocations and disturb- ances which have enabled us to gain these profound views of the Archzean mountain systems, there is one interesting topographical element which we fail to reach. Never arriving at the bottom of the Cambrian sediments, we are at a loss to know the physical characteristics of the valley bottoms which lay between the Archzean ranges. Whether they contained relics of a land detritus, or whether they were washed smooth by the subaerial drainage of the period, we do not know. There is always a complete, sharp, unmistakable nonconformity between the crystalline Archzean topography and the superjacent sediments. Considered as a whole, the Paleeozoic series constituted a conformable body, laid down over the rugged Archean mountain system. It first ap- pears in the region of the Rocky Mountains with a total thickness of about a thousand feet, the strata surrounding and abutting against permanent Archzean islands, which, during the whole Paleozoic and Mesozoic, were lifted above the level of deposition. Throughout all Paleeozoic time only 1,000 feet of strata accumulated over our part of the Rocky Mountains, and we get no glimpses of deeper hollows in which lower Cambrian beds might have been deposited. Passing westward, the series gradually thick- ens to 32,000 feet in the region of the Wahsatch and about 40,000 feet at the extreme western Paleozoic limit, longitude 117° 30’, where, from the evidences of shore-phenomena, and the non-continuation of the beds west- ward, we are warranted in assuming the Paleozoic coast. Superposed in unconformable succession over the gigantic crystalline mountain ranges, some of the tips of the highest peaks still rose above the level of the (inter se) strictly conformable Palzzoie series. At the close of the Paleozoic, the uppermost sheet of Carboniferous material, extending from the Nevada Palseozoic shore eastward through the whole Fortieth Par- allel area, was only interrupted by a few island-like granite peaks which were above the level of deposition ; the great mass of the Archzean topography by that time having been completely buried. Of the character of the Archean STRATIGRAPHICAL RESUME. 535 land which still, at the close of the Palxozoic, formed the westward barrier to the ocean and the source the main detrital material, we know very little. The Carboniferous strata which are found west of the old shore-line in California and Oregon seem to me rather to indicate shallow bays and gulfs, which permitted the westward extension of the upper Paleozoic strata, while the great bulk of the series was stopped by a bold coast. Starting with a land area of Archean ranges, and passing on through the Paleozoic period until the whole Archean topography is buried in the deposits of a profound ocean, it is evident that the area has been one of very great subsidence. From its original altitude above sea-level it has been depressed to the ocean plane, and then downward until even the ocean-bed deposits have overwhelmed all but its highest peaks. Viewed regardless of the age of the individual beds, the Paleozoic series can be divided by the character of their materials into four great groups. The first is a purely detrital Cambrian, which, although of com- paratively fine sediments, in the presence of occasional conglomerates gives evidence of repeated subsidence. The second group is the great limestone series, beginning with the Pogonip Cambrian limestone, and extending upward to the top of the Lower Coal Measures for 11,000 feet, only interrupted, in the horizon of the lower Devonian, by a sheet, from 1,000 to 2,000 feet thick, of fine quartzitic detritus. 'This enormous group of 11,000 feet of limestone, char- acterized by abundant pelagic faune ranging from the Primordial to the top of the Lower Coal Measures, represents in general an age of deep seas. Toward the Nevada Paleozoic shore, however, in all the beds of the Lower Coal Measure limestones, argillaceous and_ siliceous impurities charac- terize the western exposures, and these are marked by a single hori- zon of carbonaceous beds associated with land plants. As it is under- laid by limestone and immediately overlaid by limestone, both deep-sea deposits, it is evident that this episode of dry land was a moment of true elevation. At the close of the deep-sea lime-period came a third great stratigraph- ical division of the Palzeozoic—Weber quartzite—a body of pure siliceous detritus from 6,000 to 10,000 feet in thickness, characterized by conglom- 536 SYSTEMATIC GEOLOGY. erates both in the near neighborhood of the granitic islands and close to the Nevada shore. This is immediately succeeded by the fourth group or Upper Coal Measure limestone, a body about 2,000 feet thick of strictly pelagic material. The whole Paleozoic, therefore, may be summed up as to its material as two periods of mechanical detritus, interrupted by one and followed by another period of deep-sea lime-formation. While in the conglomerates which appear in all the siliceous members of the series we have evidence of episodes of shallow waters, yet the occurrence of 13,000 feet of limestone indicates enormous intervals of the continued sway of profound ocean. When compared with the corresponding series, as displayed in the Appalachian system, it differs, first, by the absence, as it thus far appears, of those not infrequent orographical disturbances which render the Appa- lachian Paleozoic groups repeatedly unconformable among themselves; secondly, while land areas were common from the close of the Devonian in the east, and the materials fail to show any great continuance of ocean sway in the region of the Appalachians, in the Cordilleras there is evidence of but a single temporary land episode, and that most restricted in its area. Taken as a whole, the Palzeozoie was distinctly an age of ocean sway. Accompanying this chapter are two tables, Nos. VI. and VIL, in which are given analyses of the members of all the sedimentary series whose con- stitution seems to afford a chemical interest. The tables are divided into, first, the deep-sea and lacustrine limestones and the composite calcareous Tertiary and Cretaceous rocks; secondly, siliceous and pure detrital rocks, the sandstones, quartzites, &c. It is not intended in this chapter particularly to discuss the character or causes of those mechanical movements in the solid earth which succes- sively elevated and depressed various portions of the Cordilleran area; but it is impossible adequately to conceive of the stratigraphical grouping without a passing mention of those mechanical events. After the close of this great conformable Paleozoic deposition, wide-spread mechanical dis- turbance occurred, by which the land area west of the Nevada Paleozoic shore became depressed, while all the thickest part of the Paleozoic de- posits from the Nevada shore eastward to and including-the Wahsatch, STRATIGRAPHICAL RESUME. Se7/ rose above the ocean and became a land area. Between the new continent and the old one which went down to the west, there was a complete change of condition. The land became ocean; the ocean became land. In the rising of the Paleozoic, however, the elevation proceeded no farther east- ward than the Wahsatch. East of that point, the Upper Carboniferous beds were still the undisturbed ocean-bottom; but instead of receiving sediments either from the destruction of organic life within the ocean area or from the distant continental sources to the west, the newly elevated land-mass, extending from the Wahsatch west to 117° 30’, became the area from which was derived the post-Carboniferous detritus to form the great Mesozoic series that, east of the Wahsatch, were laid down conformably upon the still submerged and still undisturbed Carboniferous. Upon the western side of the new land-mass, the Archean continent, having gone down, made a new ocean-bottom, and upon this immediately began to accumulate all the disintegration-products of the new land-mass which the westward draining rivers and the ocean waves were able to deliver. Throughout the Triassic and Jurassic periods the western ocean was accu- mulating its enormously thick group of conformable sediments upon an Archean floor, while east of the Wahsatch, in the mediterranean ocean, the sediments of the Trias and Jura were accumulating conformably upon the Carboniferous; until, at the close of the Jurassic age, there had accumu- lated in the western sea 20,000 feet, and in the mediterranean sea 3,800 feet, of Triassic and Jurassic material. The comparison of the Trias-Jura series, in these two separated seas, shows two things: first, that the western sea was very deep during the Trias; secondly, that the mediterranean was shallow during the Trias. In both cases the first half of the Trias was prominently a period of the recep- tion of pure detritus, while the second half, especially in the western ocean, was characterized by the liberal intercalation of lime. The Jura, especially in the east, was an age of shallows, and its materials were almost altogether of clays and shales and shaly limestones. At the west, the lower members, as at the east, were prominently calcareous; but later, and closing the series, is an unknown thickness, certainly over 4,000 feet, of fine argillites. At the close of the Jurassic age the western ocean, with its original 538 SYSTEMATIC GEOLOGY. floor of Archean ranges overlaid by twenty-odd thousand feet of conform- able Trias-Jura sediments, suffered abrupt orographical uplift, resulting in the formation of a series of sharp folds and elevating a portion of the ocean area, extending from the eastern shore outward and westward as far as the present west base of the Sierra Nevada, making an addition to the conti- nent of 200 miles, the Sierra itself constituting the most western and most elevated of the newly formed mountain ranges. The character of the orography of this period of disturbance is that of tangential compression, in which the gentler action was close to the old shore in the meridian of 117° and most powerful in the crumpled western slope of the Sierra Nevada, where the Triassic and Jurassic series have their enormous thickness crushed into a mass of almost indistinguishable folds, the rocks thrown into vertical dip and crowded together, making a belt of strata about fifty miles broad. This orographical action continued southward as far as the defined range of the Sierra Nevada extends, and northward along the whole shore of the Pacific, probably as far as the Alaskan peninsula. Passing north- ward from the region of the Fortieth Parallel, where the new addition to the continent measured about 200 miles from east to west, the zone of crumpled Mesozoic was depressed so that the new ocean shore at the begin- ning of the Cretaceous age touched the west base of the Jurassic fold of the Blue Mountains of eastern Oregon. While this powerful dynamic action was taking place on the west side of the land area, there still remained, so far as upheaval, subsidence, or folding is concerned, a complete calm in the region east of the Wahsatch. The uppermost shaly members of the Jurassic from the Wahsatch out to Kansas are immediately conformably overlaid by the basal members of the Cretaceous. The revolution which produced this great change in the configuration of the country, although not recording itself over the area of the mediter- ranean ocean in any disturbance or nonconformity, was, however, sig- nalized by a complete change in the character of the sedimentary material. The phenomena of the Cretaceous west of the boundary of California did not fall within the study of this Exploration, and have already been de- scribed by Professor Whitney in the Geology of California. Since the close STRATIGRAPHICAL RESUME. 539 of the Jura no marine sediments have been laid down between the west base of the Sierra Nevada and the Wahsatch. During Cretaceous time the mediterranean ocean stretched from the eastern base of the Wahsatch into Kansas; and over the entire bottom of that body of water, with the exception of a few Archzean islands, which were still, as they had been throughout the previous ages since the begin- ning of the Cambrian, lifted above the plane of deposition, a continuous conformable sheet of Cretaceous sediments was laid down. Its greatest thickness was against the western shore of the ocean, namely, against the eastern base of the Wahsatch, where conformably over the top of the Ju- rassic shales are about 12,000 feet of Cretaceous beds. Passing east- ward, this series in the province of the Great Plains near the eastern base of the Rocky Mountain system has thinned to 4,500 or 5,000 feet, and in western Kansas it reaches its thinnest development as described by the Geological Survey of that State. The materials of the underlying Jura are all of excessively fine grain. Conglomerates are absent except on the immediate foot-hills of the Wah- satch. ‘The fine summit shale-members of the Jura were immediately suc- ceeded by a coarse siliceous conglomerate which stretches in an uninter- rupted sheet from the base of the Wahsatch nearly to the easternmost exposures of the Cretaceous beds. The pebbles immediately bordering the Wahsatch are, in some instances, a foot in diameter. Farther east they gradually thin down to the size of a filbert, and in the region of Kansas are no longer to be seen. In the extreme western Cretaceous exposures in the territory of Wah- satch and Uinta ranges, coal-beds appear at the very base of the series im- mediately upon the capping members of the Jura; and from that horizon to the summit of the series, throughout the whole 12,000 feet, they recur in that region. They increase in frequency after the close of the Fox Hill group, and are most abundant through the 4,000 or 5,000 feet of the closing or Laramie group of the series. The deduction from these fre- quent coal-beds is clearly that of land areas and of repeated subsidence throughout the whole Cretaceous age over the western part of the Cre- taceous area. 540 ‘ SYSTEMATIC GEOLOGY. In the region of the Great Plains, coal-beds are unknown below the summit of the Fox Hill. Beneath that horizon there is no evidence of a land surface in the eastern part of the Cretaceous field. The series, there- fore, below the top of the Fox Hill was purely an ocean deposit in the region of the Rocky Mountains, but in the region of the Wahsatch was frequently above the limit of the marine waters, carrying upon its surface abundant vegetation. Throughout the whole Cretaceous, below the top of the Fox Hill, the molluscan fossils are invariably marine, with the exception of certain inter- calated groups of purely fresh-water shells near the region of the Wah- satch, which, from their position close to the Cretaceous ocean shore, are evidently the in-washings of a fluviatile fauna. Regarded as a whole, the basal member is a single sheet of siliceous sediments and rounded conglomerates from 300 to 500 feet thick. Over this lies the great Colorado group, 2,000 feet thick in the west, 1,000 feet thick in the region of the Great Plains, made up chiefly of fine caleareous and argillaceous material, which toward the middle of the group is promi- nently formed of marls or limestones. Above the horizon of the Colorado group the Fox Hill and Laramie are essentially of sandstones, about 9,000 feet in thickness in the region of the Wahsatch, about 3,000 feet in the region of the Great Plains. At the very summit of the uppermost or Laramie group are found Dinosaurs. The fauna up to the base of the Laramie is strictly marine. The Laramie itself carries the remains of an estuarial or brackish-water life, associated with strictly Mesozoic Saurians. With the close of the Cretaceous the con- formable series of marine and estuarial deposits east of the Wahsatch come to an end, and the last moments of deposition were immediately followed by one of the most important orographical movements of the whole Cor- dilleran history. From the eastern base of the Rocky Mountains to the eastern base of the Wahsatch the whole region was thrown either into wide undulations or sharp folds. So great a range as the Uinta, with its distinct, broad, flat anticlinal, was made at this period. Relatively to the present basin of the Colorado, the whole chain of the Rocky Mountains was elevated so as to STRATIGRAPHICAL RESUME. 541 define a broad, shallow depression, which now includes the waters of Colo- rado River. Powerful and important as this orographical movement was, it failed to disturb the coast deposits of the Pacific in California; but from reasons already given it seems probable that the first definition of Cascade Range was caused by its force. In the general geology of North America the most important result of this immediately post-Cretaceous orographical movement was the elevation of the whole interior of the continent and the complete extinction of the inter-American mediterranean ocean. From the date of this movement no marine waters have ever invaded the middle Cordilleras, and the subsequent strata are all of lacustrine origin. The effect of this orographical movement was to leave that part of the Cordilleras which falls within our study with a free drainage to the sea, with the single exception of the basin of Colorado River, which, from its configuration, immediately became the receptacle of the vast fresh-water Ute Lake, within whose area accumulated the important Vermilion Creek group, the earliest of the fresh-water Eocene strata. Throughout the entire Eocene period the basin of Colorado River was the theatre of a series of four Eocene lakes, whose deposits—unconformable among themselves, as has already been described—amount in all to 10,000 feet; lacustrine rocks characterized from the bottom to the top by an abundant series of verte- brate life covering the whole lapse of Eocene time. The Eocene of the Fortieth Parallel region was a period of four lakes superposed, the uncon- formity of their deposits due to four orographical disturbances. An important orographical movement took place at the close of the Eocene, by which the province of the northern Great Plains and a long, narrow tract of Washington Territory, Oregon, Nevada, and California, lying on the eastern base of the Sierra Nevada and the present Cascade Range, became depressed and received the drainage of the surrounding countries, forming two extended Miocene lakes. The deposits of the west- ernmost lake are chiefly the tuffs and rearranged ejecta of volcanic eruption. The deposits of the Plains are the simple detritus from the surrounding lands. The series on the west are over 4,000 feet thick; in the east they are not proved to be over 300 or 400 feet. Both contain abundant and typical Miocene vertebrate life. p42 SYSTEMATIC GEOLOGY. The close of the Miocene was signalized by a powerful orographical movement over the area of the western Miocene lake, which threw the beds accumulated on its bottom into folds. Contemporaneously with this movement the Miocene lake of the east, by the subsidence of the surrounding country, increased so as to cover the whole province of the Great Plains. The Pliocene opened, therefore, with two enormous lakes, one covering the basin country of Utah, Nevada, Idaho, and eastern Oregon; the other occupying the province of the Plains. The Pliocene deposits of the Plains lake are caleareous and sandy beds, which have no angular nonconformity with the underlying sheet of Miocene sediment, but which overlap it in every direction. The deposits of the great western lake are nonconformable with the Miocene and immensely overlap it to the east, doubling the area of Miocene sediment. Both of these Pliocene lakes—as do the Miocene— contain the remains of rich faunz. The eastern lake received a maximum of about 2,000 feet of strata; the western lake has nowhere shown over 1,400 feet. The close of the Pliocene was signalized by another orographical move- ment, which threw the sediments of the Great Plains lake into their inclined attitude, dipping 4,000 feet to the east and 7,000 feet to the south from the Fortieth Parallel region. This same orographical movement acted differ- ently upon the sheet of sediments which covered the Pliocene lake of the Great Basin. Instead of tilting the entire lake, it broke in the middle, and the two sides were depressed from 1,000 to 2,000 feet thick, the shores faulting downward. The result of the post-Pliocene movement in the department of the Plains was to give thereafter a free drainage to the sea. The result in the area of the Great Basin was to leave two deep depressions, one at the western base of the Wahsatch, one at the base of the Sierra Nevada, which, in Quaternary times, received the abundant waters of the Glacial period and formed the two lakes that have already been described in the Quaternary chapter. In summing up the general stratigraphical results of the section, it will be seen by referring to the tabular statement at the end of this chapter that there is exposed, from the bottom of the Cambrian to the close oaRA *stsd[vur jo raquiny | (3) Ks) ne) So) 64 7° fi TABLE OF CHEMICAL ANALYSES. VI—AW—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. SEDIMENTARY ROCKS. Limestomes. é Ca, Mg, and € Locality. Formation. Analyst. 4 At Fe Ca Mg (e H Total. combined. I ae a 4 Ca C|Mg€ : = —_ + — ; 62 | Conglomerate ridge, east of Bear | Pliocene- - | Wyoming conglomerate] B. E. Brewster - | 12.30 0.78 47-01| 0.49 | 37-08] 2.41 Dro! oto 100.07 | 83.05] 1.03 | River. : Es : 6 ims 63 | Garden Valley Tertiary - - - - ce - -| Humboldt - - - - = - | 12.07] 1.28 | 0.57 | 45.29] 1.86 | 36.23] 2.65 | Na} 2-90 100.85 K 12.11] 1.50] 0.44 | 45.30] 1-83 | 36.23] 2.67 | Na fost Too:93 || « = 6 | —~_—=. - . 64 | Chalk Bluffs- - - - - - - -| Miocene- - | White River - - -|R.W. Woodward] 1.49] . %| 0.37 | 54-16] 0.15 43.68 Mn o.15 100.00 ea - I-62) sue | 0-31 | 54.18] 0.15 43-69 Mn 0.15 160.00 _—_— 6s | Upper stratum, Valley Wells - - «_ - -| Truckee- - - - -|B.E. Brewster - | 32:02 0:43 35-82] 0.36 | 29.16] 2.10 Chin os 6 99:99 | ae 66! Reed’s Hill, near Carson River, east @ - - Gs Seo 5 S 5 Us - G6 0.10 53:99| 1-25 | 43:80] 0.86 Gm oh. 100.00 end of Triangular Range. { | ij 67 | Fossil Hill, Hot Spring Mountains w - - G Se oo 6 Gi - | 7-38} 0:80}| 0.68 | 48.53] 2.46 | 40.86] . . PO® 0.16 100.86 | j ‘ ‘ 68 | Bridger Beds, Henry’s Fork- - - | Eocene - -| Bridger - - - - - as - | 31-28] 1-83)! 0.22 | 34.20] o.11 | 26.79] 4.64 |K 0.33 Nao.18] 99-58 31-45 75a) 0.21 | 34.18] 0.08 | 26.82] 4.64 |Ko.33 Nao.28| 99.56 i : Go| Green River shales -- - - - - « - -| Green River - = - Gi - | 29.22 0.76, 2.16 | 33-53] 0.56 | 27.08) 6.27 {Na } 038 99:96 | im 29-19} 0:87)| 2.20 | 33.57| 0.68 | 27.03] 6.20 {Xa fo38 10012] - | 7° | Brush Creek, spheerolitic sandstone | Cretaceous - | Colorado - - - - a - | 2/).5 8) eared | Deca Sete + + | 43-90 | 71 | Dry Creek, blueshale - - - - « 2 « ea ners « Sieo o|| o 7 Aeon of ao ofl oo Oso 9 ao | Gs) —_S-_—_. 72 | WotR sos > 5 = 6 sll inegiiec slo - 2 os so oo “ =| Gsar Q.92 50-57| 0.36 | 40.18] 1.50 Gao. o- 4 100.08 | gt.11] 0.75 eet K 73 | Laramie Plains- - - - - - - Ge ies ko oa Sa eS « =| 2.77 0:79 29-90] 19.31 | 45.05] 1-35 {Na }o38 99:55 | 53:40) 40-55 2.95 O54 29-69 | 19.36 | 45-14] 1.30 {Na } 028 99-42 | 53:02] 40-66 3 (*) ; SiO, - - - - - = = = 23:4 Ah O; - - - - - - = = 5:40) CaO - - = = = = -eaamomts MgO - - - --- = - 0.06 6z.19 TABLE Number of analysis ~ ~ ~ n wm - Qi aa) a [SJ zhu TABLE OF CHEMICAL ANALYSES. VI—B.—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL SEDIMENTARY ROCKS Limestomes—(Continued.) s ., 8 Ca, Mg, and C 22 Locality. Formation. Analyst. 4 At | Fe | Ca | Mg H Total. pues Be e Ca€ |MgC | 74 | Divide between Cottonwood and | Triassic - - | Star[Upper] - - - | B. E. Brewster - 1.61 0.26 52-16] 2.47 | 43-70 PO trace. 100.20 Union Canons. | 75 | Ravine north of Wright’s Caion, fs - - ce So oS G S|} AH7 0.119 51-69] 1-04 | 41.75], 0.84 PO* trace. 100.00 West Humboldt Range. } 76 | Greenish limestone below Upper ws - -| Red beds [Lower]- - - | 13-46 1.63 36-78] 8.44 | 38.31] 2.04 Mn O 0.20 100.86 | 65.68] 17.72 Red, East Fork Du Chesne, Uinta Mountains. 7 | Rese 5 2 = 5 5 5 5 ere co ae SS s =| 222% 0.21 43-24] 0-15 | 33-94] 0-14 99:89 | 76.75] 9.32 78 | Summit of Tenabo- - - - - ~- | Carboniferous! Upper Coal Measures - Gs - | 20.99 1-09 39:76| 2.80 | 32.80] 1.06 Fe S? 1.16 99-66 | 67-54] 5.88 79 | Clover Peak Range - - - - - ss a3 a = cs -| 2.71 0-27 30:39 | 20-07 | 45-72] 1-71 100.27 | 53:75] 42-14 80 | Vermilion Gap Rocks, lower series fe “ Gs - as - || 2.02 0.54 54.06] 0.34 | 42.85] 0.41 F 100.25 | 96.54] 0.71 81 | Ridge west of Green River, between a £ g - fe - | 27-93 0-35 39:54| 0.28 | 31.69] 0.25 6 100.04 | 70-61} 0.60 Uinta quartzite and Canon sand- stone. 82 | Granite Canon, Black Hills - - - f § ce - | R. W. Woodward} 0.34 0.16 34-95 | 17-36 | 46.55) 0.23 100.11 83 | East slope of Black Hills - - - Gh Lower Coal Measures - | B. E. Brewster - \. A. bro 99:29 | 60.09) 39-20 84 | White Pine limestone - - - - - Lo a a3 - |O.D. Allen - -| 0.70 55:38| 0.25 | 43-70 100.03 0.70 55-32] 0:26] = = 85 | North of Maggie Creek Gap, Nevada a a ig - | B. E. Brewster - | 4.36 0.44 53:17 | 0.36 | 42.10 PO; trace. 100.43 86 | Humboldt Mountains- - - - - a fe us - G =| 1-35 0.36 54-51] 0.27 | 43-13] 0-11 PO® 0.35 100.08 | 97-34] 9-57 87 | East Humboldt Range - - - - (a @G G = c - | 37-037) I-51 }0-59 | 33-29| 0-75 | 25-57] 9-39 ie eet 99-43 | 56-25} 1-56 —_— 88 | Peoquop Range - - - - - - aw c “e - ce - | 34-919 0.38 34.33 | rer2 | 27.772 PO? trace. 99-76 | 60.32] 2.34 89 | City Creek limestone - - - - - te is « 2 ce = || yy 0.24 53:09] 1-20 | 42.88] 0.21 PO® trace. 100.00 | 94.45] 2.52 go | Fossil Hill, White Pine Mountains | Devonian -|- - - - - - - - « = 1-23 0.39 54-06] 0.71 | 43-29) 0-34 . 100.02 | 96.53 1.48 gi | Underlying limestone, Muddy Creek | Silurian - -|- - - - - - - - “« Ey | 6:1738 0.60 43-23] 2.18 | 36.20] 1.17 | PO® o.12 100.23 | 76.82) 4.58 1 2 3 1 4 SiO, - - 18.99 SHO; = = siesa Si O, - 13.45 AIO; = = 5:79 AN,O3; = = 2.45 Al; O73 ase FeO; - - 2.23 MgO - - o.12 1 CaO - - 4.43 Loss - - o8r | 16.57 MgO - - 3.90 ; 34:92 | » nas \\ Ni \ oe , =) _ a i} 7 —) \ 7 as = > 7 _ _ i) a3 Locality. Formation. Analyst. Si Es a g2 | Cache Valley - - - - - - -| Pliocene- - || Humboldt - - - - |B) E. Brewster - 04-44 93 | South slope, Uinta Mountains - - | Eocene - -]| Uinta - - - - = Gs - 94 Troyes Wee = = 5 > 5 = = “6 - -| Green River - - - “ “ 95 | Cathedral Bluffs, Wyoming - - - us oa « ieee “ : 96) Black Butte- - - - - - - -| Cretaceous - || Laramie- - - - = & = 97 | Ashley Creek, Uinta Mountains - Us =|] Wor Isis s S 5 ¢ & ‘J 98 | Saint Mary’s Peak, Wyoming - - a = ce Sos 6c “ z 99 | Camp Walbach- - - - - - - Gs =| Dakota: fcocctes rowel “ 2 1co | Red sandstone, Uinta Mountains - | Triassic - -]- - - - - - - = “ z ror | Divide between Cottonwood and ee ee ta ey onreaco 3 “ z Unionville Canons. 102) | (Coyote Canon = = = = = = = G3 slo = oe eo o oc “ es) 5 103 | Near Cottonwood Canon, West CS) abe a eo ch ee B - Humboldt Mountains. 104 | Cottonwood Canon, West Hum- ue oul eo ee eS 5 & = boldt Mountains. 105 | Weber Cation, below Narrows, Wah- PRS ce ol cy SS 55 Ss - satch Mountains. : 106 | Anthro’s Canon, Uinta Mountains - ce Baio oe ade ao; Sc “ = 107 | West Ridge, Battle Mountain - - | Carboniferous) Upper Coal Measures - va = + Insol.res.! 66. Cabin Quarry, Upper Weber - - « “« “ 2 “ Nee ee ala Top of Parley’s Peak, Wahsatch Mountains. “ “ Insol.res.* 60.75 Sol. Si 0.2T AT ae ee pf intra, a birth 1 i TABLE OF CHEMICAL ANALYSES. VI.—B—UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. SEDIMENTARY Quartzites, Samdstomes, and Associated @ccursemces—(Continued.) ROCKS. S a ay i ae Locality. Formation. Analyst. Si At Fe Fe Ca | Mg | Na K ¢ H Total. z* | 110 | Pilot Peak, Ombe Range, Nevada - Carboniferous| Weber Quartzite - B. E. Brewster - 94-93} und. | und. 0.17 95-10 111 | Big Cottonwood Cation, Wahsatch ce a is = cs 95-81) und. | und. und. 0.28 96.09 Mountains. | Irz | Weber Ganon = = = = = = Gs Us w - 82.99) fr. tr. und. | und. 5-47 88.46 113 | Point Carbon, East Forkof DuChesne es iw - se 97-63] und. | und tr. 0.58 98.21 114 | Agassiz Amphitheatre- - - - . g - is - 98.58] und. | und. 0.17 98.75 115 | Carico Peak, Nevada- - - - G | co as - - fe 97-59| und. | und. 0.18 9177 116 | Bear River, Geodetic Point- - - “e fe ig ce : 87.47 7-47] 0.26 0.20 | 1.30 | 2.53 0.56 99-79 87-42), - > T.09 | 2-73 0.45 “oats 117 | Ogden Canon, Wahsatch Mountains | Devonian Ogden - - a 4 we - 97-79) und. | tr. 0.15 97:94 118 | American Fork Cation, Wahsatch ut i > 8 2 = 89:75 2.38 92.13 Mountains. 11g | Three Lakes, Wahsatch Mountains | Cambrian oo (9. oc os a 59:96| und. | tr. tr. 3:16 . Irom-stome. — — 120 | Near Carbon, Wyoming - - - - | Cretaceous Colorado - SS = 9:74] 5:57| 1-93 | 38:67| 7:64 | 1.20 0.46 32:04 Mn O 2.38 99-63 Infusorial Karths. 121 | Little Truckee River, Nevada - - | Miocene - Truckee - - - - | R. W. Woodward 91-43] 2.89 0.66| 0.36 | 0.25 | 0.63 | 0.32 3:80 100.34 gi-51 2.95 0.63 0-39 0.20 0-59 0-23 3:79 100-59 122 | Fossil Hill - - - - - - - - Wi! a - - o 5 Ws 86.70) 4.09 | 1.26] 0.14 | 0.51 | 0.77 | O.4t 5:99 RO? und. 99:87 86.91] 4-00 1.22| 0.11 | 0.51 | 0.80] 0.36 5-89 PO® und. 99:80 123 | Fossil Hill - - - - - - - - Gs GO oe 5 - -|B.E. Brewster - 98.06 0.62 98.68 Greem Earth. Oo © 124 | Grizzly Buttes, Bridger Basin - - | Eocene - ee - -|R.W. Woodward 66.17} 14-95] 2.76] 1.95] 3.89 | 1.88] 2.84 | 3.77 2.61 O > trace. 100.82 (6) ; 66.42| 14-73] 2.82] 1.93] 3-89 | 1-97 | 2-97 | 3:65 2.57 O ¢ trace. 100.91 STRATIGRAPHICAL RESUME. 543 of the Tertiary, a total thickness of about 77,000 feet of beds. About 19,800 feet are limestone, while the rest is purely detrital. In the Cretaceous and Tertiary a considerable chemical proportion of the detrital beds is lime, but they are distinctly detrital formations, and the lime is the disintegration of already crystallized limestone. Embraced within the 19,800 feet of limestone are 1,500 feet of calcareous shales and shaly limestone of the Green River middle Eocene group. The great Pogonip Cambro-Silurian bed of 4,000 feet is prevailingly siliceous, and is characterized by a small, variable percentage of magnesia. The Wahsatch limestone, 7,000 feet thick, the greatest single calca- reous body in the series, is for the most part a normal limestone, mechani- cally impure at a variety of horizons by the inclusion of siliceous or argillaceous particles, and in the lower beds, especially in the region of the Waverly and parts of the Devonian horizons, chemically impure by the admixture of carbonate of magnesia. True dolomites in thin sheets are found in both the Pogonip and Wah- satch bodies, but neither chemical nor microscopic analysis discovers a considerable general distribution of magnesia in these two great series. The Upper Coal Measure limestone, 2,000 feet thick, is comparatively pure, its chief admixture being argillaceous and siliceous sediments. The series of intercalated limestone beds, amounting in all to about 5,000 feet in the Alpine Trias of western Nevada, is noticeable for the large amount of carbon which it contains, the comparatively small amount of magnesia, and the constant, but slight, proportion of quartzose and aluminous sand. Above the limit of the upper Trias, throughout the entire Cretaceous and Tertiary, the limestones are all fragmentary and are simply the pul- verized sands which are worn down from the neighboring limestone mount- ains. 544 TABLE OF STRATIGRAPHICAL GEOLOGY. QuareRrvany } Upper Quaternary .-.....---- | Gravels and loose subaerial detrital material. Lower Quaternary ....--..--. | Fine muds and silts. Man oc ONG Coarse structureless conglomerate. Niobrane { Gearee and fine friable sandstones, and siliceous limestones; Pai Goer a: eed eae horizontal where observed. Generally siliceous, fine-grained, friable beds; frequently vol- | Humboldt ....... § canic taffs ; undisturbed. : eae ¥ (a) en . . & 3 | North Pare eer and limestones, loosely agg'‘omerated; undis- ot 3 y pone { Truckee Seely, f ett! limestones, gravels, and volcanic (palagonite) tutfs; | Q] Terriary.....- \ Miocene . 2 S SS | white River. .... | Fine light-colored sandstones, with clays interstratified. (= Coarse and fine pinkish sandstones, gravel conglomerates, and Uinta. .-.-------- ; argillaceous beds. he = : Bridger .....-..-. f Drab thin-bedded sandstones, and green marls, rich in verte- Eocene .. brate remains; slight development of limestones. Thin calcareous shales, with fishes and insects; buff calcareous Green River ..... j sandstones, and lignite toward the baso. ie _ §Coarso pink and chocolate-colored sandstones, with large de- | Vermilion Creek. f velopment of conglomerates. Ooryphodon beds. - Coarse white aud reddish sandstones, heavily bedded, with large ; dovelopment of coal seams. Fossils marine and brackish- water. Unconformable with foregoing series. pe ee ee iva Speen § Coarse white sandstones, heavily bedded ; few coal seams ; less CRETACEOUS ... iron than former; fossils marine. Mostly blne and yellow clays and marls, with thin sandstones. cmeen #ozseeeColarado-+-+-=- 4 Coal. Fossiliferous. “ Gee eee Dakota ....-.-.-. | Sandstones and characteristic conglomerate, development. renrs, srrtrrccscesceeecseeeeee*) Tn Novada, Heavy limestones, shales, and argillites; greater l development. East of Wahsatch. Clays and limestones; fossiliferons; small JURASSIC....... j MESOZOIC. erous blue limestones, tire development of Triassic rocks interstratified with| eastof the Wabsatch, consistmainly Star Peak........{ quartzitic schists and of coarse, heavily-bedded sandstones, DIGYABRIG2 on asss Red Beds slates. of prevailing red color, sometimes white or buff, with some clays, thin limestone beds, and frequent depos- aston argillites,and| its of gypsum. Almost barren of porphyroids. ) fossils. Heavy - bedded, fossilif-) The Red Beds, which represent the en- Koipato.-. Permo-Carboniferous .....--. | Clays and argillaceous limestones, with ripple-marks. In general, light-colored blue and drab limestones, more or less Upper Coal Measures...-.--- siliceous, and passing in places into sandstones ; generally fossiliferous. Weber Quartzite ..-.-...--.- with local developments of interstratified calcareous and CARBONIFEROUS eth sandstones and quartzites, frequently of reddish colors, argillaceous beds and conglomerates; non-fossiliferous. Lower Coal Measures. -...--- Heavy-bedded blue and gray limestones, with some Wahsatch interstratified quartzites, more frequently in the J limestone. upper part of the series. Lower beds siliceous (Sub-Carboniferous........... PALZZOZOIC. 32,000 + ft (Wahsatch section). ( Nevada Devonian at times. Fossiliferous. DEVONIAN 3.222490 0 = rns 7 7 = a ; ) Ogden Quartzite. .........--. be pret petty quartzite, pink tints; conglomerate with SILURIAN ...... | Ute-Pogonip limestone. .....- Compact blue limestone, with included argillites, passing into Somat ss] = teal iplimestone......- | caleareous shales. More largely developed in Nevada, where (Pogonip ..... 2.22. ccieseees j the limestone carries primordial fossils at the base. renee J > whi i jron-stained, with Cc Noe Generally white quartzites, more or less _iron-stained, wi aes i Soon aeiiwase cc veameeeeee poceccn ; some development of micaceous beds, and heavy dark-blue argillites. wee SE seri 8 es FIGRONIAN|: os saacee weweleseatadeece ea perme p nies granites, diorite-gneisses, argillites, ioe ee limestones, and quartzites. 50,000 + ft. ARCHATAN. LAURENTIAN 22-2 eeccceecccccececece Coarse red orthoclase-mica granites, mica-gneisses, and schists. BS a cl aaa ; with deposits of ilmenite and graphite. ; CHAPTER VII. TERTIARY VOLCANIC ROCKS. SECTION I.— PROPYLITES — QUARTZ-PROPYLITES. SErcrion IIl.— HoRNBLENDE- A NDESITES — DACITES— AUGITE-ANDESITES. SEcTION II].— TRACHYTES. SECTION I1V.— RHYOLITES. SECTION V.— BASALTS. SECTION VI.— CORRELATION AND SUCCESSION OF TERTIARY VOLCANIC Rocks. SEecTION VII. FusION, GENESIS, AND CLASSIFICATION OF VOLCANIC ROCKS. See C al eOeNe as: PROPYLITES AND QUARTZ-PROPYLITES. It is the purpose of this chapter to assemble the more important facts accumulated by our Exploration relating to the Tertiary voleanic rocks, their sequence, geological dates, mode of occurrence, reciprocal relations, and petrographic* distinctions, and to offer an hypothesis which it is hoped may serve to advance our knowledge of the genesis and classification of volcanic species. The material will be classed under three groups: First, the detailed occurrence of species, covering sections I. to V., in- clusive; and in this the past method of treatment will be continued, namely, to begin with the earliest form and describe its special occurrences, passing always from east to west. Secondly, the larger laws of occurrence contained in section VI., the relations of each rock to the orographical actions which brought it to the *All purely microscopic details are hereby credited to Vol. VL, by F. Zirkel. 35 K od i 546 SYSTEMATIC GEOLOGY. surface, with such generalizations as seem to be warranted as to synchron- ous extravasation of each species, and the superposition and succession of all the species. Thirdly, in Section VIL. the origin of igneous fusion and the genesis and petrological classification of voleanic rocks. The area of the Fortieth Parallel has proved exceedingly rich in vol- canic rocks. Although but a small part of the actual surface is covered with ejecta, yet, as compared with other wide regions, it is distinguished by the presence of a very great number of volcanic outbursts. Were the Quaternary valley deposits removed, together with a considerable portion of the most recent Pliocene, the area of volcanic rocks would be greatly enlarged over the western part of Nevada. Reference to Analytical Map VIL, at the close of this chapter, will show at a single glance the area cov- ered and the distribution of species. At the close of the Jurassic age, a powerful mountain-building period was characterized in Nevada and Utah by scattered ejections of middle- age eruptive rocks, including diorite, diabase, felsite-porphyry, and horn- blende-porphyry, together with rare melaphyres. That these rocks were post-Jurassic is clear from their covering Mesozoic strata in western Nevada and California. All over the Cordilleras, so far as we know, the entire span of the Cretaceous age was one of orographical calm, undisturbed either by important mountain flexures, perceptible disloca- tions, or the ejection of igneous material. The changes of level which may be assumed to have taken place were altogether the subsidences of sedimental areas. East of Wahsatch Range, the entire Cretaceous series, having a max- imum thickness of 12,000 feet, are strictly conformable, and are charac- terized by detrital material, and there are no traces anywhere of sediments which may be referred to active eruption. The same is true on the west coast of California. The marine Cretaceous which skirts the western flank of the Sierra Nevada, and has more recently been upheaved in the system of Coast ranges, shows an enormous thickness of pure detritus. So far as our observation goes, the land-mass which lay between the eastern and western oceans, bounded on the east by the Wahsatch and on the west PROPYLITES AND QUARTZ-PROPYLITES. 547 by the Sierra Nevada, has no traces of Cretaceous accumulations, either subaerial or stratified. We have looked in vain for fresh-water Cretaceous lakes or for early massive eruptions. All the indications we have yet been able to obtain, point to the fact that this Cretaceous continent had free drainage to the sea, was characterized by the absence of all considerable lakes, and was eroded to an enormous extent, but never built up by vol- canic material. It is not improbable that sooner or later the traces of small fresh-water lake deposits may be found. It would, indeed, be surprising if such lakes did not exist of sufficient size to have withstood the subsequent erosion throughout the Tertiary and Quaternary periods. The value of such deposits, could they be found, can hardly be over-estimated, as this land area must have been the habitat of the progenitors of Eocene mammals. Such lakes would also, perhaps, solve the question whether over the land areas there are any ejections. Until such data shall be discovered, we are warranted in assuming that the Cretaceous was a period free from either considerable orographical motion or the coming to the surface of any igneous rocks. The relations of volcanic material to the surrounding sedimentary rocks are always among the most perplexing problems offered to the field geologist. In the case of the Fortieth Parallel area, after the greatest pains- taking, we are still unable definitely to fix the era of the resumption of igneous activity. In the extreme east of our area, on the divide between North and Middle parks, as also upon Steves’ Ridge in the Elk Head Mountains, occur two families of rocks which may not improbably be hereafter referred to one group. Those upon Steves’ Ridge have been re- ferred by Professor Zirkel to the trachytes. They are quartziferous trachytes, composed of sanidin, quartz, biotite, a little plagioclase, and rare hornblende, titanite, and apatite. The sanidins are among the most remarkable ever observed in voleanic rocks. The crystals are all completed and attain the size of an inch cube, and present many of the rare faces which are charac- teristic of the older orthoclases of granite-porphyry. All the quartz appears in macroscopic grains the size of a pea, which are rich in glass inclusions. The strikingly similar granite-porphyry from Good Pass, east of Park 548 © _ SYSTEMATIC GEOLOGY. View Peak, between North and Middle parks, is fully described on pages 68 and 69, Vol. VI. Large orthoclases, possessing the same rare planes as in the trachytes just mentioned are associated with quartz grains, a few plagioclases, strongly fibrous hornblende, a little epidote, apatite, and titanite. The chief difference between these two types of rock is, that in the so-called granite-porphyry the quartz contains fluid inclusions, which also occur in the fresh portions of the feldspars. Glass inclusions are wanting in the Good Pass rock. Otherwise they are strikingly similar, and they are totally unlike any other eruptive rocks within our field. Through the kindness of Major Powell and Mr. G. K. Gilbert, I have been permitted to look at a series of absolutely identical rocks from Henry Mountains, Colorado Plateau. Several slides from this latter locality were subjected to microscopic analysis, when it was seen that the hornblende contained beautiful glass inclusions, while certain of the quartzes contained fluid inclusions with moving bubble. The feldspars were the same remark- ably developed orthoclases, with the rare planes mentioned by Zirkel, and associated with a few brilliantly striated plagioclases. In other words, in the Henry Mountain groups, both the types—that of Steves’ Ridge, which Professor Zirkel had called trachyte, and that of Good Pass, which he referred to the granite-porphyries—were found associated. It is further of great interest that in all three of these localities the eruptive rocks are either connected with or subsequent to the upheaval of Cretaceous strata. Tertiary rocks have not been observed in immediate contact with them in our area, and consequently our only clew to their date is, that they are subsequent to the deposition of the Cretaceous. From every geological analogy we are led to believe that the disturbance of the Cretaceous con- nected with the ejection of these peculiar rocks was a part of the general disturbance which took place during or posterior to the Eocene. It is in- deed possible that the occurrence of these rocks will finally be proved to be pre-Eocene; but from the present geological indications we can only class them as post-Cretaceous and not improbably connected with the im- mediate close of the Eocene period. At the first two localities mentioned they partake, on the one hand, of the nature of trachyte, and on the other of granite-porphyry. In the Henry Mountain rocks some of the specimens PROPYLITES AND QUARTZ-PROPYLITES. 549 show a clear predominance of plagioclase and hornblende over orthoclase and mica. With these forms are associated quartzes containing moving bubbles. Taken together, the three occurrences show a series of rocks having remarkable physical similarity, yet when subjected to microscopical analy- sis showing an approach to the diorites, to the granite-porphyries, and to the trachytes. It is not a little singular to see this surprising divergence of interior constitution with such evident physical similarity and the com- mon characteristic of large, highly developed orthoclase crystals. At the present writing Iam inclined to group these rocks under one head and refer them to a point of time within the Tertiary period, and to insist that they show all the specific divergences which will afterward be traced in some of the later groups of volcanic rocks. In both cases the geological mode of occurrence of these rocks is obscure in the territory of the Fortieth Parallel. They accompany the dislocation and upheaval of thick bodies of Cretaceous strata. They cut the latter in dikes, and appear as heavy extru- sions. The country in both cases is so much covered with soil, the soft Tertiary strata are so generally removed, and there is such a dense growth of forest, that the unravelling of the exact geological relation is very diffi- cult, so that we are obliged to look to Mr. Gilbert’s forthcoming memoir * for all the particular geological relations of this interesting group. I have mentioned these in this connection simply to show that the dawn of volcanic action is at present not fixed by rigid geological dates. With the exception of this group of rocks, which is either to be placed at or since the close of the Cretaceous, all the other volcanic series are referable directly to the Tertiary. The remarkable natural sequence of volcanic rocks brought to light by the admirable researches of Richthofen has been in every way cor- roborated by us. About the time of the appearance of Richthofen’s memoir it was the writer’s good fortune to geologize with him in the com- plex field of Washoe, where, more interestingly than anywhere else within the Fortieth Parallel area, the various families of voleanic rocks were dis- played. From that time to the close of our Exploration I devoted much * Report on the Geology of the Henry Mountains, by G. K. Gilbert. 550 SYSTEMATIC GEOLOGY. time to examining the geological relations and superpositions of volcanic products, and came without hesitation to accept as law the order of se- quence laid down by him, which is as follows: . Propylites. . Andesites. . Trachytes. . Rhyolites. . Basalts. Oo eR CF DD ee PropyLite.— Wherever we have been able to observe propylite in jux- taposition with others of these five eruptive groups, it is invariably the old- est. At the southern base of the Mount Davidson group in Washoe the great flood of propylitic rocks which deluged the whole declivity was out- poured beneath the waters of a Tertiary lake. The material in the region of the Daney Mine, and for a considerable distance east and west and down toward the valley of the river until it passes beneath the soft Pliocene strata, is composed of propylitic tuff, partly arrangcd by water into truly strat- ified beds, and partly bedded in a loose manncr, as if it flowed down in vast fields of thick mud. The tuff specimens of these muddy bodies are char- acterized by the presence of numerous leaves, chiefly willow, which have been pronounced to be Tertiary. But we have learned to be a little cautious about accepting the evidence of leaves, since the history of the assignment of horizons upon plant evidence alone in Utah, Wyoming, and Colorado has revealed a series of professional disasters. This is the only direct evidence connected with the propylites themselves. The science of petrography offers no more interesting example of the delicate shades on which lines may be successfully drawn than the case of this rock. Richthofen’s subtle observation and great practice as a field geologist enabled him to detect the essential characteristics of the habitus of this rock, while at the same time he clearly saw its relations to the other hornblende-plagioclase species. The subsequent microscopic analysis of the rock by Zirkel has firmly established its independence as a species. The English petrographers especially have been inclined to deny its existence ; but the shade of habitus upon which Richthofen founded his first assertion PROPYLITES AND QUARTZ-PROPYLITES. 551 of the species is so evident in the field of the Fortieth Parallel Exploration that there has never been the slightest doubt on the part of Messrs. Emmons and Hague and myself as to the identity of propylite. When the large col- lection of specimens brought in by us came to be studied microscopically by Zirkel, it was found that we had never wrongly assigned a specimen to propylite. In certain instances the microscope revealed the presence of minute grains of quartz, and the rock thus characterized came to be classed as quartz-propylite ; but there was never any doubt as to the generic nature of the rock. There was not a solitary instance in which the rock by us called propylite proved to be either diorite, andesite, or plagioclase hornblende- trachyte. I am careful to mention this fact, not as a guarantee of the cor- rectness of our determinations, for that has been placed beyond question by the microscopical analyses of Zirkel, but because later in this chapter I shall have occasion to discuss what constitutes a species of volcanic rock, and the factor which habitus must necessarily play in classification. Whether we regard the actual number of exposures or the total area of the propylite, this rock is of the least geographical importance. In all cases it is associated with later volcanic rocks, and the paucity of its expo- sures and its restriction of area are doubtless in great measure owing to over- flow by the later species. From the few exposures in our area, we have every reason to believe that if the later volcanic rocks had not overwhelmed them, the outcrops of propylite would be more frequent and extensive. Within the Fortieth Parallel area this rock is confined to the region west of the 116th meridian, appearing only in the basin of Nevada—in other words, within the boundaries of the Miocene lake. ‘The most eastern propylites in our field are found on the meridian of 116° 15’, and a little north of the parallel of 41° 15’, in the region of Tuscarora. Here a region from three to four miles north-and-south by two miles east- and-west, the whole lying north of Tuscarora, is composed of propylite. The surface is almost altogether decomposed, and solid outcrops are rare. It is overlaid by rhyolite on the north, northwest, and northeast, and at the extreme southern end of the outcrop, in the region of Tuscarora, it is covered by the thick Quaternary beds of Independence Valley. Upon the whole it is, as an outcrop, rather obscure and unsatisfactory. ‘The surface, 552 SYSTEMATIC GEOLOGY. to a depth of three or four feet, is a loose propylitic earth which has been worked for placer gold. The solid, normal portions of the rock are light ereenish-gray, decidedly porphyritic, with a general earthy texture and rough trachytie surface. The predominating mineral is fibrous green horn- blende of a light-olive tint. Plagioclase decidedly exceeds the few decom posed orthoclases which are present. Besides the fibrous green hornblende, there are dark solid prismatic hornblendes scattered at intervals through the mass. Farther south, at Wagon Canon, in Cortez Range, a little hill to the north of the pass, in the midst of quartz-propylites, shows a greenish earthy body, of which the hornblende is almost entirely decomposed, and the large, dull plagioclases are chiefly kaolinized. A few rather fresh mono- clinic feldspars occur, besides which the microscope reveals apatite and a little biotite. This occurrence comes to the surface as an island in a broad field of distinctive quartz-propylite. In the Fish Creek Mountains, at the western base of Mount Moses, a belt of granite overlaid by Triassic strata forms the foot-hills, which to the north and south are overwhelmed by the enormously thick accumulations of rhyolitie eruptions. Where the Triassic rocks pass underneath the rhyolites are a few limited masses of propylite which the most recent erosion of the rhyolite has laid bare. The hills directly north of Storm Canon show excellent outcrops of the propylite, which is here made up of hornblende, frequently fresh and well preserved, built (as is the rule in the propylites) of thin, staff-like microlites impregnated with small, black grains. Zirkel found the hornblende in places considerably decomposed, resulting in calcite, epidote, and viridite. The feldspars are often fresh and quite large, a majority bearing distinct triclinic striations, with a few pale, small orthoclases. Brown mica occurs sparingly, and besides hornblende the rock contains an inferior amount of yellowish-green augite. In Toyabe Range, near Boone Creek, the prominent ridge of quartzite is enclosed on the east and west by rhyolitic rocks, the latter breaking through upturned Miocene strata. Near the junction-line, where the quartzite passes under the rhyolite, are two rather obscure outcrops of normal hornblende-propylite. he surface is much decomposed, and there PROPYLITES AND QUARTZ-PROPYLITES. HD is very little of the hard material that can be observed; yet the chips with which the surface is covered are characteristically of the normal green hornblendic propylite. It decomposes in soft, earthy, olive-colored slopes, which are overlaid by both rhyolite and basalt. The outcrops are too obscure and too limited to be specially instructive. An interesting locality of propylite is that at Kaspar’s Pass, north of Hot Springs Station, at the southwestern end of Montezuma Range. The termination of the Montezuma is a deeply scored mass of rhyolite, over- flowed by basalts which chiefly cover the southern slope of the hills. The base of the range, from the northern edge around as far as White Plains, is completely surrounded by outcrops of Truckee Miocene, which are inclined toward the range until in the neighborhood of the rhyolites they are thrown into irregular dips, having been burst through and over- flowed by the rhyolitic bodies. These Miocene strata are more or less covered by accumulations of Quaternary. Through Quaternary, imme- diately in the vicinity of Kaspar’s Pass, comes to the surface a body of propylite which occupies the whole of the Pass from the rhyolitic foot-hills on the east to an oval body of basalt which forms the western side of the valley. The basalts on the west, and the Montezuma rhyolites, clearly overlie the propylite; and although the relation between the Mio- cene and the propylite is obscured by Quaternary, all the appearances tend to the belief that the Miocene beds abut unconformably against a preéxist- ing body of propylite. This is rendered very probable by the material of the Miocenes, which is here altogether of the upper or trachytic tuffs. The surface of the propylite is much weathered, resulting in soft olive earth, with predominating propylitic chips. It consists of hornblende and triclinic feld- spars, more or less altered, and epidote, a pseudomorphous product after hornblende. The microscope reveals, as Professor Zirkel describes,* all the pseudomorphic changes between hornblende and epidote. The lower Truckee Canon, from about two miles above Wadsworth, for six miles up the canon, has its bottom largely occupied by propylite. It is entirely unconnected with any stratified rocks, and no clew is offered to the orographical disturbances related to its ejection. It occupies only the * United States Geological Exploration of the Fortieth Parallel, Volume VI., page 114. 554 SYSTEMATIC GEOLOGY. low land at the bottom of the valley, and is covered upon either side by more recent trachytes. A mass of diorite upon the river bank about four miles above Wadsworth is the only older rock in the neighborhood, being a hard, fresh boss of well preserved rock, around which the soft, earthy propylite has flowed. The propylite is of a dull olive-green, and is much decomposed, the feldspars reduced to soft, kaolinic masses, of which even the crystalline forms are chiefly lost. The groundmass is reduced to an almost amorphous paste, and there is a good deal of partially decomposed brown mica. The rock is full of dark green waxy spots, which, in favorable instances, were seen to retain the distinct form of augite. It is clearly an augite-propylite, similar to that discovered by Richthofen at Silver Mountain, which is here in the last stages of decomposition. It is of interest in this connection because this is the only locality of augite-propylite within the Fortieth Parallel area. It is overflowed by peculiar augitic tra- chytes, by light rhyolites, and finally by basalt. A few miles north of Truckee Canon, at Berkshire Cafion, a gorge eroded down the eastern flank of Virginia Range, occurs a fine association of voleanie rocks which have burst out in immediate contact with a body of older melaphyre. The propylite forms the earliest of the volcanic series, and occurs in a body of purple rock lying along the eastern flank of the lofty mass of melaphyre. It is invaded by quartz-propylite and by andesites, and is overflowed at the northern end by trachyte, which, in its turn, is covered by rhyolite, and that is succeeded by basalt. It is a rather earthy, compact propylite, composed of triclinic feldspar and ereenish- purple hornblende, with a little magnetite, apatite, and occasional grains of mica. The outcrops are very limited, and for the most part covered with soil and overwhelmed by later ejections. In Steamboat Valley, a little south of the west end of Map V., there is in the low lands a considerable development of hornblendic propylite, in which decomposition has reached an advanced stage. The staff-like growth of the hornblende is traceable in some of the better preserved crys- tals, the nature of the groundmass is totally obscured, and the feldspars are altogether kaolinie. At all the localities heretofore mentioned, the propylite is displayed PROPYLITES AND QUARTZ-PROPYLITES. 5D sufficiently for identification, and in nearly all cases for determining its age relatively to the surrounding eruptive rocks; but for minute study of the rock itself the occurrences are usually too disintegrated and altered for the collection of really specific types. ‘They are all very restricted localities, and all occur at rather low altitudes, and offer none of the bold characteristic outcrops which mark the high parts of Virginia Range. So far as I have seen, from Pyramid Lake southward to its junction with the Sierra Nevada, Virginia Range shows at frequent intervals enormous fields of propylitic rock. South of Carson River it recurs at intervals for many miles, and in the Washoe mining district is displayed on a scale which is unsurpassed any- where in the United States Cordilleras. In Volume III, ‘ Mining Indus- try,” page 25 et seq., a detailed account is given of its mode of occurrence. Again, in Volume VI, ‘“ Microscopical Petrography,” page 110 e¢ seq, Professor Zirkel has rehearsed the prominent features of that classic propylite locality. Without repeating here what was said there, it seems necessary to re- capitulate the broader facts of its mode of ejection and the leading petro- graphical characteristics of the rock. Prior to the propylite period, Vir- ginia Range consisted of upturned sedimentary rocks—slates, limestones, nodular schists, and quartzites—whose original disturbance was connected with intrusions of true granite. Through these had outburst great dioritic masses whose hard summits had withstood erosion and formed culmi- nating points of the range. The propylitic ejections took place from a series of fissures running longitudinally with the range and extending from summit to base on both sides. The diorites of the Mount Davidson ridge are cut by broad propylitic dikes, and similar lines of fracture may be traced north and south along the summit of the range for many miles. Down the south and east sides of the ridge the propylitic rocks poured quite to Carson Plain, and upon the west to the level ground of Steamboat Valley. Only the highest portions of the diorite summits were lifted above the enormous floods of propylite which poured out from these longitudinal fissures. The eruption was not continuous, but clearly intermittent, as is shown by the manner in which later propylite dikes cut through the heavy flows of the earlier ejections. 556 SYSTEMATIC GEOLOGY. There is no evidence of the propylite having flowed in the sense of an andesite or a basalt. It never extended in thin sheets, but was evidently ejected in a viscous condition, accompanied (if we may judge from the present aspect of its areas) by enormous amounts of water, and de- veloped a sluggish flow down the rather steep slopes of the range. The first eruptions were of normal crystalline propylite, uniformly porphyritic, and almost wholly of olive-green colors. The second ejection, which had its centres of eruption north and south of Mount Davidson, was of a coarse, propylitic breccia, which contained fragments as large as a foot in diameter, enclosed in an ordinary propylitic matrix, the breccias varying from green to purple. The third period of eruption was in the form of narrow dikes without any considerable outflow. They cut the main body of the propylites and the overlying breccias in the north-and-south lines, the dikes varying from six to thirty feet in thickness. Near Geiger Grade, north and west of Virginia City, may be seen the relics of these hard, crystalline dikes, which have withstood erosion better than the soft breccia, or even than the main porphyritic eruption. In consequence, they stand up in bold remnants of sheets which once formed the dike, towering thirty or forty feet above the surface. In immediate contact with the diorite, some of the early ejections were of an exceedingly fine, compact texture, developing a fissile structure re- sembling some fine hornblendic slates. Above the level of Comstock Lode the propylite is altogether unaltered, but east of it the whole pro- pylitie region is more or less wackenitic from solfataric action. At the lower levels, near Carson Valley, the ejections, as has been heretofore mentioned, were sublacustrine, resulting in rudely stratified, muddy tuffs. These extend about 600 or 700 feet above the present level of the river. The belt of middle altitudes below the level of the Comstock Lode is an area of earthy soft rock, frequently decomposed into white, yellow, and red clays, in which the original structure of the propylite is only indicated by soft, kaolinic white spots, the relics of the feldspars. The eruptions through which the upper Crown Point and Ophir ravines are eroded offer the best examples of fresh, unaltered rock. Specimens col- lected from these two localities are seen to be composed of a light greenish PROPYLITES AND QUARTZ-PROPYLITES. 557 or olive groundmass, which is made up of fine triclinic feldspar and the fibrous dust of green hornblende. In this characteristic groundmass are plagioclases of pale gray, white, and greenish-gray colors. Like the feldspar of the groundmass, these crystals are throughout impregnated by a dust of feldspar microlites. The hornblende, which is of green and olive colors, is seen even with the loupe to be made up of individualized hornblendic fibres. This observation was first made by Richthofen, and was subsequently sus- tained under rigid microscopical analysis by Zirkel. ; 7 Quartz-Propylites. 130 | Hills east of Havallah Mountains - |W. Kormann - | 66.34| 14-80] 4.07| . . . .| 2.99] 0.92 5.16 3:19| - - | CO? 7.03 2.31| 100.81 ia 3.90 | 6.90 | 35.38 | 0.305 35-38 6.90 1.22 are) ne 0.85 0.37 3-33 0.54 ee fiat NS ae . ts os 3.09 | 8.12! 35.38 | 0.317 . : | 131 | Hill west of American Flat, Washoe} W. G. Mixter - | 68.44] 14-86] . -| 3.80 . . 1.90 5.08] . - | CO? 0.94 2.26| 100.50) 2.63, 2.67 | 307 | 6.92 | 36.50] 0.273 36.50 6:92 ||| ‘0/84. |. sees 0.54 0.86 eae ae het Fie 2.23 | 8.19 | 36.50 | 0.285 bi, 132 | Mullen’s Gap, Virginia Range - - | R. W. Woodward | 68.46) 16.85 1.43 tr. 2.92 3:98| tr. | CO? 0.59 I.45| 100.03] 2-38, 2-44 | 305 | 7:85 |36.5r | 0/298 * 36.51 7.85 = we 0.32 aks 0.83 0.67 agro hee ae evo ee oa 2.73 | 8.33 | 36.51 | 0.303 133| Foot-hills, Virginia Range, Sheep “ Wea) AA] go ll egja oo |] Ore (@2]) 3 o 518). 0 1.79 | 100.04 Corral Cation. 30/68) |) -oxegalel|( oe sul natosasen” senile tomas 1.02 thes aa | { PROPYLITES AND QUARTZ-PROPYLITES. 561 in a crystalline dust the more decomposed feldspars, and there are the usual fluid inclusions in the quartzes. These, however, are varied by the occurrence of double inclusions of liquid carbonic acid and water. The rock has the usual field habit of all the quartz-propylites—a very roughly fractured exterior, dull, lustreless surface, and the peculiar half earthy look produced by the partial decomposition of the groundmass. This little iso- lated body of quartz-propylite is not immediately associated with any other voleanic rocks. Two miles to the east, at the base of the hills, there is a slight development of basalt; and west of Rocky Creek, in the neighbor- hood of Golconda, there are powerful ejections of rhyolite. The following table, No. VIIL., gives the constitution of several of the most important occurrences of propylite and quartz-propylite. 36 K SECTLON it. ANDESITES AND DACITES. Andesitic rocks have a somewhat wider distribution than propylites, but within the Fortieth Parallel limits they hardly cover a greater topo- eraphical area. Together with their related dacites (the quartziferous spe- cies), they are scattered in limited exposures from Cedar Mountains, in the Great Salt Lake Desert, to California. In general they occupy subordinate topographical positions, and with the exception of a few points in the Sierra Nevada, beyond the western limits of our work, they appear altogether as massive eruptions. Andesitic volcanos probably contemporaneous with the massive eruptions of Nevada and Utah, are placed at intervals along the axial line of the Sierra Nevada and Cascade Range, both hornblende and augite-andesite occurring there as true volcanos. The relics of an enormous extinct crater at Lassen’s Peak mark an andesitic volcano of the first order. Much of the crater wall, however, has been engulfed, and its place is occupied by modern trachytic and rhyolitic cones. The andesites of the Fortieth Parallel are never extensive outbursts, or rather the present exposures are never extensive. How far they may be covered up by suc- ceeding outflows can not be determined. The most eastern exposure is in the Traverse Mountains, a small group of hills which extends westward from the base of the Wahsatch, connecting that range with the Oquirrh. Hornpienpe-ANDESITE.—On the divide between Gosiute Valley and that of Deep Creek, among outcrops of rhyolite which are separated from each other by accumulations of Quaternary, rises an isolated hill of andesite. The exterior surfaces which have been subjected to weathering are of a pale-grayish mauve, almost a lavender-color; but the fresh fracture shows a dark-brownish, compact rock of felsitic habit, with a remarkably homogeneous, half glassy matrix, including small white crystals of plagio- clase, occasional brown micas, and the normal andesitie hornblende, together with a few rounded grains of quartz. The hornblende shows the exterior 562 ANDESITES AND DACITES. 565 modification described by Zirkel as one of the constant microscopic pecu- liarities of andesitic hornblende. The quartz, which occurs in detached cracked granules, does not appear to be a constituent of the groundmass, but occurs as an accidental accessory constituent, after the manner of cer- tain quartziferous trachytes. The rock could not be at all classed as a dacite, in spite of the presence of these accessory quartzes. South of Palisade Canon, facing the Cluro Hills, along the western side of Cortez Range, is a rather obscure, dark, even-grained andesite, evi- dently later than the porphyry and syenite which come in contact with it on the west, and probably earlier than the dacite which lies east of it, though their relative ages have not been satisfactorily made out. Although it con- tains but little hornblende, the absence of augite probably refers it to the hornblende-andesite. Cortez Range is one of the most broken up and geologically compli- cated of any in the Great Basin. It exhibits andesites from the region of Tuscarora at intervals as far south as Papoose Peak, some distance south of Humboldt River. Breaking through and overlying the propylite of the Tuscarora region, is a limited body of andesite, which is overlaid on the west by rhyolites. It is a dark, compact rock, rather reddish on the weath- ered surface, and shows to the unaided eye small brilliant plagioclases and black hornblende crystals in a dark greenish-gray groundmass. Under the microscope, Zirkel found the hornblende green, and more or less fibrous. Its geological habit also inclines toward the propylites, which it somewhat resembles as to the character of the hornblende. At Carlin Peaks, in Cortez Range, latitude 40° 45’, the summits of the Lower Coal Measure limestone are flanked on the west by a small body of andesite, which is surrounded on the north, west, and south by subse- quent rhyolite. The andesite is piled up in a mass, rising about 1,200 feet above the surrounding rhyolites. It is a dark-gray, compact rock, very rich in hornblende, although carrying a good deal of yellowish-brown augite and a little apatite. Besides the predominating plagioclases, there are some schistiform sanidins. A few miles to the south, where the Emigrant Road crosses Cortez Range, is a second body of andesite, overlaid by trachytes on the south, but surrounded on the east, west, and north by 564 SYSTEMATIC GEOLOGY. rhyolite. It is unimportant geologically, and possesses no petrographical differences from the rock mentioned at Carlin Peaks. Above the head of Clan Alpine Canon the summits of Augusta Range are formed of andesite masses, the crests of an earlier topography, which have remained lifted above the later floods of rhyolite, or perhaps which erosion has recently exhumed from the overlying acidic rocks. The ande- sites have a rudely columnar structure, and are made up of plagioclase and hornblende, the latter showing the characteristic black boundary, and the groundmass is distinctly made up of microlitic particles of the two minerals. The long hornblende prisms are noticeable for a rude parallel arrangement. A few miles north, the region around Crescent Peak and the head of Au- gusta Caton shows a considerable field of andesite, which has broken through and overflowed the Mesozoic limestone, in turn overlaid by trachytes and rhyolites in the order mentioned. The groundmass of this rock has a prevailingly earthy character, owing to the varying decomposi- tion of the hornblende. Zirkel calls attention to the interesting manner in which the hornblende crystals of this locality, viewed with the microscope, are seen to have been ruptured and the particles moved away from one another. In some cases nearly all the fragments of the crystal remain embedded in the ground- mass within the field of view, when the eye readily reconstructs the form of the original crystal. At other times detached fragments not traceable to the parent crystal are seen. There are certain very distinct instances of fluidal motion, the chips of a crystal being thrown into wavy lines like the figures of marbled paper. The little group of Kamma Mountains, lying west of Montezuma Range, in latitude 40° 45’, forms an isolated series of hills rising about 2,000 feet above the desert. The southern portion of the group and a few detached outliers in the lowland south of the main group are made up of hornblende-andesites. The outcrops toward the summits of the mountains form jagged, prominent peaks, with considerable exposures of bare rocks. Farther down the slopes there seems to be a distinctly bedded structure with an inclination of the sheets to the east. Still farther, the low hills are mostly covered by recent detritus and afford no very characteristic ANDESITES AND DACOITES. 565 exposures. This rock is a true hornblende-andesite, the groundmass con- sisting chiefly of plagioclase containing a high proportion of black opacite grains. All the andesites of this region south of Lander Spring have a more or less trachytoid habit, the weathered surfaces having almost the roughness of trachyte, quite that of the dacites. There is a noticeable amount of sanidin in the composition of the rock, which doubtless accounts for the peculiar roughness of the texture. The little group of andesitic hills a few miles north of Kamma Range, at Indian Springs, show a somewhat similar superficial roughness, and upon closer examination the rock, although a true andesite, is seen to contain an unusual proportion of large crystals of sanidin, together with decomposed hornblendes, in a compact close-grained, greenish-gray groundmass. There is nothing in the geological occurrence of the andesites of this region to distinguish them specially. They are the oldest eruptive rocks of the neighborhood, with the exception of the small body of middle-age diorites. The relation between the detached small bodies of andesite lying south of the main Kamma Mountains and the slightly inclined Miocene beds does not appear, the superficial Quaternary preventing any true solution of their position. Taking the outflows of these andesites as a whole, they seem to be related to the western margin of the great body of Jurassic slates which form the western flank of the northern part of Montezuma Range. Where those westerly dipping slates finally disappear beneath the low desert coun- try, is doubtless the mountain fracture which gave vent to the andesites. From the valley of Glen Dale eastward, Virginia Range is cut directly across by the cation of Truckee River. At the western or upper entrance of the canon the hills on either side rise from 1,500 to 1,800 feet above the level of the river. Those to the south are formed of thickly bedded ande- sites and andesitic breccias of prevailing grayish-brown, reddish-brown, and chocolate-brown colors. There cannot be less than a thickness of 1,200 or 1,400 feet of accumulated beds, showing every varicty of texture, from a rough, loose, trachytic, porous mass to an extremely compact, highly erys- talline body resembling the best preserved porphyritic andesites of Washoe. The beds all incline toward Truckee Canon. The lowermost members of the series are of compact reddish-gray and olive-gray flows, with a gray 566 SYSTEMATIC GEOLOGY. microcrystalline groundmass, in which hornblende and triclinic feldspar and a few large, conspicuous crystals of augite are seen. Over these, form- ing by far the greater portion of the series for a thickness of not less than 1,600 feet, are reddish-brown, highly cellular, almost scoriaceous andesites, containing both hornblende and augite, with a decided predominance of the latter, the whole overlaid by a thick series of andesitic breccias, of which most of the fragments contain augite to the exclusion of hornblende. Much of the breccia is decomposed, leaving earthy masses of which the hornblende crystals are decayed past recognition. Although distinctly a massive eruption, the physical character of these andesites partakes much more of the andesitic lavas of a true voleano. They were evidently ejec- tions from a deep fissure, coming to the surface near the summit of the range, and pouring down one over the other, exactly as upon the flanks of a true voleano; and the loose, scoriaceous habit of a large part of the mid- dle series closely corresponds with the andesitic material thrown out from the ancient crater of Lassen’s Peak. With this exception, all the andesites of the Fortieth Parallel are decidedly compact, having the habit of ordinary massive eruptions. It is not at all impossible that the inclined beds repre- sent the fragmentary remains of some old andesitic volcano, most of whose body is now covered by the later eruptive rocks of the neighborhood. The narrow andesite body which lies along the eastern flank of the melaphyres of Berkshire Canon in Virginia Range has an east-and-west breadth of not more than a quarter of a mile, but extends about six miles north-and-south. Like the neighboring propylite, it is wonderfully trachytic in appearance. The groundmass is a grayish-brown feldspathic body with but little brown hornblende distributed through it. The large crystals and fragments of crystals of hornblende, however, which lie porphyritically embedded in it, are arranged with a certain degree of parallelism. This rock most closely resembles those earlier trachytes of the Washoe region which underlie the sanidin varieties, and which by their high proportion of black hornblende and plagioclase closely approach the andesites The middle ground between the andesites and trachytes is occupied by a gray or grayish-brown rock, carrying a predominance of hornblende over biotite, with plagioclase and sanidin in about equal proportion. When the texture ANDESITES AND DACITES. 567 of the groundmass is rendered trachytic by a high proportion of horn- blende, the habitus of the rock inclines obviously to the trachyte family. But when the groundmass is composed predominantly of feldspars, and of those feldspars the plagioclases equal or exceed the orthoclase, the habit of the rock becomes truly andesitic. Out of this middle region, therefore, between the two species, when, as is often the case, one cannot decide upon the predominance of included orthoclase and plagioclase, the habitus of the groundmass gives a pretty sure indication of the general group it belongs to. Dacitr.—The eastern half of Cortez Range, from four or five miles south of Papoose Peak nearly up to Humboldt Canon, a distance of four- teen or fifteen miles, is composed mainly of a continuous field of dacite, which seems to prolong the line of eruption determined by the quartz propylite of Cortez and Papoose peaks. As an eruption, it shows no tendency to form sheets or extend itself laterally from the region of fissure. On the contrary, it behaves like granite or the least fluid of the trachytes. It is essentially a massive eruption, and north of Wagon Canon shows a thickness of at least 1,200 or 1,500 feet. Like the andesites, its surface is very easily decomposed, the prevailing character of the rock is rather earthy, and the colors vary from purple to chocolate and brown, the later eruptions north of Wagon Canon growing pale and approaching grays and olives. At the southern end the mass is overlaid by high piles of rhyo- lite, and the eastern base for many miles, as the map shows, is overlaid by basalt. Along its eastern line it quite distinctly overlaps the quartz- propylite, and is therefore later. North of Wagon Canon the basalts give way, and the Pliocene strata of Pine Valley come directly in non-con- formable contact, abutting against the slopes of dacite. The field habit of this dacite is decidedly more propylitic than andesitic. There is a lack of the resinous lustre and the easy, glassy fracture of hornblendic and augitic andesite. In the field and in hand specimens we were often unable to dis- tinguish between it and quartz-propylite. But in the case of this outburst it might readily be mistaken for the neighboring quartz-propylite. The chocolate-colored and purple groundmass encloses peculiar white kaolinic 568 SYSTEMATIC GEOLOGY. erystals of feldspar, which in the least decomposed portions show under the microscope triclinic striation, and numerous black and_ glittering quartzes. The rock is really a dacitic breccia, since the groundmass con- tains numerous fragments, both angular and sub-rounded, of a similar pur- ple dacite, whose only difference from the enclosing material is, that the kaolinized crystals of plagioclase are much smaller than those secreted in the matrix. The microscope shows that the kaolinized feldspars are pene- trated by fine crevices carrying chalcedony. In various directions through the rock are late fissure-lines, which may be traced by a rusty ferruginous color penetrating the purple groundmass a short distance on either side of the crack, resulting no doubt from the decomposition of the hornblende. Those hardly perceptible traces of motion which indicate to the eye whether the viscous movement of the body has been in horizontal beds or simple vertical planes, show in this instance that it was vertical. North of Wagon Canon, where dacite forms the crest of the ridge, the rock is decidedly less brecciated than to the south. It is purplish-green, and is very noticeable for large, opaque, triclinic feldspars. The horn- blende is fresh and brownish, and there are a few flakes of biotite in the microfelsitic groundmass. Throughout this whole mass the quartz crystals are all very dark, and but rarely visible macroscopically. ‘The microscope reveals their abundant presence everywhere, and it also shows that the glass base is of the gray type. At Shoshone Peak, the culminating point of Shoshone Range, in the midst of a broad area composed of Carboniferous quartzites, dacite forms a small, insular mass, its overflow making the highest point of the range at Shoshone Peak, 9,760 feet above sea-level. This outburst has occurred on the line of a flexure in the quartzites which still earlier was marked by a small eruption of diorite in a cation north of Shoshone Peak. It is at once the most elevated and most interesting outburst of this rock within the limits of our survey. Petrographically it is of importance as including the largest quartz grains of any Fortieth-Parallel dacite, many reaching the diameter of an eighth and some a quarter of an inch. The general color of the rock shades from purple to green. Not a little of it in the lower exposures, indicating the earlier stages of the eruption, is rudely ANDESITES AND DACITES. 569 brecciated. Between the dacite breccia and the compact, uniform rock, there is every transition, some hand specimens showing a single included angular fragment not larger than a pea. The most important structural characteristics of this exposure are the powerful vertical jointing-planes which in some places approach the regularity of a columnar structure. The groundmass is often so coarse that the particles of triclinic feldspar and fresh hornblende may be seen by using the loupe, and occasionally with the unaided eye. ‘Toward the east the cliffs of dacite are eroded down sharply in canons, modified, if not determined, by glacial action. The bold, rocky fronts of the spurs and the flanks of the cations offer admirable exposures of the rock, the slight accumulation of soil and the absence of forest trees combining to make it the most imposing exposure of dacite in the Fortieth Parallel area. In weathering, the groundmass, feldspars, and hornblendes wear down pretty evenly, leaving the erystals of quartz, which are often dihexahedral forms, standing out along the surface. The geo- logical aspect in the field of this and of the other dacites often resembles certain metamorphic quartz-porphyroids. The surface is exceedingly rough, the fracture more like that of propylite, the low proportion of the glass base rendering the lustre dull and very different from the resinous brightness of the quartzless andesites. Virginia Range, so justly noted for its varied and extensive display of voleanic species and varieties, exhibits typical dacites at three points within the limits of our Exploration. Abreast of the southern end of Pyramid Lake the range is severed by the deep pass of Mullen’s Gap. The hills both north and south of this depression, ascending to considerable heights, are composed of a gray dacite, which weathers in rough, rounded forms, and is conspicuous by a very dull surface, resembling the propylites. It varies from gray through several olive-greers to purple, and in all hand specimens shows more or less distinctly striated plagioclase and macroscopic quartz. The latter, as described by Zirkel in Volume VI, page 139, carries distinct fluid inclusions. The hornblende also is of the true andesite-dacite type, and not the polysynthetic propylite variety. Of all the dacites, in external habitus this most closely resembles the propylite type, and it is by mistake colored upon our geological map as quartz-propylite, close D770 SYSTEMATIC GEOLOGY. examination having been made too late for a change. The rounded or rudely crystalline grains of quartz are brilliantly vitreous, and are fissured in every direction by innumerable cracks, closely resembling the rhyolitic quartzes, with the exception that the latter almost never contain fluid inclusions. For analysis of this, see table of analyses No. IX. Throughout this northern portion of Virginia Range there are no ante- Tertiary rocks, except the limited development of melaphyres in the region of Berkshire Canon. The relation of the overflow of Tertiary ejecta to the earlier range cannot here be made out. Farther to the south, Archean, Mesozoic, and middle-age eruptive rocks form the distinct body and core of the range, over which the Tertiary species have poured. In the northern portion now under consideration, although the heights are maintained up to 8,000 and 9,000 feet, the entire range is masked by enormous floods of trachyte and basalt. It is only in the lower portion of the hills, however, that the earlier Tertiary eruptive species come to the surface. Along the eastern flank, at Berkshire Canon and for about four miles northward and the same distance southward, the andesites and propylites which lie along the eastern base of the melaphyres are broken through by repeated flows of dacite, the latter extending southward to the mouth of Sheep Corral Canon and forming a distinet foot-hill region, noticeable for its purple and green colors. The mode of weathering of this rock resem- bles that of the older diorites. It appears in low, rounded hills, exposing considerable stretches of smooth, rocky surfaces not covered by earth or recent débris. ‘The harder quartzes frequently stand out prominently upon the surface. Very considerable portions of this outflow are of a fine-grained, purple groundmass, with no included crystals recognizable to the unaided eye. From this fine microcrystalline condition it passes into a more coarsely crystalline groundmass, in which triclinic feldspar and more or less brown hornblende are easily detected. Through these earlier purple dacites have broken large volumes of dacitie breccia, which carries a ereat deal of dark, bronzy-brown magnesian mica. The percentage of free quartz erystals is also higher than in the earlier outflow. Last of all, and closing the dacite period in this neighborhood, came a pale, apple-green ANDESITES AND DACITES. 571 dacite, richest of all in quartz. It is interesting for the decomposition of the feldspars and their conversion into carbonate of lime and kaolin. As in the dacites of Shoshone Peak, which these often closely resemble, the quartz grains are frequently dihexahedral. The anomalous position of a crystal of quartz containing fluid inclusions in a glass-imbued groundmass is difficult to explain, unless it may be an ingredient of an older rock, which has escaped fusion. Avaire-AnpEsItE.—The limestone body of Cedar Mountains, a de- tached range southwest of Salt Lake, is accompanied by outbursts of volcanic rock. The oldest of these is at a remarkable bend in the range, near its southern extremity, a little north of latitude 40° 15’. The limestones, which have stretched southward from the northern portion of the range for about thirty miles, suddenly bend off to a southeast strike. Directly at the inter- section of these two strikes, where a very great strain must have occurred in connection with the flexure of the strata, there is an outburst of andesite which occupies the angle of the range. The desert Quaternary deposits rise high upon its flanks, and probably cover a considerable portion of the andesite flows. Four or five miles to the southwest, a small isolated butte of andesite rises out of the Quaternary, and is evidently separated from the main mass by a thin blanket of loose soil. The external appearance of these andesites is quite like that of basalt. Its structure is that of thin sheets, which often display a rude, columnar jointing. The reddish weathered surfaces also resemble some of the thinly bedded basalts. Upon fracture, the rock is seen to contain considerable pale-gray glass, the larger crystalline secretions being plagioclase, augite, and a few hornblendes, to- gether with a little brown biotite. Augite predominates over hornblende. An interesting group of andesites occurs on the northeast base of the Wachoe Mountains, longitude 114° 30’. The hills consist of a granitic core against which rest considerable bodies of limestone belonging to the Lower Coal Measure series. Diorites and felsite-porphyries are connected with the disturbances of the middle age, and andesites and rhyolites form the features of Tertiary eruptive activity. The andesites are all seen along the northeast base of the group; and with the exception of a small, isolated 572 SYSTEMATIC GEOLOGY. hill south of Last Chance Spring, are all overlaid by rhyolite. The ande- sites at the mouth of Spring Canon, as exposed where the rhyolites have been eroded away, together with the butte south of Last Chance Spring, exhibit a dark gray, rather compact groundmass, which the microscope shows to possess a pale gray glassy base. Besides plagioclase and augite, which are the predominating crystalline secretions, there are a few horn- blendes and a little sanidin. The eruption of these andesites is of the usual massive type, spread out in rather thin sheets. Although the out- flows are arranged on a northwesterly trend, yet the northernmost out- crops, north of Melrose Mountain, are of a different petrographical nature. The groundmass is dark, steely gray, the crystalline secretions being a little orthoclase, fine, brilliant crystals of plagioclase, predominating biotite, and afew broken, acicular hornblendes. It is classed by Zirkel as the mica equivalent of hornblende-andesite. Externally, with the exception of the evident mica, the rock has the same geological habit and aspect as the Spring Canon outcrops. Like that, it is surrounded and in great part coy- ered by rhyolite, and presents the ordinary characteristic dull-red surfaces of weathered andesite. Under the hammer it breaks with sharp fracture and shows the resinous lustre of semi-vitreous rocks. The River Range lying north of the Humboldt, in middle Nevada, is suddenly cut off a few miles north of Penn Canon. The range, which has been a well defined quartzite ridge for fifty miles, suddenly plunges down beneath a broad flood of rhyolitic and andesitie rocks. There is no doubt that this break in its continuity is due to a fault, and that the andesite has come up in the fracture-region. The North Fork of Humboldt River flows through the horizontal Pli- ocene of Bone Valley, and then cuts a sharp gorge, to which Mr. Emmons gave the name of Egyptian Canon, through a field of andesite For about eight miles along the canon, by four or five miles in width, is exposed a body of andesite which is overlaid by the horizontal Humboldt Pliocene strata of Bone Valley on the north and similar beds at the lower end of Egyptian Cation. East and west it is overlaid by fields of rhyolite. The physical habitus of this rock, in a broader sense, is strongly like that of basalt. It is composed of tabular layers, which along the walls of Egyptian Caton show ANDESITES AND DACITES. Dili a rude columnar structure, in which the columns are cylindroids rather than prisms. There is also a tendency to split into plates perpendicular to the axis of the cylinders. It is to those two sets of fissurings that the peculiar architectural aspect of the region is due—an effect resembling ruined columns of an Egyptian temple. Under the hammer the rock has the usual flinty fracture, totally different from the rough, ragged fracture of basalt. A speci- men from the lower end of the cafton shows a groundmass entirely made up of microlites and grains of plagioclase and augite, free from olivine; the only larger crystalline secretions being small, pellucid plagioclases. Near the upper end of the canon is a very remarkable variety of the rock, having a dark, brownish-gray groundmass which carries sanidin crystals half an inch in length, and a few cracked and rounded granules of quartz, altogether similar to those in the augite-andesites of Cedar Mountain; the main ingre- dients, however, being plagioclase and augite. Like the specimens col- lected at the lower end of the camion, it contains no olivine. The micro- scope shows considerable quantities of apatite. Between the basalts, which want olivine, and the augite-andesites, which are totally free from horn- blende, it is not easy to determine, either by microscopic analyses or by examination of hand specimens. The question of devitrification of the glassy base is not in itself sufficient. ground for a distinction between the two species. At the time Professor Zirkel’s examinations were made, the field-notes were not written out, and he was not informed as to the condition in the field. The rock is earlier than the Pliocene and surrounding rhyo- lites, and its habits are altogether those of andesite. For this reason we have decided to class it among the andesites. A few miles south of Tuscarora is found a small body of augite-ande- site, entirely surrounded by rhyolites. It is of no particular importance, except for the extremely fine development of augites and the fact that the plagioclases, which reach the size of a hazel-nut, are extraordinarily rich in inclusions of yellow glass. The valley of Susan Creek is occupied by horizontal Pliocenes which continue southward from the valley of the North Fork of the Humboldt, forming a narrow strip between the rhyolite hills of Seetoya Range. On the east side of Susan Creek Valley, about abreast of Maggie Peak, between DTA SYSTEMATIC GEOLOGY. the creek and River Range, is a small body of augite-andesite coming to the surface under trachytes and rhyolites. The weathered surfaces have a pale greenish-gray color, but the fresh fracture is very dark brown, almost black, and possesses the brilliant resinous lustre characteristic of the family of andesites or of the most glassy basalts. Crystals of sanidin and plagioclase can be detected in the fine-grained groundmass, as well as clear, well shaped augites, the latter standing out prominently on the weath- ered surfaces. As usual, the rock contains no olivine. Palisade Canon is eroded through a body of trachyte, to be hereafter described. A prominent ravine, entering the canon from the north, lays bare a body of andesitic rock of very peculiar constitution. It is a dark eray rock, having the characteristic fracture and surface of andesite, but the very fine-grained groundmass contains augite, plagioclase, biotite, and angular grains of quartz which, together with apatites, are found embedded in some of the larger feldspars. The association of augite and quartz renders the rock particularly interesting. On the gentle eastern slope of Cortez Range, south of Wagon Canon, a long, narrow exposure of augite-andesite comes to the surface, enclosed on all sides by dacite, which strongly resembles it in color, texture, and general geological habit. The two rocks disintegrate with abowt equal ease, and the earlier (for so it seems to be) andesite is probably a portion of a prior outburst, from which erosion has removed the covering of dacite. It is indeed possible that the andesite has broken up as a dike through the dacite, as data for their relative ages are wanting. The color of the mass varies from brown to purple, very much of the surface being covered with minute chips of the solid portions. The fresh fracture shows the usual resinous lustre due to gray glass, which constitutes the base of the rock. The groundmass is much discolored and decomposed, passing from the color of chocolate to a rusty iron-red, and at times pale yellow and brown. In it are plagioclases, more or less kaolinized, showing traces of zonal struct- ure, yellowish augites, and occasional but rare flakes of biotite. In the valley of Reese River, directly north of the little town of Ja- cobsville, is an isolated mass of hills connected with the southern part of Shoshone Range by a flow of rhyolite. The little group known as Jacob’s ANDESITES AND DACITES. 575 Promontory is made up largely of quartzites, considered to belong to the Weber period, which here have a very dark, ferruginous color. Through these, at the northern and southern foot-hills of the group, long anterior to the period of the trachytes and rhyolites, have burst out masses of dark augite-andesite with a distinctly columnar structure and a light-gray weath- ered surface. When broken, it has a sharp, conchoidal fracture and a dis- tinetly resinous lustre, owing to the high proportion of glass base. The groundmass is composed of plagioclase and olive-colored augite. Besides these minerals, there is a little sanidin and a few irregular, broken crystals of hornblende, the latter having the appearance of a foreign ingredient. Under the microscope, the plagioclases are noticed by Zirkel as containing well defined inclusions of brown glass with thick bubbles, the augites also containing large glass inclusions which themselves contain augite microlites. This locality is of special interest, since here the augitic andesite is dis- tinctly overlaid by basalt, the greater relative antiquity of the former rock being thus clearly demonstrated. In the southern portion of the Augusta Mountains, south of Shoshone Pass, in the region of Crescent Peak, where the stratified Mesozoic lime- stones are overpoured by heavy masses of hornblende-andesite, the latter have been broken through and in turn overflowed by a highly glassy augite- andesite, resembling in external features and in geological habit the occur- rence at Jacob’s Promontory. At the head of Augusta Canon, and over the ridge to the north, the augite-andesites superposed upon the horn- blende variety are seen in distinct columnar structure, the individual prisms varying from a few inches to a foot or two in diameter, and commonly dis- playing a fairly regular pentagonal section. The exterior surface of the blocks, to the depth of about a tenth of an inch, shows a light grayish- green color, the result of the alteration of the groundmass. Directly be- neath this altered layer is a dull-reddish, rusty zone, and then the dark, fresh, resinous, glassy material of the main mass. A few miles farther north, on the western side of the range, at Antimony Canon, similar augite- andesites appear, which have broken through and overlaid brecciated hornblende-andesite, the latter overlying, as in the Crescent Peak region, masses of older hornblende-porphyry. In both of these latter localities the 576 SYSTEMATIC GEOLOGY. augite-andesite is of distinctly later origin than the hornblende-andesite, a fact which is elsewhere repeated, and to which the field observed by us offers no exception. It is also extremely important to note that the augite- andesites of the Augusta Cafion region are overlaid by the trachytes that form the extreme heights of the range. At Jacob’s Promontory we saw that the augite-andesite was of earlier age than the basalt; here it is seen to be earlier than the trachytes. In other words, it belongs manifestly to the andesitic period, and since it clearly followed the hornblende-andesites, it may safely be held to close the andesite period. The rock, then, should be considered a true dependent of the andesite family, and not of the basalt family, to which its petrological features far more closely ally it. The im- portance of this region cannot therefore be over-estimated, as will be seen when we come to treat the natural classification of volcanic rocks. In a side ravine of Truckee Canon, three miles north of the main river, occurs a limited outcrop of dark rock resembling basalt in appearance and mode of occurrence. It is surrounded by rhyolites. Under the microscope appear both orthoclase and plagioclase in about equal proportions, green augites, and abundant olivine, the latter surrounded by an encircling band of green augite prisms arranged tangentially. It is classed by Professor Zirkel as an augite-andesite, the silica equivalent being far too high for the true basalts, to which its large tenure of olivine would naturally ally it. The silica equivalent is doubtless to be accounted for by the abundant pres- ence of a highly acid glass which fills all the spaces between the crystals of the groundmass. Directly south of Wadsworth are three detached hills of black rock, the northern one of the true basalt, the two farther south of augite-andesite. The groundmass is a dense aggregation of minute plagioclase, magnetite, and augite-microlites, in which are embedded sanidins and plagioclases in about equal proportion. Although augite is distinctly in excess, there is yet considerable light-brown hornblende with the characteristic black border of the andesite-hornblendes. Olivine is wanting. In the rolling hills west of Steamboat Valley, Nevada, somewhat north of the group of springs, are augitic andesites composed of a very light grayish-green groundmass, in which are well defined green augites up to TABLE OF CHEMICAL ANALYSES. IX.-UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. ANDESITES AND DACITES. Andesites. a a ¢ a : Oxygen ratio of— & 3 2 = Locality. Analyst. Si Al Fe Fe Mn | Ca | Mg | Na K Li 3 Total. | Specific |] 20,2 55 5 gravity. |p | |e |Fs rae D R Si |# 5 | a oa | 134 Ridge northeast of American Flat, | W. G. Mixter - | 58.33| 18.17] - -| 6.03] . .| 6.19] 240] 3.20| 3.02] - . | CO? 2.85 | 0.76) 99.95] 2-72, 2.76] 545) 846 31.10 | 44s Washoe. PE |) aS | a o roel lt eee x77 | 0196) || vote | ost | . ames ae oe SO 4.06 | 10.47 | 3.10 | 0.467 135 | Silver Terrace, Washoe - - - - ct =|) Gopal) Ghee! o ol} (NE) a o|) Hel] Boel] sgh) sees) o 3 gH 0 2.80] 100,02 2.6 5:30} 8.48 }3r.5s8 | 0.436 31.58 GO) a o oPa80i|| acne 1.57 x16 | 0.85 | 0.24 % ees iit ha ae 3.82 | 10.71 | 31.58 | 0.460 136 | Main Ridge, above Three Knobs, | R. W. Woodward) 60.71] 16.00) 2.09} 3-87) - -| 5:17] 3:07) 2-74 3-78 tr. | CO? r.o1 1.48 99-92] 2.6, 2.5 | 492] 8.08) 52.97] o.4or Cedar Mountains. 32-37 7-45 0.63 0.86 od 1.48 1.23 O.7t 0.04 5. pis o> 0 oa aes rage SPA eeeen| oes||\ be 137 | First hill north of Gold Hill Peak, |W. Kormann - | 61-12] 11-61] 11-64] - «| - + | 4.33 0:61) 3785] 3:52) - « goa 3 4:35 || 101-03 ghaid 5:39] 5.4t| 32.59] 0.33% Washoe. 32.59 5.41 Bey || oo oh a8 1.23 | 0124 || worgg) | 0.60 |. foc so ee ae: oe 3.061|| B.90\||42.59\| 0.466 138 | North Pass, Cortez Mountains - - | R. W. Woodward} 61.64] 17-44) 0.82) 3-99] tr. 5-86| 3:05] 3:45] m-r5| tr. bo 0 2.64] 100.04] 2.6, 2.5 | 485) 8.37) 32.87) 0.402 32.87 8.13 aay || Es lo 1.67 x22 | 0.8) | o19 | . « oe feat ee eae oft Nees Wercee: lee 139 | North bank of Palisade Canon - -|Reinhard- - - | 62-71) 12.10/ 14-79) - -| = = 8.34] 1-31] O73) TI5] ~« - oo 4 a of] iennng Rae 6.24) 5.64) 33.44) 0.355 33-44 5.64 4-43 : : 2,38 0.52 6.19 9.19 doo 300 8 0.0 mo 0 a 4 3-28 | 10.07 | 33.44] 9.399 (~4D 8 6.16 6 140 | Wachoe Mountains - - - - -|R.W. Woodward | 67.81) 17.60 2.11 tr. 3.15] 1-08] 2:97} 3:85) - - a0: 1.57| 100.14] 2.5, 2.6 | 322] 8120] 3646) 031 } 36.16 8.20 0.70 0.47 a0 0.90 0.43 0.77 0.65 9.6 og 3 G9 qe 8g F/G 2.75 | 8.99} 36.16] 0.322 ADA ; 8.42 36 « “ ES a Se 67.63| 18.08 2.17 tr. 3:16) 1-14 P87) 3:80) «= a6 "0 1.49] 100.40 Pare 3.22 | 8.42] 36.07) 0.322 36.07 | 8.42 Peewee ool] Gall cus | «ARI oo POP. vi fen ooo ee 2.74| 9:14] 36.07] 0.329 Dacites. i i ity, Wa ii so : 5 a z a ont et 1.3 2.0 3.6 aoe setae We 2.1 101.9 was 3.00 | 8.34| 36.95] 0.307 141 | Hills above American City, Washoe | C. Coiincler 69:3, | 1) hs an | ee |: ae 4 We Roce sion | evalltacieel Retare | 25 . * H . . 2.90] 7.53] 37-41 | 9.276 142 | Shoshone Peak, Shoshone Range - | R. W. Woodward| 70.17 14-53) 2:54) 3-74) ' | 2:29) 0:95 325) 3:35) ut 0 ey) |e SOTERA es fas at). Gor | ene | oise)| «|| oc6ng|| eee | °-57 oy ee bo ‘ | 37-46) 0. “ “ « bs « 70.25) 14.90] 2-57 1.76 tr. 2.39, 0.83} 3:24} 3-22 tr. te deo 1.51 100.67 te 2 au 17 u : 9.279 || Gs 0.77 0.39 0.68 0-33 | 0-8 HE 2 Re ie? 3 = | ANDESITES AND DACITES. SHITE the size of a pea, feldspars, both orthoclase and plagioclase, of equal dimen- sions, a little sharply crystallized magnetite, and some apatite. Not atrace of hornblende was observed in this rock. The external appearance and habitus of this occurrence are distinctly andesitic, the bedded flows resem- bling those of the hornblende-andesites which overlie the propylites near Virginia City. The following table, No. IX., gives analyses of several of the most important andesites and dacites, 37 K SEC ito Nite TRACHYTES. We have seen that the propylites, quartz-propylites, andesites, and dacites occur very sparingly over the Fortieth Parallel field, and are alto- gether confined to the region west of Wahsatch Range, with their greatest concentration at the extreme western limits of our work. The trachytes which we are now about to consider, have a somewhat peculiar distribu- tion. They occur chiefly in four well defined groups: 1. That of the Rocky Mountains, which consists of two main out- bursts, one constituting the divide between North and Middle parks, the other in the Elk Head Mountains, directly west of Park Range. This forms an entirely detached group, with no trachytes over an interval of 4° of longitude westward. 2. The next group appears in the region of Wahsatch Range and Salt Lake. North of the railway, at longitude 109° and 109° 20’, several little dots have the characteristic trachyte color on the small map at the end of this chapter. But these are so colored to avoid the expense of another stone, and are really leucitie rocks, not to be confounded with the trachytes. The Wahsatch trachyte group consists of several outbursts, the most prom- inent of which lies between the western end of Uinta Range and Clay- ton’s Peak in the Wahsatch. The line of fissure through which this ejec- tion has taken place is a great fault, slightly diagonal to the axis of the Wahsatch, and its trend is defined by a line of trachytic outcrops shown on East Cation Creek. At the western base of the Wahsatch, in the Trav- erse Mountains, directly opposite the broad field of trachyte east of Clay- ton’s Peak, are two important bodies, one occupying the Traverse Moun- tains and the other the slopes of the eastern spurs of the Oquirrh. 3. Passing over an unimportant mass in the Tucubits Mountains in northeastern Nevada, the next considerable trachytic region is that of Pinon and Cortez ranges and their continuations to the north. Here, from the 578 TRACHYTES. 579 southern limit of our map as far north as Nannie’s Peak in Seetoya Range, are exposures of considerable masses of sanidin-trachyte. 4. The last noteworthy locality is that of Virginia and Lake ranges in the vicinity of Pyramid Lake, where large portions of the mountain bodies are composed of trachytes. It is curious to observe that these four important groups are separated from each other by intervals of 4° of longitude. The group in the Rocky Mountains is directly contiguous to important folds of Archzean rocks, a region which has been the theatre of orograph- ical movements in very carly times. The group of Wahsatch trachytes accompanies one of the most important geological centres of the whole Cordilleras, where the deepest stratified rocks are exposed, and where immense dislocations of the crust and excessive erosions have taken place. It is a region of exceptional geological grandeur and activity. Passing westward to the group of Cortez and Pinon ranges, we come again to a region of unusual geological conditions. It is here that the older Devo- nian and Silurian rocks are brought up from great depths to the surface, and evidence of remarkable faults in Tertiary times is not wanting. Again, as regards Virginia Range, it may be said that it is the most important of the meridional ridges which branch off from the northwest trend of the Sierra Nevada. Itis a range in which perhaps a greater volcanic activity was maintained throughout the whole period of time covered by the Tertiary eruptions than in any other east of the Sierra Nevada. During the period of the deposition of the Cretaceous, North and Middle parks were unquestionably one basin. The orographical movement which accompanied the close of the Cretaceous epoch threw up an east-and- west ridge, dividing the basin into two parts. The character of the disturb- ance of this ridge was very complicated, being something more than a mere anticlinal. Either then or later, there was a sudden fracturing uplift, accom- panied by outpourings of great volumes of a peculiar rock, having certain affinities on the one hand with the family of trachytes, and on the other with the older granite-porphyries. The rock in question occupies a large portion of the surface of the ridge which culminates in Parkview Peak, a 580 SYSTEMATIC GEOLOGY. point rising more than 12,000 feet above sea-level. The exposures of the Cretaceous rocks indicate mere dislocated fragments wedged in between the enveloping flood of eruptive rocks, the blocks themselves being subse- quently cut through by east-and-west dikes of similar volcanic material. Aside from the supposed Pliocene beds of the Park, evidently a very recent lacustrine series, there is no means of positively determining the age of this eruption. From its intimate relations with the broken, dislocated fragments of Cretaceous strata, it is evident that its eruption was contemporaneous with the fracturing and breaking up of the Cretaceous ridge. It is indeed possible that this took place during the Tertiary period, at the time of the general trachytic eruptions which we have seen reason to place within the Miocene. But it seems quite possible that this great disturbance of the Cretaceous was coeval with the formation of other similar Cretaceous up- lifts, which in the Green River Basin are clearly seen to have preceded the earliest Eocene deposits. Rocks similar to the trachytes of Parkview Peak are found along the Elk Head Mountains, and the identical species has been brought to light by the researches of G. K. Gilbert in the Henry Mountains. In all three of these places, facts necessary to fix the actual date are wanting. In each case this rock accompanies peculiar local disturbances of Cretaceous rocks. Its affinities with the older granite-porphyries, together with its peculiar relations to the Cretaceous, suggest that it is a special group long antedat- ing the other trachytes, and to be assigned to the very dawn of the Eocene period. The east-and-west dikes which cut the blocks of Cretaceous strata, and the main fields of eruptive rock, have withstood atmospheric agencies remarkably well, and rise above the sandstone like stone walls. East of Parkview Peak, near Middle Park Trail, are some isolated hills and cones which Professor Zirkel has described as granite-porphyries. These and the rocks from Parkview Peak are petrographically similar, although the field habit is like that of true trachytes. The yellowish-gray groundmass consists of orthoclase, quartz, and a little hornblende; it is extremely fine-grained and nearly homogeneous. The most remarkable lithological point is the occurrence of orthoclases in perfect individuals, presenting faces such as heretofore have only been found in middle-age TRACHYTES. 581 granite-porphyries of Europe. Besides these orthoclases are a few small plagioclases, hornblende, apatite, titanite, magnetite, and pyrite, the latter having a brilliant, brassy color. From similar rocks at Steves’ Ridge these are distinguished by the microscopic behavior of the hornblende, which gives the green sections characteristic of the older rocks, by the fact that the quartz contains fluid inclusions, but none of glass, and by the presence of pyrite and titanite; whereas the similar trachytes of Steves’ Ridge con- tain ample glass inclusions in the quartz, and neither titanite nor pyrite, and the hornblendes have the usual brown sections. At the same time, the physical likeness of the rocks is wonderfully complete. The modes of oceurrence are similar, both are involved in dislocated Cretaceous strata, and neither can be positively referred to a later disturbance than that which marked the close of the Cretaceous. Further, the Henry Mountain rocks, which according to the observations of Gilbert, cannot be earlier than the end of the Cretaceous, have also apatite, titanite, and fluid inclusions in the quartz, besides both green and brown sections of hornblende. xamina- tion of several of these specimens shows the uniform presence of highly modified orthoclase, which in some cases has the glassy habit of sanidin and in others resembles that of granite and granite-porphyry. From a geological point of view it seems to me most correct to refer this rock to a new group, for which I propose the name of trach ytoid-porphyry, the group representing, both in geological date and in physical habits, the transition between the porphyries, whose occurrence in the Cordilleras has never been known to be later than the close of the Jura, and the Tertiary voleanic series. It is true that one extreme of the group is indistinguishable from the earlier granite-porphyries except by the trachytic mode of eruption, while the other extreme falls within the petrographical limits of true tra- chytes. The writer has examined specimens where the quartzes contained fluid inclusions with moving bubble, while the hornblendes contained ample glass particles. There is a decidedly sudden change between the Parkview rocks and the summit south of Ada Spring, the former occurring as cones, sharp peaks, and long, irregular dikes, while farther west the region is a broad trachytic plateau with escarped faces. The rock south of Ada Spring is 582 SYSTEMATIC GEOLOGY. unmistakably a fine-grained, dark-gray trachyte, the groundmass consisting of sanidin, augite, hornblende, biotite, and apatite ; the microscope showing the augite to predominate greatly over the hornblende. The main plateau shows everywhere dark-grayish and brownish-gray rocks of the same char- acter, in which augite always predominates over hornblende or biotite, and sanidin over the small brilliant crystals of plagioclase. The ordinary rough trachytic habit is well displayed, and the rock in every way contrasts with the trachytoid porphyries of Parkview. The augitic rock is later, and doubtless belongs to the regular Miocene trachyte period. The Archean mass of Park Range suffers an important change of trend about the latitude of 41°, the neighborhood of Davis Peak being the region of deflection. Within this angle and west of the range are the Elk Head Mountains, a group whose position doubtless depended upon the Archean angle. The eruptive rocks of this group consist of trachytes and basalts. The former occur close to the Archean rocks, from Hantz Peak to Camel Peak, and thence extend southward from Steves’ Ridge and Whitehead Peak in a broad field about thirty-five miles long. The highest summit is that of Hantz Peak, which reaches 10,906 feet, while the other three peaks mentioned are all over 9,000 feet, and Whitehead reaches 10,317. The greatest east-and-west expansion is a stretch of twelve or fourteen miles from Crescent Peak to Hantz Peak. The trachytic eruptions come to the surface through a preéxisting uplift of Cretaceous rocks of the Fox Hill and Colo- rado groups. As a whole, these rocks are all sanidin-trachytes. One type is made up of a rough, porous, crystalline groundmass, in which are large, highly modified sanidins, similar to those already mentioned at Parkview Peak. A prominent variety of the true trachytes of this region contains in the characteristic groundmass a great many brilliantly clear, rounded gran- ules of free quartz, which are peculiarly cracked and riven, not unlike some of the quartzes of rhyolite. All the quartz is confined to these large macro- scopical grains, the microscope showing none whatever in the groundmass. It is essentially an accessory mineral, like the tridymite of other tra- chytes. It frequently contains glass inclusions. Besides large sanidins and quartzes, the rock contains hornblende, a little mica, a comparatively high proportion of augite, and, in a few instances, olivine. The outcrops are TRACOYTES. 583 generally in rounded dome-like hills and sharp cones, offering a great con- trast with the more level plateaus of basalt to the west. It is probable that the high ragged cone of Hantz Peak formed one of the centres of eruption. Crescent Peak with its southeast spur and Skelligs Ridge are inter- esting trachytie dikes rising above the neighboring Cretaceous strata, having from their more resisting nature suffered far less erosion than the enclosing sandstones. South of Whitehead Peak the trachytic ridge has a broad gentle slope, extending out to the edge of the valley of Yampa River. The rock of Whitehead Peak is a peculiar grayish-drab trachyte, having an unusual tendency to split into laminee half an inch to an inch thick. In the purplish-gray, fine-grained groundmass are enclosed crystals of sani- din, hornblende, and augite, with large cracked globules of pellucid quartz, a few bronze micas, and numerous reddish-brown spots of serpentinized olivine. The large sanidin crystals, which frequently measure an inch or more in diameter, show a tendency to zonal decomposition. The Sugar Loaf, an isolated trachytic mountain west of Elk River, is composed of a rock of massive habit, containing in a porous gray ground- mass large, highly developed sanidin, hornblende, and black biotite, but none of the quartz which is characteristic of the main trachytie body to the north and west. Upon a spur extending northwest from Steves’ Ridge, not far from Steves’ Fork, is a very characteristic quartziferous trachyte, in which the sanidin crystals are often more than an inch long, associated in the groundmass with biotite and hornblende. Some of the earthy, soft varieties from this locality have an easily decomposed groundmass, from which the large, highly modified sanidin crystals may be readily separated. The surface of the rock here, like that upon Whitehead Peak, is peculiarly pitted where cracked granules of quartz have been weathered out. On the eastern spurs of Steves’ Ridge, which project toward Park Range, occur further quartziferous trachytes containing considerable olivine, together with a free sprinkling of brownish mica. The trachyte of Crescent Peak is mineralogically like that of Whitehead, with the same peculiar habit of splitting into amine of an inch to an inch and a half in thickness. Skelligs Ridge is one of the most interesting developments of trachyte in this curious region. The body of the dike, which is from twenty to fifty 584 SYSTEMATIC GEOLOGY. feet thick, rises out of the soft, grassy slopes of eroded Cretaceous sand- stone to a height of 150 feet, and extends in a northwest direction, with a single considerable break, for five or six miles. The walls are nearly vertical, and the rock is composed of rude columns arranged horizontally. The weathered surfaces have a peculiar, pitted appearance from the drop- ping out of the rounded granules of quartz Mineralogically it is like the rock of Crescent Peak, and is doubtless a continuation of the same erup- tion. The western spur of Crescent Peak is peculiar from the absence of all crystallized secretions from the groundmass. It is an exceedingly com- pact, fine-grained, homogeneous mass, and the only included bodies are clear, brilliant granules of fractured quartz, which are often stained brown by the decomposition of the iron of the surrounding mass. Camel Peak, which is the northernmost point of this great trachytic field, rises like a wedge for 2,500 feet above the valley. The groundmass of the rock is homogeneous, very fine-grained, and in general bluish- gray, containing besides the quartz grains only a few flakes of black mice with occasional hornblendes and augites, the microscope showing that the augites predominate. Upon the freshly fractured surfaces the globules of quartz stand out with a pale, earthy green coating closely resembling the delessite amygdules of basalt. Numbers of specimens collected between Steves’ Ridge and Camel Peak are of this same type—dark, compact rocks, containing quartz and augite, with more or less olivine; a few specimens showing considerable biotite, a high proportion of augite, and but little olivine. Some forms approximate very closely to basalt, and it seems as if the whole northern region represented a sort of transition between the true trachyte period and that of the basalts, the genuine basalts break- ing out later, Hantz Peak, the dominating point of the region, shows about 300 feet below its summit the edges of sedimentary beds, chiefly of sandstones, which are highly altered and in some cases distinctly vitrified. Above these are the mauve-colored trachytes which are seen to split easily into laminze that have generally a very felsitic appearance, the groundmass containing the usual rounded quartz, white, rather decomposed feldspar, a little black mica, and hornblende. The very summit of the rock, however, is made up TRACHYTES. 085 of a white trachyte having some of the characteristics of rhyolite. But it is considered only a local deviation from the general trachytic type. The very sharp, isolated crest has been frequently struck by lightning, and is grooved out in radiating trenches by the force of the bolts. On Slater’s Fork, near its junction with Little Snake River, is seen a small outcrop of trachyte which the valley-erosion has exposed. It is a narrow body extending about a mile and a half east-and-west, passing under the basalts at its eastern termination. It is exceedingly compact, and the groundmass is cryptocrystalline, the eye detecting only flakes of brown biotite. The microscope shows predominating sanidin, plagioclase, abundant augite, and a few olivines, but neither quartz nor hornblende. There is, however, a little distinct nepheline. The trachytes of this eastern Rocky Mountain province may be summed up under two distinct types: that which appears upon Steves’ Ridge, and which in the crystalline form of its unusually large sanidins so closely re- sembles the highly modified orthoclase of granite-porphyries; and the re- markable family of quartziferous augite-trachytes, which are nowhere so well developed in the Fortieth Parallel area as here. Their peculiarity is, that the groundmass contains no microscopical quartz, while large globules, up to one eighth of an inch in diameter, remarkably split and cracked, are very prominent among the crystalline secretions. Olivine is of not infre- quent occurrence, and augite always predominates over biotite and horn- blende. Plagioclase is invariably present, but in smaller amounts than the sanidin. It seems to be a thorough mingling of the constituent minerals of basalt and rhyolite; there being present the sanidin, biotite, quartz, and occasional hornblende, characteristic of rhyolite; and the augite, triclinic feldspar, olivine, and magnetite of basalt. In the northern angle between Green River and Bitter Creek, rising out of the plains of Green River Eocene strata, is a single isolated body of augite-trachyte, presenting abruptly escarped faces on all sides. The soft and easily eroded material around its base shows no traces of local disturbance. The recent washing and erosion of the Tertiary soil would naturally cover up any slight local disturbances, and it is therefore uncer- 586 SYSTEMATIC GEOLOGY. tain whether this isolated mass of trachyte has burst up in situ, or whether it is the sole surviving fragment of a flow. It is uncommon in the geology of the Cordilleras for jets of eruptive rock to burst up through horizontal strata without any orographical disturbance. At the same time it is common to find the fragments of a flow which have escaped general ero- sion; and in the case of Pilot Butte it is impossible to assert positively what its deeper relations may be. In composition it is an augite-trachyte, not unlike those of the Elk Head region. Next to the Elk Head trachytes, the most extensive exposure within our area is that which lies along the eastern base of the Wahsatch, separating it from Uinta Range. A reference to geological Map IIL, on which the relations of the trachyte to the surrounding sedimentary rocks may be clearly seen, will show at a glance that the main line of the trachyte eruption has a north-and-south trend, that it breaks through the de- pressed region between Uinta and Wahsatch ranges, and in passing north- ward cuts a diagonal into the heart of Wahsatch Range. The most im- portant body is that which overlies the Cretaceous and Eocene Tertiary in the neighborhood of Wanship, and extends thence southeastward for thirty-five miles, forming a belt that spreads out transversely eight or nine miles. The Jura, Trias, and Permian, and heavy masses of Carboniferous rock, dip eastward along the Wahsatch, and, passing under a synclinal, rise again upon the end of Uinta Range. From the relative position of the rocks on both sides of the synclinal, it is evident that there has been a fault, and that the end of the Uinta has been elevated above the corresponding horizons of Wahsatch Range. The fault which is thus defined through the older rocks projects southward through the Cretaceous and the overlying Eocene beds, the trachytic eruptions reaching their greatest elevation at the south at Heber Peak, where the altitude is 10,138 feet. North of the synclinal between the Wahsatch and the Uinta the trachytes had a wider spread, extending eight or ten miles northeast from the little town of Peoria. In a northwest direction they recur upon the north side of Parley’s Park, and the northwest trend is continued in outbursts of trachyte which are seen in the valley of East Canon Creek, at its bend ten miles north of TRACHYTES. 587 Parley’s Park, and again at Richville. The entire length of this trachytic vent is therefore about fifty miles. In Kamas Prairie and Provo Valley the Quaternary débris doubtless covers considerable portions of trachytic rock. Both in the region of Heber Peak and again north of Peoria, where an arm of the trachyte comes in con- tact with the Eocene rocks, it is distinctly later than the stratified sandstone. So, too, both the bodies which are seen in the valley of Hast Canon Creek are plainly later than the surrounding Tertiaries. It is the Vermilion Creek or the lowest member of the Eocene with which they are found in contact. There must, however, have been a great amount of erosion along the drainage of East Canon Creek before the ejection of trachyte, as it took place in the bottom of a well eroded canon. In middle Nevada, in the region of Dixie Valley, we have the next later member, the Green River group of the Eocene, overlaid by trachytes. The Bridger group has never been seen by us in contact with volcanic rocks, and the only time-fact about this great Provo trachyte field is, that it occurred either late in the Eocene or during the Miocene. The latter is known to be the age of the western Nevada trachytes, and there are no valid geological grounds for especially doubting that these are contem- poraneous. At the southern end of the outburst they appear to have overflowed the conglomerates of the Uinta group of Eocene, which here represents the same horizon as the Vermilion Creek beds to the north. The conglom- erates, both north and south of the Uinta, in the immediate neighborhood of the trachyte, never contain any trachyte bowlders, which must neces- sarily have been the case if the ejection had been prior to the deposition of the Eocene sediments. In several of the higher ravines in the neighborhood of Heber Moun- tains there are considerable accumulations of varied gravels and bowlders, among which are many fragments of trachyte. These probably belong to the Wyoming (Pliocene) conglomerate, which covers the neighboring ridges. Besides the superficial exposures, which are frequent over the whole tra- chytic field, good sections are obtained in Heber Canon, in the valley of the Provo, on the heights on both sides of Weber River near Peoria, and 588 SYSTEMATIC GEOLOGY. throughout the valley of Silver Creek. In general, the whole eruption was quite free from breccia, and it is remarkable for so extended a field in that it is extremely rich in well crystallized minerals from one end of the exposure to the other. The exceptions to this are on the foot-hills northeast of the town of Medway, where there is a considerable deposit of stratified volcanic ash, indicating that during the early period of the eruption sands and rapilli accumulated in a small lake. The second exhibition may be seen in the valley near Silver Creek, above the head of Provo Canon, where there is a light-gray, trachytic tuff, with a slighly decomposed groundmass and large sanidin crystals, with needles and flakes of mica. On the canon walls between Kamas and Provo are highly porphyritic forms, having reddish, purplish, and greenish groundmasses, containing brilliantly white sanidins, earthy-brown hornblende, and much specular iron, and, in a few instances, considerable bronze mica. On the heights between Provo and the head waters of Silver Creek are some interesting purple and: apple-green trachytes, having a groundmass especially compact and semi-vitreous, in which are abundant glassy sani- dins; dark-brown, dark-purple, and black, more or less altered hornblende, with occasional flakes of biotite, and small, brilliant plagioclases, the micro- scope showing a dark-gray, globulitie base. Farther down Silver Creek, near Kimball’s, a similar trachyte was observed, very rich in sanidins, and having a good deal of plagioclase, hornblende, augite, tridymite, and apatite. And not far from Kimball's Station, directly north of the road, are trachytes of a rusty brick-red color, that have broken through the Cretaceous and Jurassic strata, which are more or less altered by contact with the trachyte. The only peculiarity of the rock is, that the hornblende is a little fresher than usual, and that besides the tridymite there is a large proportion of augite. Comparison of a great number of specimens from the whole field of this extensive eruption shows a single prevalent type; a rather fine-grained groundmass plentifully imbued with a glassy base, which for the most part is devitrified, carrying predominating sanidin, few but brilliant plagioclases, hornblende (often decomposed), and sparing augite; exceptional specimens showing a high proportion of bronze mica. It is a normal sanidin-trachyte, TRACHYTES. 589 in which hornblende exceeds biotite. North from Parley’s Park, about half- way down to Morgan Valley, a body of trachyte occupies the hill slope on the right bank of East Canon Creek for two or three miles. A rather abrupt slope is exposed, made up of distinct horizontal beds, the habit of the rock being decidedly like an andesite. About four miles south of Weber Station, where East Canon opens out into a broad valley, is the northernmost of this chain of trachytic bodies. It occupies a narrow area along the right bank of the stream, and is for the most part surrounded and covered by horizontal Pliocene strata. It con- sists of a very coarse groundmass of sanidin and biotite, with little or no glass base. In the groundmass are highly developed sanidins of brilliant, glassy purity, and shining black biotites. Although it precedes the Pliocene beds which clearly overlie it unconformably, yet a considerable part of this eruption appears in the form of a rough, gritty, trachytic tuff, which must have been ejected when Morgan Valley was eroded to nearly its present dimensions and contained more or less of a lake. The great orographical feature of the Wahsatch is the line of fault and displacement which for a hundred miles has occurred through the heart of the range, severing it into halves, the western of which has been de- pressed to an unknown depth—certainly in the region of Cottonwood Canion 40,000 feet—below the level of the eastern. Nothing is more natu- ral than that this line should subsequently become the theatre of volcanic action. The smallness of the amount of actual ejecta is rather the most remarkable feature of the locality. This great north-and-south fault was crossed by a less powerful but remarkable line of east-and-west strain along the axis of the Uinta Mountains, the intersection of the two taking place in the granite region of the Little Cottonwood. It is here, in what are called the Traverse Mountains, that the most considerable trachytic eruptions have taken place. South of the granitic body of Lone Peak, a spur of hills projects west- ward to the middle of Jordan Valley, and beyond the river rises against the foot-hills of the Oquirrh. In the immediate valley of the Jordan the volcanic rocks are covered by accumulations of Quaternary and the ter- races of the Bonneville Lake period. The Traverse Mountains have 590 SYSTEMATIC GEOLOGY. a trend a few degrees south of west, or approximately at right angles to the northwest trend of the great trachytic series that lies along the eastern base of the Wahsatch. The fissure that permitted the escape of these rocks started out from the great Wahsatch fault where the Cambrian series comes in contact with the underlying Archean granite, and continues through the unknown rocks deeply buried beneath the valley of the Jordan, finally cutting through the quartzites and limestones of the Oquirrh. The hills east of the Jordan rise about 1,200 feet above the level of the plain, and probably a considerable portion of their bulk is the continuation of the Archzean and granitic spur; but it is all covered now by the broad field of trachyte which occupies the whole surface. West of the Jordan the trachytic exposure is on a larger scale, the hills rise 2,000 feet above the valley, and the trachytes are seen abutting directly upon the Weber quartzites of the main ridge. Along the eastern foot-hills of the Oquirrh, the trachytes extend north- ward as far as Bingham Canon. Near the Wahsatch, on the eastern end of the group of hills, the trachytes are dark-bluish, reddish, and brownish rocks, composed of but a small amount of groundmass, in which sanidin and biotite are the principal secretions. There is so little groundmass that certain specimens have a granitoid look, suggesting some of the nevadites. While sanidin and biotite are the prominent constituents, there appear small plagioclases, unaltered hornblendes, and considerable olive-colored augite, and the microscope reveals apatite and magnetite. In immediate contact with the Lone Peak granite, the rock is an earthy, greenish-white mass, with the feldspars kaolinized and the groundmass decomposed beyond recognition. The western body of mountains beyond the Jordan consists also of sanidin-trachytes, rich in glassy feldspar and bronze mica, and possessing a very little hornblende. Here at the northern limit of the main body, at Rose Cation, hornblende and mica are more abundant and sanidin less, Throughout the middle of the group are dark, heavy, hornblendic tra- chytes, in which the proportion of plagioclase rises very nearly to equality with the sanidin, and the rocks approach the andesitic habit. Near Salt Lake City, about two miles up the canon of City Creek, OHV] TRACHYTES. 591 the hills on either side of the stream are for a short distance (not over a mile and a half) formed of dark, reddish-brown trachyte. All around the sides of the body the Eocene Tertiaries are extremely soft, and the earthy accumulations effectually hide the relative ages of the two. There is little doubt, however, that the trachyte, like that east of the moun- tain, is more recent than the Eocene beds. This outburst is directly on the line of the great fault, which to the south has cut off the ends of the Paleozoic and Mesozoic strata, and to the north has split down the body of Archean rocks which forms the nucleus of the range. The rock shades from reddish-gray into light pinkish-gray, deepening in some cases into a dark chocolate. It has a rough, coarsely crystalline groundmass of feld- spar, hornblende, and biotite. Among the macroscopical crystalline secre- tions are abundant sanidin and a high proportion of plagioclase, deep-brown hornblende with the characteristic black border, yellowish-brown mica, and pale-green- augites. The microscope also shows an abundance of tridymite and quartz. An interesting microscopical peculiarity mentioned by Zirkel is the occurrence of minute fluid inclusions, with moving bubble, together with gas cavities in the pale, clear interior of certain hornblende sections. The augites contain none of the magnetite grains so common in basalts. Here again is one of those rocks which contain the minerals both of basalt and of rhyolite. Partly on account of the great geological interest of the region and partly as a study of canon erosion, I made in the year 1869 a short expedi- tion from Camp Halleck, Nevada, northeastward, by way of Thousand Spring Valley, to the basin of Snake River. In the lower and western portion of the same great interior basin there is an abundant exposure of lacustrine Pliocene rocks rich in a fauna comprising mammals, fishes, and mollusks, and also charged with the remains of arborescent vegetation now silicified. One of the most interesting features of that region was the inter- calation of sheets of basalt in the midst of the Pliocene series. This obser- vation, hastily made in travelling by myself, was afterward confirmed by Prot. O. C. Marsh. Pliocene rocks in disturbed positions form the divide between the basin of Utah and that of the watershed of the Columbia. The western exposure of these rocks on the divide in the region of Toana 592 SYSTEMATIC GEOLOGY. and westward as far as Bone Valley, consisted, as was shown, of rhyolitic glassy tuffs. We have seen, when examining the Truckee Miocene strata of the Kawsoh Mountains in western Nevada, that in the process of up- heaval the Miocene trachytic tuffs were invaded by rhyolites which accom- panied the post-Miocene disturbances. The rhyolitic tuffs of northwestern Utah and northeastern Nevada, already proved to be Pliocene by carrying fossil vertebrate animals referred by Leidy to the age of the Niobrara Plio- cene, are still further confirmed as such by the nature of their material, which belongs to the age of the rhyolites, which from the data in the Kaw- soh Mountains we are able to place at the beginning of the Pliocene. We have, therefore, in the region of the divide between the Great Basin and that of the Shoshone, early Pliocene beds of volcanic origin, carrying the Niobrara fauna, and in Boise Basin two divisions of lacustrine Pliocene, both horizontal, one previous and one subsequent to certain of the basaltic eruptions. It is all but certain that the sub-basaltic Pliocenes are the equivalent in age of the rhyolitic Pliocene division of western Nevada. The post-basaltic Pliocenes of Boise Basin are to be directly correlated with those of the Humboldt valley and much of the Great Basin country. The eastern portion of the Shoshone Basin has for its surface a broad, nearly level field of black basaltic beds which are seen by the magnificent exposures of Snake Canon to overlie an undulating, hilly surface of prior trachytic eruption. In this portion of the basin no lacustrine sediments are seen, and it is evident that none were laid down here, since the underlying trachytes belong to an age prior to the earliest Pliocene deposit. Through- out the great basaltic plain is traced the sinuous line of the Shoshone canon, a gorge cut sharply down through the volcanic beds from 400 to 700 feet. Geologically and scenically the neighborhood of Shoshone Falls is the most interesting point of the cafon. Plate XVII. is a view taken from a point a little below the surface of the plain on the left bank of the river, looking east. 'The horizontal sky-line is seen defined by the basaltic tables and the middle of the field is occupied by a general view of Shoshone Falls. Plate XVI. is a nearer detailed view of the Fall itself plunging over a trachyte cliff 190 feet high. The volume of the river in its fullest stage ‘an TRACHYTES. 593 is far less than that of the Niagara, but the breaking up of the brink of the Falls by deep reéntrant angles, renders the cataract one of the most picturesque in the world Plate XVIII. is a view down the gorge looking over the top of the fall, and is of especial interest as showing the narrow, abrupt character of the cation. Plate XIX. is a detailed bit on the left bank of the canon, showing the light-colored, easily eroded trachyte mass, with a vertical exposure of about 200 feet, capped by the level sheets of basalt which extend down the river uninterruptedly for many miles. From a few miles above the Shoshone Falls the river was followed for ten miles of its downward course, and although the exhibition of under- lying trachytes was almost continuous for that distance, no variation in the type was observed. The chief interest of this region, besides the evi- dent relations of the two types of the volcanic rocks, is the great horizontal extent of the basaltic beds. Whether they flowed from the two flanks of the valley, or from far eastward in the region of the Teton group, is un- certain, but the exposure is nevertheless of interest from the great distances that single thin sheets of basalt are seen to have flowed. The well known power of retaining a high temperature and of long continued fluidity on the part of the basalts, is here displayed to remarkable advantage. From a brief inspection it is my belief that single sheets have flowed at very gentle angles for fifty or sixty miles. The region is further interesting as a proof of the intensity and extent of post-basaltic erosion. One is not surprised, in studying the flanks of steep mountain ranges, to find them scored by profound Quaternary cations; but to see a long, level lava plain gashed by a cafion from 300 to 700 feet in depth shows an energy on the part of the slowly flowing rivers which is positively marvellous. On the eastern flank of the Aqui Mountains, at the base of Bonneville Peak, near the parallel of 40° 30’, is a small region of trachyte, exposed at the forks of South Willow Creek. The geological characteristics are well shown on the western half of Map III., where it is seen that the range is composed of a body of Lower Coal Measure limestones thrown into a curve which on the eastern edge of the mountains abruptly bends over into a steep, easterly dip. The western half of the range is a great body of ‘ambrian quartzites faulted wp into a position even higher than the geolog- 38 K 594 SYSTEMATIC GEOLOGY. ically superior limestones. Through the sharp flexure of the limestones a fissure has occurred, from which a body of trachytes has outpoured, cover- ing the eastern slope quite to the plain of the Quaternary desert. There are no recent rocks anywhere in the neighborhood to afford a clew. to the date of the eruption. North and south of the entrance of Willow Caton the hills are covered with accumulations of red and gray trachytic ash. The groundmass is fine and porous, varies from reddish-gray to white, and con- sists of an intimate mixture of crystals of feldspar, both orthoclase and pla- gioclase, together with a great deal of globulitic glass. Macroscopically the crystalline secretions show an enormous preponderance of distinctly hex- agonal biotite laminze and a few hornblendes, the microscope revealing a little apatite. An exposure of trachytic rock is seen at White Rock Springs, near the southern end of Cedar Mountains. The ridge already described as a double fold of Lower Coal Measure limestones is marked by the occurrence of a body of andesite at the important angle of flexure of the range. Directly east of the andesites occurs a small body of trachytes occupying an east- and-west region entirely enclosed by limestones, except the very eastern extremity, which passes under the Quaternary of the plain. The greater part of this exposure is of rough, reddish, trachytic breccia, above which rise the white rocks from which the locality takes its name. They are domed masses, about 300 feet high, of grayish-white quartziferous trachyte. These bosses of rock have such smooth, even sides that they are exceedingly difficult of access. The rock is a crystalline aggregation of sanidin (the individuals of which sometimes reach an inch in length), brilliant black prisms of hornblende, flakes of biotite, and cracked, rounded granules of quartz. It shows a close resemblance to the family of quartziferous trachytes of Elk-Mountain. It would seem that all the trachytes of the Salt Lake region naturally group themselves into two main systems of eruption—the great body east of the Wahsatch, with its northern continuation, which marks one of the orographical faults of the Wahsatch; and that of the Traverse and Aqui mountains and Cedar Range, which, though irregular in trend, is practi- cally at right angles to the first-named series. TRACHYTES. 595 Over the whole broad desert lying to the north and west there are no trachytes, with the exception of a small body on Peoquop Creek, in the northern part of the eastern half of Map IV. Peoquop Creek drains through Thousand Spring Valley a few miles north of the Pacifie Railroad, and traverses a low region of which the geology is quite simple. It consists of island-like spurs and hills of Weber quartzite, surrounded and overlaid by horizontal strata of Phocene. Through the quartzites has outpoured a small body of trachyte,-over and around which the Pliocene strata have been deposited nonconformably. It forms a long north-and-south ridge, with several dome-like points. The rock is more or less decomposed, and is characterized by pores and cavities filled with both calcite and chal- cedony. It is made up of sanidin, plagioclase, and hornblende. The two feldspars are present in about equal proportion, and the rock is to be classed with the earlier plagioclase-hornblende-trachyte which is characteristic of the region of Washoe. Humboldt Range, although the most extensive and lofty in Nevada, is conspicuous for its paucity of volcanic rocks. Minor rhyolitic eruptions have taken place in the northern part of the range, but the only trachytic occurrence is a small body a few miles north of Cave Springs on the east- ern base of the range. Here a limited flow of grayish, highly crystalline trachyte has burst out through a fissure in the Lower Coal Measure lime- stones, its appearance being accompanied by an unusual amount of shatter- ing of the limestone rocks. ‘The exposure isa low, rugged spur, surrounded on all sides by limestone. It is essentially a sanidin-biotite-trachyte, although triclinic feldspars and hornblende are present in small quantities. The plagioclases are noticeable macroscopically for their great size and bril- liant surfaces. The microscope reveals prisms and microlites of apatite, besides quite fine particles of hornblende entering into the groundmass after the manner of powdered hornblende in propylite. Rare macroscopic quartzes are present, but the microscope detects none in the groundmass. In the upper valley of Susan Creek are two small bodies of trachyte, separated from each other by horizontal strata of Pliocene and the Quater- nary valley deposit, both of which are later than the trachytic eruption; and it is most probable that the two trachyte bodies have a connection beneath 596 SYSTEMATIC GEOLOGY. the Pliocene. More recent rhyolites overlap both the trachyte bodies. Of these two exposures, that on Coal Creek, at the base of Seetoya Range, has a colorless feldspathic groundmass in which are enclosed sanidins, plagi- oclases, and a few biotites, the microscope revealing a little titanite. The more southern of the two outcrops is a pale-reddish, earthy trachyte re- sembling domite. Its base is decidedly glassy and considerably globulitic, and carries much fine crystalline feldspar. The most remarkable points about this rock are, that it contains, even macroscopically, rose-colored gar- nets in granular aggregations, and that there are also disseminated through the groundmass bright prussian-blue, hexagonal grains, referred by Zirkel to haiiyne. Zirkel remarks (Volume VI., page 151) that the occurrence of such garnets in trachyte is only recorded besides of specimens from the island of Ischia. One of the most extensive as well as interesting trachyte localities in Nevada is that in the northern part of Pinon Range. The lofty body of mountains here at its northernmost extremity consists of an anticlinal with a trend a little east of north. This broad fold involves strata of the Cam- brian, Silurian, Devonian, and Carboniferous ages. The continuity of the great axis is suddenly broken by an east-and-west fault, which has been the theatre of deep dislocation. The group of hills to the north, formed of the united River and Elko ranges, in which the most ancient neighboring rocks are the Uinta quartzites, has retained its natural level, while the Pinon anticlinal has been lifted from a great depth, exposing the lower strata. Besides the east-and-west break described, another powerful fissure passes in a meridional direction along the eastern base of the range. From out of both these cracks an enormous trachytic flood has been ejected, surrounding and burying the edges and ends of the uplifted Pinon strata. In Dixie Pass the sharply eroded edges of the Paleeozoic strata plunge suddenly down beneath a series of rolling trachytic hills, which sweep around southward, coming in contact successively with the Devonian and the Silu- rian of the western half of the Pinon anticlinal, then with the Cambrian nucleus of the fold, and afterward to the south bounding the Silurian and Devonian of the easterly dipping member of the group. There is no- where a more interesting instance of the direct and obvious connection of ’ . 4 . i . SS r ‘ i, ‘ 7 o ‘ a ae. 2 : & BF ne ai aM yan sai,’ * : ; Hn TRACHYTES. 597 volcanic eruption with mountain dislocation. The trachytes thus exposed extend about twelve miles north-and-south and four to six miles east-and- west, the surface being high, rolling ridges and spurs, those bordering on Dixie Valley forming a chain of characteristic dome shapes. Along their eastern margin for a considerable distance these trachytes overlie the up- turned caleareous shales of the Green River Eocene, and to the south are themselves overlaid by a subsequent flood of rhyolite and the horizontal Pliocenes of Huntington Valley. The higher spurs and domes all show a rounded form and an absence of any conspicuous bedding. The general char- acter of the predominating eruption was that of broad, massive accumula- tions, and even the most isolated and conoidal of the trachyte domes show no evidence of the structure of a true voleano. The main material, and that of all the later eruption, is of brownish and reddish sanidin-trachyte, with a very coarse, rough, friable groundmass, composed of vitreous sanidin and magnesian mica, in which a multitude of the larger crystals of both are in- cluded. There is a very close resemblance between certain specimens of this rock and the Sugar Loaf trachytes of Washoe. They exhibit the same method of mingling the biotite and sanidin, and the latter is in the same abun- dantly fissured condition as the former. At several places near the Cambrian and Silurian foot-hills, and along the northern slopes of Dixie Hills, deeper erosion has exposed a lower family of trachytes These are characterized by the sparing presence of biotite and the decided predominance of horn- blende, which occurs, both in brilliant black crystals and in earthy, gray prisms, associated with plagioclase which equals or exceeds the sanidins. Among these hornblendic trachytes the groundmass is far more compact, the rock is evidently bedded and has a habit approximating to that of ande- sites. The only very similar rock obtained in the Fortieth Parallel area is that which has been described in Volume IIL, Chapter IL, from the cross- spur at Virginia and Washoe, from which this only differs in having rather smaller plagioclase crystals. In fracturing the rock, it is noticeable that it breaks most easily parallel to the planes of bedding, and that all the larger crystals are arranged in such planes that the surface of a fractured speci- men usually displays several split hornblende prisms with brilliant black surfaces and large slabs of feldspar. It is interesting to note that this 598 SYSTEMATIC GEOLOGY. plagioclase-hornblende-trachyte, which verges very near the andesites, is older than the sanidin-biotite-trachyte, the same sequence being observed at Washoe. At Palisade Cation the Humboldt has worn a gorge through an area of trachyte about five or six miles from north to south by four from east to west, along the course of the river. The hills to the north rise 1,500 to 1,800 feet high, and to the south reach about 1,000 feet. In the very middle of this trachytic exposure, in a ravine which enters the canon from the north, erosion has laid bare an underlying massive andesite, which again occurs on Emigrant Road directly north of the northern limit of the trachyte body. It is plain that the fissure which gave vent to the trachyte was a reopening of the weak line of the andesitic break. So many oro- graphical periods had disturbed the whole Cordilleras prior to the Tertiary, that there were innumerable lines of weakness, which the earlier Tertiary eruptions easily found; and although the period of each successive volcanic family enlarged the limits over the previous one, yet in many instances the later voleanic rocks are found to follow the fractured lines of their immediate predecessors, as in this case. Although the whole body is essentially a group of sanidin-trachytes, the hills north and south of the canon present some different varieties. The cliffs along the southern wall are of normal sanidin-trachyte; the brownish-gray groundmass, composed of sanidin and biotite, containing larger crystals of these two minerals. The microscope reveals the presence of a few hornblendes and apatite. Upon the northern wall of the canon, in the hills which form the main eruption for several miles, are observed more recent trachytes than those just mentioned. They have a light-gray, porous groundmass composed of biotite and sanidin, in which are remarkably perfect yet earthy prisms of hornblende, together with interesting casts of these crystals where all but the granulated border-material of the hornblende has been removed. The sanidins always obviously outnumber the hornblendes. The body of quartz-propylite which extends along the ridge of the Cortez Mountains, south of Wagon Canon, is margined along the west by a narrow exposure of sanidin-trachyte, which to the west is covered by rhyolites. The groundmass resembles that of propylite, from the amount TRACHYTES. 599 of small hornblende crystals that enter into its composition. Small sani- dins, lamin of partially decomposed biotite, and a few well preserved hornblende crystals make up the list of crystalline secretions. But for the predominance of sanidin over plagioclase, the rock, from the peculiar dispo- sition of the hornblende, would be closely related to the propylites. The microscope shows in the biotites an interesting interposition in the laminz of colorless muscovite. Zirkel also describes the feldspars as being covered with a glittering dust, the product of alteration, and probably calcite. The instrument also reveals apatite. Between the trachyte and the neighboring volcanic rocks, the question of age is too obscure to allow of any definite conclusions. The Wahweah Mountains, of which only the northern parts come within the limits of our map, lie, as do most of the Nevada ranges, between two open desert valleys. That upon the west is much the lower. Large parts of the Wahweah group are formed of tabular fields of trachytic rocks which all slope toward the lower or western valley. Above the general plateau-like surface rise rugged hills and points, and the slopes are scored by deep ravines and canons, which afford excellent exposures. The northern part of the mountains is composed of granite, overlaid by Silurian and Devonian strata, which, in extending southward, pass beneath the great trachytic covering. Hxamination of the specimens collected here discovers a rich variety, representing nearly all phases of the trachytic family. There are quartziferous trachytes which in the ordinary microcrystalline ground- mass carry brilliant sanidins, some fresh plagioclase, and well developed biotite, with large hexagonal crystals of quartz surrounded by a fibrous spherolitic crust. A second variety is a typical sanidin-trachyte with large sanidins, abundant biotite, plagioclases, and a little hornblende with which decomposition has usually proceeded very far. The microscope reveals apatite and haiiyne. The plagioclase-hornblende-trachytes, in which triclinic feldspars rise nearly to the proportions of sanidins and the hornblendes greatly exceed the biotites, also occur, and last of all comes true augite-trachyte with a dark, homogeneous groundmass, enclosing large numbers of plagioclases, macroscopic augites, and microscopic apatite. The relative ages of these varieties were not worked out. 600 SYSTEMATIC GEOLOGY. On Jacob’s Promontory, a little group of hills in Reese River Valley, north of Jacobsville, intimately associated with some rhyolites which have partially overlaid it, is a small body of gray trachyte, which besides the prevailing sanidin contains some plagioclase and augite, with, however, a predominance of hornblende. The habit of this rock resembles the andesitoid gray trachytes of Virginia. Not the least remarkable among the isolated outbursts of trachyte is that which occurs on the heights of Havallah Range, near Cumberland, having poured out near the junction of the Triassic quartzites with the Star Peak group. The general inclination of the structural lines of the trachyte is to the east, and its summit is that of a high ridge rising in several rude conical points. The rock itself is a very porous sanidin-trachyte, of a dull gray groundmass, carrying sanidins from an inch to an inch and a half in length, many of the crystals being dislocated and broken. Small flakes of brownish biotite are scattered through the groundmass; and that which above all distinguishes this trachyte is the occurrence of large limpid gran- wes of quartz, a mineral which does not enter into the composition of the groundmass. It is most nearly allied to those trachytes of the Elk Head Mountains, in Colorado, which also carry an abundance of macroscopical quartz, but none entering into the rather basic groundmass ; the quartzes in these instances playing a peculiar réle, since they are enclosed in a ground- mass by no means either as acidic or as glassy as in the rhyolites. In Pine Nut Canon, of Pah-Ute Range, east of Chataya Peak, is a body of trachyte which has broken out east of the diorite, immediately followed eastward by subsequent eruptions of rhyolite. The habit of the rock is distinctly trachytic. The colors are gray, yellow, and brown. For the most part, the groundmass is a combination of feldspar, opacite, and ferrite, and for a limited portion of the body is decidedly rhyolitie in type, con- sisting of axially fibrous bands separated by masses of felsitic substances rich in ferrite and opacite. The rock contains no quartz; but the sanidins, reaching a quarter of an inch in diameter, are peculiarly brilliant in lustre and at times are drawn out, showing an almost silky fibre like the threads of pumice. The outcrop is limited, occupying a low position on the flank of the range, and has no orographical importance. TRACHYTES. 601 The chain of mountain elevations consisting of the Pah-tson and Kamma groups, really part of the Montezuma system, is continued north- ward by a range of hills having its rise a little north of Indian Spring and extending beyond the northern limit of Map V. The main body of the southern end of the range is formed of trachytes, which tower above the desert valley of Quinn’s River about 3,500 feet. The culminating summit and the ridge extending northward, as well as the abrupt, promontory-like southern front of the range, are made up of sanidin-trachytes, which, in turn, are broken through and overflowed on their western base by rhyo- lites. At the eastern base of the hills, directly east of the culminating summit, the trachytes are seen to overlie the slates of the Jura, while upon the west they are indistinctly connected with the upturned Miocene beds. The trachyte itself is of a variety of purplish-red colors, having a decidedly conchoidal fracture. It is mostly very fine-grained, consisting of a ground- mass of sanidin, opacite, and magnetite, in which are embedded no macro- scopic crystals except a few small, brilliant sanidins. A small and rather unimportant trachytic outcrop occurs in the low foot-hills at the northeast point of the Kawsoh Mountains, directly oppo- site Carson Lake. Here, rising above the Quaternary desert slopes, are low hills a few hundred feet in height, which above are conspicuously capped with black basalt. The material of the hills is a fine-grained sani- din-trachyte, of a dark, grayish-brown color, with often a dull earthy exte- rior. Indistinct beds make up the mass of the hills. Lithologically there are no points of interest about the trachyte, except that it is rather com- pact, and when undecomposed breaks with an unusually lustrous fracture, and contains in the gas-cavities and cavernous spaces considerable amounts of tridymite. Professor Zirkel, who calls attention to this fact, also notices blood-red laminz of specular iron. Of the trachytes of Lake Range, which evidently occupy a consider- able portion of its body, only those bordering Pyramid Lake and the ex- tension of the same system at Anahé Island have been examined. The western slopes of Lake Range, and the mass of trachyte of the island itself, are rugged piles, showing little or no tendency to lines of flow or bedding. The mountain surfaces are more or less eroded by ravines, which display 602 SYSTEMATIC GEOLOGY. the rough, dark slopes of trachyte. Under the hammer the rocks of this region break with a rough, hackly fracture. In the hand specimens they are almost always of dark grayish-brown or reddish-brown colors, the groundmass consisting of fine sanidin with magnetite, ferrite, and opacite, in which are frequent large, vitreous sanidins and occasional but rare bio- tites and hornblendes. Of the trachytic hills which form the northern part of Virginia Range where it descends to the level of Mud Lake Desert, Mr. Hague says :* “North of the basaltic body, Virginia Range terminates in a group of low hills, which border Pyramid Lake on the northwest and connect with the southern end of the Madelin Mesa. Astor Pass cuts through these hills, connecting Pyramid Lake with Honey Lake Valley of California, and lies below the level of the ancient Lahontan Lake, the calcareous tufas covering the flanks of the hills, and showing conclusively the flow of those alkaline waters westward beyond the boundary of Nevada. “On the geological map, these hills are colored as trachytes; it is probable, however, that rhyolites are represented here; indeed, the entire group belongs to that class of rocks which stands on the border line between these two types of acidic rocks. They are characterized by reddish-brown and gray colors, and a decidedly crystalline texture, with the individual min- erals usually well developed. One of the most striking rocks of the region, and one characteristic of Astor Pass, is found near the entrance of the pass, about four miles northwest from Pyramid Lake, where it forms broad table-like masses. The prevailing color of its groundmass is brownish gray, in which, forming the greater part of the rock, are porphyritically enclosed crystals of feldspar, mica, hornblende, and quartz. Many of the feldspars have a dull white color, quite unusual in rhyolites, and are fre- quently three quarters of an inch in length, carrying impurities which may be recognized by the aid of an ordinary magnifying glass. Mica is very abundant and of a brilliant black color, while the hornblende, which is also black, plays quite a subordinate part. The quartz-grains are large, but are by no means frequent, and resemble those usually found in that some- what limited group of quartz-trachytes; that is to say, they appear more * United States Geolog cal Exploration of the Fortieth Parallel, Volume Il., Chapter V. TRACHYTES. 603 like an accessory mineral than a primary constituent of the rock. They are quite clear and colorless, and apparently free from microscopical im- purities. Under the microscope, mmute crystals of apatite may be recog nized. The presence of quartz and the microscopical structure of the groundmass relate this rock to the rhyolites.” The most important body of trachyte upon Map V. is that which is displayed in the canon of the Truckee, and which forms the body of Vir- ginia Range thence northward to Pyramid Lake. The summit and slopes of this elevated mountain body are for the most part made up of broad, thick beds of dark earthy-brown and reddish-brown trachytes. From Ormsby Peak, an elevation of 9,388 feet, down nearly to the shores of Pyramid Lake, are deeply scored canons which show lofty, rugged slopes made up of the edges of heavy trachytic beds. With nothing like the evidences of flow that one sees in many rhyolitic regions, there is never- theless a tendency to form sheets, and a tendency of the sheets to slope both to the east and west and down the flanks of the range, the general impression being that of a body having its source of outflow near the heart of the range, with each paroxysm of ejection superposing a new bed which declined slightly toward the plains on either side. A cross-section of these trachytic tables would show a low, broad arch, resembling the curve of a flat anticlinal. This structure, very common in the basaltic ridges of the region, is certainly indicative of a considerable amount of fluidity retained for some time after the actual delivery of the trachytic matter from the vol- canic vent. More commonly the trachytic eruptions are distinctly structure- less—that is to say, they betray no lines of flow and no bedding by which the material may be traced to the region of vent. This arched ridge, how- ever, plainly shows the existence of a central fissure following approxi- mately the axis of the range out of which the still plastic trachyte poured, and from which it flowed down to the east and west. This field of trachyte surrounds and overflows the melaphyres, propylites, andesites, and dacites of the Berkshire Canon region, makes an island of a summit of diorite south of Sheep Corral Canon, and forms all the low hills bordering the bot- tom of Truckee Canon from Clark’s Station westward nearly to Wads- worth, except in the lower part of the canon, where a deeper erosion has 604 SYSTEMATIC GEOLOGY. laid bare the earlier propylites and diorites. Upon the eastern flank of the range, and in the region of. Spanish Peak, rhyolites have broken out upon both sides of the trachyte, and toward the south it is completely overlaid and bounded by deep and extensive accumulations of gray basalt. A considerable variety of trachytes is found in this great field, of which the following are some of the more important and interesting. The trachyte which appears upon the south side of the lower portion of Truckee Canon, occupying an intermediate position both as to age and superposition, is a light-colored, friable rock, containing a considerable amount of glassy base, varyingly devitrified, in which are embedded sani- din, hornblende, and biotite. The glassy material and the sanidins are sometimes slightly fibrous, suggesting a tendency toward pumice. Besides these minerals, the microscope discovered to Professor Zirkel augite, apa- tite, and biotite. The rock, therefore, owes its interest to the concurrence of augite and sanidin. On either side of the river north of Truckee Ferry is also a sanidin-trachyte, rich in magnetite, but containing neither augite nor magnetite.* Directly overlying and immediately subsequent in age to these dark purple sanidin-trachytes are beds of dark, loose, reddish and brown trachytic breccias, containing blocks up to the size of a foot or two in diameter, the whole held together by a friable mass of trachytic rapilli and fragments. It is noticeable that a small proportion of augite is found in all the hand specimens we collected. Directly over this are lofty blufts with several hundred feet of precipitous front, composed of a pure gray augite- trachyte varying from light ashy-gray to dark, almost basaltic shades. It is distinctly bedded in horizontal tables, and would at once pass for a rather acidic basalt. More than any other trachytes of massive eruption in the Fortieth Parallel area, this occurrence displays the distinct habit of a sheeted flow, a habit ordinarily confined to the true basalts, the augite-andesites, and rare instances of hornblende-andesite which came to the surface in an exceedingly fluid condition. The joinings and superficial cracks of these gray trachytes are perpendicular to the horizontal flows, producing the ordinary bluff edges characteristic of basalts. The rock itself is of an ex- tremely fine-grained eroundmass, in which only a few feldspars can be dis- to} oO ’ v } * For analysis, see Volume II., page 833. SE “sisAyeue jo Jaquinyy 144 145 146 147 148 149 TABLE OF CHEMICAL ANALYSES. X.—A.-UNITED STATES GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. Trachytes. % ee e a ; Oxygen ratio of—| 5 “4 sp Locality. Analyst. Si At Fe Fe | Mn | Ca Mg | Na K Li Ss Total SS | | 20,0 Es =| ‘ gravity. R/|RIg De Zz = mio st 143 | Truckee Ferry, Nevada - - - - | R. W. Woodward 50-36 17-00] 6.12] 3.84] 0.30] 8.85] 3.02] 3.21] 1-95] - -|CO?+HO] 5.35] 100.00] 2.6,2.7 | 58:]| 9.75] 26.86] 0.579 26.86 7.92 z.83 | 0.85 | 0.06] 2.53 miaxiilimmo.83 | 0.33)| . ee mies a 8 aa peel fede o || as. x Gs wy = 5 5 9 a 50:03] 16.99| 6.05] 3-86] 0.42] 8.81] 2-98] 3.33] 2-27| - -|CO?+HO] 5.26] 100.00 ga 5.89 | 9.73] 26.68] 0.585 26.68 7-92 1.81 0.86 0.09 2.5r 1.39 0.86 0,38 ot oe oe Sores ie else lee ted | ae 144 | Ridge of Divide between Slater’s and @ 53-12) 14.54] tr. 6.01 tr. 6.01 e|| Keely) oo secant -58| 100.02 |2.7, 2.7, 2.7] 668] 6.77] 28.33) 0, Southwest Fork of Snake River. 28.33 G7 || ao BEB || o 9 1.72 Bs 0.78 ° 2 FP aaa ce G0 Us b yi alpsoun 4 oe q GF @ 8 e 53:25| 14-42] tr. 6.00] tr. 6.01} 5-06] 3:13) 4-58] - . Do oso 7.63| 100.08 a 8 6.66 | 6.72] 28.40] 0.471 28.40 6.72 tote 1.33 aly 1.72 2.02 0.81 0.78 races Sens b fis ae ee ‘eure || gated bears | eae 145 | Leucite Hills, Wyoming - - - - Gs 54.42| 13.37| 0.61] 3:52) - + | 4.38 6-37] 1.60] 10.73] tr. | CO? 1.82 2.76 99-58 |2-2, 2.2, 2.2] 6.8} 6.4r| 29.02] o.455 29.02 6.23 | 0.28 | 0.78 | . . r.25 | 2.55 | or 7:82 |e eee a ome ett polska Aull ow Gi 3 Sag or w Geile nic ai oe) 6 o|] > || /GyAlibwersts 3. a 6 4 50 146 | Purple Hill, Truckee Canon, Nevada « 6.51| 19.61 -10| 0.98| 0.11 6 tr. Sates 0.40] 100.0 2.0, 2.6 4.97 | 10.67] 30.14] 0.518 Dees) 9 5 9 3307] 4 5 5) 30.34 | 9.74 z.53 | 0.22 | 0.02 0.62 SS iieG Salina « “« “ 56.45] 19-85] 4.95] 0.97] 0-11 3:84. tr. Ce Ro 0.38] 100.06 A ae 4:95 | 10.73] 30.10] 0.520 30.10 | 9.25 1.48 | 0.21 0.02 0.65 oo + is i= _ “ ’ a +e oe RHYOLITES. 641 fied mass. From the desert plains upon either side the rhyolites rise to a height of 1,000 feet, and are made up of a wonderful variety of colors and forms. Taken as a whole, they are finely microfelsitic; the ground- mass, made up of quartz and sanidin, containing singularly few secretions of macroscopic crystals. Small but brilliant sanidins, and quartz both black and colorless, are the only visible minerals. The earliest eruptions were of gray and pink breccias, altogether made up of the fine felsitic materials. These breccias formed a considerable portion of the whole eruption, and are noticeable for the sharp, angular character of the fragments which they enclose. The proportion of angular fragments to the magma is ex- ceedingly large. The ejection was really a rush of finely crushed rock, merely given a sufficient fluidity to insure motion by a scanty magma of finely felsitie material. White and flesh-colored felsitic and porcelaneous rhyolites broke through the breccias, and these again were invaded and capped by gray pearlitic types. Among these hills were collected some of the most singularly beauti- ful lithological products that can be imagined—ribanded varieties made up of chocolate-colored, pink, salmon, white, and pale-green. Upon the southern slope of the hills are porous, earthy types in which a kaolinic decomposition of the sanidin has occurred. The northernmost limit of this flow, directly south of the outlet of Humboldt Lake, shows some interesting rhyolites containing abundant crystals of sanidin and triclinic feldspars. A dark, chocolate-colored variety rich in biotite, and a further reddish-brown variety, with dark, chocolate- colored spherolites, are among the interesting types. Striped and banded varieties, resembling the ribanded jaspers, are very common here, with a cream-colored and gray groundmass, lined with red and purple. These northern foot-hills are deeply fissured, and at certain places there has been a great deal of local decomposition, the cavities of the rock being filled with carbonate of lime, and many of the fissures being incrusted to the thickness of a quarter of an inch with common salt. Analyses of two types are given in the table of analyses at the close of this section. These analyses are of interest as showing that two specimens of the same outburst, of widely diverse appearance, are really chemically identical, and that the divergence 41 Kk 642 SYSTEMATIC GEOLOGY, of texture and color may be ranked as accidental results, depending upon phenomena of devitrification and decomposition. The only other eruptive rock associated with the Mopung rhyolites is a small body of basalt near Mirage Lake, which overflows the western terminus of the rhyolites. Next to the great rhyolitic area made up of Augusta and Shoshone ranges and their northeastern continuation, the most interesting and at the same time the most extensive region in Nevada is that of Montezuma Range and the adjacent Kamma Mountains. The northern and middle parts of the range are made up of granite and the associated Archean schists overlaid by the unconformable Jurassic slates. Important masses of basalt and rhyolite make up the rest of the ridge. No range shows a more diversified profile, and in none is the geological relation of the volcanic to the older rocks more difficult to ascertain clearly. The rule which I have traced with such apparent uniformity so far, that the rhyolites have come up in a region of depression, seems to hold here. Where the granite and Archzean schists of the region of the Monte- zuma Mine, passing northward, are abruptly terminated, there are upon the eastern side of the range bodies of rhyolitic hills, and upon the western, basalts. So to the south of the central mass which culminates in Trinity Peak, the Archean schists and granites fall off and are immediately overlaid by extensive accumulations of the eruptions of rhyolite and basalt. The rhyolites northwest of Black Cafion make a group of hills through which rise occasional islands of granite, and which are margined along the north and east by slightly disturbed ashy strata of the Truckee Miocene. The low character of the hills, and the granite islands that penetrate them, give the impression of a rather shallow covering of rhyolite, and the structure of the rock itself is that of a thin flow. The rock is gray, of a rather uniform microfelsitic groundmass with few visible sanidins, but clouded and penetrated by very peculiar, irregular masses of pearlite, hornstone, and obsidian, the latter varying in color from nearly black to almost pearly gray. An interesting occurrence is that along the southern margin of the rhyolite body. Here is a buff, purple, and isabel-colored body having a fine lithoidal base, with a few small, brilliant, uncrystallized granules of RUYOULITES. 643 quartz and a little sharply defined sanidin. The aspect of the rock is decidedly porcelaneous, resembling a great many forms of petrified wood. In the prevailing gray and yellow color are stripes and wavy cloudings of purple, lavender, and pale-gray, sometimes with passages of a bright sulphur-yellow. It breaks with a distinctly porcelaneous fracture ; and the analysis, given in Table XI., shows a composition strikingly similar to that of the opposite type of rhyolites from Pah-Ute Range. The latter, rich in crystals, has a rather coarsely microfelsitic groundmass made up of sanidin and quartz, while in this the abundant silica, reaching 75 per cent., has gone into solution in the porcelaneous groundmass. The microscope reveals a few quartzes and feldspars, but no biotites, and the groundmass develops a structure decidedly worth noting. (See Volume VI., Plate VIL, Figure 3.) A rhyolite deserving mention occurs at Lovelock’s Knob, an isolated hill a few miles south of the mouth of Valley Canon. Here is a granitic boss rising like an island out of the horizontal Pliocenes, which in this neighborhood are thinly covered with Quaternary. The granite is broken through and overflowed by a mass of rhyolite showing a wonderful variety of texture and color. The prevailing type is a creamy or gray earthy breccia, which passes into dark umber colors and again into red and pink tints. The mass forms a capping upon the surface of the granite 500 or 600 feet thick, the only other associated rock being a small development of basalt on the north side of the knob. The southern half of Montezuma Range is mostly made up of rhyo- lites, here and there masked for no great thickness by black and steel- gray basalts. In the region of Valley Canon are exceedingly interesting pearlitic rhyolites, which have broken through the more crystalline varieties that lie west of them. These glassy and half glassy rocks are rich in large, cracked sanidins half an inch long, considerable shining hexagonal plates of biotite, and a little rather earthy hornblende, all embedded in a gray, yellow, and brownish-yellow base. Their mode of occurrence lends them their main interest. The pearlite ridges which stand out distinctly from the surrounding surface of easily eroded rhyolites show a development of fine, hexagonal columns, whose axis is inclined at an angle of about 80° from the horizontal. 644 SYSTEMATIC GEOLOGY. The great body of rhyolites forming the southern end of the range is made up of a wonderful variety of superficial appearances—differences of habit and texture, differences of color, and behavior of groundmass; but all, with few exceptions, belong to two general types, namely, the glassy and half glassy varieties, and the lithoidal microfelsitic. In Bayless Cation occurs what is perhaps the most remarkable rhyolitic display of the whole region. It consists of a ridge more than a mile long and rising 300 or 400 feet above its surroundings, altogether made up of well developed prismatic columns, varying in size from two feet in diameter down to an inch. The cross-section along the ridge would show a sharp, roof-like form coming to an exceedingly thin blade, which bristles with fine vertical columns. Upon either side, in descending toward the foot of the slope, the columns are seen to incline from the centre outwardly, while at the middle of the ridge they are tossed into a variety of angles, but approach the vertical. The steep slopes are formed of sharply divided col- umns, still in situ, resembling a pile of architectural ruins and suggesting the name of Karnak. Plate X.XI. is a view of the crest of the Karnak rocks. The exterior of the columns, generally of a dark, almost chocolate-brown color, fades in many instances into a reddish-gray. The interior is an exceedingly brilliant, pure gray, formed of a rather coarsely crystalline groundmass in which are embedded brilliant sanidins, well preserved biotites and hornblendes, occasional but rare limpid granules of quartz, and a few triclinic feldspars, the microscope adding to these an abundance of apatite. The western fork of the same cafion enters a region which is one of the most brilliantly-colored bits of geology in the whole West. The rhyolitic hills show a general tendency to horizontal bedding, and are made up of lithoidal varieties, some of which have passed into an almost earthy condition, and which vary from snowy white, like those of the Mopung Hills, through brilliant vermilion-red to orange, gray, purple, yellow, and green. A more bizarre and extraordinary assemblage of colors is rarely to be met with in nature. At the southern base of the range, near White Plains, is also an inter- esting locality. Here the inclined Miocene strata, made up of trachytic tuffs and ashes, and beds of infusorial silica, are broken through by two RHYOLITES. 645 successive outpourings of rhyolite. The first is of a rather warm gray, and is distinctly bedded, the layers inclining toward the east about 80°. Across these most prominent structure-planes are jointings that divide the rock into rude approaches to columnar forms. Examined in detail, these rhyolites are seen to be laminated almost as finely as the leaves of a book. The gray material is striped with fine, delicate lilac and brown bands. Through this laminated series has burst a gray and olive glassy rhyolite, rich in flakes of biotite—a rock which has the singular property of forming a brilliant varnish-like glaze upon the surface of all exposed blocks. This glassy rhyolite contains large crystals of sanidin and a few granules of quartz, and is not far removed petrologically from the columnar pearlites at Valley Canon. The little group of the Pah-tson Mountains is distinguished by an in- teresting assemblage of rhyolitic types. The long ridge projecting south- ward from Aloha Peak is formed of dark-brown tabular masses of rhyolite escarped toward the north and east, developing a rude bedding which is not unlikely to be the original planes of flows, having a dip reaching 30° to the east. It is suggested that this high angle may be the result of a dislocation at the time of the subsequent basaltic eruptions. The main material is of trachytic habit and reddish-gray color, the felsitic groundmass showing alternating stripes of red and gray pores and carrying a little mica and glassy sanidin as macroscopical secretions, the microscope revealing also plagioclase, quartz, and certain undetermined microlites. Surrounding the basaltic ridge west of Aloha Peak are gray rhyolites of pearlitic type crowded with black biotites and carrying a few sanidins and brown hornblendes. The eastern foot-hills of the range, at the base of Pah- keah Peak, show two varieties of rhyolites, one a compact, fine-grained rock, largely made up of minute glassy sanidins and quartz, the other a mauve breccia, containing opaque kaolinized feldspars. Directly north of Pah-keah Peak, on the heights of the range, is a com- pact, greenish-yellow, quartz-bearing rhyolite having a dense microfelsitic groundmass, the average specimens resembling older porphyries. With this was observed a white rhyolitie breccia containing fragments of a lithoidal green variety. The felsitic groundmass and the binding magma being harder 646 SYSTEMATIC GEOLOGY. than the included fragments, the fracture-planes pass through both alike. Farther north, near the head of Grass Canon, are more white rhyolitic breccias of scoriaceous habit, the interior of the cavities being colored red, the groundmass bearing sanidin and quartz. The pearlitic varieties dis- played along the head of Grass Cation merit so particular a description that the following paragraphs are quoted from Volume IL.: “Grass Canion, which is a long, narrow ravine running out at the north- ern end of the mountains, presents along its slopes the most interesting occurrences of volcanic rocks in these mountains. At its head, and along the upper walls, are gray pearlites of the crystalline type. A characteristic specimen is rich in black biotite, and contains macroscopical crystals of san- idin, plagioclase, and quartz. Under the microscope, the feldspar crystals are seen to contain great numbers of angular bubble-bearing glass-inclu- sions, sometimes so closely aggregated as to form entire portions of the interior of the crystals. Mica is most abundant in hexagonal lamine, 0.008"™" in diameter, while in the colorless glass base are feldspar-microlites and pale-green needles, together with gas-cavities containing magnetite. This pearlite passes into one in which the crystalline ingredients are still present, but the groundmass is a colorless glass, in which are developed concentrically curved cracks, giving a spherolitic structure to the mass. Microlites are present as products of devitrification, and, as already stated, crystalline ingredients, feldspar and mica, which are difficult to detect with the unaided eye. Beyond the pearlites, on the west side of the canon, about opposite North or Basalt Peak (not named on the map), is a peculiar greenish rock, having in general a granular structure, and showing no crys- talline ingredients, through which run many bands, alternately quite porous and again compact and lithoidal. The latter pass into chalcedony, which covers the weathered surface, and sometimes forms the mass of the rock in bands a foot or more in thickness. “At the head of a side-ravine, where, in a low saddle, the underlying rocks have been denuded, is disclosed a most interesting series of rhyolitic pearlites, chalcedonies, and tuffs, which, from the occurrence of rounded obsidian balls within the pearlite layers, have been designated the Ball Rocks The upper layers on either side of this saddle are composed of 2H YOLITES. 647 the green rhyolite already mentioned, and layers of brown chalcedony, on whose weathered surfaces are curious rounded excrescences, of concentric structure, resembling the gnarled growths found on old tree-trunks. This similarity is heightened by the color and interior banded structure of the chalcedony, which resembles woody fibre. Within the chalcedony mass are frequent druses, lined with white banded opaline agate, and containing quartz crystals. Zirkel describes the microscopic structure of the chalced- ony as consisting of concentric globules and botryoidal concretions in a seemingly colorless substance, which by polarized light is seen to be an ageregation of siliceous spheerolites. A section is represented in Volume VL, Plate XIL, Figure 2. “On the saddle are exposed layers of pearlite, containing rounded ob- sidian balls, from half an inch to an inch in diameter, associated with a white pumiceous tuff, enclosing fragments, generally rounded, of the pearl- ite. The pearlite is blue-gray, devoid of crystalline ingredients, with a tendency to form layers from an inch upward in thickness. It has a wavy appearance, and is entirely made up of spherolitic concretions. The spherolites have a concentric structure, and are formed of thin layers. Under the microscope, these layers are seen not to be complete rings, but to be grouped round the centre like the leaves of an onion, and the micro- litic products of devitrification to be arranged in parallel wavy bands through the mass, quite independent of the concentric structure, from which Professor Zirkel concludes that this structure is merely a phenomenon of contraction. The pumiceous tuff, which is found abundantly along the slopes of the ridge, is a white porous mass, containing small fragmentary crystals of quartz and sanidin, and enclosing larger fragments of the gray pearlite, in contact with which the white frothy matrix is seen to be com- pressed and hardened, so that the surface of the cavities left by these frag- ments is smooth and hard like a plaster mould. “The obsidian balls, which have an almost perfectly spherical shape and occur imbedded in a layer of pearlite, near the summit of the saddle, are seen by microscopical examination to be remarkably pure, containing only a few trichites in a light-gray glass. “ About a mile from the mouth of Grass Canon occurs another white 648 SYSTEMATIC GEOLOGY. rhyolitic tuff or breccia, of much more compact mass than the above, and enclosing fragments of dark porphyritic rhyolite with free quartz, which forms quite high cliffs on the west wall of the cation. ‘Tn this vicinity, also, is a considerable development of basaltic rocks, which have apparently poured out on the east side of the cation, and have covered the upper part of the ridge on the west. These basalts develop a columnar structure, particularly on the slopes of the peak on the east side, which has been called Basalt Peak, where they are remarkably perfect and arranged horizontally. They belong to the same general type as those of Aloha Peak. The main mass is a compact, dark, rather vitreous-looking rock, with conchoidal fracture and somewhat coarse texture, in which only small plagioclase crystals can be detected macroscopically. The micro- scope detects also olivine and augite, and in the groundmass an amorphous globulitic base.” The Kamma Mountains, which are really a northern continuation of the Pah-tson, are divided into two distinct groups. The southern one is composed chiefly of andesites that have broken through Jurassic slates, while the northern body, made up of lofty, rugged hills, is almost entirely of rhyolite and rhyolitic breccias, and, around the lower portions, of a group of tuffs. The predominating breccias display in the angular fragments which they conain a very great variety of microstructure of groundmass. Earthy, rearranged, rhyolitic tuffs occupy the lower foot-hills. Northward from this group the desert slopes are dotted with little rhyolitic and ande- sitic hills, the former not greatly differing from the Kamma rhyolites. Farther north the western foot-hills of the group which forms the eastern boundary of Quinn’s Valley are of porous, earthy-white rhyolites, contain- ing only sanidin and quartz. These rhyolites are of interest, as they are seen to have disturbed and tilted the Miocene strata. West of the valley of Quinn’s River, in the very heart of Mud Lake Desert, is the group of Black Rock Mountains, rising at extreme points about 1,000 feet above the desert level. Within the area of our map it is built of rhyolitic and basaltic eruptions; and the minor ridges which make up the topography are usually capped with a sheet of basalt that inclines to the east, the rhyolites showing along the western base of the hills. RHYOLITES. 649 This is repeated several times, giving the impression that the region has been disturbed since the eruption of the basalts. In one instance rhyolites appear to overlie the basalt directly ; and since this is the sole exception to the law of Richthofen within our limits, it was examined with some care. It was not clear whether the rhyolite had really come to the surface later than the basalt, or whether the basalt had broken through between beds of rhyolite, as it is often seen to have done between the strata of a sediment- ary series. The basalt is a true olivine dolerite, not at all to be mistaken for an augite-andesite. The problem, therefore, is purely one of structure, and requires further study to clear up all obscurities. Standing as a soli- tary exception in the face of such a multitude of concurrent examples to the contrary, this apparent succession of rhyolite after basalt must be attributed either to an obscurity of structure or to one of those curious alternating eruptions which are described by F. von Hochstetter.* A supposed exception was brought to light by the late Archibald R. Marvine at Truxton Springs, Arizona, where a light purple and gray rhyo- lite, rich in crystalline minerals, and having a rather coarsely crystalline groundmass, was observed to overlie a doleritoid rock. The writer ex- amined thin sections of the latter, and found it to contain minute grains of quartz, with specks which had the appearance of very minute fluid inclu- sions. The olivine had in large part passed over into a serpentinous con- dition, and the glass base was globulitically devitrified, as is so common in the middle-age diabases. The rock was therefore pronounced, without much hesitation, a diabase, and the law of Richthofen sustained. Westward from the Black Rock Hills, across an arm of Mud Lake Desert, rise the Forman Mountains, a group of irregular rhyolitic hills reaching about 1,200 feet above the level of the desert. Wherever examined, they prove to be altogether of rhyolite, for the most part a pure felsitic mass, of flinty, conchoidal fracture, containing as macroscopic secre- tions only a few half kaolinized feldspars. Farther up the range are some reddish, highly crystalline rhyolites, with rough, trachytic fracture, made up of sanidin and free quartz in a compact felsitic groundmass. With this is a breccia similar to the solid rock; and from a little north of our map * Reise der Oesterreichischen Fregatte Novara um die Erde, in den Jaren 1857, 1858, 1859. 650 SYSTEMATIC GEOLOGY. was brought in a very wonderful example of minute rhyolitic columns closely welded together, each prism about one eighth of an inch in diame- ter. They are quite accurate hexagons, and are composed of a dark, steel- gray rhyolite, the fine, microcrystalline groundmass containing limpid quartz and small, slender crystals of sanidin. The rhyolites of Truckee Range are confined to the southern portion, directly abreast of the south end of Winnemucca Lake, and a single rhyo- litic summit which rises above the broad, basaltic masses directly north of Desert Station, in the most southern ridge. Here a single peak of gray and grayish-brown, half-glassy rhyolite is exposed, rising like an island above the basalts. It is very rich in brilliant biotite, and contains a little greenish-black hornblende, but no quartz; and the abundant glassy base shows the most interesting products of devitrification, as described by Pro- fessor Zirkel. Among the rhyolites east of the southern end of Winne- mucca Lake are none of special petrographical interest. They directly join the granites, diabases, and metamorphic Triassic strata, and are made up of rugged piles of brilliant pink, red, white, ashy, and lavender-colored rocks, which are quite conspicuous in their contrast with the darker masses of the metamorphic series. Since all of Virginia Range within the limits of our map is made up of eruptive rocks, and, with few exceptions, of Tertiary volcanic rocks, we have no clew to the relations of the rhyolites to the ancient series. They are quite subordinate, both in amount of exposure and in the position which they hold in the broad topographical features of the range. They are actu- ally confined to the skirts of the group and the low region of Mullen’s Gap. Between Black Mountain and the granite ridge which projects southward of State Line Peak, overlying the granites and in turn capped by more recent basalts at the extreme head of Louis’ Valley, is a small development of reddish-gray rhyolites with a finely felsitic groundmass and the most char- acteristic banded structure. Biotite, sanidin, and occasional quartz are the only visible secretions. At Mullen’s Gap, both north and south of the pass, are limited expo- sures of rhyolites which have broken through and overlaid the foot-hills of quartz-propylite, and northward they are themselves overlaid by broad RHYOLITES. 651 basaltic sheets which come down from Black Mountain. How far the rhyolites may continue under the heavy, overlying masses of basalt is, of course, an open question. In these few foot-hills are to be seen a very great variety of rhyolitic types; some with felsitic groundmass crowded with secreted minerals—sanidins, plagioclases, quartzes, and biotites. With these are associated light, cream-colored tuffs, dark pearlites, and a wide range of glassy and half glassy varieties. The prevailing color of all the Mullen’s Gap rhyolite is a very brilliant Indian-red, not unlike those from Sou Springs. The most porous pearlites and the pumices, which here occur in great profusion, are of pearl-gray and lavender colors. Here, too, are found stratified pumiceous tuffs in which the material has been evidently rearranged in lacustrine waters. They are remarkably friable, crumbling at the touch like beds of volcanic ashes. An ash-gray breccia from the north side of the gap is made up of a loose, rather incoherent binding material and fragments of several varieties of more or less decomposed rhyolites. Sanidins are the only secreted crystals. That which lends the rock its interest is the occurrence of liquid inclusions in glass, and of an apatite included in glass, itself carrying a minute fluid inclusion. The most extensive rhyolite body in this part of Virginia Range occurs directly north of Truckee Canon, having its culminating-point at Spanish Peak. Here is a lofty, rugged hill, from which a rude bedding declines in every direction. These rocks have overflowed the sanidin-trachyte that forms the main summit of the range to the west, and in turn are nearly sur- rounded by basaltic outbursts, as seen upon the geological map. It is a pinkish-gray and lilae rock, of a fine-grained felsitic groundmass, contain- ing only a few macroscopic individuals of sanidin. Under the microscope it is seen to be very rich in tridymite and well rounded spheerolites. The most interesting petrographical feature is the extremely fine lamination visible at various points of its body. Hand specimens show laminations of not over a fortieth of an inch in thickness, and these are not merely parallel, straight lines, but are often contorted into regularly defined scollops, sharp points, and complicated, compressed waves. For the most part, these lami- nations are present in perfectly parallel, smooth planes, upon which the rock has a slight tendency to break. Approaching the river, the gray 652 SYSTEMATIC GEOLOGY. and pink rhyolites overlie a dense white felsitic variety which is very rich in large, brilliant granules of quartz—a rock closely resembling the white felsite porphyries of middle age. Over this extremely white, pure variety of rhyolite, are the ends of a flow of excessively black, fine-grained basalt, affording the most extreme contrast in color and texture. In the region of Berkshire Cation, the eastern foot-hills of Virginia Range are composed of an important belt of rhyolites which have burst through and overflowed the trachytes and dacites. Seen from the valley of the Truckee, these rhyolitic foot-hills rise from 1,200 to 1,800 feet above the level of the Pliocene mesa, and in their rough exterior and suddenly variegated colors make a thoroughly characteristic rhyolite display. They are white, pale pea-green, salmon-colored, pale lilac, Indian-red, olive-brown, and deep purple. Directly north of Berkshire Canon they are broken through and overlaid by a small mass of basalt. Taken as a whole, this field of rhyolites, about twelve miles in length, shows almost no bedding whatever. It is a fine type of structureless, massive eruption. It embraces several petrographical varieties, shading through a dense white felsitic rock with- out a single macroscopic crystalline secretion, and through mica-bearing, quartz-bearing, and sanidin varieties, up to a highly crystalline rock with a scanty felsitic groundmass and a crowd of brilliant crystals of quartz, plagioclase, sanidin, and biotite. The quartz is invariably in rounded, cracked granules, the sanidins often dislocated and varying in dimensions from a fine point up to the size of a pea. One salmon-colored variety was characterized by an enormous amount of large, open cavities lined with a thick coating of siliceous sinter. The more solid parts of this rock were salmon-colored felsitic masses, so fine as to resemble the most close-grained jasper. Decomposed spheerolites are seen by the microscope to be very common. 7 A 7 ' ) , 7 aan ’ ae) 7h os a > = 1 ¥ - oa 7 4 (AS : b ia, 7 oe 1 ep § i. U 5 ies , fi! & — ca Be - eee i ; aa my - a a , i ] ie wei = / _ , = a 1 > ‘ i 4 _ ald ay ae ANALYTICAL GEOLOGICAL MAP OF Siem orsvve A ‘ KPILORATION OF EVES POUR IIENIMED TAURVACISIEVE Li ceee Vill ROCKS CANIC mate Miles w one Inch. DACITY [ ANDESITE Esa QUARTZ PROPYLITE | PROPYLITE (esl . $ ‘ - : 1 A * - b z i : : ' : ’ - i " ‘ 7 - i - a J i ‘ 7 * ’ , ie A y ‘ i 7 , a , i A ' 7 , e ‘ ‘ : ( 7 i _ cj : , > ‘ ' t - , ‘ n i i ' : 7 - ‘ : ‘ = : / at -_ : p 7 . 7 ' oY | igh 1 ' x ' if i . +5 : 4 : : : 1 ‘ bs : i - “a " ' : ' s i aK . : * i ‘ . ‘ yy “ ; bs ‘ ‘ i ’ : 7 ; ’ . + ‘ ‘ a) 7 a : i - y * ‘ * ‘ ake i j ' 7 - $ ie * ? 2 7 7 . | ‘ ‘ ‘ ‘ i ‘ 7 . BASALTS. 677 are of the ordinary feldspar variety, and poor in the globulitie or glassy base. The triclinio feldspars are correspondingly large, and the olivines small. At the entrance of the canon, opposite the andesite flows which form the southern hills, is a body of sanidin-trachyte overflowed by black vesicu- lar basalt which is for the most part a compact, fine-grained rock with few macroscopic crystals and little globulitic base. The microscope shows it to be made up of abundant triclinic feldspars, extremely minute olivines, a high percentage of magnetic iron, and occasional apatites. SECTION Vi: CORRELATION AND SUCCESSION OF TERTIARY VOLCANIC ROCKS. QuanTITATIVE CHEMICAL Retations.—Regarded from a chemical point of view, the Tertiary volcanic rocks of the Fortieth Parallel conform in general to the law of Bunsen. 7,\|(95) 28>471\| | --0-23) reese rece eee eiece|cmeceeels From the final column of this table it appears that the difference in latitude between results by triangulation and zenith telescope observations, corrected for attraction of mountains on the plumb-line, is much too small to be seen on the maps. GEODETIC APPENDIX. 767 In 1872 a base of verification was measured with a steel tape near Fort Steele, in longitude 107°. When reduced to sea-level it is 4.7900 statute miles long. The length of this base, as computed by triangulation from the Star Peak base, is .0004 greater than by measurement. When the geodetic difference of longitude between Salt Lake and Sher- man was calculated by the Star Peak base, it proved to be .00256 smaller than the astronomically measured difference. Owing to the positions of the mountain masses in relation to the United States Coast Survey astronomical stations at Verdi, Salt Lake, and Sherman, it is probable that the astronom- ical difference of longitude between Verdi and Salt Lake is too small, and that between Salt Lake and Sherman too large. It therefore seemed prob- able that the discrepancy between the astronomical and geodetical differ- ence of longitude from Salt Lake to Sherman was partly due to the Star Peak base being too small, and partly to the astronomically measured dis- tance being too long. For this reason the triangulation for Maps I. and II. was calculated with the Star Peak base, multiplied by 1.0013. There remains a disagree- ment of 30’ between the two methods of measurement of the distance from Salt Lake to Sherman. The agreement between observed and com- puted azimuths showed that no large errors existed in the adjustment of the triangles. Geographical positions on Map I. are computed by triangulation from the United States Coast Survey astronomical station, Sherman, while those on Map IL. are reduced from Salt Lake as the initial longitude. Between these two maps there must therefore be a disagreement in geographical positions. The error in either will be equal to the true station-error at the initial astronomical station, combined with the error of the triangulation. I am inclined to believe that the probable uncertainty in distances measured by the principal triangulation does not exceed 0.001. SECONDARY AND TERTIARY TRIANGULATION. Secondary points were located by cuts from the principal stations, and from these a smaller system of triangles was carried over the country by 768 SYSTEMATIC GEOLOGY. the topographers. The angles were measured with the gradienter, a light instrument having a very effective telescope and a four-inch circle reading to minutes. Rocky peaks, five to ten miles apart, commanding the best views of surrounding country, were chosen as stations. Signals were seldom used, the summits being generally sharp enough to be observed with suffi- cient precision Elevations of stations were determined with the mercurial barometer of James Green. Base stations, where the barometer was continually observed while the survey progressed in the neighborhood, were established at intervals of 100 or 150 miles along the line of work. Field observations were all referred to one or more of these bases, and the bases afterward connected by syn- chronous barometric observations with the levels of the Pacific railroads. TOPOGRAPHICAL METHODS. Regarding its trigonometrical foundation, the Fortieth Parallel work is allied to regular surveys; but the topographical methods employed were more like those of the best reconnoissances. From each occupied station the adjacent territory was carefully sketched, in plan of drainage, in leading horizontal contours, and in profiles. As many points on these sketches were located as could be cut by intersecting lines from the occupied stations, and their altitudes determined by angles of elevation and depression; these points fixed by measurement are con- fluences of streams, lakes, buildings, and conspicuous rocks, knolls, and peaks on mountain spurs and crests. In a dry region of sparse vegetation, where the ridges are serrated and water-courses and ravines deeply marked and clearly visible in the distance, where every mile of territory is overlooked from bare commanding summits, and where the atmosphere is remarkably clear, this method of taking topog- raphy gives a far closer approximation to the truth than would be possible in a country where drainage-lines and details of form are masked by foliage or dimly seen through moist hazes. The sharply cut features of the Cor- dilleras stand out so boldly that the topographer has only to locate enough points and make careful contour, profile, and drainage sketches, in order to produce a very fair representation of the country. GEODETIC APPENDIX. 769 The maps were made by laying down on polyconic projections the geographical positions of principal and secondary points, then plotting by intersections the tertiary stations and located points. Between such of these as are on streams the water-courses were filled in from drainage sketches, and from profile sketches the slope angles were estimated and the contours spaced in between points whose altitudes were determined instru- mentally. The contours, therefore, are located by barometrical and trigonomet- rical measurements at certain points and sketched between these with the eye. 49 K GENERAL INDEX. OBSERVE SPECIAL LISTS OF AUTHORS, CANONS, FOSSILS, LAKES, MOUNTAINS, PASSES, PEAKS, AND RANGES. Page. Page. Actinolite in Archean quartzite ..-..-..------+----- 69 | Andesite (augitic), River Rango .----..--.--------- 572 Adara, Donegal, Ireland, granite......-------------- 60 Steamboat Valley .--..--.----- 576, 577 Ada Springs, basalt of .-.....--..------+----+--++++-- 653, 654 Susan Creek, Seetoya Rango -- 573 trachytoof....-....---------2. + +--+ 581 Truckee Caiion..- 576 Agassiz, Louis .......----------------2e-ee22 eeeeeee 4717 Tuscarora.-.-.---- . 572 Agate Pass, basalt of......--------------++--++---+++ 661 W achoe Mountains....-...----- 571, 572 Weber quartzite of - --- 219 Wadsworth .....-.-...-------- 576 Age of dryness in interglacial period. 524 (hornblendic) .-..............-------.--=-- 562 Vermilion Creek group .----- --------+------- 377 Berkshire Cafion, Virginia Albion Peak, Coal Measures (Upper) of. ------------ 224 (Rane Oeceaeera atm cincisies sala 566, 567 Albite in granite of Humboldt Range ..-..---------+ 64 Carlin Peak.........-:-.s---- 563 Alkali Flat, Diamond Valley 503 Cortez Range)....0---=s<- sos 563 Smoky Valley ...-..---.--------++---+-- 503 Crescent Peak .-....-...----- 504 Alkaline carbonates of Lake Lahontan 513 Gosiute Valley ....-..-.------ 562 deposit, North Fork, Humboldt.-..-------- 502 Palisade Cafion -....-.------- 563 incrustations of middle Nevada ....-...--. 502 Truckee Cafion, Virginia Allen, O. D., analyses by 496, 511 Lit saceoussopaye sosecese 505, 566 Aloha Peak, basalt of ..-..-----------------++- 669 volcano of Lassen's Peak....-------------- 566 rhyolite of ...---------------- +++ C 645 | Andesites, succession of...----.--.-------------+---- 684 Alpine Trias fossils, Desatoya Mountains...--..---- 283, 284 hornblendic, Kamma Mountains. -... - 564, 565 SOChloN-ceshecesacseseserisawcesesenc w= 269 SNCIGACILCS ea = asin a-ew el ew eenmee nc censsee 562 Star Caiion 276, 277 distribution of. work of glaciers 483 | Andrews, Dr., experiments of.....---.-------------- Alps, arrétes of .---------.- 472 | Anita Peak, basalt of ..-...---..----+-+22+eeeeeeee es Altitude of Lake Lahontan - 505 | Antelope Creek section, Trias.. Ammonite Cafion, Trias of ....--.------- 283 | Antelope Hills, rhyolite of ..--- Amphibolite, Grand Encampment Peak...---.------ 40 | Antelope Island........---- Amphibole rock, Garnet Cation, Uinta Range. --.... 43 | Antelope Peak, basalt of......-.--------------+++-+-+ Anabé Island, thinolite of......-.-.----------- 515 | Antelope Spring, Wahsatch limestone of ..---------- 196 trachyte of.....-.---------- 601 | Anteros Cafion Trias....--.------------- pease stO50 263 Andesite of Cedar Mountains 562 | Antimony Cafion, Augusta Mountains, andesite (au- Clan Alpine Caiion, Augusta Range. .----- 564 gitic) of 57. (Gita iG) eeoteaneaacoossneeoenec esse ceeceonc 571 rhyolite of.....--------+--------+- 632 palagonite referred to..-..--..---- 419 | Antler Peak 219 (augitic), Antimony Cafion, Augusta Upper Coal-Measures of .-.. : 225 Mountains 2o2ccacccecececens 575 | Apatite in hornblendic plagioclase schist. . 33 Cedar Mountains 571 | Aplitic granites of Colorado Range. ..--.---- A 22 Cortez Range.scccs seen oo --= 574 | Appalachian series compared with Cordilleran ...-.- 536 Crescent Peak, Augusta Moun- Appendix, geodetical and topographical. .-...------- 763 TAINS eeercs = eeeresesseac esa 575,576 | Aqui Range, Cambrian quartzite Ofeecececssemieceees 185, 186 Egyptian Canon. . 572,573 | Archwan and Palmozoic, relations of .----..--------- 122, 123 Jacob’s Promontory ..--------- 574, 575 anticlinal of Colorado Range ---- 21, 22 Last Chance Spring ..- ------- 572 beds, absence of chemical action between Melrose Mountain...-...-.----- 572 contiguous strata ..-..-.---------- 112 Palisade Cafion.......--..----- 574 chemical persistence of....-.-.------ 104 BR Bue Heme ewe vi Se) a hi uf ee ee Ee a ae Bann B Snetesschiger. Wet Hambold: a & # ry Posqeep Ses pewolorical smplictty of Candilleras...... primitive swmamiis of _..........-..---..-- qmerurite, actinolite im -.--_---.-.--..---.. Baw ie B B | H 1 2 HB4OHR BoNBes Humbeld: Range, accessary min- Rewinss Sel: Lake and the Promontary-.. Seciegs Gees Shoshone Bange ..-............-- ee jenessenwane Me pe Gstribution of ...................... 32538 ‘Wahssitch, relation to liter rocks..-..-- Area and aspect of Lake Lehonten --.........---.... 06, Wi and Exploration of the Forticth Parallel -..... INDEX. Page. Ashley Park, Paleozoic....- -- 148,149 Aspen, Fox Hill Cretaceous 326 Aspen Plateau, Vermilion Creek group of -..-.....-- 370 PASLODP Res eLrachy too fieeaeeseeeacsies saan menieee moe 602 Atlantosaurus beds....- fossils ... Atlas accompanying Fortieth Parallel Report. J Nae eG Sen Seeeee seeesaces: Seaneercecccecas 71 Augusta Mountains, Antimony Caiion, andesite (au- Pati) Oo os co-coaneSeeead 575 Archean rocks ... 79, 80 basal eee ene mae ee aoe 663 Clan Alpine Caiion, andesite. -- 564 Crescent Peak, andesite (au- PUT) Sacco SHER OSoSSSQURCEE 575, 576 PTAnILO seeaee eee ena=aeien sea awe 80 Jura.... 294 rhyolite. 631 Trias .. 281 Austrian Alps, Trias of....-.....- BOSS CD RE SSR SE OSEO 74 Authors, Agassiz, L ............- See eeeas es seca ae 477 Allen, 0. D..-. ---- 496, 511 Andrews.......- 78 Babbave\-n.~<2--a 727 Bonneviile, Captain ------- - <5. <2 55. 2-28. 1 Bradipyy rank? Hieseesceanaioasaen=eenaaa 38, 178 Dye Gue, \Wi’od lace ac aacdcassacsneseccecase 450 IBrewstersbolieee sencene ses eens eee ance 131 Bunsen, R ------ -417, 678, 691 Clayton, J. E...-. -197, 198, 213 Cope, E. D ...- 353, 354, 376, 391 (O5faLA SYNOTh sonmossonceosenonessoceaosesta 417 Mana Steen ecss see se sana 408, 410, 455, 517 Danae) pera 117, 191, 459, 465, 517 Darwine Gharlegmencesseesessaseesn ancl nee 715, 716 Dawson, G. M... 101, 103, 459, 463, 464 ‘Delabeche cecesaeesetaae- sana caaseeccnces 117 Delesse tern saeeeerneee eens an aneanencincas 706 Duong tienen aaaasecenanans cs ceccas = 698 ihren bere Oakes esses sae erase eens ee 420 MMOUS | Sah ee sesan aan cesnceecice=sce 4, 303, 324, 433, 449, 551, 572, 613, 629,743 Hnvelmann Or acaae eee seeeaeacaiesace=coe= 211 Rrémonicd ODN) Ges enaseceaen ese =asnee a= 1 ishereneve Cin eameeateee cance s se ceecaes 698 TENG) Sas sonosbaossads <= Sil GatboWa Mier aceeenenemcoe ~- 275, 279, 450 Gale, L.D'----..-- cess ata 497 Garduer, James T . saccceecrsegaso+cs 20, 763 Gilbert, GK... .. 445, 466, 490, 491, 492, 493, 523, 525, 548, 5£0, 581, 633, 725, 746, 749 Grinnell "GeBlee ee cceeenee eee 132, 408, 410, 455 (Gnmmisone-===--—--=s- eee eane seers 1 Hague, Arnold ....-..--..--- . 4, 551, 602, 629 BEGAN) --oscedesnas peeps ceboseeEeoosee 79, 110 “Hall, Prof. James.-......- 187, 206, 207, 210, 20, 294 Haydons ieiViecs<=sieeeeer= vee. 2, 3, 127, 298, 347, 348, 354, 391, 445, 451 Herschel..-..-..-- co -- 703, 727 Hochstetter, F. von BASU EEE ORCS 649, 687 Hopkins, William .....-...--.- 696, 697, 701, 702, 718 Humphreys, General A. A 427 Hunt, T. Sterry TANG Or seen eee eee sees == Marsh, O. C-. ..285, 423, 439, 443, 445, 449, 450, 454, 591 Marvine, Archibald R ....-........-...... 23, 649 Meeioih cece steeeae 211, 328, 423 Meek and Hayden ............. cot eeacnscs 331 Muir, Jobn 417 Newberry, J.S 331, 353 Pfafiiceas-esacnianaeeean 693 Powell, Maj. J. W..--. 148, 290, 331, 385, 328, 445, 448, 450, 478, 633, 735, 748 Pratt, Archdeacon: sessse.----eeacesmee === 705 Unit) Eo bemanee mae sco cece mac OmOnCae SEC CUISSES 477 Pumpelly, Raphael ..............---...--- 51, 105 Richthofen, F. yon... .549, 550, 554, 649, 681, 682, 687, 689, 707, 710, 711, 716, 721, 722, 724 Scrope, Poulett Soresosee sass VERT DleOLen sees ae eee eon een ane =e eeeee 114 SUM PSN see eeleecaa eee enceseaenee one 1,211 Smith, J. Lawrence - 499 Stansbary, H .-...-- 1, 497 Stevenson, J. J.- 331, 332 SUOKES eos sncee = on omn ee eena sear =n cece n = 705 Rip EN esecoseesecccncs sano san oer e Sse 706 Thomson; AMES == 2o— 2 saneaw aa cone aaenee 704, 728 Thomson, Sir William 696, 697, 701 Waltershausen, Sartorius von --417, 707, 718 WE ibd BG Ta 7 eS eee cee sacesasoae 79 Warren, Genenal G. K..--..---...-.-- 2, 427, 483, 757 RWiheelet Gee io ean enone eee eee 490 Whitfield, R. P -..-. -187, 191, 206, 207, 210, 280, 294 Whitney, J. D...... --. 2,3, 266, 295, 450, 460, 689 WWalliamson, Major 213, 214 Biotite-hornblende, granite type IIL . 108, 109 Bishop Mountain, Green River group of. .......----- 387 Vermilion Creek group of ..-...--- 368 Bitter Creek region, Laramie Cretaceous of....-..-. 335, 336 uplift in Vermilion Creek group.....-- 369 Black Butte, Laramie Cretaceous ....-.-..---- - 336, 337 Black Butte Station, Vermilion Creek group -.----- 364, 365 Black: Cationirhyoliierccnsssesacncmeeaceaas scteaesee 642 Black Rock desert, efforescence...---. 513 Black Rock Mountains, basalt ..-..... - 669, 670 rhyolite - 648, 649 Black’s Mork, Juranca-caccedesneeaaetecneseeaeeoee 291 Palie0z0l0ze ec cscesrecence veewan/anianestse 142 Black shales, Wahsatch limestone. .....-...-.---.--. 199 Blue Ridge, Wahsatch limestone..........-......--- 207 Blue Mountain Range ......--- : =a 452 Boise Basin, Pliocene .... a Eas 440 volcanic rocks of, reJation to Pliocene in 592 Bone Valley, Humboldt group of ...--..-...--.------ 439 Pliocene vertebrates .----..-...-s2-.000 439 rhyolite 617 Bonneville, Captain : 1 Bonneville beach, altitude of Aon 492 Bonneville beds, Gilbert's deductions from .--..----- 523 Bonneville Lake, terraces of ...........-.--.----2e0 436, 437 outlet, Red Rock Pass............. 492 Bonneville’ Peak -s2ec-s3-.c--cen<-caseeastes ocr eee 185 trachyte of 593 Bonneville region, saline efflorescences .......--.---- 501 Bonpland, Mount, glaciers of .........-.-.-.------+-- 475 Boone Creek, Truckee group, Miocene of.......----- 414 Bosjemanite: can -eceer ees eases ear oaseneaeeceenamans 499 Botryoidal surface of thinolite 517 Boulder clay, absence of, in United States Cordilleras 460 British Columbiat--c-s=----s<-ssceceue 459 Boulder Creek, Ogden, quartzite of .........--------- 194 Boussinpault.-sccccecsss sce e seeree cncanaaseeenans 511 Box ‘Elder'Cation; Triassic: 522222 2sec.-ceeneseseceees 255 Box Elder Creek, Triassic .........-.-- 251 | Bradley, Frank H ...... Brewer, W. Il ...... Brewster, B. E.. BridperBasin..cevecscsescisceccccecsnacensseecoe cent. INDEX. T15 Page. Page. Bridger Basin, general section of Bridger group in.. 400 | Cambrian and Silurian of Oquirrh Range ....- Seatac 184, 185 Green River gronp of....-..-.....---- 388 Pifion Range ...-.-..----- 1£9, 190 Brig PereTOUD yes e meee es sae an eee een aes Seeeeen 394, 395, 448 Roberts Peak Mountains . 191, 192 BadeanGseeececaceeace aah comme) C(t |) (OBI) Ura eRe AS cen coceecooosbpeecc Score sscO0 EoEAeS 582, 584 BridpersBasin@e--oseo cee ee este e aero 399, 400 | Camp Baker, Montana, Miocene of 408 Cherokee anticlinal ...........--..--. 397 | Camp Douglas Trias ...-....--....--.--.-- 265 Cherty Stratasee- me nentem lean =seemce 401 | \Camp Halleck, Nevada.---...<2--- 22. cose ccccnesces 590, 59L Church) Buttea=----0ccen 333 Amnicola Cincinnatensis .......-..-..-..... 494 PAMOGIO Woon ccna ca cen teases eee ee eee 336 Amplucyon vetus ......-- 41 angustidens. - 411 Amynodon advenum.....- . 407 Anchippodus minor... 404 Anchippus brevidens . ss 443 Ancylus. undulatus << <.5<20csicaessccasnsleece 422 PANOMIIB 30:5l02 cce,2 Se aseig swe some seta 328, 336, 337, 338, 376 PANOBUCITALOTNAA: sorcn/ceccceser sme estan sames 404 Antherophagus priscus..............2....-. 394 Apatemys bellus-................. 5 404 ADALOSRULUS AJAX: 5 --. cc emaacieacyocssueecees 346 PTANGIG\020%5~2ccmsecnecocs See 346 Aquila, Dananus:~<-.c-<:- -2a2-ss\csecsn ess cess: 173, 246 IM VOcltes Sees ee aan eeeeen an aaa seee cae 283 RVICUIOIdeS) ~saseae erase’ sossscsss 5. 246 INCONEPICUUA)— sae aSere =. cosas 246 (Panopxa) Humboldtensis .......-. 275 subcompressa........--.-.---..-.- 293 Wreberensis\.2-.-- <== scscoscosce ee 164, 246 Myophoria lineata ............------...----- 291, 293 Mys0psiminimusSnccccsdacccccescconseseseee 404 Naiadites ...-. -144, 243, 244 Nanosaurus agilis....................------- 346 INatiCarae ten oaaneccoeasareceensicsssemncece = 138 lelinvcesinacsantceascattreas cose ooo ee 137 Naticopaisi-co--cccesecceseseccecasace 206, 236, 240, 244 INADUIUS sesccetentasesaeniacnscece ssn ces 275, 278, 282 Neritellatoecnasseceee cereaes coomoScaadasoes 291 Neritina Bannesteri .........-....-..22...-- 328 (Dostia?) bellatula..............--. 328 carditiformis ..........--. 328 : 318 te 142 - -142, 243, 244 . 144, 243, 244 Nuculites triangulatus..............--..---.- 208, 237 Nyctilestes serotinus..... 403 Nyctitherium priscus. - 403 VOLO ste weasese ss aencane ance 403 Qhbolellasessseess sea e nae aeeeaane ose 187, 231, 233 CIRCOID See een eee a ee eae a 189, 231 Odontobasisiessnsc5-neceeese= eee aeeatane ens 338 OBy2iGtcocesececesienre ac <-onccomnennanenns 185 FEET LI) EY osnccccenScUCnCe cCOUnOnKCRonES 125 ParabolOldgus se. nonsense eee 233 prodncta....---..-----.-..-2<. saskces 185, 233 Ophileta complanata - --- 180, 233 Oreodon Culbertsoni - = 411 gracilis ..... 4\1 Oreosaurus lentus..--.-. 2.2.2 - 2s scenes eee 405 Orocyon latidens. - - 403 Orohippusigilishense-ssecececcecescoeenes= 404 VASACCIGNSIS| occas asmen asics = seems Orteoglossum encaustum....-.-..---.------- 394 Orthishes=seaqacseep ee ese a 192, 201, 206, 210, 234 ONrbonarid..----- esssen scene 144, 225, 242, 243 multistriata 201, 234 OD Ntaieseence coco eeetinecstes= ane ee== 210 Pogonipensis .........--..----.------ 183,233 TOSUPiNGta .<-...<..ccce enw ~~ =~ see- 197, 238 Orthoceras) sp.?.--0-- 0 --.se~---a55~-5 135, 145, 207, 237 Blakei ......... 274, 233 cossator..-..- 208 crebrosum 144, 243, 244 Fossils, Orthoceras Kingii 785 Page. 236 Ostrea -.. - . .290, 291, 310, 311, 323, 329, 332, 336, 337, 338, 352, 376 congesta .............. 306, 309, 313, 314, 348, 349 Boleniscaesesensascee= eas 318, 325, 326, 328, 329 Oxyeena forcipata ---- 2 -onocewiewccsan ees 376 376 Pachywenn ossittapaonaccseseneecosssseeaces 376 Paleocastor Nebrascensis. 4 412 Palseacodon yerus. ....-... . 403 vagus -. - 403 Paleolagus Haydeni .......... 412 Palwosyops paludosus..-...-. 404 Pappichthysplicatus) --<-2.--.--s-cc-+-sees 405 Paracyclas peroccidens. .............-.2.2.<- 206, 237 Paradoxides Nevadensis ...........-...----- 231 Parahyos Vacane oan .c cas ceeesscsace===== 377 (Raramys|delicatnsiss--.casaactsces=saneceee 404 Passalacodon littoralis .. 403 IPecteneesaaeseewiessone 2 294 Clevelandicus . : 245 doformis paenensses eae en eee ee ece sees 283 Pentacrinus asteriscus .........-..-.. 263, 280, 289, 291 POULRMORIS Socneseeecaciccissnnssmceeecioaas 206, 207, 236 galoatusiecaccsepaseonecenceesa== 192, 237 Perchmrug! propusl-s.ccncsecsccevesecssasena 411 Phenacodus primevus...............-2..-6- 76 Phareodus acnlus:.-s2---j.s0>aciese nese enasese 405 Physa Bridgeronsis .-.........0...---scccee = 402 Phy tolethariay on-nessesceeesesasececan=neoe 420 Pinnubaria invequalis. 421 Planorbis -....-- 509 spectabilis .. 402 Plastomenus communis . 377 Platygonus Condoni .. 443 BUMAQUS Socese en seeasmeneeesaaee 430 Plenrovomanis ee -ecccecincenceos 279 Gosiute: Peake: i... sc.ccncsdies-saacce 203 basaltof So-censcseeceeees 605 Gosiute Range, Archean granite of... 57 of Pah-Ute Range. ........ 83, 84 Weber quartzite of. . . 216,277 | Granite Point, basalt of ..............- 668 Gosiute Valley, andesite, hornblendic, of............. 562 rhyolite of ... 2 634 Grand Encampment Creek, Archwan rocks of. ...... 39 | Granite porphyry of Clayton’s Peak, Wahsatch.... 46, 47 Grand Encampment Peak, amphibolite ot........-.. 40 Good thas senstiscsescoseacaaen. 547 Granite of Adara, Donegal, Ireland................. 60 Goose Creek Hills............. 55, 56 Antelope Peak, Montezuma Range. - 89, 90 Seetoya Range ..... 73 aplitic, of Colorado Range. ...... 22,23 | Granite Range, Archwan ..............-- 55 Augusta Mountains............. é 20 TOCKS)\Ofs--s=.-- <= 93 Bardmass’ Pass, Havillah Range...-.-....-. 83 | Granite Springs Range, glaciers (extinct) of......-... 76 remarkably basic, of Wachoe Mountains ... 60 | Granite and crystalline schists, genesis of .......... 112 bedded, of Long’s Peak. .-.....:....-....2- 26 petrologically com- Californinsborder:-2-a.-- 290 | Lake Lahontan............-...--. 13, 490, 495, 504, 506, 507, 524 North Peak ..- 288 alkaline carbonates of....-.-.---.--- 513 Obelisk Plateau.....-...--. 292 SGU Ofe es aee eee ese een ne eee 505 O-wi-yu-kuts Plateau 290 area, aspect Of ---<-----2.----------- 006, O07 Parley’s Park......-. SER SAS OaSSSCESSCoaaSS oose 293 chemical history of...-....--- 519, 520, 521, 522 IettyetY oe anascob caDoeOnOeee 292 chemistry, climatic deductions from. 523 Rawlings Peak fossils 290 Gesiccstioniofiess--er=-aese=e-n--5 ee. 522 Red Buttes .......-....-.-... 288 productsjof. =~. -.--...--- SIL Rocky Mountains .--...-.- Osroce SoS Saas RScHoSS5 285 flood-periods of, correlation of Glacial GENO: osoes5ss5 00soRSs apscoce necconcoec es OcoSES periods with 524 Sheep Creek .. FOSSil5 OSes e eae 2 509 Uinta Range ..-- height of terraces...---..-----.----- 518 Wahsatch Range ARGUE tee eres ooe aoe ssoscon- 404 Western Nevada Lower Quaternary of. ----- - 508, 509 Jura and Trias, comparison of, Eastern and Western mechanical deposits of . 508, 509 Prov IN COS hence sea eines sees clean = 343, 344 possible outlet of ....-...---- 2 505 Jurassic crocodiles . 346 relation to Lake Bonneville. .-.-.-.-. 504 Dinosaurs - TRVOLS| Ol gee a salen eee an ate atrnee 504 LOSBLLS eee eee eene oe eee eeencemen nese sees saline efflorescences .....------------ 513 PC VDSUM eee aceeaa seenereeaaa een eseeanicnan = thinolitelofees=-—-eee-eheee nessa 514 TOptilesiecaaeeeees sna tufa of 514 Caiion City Lake Lahontan and Lake Bonneville compared. ..--- 507, 508 Morrison ..-.-.. ake; Marian; glaciers /0fcc---< pececnacenerieeen ev amar 476 slates, microlites in -........-...---...-.-- 295 | Lake Range, Archwan mountains...--....--..------ 96 Pana pees oss seccesas ceeceseecas cae 96, 97 granite ..- 96 Kawmma Mountains, basalt of.......-...-...--------- 668, 669 thinolite of. . 515 Grass Cafion, granite ..--------. 92 trachytes of. 601 hornblendic andesite of......-.. 564,565 | Lakes, Bonneville .........-. 12, 436, 437, 466, 490, 492, 495, 496, rhyolite of-.------.-...-- senses 648 498, 499, 507, 508 trachytelOfcen-sre-aess so sste- a 601 Carnicde-cceaciconereseeseeerceaseescem eaten 622, 623 Kamas Prairie, Palzozoic of ......... ---.------.--- 146, 147 441 trachytes of -. 586 455, 456 Trias 264 Compass sceaseeeee eae Cen OSGHOdaSOEES 289, 310, 312 Karnak, rhyolite of 644 Magle sraceciseeela seme sain meee ee ae 660 Kawsoh Mountains, basalt of ...... ....-....---.---- 674 rani eee asec see eae 475 REACH Yt Olisessmceseese sess == see 601 Gosiuteessesseeee = ene ecee ac eoe = -- 446, 447 Truckee group, Miocene of ..--. 415 Humboldt 510 LIGA E ssscooseseeo cass Bentigg -eescOnccOoSSBeRHSenie 716 Lahontan ....13, 490, 504, 505, 508, 509, 511, 513, 514, 518, Kinsley District, Archzan dolomites of Seas 61 219, 520, 521, 522, 594 marbleol---o- eee Gil |) AMIN coh cohen ccorencesccaass cceeisssssacece 476 fluid inclusions -- 512, 513, 525 in calcite of. -- 6L rocks of ~ GOR) EARS eR cesses ceo she saose bees sSSsaSs PTQNILG Ofeeseee seen aeeee eee ee quartz of granite porphyry of, in- clusions, fluid and carbonic acid, see sene Setconnd SSSpanascHNCOHaCS 61 -- Koipato group, Buena Vista Cafion, Trias. ..-........ 273 Soda ...--...-...-.--0enc---000- cesaen 510, 512, 513, 514 Triagnesecceccscsecesee es 269, 270, 276, 279, 349 Winta tecasscs sos occ wees Se ws ec ooeees 444, 449 Why coe o9s ssaasseroncdassoosa cascosdeaSesces 445, 446 VA SG) 5s ceeoaacenns cen coscos cosacean 447, 448 eapradorites--. = SCer oOo EEeaS 12 relations with Vermilion Creek group -.--- 375 tufaiofe ans anpaeeceaeneceeseeanere 495,496) |) Laramie Hills. --- 2. ose se a= 141 Dakota Cretaceons .... ---. 301,302 | O-wi-yu-kuts Plateau, Weber quartzite of .....-.... 148, 149 QI Rees Brccraeaeacnces 288: | Owl Butte;rhyolitelof <<... 2.22.2. -cese-=osseennce 608 moraine (terminal) of ..............---- 467 | Owl Creek, White River group of . Sciscceo 410 North: Parkigroup Oljcssncseces cesses 433 | Owl Valley, Coal Measures (Upper) ........ --...-.- 222 INDEX. 793 Page. Pago. Owyhee Bluffs, rhyolite of.--.-------------- BocOSeLDa 624 | Palagonite, Etna. .-.-.---------- See eeeeecce sae = =so60 417 Oyster Ridge, Fox Hill Cretaceous --------- 50 325 Hawes’s Station 416 Vermilion Creek group of ..---------- 372 Mirage Station 416 referred to angite-andesite..-----.-- 419 Thingvellir Lake 417 Pah-keah Peak, rhyolite of-----------------+------>" 645 Ih Panonenue sd aenee oS 5 671 Puh-supp Mountains, Archean rocks of. 92 Warm Spring Valley .------------++---- 416 gravite of......-.--------++--- 92,93 | Palisade Cafion, andesite (augitic) Oh pees nase anne == 574 quartz of granite, fluid incla- hornblendic andesite of 563 sions in ...------------------ 93 trachyte of .-.--.------------- 588 Pah-tson Mountains, Archwan rocks in .-.---.------ 90 | Papoose Peak, dacite of. .---------------- 567 schists 91 quartzose propylite of 558, 559 Crusoe Cafion granite 92 | Paragonite schist, Garnet Cafion, Uinta Range...--. 43 lepidolite in Park Range . 57,20 granite....---- 91 Archean geology of .---------------»--- 36, 37 tourmaline in Archean recks, minerals in ...--------- 41 granite....---- 91 Archean structure of .----------------- 37 Pah-keah Peak, granite near... 92 Dakota Cretaceous ..------------+------ 303 rhyolite of..----. 645 geology Of. ..----.-+---+2eeeeeseee root 20, 21 trachyte of. - 600 SYONItC ...-.--0----eee eee ee eee eee 40 Pah-Ute Lake.-.------------------ 454 'DIG8scpeessincesceses ese ==e-- === 259 deposits of.-..-..-------+ s++-++- ==> 454,455 | Park’s Ranch, Colorado Cretaccous. .----- ---- 308 disturbance of beds. .-.---------- asseos 456 | Park Station, Laramie Cretaceous. - - - 332, 334, 335 Miocene of... ------ 454 | Parkview Peak, trachytes of....-..----------------- 580 Pah-Uto Range, Archean rocks of. 83 | Parley’s Cafion, Dakota Cretaceous -.- 304 basalt of _.. 664,665 | Parley's Park, Colorado Cretaceous. ..-.-- > 319 gneissoid porphyry of .------------- 84 Jura Of .....-.-------~---2 = 293 Granite Mountain of ...--- eee soce 83, 84 trachyte of ..------ .- 586, 587 rhyolite ...---------------- . 637,638 | Passage Creek, rhyolite of ....-------------++--++-* 610 Spaulding’s Pass granite -- 84,85 | Passes, Agate ....-.---------------ce cere etre 219, 661 trachytes of ...---------- S506 600 PAtatOle soneccccumencesecenseee see caaelea =e 602 Trias . 278 Wrémontwecessceccsececeoeeeren==1s=2= 63, 64, 193, 203 Palseozoic.....-.-------- 127 Golconds .-.-----.-.--.- . -280, 560, 561, 664 Chimney Station 21 Good. ..---00--ce-2-cc0-ccheccocecescceccecen= 547 Clayton’s Peak..--------------+-- 173 Hastings. .------ 204 Colorado Range , 133, 134 Indian ....-..- 667 Cottonwood section .--..------------------ 165 147 Du Chesne.....--------- +220 rere erent 146 94 Escalante Hills 144 631 @XPOSUTES .--------- 22 eee e ee eee etn 127 215 Gilbert’s Meadows. 150 Peoquop ---.------------- 438 limestone ---.------ 535 Pine Mountain. 620 Medicine Bow Range 135 Pifion . .. Ogden Canon section . 174,175 Sacred ...- Ogden Peok...--------+--+-+--+++7+- 174 San Gorgonio O-wi-yu-kuts Plateau. .-..----- 141 Shoshone. ...-..-------- province of Great Basin ..--.--- -181, 182, 183, 184 Sommers’ province ef Rocky Mountains...-----.---- 127 Spaulding's .....----. Rawlings Peak ..---. ------++-+------+---- 136, 137 Spring Valley recapitulation Se eC BROS COLLLL Dereon 227, 228, 229 MonnO toot coleesesseesaeeeeaa-—=ac= section ....-----------+ sees eee enerterreen? 129, 130 Yampa .....--------ee---es-ee20 > generalized...--+..-.----+---+++-+- 246,247 | Peak forms due to snow-erosion 480 recapitulated.....-----------+----- 164,165 | Peaks, Albion .....-.---- 224 Weber Caiion ..-..-------- eee ote 156, 157 Moh eeteeoetesceceaee ss cee=ss === =e cenn soe 645 White Pine .......-.-------------- 208, 209 Anita...-- 655 series, general geology of...-------- 534, 535 Antelope . 667 generalized ...-. ------------ 5 536 Amntlor tote o ccnese sece caso ceecnec--ceseesees 219, 225 subdivisions, tabular statement - - 5 248 Manaltnecocceeccusisceceectincccs=-s=— stuns 669 Tim-pan-o-gos Peak ......-..--+++++-++---- 172, 197 Black: Butte -....-cssccccccccencscrescoeccen= 336, 337 Uinta Range..----.------------ 139, 140, 141, 153, 154 Bonneville. .......-.--+ eee ee connect eeeeeeee: 185, 593 Wabhbsatch foot-hills .......-------+-------+ 173 Box Elder - 18L Yampa Cafion......----------++++-- 144 Bruin......--.------- = 38 Palagonite .--------------++----++2-° -. 416, 454 Buitalo!c-----sccess=-0 268, 654, 665 age of .....--.---------- ~--. 418, 419 Carlin .....-. .cececeeee cnen eee ere neceeeesn es 563, 621 analysis of ..-.--------+-++--+-2-+-20e0e0" 417 Chataya - -600, 640, 664 dependence of basalt ..-..--------++-++++ 419 OlarkBses sucess cecccceccecucesccocsedsoes ity 10,00, 9L 794 INDEX. Page. Page. PoakssClayionsi--scecccassccccrcccresceesss 45, 46, 47, 126, 173 | Peko Peak, rhyolite of ........ Btncaéasscceccoce arecos 617 Cloventesssscascsonescescsacccceenmecicee eee 66,475 | Pelican ‘Hills, Palw@ozoic--.2--.-.....<-.-.-.-.-----+- 197 ‘Gonnorlsisa-c os ssc aee concns cen ceecse ene anes 214) 221" Penn Canopeccessteesscetes ccceceeeeecer eee 217 Cortez 621, 622 | Peoquop Creek, trachyte of .....- mons 595 Orescentinessscon--ceeeees 564, 575, 576, 581, 582, 583, 584 | Peoquop Pass, Humboldt group of -................. 438 Diamond 367 |) Reoquop Range,Arch@an--...-2--2---=--5) ceeseeoee 58 Emmons’ . Coal Measures (Upper) of .......--. 222 Rtheliee. ss. Green River group of .............. 391, 392 Fairview Spruce Mountain, Archean schistsin 58 Fortification zircon in musco- Gilbert's 151 vite schist...... 58 Gosiute 203 Wahsatch limestone of..-........-. 200 Grand Encampment... 40 | Peoria, Dakota Cretaceous ....-....-....---..------- 303 Hague's 6,18 Chr Mek etsces seresnscos 292 Hantz .......-.22.02---.000---314, 582, 583, 584, 654, 657 Trias. c= 264 586 | Periods, orograpbical . 40) Permian). << sc02-----eseeeesseaeeeracee 141 | Permian and Coal Measures, relations of ............ 343 562 | Permo-Carboniferous .--.........20cccce--cecceeneee 144 26 Cottonwood section 171 95 fossils): 5 s<<<<.shen6 245, 246 619 LOST epee Somee acess 146 Mahogany. . 203, 613 Wahsatch:-<2--.0c-<.ssessass 155 Medicine ... - 7,19, 34 foot-hills=.-<.-+----= 173 35 Weber Cafion section..-......- 163, 164 Santee de Anococctiesaoookcoo Sas sdest As P18) 2245] Plath: ee en sac ccan sgn nae ceceenee nee coe ee eee 698 5 94 | Phlogopite in gneiss, Clover Peak, Humboldt Range. 66 - 617 granite of Wachoe Mountains ........ 60 =96); 654,655) Bickeringite)-ce-sse--seos=sseeeeeeeseeseeee =s 499 Sash aansaache ss ssemamelse seem e see nee 288 | Piedmont, Green River gronp of ....- -- 390, 391 174 | Pilot Butte, trachytes of ...........-- - 585, 586 21:7::223) | ePilotePeak-s-..---+s+--=<= ACESS cH One Case Stee OS 215, 221 603 débbrisjofi tes eee eetocsceccctsc 481 92,645 | Pine Bluffs, Vermilion Creek group of .-.. - 303 ‘Papoose: =---e-ce-secenseses 558, 559, 567 | Pine Mountain Canon, trachyte of ..---.. A 600 Parkview 580 | Pine Mountain Ceal Measures (Upper) . - ; 222 POKO#2 ces sewnessccceeceteeeesesee Soosondess 617 | Pine Mountain Pass, rhyolite of .....-.............. 620 Pilotic22---csecsenseaseass= steam ateeees 215,221 ,4815)\ Pinto -Peak: cc. sence gece cccensas sacs cess aneanceane 190 (PintO:s =o -eeescaee So -- 190, 660 basalt of .. 660 Quiednanove........ a3 = 476 | Pinon Pass, basalt of. - 660 Rabbit: Kars--cscoccacscccececisacnees ae 633 rhyolite of .. . 619, 620 Railroad!s2n-socccescenasacieees smemaenaneee 622, 622, 624 | Pinon Range...... COHCE CRSA ABSaactedeosteoss denice 619, 620 Raven's: Nests. .cs\sssscaseancicates SOCCEECES 189 Cambrian and Silurian of...-......... 189, 190 Ravenswood : soon 18509 Devonian, Ogden quartzite of........ - 193, 194 Rawlings... 136, 137, 289 Humboldt group in........-.--.....-. 439 Signali;cicc sssasestseccnnceleseosecscecee sicees 280 rhyolite of 620 Shoshone 476, 568, 569 LACH Y tO Ole ceemcs enemas cen ececinees= 596 Spanish 651 Upper Helderberg .......-......... son 210 Star .--.- 270 Wabhsatch limestone in.........-..... 209,210 State Line 650 | Plagioclase-hornblende-titanite granite, type IV .... 109 Tebog 640 | Plateau of central Nevada ........-.-.--.----.. c 12 Tim-pan-o-gos 172,197 | Platteville, Laramie Cretaceous 332 Toano 222 | Pliocene lakes and their deposits 3 542 Tokewanna ............ Boa nacasaAaaaeasooas 150 | Pliocene of Boise Basin ............-..-.------..-00 : 440 PTinity <2 32 -.20.2 ce encccese cece nee ee renee 667 Cheyenne Lake. 2-2-2. -2-<2<.c- SAOCSSEO 455 Tulasco. ---202, 216, 610 conditions at close of 488 PE WAIWsian. ceewusesan's saocs pence tee eeene ates 229 conglomerates, Big Thompson .- 431 Utes a.itecn nov cccacaaestaas seen aeeeetee 145, 179, 180 Sybille 431 Whitehead ~ oc... s.ccsscceas cae ceeeee eee 582, 583 Great Basin, vertebrate fossils in 443 AMPA 22-2. 22 semen nan sees coat ere ne eee -——s 141 427, 428 Peaks, rapid degradation of ............. 472, 473 Humboldt group. .--....--..---- 434 Peak topography the result of névé erosion......... 479, 480 Niobrara group. .-. Sees 425 Peavine Mountain, Archean rocks of ..........-..-- 97 North Park group .......-...----- 431 quartzites, Archwan............. 97 of the Plains, vertebrate fossils 430 Pormatitey: ooo sc case --csan ene cee ee ee 38 Thyoliticstults so ses 451, 452, 453, 454 talus-slopes - - Prescott, Arizona, specular iron schists of ..-------- 105 | Quebec group .-------------+--2-22205 cote ner nese 178 Present distribution of perpetual snow.------ 462 fossils.....----+-------- 22 eee een nnn 188 Present rise of Great Basin lakes .-- --- 525 Ute Peak 180 Pressure-gradient, terrestrial .......---- 702 | Quebec and Lower Helderberg fossils.-- ----------- 192 Problem of volcanic fusion - ------------- : 696 | Quiednanove Peak, glaciers (extinct) Olfe-seene == 476 Prilss, palagonite analysis by---------- --------7-7" 417 | Quien Hornet Mountains, Green River group of ---- 390 Promontory Range, Wahsatch limestone Ofeeeree aan 196 Vermilion Creek group of 368 Propylite .--...---------+---++-2 2000 _. 545,550 | Quinn’s River sink, efflorescence of 514 (augitic) Silver Mountain ----- = 554 | Quinn’s Valley, rhyolite of .----------- ------ 648 Truckee Caton ..----- .. 553, 554 Berkshire Cation, Virginia Range ----.---- 554 Boon Creek, Toyabe Range .-------------- 552, 553 | Raft River Mountains, Archean of ..----------+---- 54 Cortez Range .-------------------++0rre7t* 552 Citadel Peak, granite of. .--- 55 Fish Creek Mountains ..-------------+---- 552 | Ragan’s Creek, basalt of 664 Kaspar’s Pass, Montezuma Range -.- 553 | Ragtown, Soda lakes....-------------+++--270700077" 512, 513 most limited of volcanic rocks. ------------ 551 | Railroad Cafion, basalt of --.-----------++-----+7-77° 660 (quartzose) ..--.-----------+2+2++--0 20077" 557 Wahsatch limestone in --.--------- 209 Cortez Peak 558, 559,560 | Railroad Peak, rhyolite of .--------- .. 622, 623, 624 Cortez Range 557, 558, 559 | Ralston Creek ....--------2-----02eeeectes rr 23 Golconda. ------------ .- 56(,561 | Rampart, The, basalt of..----.--.----++--+-+-507777* 654 Tron Point .-.--.---------------+ 560 | Ranges, Aqui 185, 186 Papoose Peak..---.-----+------- 558, 559 Augusta ...---------------- --2----== =-="=" 564 Wagon Cafion 558 Cascade..-.---------------ee2-- eer 452, 453, 454 Steamboat Valley .--.------- ----- 534 Colorado. -. -5, 6, 17, 18, 19, 21, 22, 23, 24, 28, 104, 132, 133, Virginia Range ------------ 555, 556 134, 249, 250, 292, 299, 305, 467 Washoe. .----- ceeeeeeereeee -550, 555, 556, 557 Cortez ..----- 70, 71, 72, 73, 74, 219, 552, 557, 558, 559, 563, Propylitic tuff, Daney Mine, Washoe 550 566, 567, 574, 620, 621, 660, 661 Protogenoid granite of War Eagle Mountain.....--- 105 10} VY pepe EOS IEHOOODII CUS OSE OESION ... 393, 616 Province of western Nevada Triassic ..------------- 266, 267 Gosiuteceencessecenene=-l-===" . .5T, 216, 217 Provo Beach. .-.------------ ceencn eens 492 Granite .....-- 600 BE ee eee ae 00) 99) 08 Provo Valley, trachyte of ..----------- Havallih)-c------------- 81, 82, 83, 87, 280, 281, 600, 636 Pseudomorphic chlorite after garnet Humboldt ...----5, 12, 62, 63, 64, 65, 66, 67, 68, 69, 70, 85, Pumpelly, Raphael ...-----------+--++-++reereest eee 86, 393, 475, 476, 502, 614 Purpose of this volume ...----------+----++--7-"""" Pyramid, thinolite of tho..-.-------+-+++++++reseeee* Take coesesasccecesee=) @a===s5=r--—=en- 96, 97, 515, 601 Medicine Bow - ..7, 20, 28, 29, 30, 31, 36, 135, 250, 310, 407 796 INDEX. Page. Ranges, Montezuma.....- seccescessecerss 87, 88, 89, 90, 642, 667 | Rhyolite, Antimony Cafion .......... etait Ombe...- .-- 56, 57, 608, €09 | Augusta Mountains Oquirrh. . -213, 221, 393, 590 Battle Mountain ....... iPah-taon-sesceceeesen ee ace oe aaneeee eee ees 91 BaylessiCanion\ on. <2 oe eae eee ee Pah-Ute .....-.. 83, 84, 85, 278, 279, 600, 637, 638, 664, 665 BOGNLY CS aioenjam Sosan em eieesea sen netceeeee (Parkmeasacs = asasane --5, 7, 20, 21, 36, 37, 41, 259, 303 Berkshire Cafion ....-... iPeoquopiss.sscssee- ---- 58, 200, 222, 391, 392 Black Caton ....... Scetee : PEN Olean seat 189, 190, 193, 194, 596, 620 Black Rock Mountains. . ---- 648, 649 PLOMONtOLY, son atensanicais caa|sestestiaatsiasicisaa a 196 BonewWalleyeesesesseaseaten cases ees 617 Riverses-cs-s-ese eae eee 117, 392, 572, 616, 617, 618 CaricoWbake)-...ncmeccesiscasenlcleseeecers 622, 623 Seetoyarccc-ccacecesneecocs 74, 75, 211, 573, 596, 618, 619 CarlintPeakstc.cos.ccennaeecaces cecteeeees 621 Shoshone .......... 77, 78, 219, 220, 622, 627, 628, 629, 662 ChatayalReak, 2c. scare -shaceeeattanstaesee 640 Toyabe .... 75, 76, 481, 552, 553 Clan:Alpine!Canion--nc.<" 154, 155 Fox Hill Cretaceous .-.----------+------ 327 | Section Ridge, Trias...----------+----srrrett et 201 Valley, rhyolite of --------+----++------* 626 | Sediments, subsidence of -----------+-----*> 115 Rocks, Plutonic and volcanic, differences of .---.---- 206 | Seetoya Range, Archwan rocks of..----- 74, 75 Rock Springs, Fox Hill Cretaceous ------+----+-+--- 324 Coal Creek, trachyte of.------------- 596 Rocky Creek, Basalt of ..-..------+-+eresters seer 664 granite porphyry O) Ba mato: aeabeseoo 75 798 INDEX. Page. Page. Seetoya Range, quartz of granite, inclusions (fluid) Slope of the Great Plains, Niobrara group of ....... 426, 427 with salt cubes in.........-...--.- 74 | Smith, J. Lawrence, analysis by 499 quartz with granite porphyry inclu- Smoky Valley, alkali flat of ..... 503 sions (fluid) with salt cubes in .--.. TAY | SEV CHOP OY S53 e ha -emaenocsssaassemnemcaececeace 592 rhyolite of......-...---------------- 618,619 | Snake Plain, Pliocene of .._..........--.-.-.25-..--- 440 Susan Creek andesite (augitic) of... 573 | Snake River; redigneiss of --.-----.-----_ses---oesee 41 Wahsatch limestone -......-..-..--- 211 | Snow distribution of Glacial period..............-.-- 477 Weber quartzite of..... ~ 219 erosion, peak forms due to..-.......-.-..-.---- 480 Separation Station, Laramie Cretaceous..-.-.--..--- 334 line, downward encroachment of .........----- 526 Sepiolite of Paris Basin........-.---.--------------- 116 perpetual, present distribution of ...-......--. 462 Sheep Butte, Colorado Cretaceous 313 | Soda lakes, Ragtown, Nevada ...-.... --510, 511, 512, 513 Sheep Corral Caion, trachyte of ...---- .. 603,605 | Soldier Cation, Weber quartzite of .........-...----- 213 Sheop Creek, Jura..........----------- 291), | (Soldier|Creek, rhyoliteof-.-4-ssesey meee eases esse =e 624 TTIAG)-\o\-s~ cies sacs ca'smne sine cenmncinele cic 260; 261, |; Sommers? Pass; rhyolitolofcena--eseaa- saat e ae scaas 639 Sheerer, mentioned 1145 eSoutSprings basal viotseeastessseseee nen eecasetescen 664 Shoshone Basin 592 Thyoliteiofsccsase esac eeaaa see aes 638 Shoshone Falls 592 | South Bitter Creek, Vermilion Creek group of .-.--.. 365 Shoshone Lake 456 | Spanish Peak, rhyolite of 651 457 | Spaulding’s Pass...........-...-.- 278 Shoshone! Mesa: esn--c-s-oc en cveseetenn= = slemas= meer 662, 663 | Specular iron schists, Prescott, Arizona....-....-..- 105 rhyolite of.. -- 624,626 | Split Mountain, Trias.............- Gescéoccoocoscess 261 Shoshone Pass, rhyolite -- 632,634 | Spriggs coal mine. .............2---..-----eeeese- == 317, 318 Trias ....- BO 281 Fox Hill Cretaceous .....-....-.. 328 Shoshone Peak, dacite of.......-..-.--------20------ 5684569!) (Spring Valley Pass, ([rias)---..2---------sa=—=—=ce= =< 270 iaciers| Of. conc csecseseces-no=s'e-=0- 476 | Spruce Mountain, basalt of ...-.-.-.--..------------ 660 Shoshone Range, Archean rocks of .. 77, 78 Wabsatch limestone - 200 basalt of --- 662 ; granite of ...-.. SSS CHB SSCS CCEA cic Ravenswood Peak, granite of ..-.. 77 | Stansbury Archean rocks 78 | Stansbury Island, Wahsatch limestone of ..-.....--. 199 Archwan Stanton'Creek, Trias). .2--\sescesacmaessnass—e 264 schists of..-. 79 | Star Cafion, Koipato, Trias... 273 rhyolitojof ----<.---.-<.-=-- 622, 627, 628, 629 | Star Peak group ........-... 347 Weber quartzite of ..........---.- 219, 220 AMEE nee Socmacepacecocacinecderencecs 270 Shoshone Springs, rhyolite ...-.-.-...-------------- 634 | State Line Peak, rhyolite of ........-.- Soressacaosss 650 Mrigsicco=-acaeeesices 281 | Staurolito in schist, Garnet Canon, Uinta Range - 43 Shoshone Valley, basaltic plain of...-.--. 679 | Steamboat Valley, andesite (augitic) of. - 576, 577 Sierra Nevada ---<-..-2<0nnsceee==0= 452 propylite\of-<-----.- <2... 554 glaciers Of ..........-0-22200-see--050 463 | Stevenson, J.J. ......0-- --< 200 caneaeencenecseenes--- 331, 332 mountain disintegration of........... 472 | Steves’ Ridge, trachyte of .........------547, 581, 582, 583, 584 talus-slopes of ......-----------eee--- 485 | Stockton, Green River group of. 393 Signal Peak, Trias .......-.--..----+-----+---+sseeee 280 | Stokes ....-..---....--..---- 705 Siliceous schists 34 | Stony Point, basalt of. - - 663 Silurian (Niagara) fossils ...... OS40 StOppalll aaonsee ace ese ates sa aene nner ecs= eee nee 706 (Quebec) fossils ...-..--.-. 233 | Strata, contiguous, absence of chemical action be- Uteilimestone>..-2s----ssesesese- cere ==--—= 175, 176 tween, in Archwan beds .......--.....--.-0--+---- 112 City Creek Cafion..-...--..- 173,174 | Stratigraphical geology, résumé of..-...... 531 Cottonwood section .....-.-. 167, 168 sections summed up 542, 543 recapitulation......-... .-- 231,232 | Strong’s Knob, Wahsatch limestone of .--..--.------ 200 Weber Cafion section ...... A 157 | Structure, microscopical, of thinolite........-.-.-.-. 517 White Pine’ Range) <<: --<.cssece-e=se=—- == 188 | Subaerial Quaternary -........------------ 484 White's: Ranchiass.ceccessceceoseescen= Sach 192 | Sub-Carboniferous, Dry Cafion .--..--..---- 197 Silver Creek, Miocene of. .....--.----02- cesses ece--+ 414 fOSSUS eases semaines cient é 238 trachyteOfs-ccsccecsecesese easecene sma 588 | Subsidence, two types of.....---.. .--.-----+---+---+ 732 Silver Mountain, propylite (augitic) of .....--....-- 554 | Succession of andesites.....-.-.....---------+-++--+: 684 Simpson) cose. cose as-satccashenestesaciecieaseiceeancs 1 trachytesi.--s-cmcesa= socio —=—= 684, 685, 686 Simpson's expedition ...................cccncceccece 211 volcanic rocks ........---.----- - -683, 624, 687 Sioux /Creek; rhyolite ofi-<----2---cossccesencscecoe= 607 | Summit Spring, Trias...--. Aco 280 SiouxtbakesMiocenoss<--nss.scceccess ceceteoteescceae 451 | Summit Valley, Uinta.........--.....---------+----- 145 distribution of .........-.------ 451 | Sunny Point, Green River group of ...-..----------- 385 Siskiyou Ranges. 9c=--se+ccataaeeeeaccceeacesacs Susan Creek, rhyolite of 619 SkolligstRidget:---- cases ceanaceesaseenanesecen=s == trachyte of 595 Skull Rocks...<..5.....-... Sybille, Pliocene conglomerates of. 431 Slater's Fork, trachyte of.. A Syenite, Cluro Hills...........--------------2--2++- - 172,73 Slates on French Creek ......5.....-cccccccccccccncs Park; Range). -cccnescoesscacencrleccaseasi=-=— 40 INDEX. 799 Page. Page Table Mountain, basalt of..............--- Saas ee eee 664 | Trachytes, Aqui Mountains ...............-.-------- 593 rhyolite (ofe-sece-senceaeeeseneceas 639 Astor Pass....-..---- C02 Tabor Plateau, Green River group of..-........---... 387 Bonneville Peak 593 Vermilion Creek group of. --. 368 Cave Springs .----- 595 Tabular statement of Palawozoic subdivisions. . Cedar Mountains .............-...--..--. 594 Talamantes Creek .-........-------.----00s =o Chataya Renkieere=slaneea=-ens eee =e le 600 Talus-slopes of Arizona .............-..0-----. neces City Creek, Wahsatch .............--..-- 590, 591 Oh CAliOnia jac. sesanen a= eseoeaee eee Coal Creek, Seetoya Range. .-.-.---.-.--- 596 formation of - Cortez Mountains..-..-. 598, 599 OfeNOVAGS ace essscessee=e= Crescent Peak==--cssne-ssens-o2-" 581, 582, 583, 584 Quaternary of.-...- wderreece--- > Davis Peak -....-. Be eee ee 581 of Sierra Nevada. .........--......----- 485 distributioniofesscssesos-sio=so-seesee ees 578, 579 Tebog Peak.....--.-----.----++---22 222s eeeeee eee 640 IDS SEN cece eeconoceasose Snquetcoss 597 Terraces, absence of 484 Dixie sPasseteee sees nena senna etesenee 596, 597 in Cordilleras ....- 466 Hast|Canotessssceeesaaseaseseaw ase 589 height of, Lake Lahontan...-. 518 Elk Head Mountains .- «aeece= OGL, 082, DES: lacustrine, Quaternary.......-----.--.---- 488 geological connection of. ....-.---...----- 579,580 TakesbonnevallOs ess sacs sees eran s soe = Han tak etkessen-mosaes cher sae 582, 583, S84 Terrestrial heat-gradient. -. Havallah Range - ze 600 pressure-gradient. Heber Cain... 587 rigidity ...-...- Heber Peak .........- 586 Tertiary lakes, résum6 of...--..---..------------+-- Henry Mountains, age of......-..--.----- 548 table of Undian/S prin geese .eos en eae ee ena ee nee orography ----- Jacob's Promontory - - yoleanic rocks Jordau Valley ..--- and Cretaceous, Great Plains, age of. Kamas Prairie .-..- Thingvellir Lake, palagonite of. ......-..-.---------- 417 Kamma Monntains ......-.....-.----.--. WEST nae ce coseca nes aeHe sacra aes Soon Dens Seccrs 508 Kawsoh Mountains ......-..-----.------- ‘Anah6 Island’< <2. <-2--5..--- 515 Lake Range botryoidal surface of..-...-..-- 517 Medway chemistry of ......-..-.-..--- 518 OquirrhtKan2@s—- oe esscaneeosea=oe === crystals, gaylussite. ........-..------------ 517 Ormsbyihea keer sa.-=eae aaa distribution of .--.. 514 Pah-tson Mountaina.-.-.......-..-.-------- GTNED Spe dccaecte Ssodeccocshoeenaadccans 515 Pah-Ute Range ..-.. Lake Lahontan ....:....--..--------c-00-- 514 Palisade Caiion .. 5 Lake Range. .......-------- 515 Parkview Peak -. - 580 microscopical structuro of. - 517 Parley seal ksweene=eeeeee ae eccee se iese ee 586, 587 octahedral crystals of ...-..-- 517 PeoquopiCreeks-.-s--eseceuns ss eeneee sane 695 pseudomorph after gaylussite..-...------.- 518 Pilot Butte. ....-- -- 585, 586 thopeyrarid one aseoericeeeceee= ace as mms 515 Pine Nut Canon . 600 Pyramid Lake region 515 Pifon Range. .- 5 596 ‘Truckee Valley ....-.---.-- 516 IPLOVO CANON eeesn sea eeatanne tea mane 58 Virginia Range .......-.- 515 IPTOVON Gl lOyoe nase eames eee 587 ThomBon! sAames esses os aee = 2 eae Sos. noe esse see 704, 728 Pyramid Lake region. - 602, 603 Thomson; Sir: William... --<-2-22:----0--2+s--=-- 696, 697, 701 Rocky Mountains......--.------.- - 579, 585 Thousand Spring Valley, Humboldt group ----.----. 438 Rose Caiion ..-.....- 5 z A 590 Tim-pan-o-gos Peak, Paleozoic of ......-...--------- 172, 197 Sheep Corral Cafion............-----..--- 603, 605 Tiraks ysl AlGaAs = sae ese aoe ca seca a's =e 262 Silver Creeks /.cos=--aeesen==Seennnen ane 588 Titanite in granite of Wachoe Mountains .......--. 60 Slateris hotkses--ceeeaseae ease seeneceoes 585 Toano, Upper Coal Measures of......--..--.-------- 222 Spake Cavoneenassscassa-\sae== 599 Boon Creek, propylite of. . = 552553: SwWihitehead Peake... -----n-ccceaecerceea= 582, 583 Dome Mountain, débris of.........-. 481 White Rock Springs ........----.-------- 594 RTANite Of ae seen/e7aceee aa csaseaeas 75, 76 Willow Creek............------. -- 593, 594 Park Mountains, granite of........-. 76 | Trachytic tuff ........---.------------+---- 454, 589 Mracny tes! -meeeenees==secese enone =n ciaee 578 Miocene of. ...--..--.---.. -- 422, 423 Ada Springs ...--..----- 581 | Trachytoid porphyry-....-.-.-..---------+---0++-+-=+ 581 Anah6 sland ii2 258 Miocene .ofc-ssescensnesso ese eseeers 412, 414 Chngwater. ..-.-- - 253, 254 BOCtION OL seaees esse ayeannaienesen=e 415, 416 Colorado Range .--- 249,250 | Truckee Miocene ..--.. ...-..----- -<- 00 ecnncee cen en- 454 cross-stratification .-. A 344 | Truckee Range, Arch@en. .....-.......-----.---00-- 94 Dead Man's Springs.........------- PROS OeEEES 261 basalt Ofess— so-so eeecie- ede neeecete 672, 673 Desatoya Mountains ......0.2.c00---e-0-----2 252 Luxcer Peak, Archzan schists --.--- 95 ddlomitejseassscorenwecicececesocaccnae= 344 Nache’s Peak, granite .......--..-.. 94 DuiChesueenaccerescstecrceceesnaciace - 263, 264 PNY OlitO Obes eee seen eee ects er 650 Dunn Glen... 279 Winnemucca Lake, granite near -.. 95 Elk Mountain. - O580l PTrnckee ni vVencass- a2 secant ele enn eee 13 Escalante Platean .- 261 bifurcation of 405 ish’ Creek Mountains: ..+ ..00ea<-0-css~cnnee= 281 | Truckee Station, basalt cf .- 676 Flaming Gorge. ......... 202 --secsccsesccnenes 259,260 | Truckee Valley, thinolite of........--.-------------- 516 fossils =-s 360, 361 species, genesis of.......------------+-+-+- 705 Evanston -..........-------- 70 theory, Mallett's ....-..-----.---+-- 698, 899, 700, 701 Flaming Gorge ...--..----- 368 Fortification Peak ....--... 362 fresh-water mollusks of. --. 373 | Wachoe Mountains, andesite (augitic) general extent of ......---- 374 Arch@an ....---2------seeee-ees 51K 802 Wachoe Mountains, hasic granite. granite ......----202ss--s52--=-- inclusions (fluid) in apa- tite Olceeeeee eee een 60 phlogopite in granite of ........ 60 quartzofgraniteof, with saltcubes 60 rhyolites/of---s-cssssesseese= es 611 Spring Cafion, rhyolites of. ..... 612, 613 titanite in granite of....-..--.-. 60 Wahsatch limestone of .- -- 202, 203 IWIRGB WOLD) coesmactcccesscisercie= i 376 andesite (augitic) of .........----------- 76 Wagon. Gafion, basalt ofc. 22 25 ce ececceene------- 661 (EO IGK) etesapecercsospaSebcocosbasscoc 567, 568 propylite quartzose of. - 558 trachytes of .......-. “in 2 598 rWahsatoh Hmest0ne 2.04 «ssseests sss seca e= eee as 155, 195 absence of lacustrine Quater- MOE CABG Olsesccaseser scm 448 Antelope Spring .--..--.---- 196 Aqui Range... 199 Babylon Hill 206 black shales of .......--.-.--. 199 . Blue Ridge ---2-co el - anne ae 207 Carlint Valley: -----<..6-.5.-<. 212 Carrington Island.......----- 200 Cottonwood section.....-. 168, 169, 170 Dolpbin Island ........-. .-.- 200 Egan Mountains.-.-....--...-- 203 fossils in Lower Coal Measures 239, 240 Gunnison’s Island....-...---- 200 Hat Island ic 200 Humboldt Range. .....------- 204 Lakeside Mountains...-....-.. 200 Ogden Cation section -. - 176,177 Peoquop Range ---.--- . 200 Pifion Range ..-....-... . 209, 210 Promontory Range ....--.---- 196 Railroad (Canonysccssesces- <== 209 recapitulation .......--.. , 236 RuabyiProup)---- coe----- Pree 217 | Witch’s Rocks, Fox Hill Cretaceous 330 Salt Lake Basin 214 | Woodward, R. W..- 499 Seetoya Range ............ 219 his determination of zirconium.... 52, 53 Shoshone Range a PIMLCST) |) Wiebe Ob) ob acoscasnosbosponcoocnesnnedoseecocooboo 420 Soldier Canon ....- 213 Tucubits Range WEES HESIE® co noseecosenecoo-cece Via palb Oakceeecee cece cman eee ae cecectescer ce ae 141 Wishkatoht.-= S Reis Plateau, Colorado Cretaceous).---.----<--<.- 315 z 8 oeceslecenceceeate see teres oe 261 WGISER CEE BEEEIOA coc Yosemite Valley, granite of 120 Weber River ..c22 secae cesses osc eyecete Biel iid MOR) , . ‘ uM Wed ey Rhema: Poe haa Oo s MN Pe ; Oh : esha etibestoararesarmateorey pass Na Agta a oy SRE eels ? : ibs alee ul ae Rt el aes eke “ 5 \ 5 Sgt re at bef Pes OT atere Bier Mod nahi , p . ) Neck tents 1h hte : ieee tt ay ve : ; , ely tes seedine eter i ° if + Pe . Ich apipeetbtylererm speondeereraemeReiid wicker eePhMtere pis th, mee Ural ely bt ini itristeae ih dteee escbroren aber ion yore hts SA ibebtnide-pipeee per r chabert TENS Paarl aller g 4 EASY A eben Ga aheeaneats Paina tate tian Stepan ! UT , ! iets RT Tae tateta rien atric He ‘oe . reer Tee abaapensaeyis evyehed syapenatghadevirke: faites gearesyity oo bee : ora Peeengit Pepteraed sines anh ha rep ARNO de De Pubtan bel ps as heals ( y ’ wie r arrests elites ae et eT re ater add Bll tama fe vaste Sits WANE Poti? Mant ari eS ihe peatoae HTL CANE ri totenyas edad spearalouathsenr Say hale Wbsheswtne Wah s 64 | vee ‘s) ‘ , ones tet shor s et p Dae pe ses UE x i ; Se , cere ope llasbenten eebrpNb tie thy Fed) meg AT Mit Bebb i b-8 Ui hed b r iota es Port arin 35) bine bibs bene) " , } beet fia ‘elite ete Soe a FU ae Pay . . \, apis Retry atat: EB esWee Deb wisi 6 oF eer ewe AAS: Ba Ne Wve Pere + ppg Seid rf ¥ “ye ye D . yf Lad ) he (arnt ote ie \ hp iw =a" ’ her. ,