2 pete de SWE nat Perr ess : Tek tee Bah madera sins AO PTET ms aevsoh ape naman abet eeheae eerie, HD eee SSS Patina oeeters aa eanersenenstonreaeersersch a aie — - ree —_ a ; o “ee — , e see ee Pieter he are Ginetta eet cine Sa ee See <5; Ames en, Spee et tcnintee De wens alae eee ead ae eeu egg es bape Ap hye PG Le Sete eeetod TepA eh dL) a ¥ a ve ; Rey ae ee» . ' “ _e a) WS) GEO |. Expl. 40 Parallel T G (WE BASIN _WYOMIN EOCENE BAD-LANDS _ WAS! 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 BYT. MAJOR GENERAL A. A. HUMPHREYS, CHIEF OF ENGINEERS, BY CLARENCE KING. U. S. GEOLOGIST. I-II CLARENCE KIN G,- GHOLCGIST-IN-CHARGE UNITED STATES. GEOLOGICAL EXPLORATION OF THE FORTIETH PARALLEL. + SDP ae. DESCRIPTIVE GEOLOGY. BY ARNOLD HAGUE AND §. F. EMMONS SUBMITTED TO THE CHIEF OF ENGINEERS AND PUBLISHED BY ORDER OF THE SECRETARY OF WAR UNDER AUTHORITY OF CONGRESS. WASHINGTON 1877. ‘ GOVERNMENT PRINTING OFFICE. vV-VI ILLUSTRATED BY BONA PLATES Aj eR 3 epg hare on Be 1381. a ae tf at la iret eta ‘i Zp STE | fs CG 2, \ 4 - S| cad 3 2 fe 2945 oe v4 align a! Wyse? oe” “Riy, Che Mv 2s ; a a Teall TABLE OF CONTENTS. Page LN OD CRO R Ver lan lh Ey se seer eo ee a eran ih vay aioe! Saleen cick cAle o- Xi EO RIER LO. Bb GC hOLOGISTAIN @HAB GH cso so. see to Dee casas Sec cece see's XIII CHAPTER SOCK YeMOUNDAING cs =i. e.r occas thes ona to an ein gs eee cessed ca we ss 1 SECTION I. COLORADO RANGE. BY NER ODD HAGUE....... 2 Il. LARAMIE PLAINS. By ARNOLD HAGUE....-.... 73 Ill. MEpIcINE Bow RANGE. By ARNOLD HAGUE.... 94 IV. NorRTtTH PARK. By ARNOLD HAGUE........... 112 V. Park RANGE. By ARNOLD HAGUE........... 130 - VI. CRETACEOUS REGION FROM CoMO TO SEPARA- - TION.: By ARNOLD HAGUE.................. 142 VII. WEstT oF NoRTH PLATTE. By S.F.EmMMons... 156 VIII. ELKHEAD Mountains. By S. F. Emmons ..... 167 TX. VALLEYS OF THE YAMPA AND LITTLE SNAKE RIVERS: BIS BD MMONS Ge). case okey... 181 CHAPTER IL GREEN RIVER Basin. By S. F. EMMONS............-.. -.-.- 191 J SECRON,: — «9.7 PHYSICOAT DESORIPTION. XIV. Wabsatch Limestone Cliffs, Provo Cafion, Wahsatch Range.do.... 348 XV. Granite, Little Cottonwood Cafion, Wahsatch Range.......do... 356 XVi. Cambrian Rocks of Big Cottonwood Cation, Wahsatch 4: JEEINEG 2 2 SARE Se se ea sii ee -do.... 368 XVII. Caiion in Limestones, Hast Humboldt Range, evade Byatt do.... 530 XVIII. Glacier Cafion, near Clover Peak, East Humboldt Range, “UNE sy FS. 0.2 Be 2 Seep ee eee : O02 TSO Carbonic, acid) Doses: CUTIE oe een 33. 937 Watemestn e000. 222 8 ed POLS 0. 140 99. 890 which, when combined, yields— Carbonate of lime. 4:1. 4/25) seen eee 16. T48 Carbonate of magnesia= 9325.32). eee 0. 821 Along the east side of the plains, the Dakota sandstones may at times be recognized, cropping out above the accumulations of Quaternary débris, sufficiently well defined to trace their horizon. At the north, the beds appear to incline westward, with an angle of 2° to 3°, but become hori- zontal to the south. They crop out just east of Lake lone, and, so far as observed, are found only on the east side of the Laramie River till within 6 or 7 miles of Laramie City, which they appear to underlie as well as Fort Sanders, and to form the banks on both sides of the river; on the west side rising above the stream.in a low rounded ridge, sloping west- ward. : The rock is a yellowish-brown, medium-grained sandstone, with some carbonaceous material scattered through the upper beds. South of the railroad, the Triassic, Jurassic, and Dakota Cretaceous, following the boundary of the Archean, curve around to the southwest, lying inclined at not more than from 1° to 4° toward the plain. The Tri- assic Red Beds rest directly on and overlap the granites, jutting up against LARAMIE PLAINS. 19 the steeper slopes. All the beds fall away gently, with an occasional ridge formed by a layer of hard sandstone, capping softer beds, which presents a slight escarpment toward the mountain, and through which the streams have cut their channels, exposing portions of the strata. On Antelope Creek, the gypsum deposits are well shown, just north of the Willow Creek and North Park Road, interstratified in dark red sandstone. South of the road, about one mile, bordering the creek on both sides, the light-colored Triassic strata have been eroded into the most fantastic and fanciful forms, which very readily suggest the name, which has been applied to them, of the “Ruined City”. They are neither as prominent, nor cover so large an area, as the similar formation at Red Buttes, but, on the other hand, are much more compact, with great diversity of outline, and suggest a variety of architectural designs. A short distance west of Antelope Creek, the Triassic rocks occupy a re-entering angle, or depression, in the Archean body, extending some twelve miles to the southward of the Colorado and Wyoming boundary, and westward to the Laramie River. Along the east side of the river is a nar- “row strip of Archzean rocks, upon which the Triassic beds rest. Here the Red Beds, and probably the overlying Jurassic marls and limestones, are well developed, exhibiting a series of nearly horizontal strata, between 1,000 and 1,200 feet in thickness, with perhaps a very slight inclination toward the north and northwest, the beds dipping away from the Archean body. Facing the plains, the red sandstone presents an abrupt wall from 600 to 1,000 feet in height, showing in a marked manner the variegated beds, with the interstratified marls and limestones; while, on the east side, Sand Creek, which rises on the top of the plateau, cuts a deep, narrow canon through the Red-Bed formation. These exposures exhibit a development of Triassic beds at least 1,000 feet in thickness, and are overlaid by the light-colored Jurassic strata, forming the summit of the plateau. Resting upon the Archzean body, the lowest beds wae of coarse, fri- able, ash-colored sandstone, with pebbles and angular fragments, over- laid by a thin bed of hard, cherty limestone, which is, in turn, overlaid by reddish-gray sandstone. Above this comes the usual persistent red sand- stone, passing up into clayey beds, more or less shaly, developing into a 80 DESURIPTIVE GEOLOGY. series of argillaceous sandstones, with thin layers of fine red clay and beds of gypsum, the latter varying in thickness from two or three inches up to several feet; the thickest deposit of pure solid gypsum, measuring 22 feet in width, lying between two beds of hard red sandstone. Nowhere in the — region of the Rocky Mountains, within the belt of this exploration, are the gypsiferous deposits so well developed, at the same time so easily accessible from the railroad. Overlying the gypsum series, again occur the red sand- stones, passing up into yellowish-red friable beds, shading off into white sand- stones and marls, which may represent the base of the Jurassic series. Above the white sandstone occurs a bed of fine bluish-gray cherty limestone, which crops out prominently, and probably represents the stratum which is so persistent east of the Colorado Range; this, in turn, is overlaid by white and cream-colored sandstones and mazls, passing into brownish beds, with layers of variegated clays and marls, and again overlaid by fri- able white sandstone, which appears to form, in many Pee the summit of the plateau. The following section represents more clearly the succession of strata, with estimated thicknesses, beginning with the Jurassic on the summit of the plateau, and descending to the base of the Triassic, which rests on Archean rocks: Jurassic. L.: Friable white-sandstone}. 2: 225 te pe tenes Ce ee ee eee ») 2. Reddish brown sandstone, with layers of variegated clays and! Maris 2 ts. le oe PR NE Nl pS oe Ne at ARE a tae Lo, poy feet. 3. Cream-colored pandeeane: and mars, ..os.09 ose 7 eee setae at 3. oie ’ 4.) Binish-eray Cherty, limesteneu-:. 8 sss4eee see = ee ee eee 25 feet. 5. Grayish-white sandstone...... ... Stes Ss renee Say aes ic duseseebe ssa s: 75 feet. Triassic 6. Yellowish-red:isandston@:/2:5-)..022. 5 Senco ae ee eee ae 7. Fine deep-red sandstone... eS ee | ae? ee 8. Argillaceous sands and shales, with interstratified layers of fine clay and gypsum, including one bed of gypsum 22 feet thick........... 150 feet. 9. Red: compact sandstone. . =. 222-2) 2 taon- 24-2 | 0 eee 250 feet. 10) Reddish-grayesandstone |. size ast eae ke eye oe eee eee 11. Thin bed of gray cherty limestone ...........--.--+--+- ---eee--e f 225 feet. 12. Coarse, friable, ash-colored sandstone, with pebbles. .......---.--- 1, 200 feet. LARAMIE PLAINS. ~ 81 Near where the North Park road leaves the plains, going over to the Upper Laramie River, the Triassic and Jurassic formations jut up against the Archean, which here occurs as a low, narrow ridge, only 300 or 400 feet in height, forming the east side of the Laramie Valley. On the oppo- site side of this ridge, in the broad river-valley, occurs an isolated body of Red Beds, the sandstones which formerly covered the ridge having been entirely eroded. The exposure of Red Beds, however, is limited, as a short distance below, where the road crosses the valley, the river runs through a narrow gorge in the Archean rocks, west of Sheep Mountain. Under the characteristic red sandstones is found a narrow layer of blue limestone, only a few feet in thickness, below which occur white sandstones. - Returning to the Plains again, we find that east of Sheep Mountain the beds of the Colorado group are the oldest formations found lying upon the Archean body. The older rock-mass presents a steep slope toward the plains, around which curve the Cretaceous clays and marls, with a very varying strike and a somewhat varying dip. The line of junction between the two formations is very much obscured by detrital accumulations from the mountain, the clays presenting few well-defined outcrops. Approach- ing the mountain by the North Park road, the first outcrops that are seen, after leaving the nearly level plain and commencing to ascend the gentle grade, are a series of dark brown and black, thinly-bedded shales and clays, with interstratified layers of impure limestone, more or less mixed with coarse sand. In the limestone occur some fragments of organic remains, but too poor for specific determination, while the purer black clays carry thin seams of carbonaceous material, with occasional coatings and incrustations of gypsum. Underlying these dark clays, which have been referred to the Fort Pierre division, occur yellow and blue marls, which crop out in low, rounded banks, rising but a few inches above. the level plain, but which mark very clearly the horizon of the Niobrara beds. They are character- ized by the presence of large numbers of the species Ostrea congesta. Below the light-colored marls, the beds pass down into slate-colored mud-rocks, becoming more and more argillaceous, and apparently losing the calcareous character of the overlying strata; these clay-beds, in turn, are underlaid by 6DG : 82 DESCRIPTIVE GEOLOGY. brownish, rusty sandstone, with occasional concretions of ferruginous mate- rial. All of these beds dip at low angles, varying from 8° to 15°. On the north side of Sheep Mountain, where the Big Laramie River leaves the Medicine Bow Range, running out on to the plain, the entire series of sedimentary rocks again appears resting upon the Archzean body. The Carboniferous beds, here a light blue arenaceous limestone, stand nearly vertical, close up against the metamorphic rocks, and overlaid by the bright-colored Red Beds, with the fine gray marls of the Jurassic indi- cated by their characteristic soil and peculiar topography, lying between two formations of massive sandstone. Every formation, from the Triassic to the Niobrara division of the Colorado group, appears well developed along the south bank of the river, inclined at 16° to 18°. Above the bank, the Fort Benton clays are somewhat concealed by overlying soil; but along the bluffs, where the river cuts the beds at right angles to their strike, the dark, almost black clays, passing up into slate-colored marls, are well exposed. The bluish-gray marls, which characterize the junction between the Fort Benton and Niobrara divisions, and form a prominent feature east of the Colorado Range in the region of Big Thompson Creek, are shown here, carrying the well-known IJnoceramus problematicus. On the north side of the river, outcrops of the light-colored marls stand out prominently, but would seem to be quite thinly developed; at least, they rapidly pass into coarse, friable sandstones, which, in long, gentle, bench-like ridges, extend out upon the plains. Between the Big and Little Laramie Rivers, east of Bellevue Peak, the Colorado beds are again found resting on the Archzean, as in the case of Sheep Mountain, but are still more hidden by overlying Quaternary deposits. At the northern end of Bellevue Peak, the lower sedimentary rocks again reach the surface, and adhere so closely to the Archean out- line as to form a semicircular wall, with a diameter of less than 4 miles, showing all the formations, from the Carboniferous to the top of the Colo- rado group, curving around the older rocks. The Carboniferous beds lie 1,000 feet or more up on the sides of the mountain, inclined at varying angles, having, where they first appear on the east slope, a dip of 20° to 25° to the northward. These Carboniferous limestones possess a saccharoidal _ LARAMIE PLAINS. 83 texture, and seem highly arenaceous throughout most of the beds. Of the Mesozoic strata, the Red Beds, Jurassic, and Dakota Cretaceous lie inclined from 20° to 80°. Here the bluish-drab, cherty limestone of the Jurassic forms a prominent outcrop, rising slightly above the enclosing marls. Over- lying the Dakota Cretaceous, the clays of the Colorado group incline at a gentler angle, affording few exposures, except the two low rolls of blue and yellow marls in the Niobrara division. [xcept in the latter beds, no organic remains were found in the entire series, and these were confined to the genus Ostrea. The Fort Pierre black clays dip away from the Niobrara beds with a slight angle, soon becoming nearly horizontal, and, so far as visited, appear to occupy the greater part of the circular basin north and west of Bellevue Peak, through which the numerous tributaries of the Little Laramie River run, and as these streams cut but little into the clays, their banks offer poor exposures of strata. It is possible that at the upper end of the basin older rocks than Cretaceous may be exposed resting against the Archzean range. The surface of the basin is quite level, and furnishes excellent grazing-land for large herds of cattle. Along the broad valleys of the Big and Little Laramie River, and, indeed, over the greater part of the plains, long bench-like ridges form a characteristic feature of the region. Except on their edges, the benches present but few outcrops, and these usually exhibit coarse sandstone beds, lying in a nearly horizontal position. In numerous localities, organic remains have been found embedded in the sandstones, and have in every case been sufficiently characteristic to show that the beds belong to the Colorado group, without clearly determining the more limited subdivisions of the series. It seems evident, therefore, from our explorations, that the central portion of the Laramie Plains is underlaid by the Colorado group, and that all the beds may be present, but with more or less of an arena- ceous texture. At the northern end of the plains, between Lake Ione and the Laramie River, in a yellowish-brown sandstone, was found the charac- teristic Fort Pierre species, Baculites ovatus, their surfaces being coated with exceedingly beautiful iridescent hues, associated with the genus Ammonites. At the southern end of the plains, near where the Laramie River crosses the western boundary of the Fort Sanders military reservation, the banks * 84. DESCRIPTIVE GEOLOGY. of the stream have exposed some arenaceous black clays, carrying inter- stratified narrow beds of purer sandstones, which dip about 1° to the westward, and in their general habit closely resemble the Fort Benton beds. From these clays were collected Ostrea congesta, and minute but well-preserved fish-scales lying with their broader surfaces parallel with the stratification. On the west side of the river, the Colorado group extends well up on the steeper slopes of the Medicine Bow Range, underlying the railroad as far westward as Como Lake, but affording few characteristic outcrops. Between Lookout and Miser Stations, beds of argillaceous sandstones are well exposed, from which were collected specimens of the genus Inoceramus. A short distance east of Miser, the railroad cuts through a heavy bed of brown sandstone, dipping slightly eastward, remarkable for its concretionary structure. These concretions consist of coarse, reddish sandstone, firmly held together by a ferruginous paste, which causes them to withstand erosion much better than the sandstone in which they are embedded. They occur of all sizes, from a few inches up to two feet in diameter, many of them quite smooth and symmetrical, and having weathered out from the bluff lie strewn over the surface of the plains. About one-half mile west from Miser Station, the railway cuts through another ridge of hard gray sandstone, also dipping east, in which were found large numbers of Colorado fossils, chiefly of the genus Inoceramus, but associated with Ammonites and Saurian teeth, the latter showing the enamel well preserved. High up, along the gentle nearly uniform slopes of the iediome Bow Range, overlying the Colorado group, occurs a very considerable develop- ment of Fox Hill beds. The junction between the two series is a very dificult one to trace out, the upper beds of the Colorado group being highly arenaceous, passing into the Fox Hill division of coarse, reddish- yellow sandstone by almost imperceptible’ gradations; a lithological difficulty enhanced by the absence of all marked physical boundaries, and the very general accumulation of detrital material derived from the elevated ridges of the range, which lies scattered over the slopes. The ox Hill beds, resting unconformably upon the Archzean rocks, extend from Mill Creek, a branch of the Little Laramie River, to the northern LARAMIE PLAINS. 85 end of the range, circling-around the spurs of Rock Mountain. They con- sist of coarse, friable sandstones, usually of a reddish-brown or yellow color, with, occasionai layers of harder brown beds; all of them lying nearly horizontal, or with a gentle dip to the eastward. On the south bank of Mill Creek, not far from the Archzan mass, and almost completely surrounded by Quaternary deposits, occurs a body of brownish-gray sandstone, probably belonging to the Fox Hill group, which carries a layer of rich carbonaceous shales, with thin seams of coal cropping out along the exposed bluff; the shales exhibiting a thickness of 3 feet between the sandstone layers. ' These sandstones were searched for organic remains, but they only yielded a few imperfect impressions of deciduous leaves. The strike of the sandstone is north 35° to 40° east, with a dip of north Ds ALOE GW ss . Between Mill and Cooper Creeks, numerous: small stream-beds cut deeply into the sandstones, but offer no exposures of special interest. Cooper Creek, a very considerable stream, which debouches through a narrow cation in the mountains, has worn out by erosion a broad valley in the softer Cretaceous rocks, leaving high banks upon each side, composed of coarse sandstones. The valley for several miles from the mountains is remarkable for the large amount of coarse detrital material, which every- where covers the surface; the large Arehzan boulders lying high up on the benches and ridges. At its lower end, the valley cuts through the Colorado beds, which, farther up the stream, are overlaid by the Fox Hill group. This formation apparently extends up to the Archean ridges; at least, no structural or paleontological evidence was obtained of any later formations, all organic remains collected from a number of localities in the exposed banks being forms decidedly characteristic of the Fox Hill divisions, prin- cipally of the genus Inoceramus. On the ridge, which forms the south side of Cooper Creek Valley, just above the upper wagon-road, and but a short distance from the Archean foot-hills, was found a new species of the genus Axinea, which Professor Meek, in his report, has described under the specific name of Aximea Wyomingensis. 86 DESCRIPTIVE GEOLOGY. Associated with it, occurs the well-known form, Inoceramus Barrabini, which is also abundant in the long sandstone banks on the opposite side of the valley, which dip only 2° to 3° eastward. Between Cooper and Rock Creeks, the country “tears but little variety in its general features; the nearly horizontal sandstones terminating in abrupt walls toward the plains. At Rock Creek, the Fox Hill beds are well developed on both sides of the valley, lying close up against the Archean body in flat-topped hills, rising 300 feet above the stream-bed, from which were collected several specimens of the genus Inoceramus. In the Fox Hill sandstones, between Cooper and Rock Creeks, layers of carbonaceous clays and shales occur cropping out along the benches, and carrying several thin beds of lignite. Of these coal outcrops, two have been to some extent explored,—the one known as the Cooper Creek, and the other as the Rock Creek coals. The Cooper Creek coal occurs on the north side of the valley, interstratified in a bed of hard clay, which is both overlaid and underlaid by sandstone. The beds have a gentle dip to the eastward. So far as known, no Molluscan remains have been found in immediate connection with the coal strata, yet it seems quite evident that they underlie beds characterized by Fox Hill species. The coal possesses a lustrous black color, a moderately compact text- ure, and resembles that found east of the Colorado Range. An analysis of this coal was made by Dr. F. A. Genth,’ of the University of Pennsylvania, with the following result: Moisture: .5. ae ae Anes eee 9.28 Volatile matter.) e202 een) ee eee mas ys OLED Carbomn.'s Ser). ok os 2g Sage ee 47.04 Ash, ‘yellowish=brown-. 222-9. 2 222 sees eee 4.56 100.00 It contains 1.38 per cent. a sulphur, which is equal to 2.59 per cent. of pyrites. The Rock Creek coal is situated about 6 miles southeast from the 1Report of U. S. Geological Survey of Wyoming, Dr. F. V. Hayden, 1870, 185. a LARAMIE PLAINS. 87 ~ Rock Creek Station of the old Overland Stage Road. Owing to some misunderstanding in regard to the directions for finding the deposit, it was not visited by our parties, but through the kindness of ranchmen living on Rock Creek, we were able to procure specimens of the coal, together with the overlying sandstone. It would appear from descriptions, and general structure of the country, that the coal beds occur in the Fox Hill formation in a somewhat similar manner to those on Cooper Creek, and in nearly the same geological horizon. The coal is said to occur in a rich carbonaceous clay, with a dip slightly to the eastward, and has been known for many years, having been used by the Overland Stage Company for blacksmithing purposes. Neither of these coal banks have been thor- oughly opened, nor their true value and extent for commercial purposes made known, although they are situated within 15 miles of the railroad, with a gentle down grade for the entire distance. Rock Creek, which has a broad open valley, is the most important stream north of the Little Laramie River, and drains, as has already been mentioned, into the Medicine Bow River north of the limits of the map. The upper valley runs through Cretaceous sandstones, stretching from the Medicine Bow Range, far out to the eastward. A short distance above Rock Creek Station, on the railroad, the soft clays and marls of the Fort Benton group reach the surface, the character of the country changing very greatly, while the broad valley narrows and cuts a deep channel through _ the easily-eroded clays. West of Miser Station, the sandstones give place to the argillaceous beds, and from there westward, nearly to Como Station, the Fort Benton and Niobrara Cretaceous occur as the surface formations. At Rock Creek Station, the Fort Benton beds are well shown on the high banks, and in the numerous narrow ravines and gullies, cutting through the clays at right angles to the main stream, which expose between 350 and 400 feet of dark plastic clays, with interstratified beds of sandstone and -arenaceous clays. The Fort Benton formation is in many localities char- acterized by beds of ferruginous clays, which, when the iron is present in only small quantities, gives them either a black earthy appearance, or is indicated by a nodular and concretionary structure, with a considerable variety in color of the different layers, especially on exposed surfaces. 88 DESCRIPTIVE GEOLOGY. The presence of iron in the clays frequently affects its physical appearance to such an extent as to suggest, when in doubt, to which group the clays may belong. In many localities, the lower clays are quite rich in iron, which forms marked layers or deposits of clay ironstone, cropping out for long distances. At Rock Creek, these clay ironstones are well developed, presenting a characteristic feature of the bluffs, which, owing to the great variety of color derived from the different degrees of oxidation of the iron, and its admixture with clay, gives, on the sures the appearance of a vol- canic formation of ash and scoria. The iron deposits lie with the strata, and are found approximately horizontal, but with a thickness varying from a few inches up to 2 or 3 feet. In composition, they are argillaceous carbonates of a brownish-black color and compact texture, which, upon being treated with acid, effervesce briskly, leaving a residue of sand and particles of fine clay. They fre- quently appear considerably fissured, with the seams and cracks filled with crystallized spathic iron. They bear a close resemblance to other beds found in the same horizon on the Wyoming Plains, but especially to the deposits at Klik Mountain, where they are largely developed, and but for the fact that at the latter locality they are turned up at a high angle, show the same mode of occurrence. An analysis of the clay ironstone from Elk Mountain, which will be found in the description of the Cretaceous forma- tion of that locality, probably oe the general character of the Rock Creek deposits. : In the dark-colored stratified clays, which overlie the carbonate a iron deposits, were found numerous small fish-scales, so characteristic of the Fort Benton division. Beyond the railroad-station, Rock Creek runs through a narrow open- ing in the Colorado clays, which offers steep, almost impassable walls from the stream-bed to the summit, on the top of which the country presents a dreary parched plain, with scarcely any vegetation to relieve the clay barrens or dull monotony of surface features. The Cretaceous strata, which have been dipping eastward, here begin to show the influence of the dying- out of the Medicine Bow Range, and are seen encircling the northern Archean flanks, gradually trending off to the westward, with east and west LARAMIE PLAINS. ; 89 strikes and northerly dips. Six miles east of Como Station, the country presents a somewhat strange appearance; the arenaceous clays on the south side of the railroad being traversed by numerous cracks or fissures, which suggest earthquake-openings or crevasses in glaciers. They are, however, the courses of old stream-beds, now dry, except in seasons of unusual flood and freshet: some of them are but two or three feet wide, and at least 200 feet deep, with nearly precipitous walls of clay. On the north side of the railroad, a broader drainage-channel affords a good exposure of these beds, which, without doubt, belong to the Fort Benton division of dark blue clays, with layers of fine-grained, hard ferruginous clays and marls, carrying large numbers of fossils of the genera Inoceramus and Ostrea; while in the more fissile slaty beds imperfect remains of fish appear abundant at certain horizons. On the top of the clay wall, close by the railroad, occurs a layer of brown medium-grained sandstone, which derives some interest from its having been quarried at one time quite extensively by the railroad company for building as well as for construction purposes, and transported for long distances. ‘The formation belongs to the sandstone strata, which characterize the Fort Benton division, and, although it in no wise appears superior as a building stone to other similar beds, it may, from its position and occurrence, be worked to great advantage. The lines of bedding are distinctly marked, the blocks quarrying from one to two feet in thickness, with the formation lying inclined at an angle of from 24° to 34°. Embedded in the sandstone are found numerous fragments of stems and deciduous leaves, most of them ina very imperfect state of preservation. It is possible, however, that a collection might be made sufficiently well preserved to allow of specific determination, which would be of considera- ble importance, as the sandstone, which is about 60 feet in thickness, lies _ between well-defined beds of the Colorado group. | The sandstones are overlaid by bluish-gray marls and clays, which probably belong to the Niobrara division; at least, the latter formation occurs not far distant, with the well-characterized yellowish-white chalky beds, and the sandstones cannot be far below the junction of the two groups. 90 DESCRIPTIVE GEOLOGY. These yellow marls stretch off to the north with a low dip of 3° or 4°; the Colorado group extending northward beyond the limits of our map. Still farther westward, the Colorado group forms the surface formation, inclined at a gentle angle, and presenting but little of special interest. Between one and two miles east of Como Lake, they begin to show a higher dip, and to indicate the structural features produced by the Como Ridge, a somewhat singular uplift of the lower Mesozoic strata. Como AnvTicLinAL.—Como Ridge is situated in the extreme northwestern corner of the Laramie Plains, just west of the 106th meridian, and along the northern border of the map, the boundary-line cutting through Como Lake. The ridge, which takes its name from the lake, derives its importance solely from the geological interest which centres in the region, where it forms the southern side-of a local anticlinal axis. The upper Cretaceous beds form the overlying strata of the plains over wide areas; but here, at Como, the lower rocks down to the Red Beds are exposed in a gentle uplift, the later beds dipping away in all directions. The main elevating force has acted approximately in an east and west direction, producing an anticlinal ridge, with its southern side again lifted up above the main axis of elevation. Directly along the axis of this fold lie the Jurassic marls and soft friable sandstones, which have undergone considerable erosion, leaving a‘ shallow basin now occupied by the lake and a narrow anticlinal valley. On the south side of the lake, through the valley, runs the railroad, beyond which stands the main ridge, forming the south side of the fold. This ridge rises between 200 and 300 feet above the level of the lake, with a steep mural face toward the north, but falling off gently on the opposite side. On the summit, the ridge has a strike of north 60° east, with a uniform dip of 20° to ¥5° to the southward. Southeast of the lake occur the lowest beds exposed, which consist of hard yellowish-red sandstones, and may belong to the uppermost members of the Red Beds, or may simply be a compact reddish stratum in the Jurassic. On account of this doubt, the Triassic formation is not represented on the geological map, although it is not at all improbable that the lower red sandstones should be so referred. Directly overlying these red sandstones occur well-defined Jurassic strata, which form the northern face of the ridge, and are in turn overlaid fe COMO ANTICLINAL. 91 by Dakota sandstone, which serves as the capping-stone to the ridge, and the overlying rock on the southern and gentler slope. Nowhere in the Rocky Mountain region, within the belt of exploration, are Jurassic rocks better defined, exhibiting all the characteristic strata which have heen observed in other localities, and at the same time associated with organic remains about the age of which there can be no doubt. The following section along the bluff-face of the ridge was taken from top to base, in descending series: Dakota Cretaceous. 1. Compact yellowish-brown sandstone, forming the summit of the ridge. Jurassic. REC TUV ASIC IAT lente ere terete se coe efels ete eis Sle ee tnd) 2 popes es } . Cream-colored marls, with sandstone layers ....-.....-.-----..-. . Bluish-drab cherty limestone..-.-.....-...--.-2-.-- e-- cee eee ee: . Fine ash-colored marls, with thin beds of light-colored limestone. . . Gray and Orange marls, with coarse sandy material ............. PREddisn-vellowesandstonG ier. -. onic. - 5) Gass see vise eens eee + 175-200 feet. a1 OF Rm OO bd Triassic ? 8. Brick red compact sandstone. The Dakota beds are a dense, tough series of sandstones, distinctly bedded, and breaking up into rough angular blocks in a similar manner as observed east of the Colorado Range. In the Jurassic, the bluish-drab limestone, which is everywhere so persistent a stratum, is here well devel- oped, of a characteristic light drab color, flinty fracture, and carrying numerous small calcite crystals, scattered through the rock. Diligent search was made in this limestone for fossiliferous remains, but without success. In the marls and limestones, however, both above and below it, occur well-marked forms, which are sufficient to prove the Jurassic age of this horizon, although no very great variety in species has been identified. The following species have been found by our parties: CRINOIDS. Segments of the column of Pentacrinus asteriscus ; CEPHALOPODA. Belemnites densus. LAMELLIBRANCHIATA. Tancredia Warreniana. “Trigonia quadrangularis, h. sp. 92 DESCRIPTIVE GEOLOGY. About two miles east of Como Station, in the cream colored marls. were found a few small Lamellibranchiate shells, but not sufficiently well preserved to allow of specific determination. It would seem somewhat remarkable, that while organic remains should be so difficult to find over wide areas of exposed Jurassic strata, here certain species, as Pentacrinus asteriscus and Belemnites densus, should prove to be so abundant. The latter type, pencil-shaped and of.a dark slate color, occurs from 2 to 6 inches in length, and as they withstand atmospheric agencies remarkably well, and the marls in which they are embedded erode so readily, large numbers of them may be picked up along the foot of the bluffs, from which they have been washed out. As shown in the section given above, the well-defined Jurassic rocks have a thickness of nearly, if not quite, 200 feet. Only a limited development of red sandstones is exposed, consisting of yellowish-red beds, and compact mud-rocks, with but little local interest. East of the lake, on a gentle slope, they exhibit in a most marked manner the peculiar cracks and ripple-marks so charac- teristic of Triassic sandstones. Here we have deep symmetrical grooves occurring at intervals of 2 or 3 inches, for nearly 100 feet, covering the entire exposed rock-surface with the regularity of human workmanship. On the north side of the lake, the Dakota Cretaceous forms a low but abrupt wall along the shore, dipping to the northeast at an angle of 35° to 40°. At the extreme northeast corner beds of fine marl and coarse friable sandstone would indicate that the Jurassic beds occurred directly under the level of the lake. Along the anticlinal valley, on the east side of the lake, no outcrops are visible, the surface being covered with low, irregular sand- dunes; but on the opposite shore it is hemmed in by a low bank of Dakota sandstone. Como Lake, which is probably quite shallow, occupies the anticlinal valley, and measures about one mile in length by half a mile in width. It scarcely differs from the many other small lakes, which occur scattered over the Cretaceous and Tertiary plains of Wyoming, unless it be that the sur- roundings are somewhat more than ordinarily dreary and desolate. Irony certainly prompted the name for this sheet of water. The water possesses a mild brackish, alkaline taste, but deposits only a slightly saline incrustation COMO ANTICLINAL. j 93 along the shore during the dry season. A spring at the southeast corner, and- one-fourth of a mile from the railroad-station, pours a considerable amount of fresh water into the lake. It is not impossible that, scattered over the area of the Laramie Plains, may be found isolated patches of Tertiary strata; but none were positively recognized as belonging to beds older than the Cretaceous. In one or two localities, where rocks of Cretaceous age lie nearly horizontal, beds of coarse, friable sandstone cover the surface, whose age is perhaps doubtful, as they afford no paleontological or distinctive lithological evidence of their true position. Quaternary deposits occur along the steeper mountain-slopes and in the eroded basins and depressions of the plains, but are of such shght importance that, except along the broad river-bottoms, they have not been designated on the geological maps. 94 DESCRIPTIVE GEOLOGY. SECTION I[1t. MEDICINE BOW RANGE. BY ARNOLD HAGUE. — Puysicat Drescription.—The Medicine Bow Range may be considered the second great range of the Rocky Mountain system. It extends from about the latitude of 40° 15’ northward to latitude 41° 40’, with a trend approximately northwest and southeast. The eastern slope borders on, and is closely connected with, the Colorado Range for some distance, but grad- ually trends off more to the westward, and forms the western rim of the Laramie Plains. The western side of the range shuts in the North Park on the east and north, and still farther northward forms the boundary of the North Platte Valley, which lies between it and the Park Range. As thus defined, the Medicine Bow Range is about 100 miles in length. In width, it varies very considerably, the southern end only measuring 10 or 12 miles from east to west, but across its broadest expanse, in the region of Medicine Peak, it reaches 30 to 35 miles. E The highest peaks in the range are: Mount Richthofen, at the southern end, nearly 13,000 feet high; Clark’s Peak, at the northeast corner of the North Park, 13,167 feet; Medicine Peak, 12,231 feet; and Elk Mountain, 11,511 feet, at the extreme northern, end, which stands out boldly as a prominent landmark, somewhat isolated from the rest of the range. South of Mount Richthofen its trend is nearly north and south, a nar- row serrated ridge, with short but deep glacial cations putting out both east and west. Mount Richthofen rises above the surrounding peaks 800 or 900 feet; and from the Park Basin looking eastward, its summit presents a rug- ged, irregular mass of granite, with graceful outlines. North of the peak, the strike of the rock changes to a few degrees west of north, and it is of special interest that just where the change of strike sets in occurs the great flow of rhyolite that covers the western base of the range; the greater MEDICINE BOW RANGE. 95 part of the slope of Mount Richthofen lying concealed beneath volcanic lavas. The east side of the mountain forms the divide between the waters that flow north and south. The main fork of Grand River, the great tribu- tary from Colorado to the Colorado River, takes its rise on Mount Richthofen, flows south along the depression between the two ranges, and drains through the Middle Park. A branch of the Cache la Poudre also rises on the same mountain, draining the east side of the range, and joins the main stream near the bend. At Clark’s Peak, the culminating point, the range widens rapidly, and trends more decidedly to the northwest. The main crests form a high ridge, with an abrupt slope, along the edge of the Park, but falling off on the opposite side in a broken mountainous country. Here the longer and gen- tler slopes are to the east, as in the Colorado Range, with the drainage con- sequently mainly eastward toward the Laramie River. Near the line of the forty-first parallel, where the range has a width of 25 miles, two well- defined ridges are developed, with a trend approximately parallel, which changes the entire character of the range to the northward. The eastern and lesser ridge borders the Laramie Plains; a few miles above Bellevue Peak it suffers an abrupt-depression where the Little Laramie River leaves the mountains, but it again rises, and continues unbroken for twenty miles, until the entire Medicine Bow Range passes under the sedimentary beds. The western ridge, which is less regular in outline, culminates in Medi- _ cine Peak, a grand, broad central mass, at least 1,500 feet higher than the - surrounding summits. Between these two ridges lies an elevated plateau country, nearly 10,000 feet above sea-level, gently undulating, but without any marked topographical features, covered with timber, and dotted over with open glades and numerous alpine lakes. The Laramie River is the principal stream of the Medicine Bow Range; it has its source on Clark’s Peak, in a small glacial lake at the foot of an escarpment, from 1,200 to 1,500 feet below the summit; it runs northward through the central portion of the mountains for 35 or 40 miles, and, finally rounding the northern base of Sheep Mountain, runs out on to the Laramie Plains. From the eastern slope, a considerable number of small streams reach the plain; but all with the exception of Mill Creek, which joins the 95 DESCRIPTIVE GEOLOGY. Little Laramie River, end in small lakes or ponds, or else are lost in the sands before reaching the main river. On the opposite side of the range, six good-sized streams drain the waters into the North Platte River. Com- mencing from the south, they occur in the following order: Douglas, French, Brush, Cedar, Cottonwood, and Pass Creeks. On the east side of the Medi- cine Peak group, the waters, restrained from flowing eastward, drain north by the Medicine Bow River and Rock Creek; both streams, after a circuitous course through the sedimentary strata, emptying into the North Platte beyond the limits of our map. oe . On the southeast side of Medicine Peak, however, the creeks run toward the Little Laramie River, which, as already mentioned, cuts the eastern ridge. Elk Mountain, a comparatively small mass, standing isolated, sends out no large stream, but numerous small creeks, which empty into the Medicine Bow River on the one side, and Pass Creek on the other. Thus, it will be seen that of the leading river features of the Rocky Mount- ain system, the North Platte, and the Laramie, which, however, ultimately falls into the North Platte, drain almost the entire area of the Medicinc Bow Range; that but a small proportion of the water seeks the South Platte, and an equally small amount is added to the Grand River. All the higher regions exhibit well-marked evidences of glacial action. The summits of the main peaks are everywhere worn in a manner which shows unmistakable signs of ice erosion, and glacial boulders and detrital matter cover the lesser depressions and slopes. The valleys of Grand River, and the branch of the Cache la Poudre, which comes down from Mount Richthofen, are both examples of glacially-carved basins. At their upper ends, they are both somewhat similar in outline; but below, the Grand descends more rapidly, receives numerous tributaries, and the glacial phenomena are on a more extensive scale. Opposite Mount Clark, the Cache la Poudre receives a small tributary from the main peak, and near their junction isa fine glacial lake. From Mount Clark also descended the glacier of the Upper Laramie Valley, while on the south side short but deep trough-shaped cations extend down to the North Park. In the region of Medicine Peak, glaciers occupied all the upper val- leys, and the amphitheatres, with mural faces 1,500 feet deep, cut out of MEDICINE BOW RANGE. 97 pure white quartzite, are very striking. The valley of French Creek, on the south side, may be especially mentioned; here the escarpment is 1,500 feet in height, and the basin-shaped caiion, with its glacially-eroded lake-bottom, presents a fine example of ice action upon brittle, massive quartzite, which splits and breaks up easily into blocks under the action of frost and ice. There are ridges here entirely covered with huge blocks of quartzite, many tons in weight, piled up in the most irregular manner, and one may travel long distances without finding any rock in place. Coniferous forests cover the greater part of the Medicine Bow Range, and there are many large areas, especially in the regions north and east of Medicine Peak and the headwaters of the Little Laramie River, where tree-growth is quite dense. Already much valuable timber has been cut. Abies Douglasii, a tall graceful tree, often over 100 feet in height; Abies Engelmann, known as “‘white pine”, and Pinus ponderosa, or ‘yellow pine”, are among the species found. ‘The timber-line, as in the Colorado Range, may be placed at 11,000 feet above sea-level. ‘Geotocy.—Like the Colorado Range, the Medicine Bow is made up almost exclusively of Archzean, highly crystalline rocks; but while in their general habit they resemble the formations of the eastern range, they exhibit certain mineralogical and petrographical differences, that are char- acteristic of the entire range. All the varieties of rocks observed may be classed under the following heads: granites, gneisses, hornblende-schists, mica-schists, dioritic schists, slates, argillites, quartzites, chert, hornstone conglomerates, and limestone. All the larger bodies of true granite appear to be confined to the southern end of the range, where it is closely con- nected with the Colorado Range and the borders of the North Park. Even these, however, show more or less tendency to bedding with the constit- uent minerals arranged in parallel bands and layers, and passing into a _ gneissic structure. A typical granite of the North Park ridge occurs on the summit northwest from Clark’s Peak. It is a fine-grained compact rock, with a uniform texture, and a sharp angular fracture. In color, it is dark gray. It is composed of translucent quartz, white and pearl- colored feldspars, and dark thin plates of mica. Both orthoclase and plagioclase are present, the latter very abundant; deep red orthoclase, so 7DG 98 DESCRIPTIVE GEOLOGY. abundant in the Colorado Range, does not appear to be present. In this rock, the quartz and feldspars are intimately associated together, with some — thin flakes of mica adhering to the feldspar crystals, in bands of greater or less fineness. ‘The mica, which is quite prevalent, occurs in well-defined layers. : Clark’s Peak is a mass of true granite. It differs from nearly all the rocks of the range in showing but little, if any, tendency to bedded structure, and no parallelism in the arrangement of the constituent minerals. The rock in many respects resembles an intrusive body, and such, on further observation, it may prove to be. It is compact, moderately fine-grained, with no large crystals porphyritically enclosed, and resists atmospheric agencies remarkably well. In color, it is pearl-gray. Like the other rocks of the region, it is rich in triclinic feldspars. The quartz occurs in limpid white grains. Both orthoclase and plagioclase are present; the latter have a brilliant lustre and present the characteristic strie well marked. The mica, probably a biotite, is finely disseminated through the mass with- out any apparent order. Hornblende, which is present in so many of the rocks of this range, is not observed in the specimens obtained on Clark’s Peak. Under the microscope, apatite may be seen, but no titanite; and the quartz carries many liquid-inclusions. This rock is one of the finest granites in our collection, and would make an admirable building-stone if it were only accessible. In the imme- diate region of Clark’s Peak there are some similar-appearing granites, which probably belong to the same formation, and it might be possible to — trace their connection. In one, 3 or 4 miles southwest from the peak, near the base of the range, Zirkel detected the presence of zircon in red grains, closely resembling the minute zircons found. in the syenites of Norway. The granite is lighter-colored than the Clark’s Peak variety, and carries | vitreous oligoclase crystals, an half-inch in length. . Due west from Clark’s Peak, and separated by a low divide and two glacially eroded cations, stands a prominent peak of gneissic rocks. Near | the base occurs a typical variety of the region,—a fine-grained compact gneiss, composed of mica and orthoclase with much hornblende and plagio-. MEDICINE BOW RANGE. - 99 clase; the feldspars are nearly white, and the mica and hornblende black. Under the microscope, apatite may be easily detected. Near the base of the same peak are found. outcrops of coarse-grained granite, which bear some resemblance to the granites of the Colorado Range, and probably belong to the older series. They are so covered by morainal detritus and soil, that their extent and relation to the surrounding rocks are very obscure. ‘They carry no hornblende, but small white mica flakes, and are interesting for the large size and great activity of the liquid-inclu- sions contained in the quartz. Near the last-described locality occur gran- ites, also coarse-grained, with the feldspar in large masses, and the quartz disseminated through it, producing the forms known as graphic granite. North and west of the region just described, the rocks are almost entirely mica and hornblendic schists and gneisses. Along the crest of the ridge bordering the North Park, hornblendic rocks prevail, occurring both coarse and fine-grained, with varying amounts of quartz and mica. Many of them are characteristic diorite-schists. A typical rock, in the collection from this ridge, is made up of dark green hornblende and bluish-white plagi- _oclase feldspars, many of them a quarter of an inch in length. A thin sec- tion, examined under the microscope, gave no indication of any monoclinic feldspar. Mica in black flakes and limpid quartz are present in very sub- ordinate amounts. ‘The mineral constituents are intimately mixed, and the _bedding-lines are only seen when viewed at a distance in the field. At other localities in the same region, however, the green hornblendes never show broad faces, but are always-present in long, narrow seams, or layers, which give the rock a gneissic structure. The narrow, deep cation of the North Platte, which extends for 30 miles along the western edge of the range, everywhere exposes a series of dark hornblendic schists, with but little variety in constituent minerals, but great differences in the proportions of horn- blende and feldspars present, the exposures occasionally showing beds carry- ing but little of the iron mineral.. The beds are inclined at varying angles, most of those noted, however, standing very steeply. On the-east side of _ the cafion, the prevailing dip appears to be easterly into the range. Near the mouth of French Creek, the cafion of the Platte terminates, and the east side of the river presents a low, undulating country, rising 100 DESCRIPTIVE GEOLOGY. gradually toward the higher portions of the range. On the west side, there are two prominent hills, which, from their isolated position, serve as Jand- marks in the valley. Bennett's Peak, opposite the mouth of Brush Creek, rises 600 feet, and River Butte, 5 miles below, at the mouth of Grand En- campment Creek, 900 feet above the river-bed. They are both made up of very dark, heavily-bedded hornblende-gneisses, dipping to the westward at a high angle. They are probably metamorphic diorites. Between the Platte Cafion and the Laramie River, the country is either covered with a dense growth of forest, or else with soil and detrital matter, to such an extent that geological relations are difficult to make out. Along - the Laramie and North Park road the rocks are chiefly coarse-grained, but showing more or less bedding. Hornblende appears to be a constant con- stituent, and the feldspars are usually light-colored. Between French and Brush Creeks, mica-bearing rocks prevail. A typical specimen, collected on the flat-topped ridge 2 miles north of French Creek, is a light-colored rock, crumbling easily, with a coarse, sandy texture. It is made up of limpid quartz, both monoclinic and triclinic feldspars, and small, minute flakes of dark mica. No hornblende was noticed, and our observations tend to show that it is somewhat remarkable to find mica present with so much plagioclase, and free from hornblende. The mica occurs in narrow layers, giving the rock a finely-banded appearance, but with the evidences of bed- ding much less marked than is usually seen in this region. The strike was from north 45° to 55° west. In this light mica-gneiss occurs interstratified a narrow belt, only a few feet in width, of diorite, which stands up prominently above the surrounding rock, and has much of the habit of an intrusive dike. In many respects, however, it closely resembles the finer-grained varieties of the metamorphic diorites; but a careful study of a specimen indicates certain mineralogical differences that have not been detected in the clearly metamorphic dioritic schists of the region. To the unaided eye, the rock presents an irregular admixture of a mass of hornblende and feldspar, of a dark gray color, with only a few long, acicular crystals of striated feldspar. Under the microscope, a thin section shows only hornblende, plagioclase, and a few orthoclase crystals, but no mica, quartz, or apatite. Zirkel calls attention to the singular arrangement of the groundmass. MEDICINE BOW RANGE. 101 From Brush Creek northward for 15 or 20 miles, the same light-colored mica-gneisses and dark hornblende-schists, with occasional interstratified beds of vitreous quartzite, prevail. Theyform the higher ridges, aswell as the long, gentle slopes that extend out toward the North Platte, until hidden under the later Tertiary sandstones. The geological relations of the beds are very complicated, varying greatly in both strike and dip, and but little could be made out as to their structure. South of Brush Creek, the prevailing strike appears to be northwest and southeast, with a southerly dip, while to the north of the creek the strike remains the same, with a northerly dip, thus indicating, in a general way, a broad anticlinal axis. The summit of Deer Mountain, at the head of Cedar Creek, is made up of the very light- colored gneiss, similar to that already described from French Creek, except that it contains even less mica than the former, and the feldspars are unu- sually white and clear. Minute grains of red garnet were found in the rock, 100 feet from the summit. On the slopes of the mountain, hornblendic beds occur, largely developed, with the dark green hornblende, and both white orthoclase and plagioclase-feldspars, but they scarcely require mention here, except to note the large number of accessory minerals revealed in a thin section by the microscope, which include titanite, zircon, apatite, and an undetermined chlorite-like mineral. From Deer Mountain northward, for 6 or 8 miles, the long slopes and ridges that jut out toward the valley afford excellent opportunity for observ- ing and following the hornblende-gneisses that form the western foot-hills. A recorded strike gave north 40° west, with a dip of 60° southwesterly. They vary from fine-grained up to heavy coarse beds, and from beds carrying but little quartz to those where the groundmass is largely composed of siliceous grains. The rock from the slope of Cedar Mountain bears a close resem- blance in its external features to the diorite-dike already described from French Creek, although the former is undoubtedly a metamorphic product. It is a hard, compact rock, with no regularity in the arrangement of the constituents. Unlike the diorite from French Creek, however, the ground- - mass is composed of quartz and dark-green hornblende, while the feldspar is very minutey striated plagioclase. North of Cedar Mountain, our obser- vations tend to show that the character of the rock changes, and the dark -4102 . DESCRIPTIVE GEOLOGY. schists and gneisses, with hornblende as the predominating constituent, which have been so persistent along the entire western edge of the range, © give way to lighter-colored mica-gneisses; still, however, carrying some horn- blende. At Cherokee Butte, the connecting mass between Elk Mountain and the main range, occurs an altered Archzean granite, which is of special interest, as it differs from anything observed elsewhere in the range. It is a hard, medium-grained rock, composed chiefly of gray quartz and white and flesh-colored feldspars, both monoclinic and triclinic species being present. Micas, in minute plates, are scattered sparingly through the mass, but hornblende appears to be absent, at least in the specimens collected. _ Professor Zirkel has given a detailed description of the quartz under low magnifying power, which indicates worn fragments and rounded and polished grains, closely resembling the quartz-grains in the sedimentary gray wackes of Germany, which is especially noteworthy here, as the habit in the field is such as to suggest a metamorphic product. It has also many lithological characteristics like the granite from Granite Mountain, in the Pah-Ute Range, Nevada. On the western slopes of Cherokee Butte is found a typical gray oneiss, the relations of which with the altered granite were not determined. It is of medium texture, somewhat friable, and finely laminated. Hornblende is present, but in a very subordinate amount; thin sections develop titanite. As already mentioned, Elk Mountain stands nearly isolated from the main mountain mass, and has a higher elevation than any point in the northern end of the range, except Medicine Peak. The flanks of the north- em portion are covered with the sedimentary beds, which rise in many localities to within 1,200 or 1,500 feet of the top, but the rest of the mount- ain belongs to the Archean series. The summit, with four points of nearly equal height, is an irregular-shaped mass, which descends abruptly, but regularly, toward the valley of the Medicine Bow, while on the west side deep, rugged carions penetrate the slopes. In lithological habit, there is considerable variety in the rocks, but they are all a hard compact, distinctly- bedded series of gneissic strata. The recorded strikes of the beds differ somewhat, but all have a prevailing northeast and southwest direction; © a MEDICINE BOW RANGE. 103 varying from north 45° east to north 70° east, with a dip always to the north, at angles frequently as high as 75° and 80°. The rock is chiefly made up of gray quartz, with both monoclinic and triclinic feldspars, but so fine-grained that it is difficult to form any correct opinion as to their relative proportions. ‘There are also present what appear to the naked eye as exceedingly fine particles of dark brilliant mica, but which, under the microscope, Professor Zirkel considers as a chlorite-like mineral. It is this mineral which gives the banded gneissic structure; and although there is frequently but a small amount present, it is so evenly dis- seminated that it gives a decided character to the strata. Many of the finer- grained beds show a vitreous aspect, and where thickly bedded, or where the bedding-lines are somewhat obliterated, suggest at first sight an impure quartzite. . In the specimens collected, hornblende does not appear to be present. One taken from the summit near the geodetic station, a dark, hard quartz- ose-looking rock, analyzed by Mr. R. W. Woodward, gave the following result : Specific gravity, 2.6. STIR heed ims eka bie 13 Eder Path: coteee 2) vita 72.72 > AUNT IGS 2 a lee et ine =e ee eee 15.16 LENGTEEOULISI NOD-CUG (ee ae a scene ees 2.00 Di AE oe eee ae Sake eas hee 2 oneeh ES 2.44 Magnesia Stel Sane Mae DR GE ge ae ae 0.34 OCR S ee OSS Sein, Mere ens ee ene 4.()3 IP@ARR Bhs & etn) oe ae ee arte 2.43 Teale. Sek res he URN SADR ania ae ae ee ae a Re trace Noamiioi ee apeer et eet eet tg ee. a 0.73 99.85 This shows a marked difference from the analyses of the Archzan series of the Colorado Range, and would seem to indicate that the feldspars are mainly triclinic. The percentage of lime present is also much higher than in the eastern range. Medicine Peak is a mass of pure white quartzite, rising nearly 2,000 104. DESCRIPTIVE GEOLOGY. feet above the surrounding country, and commanding a grand view of the Laramie Plains and the low country to the north, with a panoramic out- line, 100 miles in length, of the Park Range to the west, while the peak itself suggests the prominent, bold quartzite summits in the descriptions of Scandinavian scenery in the Archean regions of Northern Europe. The main ridge has a trend approximately north 20° east, with what appears to be the strike of the rocks. The dip is to the eastward ata high angle. No accurate measurements of the thickness of the formation could be made, but it certainly is not much under 2,000 feet, while escarpments cut 1,500 feet deep through brilliant white rock. The quartzite is compact, brittle, with a uniform texture. It is traversed by thin, irregular iron seams, and in places is slightly stained a pale red from the oxidation of the iron. Crystals of quartz and feldspar are exceedingly rare. Near the base of the formation, the quartzite has a pale bluish tinge, is somewhat coarser-grained, with interstratified beds of smooth and rounded quartz pebbles, many of them having been pressed and elongated in the direction of the strata since their deposition, showing conclusively their sed- imentary origin. They vary in size from that of a pea to a hen’s egg. The rock from. the summit yielded— the residue showing considerable quantity of alumina, with traces of iron and lime. A large part of the alumina present in the quartzite would appear to be segregated, as nearly pure, simple silicate of alumina, in the form of cyanite, which was observed at rare intervals in narrow veins or seams a few inches in width. The cyanite occurs in long crystals of a pale-blue color, with a pearly lustre and hardness not above 5. It is associated with colorless quartz, but free from all accumulations of iron. Another marked feature of this formation is the number of narrow, well-defined dikes of dark intrusive rock, which penetrate it at a number of localities on the west side. The widest observed was 20 feet, with a strike northwest and southeast, or against the observed strike of the beds. They are probably. diorites. The only one from which a specimen was MEDICINE BOW RANGE. 105 taken is a fine-grained crystalline rock, made up largely of hornblende and fine acicular crystals of brilliant triclinic feldspar. At the head of the northern branches of French Creek, and directly under the great mass of quartzite which forms the summit of the ridge, is a series of thinly-laminated beds, which have not heretofore been met with in either the Archzean series of the Colorado or Medicine Bow Ranges. They consist of dark argillaceous slates and schists, underlying conformably the quartzite, and dipping eastward into the mountain. The upper beds consist of exceedingly fine iron-gray slates or fissile argillites, having a slight wave-like structure, and forming a sort of impure roofing-slate, with an imperfect cleavage. To the unaided eye, they exhibit only minute mica plates. They were estimated at about 400 feet in thickness. Directly un- derlying them, and passing from the one to the other, is a series of harder quartzose argillites, less thinly laminated, less uniform in character, with layers of ferruginous material between the beds, and with occasional nar- row seams of quartz-grains. Underlying this in turn is a highly crystalline schist, differing widely from the last-mentioned beds. There are no cleavage-lines, and the bed- ding appears to be in a great measure obliterated. It is dotted over with rounded nodules of hornblende, similar to the limestone concretions in the ‘“‘knotenschiefer” of Germany, and is made up largely of highly-altered fibrous hornblende, of a bronze color, highly iridescent, with various hues of green, red, and purple. Very minute quartz-grains are visible in the mass of hornblendic rock; and in thin sections, under the microscope, may be seen minute crystals of feldspar. In places, the rock has somewhat of a reddish coloration, arising from the decomposition of the altered hornblende. The thickness of these beds and the nature of the underlying rock were hidden by the soil and débris of the mountain-slope, but there cannot be less than 600 feet in the entire series of slates, schists, and argillites. Several miles farther down French Creek, on the ridge, just above the bed of the stream, occur outcrops of quartzose slates and silver-white mica- slates. They strike north 15° east, and dip as high as 70° to 75° to the eastward; apparently they were underlying a massive quartzite. The south wall of French Creek Canon, a high, almost unbroken ridge . 106 : _ DESCRIPTIVE GEOLOGY. of quartzite, is probably the continuation southward of the Medicine Peak _ beds, which, if the observed strike of north 20° east is correct, would follow the trend of the creek; and, in passing down the cafion, we follow along the strike of the rocks. Now the argillites, slates, and fine schists observed at the foot of the quartzite mass, near the summit, may be closely related to the quartzose and mica slates noted farther down the stream, while the recorded strike indicates that such is probably the case. Still farther down the stream, and before leaving the rougher portions of the caiion, the heavy beds of light-colored mica-gneisses, which occur along the western ridges of the range, make their appearance, and continue down to the mouth of the canon. Mill Peak, at the head of Mill Creek, is the culminating point of the eastern ridge, and is situated from eight to ten miles, a little north of due east, from Medicine Peak. Here the prevailing dip of beds is to the west- ward, as if forming a broad synelinal fold with the Medicine Peak group ; the synclinal valley being occupied by the broad plateau, which separates the two ridges. The eastern slope of Mill Peak is covered with a dense growth of tim- ber, and loose soil, which conceal nearly the entire geological structure. The rocks appear, however, to be made up almost exclusively of reddish- white vitreous quartzite, closely resembling in physical and lithological habit the Medicine Peak strata, but less free from foreign impurities, more discolored by the decomposition of iron secretions, and carrying beds hold- ing more or less feldspathic material. Not far below the summit, and directly overlying the white quarzite, rests a body of heavy, compact, red conglomerate. It varies considerably in texture, color, and character of the groundmass, and any description of one locality seems hardly applicable to other beds. The lower beds, however, are made up of pebbles and irregular-shaped pieces of both opaque and opalescent quartz, chert; and hornstone of various hues, held together by a siliceous fer- ruginous cement, making a mass which is exceedingly firm, and breaks with great difficulty under the hammer. Some of the quartz pieces are 3 or 4 inches in length, but penetrated by narrow seams filled with red ferruginous mate- rial. There are layers which contain much less iron in the cementing material, es MEDICINE BOW RANGE. 107. when the rock, of course, is much whiter; in other beds, it is finer-grained, but still made up of sharp angular pieces of siliceous minerals. It is de- scribed thus somewhat in detail, as in many respects it bears a close resemblance to what have been called the Red Jasper Conglomerates of the Huronian series, as observed in the region bordering the north shore of Lake Huron, by the Geological Survey of Canada! These red beds of the Medicine Bow Range, however, are not over 500 or 600 feet in thickness. They are overlaid by a thin formation of fine crystalline, almost amorphous quartzite, of a bluish-gray color, and traversed by seams of translucent quartz. The rock resembles the narrow siliceous belts inter- stratified in the Triassic, Star Peak limestone of Western Nevada. The interstices and cracks in the quartzite are everywhere filled with carbonate of lime. Thin sections, examined under the microscope, show minute calcite particles disseminated -through the rock in a manner, as Professor Zirkel has pointed out, that is exceedingly rare in highly crystalline quartzites. The top of the peak is capped by patches of light gray and white siliceous lintéstone, that have escaped erosion. In texture and general habit, it resembles the underlying quartzite, and seems only to have passed from a prevailing siliceous bed to one of a calcareous nature. Weathering has produced very characteristic outlines, and the exposed surfaces are usually very rough from a confused net-work of minute ridges, formed by the preservation of red siliceous seams, while the surrounding limestone has been carried off, producing, when seen in the field, a most singular effect. ij But little opportunity was afforded for an examination north of Mill Peak of the higher portions of the eastern ridge of the Medicine Bow Range, and it was therefore impossible to trace northward the white and ferruginous quartzites and limestone. For 10 or 15 miles along the foot- hills, and for long distances up Rock Creek, Cooper Creek, and the other large cafions, heavy dark schists and gneisses prevail. They all appear to be more or less distinctly bedded, with the same general lithological habit and forms of erosion as mark the rocks of the east side of the Platte Valley. South of the Little Laramie River, in the region of Bellevue Peak, peer a Geolocival Survey of Canada, 1863, 57. 108 DESCRIPTIVE GEOLOGY. mica-gneiss and hornblendic rocks characterize the ridge. The purely mica-bearing beds show a close resemblance to the white gneissic rocks already described as occurring near the mouth of French Creek and on the summit of Deer Mountain. A specimen taken from the north end of the ridge is a white or silver-gray gneiss, made up of translucent colorless quartz, bright pearl-colored feldspars somewhat altered, and a small amount of brown mica disseminated through the rock, but also segregated in bunches and nodules. These beds also contain minute red grains of garnet. On the eastern and northern slopes, hornblendic beds prevail, usually close-grained, with the hornblende and feldspars sometimes intimately blended, at others separated by layers of either mineral more or less pure. These layers or bands vary in width: they are frequently lenticular beds of irregular shape, which give the hills and escarpments a highly-altered, metamorphosed appearance. South of the Laramie River, rocks of the same. general character prevail. At Sheep Mountain, the rocks are distinctly bedded, and inclined toward the river. They are perhaps somewhat more coarsely grained than those to the north. At the river, near the crossing of the Laramie and North Park road, those of the high steep slopes seem generally less compact, decomposing more readily, and in physical habit seem to approach nearer to granite than the rocks already described. In addition to the larger rock-masses which constitute the great mount- ain features, the Medicine Bow Range is characterized by the presence of certain accessory minerals, which are of importance in comparing the series of Archean Rocks under consideration with those of the Colorado and other ranges; and, although but little was accomplished in this line of investigation, such facts as were noted should be mentioned. Narrow veins of quartz penetrate the mica and hornblendic schists and gneisses. They are especially marked along the western foot-hills in the neighborhood of Brush and Cottonwood Creeks. The quartz is usually quite pure, accompanied occasionally by fine particles of magnetite, and on Deer Mountain a vein was observed carrying small amounts of pyrites. Hpidote occurs massive, associated with quartz veins, in the interior of the range, in the neighborhood of the Laramie and North Park road. MEDICINE BOW RANGE. 109 Small grains of reddish-brown garnets occur in several localities; where observed, they were always associated with the characteristic light-colored gneisses. They were seen on French Creek 2 or 3 miles above the mouth, near a small tributary coming in from the south; also on the summit of Deer Mountain. Gold in small quantities seems to occur in many districts throughout the range. For several years, miners have been at work wash- ing for gold on Douglas Creek. At Rock Creek Canin, fine yellow gold has been obtained, and it is said to have been found also in Cooper Creek Cafion, and on the smaller streams that come down from the southeast side of Elk Mountain. It will be readily seen that the larger rock-masses which form the Medicine Bow Range present but comparatively few species among their essential mineral constituents, however varied may be the lithological habit of this great series of crystalline rocks. They embrace quartz, orthoclase, plagioclase, hornblende, mica, chlorite, and carbonate of lime. As accessory minerals, there occur garnet, epidote, magnetite, pyrites, cyanite, gold, and calcite. Under the microscope, in addition to the above, were detected zircon, apatite, and titanite. Conciusions.—The Archean series of the Medicine Bow Range presents many marked features characteristic of beds which have been referred to the Huronian formation on the shores of Lake Huron in Canada, and in various localities throughout the Appalachian chain. As these points of resemblance are in many respects so strong, the greater part of the uplift is referred to the same formation, with considerable hesitation, however, as they are widely separated from any beds distinctly recognized as of Huronian age, and such reference is based entirely upon lithological evi- dences. Itis also possible that they may simply be higher members of the same great series with the Colorado Range. The Medicine Bow Range also presents many features which are strikingly in contrast with the Laurentian rocks of the Colorado Range. Although but few mineral species occur in the rock-masses of the one range that are not found in the other, the relative proportions and dif- ferences of arrangement of the constituent minerals is very marked. The Colorado Range, as already mentioned, is almost entirely formed 110 DESCRIPTIVE GEOLOGY. of orthoclase-mica-granites, and gneisses, holding but little hornblende, with the feldspars characterized by a prevailing reddish color. | On the. other hand, the Medicine Bow Range is formed largely of plagioclase-hornblende and plagioclase-mica-bearing rocks. The feldspars of the granites, gneisses, and schists are either composed of triclinic species, or else they are present in such large proportions as to characterize the rocks in which they are found. In color, the feldspars are either white or of very light tints. Hornblendic gneisses and schists, which occur all through the-Huronian series, predominate over large geographical areas in the Medicine Bow Range. They are usually compact and heavily bedded, many of them so free from orthoclase as to deserve the name of dioritic eneisses. The mica-bearing rocks differ entirely from those of the Colorado Range. They are very light in color, with a crumbling, sandy texture, and the mica usually present in subordinate amounts. A striking charac- teristic of this entire series of Archzan rocks, whether loose or compact in texture, is the banded and laminated appearance of the constituent min- erals. Beds as hard and firm as any crystalline mass seem to show the same parallelism in arrangement as the typical gneisses, and it is especially noticeable in the alternate bands of dark green hornblende and white plagioclase-feldspars, which form the rocks that have been designated dio- ritic gneisses. | | The other rock formations of the Medicine Bow Range which overlie the gneisses and schists are perhaps still more characteristic of the Hu- ronian age as developed elsewhere. At the same time, they have no equiv- alent in the area of the Colorado Range included within the limits of this survey. They consist of the argillites, clay-slates, hornblendic irides- cent schists, quartzites, conglomerates, and limestones, as described above with considerable detail. Intrusive rocks of later age, if we exclude some of the granite bodies in the region of Mount Clark, seem to have penetrated this Archzean series only in narrow dikes.’ They do not appear to have produced any marked physical or geological changes in the leading surface features of the range. So far as observed, they are limited to dikes, with sharp well-defined walls, MEDICINE BOW RANGE. 111 of fine-grained dark diorites, some of which have been described as occur- é ring in the ereat white quartzite formation of thé Medicine Peak group. Volcanic rocks of Tertiary age were not observed, and probably do ‘not occur within the Archean belt. They do, however, occur, as pre- _ viously mentioned, along the flanks of the range, on the east side of the North Park, where pee one of rhyolite neve poured 208 from etn 112 DESCRIPTIVE GEOLOGY. SECTION IV. THE NORTH PARK. BY ARNOLD HAGUE. PuysicaL Derscription.—Of the great areas of depression lying west of the Colorado Range, known as the Parks, which form so characteristic a physical feature of the Rocky Mountains, the North Park is the only one that comes within the limits of this exploration, and, as its name would suggest, occupies the most northerly position of these basins. The North Park is situated entirely within the Territory of Colorado, its northern rim lying about 5 or 6 miles south of the forty-first parallel, the boundary-line between Wyoming and Colorado. It lies depressed between two great Archean uplifts, the Medicine Bow and Park Ranges, measuring at its widest expanse, from the base of the one to the foot-hills of the other, between 28 and 30 miles, but narrowing toward the north. To the north- ward, these two ranges come together; the former trending to the north- west, and the latter stretching out eastward, so as to shut in the Park basin on the north. In this way, the Park is enclosed on three sides by great walls of rugged Archzean rock, with clear, sharply-defined limits. On the south side, the boundary between the North and Middle Parks is by no means so prominent or so regular a feature, and is formed by a compara- tively low cross-ridge of Tertiary volcanic outbursts, which stretch the entire width of the Park from Rabbit Ears in the Park Range to the slopes of Mount Richthofen in the Medicine Bow. The topographical divide of this southern ridge lies one or two miles beyond the limits of the map, but the northern slopes are well shown, furnishing the evidences as to both its physical and geological aspect. From north to south, the Park measures about 35 miles, being roughly quadrangular in form, with its meridional sides the longer. Some of the structural details of the Medicine Bow Range have already been given, and those of the Park Range will be found under the proper THE NORTH PARK. its - division of this chapter. It is sufficient for present purposes to mention that the mountains on the east side attain an elevation of from 12,000 to 13,000 feet above sea-level; that they are massive and grand in outline, snow-capped for the greater part of the year, and descend with steep broken ridges to the basin. On the opposite side, the Park Range reaches nearly 12,000 feet, is more regular in its leading features, and falls away abruptly, with an almost precipitous wall, toward the east. The average altitude of the Park may be taken at from 7,500 to 7,700 feet above sea-level, presenting a sunken basin from 4,500 to 5,000 feet below the top of the high walls which surround it. An undulating surface characterizes the North Park, yet changes in level are so gradual, that a greater part of the area, when seen from any elevation that overlooks the basin, appears essentially a plain; only one or two points rising more than a few hundred feet above the Platte bottom. From the east side, a long low ridge of rhyolite projects into the Park, and from the opposite side, but with the same trend as the volcanic flow, a ridge of Archzean granite, nearly 12 miles in length, also extends out into the basin. The draimage-system of the North Park forms one of its most striking physical features, the entire waters finding their outlet through one stream, the North Platte, whose sources lie high up in {he surrounding mountains. Numerous small streams descend from all the steep slopes, which, uniting below into larger creeks, flow out toward the centre of the basin, and make the three main streams, the Hast, Mid- dle, and West forks, which at the extreme northern end come together, forming the North Platte, already a very considerable river, where it breaks through the Archzan wal! of the Park. Along the slopes of the mountains, coniferous forests extend far down upon the outlying spurs, beyond which ‘there may be generally found a narrow belt of deciduous trees, chiefly aspens; but over the entire area of the Park basin there is scarcely a tree to be seen, except along the alluvial banks of the broad streams, where _ there are many small willows and a few stunted cottonwoods. The valleys are unusually wide, and covered with an exceedingly rich growth of gyass. Tf abundant streams of water and immense areas of grass-land are only to be considered, the North Park cannot be surpassed by any portion of Colo-_ rado for stock-raising purposes. 8DG 114 DESCRIPTIVE GEOLOGY. Patzozoic AND Mesozoic Formations.— Within the area of the North Park may be found strata representing all the sedimentary divisions, which occur east of the Colorado Range, from the Carboniferous limestone to the top of the Colorado Cretaceous, but which, unlike the beds bordering the Plains, are here associated with volcanic outbursts of trachytes, rhyolites, and basalts. Still later Tertiary beds, essentially horizontal, are found cov- ering the greater part of the basin. The upturned sedimentary ridges are all, from base to summit, con- formable, and in their main features, as their mode of occurrence, their rela- tion to the Archean foundation, and topographical structure, closely resemble the same beds east of the mountains. They rest unconformably upon the Archean, lying inclined at all angles from 50° to 10°, but usually occur from 15° to 80°; flattening out with less and less angle, away from the high ranges, until concealed beneath the Tertiary strata. At different localities, along the Archean rim of the Park, beds of the Carboniferous, Triassic, Dakota sandstone, and Colorado Cretaceous may all be observed resting directly upon the older crystalline rocks, the underlying sedimentary beds failing to reach the surface, but the upper members of the series to the top of the Colorado group being usually well developed. Carboniferous limestones were recognized at only one locality, and that upon the northeast side, where they lie up against the Medicine Bow Range, inclined at a low angle. They occupy but a comparatively small area, and derive their chief interest from being the single instance ob- served of Paleeozoic strata within the Parks. No fossils were found; but there can be no doubt that the beds belong to the Carboniferous series, inasmuch as they underlie a very considerable development of Red Beds, and measure, at least, two or three hundred feet in thickness, which is far: too heavy to represent one of the limestone strata included within the Triassic. Moreover, in their bedding and texture they resemble the upper members of the Coal-Measure limestone wherever seen below the red sand- stones. The Red Beds, although showing considerable variety in composition and color, possess prevailing deep reddish tints, and are made up of fine sands, with red clays and shales far less prominent than along the Colorado TOE NORTH PARK. 115 Range, while the calcareous and gypsiferous strata, although they may be de- tected in thin layers, are rarely exposed in sections along the creeks. Near the base, they show, in many localities, beds of fine conglomerate, which con- sist of small, rounded, siliceous pebbles cemented by a fine, ferruginous sand. At the top of the series, the sandstones pass gradually up into lighter-colored beds of Jurassic marls. In thickness, they vary considerably, but appear to have an average development greater than along the east base of the Colorado Range, attaining in several places nearly 1,000 feet. As, over long distances, the Red Beds rest directly upon the Archean rocks, the great differences in thickness may in part arise from the lower beds failing to reach the surface. Although from the Jurassic beds of the North Park no well-defined organic remains have ever been found, they show too close a resemblance with undoubted Jurassic rocks, lying between the Red Beds and Dakota sandstone, to question their true position. The light-drab or dove-colored cherty limestone, which forms so characteristic a feature of Jurassic beds, seems a very persistent stratum in the North Park, and, as in many other places, stands out prominently a few inches above the surface of the more easily eroded, crumbling marls, which usually possess light cream and ash colors. An analysis of this cherty limestone, Bea by Mr. B. E. Brewster, yielded as follows: SMUCD, wo MESES eee eae ae ene ee 6.535 iemicsoxide andtalumimay. 22222-0202) 5. y 22.26. 0.921 Winer er ea ere ee ke ee DOLDTE Micternes ae taps sep es ade site tlt. Lee rie ree ae 0.358 (Chee baat PGC 2 = ee Steed A Ae eens enn ene ea 40.177 Vite ieee ee ep ere meee ae Ms Ns 1.498 100.086 Combining the carbonic acid with the bases, we have: Cansonmate of limeremeen ys see ees foe eee Geis Carbonate of manera eee sees 6 5 os oe cls 0.75 In thickness, the Jurassic beds were estimated at from 200 to 250 feet. As already mentioned, both the Dakota and Colorado groups of the 116 DESCRIPTIVE GEOLOGY. Cretaceous are well represented in the North Park. The Dakota beds present identical topographical and lithological features with the corre- _ sponding horizon along the Colorado Range,—a prominent ridge or wall of yellowish-brown sandstone, frequently so well compacted as to form a hard quartzite, with well-marked bedding-planes, and with occasional layers of fine cherty conglomerate, so characteristic in many places of the Dakota sandstone. This lower division of the Cretaceous is estimated at 350 feet in thickness. Of the Colorado group, all the subdivisions,—the Fort Ben- ton, Niobrara, and Fort Pierre beds,—which have been recognized east of the Colorado Range and on the Laramie Plains, may be recognized here, but not always so sharply defined... Beds of pure clays and limestones, although present, and giving character to the Middle Cretaceous rocks, are usually less thickly developed, being more arenaceous throughout the series, which would naturally tend to obscure all divisions. Never- theless, the dark fissile clays, with the ferruginous layers of the Fort Benton, passing up into fine argillaceous limestones and variegated white, blue, and yellow marls, associated with gypsum and selenite, which mark the Niobrara, and in turn pass up into bluish clays, and sandy argil- lites of the Fort Pierre, may all be observed at numerous localities. At the junction between the Fort Benton and Niobrara beds, the limestones attain their greatest development, but are rarely more than 20 feet in thickness, and are marked by a fine, almost impalpable, texture, with sufficient silica in their composition to give them a conchoidal fracture when broken by the hammer. They emit a strong bituminous odor. A peculiarity of the hori- zon is, that while in many localities the overlying marls are easily recog- nized, in others the beds pass so rapidly into sandstones as to lose all lith- ological characteristics. : The uppermost members of the Cretaceous series represented in the ~ North Park consist of heavy beds of yellowish-white sandstones, with a somewhat friable texture, and generally roughly bedded. They have all been included in the Colorado group, although the great thickness of nearly pure sandstones would suggest still later horizons, and it is not impossible that in a few localities they may prove to belong to Fox Hill strata. The reference, however, of the entire series to the Colorado greup rests partly THE NORTH PARK. DUE upon the great uniformity throughout, in composition and physical habit, and, in part, upon the palaeontological evidence procured from the upper- most beds, at several places, before they passed under the Tertiary deposits. _ Organic remains from this horizon are abundant all over the Park, and consist chiefly of the following forms: Baculites ovatus, Inoceramus Barrabini, - which may occur in the lower sandstones of the Fox Hill, but which characterize the Fort Pierre beds, even where the latter are made up of nearly pure black clays. It should be stated that all through this massive sandstone may be seen thin seams and partings of impure clays. The entire thickness of the Colorado group, from the top of the Dakota to the overlying Tertiary, has been roughly estimated at from 1,500 to 2,000 feet of strata. On the north side of the Park, lying directly upon the Archean spur of Bruin Peak, occurs an interesting development of the lower mem- bers of the Colorado group. They are well shown along the Platte River, which exposes a steep bank of marls and dark, earthy limestones, carry- ing a small species of Ostrea. : Kast of the Platte River, about 2 or 3 miles, and midway between the river and the Laramie and North Park road, lies Sentinel Hill. It stands out boldly, and somewhat isolated from the main range, and, rising from 1,200 to 1,500 feet above the river-bottom, forms a prominent landmark, plainly visible over the entire Park. This hill offers one of the most instructive sections across the Mesozoic strata to be found in the region, as all the strata are well represented from the base of the Red Beds well up into the Colorado Cretaceous. On the north side of Sentinel Hill, the bright-red sandstones of the Triassic occur, dipping into the hill. Over- lying these are light-colored marls of Jurassic age, with the prominent drab limestone, in turn overlaid by more marl beds, which pass up into compact sandstone. The summit consists of Dakota Cretaceous, which also forms the greater part of the southern and outer slope of the hill, but near the base is overlaid by the bright beds of Colorado marls, which 118 DESCRIPTIVE GEOLOGY. are soon lost beneath the later Tertiary strata of the basin. These con- formable beds dip to the southward at angles varying from 22° to 25°. Just where the road from the Laramie Plains enters the North Park, the Dakota Cretaceous occurs, apparently resting next the Archzean founda- tion, and standing in bold characteristic ridges, with a mural face toward the mountains, and with a gradual slope in the direction of the plain. They occupy a slight re-entering bay, or curve, in the Archzean mass, and dip with an angle of 18° to 22°. A point of some interest in these ridges consists in the development of conglomerate, which forms so marked a feature over wide areas, at the base of the Dakota group; it is only to be observed in most locali- ties in cross-sections, but here the ridge-summits consist of conglomerate beds offering very excellent exposures. This conglomerate is formed of small fragments of worn and rounded quartz, associated with pebbles of dark chert, the mass held together by a cementing material of fine sand and ferruginous earth. A peculiar feature of the conglomerate is, that many layers are so extremely hard that under the hammer the rock fractures in lines across the chert, as well as through the binding cement. The beds dip 18° to 20°. Still farther eastward, on Retreat Creek, just above the camp station, the probable line of junction between the Dakota and Colo- rado groups is well shown along the banks of the stream. Here the dark black clays lie directly upon the lower sandstones, both formations dipping with an angle of 17° to 19°. The former rises abruptly in a high ridge, while the latter dies away in low, rolling benches. The low bench just south of the camp station probably represents the Colorado marls overlaid by the upper sandstones. From Retreat Creek southeastward to Elk Camp, some 16 or 18 miles, the sedimentary ridges present a nearly uniform appearance that calls for but little mention, rising to about the same height above the plain, and with an average inclination of 20° to 30°. Unlike the Mesozoic strata, however, of Northern Colorado, instead of forming long unbroken lines of upheaval, the beds show a constantly changing strike, which produces short broken ridges, between which small streams have found their way from the main range to the forks of the Platte. From 1 to 2 miles east of Retreat Creek occur a number of prominent THE NORTH PARK. 119 white hills, which have probably attracted the attention of all visitors to the North Park, whether for pleasure or exploration, on account of their striking contrast with the surrounding country. They are found to consist of loose quartz sands, collected here in a somewhat remarkable manner by the pre- vailing west winds. ‘These sand-dunes rise from 100 to 200 feet in height, and, although constantly changing in form, are, from the position of the sur- rounding hills, kept together with but little variation in their main outlines. Voucanic Rocxs.—Along the east wall of the Park, from Elk Camp nearly to Good Pass, which goes over into Middle Park by the way of Willow Creek, the lower spurs and foot-hills of the Medicine Bow Range ‘are entirely covered by immense flows of volcanic rocks, chiefly rhyolites. The central point of eruption would appear to be on the slopes of Mount Richthofen, near the change in strike of the Archeean rock-masses. Here they lie somewhat higher than at any other point, and the flows of dark- colored rhyolites contrast in a marked manner with the gray Archean body. Long volcanic flows send out low ridges into the Park, 300 or 400 feet in height, between which numerous streams have cut broad valleys, more or less filled with coarse, detrital accumulations. These ridges pre- sent a rough, broken surface, and are for the most part covered with timber. In their lithological aspect, they offer, so far as examined in the field, but little variety in texture and composition, and over wide areas present the same general features. ‘They are, however, characteristic rhyolites, and, from their position as the most easterly outburst of a rock, which plays so important a part in the Tertiary volcanic phenomena of the Western Cor- dillera, deserve some special mention. They are usually composed of a fine-grained groundmass, in which small fissured crystals of sanidin, and broken grains of black and dark gray quartz, and occasionally black horn- blende are imbedded. They also carry the globular grains, or spheerolites, which are often so marked a feature in rhyolites. In color, they vary from reddish to purplish-gray. At the head of Sioux Creek, rhyolites of a some- what different type occur, the groundmass being more compact and lighter in color. The enclosed feldspars are larger, giving the rock more the appear- ance of a porphyry, and include opaque orthoclase crystals, as well as sani- 120 DESCRIPTIVE GEOLOGY. din. Macroscopical quartz occurs in comparatively large grains, while the hornblendes, though small, are very abundant. It has already been mentioned that the divide between the Middle and North Parks is composed of eruptive rocks, which stretch between the two ereat Archean ranges. Although the summits and the greater part of the northern slopes are thus formed, this east and west ridge does not exclu- sively consist of eruptive material; the foot-hills in many places being made up of long ridges of Cretaceous sandstones, which have been elevated into their present position by the Tertiary voleanic outbursts. These volcanic rocks consist of both trachytes and basalts, and occur both as large, massive bodies, and as narrow dikes, penetrating the Mesozoic strata. The trachytes occupy by far the most considerable area, and have influenced to a greater extent the present form and outline of the ridge. Parkview Peak, the highest point along the divide, stands out prominently from the surrounding country, rising over 12,000 feet above sea-level. It is situated just south of the limit of the map, near the southeast corner of the Park, one of the tributaries of Sioux Creek draining its northern slope. Its summit consists of light-colored rocks, probably trachytes, which form, upon the northern side, long spurs and ridges extending down to the Park. An instructive geological feature of Parkview Peak, and one rarely met with within the area of this survey, is the occurrence of heavy beds of Cretaceous sandstones, elevated by trachytic outbursts, and now found imbedded between large masses of volcanic rocks, and in places penetrated by dikes, frequently only a few feet in width, which, withstanding atmos- pheric agencies better than the enclosed sandstones, rise above the latter like abrupt walls, with a general strike of east and west. The sandstone beds appear quite hard, and somewhat metamorphosed, showing the effect of the intrusion of adjacent trachytes. All the observed beds dip to the northward, with varying angles, but their inclination is of little importance, owing to the irregular manner in which the trachytes have reached the sur- face. Of the age of the sandstones, no definite proof was obtained, although it would seem more than probable that they belong to the Colorado group, as very similar beds are found to the westward upturned by tra- chytic and basaltic outbreaks, whose age is undoubtedly that of the Colo- THE NORTH PARK. Toy rado Cretaceous. These latter beds, which are of considerable geological importance, as indicating the age of rocks through which the volcanic out- bursts have poured, extend for several miles along the foot-hills in regular ridges, rarely inclined more than a few degrees, stretching down to the Park Basin, where they are unconformably overlaid by Tertiary deposits. At Ada Spri ing, this Cretaceous ridge is cut at right angles by a narrow ravine, exposing sandstone strata, and leading to the south side of the ridge, which presents a precipitous face to the main divide of the Parks. Here we have an exposure of some 400 or 500 feet, near the base of which crop out characteristic blue limestones and argillaceous marls, which form so marked a lithological feature of the junction between the Fort Benton and Niobrara divisions of the Colorado Cretaceous group. From the lower bed of lime- stone were collected a number of specimens of a small Inoceramus, together with an Ostrea, which Prof. F. B. Meek identified as belonging to the Fort Benton division, and. similar to species found along the east base of the Colorado Range, and on the Laramie Plains, from the same horizon. The bituminous odor emitted from these limestones in many localities is here quite strong. These beds have a thickness of about 75 feet, and are over- laid by argillaceous shales of a yellowish-gray color, but very sandy in texture, which probably represent the Niobrara division, although no fossils were found, and the marls not very characteristically developed. They were estimated at 100 feet in thickness. Overlying the yellow-gray shales, and reaching to the top of the ridge, are beds of coarse, crumbling sand- stone, with interlaminated beds of arenaceous clays; the latter occurring quite hard, and of a fine-grained texture. Several of the sandstone beds would appear to be derived directly from the decomposition of old crystal- line rocks, as they are made up largely of fragments of feldspar, flakes of mica, and grains of quartz, firmly compacted together. On the summit of the ridge, the sandstones carry impressions and fragments of stems and leaves of a deciduous growth. To the southward of this ridge, the Cre- taceous strata extend up the slopes of the main divide, until broken up and concealed by the volcanic rocks of the summit. West of Parkview Peak, the summit of the divide is somewhat lower, and presents a plateau-like character, formed by a heavy mass of dark-gray 122 DESCRIPTIVE GEOLOGY. trachytes, which extend westward nearly to the West Fork of the North Platte, where they end abruptly in steep cliffs. This trachytic area stretches over 20 miles, in an east and west direction. In its lithological aspect, this area of intrusive rocks, lying between the North and Middle Parks, presents several features of special interest, which distinguish it from all others, and call for something more than mere men- tion. Indeed, none of the trachytes show the same physical habit which marks the outbursts of this speciesin Utah and Nevada. Just beyond the limits of the map, and to the east of EMiees Peak, near the trail which goes over into Middle Park, occurs a number of isolated hills and cones of a somewhat peculiar composition. ‘That the rocks are intrusive there can be.no doubt, and at the time of their examination in the field were regarded as belonging to the trachytic family, both from their pecu- liar habit and general appearance, and from their mode of weathering, and — association with related rocks. At that time, however, no definite evidence was obtained as to their age, as is the case with the eruptive rocks to the westward. Subsequent detailed study of hand-specimens threw some doubt upon the reference to the trachytes, and examinations of thin sections under the microscope led Professor Zirkel to place them among granite-porphyries. The arguments brought forward in favor of this latter classification are sa strong that it would seem highly probably that they were older than any trachytic eruption. On these grounds, we have been led to regard them provisionally as granite-porphyries, possibly breaking through the Archean foundation, and occurring here as an outlier from the Medicine Bow Range. With these rocks, Professor Zirkel has classed others from the summit of Parkview Peak, which, in most of their microscopical details, develop the same characteristics, but, in their field habit, present still more the aspect of trachytes; and, as to their age, it would seem quite clear that they have broken through Cretaceous strata. The rock from the pass east of Parkview Peak possesses a decidedly porphyritic texture, with large, well-defined crystals, chiefly feldspar, em- bedded in a fine-grained, brownish-gray egroundmass. It weathers in large angular blocks, and, in its broader outlines, shows great diversity of form. On the surface, it appears somewhat porous, owing to the decomposition of =m THE NORTH PARK. 123 iron minerals, magnetite, and pyrites, the latter, on exposure, falling out from therock. Itisan exceedingly tough, dense mass, breaking with a rough, hackly fracture and angular edges. In its mineral composition, this rock, both macroscopically and microscopically, is exceedingly rich in species, the following being recognized by the eye: orthoclase, plagioclase, quartz, hornblende, mica, magnetite, pyrites. In addition, by aid of the micro- scope, numerous crystals of titanite and apatite are seen. — Orthoclase is the predominating feldspar, and, from the large size of many crystals, as well as from their abundance, gives character to the mass. Many opaque orthoclase crystals measure from 14 to 2 inches in length, and are remarkable for the well-developed terminal planes, exhibiting forms heretofore entirely unknown in recent volcanic rocks. The faces shown will be found in Professor Zirkel’s report.*» But singu- larly enough, these rare forms are found again on Steves Ridge, in the Whitehead Peak trachyte region, west of the Park Range, in an undoubted sanidin-trachyte. | : Plagioclase crystals occupy a much more subordinate position, are always small, but marked by a resinous lustre. Both quartz and horn- blende play a secondary part. The former occur as clear, colorless grains, and the latter as small, brownish crystals. The mica, which is quite abund- ant, forms well-developed flakes of a brilliant bronze color. The cubes of iron pyrites on a fresh fracture present a bright-yellow color, and appear to be everywhere scattered through the rock-mass. Both the pyrites and the magnetite decompose so readily that the surface of the rock shows frequently a dirty-brown color. In the specimens collected from Parkview Peak, the rock presents a somewhat different appearance, although, as already men- tioned, the microscopical analysis shows the same detailed structure. The latter rock possesses a much lighter color, with a slightly greenish tinge, and a characteristic trachytic texture. All the mineral ingredients found in the rock from the Middle Park Pass occur here, but in different proportions; the individual crystals being smaller, with less of a porphyritic texture, and the bronze mica less prominent, being replaced by dark-green hornblende, 1 Microscopical Petrography, vol. 6, 68. 124 DESCRIPTIVE GEOLOGY. associated with a decomposed mineral, which, under the microscope, looks like epidote. , : Professor Zirkel has given, with some detail, in his report, the reasons for regarding these rocks as granite-porphyries. Perhaps the most import- ant one, next to those already stated, the forms of the monoclinal feldspars, and the occurrence of pyrites, may be mentioned the absence of glass and the presence of liquid-inclusions in quartz-grains. This distinction, no doubt, forms a sharp line, separating the two classes of rocks. Another point is, the presence of a considerable quantity of titanite, a rare ingredient in Tertiary trachytes, but nevertheless one of the component parts. of trachytes from the Whitehead Peak region. In this connection, it is not without interest to state that, upon the slopes of Whitehead Peak, is found a local occurrence of granite-porphyry too limited to be indicated on the map, which is entirely surrounded by trachytes. If further observations should lead to placing these rocks from the North Park region among granite-porphyries, it would be necessary to admit their outbreak as late as Cretaceous times, which is more recent than has generally been supposed. The connection between the rocks of Parkview Peak region and the plateau-like mass of trachytes lying to the westward was not visited by our parties, the upper portion of the divide having been reached from Ada Springs. The contrast in topographical outlines between the two masses is very marked; the former occurring in cones and sharp peaks, as well as in long irregular dikes, while the latter is characterized by broad masses, with steep acelivities, and deep mural faces. It is without doubt a trachyte, although it offers some marked peculiarities, which distinguish it from other regions. It is a fine-grained, dark gray rock, with few crystals observable to the unaided eye, except a white, glassy sanidin and minute flakes of dark biotite. The mineral ingredients of the groundmass consist of sanidin, augite, hornblende, biotite, and apatite. Under the microscope, the augite is seen greatly to predominate over the hornblende in a sufficient degree to class it as an augite-trachyte, which is a somewhat rare occurrence within the belt of the Fortieth Parallel Survey. THE NORTH PARK. 125 A specimen of this trachyte was subjected to chemical analysis by Mr. ~R. W. Woodward, with the following result: SIUC: Wece Sin ota ed bie es ea ea 61.95 61.95 JNINUITSIT A, Sas 2 oS eee cee Rane eee eee 16.75 15.80 Merroussoxide 2200.0 225! hh de oa Saga 0 5.76 JOINS Aes kate eee Been ppt tes eget © 4.24 4,24. Walemiesia 67. aie SS Sls eeaere 2.54 2.63 NEinilnamermes Asters Ot cee oe trace trace DOue a ee pies gee se eo oe Ee 4 Al 4.50 | PCIAGR ieee ES Seen © amen os ee ee 3.48 Bil OE ere Soe ial OC a ae ee ye Nae 122 1.34 100.12 99.73 Specific gravity, 2.7, 2.6. In this trachyte are enclosed fragments of unaltered, fine-grained gran- ite and dark hornblende-rock. Other trachytes from this same region present much the same physical habit, with the same mineral constituents, varying chiefly in the compact- ness of the rock and in color. The basaltic formation, which enters into the structure of the divide between the two Parks, lies almost entirely westward of the trachyte region. It rarely attains the elevation of the older outbursts, but presents a more broken, irregular surface, with several outlying buttes and hills. These hills form a striking feature in the scenery, rising from 200 to 700 feet above the level of the Park basin, with a crater-like shape, that recalls the small cones which are frequently seen surrounding the base of large volcanoes. That they are connected a short distance below the surface with the main mass of basalt would seem highly probable, but are now separated by hori- zontal Tertiary strata, which abuts up against their steep slopes. Buffalo Peak, just east of the west fork of the Platte, is the most prom- inent of these basaltic hills, rising nearly 700 feet above the stream-bed below, while its summit, a level surface, measures only some 300 feet across. The lithological character of all these basaltic hills is quite similar, being normal fine-grained basalts, varying from black to dark gray, and, with the 126 DESCRIPTIVE GEOLOGY. exception of olivine, exhibiting no well-defined mineral constituents. A specimen from a hill southwest of Buffalo Peak, under the microscope, indi- cated triclinic feldspars, augite, olivine, and specular iron in an ener fine groundmass. From this same hill, Mr. R. W. Woodward analyzed the rock, with the following result : SHEGA oc os ee cet eee eee 49.04. 49.01 ‘Eitamie- acids. . <5. oP eee 2.46 ZED AlUMING |... cn eee ee eee 18.11 18.32 Hermicvoxdes a nea sade etre ey RNASE his Ct 21 2.63 Ferrousioxide: 2: ace... seer Eee 7.70 UT4 Maneanous oxides. =ss2 ee ete eee trace trace Juimies 22). Ge ele ee ee ee ele T14 SMaenesiae: 222 etc tae nie a cee: eee 4.72 4.72 ods, 03.28 PE es NAL ace eee ee ALD) 4.21 d 0) EN Sct ae MP Se are eS NST ie Nyy SI Papi 2.18 Weaitier: Ste 2 ee hic od es eee eae 129 1.35 9977 99.85 Specific gravity, 2.8,-2.7. This analysis shows a typical basalt, containing, however, a large amount of titanic acid, which is of some interest, when we remember the occurrence of titanite in the eruptive rocks of Parkview Peak, as well as in the trachytes from Whitehead Peak.. East of Buffalo Peak occur some interesting dikes of basalt pene- trating the Cretaceous strata like ramparts, and standing above the sedi- mentary beds in almost unbroken walls for long distances. Where observed, they strike north 40° to 50° west. They resemble the rock from Buffalo Peak, except that they appear richer in olivine. West of the Platte, very similar basalts extend to Rabbit Ears, a peak which rises with considerable prominence above the surrounding country in rough jagged points of dark- gray vesicular basalt. It lies directly against the Archean rock-mass of the Park Range, and forms the most westerly outburst of a most interesting THE NORTH PARK. 127 eroup of volcanic rocks, stretching in an east and west line, between two great longitudinal ranges of highly-altered metamorphic schists and gneisses. On the west side of the Park, north of the basaltic area, the only Mesozoic beds observed were Dakota sandstones and the Colorado group, and these are traced with difficulty, owing to the rough nature of Archean foot-hills and great accumulation of glacial detritus, which not only con- ceals the Cretaceous strata, but renders travelling impracticable. The Dakota beds, resting upon the Archean, dip at angles varying from 25° to 50°. The Colorado clays incline much more gently, and stretch out into the Park basin, with a dreary arid appearance, with scarcely any vege- tation, and dotted over with alkaline incrustations, chiefly sulphates of soda and magnesia, which permeate the argillaceous beds. Along the Archzean spur, which projects out from the main range and terminates in Crawley Butte, are found, on the north side, all the Mesozoic strata from the Red Beds to the top of the Colorado group, inclined at low angles; while, upon the south side, the horizontal Tertiary beds would appear everywhere to abut against crystalline strata. Tertiary Beps.—Overlying the uppermost Cretaceous strata repre- sented within the Park, occur the beds of approximately horizontal 'Ter- tiary deposits, to which allusion has already frequently been made. They _ were rarely observed inclined at a higher angle than 4°. They lie uncon- formably upon the older rocks, resting in places against every formation from Archzean to the top of the Colorado group, and are seen in an undis- turbed condition, resting against the basalts. They extend over the entire Park basin, giving it the level, prairie-like aspect, which it presents from all the higher elevations. Through these beds, the many streams of the Platte drainage have worn their present channels, leaving everywhere long bench-like ridges, with steep sides, which, although offermg numerous good exposures, appear in no case to have cut deeply into underlying strata, making any determination of their thickness uncertain. Within the Park, they probably do not exceed a few hundred feet. Lithologically, these deposits possess a somewhat local character, the material of which the uppermost beds are formed being derived exclusively from the relatively narrow limits hemmed in by the Park walls, rendering any comparison 128 DESCRIPTIVE GEOLOGY. with other basins almost impossible, although they present certain features like the Niobrara Pliocene beds east of the Laramie Hills. So far as known to us, neither vertebrate nor invertebrate forms have as yet been obtained from these deposits, so that palzeontological evidence, so desirable in determining the age of Tertiary basins, is still wanting. for the North Park deposits. It is quite probable that there may be found included within the Park two distinct Tertiary series. Some observa- tions were made at the time of our explorations, which would tend in this direction, showing a lower set of unconformable beds, which, however, only reach the surface in a few localities, the greater part of the area being covered with more recent deposits. From the difficulty of sharply defining the two horizons of these beds, they have been given a local name, the North Park Tertiary, and a distinct designation upon the geological map. Partly from the general appearance of the strata, and in part from their relation to the basaltic rocks, they have been regarded provisionally as of late Pliocene age. , i . Lithologically, as already stated, these deposits within the Park develop. a local character, the uppermost beds being invariably loose friable sand- stones, formed from the comminuted detritus mixed with the re-arranged sands of the Colorado beds. Where the old crystalline rocks prevail, the sandstone is generally coarse, and of a gray color, while in the other beds yellowish-brown shades prevail. Beneath these overlying sands are finer beds, with interstratified layers of impalpable grayish-white and cream- colored marls, which cannot be told from similar beds east of the Laramie Hills, in the neighborhood of Horse Creek and Shelter Bluffs. Many of these cream-colored beds are exceedingly friable and rich in lime, and, upon being treated with dilute acid, give off a brisk effervescence. Under the microscope, the mass seems made up of exceedingly minute angular crystalline erains: other beds consist largely of trachytic and rhyolitic — material. On the south side of Bruin Peak occur beds, which differ some- what from those found in other parts of the Park, being made up of loose coarse crystalline detritus mixed with gravel and fine sand. Beyond the - Park, the North Park Tertiary deposits extend down the Platte Valley, and may be traced northward between the two oreat ranges, along the Medicine THE NORTH PARK. 129 _ Bow Range as far as Elk Mountain, and around the northern end of the Park Range. At the upper end of the valley, south of Grand Encampment Creek, they are quite thin, but appear to thicken northward. On the lower geological section given on Map I may be seen the rela- tion of the North Park and its sedimentary beds to the Archzan uplifts. The section is drawn through Crawley Butte, near the broadest expanse of the Park, and represents all the Mesozoic fcrmations resting upon the Medi- cine Bow Range, and passing under the North Park Tertiary deposits, which lie horizontally against the Archean island. To the west of Crawley Butte, the Dakota and Colorado Cretaceous alone, of the older senies, come to the surface along the Park Range. 9DG 130 DESURIPTIVE GEOLOGY. SECTION V. PARK RANGE. BY ARNOLD HAGUE. Puysicat Description.—The Park Range forms the third and last great Archean uplift of the Rocky Mountain system included within the limits of this survey, extending from about the latitude of 41° 20, in an | unbroken line, far to the southward into Central Colorado. Within the boundaries of the map, the range embraces, in a north and south line, about 70 miles. In width, it varies considerably; the southern end, opposite the North Park, measuring only 12 to 15 miles from east to west, while to the northward, in the region of Pelham Peak, its broadest expanse, it reaches from 30 to 35 miles. ; In its topographical features, the Park Range presents much less that is grand and rugged than the Colorado, and much less diversity of structure and intricate drainage than the Medicine Bow; and, while its general eleva- tion is as high as the other ranges, the culminating peaks are much lower, _ only one, Mount Zirkel, attaining an altitude of over 12,000 feet above sea- level. The highest peaks in the range are Mount Zirkel, 12,126 feet, and Ethel Peak, 11,976 feet, on the western rim of the North Park; Pelham Peak, 11,524 feet, a picturesque, graceful summit, just north of the Colorado line, in the Territory of Wyoming; and Grand Encampment Mountain, 11,063 feet, in the northern end of the range, at the head of Battle and Savory Creeks. From the southwest corner of the North Park, the trend of the range is nearly due north and south for 45 miles, with a narrow plateau-like summit along the eastern edge, falling off with gentle undulating slopes to the westward, but terminating in a somewhat abrupt wall toward the depression known as the Park. This wall, to the north of Mount Zirkel, _ is broken by a long narrow spur that puts out from the main ridge ina southeasterly direction into the Park, while a nearly parallel ridge, still PARK RANGE. 131 to the north, forms a portion of the Park. boundary, and connects the Medicine Bow with the Park Range. North of Davis Peak, the range strikes off to the northwest in a broad flat-topped mass, presenting uniform unbroken slopes, with no prominent outlying spurs, and with a trend nearly parallel to the peenteiie Bow Range. The drainage-system of the range is remarkably simple. Streams at regular intervals from each other, having their sources high up on the axis of the range, drain both east and west in very direct courses. Only one, the Grand Encampment, an eastward-flowing stream, breaks through from the opposite side, receiving the waters from the western tributaries of the Pelham and Davis Peak group. y All the eastward-running creeks contribute their waters to the North Platte, while the western streams flow into the Little Snake and Yampa Rivers, the main eastern tributaries of Green River. The streams of the east side, enumerating from the south, are Cheyenne and Arapahoe Creeks within the North Park, and Grange, Beaver, Grand Encampment, Cow, Warm Spring, and Jack’s Creeks, in the Platte Valley. On the west side, there are Moore’s Fork and Elk River of the Yampa, and Battle and Savory Creeks of Little Snake River. Traces of local glaciers, such as groovings and moraines, are abundant throughout these hills, as through most of the higher mountain-regions, and are shown also in the character of the topography. In the southern end of the range, in the region of Mount Zirkel and Ethel Peak, the eastern face exhibits a number of remarkable glacially- eroded cations. The upper portions are large amphitheatres, with grand mural faces, which soon contract into deeply-cut trough-shaped valleys, with all the characteristic features of glacial erosion. ‘These valleys are never more than 3 or 4 miles in length, and at their mouth, considering the limited size of the ancient glaciers, are found immense terminal moraines, which have undergone but little erosion in post-glacial times. It is as if the entire former contents of the cation had been carried down and dumped at the entrance, and had never been disturbed. | In the northern portion of the Park Range, there are some secluded, 132 DESCRIPTIVE GEOLOGY. open basins, shut in by high hills, which are usually filled with recent Qua- ternary deposits, and form a characteristic feature of the region. Encamp- ment Meadow is a little mountain-valley, having some few acres of grassy bottom at the head of Grand Encampment Creek. Grange Valley, east of Davis Peak, is another basin of similar character. | ' The high ridges and mountain-slopes are generally covered with a good growth of coniferous forests up to about 11,000 feet, the average height in these latitudes in the Rocky Mountains, although varying some- what with the exposure. The higher plateaus and summits are mostly bare. On the western slopes, the growth would appear to’ be quite dense, but per- haps not so vigorous as on the opposite side. The same species are found as characterize the Medicine Bow and Colorado Ranges. Geo.ocicaL Descriprion.—In its geological structure, the Park Range for its entire distance belongs, like the other great uplifts to the eastward, to the Rocky Mountain system of highly crystalline rocks of Archean age. Rocks of later ages form but a very subordinate part of the uplift, and are found only along the lower flanks, seldom rising more than a few hundred feet above the plain, where they rest unconformably at varying angles upon the older series. At the extreme southwest corner of the Park, Tertiary basaltic rocks conceal the spurs of the Archean series; but in one instance only, at Rabbit Ears Peak, do they form any considerable part of the slope. Farther to the north, between Cheyenne and Arapahoe Creeks, the Dakota sandstones occur inclined at a high angle. Still farther north- ward, rocks as low as the Red Beds of the Triassic, with the conformable series exposed, as high as the Colorado marls, are found uplifted against the granites, while near where the Platte River leaves the Park, the Colorado beds appear lying next the Archean. Above these, the horizontal beds of the North Park Tertiary, which cover the Mesozoic rocks of the Park Basin, lie up against the Archean, concealing the older rocks, and breaking the continuity of their exposures. Over that portion of the Park Range north of the Park, the later sedimentary beds have never extended, except possibly in some lower portions, which cannot now be traced. To the north and east, the hori- PARK RANGE.. 133 zontal Tertiaries cover unconformably the Mesozoic beds, so that their angle of dip cannot be determined. On the west of the northern end are horizontal beds abutting against the flanks of the Archean uplift, which have been referred to the Laramie group of the Cretaceous. As these beds, © however, show no unconformity of dip, and no great difference of litho- logical character with the overlying Tertiaries, there is a possibility that they may be a lower, hitherto unrecognized member of these beds. South of the Little Snake River, in general, only outcrops of the Cretaceous rocks are exposed along the western flanks of the Park Range; in one instance only have rocks as low as the Triassic been found in contact with the Archzan. The structure of these sedimentaries, as well as could be seen under the great accumulation of voleanic material, is that of a series of secondary rolls, approximately parallel with the axis of the range, but showing no signs of having for any great extent covered the Archean _ rocks, since their beds, never upturned at very steep angles, are as often in- clined in an opposite direction to the slopes of the main Range, as with them. In regard to the geological features of the Park Range, too little oppor- tunity was afforded for working out with any degree of accuracy the detailed structural relations of the different beds. Only the broad leading features that characterize the range can here be pointed out, and even these may require considerable modification. The narrow portion from the southern limit of the map northward to Davis Peak appears to have a nearly uniform monoclinal structure, with the prevailing dip of the beds to the westward, which on the summit, so far as observed, are inclined at low angles, falling off gently to the west- ward, while near the foot-hills they dip much more steeply, passing under the later rocks. The entire mountain-ridge suggests the western fold of a broad anticlinal axis, whose eastern side has been carried away either by erosion or downthrow. On the outlying spur which forms the northern rim of the Park, west of the Platte River, near Bruin Peak, the existence of this eastern side of the fold is Mange north and south strikes being observed with easterly dips. North of Pelham. Peak, the axis ae the main fold appears to undergo a somewhat abrupt change, curving round to the northwest, and striking 134 DESCRIPTIVE GEOLOGY. approximately with the topographical trend of the range. This change in ~ the direction of the geological axis produces a sharp bend on the eastern side of the range; the beds dipping in opposite directions toward each other, forming a synclinal fold, narrow near the angle of the bend, but widening to the westward. This structure is first indicated by the rocks on the north slope of Davis Peak dipping distinctly to the northwest. Near where the Grand Encampment Creek leaves the mountains, the beds dip a little south of west, and strike west of north. In the higher portion of the range at this point, the prevailing strikes are east and west, while the basin-like depression of En- campment Meadows seems to occupy a synclinal trough, the beds to the south having a prevailing northwest dip, while to the north their inclination is generally southward. Northward, the broad axis of the anticlinal passes through the region of Grand Encampment Mountain, with the sides of the fold falling off to the southwest and northeast at highly-inclined angles. At the bend of Snake Creek, below Camel Peak, the red gneissic beds dip as steeply as 45° to the southwest. In the cafion on the spur between the forks of Battle Creek, the rocks are seen dipping 45° a little west of south. To the east of the head of Jack’s Creek, the strike is about north and south with a westerly dip, while at the northern end of the range the beds sink suddenly at an angle of 60° to the north, with a strike of east and west. | In their lithological character, the highly crystalline beds of the Park Range vary considerably in texture, color, and habit; but all the promi- - nent rock-masses may be classed under granites, micaceous and hornblendic gneisses and schists, and probably interbedded syenites and diorites. They differ in many respects from the beds of the Colorado and Medicine Bow Ranges, although they more closely resemble the former than the latter, and for that reason have been referred to the Laurentian. They are character- ized by the presence of much structureless granite of a decided reddish tint, overlaid by gneisses and schists, similar to the series of the Colorado Range, but carrying more hornblende-bearing beds in the upper members. On the other hand, they are wanting in those rocks that are more especially PARK RANGE. | 135 characteristic of the Medicine Bow series, which was referred to the Huro- nian formation. A characteristic granite from the southern end of the range is found upon the summit of Ethel Peak. It is a moderately coarse-grained rock of a reddish-gray color, and a somewhat friable texture, breaking up readily into small, irregular-shaped pieces. It is distinctly bedded, but without any lamination in the arrangement of its constituents, and closely resembles many of the granite bodies from the Colorado Range. It is composed of quartz, feldspar, and mica. The quartz is present in small angular grains, slightly tinged with gray; the feldspars, mostly orthoclase, are reddish in color, and frequently stained with an earthy, ferruginous coating, while the mica, in dark biotite plates, is not very abundant, but well disseminated through the mass, occasionally adhering to the broad faces of the orthoclase crystals. The outlying spur east of Arapahoe Creek, where observed, is a somewhat similar-appearing granite, a reddish, crumbling mass, with rounded outlines, which probably belongs to the same body. Separated from this spur by the broad valley of Arapahoe Creek, stands Crawley Butte, an isolated and prominent. landmark in the North Park. It rises above the Tertiary plain some 1,000 or 1,200 feet. Geologically, it is closely con- nected with the spur, and the eroded forms and outlines are similar in both masses, being the result of the same agencies upon rock-masses of the same composition and texture. On the northern rim of the Park, granites would seem to be the prevailing rock. From Bruin Peak, the highest summit of this ridge, ‘ were collected a number of interesting rocks. Coarse-grained graphic granite occurs, similar to that found in Grand Encampment Canon, and on the west side of Long’s Peak, in which the individual crystals of quartz, feldspar, and mica have frequently attained the dimensions of half an inch or more in diameter. The feldspar is chiefly orthoclase, of a bright red color, and the quartz massive and usually white. Both muscovite and black biotite are present, the plates of the former being much the larger. One variety of this rock is made up mainly of flesh-colored orthoclase, with but little quartz or mica, and these are usually present in segregated masses. Between the feldspar masses occur narrow fissures of yellowish-green epidote. 136 DESCRIPTIVE GEOLOGY. . It resembles the rock described by F. H. Bradley,' from the Unaka Range, a part of the Blue Ridge, which forms the boundary between North Caro- lina and Tennessee. Last of Bruin Peak, the granite assumes a more uni- form character, composed chiefly otf orthoclase and quartz, with beds carry- ing more or less hornblende or mica. Both hornblende and mica-gneisses are found here, the former, an exceptionally beautiful rock, being made up largely of crystals of dark, brilliant hornblende, with an admixture of white feldspar, which is, however, at times almost entirely wanting. Much of the. feldspar is shown, under the microscope, to be well-developed Plagioclase, while the quartz appears to be a subordinate constituent. Hornblende also appears to be present in considerable amount in some varieties of the mica-bearing gneisses. These gneisses become so fine- grained that they may be properly classed as mica-slates, consisting of minute grains of quartz, dark-greenish flakes of biotite, and some little white mica, probably muscovite. Under the microscope, thin sections dis- close abundant grains of magnetite. Zirkel calls attention to the interesting manner in which the octahedral crystals of magnetite are penetrated by prisms of colorless mica. On Mount Zirkel, a somewhat similar series of mica and hornblende beds occur, which are finely exhibited in the rock exposures of the glacially- eroded cafions. Here the bedding is distinctly seen on a large scale, and presents a series of rock formations, highly altered, with an exceedingly variable lithological habit. Hornblende, associated with both orthoclase and plagioclase, forms the prevailing rock, while other beds are made up of mica and orthoclase, carrying some little hornblende and probably always a small amount of triclinic feldspar. They are characterized by a banded structure, in which the individual minerals are separated in layers, but vary- ing greatly in width and outline, expanding from a mere line up to several inches, and again narrowing down to the former dimensions, and mingling in with the other constituents. Usually, the dark hornblende layers will be penetrated by small quantities of feldspar, and the feldspar bands, in turn, finely striped with hornblende. Segregations of the different minerals, 1Am. Jour. Sei., May, 1874, 519. PARK RANGE. 137 especially hornblende and quartz, which are always present in varying quan- tities,. in irregular-shaped bodies, are of common occurrence. Along the trail which leads up Grand Encampment Creek, across the mountains to the westward, are found many excellent exposures of the Archean rocks. At the mouth of the creek occurs a gneiss, the mass of which is largely quartz and feldspar, with the laminated structure very irregularly developed. The mica, which is mostly biotite, seems to occur im lenticular masses. The rock has little of the schistose structure of most gneisses, and passes into a coarse-grained rock, in which large masses of quartz and feldspar are enclosed in this gneissic material in a somewhat similar manner to the segregations in the beds on Mount Zirkel. Above ‘this is a compact, dark-gray hornblendic rock, containing a slight admix- ture of white feldspar, which gives it a porphyritic appearance. Still farther up the creek occurs a large, interesting body of granite. It resem- bles, in its mineralogical habit, many of the features of the granites in the Colorado Range. It varies in texture and compactness, and is char- acterized by reddish orthoclase and quartz, with but little plagioclase. or mica, and probably no hornblende; at least none was observed. The coarse- grained granites are one of the most characteristic rocks of this region, and show macroscopically what is usually only revealed by the microscope, that the feldspar crystals enclose masses of quartz filling the fissures, which often contain other feldspars, as well as well-developed crystals of mica, In these coarse-grained beds, the crystals of flesh-colored orthoclase often attain a size of several inches. The coarse rocks pass again into the opposite extreme of granites, of which a specimen collected is a compact pinkish rock, composed chiefly of flesh-colored orthoclase and translucent quartz, with but little mica. Frequently, the mica is entirely wanting, or at least can- not be detected by the unaided eye; when present, it shows a tendency to gneissic lamination, its crystals almost always lying in parallel planes, even when irregularly disseminated.. Zirkel has shown, in his examination of a thin section under the microscope, that the red color of the feldspar is in a measure due to fine laminz of oxide of iron in microscopical fissures in the erystals; and that the mica is accompanied by a dirty green, strongly dichroitic, chloritic-like mineral. The quartz of all these granites is very 138 DESCRIPTIVE GEOLOGY. poor in liquid-inclusions. It is an interesting fact that these microscopical observations hold equally well in the examination of the red granites from the Laramie Hills. The slopes of Davis Peak, southeast from Encampment Meadows, pre- sent a series of hornblendic and micaceous gneisses, very similar in petro-< graphical habit to those found on Mount Zirkel. The micaceous rocks are a very fine-grained admixture of black mica-flakes, reddish-gray orthoclase, and white, limpid quartz. Scattered through the gneiss are numerous small garnets of a deep-red color, mostly about the size of a pin-head, sometimes, however, as large as a pea. Under the microscope, no hornblende could be detected, and the quartz was poor in liquid-inclusions. Near the summit of the peak occurs a characteristic hornblende-gneiss, in which the lamina- tion is very regular. It consists of alternating white layers made up mostly of plagioclase, and black ones in which hornblende predominates.. As in the mica-gneiss no hornblende was detected, so in this rock no mica is visible. Under the microscope, minute apatite crystals are seen, while the ‘quartz shows interesting double inclusions of liquid carbonic acid. In this gneissic series is sometimes seen the same zonal structure with alternating black and white bands, frequently an inch or more in thickness, as already noticed in the Mount Zirkel series. The very summit of Grand Encamp- ment Mountain is formed of a mass of hard, compact, dark-green horn- blende, which is almost entirely free from other constituents, but which carries interstratified a bed of white micaceous quartzite; it may be classed as an amphibolite. On both the east and west flanks of the range, the attitude of the beds is very similar, and in their larger general features resembles the rocks of the range already described. A few especially interesting characteristics should, however, be mentioned. At the north end of the Park Range, just north of the upper end of Jack’s Creek, where the first Archean rocks are found emerging from the horizental Tertiary beds which form the divide, occurs, interbedded in the hornblende rocks, a remarkable bed of pure white quartz, some 50 feet in thickness. Such is the dazzling whiteness of its mass that it was at first mistaken, at a little distance, for a snow-bank. It is a vitreous struct- ureless mass, of a milky white, and at times almost limpid quartz. A thin PARK RANGE. 139 section under the microscope reveals, in its interior, a series of lines and spots to which the milky appearance is due, a high magnifying power, showing them to be an aggregation of liquid-inclusions, carrying some- times water with a moving bubble, and sometimes liquid carbonic acid - containing a bubble which disappears with a slight elevation of temperature: the same phenomena are seen in the quartz of the accompanying gneiss. Associated with the gneisses of this region is a hornblendic rock, closely resembling that from Rawlings Peak, but in which the granitic structure predominates over the gneissic, and the hornblende shows a tendency to distinct crystallization. It is a compact, medium-grained rock, composed of hornblende, orthoclase, and plagioclase, with but a small amount of quartz. Orthoclase appears to be the prevailing feldspar. The rock has the mineral composition of a syenite, with much of the habit of an erupt- ive body. Closely related to this rock is another made up almost exclu- sively of feldspar and quartz, but carrying also some plates of white mica in subordinate quantities. In the metamorphic series of Jack’s Creek occur beds that in a marked manner resemble intrusive bodies, and in the hand-specimen it seems impos- sible to distinguish them from well-known eruptive diorites. A specimen in the collection may be described as a compact crypto-crystalline mass, with no observable regularity in the arrangement of the mineral constituents, with a rough, angular fracture, and of a dark-gray color. In mineral com- position, it appears to be chiefly an admixture of dark-green hornblende and white plagioclase, the latter frequently present in long, acicular crystals, of a vitreous lustre. The western slopes are generally densely wooded, and the exposures much less favorable for observation than on the eastern side. The predom- inating beds seem to be the hornblendic rocks, and but one or two localities require special mention. Under the lavas, at the head of Little Snake River, is exposed a rock, which is different from any of those already men- tioned. It is a compact rock, having no schistose structure, but a peculiar banded appearance, owing to the parallel arrangement of the fine quartz and minute mica flakes between the feldspar crystals. Both orthoclase and plagioclase are present; the former, however, is the more abundant, and 140 DESCRIPTIVE GEOLOGY. gives a decidedly reddish tint to the rock, while the latter is only observed in brilliant acicular crystals. The following analysis was made by Mr. R. W. Woodward: Pe Ges APRA kn al cr htaa i ee Me ONE AM a Ct 78.49 Alominae oe oe ce ee ce ee ee Ce ee ene 11.63 Ferrous OXGG. 20 oe ee eee acme eee 1.76 SOG aie Pee re ce ees eC eee eee Berl Potassae 2 2 25. 22 oe ee ee 5.31 lonition o-oo eae oe ee eee eee 0.45 100.85 Specific gravity, 2.6. This analysis is characterized by a somewhat high percentage of silica. At the bend of Little Snake River, below Camel Peak, the same red gneiss is exposed, interbedded with the hornblende-rocks. On Buck Mountain, at the head of Elk River, on the west side of the range, occurs a compact dark-gray crypto-crystallme hornblende-rock, almost identical in lithological characters with the one described from the head of Jack’s Creek; there is something in the physical habit of the groundmass which suggests that they may both be interbedded intrusive rocks. The essential minerals which form the large rock-masses of the Archean series of the Park Range are, so far as observed, like the minerals of the other great ranges to the eastward, limited in numbers. The list comprises quartz, orthoclase, plagioclase, biotite, muscovite, hornblende, and epidote; as accessory minerals, garnet, magnetite, and gold. Under the microscope are detected, not already observed macroscopically, chlorite and apatite. Epidote, as an essential constituent of the rock, was seen only at Bruin Peak in deep-red granite, where it occurs in considerable quantities. It is found, however, in one or two localities scattered through the coarser gran- ites. Red garnets occur in the finer-grained mica-gneisses, usually very small, but on Davis Peak they were found of considerable size. Fine — gold occurs in the stream-beds in the region of Buck Mountain, where miners have been engaged in washing for this metal for several years past. b) y PARK RANGE. 141 Chlorite was detected in the red orthoclase-granites, with an association and habit similar to that observed in the granites of the Laramie Hills. Minute apatite crystals occur in the hornblende-gneisses of Davis Peak. The red orthoclase, structureless granites, poor in mica, of the Park Range, bear a close analogy to the Colorado Range granites. The overly- ing mica-gneisses are, in habit, also more closely allied to those of the Col- orado Range than to the Medicine Bow series. They are characterized in general by a somewhat compact texture, gray color, with broad mica flakes; while the Medicine Bow series have a much more friable and crumbling nature, are white or silver-gray in color, and the feldspars more decomposed. The mica is present usually in minute, thin plates. Hornblendic beds, however, recall the Medicine Bow series. They are, indeed, the only rocks that indicate any very close analogy, and even these have some points of difference. In the Park Range occur beds of very fine-grained hornblendic gneiss, carrying considerable quartz, which resemble the beds in the Laramie Hills, in the Sybille Cafion, while the finely-laminated rocks, made up of fibrous hornblende and bluish-white plagioclase, which so characterize portions of the Medicine Bow Range, do not appear to form a marked feature of the Park Range. On the other hand, the massive white quartzites, argillites, iridescent slates, red con- glomerates, and limestones are wanting in the Park Range. Intrusive rocks later than the Archzean series do not appear to have penetrated the Park Range. At least, dikes or outbursts of such material were not observed, This, however, is not remarkable, as they play a very insignificant part in the other Archzean uplifts to the eastward. The later ‘Tertiary volcanic rocks may also be said to be absent from the interior of the range, although, as already mentioned, they occur all along the west flank. 142 DESCRIPTIVE GEOLOGY. SECTION VA: CRETACEOUS REGION FROM COMO TO SEPARATION. BY ARNOLD HAGUE, VALLEY OF THE Mepicine Bow River.—North of the two great Archean masses, the Medicine Bow and Park Ranges, Cretaceous strata are found over the greater part of the area, extending from the Laramie Plains west- ward to the limits of Map I, where they pass beneath the Kocene Tertiary deposits of the Green River basin. Over this wide extent of country, the crystalline schists reach the sur- face at only one point, Rawlings Peak, while Paleozoic and Mesozoic rocks below the Colorado Cretaceous occupy nearly as restricted limits. The country presents a broken, undulating surface, varying in average alti- tude from 6,500 to 7,000 feet above sea-level. The structural features are somewhat complicated, consisting of a series of anticlinal and synclinal folds, with sharp, prominent ridges of Fox Hill sandstone, and basins and level plains of Laramie beds. Between Como and Medicine Bow Stations, the country is overlaid by the Colorado Cretaceous, all the divisions being recognized. The Niobrara yellow marls would appear quite thin, although characteristically developed, and both the upper and lower clays seem highly arenaceous. Just north of the river, at Medicine Bow Station, the beds strike north 65° to 70° west, and dip 16° to 18° southwest. In the bright-colored marls were found Ostrea congesta associated with imperfect fragments of Inocerami. | Below the Niobrara beds, in the sandy clays, occur Inoceramus altus, and in a low ridge or bench not far distant, but above the latter, were collected Scaphites Warrent. . The Medicine Bow River, after leaving the mountains, runs almost exclusively through beds belonging to the Colorado Cretaceous; its course being guided by the clays and marls, and the overlying Fox Hill sandstone. Beds of the former formation occupy a deep bay, or recess, penetrating the VALLEY OF THE MEDICINE BOW RIVER. 143 Archean gneisses between Rock and Elk Mountains, through which ‘the river cuts a narrow channel, trending in a nearly north and south direction, until reaching the overlying sandstones, when it turns abruptly eastward, following the line of junction between the two series of beds; the Fox Hill strata appearing as a long line of prominent bluffs upon the north side of the stream. To the eastward, where the overlying sandstones turn toward the north, the river also runs in the same direction, but, before reach- ing the railroad, makes a bend to the eastward, flowing through Colorado Cretaceous strata. A short distance west of Medicine Bow Station, the Colorado Cretaceous passes under the Fox Hill sandstone, and from here the latter formation occupies the surface for at least 5 miles to the westward, _ or to within 3 miles of Carbon. All the beds appear to dip westward, but with a varying angle, and with a general strike of northwest and southeast, curving around somewhat to a north and south course as we proceed westward. The surface presents a gently rolling, barren country, with occasional edges of sharp sandstone rising a few inches, or, at best, a few feet, above the plain, but sufficient to indicate the position and inclination of the beds. Near the base of the series occurs a prominent but low ridge of sandstone, which strikes north 60° west, with a dip to the southwest of 32° to 37°. “It consists of coarse, yel- lowish strata, interstratified with beds of ferruginous clay-shales and black carbonaceous clays, underlaid by deep-red ferruginous sandstones, passing down into gray and steel-colored beds. At the base on the west side of the ridge are found two springs, highly charged with sulphur and salts of iron, probably derived from the adjacent impure clay strata. Farther westward, observed strikes gave north 40° to 45° west, and a dip of 25° to 30° west. This ridge is followed by a broad, open country, without outcrops, and then other ridges still dipping westward, but at lower angles; the rocks present- ing much the same general aspect. It was impossible to determine the thickness of these beds, but there must be at least between 4,000 and 5,000 feet of strata represented. Carson Basin.—The town of Carbon is situated directly on the line of the Pacific Railroad, 656 miles west of Omaha, and 83 miles to the westward of Laramie City. It lies 6,760 feet above sea-level, on a bleak, 144 DESCRIPTIVE: GEOLOGY. dréary plain of nearly horizontal sandstones. In an economical point of view, it derives its sole interest from the heavy deposits of coal underlying the town, which have been extensively mined for a number of years. Geo- logically, the place has also received considerable attention in examining the question as to the age of the Wyoming coals. There would appear to be but little doubt that the beds belong to the Laramie division of the Cretaceous sandstone. In determining the true horizon of these beds, how- ever, it is necessary to trace out their relations with the great sandstone formation, which forms all the higher ridges of the region, and to compare the strata with other similar localities. The beds at Carbon occupy a broad, irregularly-shaped basin, the rocks on the west, south, and east all dipping in toward the centre, surrounding it completely on three sides. Between one and two miles west of Carbon, a high, prominent ridge of Fox Hill sandstones, known as Simpson Ridge, whose highest point, just south of the railroad, rises some 800 feet above the level of the town, shuts in the valley on that side. South of the railroad, this ridge, which is quite regular in outline, trends approximately north and south, but to the north falls away consider- ably, curving around to the northeast. Its structure is that of a very per- fect anticlinal fold, whose axis passes through the high point already men- tioned. The beds upon the east side of the ridge facing Carbon dip at 55° to 60°, while upon the opposite side of the fold the same rocks dip westward at 35° to 40°. In the axis of the fold lies a brilliant pearl-gray, medium- grained sandstone, which is overlaid on both sides by a series of arenaceous and ferruginous clays, with the following subdivisions: . Thinly-laminated arenaceous clay. . Rusty sandstone, with ferruginous seams. . Ferraginous fine-grained claystone, 4 feet. . Fine black clay, 50 feet. . Ferruginous claystone, 3 feet. . Crumbling rusty sandstone. Dor ON Overlying the latter are sandstones similar to those from the summit, but perhaps not quite so white, which are in turn overlaid by coarse red sandstones reaching to the base of the ridge. A marked peculiarity of outline, seen upon both sides of the ridge, and one that adds a striking feature to the anticlinal structure, is the similar shallow valleys formed, high CARBON BASIN. 145 up on the slopes, by the erosion of the softer clay-beds, protected by the outer overlying sandstones. Along the east base of the ridge, the coarse sandstones may be traced northward to the railroad-cut. Here, one mile westward from town, a thin bed of coal is seen in a hard sandstone, which earries a large amount of half-carbonized bits of wood, and is overlaid by beds of arenaceous clays. A short distance farther north, on the west side ._ of a low ridge, with all the beds still dipping eastward, occur similar clay and iron strata, as seen high up on Simpson Peak, associated with fine calcareous sandstones. The beds of Simpson Ridge, in passing eastward, shallow in dip, and may be traced passing conformably under the level coal-bearing strata of the valley. Leaving, for the present, the detailed description of the beds underlying Carbon, we find the strata for nearly 3 miles east of the town lying horizontally, and then gradually assuming a westerly dip, forming the opposite side of a broad synclinal fold from the. Simpson Ridge beds. About 4 miles east of Carbon, near the first snow- shed, rusty, yellow sandstones occur, dipping west at 25°, and carrying a thin stratum of impure coal. A short distance farther eastward are found very similar yellowish sandstones, with concretionary fragments of iron, black clays, and friable sands, with intercalated thin seams of iron, still preserving the same dip. South of Carbon, the beds incline gently north- ward, and would appear to be perfectly conformable with the basin strata. How far they extend southward was not carefully determined, but coal outcrops in very similar beds are said to occur 4 or 5 miles south of the railroad. Returning to the railroad, which crosses the synclinal basin near its centre, the strata appear approximately horizontal, although, imme- diately underlying Carbon, they are somewhat disturbed by local faulting, bringing the beds which carry the main coal seam to the surface a short distance west of the town. In company with the superintendent of the mines, the following sec- tion was made of the beds underlying Carbon: Feet HERA len GUSANG: ' 5 ta apie eee awe sioc lo clas oe nee soe be Saeco aces eel lee 5 2 LOM MSIE BE NEN ORO vobccuose 7 eeuod 2 bO5ee COR RBE SS COME Sree aon eeeen 6 Gt, SINISE Sa an nce otal aera oo ous oidc cis ecco Hes rer senc ars DEAD WY SOBA RSE en 4. 4. Sandstone 222226. cL eee vee ee et MRR aos Se sO REGS IEC Oe eee 4 Bs SIMMS 46.5 Abe oS GOO OMOOUE CO Beis bin O co Mt ROORRS TG OPI erat tes ae aaa er 4 10DG , 146 DESCRIPTIVE GEOLOGY. Feet. (Hs MONG He) SEMITONES oil PRINI) Zooensons Sooscs oases todas acd os0cs 4 345c85s00 8 Ge Warlkoclayas. eee cs es ae ena nae Ge Soi A eh aa ee cee ee eee SE A i 8 SMO Od atx. terete eins crew mererats eateds SE S loner ya. 2 \ale ee Ab See 1 9. Sandstone and interstratified shale, with plants...... . a minve resect seneerias aeateee 11 aCe 002) Neca reales eRe mri we Nes crt a aa AT Be eee eps e 4 i, Ar cillaceous sandstones... 22. tccs shee ore iis cea inlet eee oe eee 18 Beet) SO COP) ee Ree ote niet AOE in in Sos ee Bic Gn RS cine. Sendo Ooo 40 ate: 9 Idi Clay, and sandy shales; with plants exer ae re oii ee eee ee ate 20 TA, Coal’ Boe Sasa oe Se oA Wan lik Oa ene eles ae ep 4 102 Below the lower coal, yellowish-gray sandstones occur, which were not estimated. The third stratum of coal, number 12 in the section given above, is the only coal that has been worked. In its physical appearance, it resembles the other Cretaceous coals of Wyoming, and is regarded as one ~ of the best for railroad purposes. It is highly prized, although it carries narrow seams of earthy impurities and slate bands. In the cracks and fissures of the coal are thin layers, or films, of yellowish-gray carbonate of lime. It crumbles readily on exposure to the air, and takes fire sponta- neously on the dumps. When burned, it yields a large percentage of yel- lowish-gray ash; but the amount of water present appears to be lower than most of the Wyoming coals From bed number 6, a fine-grained, calcareous sandstone, large quantities of fossil leaves of dicotyledonous growth have been collected, many of them well preserved; also, from bed number 9, below the first coal stratum, and from number 14, below the main working- seam, other collections were made. Professor Lesquereux, who gathered a large swite of specimens from these beds, has determined fifty-six distinct species, and has come to the conclusion that the beds are, without doubt, of Miocene age. From this collection, eighteen species are identical with the Miocene flora of Europe, and thirteen with that of the Arctic regions: Among the species found here which Professor Lesquereux regards as indicating a Miocene flora may be men- tioned the following: Betula Stevensoni, Acer trilobatum, Alnus Kiefersteini, and Hquisetum Haydeni. Associated with these, however, in the same beds, are other species, subtropical types, which Professor Lesquereux says are CARBON BASIN. 147 characteristic of a much lower horizon; among them, a Smilax grandifolia, Rhamnus Goldianus, Cinnamomum Mississippiense, and Ficus tiliefolia. At the time of our visit to this district, we made diligent search for Molluscan remains, but without success, and, so far as known to us, no ver- tebrate or invertebrate forms have as yet been found in the Carbon Basin, with the exception of a single imperfect and distorted specimen of a Viwipa- rus, having no specific character. The evidence as to the age of these deposits rests either upon the fossil plants which they contain, or upon their stratigraphical position, and, where such testimony disagrees, it would seem that the latter must necessarily receive the greater weight. This is especially the case where so much doubt has already been raised in other localities of the Rocky Mountains as to the importance of plant evidence in determining geological horizons between Cretaceous and Tertiary beds. Professor Lesquereux, notwithstanding he feels so positive as to the Miocene age of the Carbon beds, does not hesitate to place them below the Green River series, giving them a position, in relation to the latter horizon, which few geologists will be disposed to dispute, and which the geological maps and sections accompanying this report conclusively prove. In the second chapter of this volume, it will be shown that the Green River beds are undoubtedly of Kocene age; that they are, moreover, overlaid by several thousand feet of Eocene deposits, and underlaid by a heavy thickness of the Vermillion Creek series, also Eocene; and that the latter overlies uncon- formably beds occupying the same horizon as the Carbon formation, which we regard as of Upper Cretaceous age. — West of Simpson Ridge, the Fox Hill sandstones pass under the Laramie beds, and the latter extend westward as far as Saint Mary’s Peak, a dis- tance of 15 miles, where they are again limited by the coming to the surface of the underlying sandstones. North of the railroad, the Laramie formation stretches beyond the boundary of our map, and its limits in that direction have never been determined; while, to the southward, it is hemmed in by outlying ridges of Fox Hill sandstone connected with the Elk Mountain upheaval. The rocks of the Laramie division are chiefly loose, friable sand- stones, of rusty-yellow and reddish-brown colors, and in places carrying 148 DESCRIPTIVE GEOLOGY. thin seams of clay. Occasionally, carbonaceous clays crop out in ravines and gullies, with indications of coal, but no workable deposits have as yet been opened. North of Saint Mary’s Station, the beds strike north 70° tu 15° west, and dip 16° to 20° to the northeast; near Dana, they strike nortn 55° to 60° west; and, still farther eastward, strike north 35° east, but with the same dip. Over this area of Laramie strata are dotted, in the spring and early summer, numerous small ponds and lakes, which, in many cases, suffer com- plete evaporation during the dry season. As the country is very poorly drained, and the clays highly impregnated with saline matter, most of the waters are strongly alkaline, and leave behind considerable incrustations. _ From the shore of one of these lakes, south of Percy, a quantity of salt was collected, which, upon being subjected to chemical analysis by Mr. R W. Woodward, yielded the following: © , Soluble matter, 48.36 per cent. MIO eee eee ee ee 1.84 1.69 Malomesiay - cto naree c ae yieerc en ween ee eee 16.09 15.88 Sota. er ome eer eet eee 20.48 20.65 Potdssae feo cee k oe yea: oceans ae eee trace trace Sulphurte acid. 25-282 2 OO oe ty Oot OMG rie oe rg ee ent ee eo a aioe 0.57 0.57 Phosphovicacidie: ayer ee ey eee trace trace 99.74 99.07 Combining acids with bases, we have: _ Sulphate ofdime i.56R metiasia ee sy ie 4.45 4.10 Sulphate of maenmesia Sse ss psec. ae 48.28 47.56 Sulphate of soda -..-- Sl tk ee eee ee 46.27 46.46 ‘Chioride etiso dim se ee ee ee 0.74 0.95 99x(4: 99.07 Kix Mountain Ree1on.—Nine miles south of Percy lies Elk Mount- — ain, the most northern point of the Medicine Bow Range. Some descrip- tion of the schists and gneisses forming its main mass has already been given, but on its northern slopes are found all the beds from the Coal- ELK MOUNTAIN REGION. 149 Measure limestone to the Fox Hill sandstone, uplifted at high angles, lying against the Archzean foundation. All the geological divisions are well rep- resented, in general exhibiting the same characteristics as séen elsewhere in the Rocky Mountains, and only a few salient features require special mention. Unlike the rigid beds east of the Colorado Range, which stand out from the main mass in unbroken lines of strata, the beds at Elk Mountain conform much more closely to the Archean outline, and curve around the older rocks lying directly upon the sloping sides. All the later sedimentary strata are more or less disturbed, and show considerable crumpling and local displacement. The Carboniferous limestones lie high up on the mountain, in places reaching within 1,200 or 1,500 feet of the summit, and extend from the first cation east of Scotch Creek to the west side of Sheep Butte. In the narrow canon east of Scotch Creek, the limestones occur at the entrance in a steep cliff, then, rising up over the gneisses, form a covering 200 or 300 feet in thickness, concealing the crystalline rocks beneath ; both formations, however, being distinctly seen from the cation. These limestones would appear to be much more arenaceous than the same beds to the eastward. They all. possess a coarse crystalline texture, more or less sandy, many of the beds consisting largely of siliceous material of a bluish-white color, interstratified with yellowish-white layers, and at the same time are not so characteristically bedded as the Paleozoic limestones of the Laramie Hills. At Sheep Butte, the arenaceous habit of the lime- stone is clearly shown. Here the beds stand at 80°, many of them almost pure sandstones of a bluish-gray color. The Red Beds, Jurassic, and Da- kota Cretaceous all occur on the slopes of the mountain, but much lower down, and less regular in outline than the Carboniferous. East of Sheep Butte, they all conform with the latter beds in following the deep re-enter- ing bay in the Archzean mass, and then curving around the northern side of the butte, completely encircling the projecting spur of Archean rocks. Just east of the summit of Rattlesnake Pass, the Dakota Cretaceous stands out prominently, with its characteristic wall, above the softer Jurassic marls on one side and the Colorado clays on the other, at an angle of $5°, striking north 75° to 80° east. From here eastward, nearly to Foote 150 DESCRIPTIVE GEOLOGY. Creek, the Colorado Cretaceous is well represented in a series of three or four low rolls, rising gently above the surface. The strata bend slightly in long gentle S-curves, with a general strike of north 65° east, and dip 85° east. Overlying the Dakota, the Fort Benton black shales and bands, with brown earthy marls, appear quite prominently, the latter weathering light gray, with a peculiar dotted, speckled surface. In the marls occurs an undetermined species of a small Jnoceramus. ‘The Niobrara light-colored marls, although very characteristic, forming a low continuous ridge of purplish and yellowish beds, would appear to be hardly more than 100 feet in thickness, passing up into the overlying clays. North of Sheep Butte, along Rattlesnake Creek, the Colorado Cretaceous, which forms the creek-bed, may be well studied. Here the two lower members of the series crop out upon the south side of the stream, and the Fort Pierre sandy clays on the opposite side pass up into well-defined Fox Hill sand- stones. These upper clays dip 55° to the northeast. | East. of Sheep Butte and south of the Rattlesnake road, the Fort Benton clays are characterized by an extensive development of the fer- ruginous beds, which, in many localities, mark the underlying clay strata in thin bands and nodular concretions. The clays have undergone a very considerable erosion, and are cut by narrow ravines and gullies, exposing the harder iron layers along the ridges for several hundred feet in length, but with a very varying thickness, and with interstratified beds of clays. The iron occurs both massive and in concretionary nodules, associated with rather striking and delicately-marked clay concretions. It presents a steel-black color, weathering to brownish-black, a very even crystalline texture, a conchoidal fracture, and a hardness about 4. In the cracks and fissures and between the surfaces of the nodules occurs a secondary for- mation, caused by percolating waters, of crystalline spathic iron, and an occasional seam of carbonate of lime. The following analysis, made by Mr. B. E. Brewster, shows it to be an argillaceous siliceous carbonate of iron, with a trace of carbonaceous matter, and, like many of the English clay ironstones, containing a considerable amount of manganous oxide. ELK MOUNTAIN REGION. 151 Ralten. 2h se ce Che See Oe ee ene 9.74 Sibi, ole | ee ee ee 5.57 NCES CHC a2. 6 See ce es Seo es eee 18 He rrmulsROmi Chien ee a ee kk 38.67 Niammain Ot CSIC GSO as = ee ae ee 2.38 ime 2-2. 2. caf Gch a ena Nek rn cad et eal 7.64: EET Tate Sia een = oe Aven steerer es ee EIS 1.20 Soca ama ipotassal a aun Ursus ear Ne oe 0.46 Biesphontcacidias s+. Seis: Ree se ieee sss trace (Clare Onan G arCnGls es ae are ere ne eee eee ee 32.04 GIST ee Eee se ann aera LONE Supine ee eee trace (OMEN TOE ee So ctr ee eek eee trace 99.63 Although these clay ironstones of the Colorado Cretaceous have as yet nowhere been observed in extensive deposits, it is by no means impos- sible that they may be found near the railroad in close proximity to limestone bodies and lignite beds of the Laramie formation; in which case they may at some future time prove to be of practical value. One of the most marked structural features in the region of Elk Mountain is seen in the prominent ridges of Fox Hill sandstone, which lie just outside the eroded valleys of the Colorado Cretaceous. In many localities, the Colorado clays fall away in dip, and the overlying sandstones pass out upon the plain in low rolls with diminished dips. Here, however, along the face of the mountain, the Fox Hill presents very persistent ridges, with mural faces toward the range, and dipping at high angles. To the eastward of Elk Mountain, along the north side of the Medicine Bow River, these ridges extend in an east and west line. North of Scotch Creek, the beds are con- siderably broken up, and Simpson Ridge, a long anticlinal fold, trends _ off to the northward. West of Simpson Ridge, the west side of this fold curves round, striking east and west, until north of Rattlesnake Creek, when it bends off to the northwest im the direction of Saint Mary’s Peak. A recorded strike of the main ridge, north of Elk Mountain, indicates north 35° to 40° east, with a dip of 52° to 57° northwest. At the southern base of the ridge, the Fort Pierre beds pass up into brownish sandstones, over- laid by gray beds, and in turn passing up into others of a rusty-brown 152 DESCRIPTIVE GEOLOGY. color, carrying argillaceous and ferruginous material, with impressions of deciduous leaves and stems. Above these occur massive white sandstones. VALLEY OF THE NortH Piatte—Along the bluffs between Elk Mount- ain and Saint Mary’s Peak occurs another anticlinal fold. To the northwest of Elk Mountain, along Pass Creek, the beds fall away gradually to the west and southwest, bending in strike as they go northward, until south of Wolcott Station, their dirction is a few degrees north of west and south of east, the course of Pass Creek roughly indicating the outlines of the uplift. Just north of Pass Creek occurs a very sharp, clearly-defined anticlinal fold, the beds on the upper side dipping north and northeast. North of the railroad, and on the east side of the North Platte, the Fox Hill sandstones form a prominent monoclinal ridge, dipping northeast, which below Fort Steele determined the course of the river in a similar manner as beds of the same horizon have marked out the course of the Medicine Bow River. At the southern end of this ridge, at Saint Mary’s Peak, the beds occur considerably disturbed, and metamorphosed into a hard sandstone, with a strike north 15° east, and a dip 16° east. The ridge on the south side of the fold mentioned as north of Pass Creek crosses the North Platte River, in a nearly due east and west line, about 2 miles above Fort Steele. It is formed of sandstone beds, which dip 45° to 50° to the southward. This ridge presents singular narrow crests of the harder upright strata, forming straight ridges only a few feet in width, and enclosing narrow monoclinal valleys worn out of the more yielding beds. It extends to the westward in an east and west line for nearly 10 miles, forming the southern boundary of the open Quaternary valley west of Fort Steele, then gradually trends to the southward with a constantly- decreasing dip to the south and east, joining the Sage Creek Bluffs. The latter form the line of bluffs which border Sage Creek on the north, possessing an easterly strike and a dip northward, which gradually shal- lows passing eastward, until near the mouth of Sage Creek they are — practically horizontal. On the surface of the flat country to ip north of this line of bluffs, where the soil accumulation is very slight, the jomting planes of these sandstones present a line of cracks of remarkable regularity; the grass VALLEY OF THE NORTH PLATTE. 153 growing in little ridges along these cracks gives to the surface the appear- ance of a planted field. ‘These sandstones form the southern member of a broad, shallow, synclinal fold, which occupies the valley north of Sage Creek, the northern member of which, as already described, is very steep. On the opposite side of the Platte River, east and southeast from the mouth of Sage Creek, the Cretaceous beds, dipping from 1° to 3° to the northeast, _ rise in long level benches of friable coarse gray sandstone, stretching com- pletely across the valley to Elk Mountain, where they again dip westerly, and may be traced to the beds, already described, on Pass Creek. South- ward the limit of Cretaceous strata is less definitely determined, as, in a nearly horizontal position, they lie concealed beneath Tertiary deposits of similar lithological habit, which have been referred to the North Park beds. ‘These Tertiary beds extend down the valley of the Platte as far as Cottonwood Creek, and rest in plateau-like ridges against the crystalline gneisses of the Medicine Bow Range. Near the mountains, in a number of localities, they may be seen lying unconformably upon the eee edges ‘of the Cretaceous. As thus described, by the aid of the geological map it will be seen that the Fox Hill Cretaceous forms a remarkable synclinal basin, irregular in shape, but extending in an east and west line for 32 miles, and measuring across its broadest expanse about 16 miles in width. The persistency of the bluft-like formation of the Fox Hill beds over so wide an area is a marked feature in the geological structure of the region. Perhaps equally noteworthy is the occurrence of the upper members of Colorado Cretaceous clays, which crop out along the base of the bluffs, as seen on the Medicine Bow River, at Elk Mountain, along the Sage Creek Bluffs, and at the Mount Steele Ridge, in all of which localities the beds of the lower series pass up gradually into the upper sandstones, both divisions being perfectly conformable. sibs In general, these Fox Hill beds are not rich in organic remains; but sufficient paleontological evidence was obtained at various points, in rude casts of Inoceramus and Baculites, and some characteristic plant-remains, to define their horizon as belonging to this group. A number of sections were made through portions of the [ox Hill 154 DESCRIPTIVE GEOLOGY. group. A section across the ridge, on the west side of the Platte, near the river, two miles south of Fort Steele, shows, in the lower 2,000 feet, princi- pally beds of massive sandstone, 50 to 100 feet in thickness, with a few shaly seams at the base, overlaid by a thickness of about 1,500 feet of more thinly-bedded sandstones, in thickness varying from 5 to 10 and 15 feet, with interlaminated shales, sometimes bituminous, and two or three thin seams of coal. In the valley south of the ridge, the upper beds run into more reddish, iron-stained sandstones, which have been considered to rep- resent a remnant of the lower beds of the Laramie group, in the trough of the synclinal. The whole thickness of the Fox Hill beds, which we esti- mate at between 3,000 and 4,000 feet in this region, is not exposed in this ridge, the lower beds being concealed beneath the Quaternary of the valley. Some of these beds can be seen on the low hills just west of Fort Steele, where there are indications of a narrow anticlinal fold having an east and west axis parallel to this ridge. 2 About 4 miles east of Fort Steele, in the railway gap, which cuts a high, prominent ridge, dipping about 16° to 20°, the following section was taken in descending series: . : Feet i Heavy-bedded) white sandstones ej. -.)42 torn) oe ett ree eer 1, 000 2. White and buff sandstones.......... PPE Bee tial tha) Re Ra netoy ete ee eer 200 3. White blocked sandstone ..... RAE Me atte eo keln ars ma neler oe SMe ee ang eS 50 4: Vellowasandstonewcs-me.cc cose eines eer ee ce “uta telat al oars Sines ane perete aoe 25 5. Shaletbedsaceats-2 2 hee oe eee ee oe ence fer escent Pie? tes 75 6, Yellow Sandstone fake ee eee os fen Se ieae lake aan ee ee 50 UOMEROWANY SENNUSONESIe6a ces sa5ss>so05s9 Hreavasegencseesesso sacncsseoos = MND) 8. Brownish-red sandstone..............-- Beg Songs ale nee See ee eee { 9. Sandy shales, with impressions of small bivalves........-...........-- ¢ 150 10:* Coarse sandy. Shales e272 Fee tists ois oe ssi c/lee a Sena eee ie oe eee \ 2; 300 The North Platte River cuts through the nearly horizontal rocks of the syuclinal basin, exposing along its bluffs many good, but limited sections, showing between 400 and 500 feet of strata. In general, they do not differ greatly from those already given. The following section, made near where VALLEY OF THE NORTH PLATTE. 155 the old overland stage-road crosses the river, was taken from the water- level to the top of the overlying bench: 1. Hard rusty-gray sandstone ............ Saccic SOO e Cty Re ee eae . 2. Black shales, with thin sandstone layers, carrying Ostrea....... 50 ret. 3. Friable yellow sandstone, rich in the genus Ostrea.........-.--. 30 feet. Aakeddisheyellow sandstone. acs. 0-6 2 4-.200026- sc ee- te RAWLINGS PEAK. 161 through which the railroad passes. Their greatest thickness exposed can- not be less than 700 feet of beds, generally not more than a foot or two in thickness of gray-white quartzite and sandstones, having something of a reddish tinge on the weathered surfaces. The lowest bed found is a fine- grained conglomerate, about 70 feet in thickness, made of small pebbles of white quartz in a siliceous matrix, while the upper bed is a ferruginous sandstone, about 15 feet thick. The only traces of organic life found in them were a few indistinct fucoidal remains, but their general lithological character, and position beneath well-defined Carboniferous limestones lead- us to consider them representatives of the lower Paleozoic series of the Laramie Hills. | At the extremity of the eastwardly-projecting spur of Rawlings Peak is an interesting deposit of red hematite. It forms a body some 20 feet in thickness in the sandstones immediately underlying the lower limestone bed. The extent of the body in strike could not be determined; at the time of visit, however, it had already been extensively mined for use as a flux, and as a mineral paint, for which it is peculiarly valuable. The ore is remarkably free from impurities, and contains almost the theoretical percentage of iron; although its surface, when fresh, shows a metallic lustre, it is so soft and fine-grained that a very slight attrition reduces it to an almost impalpable powder of brilliant vermillion color. The horizon _ of this deposit is probably represented by the ferruginous band found in other parts of the ridge. Above the iron deposit at this point is a bed of some 50 feet of drab limestone, so compact and fine-grained as to resemble a lithographic stone. The same bed occurs capping the sandstones in the low hills south of the railroad gap, where they furnish large springs, and are overlaid by darker-colored limestone beds, all dipping 10° to the south- ward, and soon disappearing beneath surface accumulations. On the western ridge, a few miles northwest of the railroad station, the best section is obtained, where the beds dip 30° to 40° tothe westward. A thickness of only about 150 feet of the underlying quartzites is exposed on the slopes of the valley. Above the ferruginous sandstone, which caps the quartzites, is 50 feet of fine-grained drab limestone, darker in color toward the base; over this 30 feet of white siliceous limestone, succeeded by a bed THe DG: 162 DESCRIPTIVE GEOLOGY. of varying thickness of dark-blue earthy limestone, from which was obtained Pleurophorus oblongus and some fragments of a strongly-curved Productus. Above the blue limestone is a bed of 40 feet of dark, earthy limestone, frequently of reddish color, followed by 40 feet of grayish granular lime- stone. This thickness of 200 feet of limestones is overlaid by 50 feet of arenaceous shales, beyond which is a gap of about 500 feet, showing only occasional outcrops of thin arenaceous shales, but including probably argillaceous and calcareous beds in the intervals covered by soil. A gap of some 400 feet now occurs before the ridges of the characteristic red sand- stones of the Triassic are reached. Near the base of these, in a bed of light- drab, fine-grained, semi-crystalline limestone, was found a Natica Lelia. Individuals of the same species were found in a similar position in a lime- stone of the Red Beds on the East Fork of the Duchesne in the Uinta Range. This species, being new, does not suffice to characterize the horizon, but is interesting as being the only one found between the hori- zons of distinctly Jurassic and Permo-Carboniferous types. . The beds thus far noticed occupy the higher portion of the ridge, whose surface is but little incidented. On this ridge there is evidence of one, if not two, slight displacements along a line approximately at right angles to the strike of the beds. From the fragments of granite seen along the principal line, it would seem probable that a sharp ridge branches out from the main granite body to the westward, which has determined the direction and position of the faulting. Along the western slopes, the harder or more massive beds of the Mesozoic formations stand out in monoclinal ridges, and are easily distinguished by their lithological habit. These upper beds where observed have a steeper dip than those nearer the axis of the fold; their angle being over 40° to the westward, while that of lower beds is scarcely 30°. In general direction of strike, they follow the shape of the uplift, curving eastward toward the south, and toward the north assuming a trend of due north and south; the line of the ridges is, however, rather sinuous and irregular, following short re-entering and projecting angles, and consequently presenting varying dips. The Triassic formation is represented by a thickness of about 600 feet of sandstones, of a light pinkish red and more massive habit in the upper RAWLINGS PERAK. 163 portion, and of a deep Indian red, and frequently thinly bedded, and of much finer texture toward the base. About midway in these sandstones is a bed of about a foot in thickness of a pale greenish drab, compact, litho- graphic limestone, enclosed in beds of purple and green argillaceous clays and shales. This bed seems very persistent throughout this formation east of the Wahsatch Range. At the base of the series is a gray sandstone, rather thin-bedded, with very regular jointing planes. The red sandstones are overlaid by about a hundred feet of red and white, soft, argillaceous beds, including thin seams of arenaceous shales. Above these were found two outcrops of limestone, a dark, earthy bed of 10 feet, overlaid by 15 feet of gray, somewhat arenaceous limestone. In these were found the following Camptonectes bellistriatus. 7 extenuatus. ; pertenumstriatus. Belemmites, sp.? Ewumicrotis, sp.? Astarte, sp.? ° Adjoining these limestones, the outcrops were too much covered to make it certain that 25 feet is the maximum development of Jurassic lime- stone here. No other outcrops were observed, though in the gap of nearly a hundred feet between them and the characteristic conglomerate of the base of the Cretaceous, which shows on the surfaces only fragments of thin sandstones and rusty shales, there may be some limestone beds hidden. Beyond the outcrop of the Dakota conglomerate, which is here white, the successive ridges are occupied by beds of the higher groups of the Creta- ceous, still conformable, but with ever decreasing angle of dip. To the westward, the high plateau region is occupied by nearly horizontal beds of the Laramie group. Along the line of the railroad, west of the gap near Rawlings Station, the first prominent outcrops are seen in low ridges of shales of the Colorado group, overlaid by «white sandstone beds dipping westward, which, to the north, have a strike of nearly north and south, while beyond the railroad to the south they bend eastward, assuming a trend of south 70° east. Above these, the series of heavy-bedded white sandstones of the Fox Hill group is 164 DESCRIPTIVE GEOLOGY. crossed in section, dipping conformably westward. West of the divide toward Separation Station, the rusty sandstones and arenaceous clays, with their included coal beds, of the Laramie group, are crossed, dipping at first with the lower sandstones 10° to 15°, but beyond the open shallow valley to the north they are seen to lie nearly horizontal, perhaps dipping 2° to 4° north. About two miles to the south of Separation Station, these rocks form paral- lel ridges running northeast and southwest, in which the beds dip 10° te the northwest. The upper sandstones are full of impressions of deciduous leaves, and constitute the characteristic leaf-beds of the Laramie group. From Separation, the beds flatten out to the west as well as to the north, and form a high barren plain country, in which the dry, shallow water-courses present but few exposures of rock. One can only distinguish that the strati- fication-lines occupy nearly horizontal planes, but of the character of the beds little definite idea can be formed. It is probable that the Laramie beds occupy the greater part of the surface of this region, though in some coarse sandstones are found plentiful casts of fresh-water shells, Lymnea, Viviparus, Goniobasis, which probably represent the same horizon as the beds found at the junction of the Little Snake River and Little Muddy Creek. They would then be remnants of the Vermillion Creek Tertiaries, which may doubtless at one time have extended as far east as the base of the Rawlings Peak uplift. About ten or twelve coal beds of various thick- nesses can be distinguished in this region. None have been worked on account of the exposed and dry nature of the country; but the compara- tively horizontal position of the strata presents a very favorable condition for the mining of coal on a large scale. . Savory Piateavu Recion.—From the depression of Bridger’s Pass and the valleys of Sage and Little Muddy Creeks, southward to the base of the Park Range, extends an elevated plateau region, cut through by deep canion-like valleys, the higher portion of which, immediately adjoining these valleys, and which is about 8,500 feet above the level of the sea, has received the name of the Savory Plateau. This region is principally covered by horizontal beds of the North Park Tertiary, which, as proved by exposures in the deeper cuts on its northern edge, overlie the upturned edges of Cre- taceous and earlier beds, while the higher portions of the ridges are capped SAVORY PLATEAU REGION. 165 by remnants of the Wyoming conglomerate. The best exposures of the Tertiary beds are found in the open valleys at the heads of Savory and Jack’s Creeks, and on the pass between the Archean body of the Grand Encampment Mountains and the Savory Plateau. A thickness of not less than 1,000 feet of these beds is here exposed, which is made up in the upper portion of a thickness of about 300 feet of a drab, earthy, somewhat porous, limestone, sometimes enclosing small pebbles, underlaid by beds, which erade off insensibly from limy sandstones into coarse gravel beds. In the lower part of bluff-exposures bordering the meadows, at the head of Jack’s Creek, was found a seam of greenish, indurated clay, containing streaks of fine, hardened gravel, in which are flakes of brown and white mica, deposited with their broad faces parallel to the lines of stratification. In the same bluff was a peculiar seam, a few inches thick, of dark-green, cherty mate- rial, which also contained a few scattered flakes of mica. To the west of the divide, at the head of Savory Creek, the Tertiary beds can be traced for some distance, and are found to cap the underlying Cretaceous sandstones, which are here almost flat, and show no discrepancy of angle. 'To the west of Savory Plateau, however, and south of the Little Muddy Creek, is an open valley, whose surface is covered by detrital material and considerable accumulations of sand blown in from the open country to the west, in which no outcrops were found. It was impossible, therefore, to ascertain the stratigraphical relation of these Tertiaries with the different groups recog- nized in the Green River Basin; and no beds, corresponding lithologically to these, are found west of this line. Their angle of dip at the most westerly exposures would carry them apparently over the beds of the Vermillion Creek series, and the large proportion of limestone they contain would ally them with the overlying Green River group. They may, however, repre- sent an entirely later series, and be a local development confined to the region of the North Park and the Platte River; for this reason, as has been already stated, they have been designated by a special color, and assigned provisorily to the Pliocene. They occupy the valley of the North Platte to the south of Jack’s Creek, forming long, gentle slopes, extending up from the river to the flanks of the Grand Encampment Mount- ins, which, though so covered by recent Quaternary deposits that only few 166 DESCRIPTIVE GEOLOGY. exposures of the underlying Tertiary are found, sufficiently show the continuity of their original deposition. Their beds may be traced along the line of bluffs bordering the valley of Sage Creek on the south and west. Here the upper member is a hard siliceous shale, more like an older rock, under which are seen the white limy sandstones; the lower beds being concealed beneath débris accumulations. ELKHEAD MOUNTAINS. 167 SECTION VII. ELKHEAD MOUNTAINS. BY S. F. EMMONS. GENERAL Description.—To the west of the Park Range, on the borders of the broad Tertiary plains of the Green River Basin, lies a singularly pic- turesque and beautiful group of high volcanic peaks, known as the Elkhead Mountains. Their steep, rugged slopes are covered for the most part to their very summits with a dense growth of pine forests, while the valleys which are enclosed between them present a pleasing variety of open glades and groves of quaking-asp and pine. The highest peaks, which attain an elevation of over 10,000 feet above sea-level, are’ arranged somewhat in the form of a cross, of which one bar is formed by the north and south trachytic eleva- tions of Whitehead Peak and Steves Ridge, and the other by the east and "west ridge of basalt, of which Anita Peak and Mount Weltha are the cul- minating points. Out of the gently-sloping plains in the northwest angle of this cross rise a number of isolated peaks and dike-like ridges both of _ trachyte and basalt. From the few outcrops of sedimentary rocks exposed along the bases of these peaks, and in some cases high up on their slopes, it is evident that the eruptive rocks broke through and covered a pre-existing line of elevation of Cretaceous, and possibly also Tertiary beds, whose summits, and a portion of whose slopes, have thus been preserved from erosion by their envelope of more resisting volcanic rock. From a mineralogical point of view, the eruptive rocks of this region form a remarkably interesting and peculiar group, being characteristically different from any of the widespread groups of volcanic rocks, which cover so large an area in the western portion of the region embraced within our explorations. They consist mainly of quartziferous trachytes and nepheline- basalts. The trachytes, which belong essentially to the class of sanidin- 168 DESCRIPTIVE GEOLOGY. trachytes, containing generally large, well-defined crystals of this feldspar in a rough, porous, and mostly crystalline groundmass, are characterized by the presence of a large amount of free quartz. They have, nevertheless, a physical habit which is not rhyolitic, but decidedly trachytic. The quartz occurs in rounded grains, which have a dull, greasy lustre, and are cracked and riven, like a glass which has cooled suddenly. While this quartz is evidently an unessential and accessory constituent, like tridymite in other trachytes, occurring only in grains large enough to be distinguished by the naked eye, and not, therefore, forming part of the groundmass or influencing the general aspect of the rock, the fact that it frequently contains glass-inclusions proves that it is a primary product, and not the result of later secretion. These trachytes, besides the normal constituents, sanidin, horn- blende, and mica, contain also a relatively large proportion of augite, and in some cases considerable amounts of olivine, generally, however, where the rock has a decidedly basic character. The basalts of the region are no less remarkable than the trachytes, being the only representatives of the group of nepheline-basalt found within the limits of our exploration. . The trachyte outflow forms, as we have seen, a north and south ridge, nearly parallel with the line of outcrop of the Archean rocks of the Park Range, which, at the northern end of the ridge, it comes in contact with and partially covers. The dense forest, which covers it almost continuously, renders its exploration somewhat difficult. Its forms are generally rounded and dome-shaped ridges, with sharp conical peaks, in striking contrast with the prevailing flat-topped peaks and ridges of the basaltic outflow. North of the east and west line of elevation, the trachyte-flows have been more deeply eroded, leaving sharp, jagged peaks, of which the most prominent is Hantz Peak, a comparatively regular cone, 10,906 feet in height, while a number of similar shaped peaks of less height form the pro- jecting summits of Steves Ridge. In the angle of the two ridges, a line of sharp ridges and narrow dikes extend out in a northwest direction, partly covered by the more recent basalt flows, of which Crescent Peak and the Skelligs Ridge present the most striking topographical features. ‘To the southward, the trachyte ridge has generally broad, gentle slopes. Its crest ELKHEAD MOUNTAINS. 169 rises from the Yampa River northward, finding its culminating point in Whitehead Peak, a dome-shaped mountain-mass, abruptly escarped on its eastern side, whose summit has an elevation of 10,817 feet above sea-level. Tracuytic Recron.—The trachyte of Whitehead Peak is one of the most interesting and curious of the remarkable group of trachytes of this region. It is a grayish-drab rock, having a tendency to split into thin laminze, from half an inch to an inch in thickness. It is formed of crystals of sanidin, hornblende, and augite, with large rounded masses of cracked quartz, in a purplish-gray, fine-grained groundmass of a rough porous texture. Besides the hornblende and augite, it contains a few sparse grains of bronze-colored mica, while sonie portions of the rock are filled with reddish-brown spots, which the microscope shows to be half-serpentized olivine, “‘a mineral which,” Professor Zirkel remarks “‘ has never before been observed in a sanidin rock”. He suggests, with regard to the occur- rence of this mineral in connection with free quartz, that it almost seems as if the unusual secretion of free silica had been counterbalanced and neu- tralized by the introduction of so basic a mineral as olivine. Large sani- din crystals are frequently found in this rock measuring an inch or more in diameter, and showing a tendency to zonal decomposition. At White- head Peak, there is also an extremely local occurrence of granite-porphyry, which is too small to be indicated on the map. It contains both orthoclase and plagioclase-feldspars, with black mica and a large amount of black horn- blende prisms, in a grayish felsitic groundmass. On the bold eastern escarp- ments of Whitehead Peak, the trachyte is seen to be underlaid by a very considerable thickness of white fine-grained sand-rock, often quite thinly bedded and shaly, with somewhat of the appearance of a volcanic ash. Under the microscope, however, the rock is seen to be made up of rounded grains, largely of quartz, with some colored jasper, and black grains, which may be magnetite. No angular crystals can be detected in the rock, and it may possibly be a remnant of some later Tertiary formation, which cov- ered this region before the trachyte overflow. To the south of Whitehead Peak, the tr achyte- -flow forms a high idee; dividing Elk River from Elkhead Creek, on the spurs of which it spreads out, covering the underlying Cretaceous beds, nearly to the banks of the 170 DESCRIPTIVE GEOLOGY. Yampa River. From the Sugar Loaf, an isolated flat-topped hill near the forks of the Yampa River, was obtained a gray sanidin-trachyte, which contained none of the grains of quartz, which are so unfailing an accompani- ment of most of the other trachytes of this region. It has a more massive habit than the trachyte of Whitehead Peak, but contains like it large erys- tals of sanidin, imbedded in a gray porous groundmass. Associated with the sanidin are numerous hornblendes and black biotites, while the ground- mass is made up of micro-crystalline feldspar, and hornblende. To the north of Whitehead Peak, an outlying western spur of Steves Ridge, which forms a secondary parallel elevation between the main ridge and Steves Fork of the Little Snake River, is formed of a still more char- acteristic quartziferous trachyte. ‘This rock bears a remarkable resemblance to the famous trachyte of the Drachenfels on the Rhine, containing large, well-defined crystals of sanidin-feldspar, often an inch or more in length, in a rough, gray groundmass, associated with erystals of mica and a few hornblendes. Like the trachyte of Whitehead Peak, the weathered sur- face of this rock is full of rounded cavities, from which the grains of cracked, glassy quartz, in which it abounds, have fallen out. Some varieties of the rock present a white color, with a porous, almost earthy texture, from which the harder sanidin crystals can easily be separated. These sanidin ecrys- tals possess remarkably distinct, well-defined crystalline faces, having a dull, smooth, compact surface, and resembling the orthoclases of some of the porphyritic granites or felsitic porphyries. Under the microscope, no augite or microscopical quartz could be detected. It discloses, however, some titanite and apatite prisms, while in the dark quartz grains are seen well-defined glass-inclusions, and the groundmass is made up of feldspathic particles. A thin section of one of the larger sanidins shows that it is made up of smaller crystals of sanidin, with a few striated plagioclases, and also contains some hexagonal and’ rhombic sections of quartz, but neither glass- nor fluid-inclusions. ' From the eastern spurs of Steves Ridge, toward the head of Little Snake River, was obtained a trachyte, almost identical with that from the summit of Whitehead Peak, in which olivine is present, with a considerable i, ELKHEAD MOUNTAINS. 171 development of bronze-colored mica. The large quartz grains and crystals of feldspar are somewhat less frequent than in the Whitehead rock. Crescent Peak is a high, sharp ridge, having a somewhat curved out- line, which is isolated from the main mass of the trachyte hills by the val- leys of Slater’s and Steves Forks. It is composed, however, of a trachyte, which is in every way analogous to the main body of Whitehead Peak and Steves Ridge. The rock of the peak itself has the same sherdy habit as that of Whitehead Peak. It consists of a light-gray groundmass, in which, to the naked eye, only crystals of sanidin, with occasional hornblendes and micas, and the peculiar rounded grains of cracked quartz, are visible. The microscope detects a few yellowish-brown augites, and around the quartz grains a peculiar greenish ring, made up of an interwoven mass of micro- lites. The quartz contains glass-inclusions, and the groundmass is made up of feldspar-microlites, with small prisms of augite and hornblende, and bio- tite plates in a brown, globulitic, amorphous base. ‘To the north of Cres- cent Peak is a curious dike, called Skelligs Ridge. It is a wall of semi- columnar trachyte, in which the columns are arranged horizontally, from 20 to 50 feet in width, rising vertically out of the soft grassy slopes to a height of from 50 to 100 feet, and extending in a northwest direction for several miles. Its walls, especially on the southwest side, are almost per- fectly perpendicular. The surface of this rock presents a peculiarly rough appearance, from the holes or cavities left by the weathering-out of the quartz grains. It resembles mineralogically the rock of Crescent Peak, but is more massive in habit, and is remarkable for the fine definition of its crystalline constituents, particularly the hornblende and mica. In this, as in all the other quartziferous trachytes, no more quartz can be detected by the microscope than by the naked eye. On the low saddle and ridge, which extends to the northeast from the base of Crescent Peak, is found a rock of rather a different habit. It has, in general, a rather homogeneous groundmass, in which no crystalline ingre- dients are visible, but which contains still these same curious grains of cracked quartz. This rock has often a shaly texture, and weathers with an earthy-brown surface, so that, at first glance, it might be mistaken for a sedimentary rock. The quartz grains are frequently colored brown, appar- 172 DESCRIPTIVE GEOLOGY. ently by a coating of ferruginous material, resulting from the decomposition of the surrounding rock-mass. To the naked eye, the groundmass has almost the appearance of a fine-grained sandstone, but is seen to be filled with minute dark crystals and flakes of mica. The microscope detects erystals of glassy sanidin, but neither hornblende nor olivine. Beneath the trachytic rocks, at the head of Steves Fork, was found a small out- crop of sedimentary rock, a compact, black, mdurated clay, containing fossil impressions. ‘The fossils could not be identified specifically, but were thought, when combined with the lithological character of the rock, to indi- cate the horizon of the Colorado Cretaceous, and the beds have been, there- fore, colored as such on the map. The microscope detects in this rock some grains of quartz and fragments of long, slender, transparent crystals, together with a few opaque grains of magnetite. Camel Peak, near the bend of the Little Snake River, is a remarkably sharp, wedge-shaped ridge, rising abruptly about 2,500 feet above the val- ley. It is composed of a light-gray, compact rock, somewhat resembling a basalt, but containing the same cracked grains of quartz which abound in the trachytes. These quartz grains often occur as little spheres, from the size of a pinhead upward, which stand out upon the fractured surfaces, covered with a greenish-white coating of decomposed material, and looking like amygdaloidal inclusions ina basalt. In the bluish-gray, homogeneous- looking groundmass, besides the quartz grains, only a few flakes of black mica and occasional hornblendes or augites are visible. The microscope detects the presence of small sanidins and much magnetite, with a preva- lence of augite over hornblende. This rock, therefore, forms, as it were, an intermediate step between the basalts and the trachytes, but from its asso- ciation it bas been classed with the latter group. From the broad bench- like spur of Steves Ridge, to the east of Camel Peak, were collected a number of different specimens, whose general habit resembles this rock, which have, therefore, been also included in the trachytes. One of the specimens collected from this ridge has been classed by Professor Zirkel as a basalt. It is a dark-blue, compact rock, containing the usual large grains of quartz, together with crystals of augite, and a few of, what are apparently olivines, in an almost homogeneous groundmass. A second specimen, ELKHEAD MOUNTAINS. 5 hr} from the same locality, a rock of somewhat similar appearance, shows, together with the great number of large glassy quartz grains, a few sani- din crystals and a large proportion of brown biotite plates scattered through the mass. Under the microscope, considerable augite is seen, but no hornblende or olivine. These spurs were so densely wooded that it was impossible to determine the relations of these different flows of volcanic rock, but the occurrence of a well-defined basalt on the northern spur of Hantz Peak would seem to indicate that this series of rocks marked a gradual transition from the more acid trachytic flows to this final basic outburst, along the contact-line of the volcanic flows with the Archzean body. The Hantz Peak basalt body occurs on a densely-wooded ridge, running out to the northeast from this peak, in which few rock-outcrops are visible. The rock itself is a dark-blue, compact mass, rich in olivine, in which a few scattered crystal of plagioclase-feldspar could be detected. In this basalt, the microscope detects the presence, besides olivine and plagioclase, of augite, biotite, and apatite, while that of nepheline, though not distinctly recognized, is confirmed by the general resemblance of this rock to the nepheline-basalts found to the west, particularly at Bastion Mountain. Hantz Peak is the highest and most prominent point in this region. Its summit is a very sharp cone, whose slopes to the south and east are extremely abrupt, falling off at an angle of nearly 40°. On the north shoulder of Hantz Peak, about 300 feet below the summit, is a remnant of sedimentary beds, consisting of horizontally-stratified sandstones, which have been much metamorphosed, and, in some cases, completely vitrified. Within these sandstones is a development of a fine-grained conglomerate, made up of small pebbles of black and greenish chert and jasper, which is quite identical with the characteristic and persistent conglomerate, which we find throughout this region at the base of the Dakota Cretaceous. . For this reason, and from the fact that to the east of Hantz Peak, in contact with the Archzean rocks, is a small development of Triassic sandstone, these quartzites or sandstones have been referred to the Dakota group of the Cretaceous. The trachyte which forms the main mass of Hantz Peak is a mauve- colored rock, which separates easily into sherd-like lamine. It shows 174 DESCRIPTIVE GEOLOGY. occasional grains of rounded quartz, with white, decomposed feldspars, and | considerable amounts of black mica and hornblende, in a grayish felsitic groundmass, and mineralogically belongs rather to the basic group of trachytes of Camel Peak. Singularly enough, however, the very summit of the peak is made up of a white porous rock, which has all the character- istics of a rhyolite, consisting mainly of grains of free quartz and crystals of sanidin-feldspar in a white, porous, felsitic groundmass. In it the micro- scope detects no plagioclase, hornblende, or biotite. Some of the quartz crystals of this rock are seen to contain very perfect dihexahedral fluid-inclu- sions containing a moving bubble. F luid-inclusions occur also in the feld- spars. As this is the only occurrence of a rhyolite found in this region, and its external habit is not essentially different from that of the trachytes around it, it has been considered merely a local deviation, and not designated by a special color. The prominence of this peak and its peculiar shape have rendered it a point of attraction for the summer thunder-storms, which collect in these hills from the open country to the west, and the loose rock, which forms its top, shows shallow trench-like gullies, radiating out from the cairn on the summit, made by the passage of the electric fluid. A sin- gular result of the action of lightning was observed in a tin can, which had been placed on the end of a pole at the very highest point of the peak by some of the early explorers. When found by us, this can, which had been thrown. to the ground, was found to be perforated with twenty or thirty holes, some as much as a quarter of an inch in diameter, whose rounded edges showed that the iron had been completely melted by the heat gen- erated by the passage of the electric fluid. At the eastern base of Hantz Peakis an open mountain-valley, faves a considerable extent of meadow-land, to the east of which, in contact with the Archzean rocks, was a small development of bright-red sandstones rest- ing directly on the Archzan schists and gneisses, which have been referred to the Triassic, though it was impossible to detect any outcrops of the overlying Jurassic limestones. The Little Snake River, which rises in the hills bordering ditee meadows, runs for a distance of about 15 miles in a northwesterly direction, ELKHEAD MOUNTAINS. 175 its bed marking approximately the line of contact between the volcanic and Archzan rocks. Below the meadows, it runs for a short distance in a deep rocky cafion, which opens out into a broad valley largely covered with recent detrital material. 'To the east of this valley rise the densely-wooded spurs of the Park Range. Its western slopes are covered by the gently- inclined trachyte flows of Steves Ridge. In the deeper cuts, made by streams flowing from this ridge, are disclosed a few indistinct outcrops of fine-grained, gray, calcareous sandstones, containing minute black grains like magnetite, which are evidently of Cretaceous age, but afford no clue to the horizon they occupy in that formation. Some remnants are also found of a light-gray trachytic tuff, enclosing fragments both of trachyte and of Archzean gneiss. Toward the northern end of Steves Ridge, a red, striped hornbleridic gneiss, which has already been described, is found directly underlying the benches of the more basic trachytes already mentioned. The same red gneiss, enclosed in beds of dark-green hornblendic gneiss, is found exposed at the north base of Camel Peak, just below the bend of the river. It here forms a little rocky knoll overhanging the south bank of the stream, and to the north passes under the horizontal beds of soft sandy and clayey material, forming the plateau country to the north. Its strike is here north 30° west, with a dip of 45° to the southwest. found the following ele of the “ONE TY group: Dikellocephalus Wahsatchensis. Dikellocephalus gothicus. Crepicephalus (Loganellus) quadrans. Lingulepis Ella. 406 DESCRIPTIVE GEOLOGY. It is impossible to obtain here an accurate estimate of the thickness of these lower limestones, but in the continuation of the range to the north, beyond the limits of the map, and in the uplift to the east of Cache Valley, they are found with a thickness of nearly 2,000 feet, showing a very con- siderable increase in the amount of deposition over the beds of the same horizon observed in the southern part of the range. 7 To the north of Box Elder Peak, the beds slope gently to the north- ward, until, at the northern point, the ridge is completely occupied by the Wahsatch limestone, which passes under a deposit of Pliocene Tertiaries which have filled Cache Valley, and extended over the low pass at the “Gates” of Bear River into Salt Lake Valley. These Tertiaries consist here mostly of grayish-white limestones and sandstones, partly fine-grained and compact, and partly coarse and porous. Some of the beds are more or less odlitic, and some again are almost completely made up of aggregations of fresh-water shells of Pliocene and recent species. They are generally much obscured by the Quaternary gravels of the terraces, but, where sections can be obtained, are shown to have had a thickness of at least 350 feet. At the northern end of the range, where the narrow-gauge railroad crosses into Cache Valley, they are found to have been considerably uplifted, showing angles of dip of 10° and 15°. An appearance of volcanic rock in the cation of Bear River, at the “‘Gates”, which, however, was not examined closely enough to determine definitely its character, suggests the possibility that ‘this uplift may have been determined by a late volcanic outburst. Eastern Urrirr.—Cache Valley occupies a broad synclinal fold in the Wahsatch limestone, which, on the west, forms the flanks of the main range, while to the eastward, with a slight secondary roll, it occupies the broad mass of hills between this valley and Bear River Plateau, in the interior of which the lower formations gradually rise up from beneath it. In Logan Caiion, for a few miles above the entrance, the beds of the Wahsatch lime- stone dip to the eastward. This dip, which is 35° at the mouth, rapidly decreases as one ascends the cafion, and opposite Logan Peak the beds are virtually horizontal, then rising again with a dip of 20° to the westward. The lower beds, as exposed at the mouth of the cafion, are generally of dark, rather siliceous, thinly-bedded limestones. About 1,500 feet above BASTERN UPLIFT. 407 the lowest beds exposed were found the following fossils, which correspond closely with those obtained from Ogden Cation: Chonetes Loganensis. Lthynchonella pustulosa. Euomphalus latus var. laxus. Spirifer alba-pinensis. Spirifer centronatus. Proétus peroccidens. Proétus Loganensis. At the forks of the camion, the beds rise more steeply, and a quartzite belt is seen which may correspond to the Ogden Quartzite. In the north fork of the cation, fragments of granite indicate the probable existence of a granite core to this ridge beyond the limits of the map to the north. While numerous small streams and cafions are found along the face of the range toward Cache Valley, only two large streams to the south of Lo- gan Cajion, Blacksmith’s Fork and Muddy Creek, cut entirely through the ridge, coming from the still higher country of the Bear River Plateau. A short distance to the south of Logan Caiion the beds are found dipping into the range at an angle of 20°. Still farther south, back of the town of Providence, they seem to have a still lower dip. Ascending to the summit of Logan Peak from the valley, in crossing the eastern dips, the strata are seen to shallow out until they become perfectly horizontal; while on the summit the beds dip 12° to the westward. The strata thus crossed are dark bluish-gray limestones, with many interstratified beds of calcareous grits, cherts, and highly siliceous limestones, together with beds of dark compact quartzite, always carrying some calcareous material. Occasionally, there occur narrow beds of argillaceous sandstone. Near the summit of the peak, ina dark-gray limestone, is a stratum of yellowish fine-grained sandstone, which appears to be nearly free from any calcareous matter. Fragments of corals too poor for specific determination were found on the slopes of the ridge associated with a small Productus. From the summit of Logan Peak were obtained at least two species of corals, Zaphrentis Stansburyi, and Lithostrotion too poor for identification. To the eastward of Logan’s Peak the beds all appear to possess a decidedly westward dip. 408 DESCRIPTIVE GEOLOGY. The cafion of Blacksmith’s Fork breaks through the range some seven or eight miles south of Logan Cafion. From where the stream leaves the mountains to the Bear Lake road, on the Cambrian Plateau, the cation measures about twelve miles in length. It affords some of the most bean- tiful cafion scenery to be found within the limits of this survey. Other gorges and passes possess doubtless more grandeur, and are built up of larger proportions, but few combine grandeur, picturesqueness, and variety of outline to the same extent as Blacksmith’s Fork. In width, the cafion is exceedingly narrow, with abrupt, precipitous walls rising from 2,000 to 3,000 feet in heavy masses above the stream-bed. At its entrance, the beds of Wahsatch limestone are found dipping to the eastward. They gradually become horizontal, and then assume a westerly dip, forming a continuation of the synclinal fold seen to the north. The westerly-dipping beds seldom reach a high angle, inclining rarely more than 12° to 14°. The limestone is a dark bluish-gray rock, compact in texture, with occasional beds more granular and of lighter color. The bedding-planes are distinctly marked, and the thickness of single beds sometimes reaches 20 or 30 feet. As the upper beds are never seen, it is impossible to estimate the entire thickness of limestone at this point: probably not less than 5,000 feet are exposed. The only fossils observed were a few indistinct impressions of coralline stems protruding from the surface on the walls of weathered limestone. Beyond the Wahsatch limestone occur the beds referred to the Ogden Quartzite and the cherty, siliceous strata of the Silurian or Ute lime- stone. Some eight miles above the entrance of the canon, the Cambrian quartzites come in with a gentle dip to the westward, gradually flattening out to a horizontal position. Between Blacksmith’s Fork and the canon of the Muddy, a distance of six to eight miles, the limestones lie nearly hori- zontally, the easterly-dipping beds occupying less and less area, and the little synclinal roll gradually dying out under the valley. Muppy CaNon.—In its general features, the Muddy Canon presents much the same character as Blacksmith’s Fork, the dark heavy beds of bluish-gray limestone of the Wahsatch group forming the abrupt caton- walls at its entrance. Here the beds are inclined at a low angle to MUDDY CANON. 409 the westward, the minor fold along the foot-hills, as already mentioned, having disappeared. The dip gradually becomes steeper in ascending the cation, reaching a maximum of 30°, and a thickness of nearly 6,000 feet ‘is exposed in the Wahsatch limestones. Near the entrance to the cafion, the beds are more or less siliceous andimpure, and at one locality occurs a thin stratum of compact bluish sandstone, containing but little calcareous matter. A thin section of this rock under the microscope reveals, in the interstices between the rounded grains of quartz, minute crystals and frag- ments of calcite. But few fossils were found along the section exposed in this cafion, and are mostly confined to fragments of corals, among which were recognized Zaphrentis and Syringopora. Underlying the Wahsatch limestone occurs a considerable thickness of quartzose beds, associated with some calcareous matter, which, from their position in the series, have been referred to the Ogden Quartzite. These trend across the cafion with a strike of about north 10° to 15° west and a dip of 20° to 25° to the westward, their lowest beds resting upon the western base of Ute Peak. Immediately underlying the Ogden Quartzite occurs the Ute limestone, which includes here the entire series of calcareous and cherty beds exposed on the abrupt walls of Ute Peak, which has furnished.the name for this great thickness of Silurian rocks, so characteristic of the lower portion of the Palaeozoic section as developed in several widely-separated regions of the Wahsatch Range. Ute Peak is situated between seven and eightmiles above the entrance to the caiion, on its south side, just below the junction of the two forks; its steep slopes forming the southern wall of the main cafon and ‘that of the south fork. It rises from 2,200 to 2,400 feet from the level of the stream, presenting, on its eastern side, a precipitous face, while to the west its slopes fall away gently, more nearly in accord with the inclination of the strata. The summit forms a broad, slightly-inclined table, the cul- minating point being but little higher than the long ridge that rises above the south fork. The beds of the Ute limestone cross the canon with an observed strike of north 15° to 20° east and a westerly dip of 15° to 18°. In the cafion-bottom of the south fork, the stream-bed has cut through the argillaceous slates and shales of the Cambrian series, which extend up the lower slopes of the peak from 50 to 50 feet, and are directly and conforma- 410 DESCRIPTIVE GEOLOGY. bly overlaid by the beds of the Ute limestone. The line of junction at the top of the series, to the west of Ute Peak, between the Ogden Quartzite and the Silurian limestone, has not been well determined; but, as the entire western face of the mountain comes within the limits of the formation, it is evident that there are exposed here a thickness of not less than 2,000 feet of Silurian beds, which, from paleontological evidence, have been referred without hesitation to the Quebec group of Canada. As, however, the beds containing Quebec fossils are still overlaid by a considerable thickness of calcareous strata, the Ute limestone may yet be found to contain beds be- longing to the Upper Silurian formations. Within the 2,000 feet of exposed strata of Ute Peak, there is presented avery great variety of lithological characters, dark, nearly black, compact limestones, coarse granular, lighter- colored beds, carrying greater or less thicknesses of calcareous and argilla- ceous shales, sandstones, cherts, and grits, in color varying from black to gray- ish-white, with intermediate shades of blue. Occasionally, some of the — finer-grained homogeneous beds develop a striped and banded mode of weathering. In general, it may be said that the beds are characterized by less uniformity of texture and color, while the arenaceous and cherty beds predominate over the purer limestones to a greater extent than is the case in the Wahsatch limestone. . Within 25 feet of the base of the series occurs a body of calcareous shales, interstratified with narrow beds of a dark, fine-grained limestone, — which is filled with abundant remains of Entomostracea, containing new species of at least two genera: Dikellocephalus quadriceps. Conocephalites subcoronatus. ‘Two hundred feet above these beds, in a compact cherty black lime- stone, on the north side of the peak, was found an undetermined species of the genus Obolella. From the upper bluffs, some 200 feet below the summit of the ridge, in a coarse, gray, granular limestone, were found: Euomphalus (Raphistoma) rotuliformis. Euomphalus (Raphistoma) trochiscus. Maclurea minima. a MUDDY CANON. 411 From the summit of the ridge, in addition to the Gasteropoda already enumerated, were obtained the following : Ophileta complanata. Liaphistoma acuta. Prof. F. B. Meek says, in his Report, referring to the genus Ophileta : “One of these is a small Ophileta, scarcely distinguishable from O. complanata of Vanuxem, as described from the Calciferous sand rock of New York”; and of the others, that they are “nearly allied to forms found in beds of the age of the Calciferous period in Minnesota, Wisconsin, and Texas”. A specimen of the grayish-black, cherty limestone from the base of Ute Peak was selected for chemical analysis. It is a compact, homogeneous rock, with a few grains of brilliant calcite scattered through it. The anal- ysis was made by Mr. B. E. Brewster with the following result : Imsoluiblemesidue 24.05 fai. se 8 oe oe ats eee 16.567 Slee SiG) 2 sos See ns ee eee 0.164 Herrichoxide amdsahumilass sae. se) ) ees ee 0.601 ALS ira era Rear orth en et ie NS ee Gn a LS 43.231 MIRGINESIS SAE 8 Yee BSE ae Se eee eee rr 2.180 JE1T@ RYO) NOLEN: CIOL EES aah oc ee eae pe Onlaks WaMomichaclde yer ey ames ic = 36.200 Water andtorvanie matters =). 22... 2. - ++ 5- 1.169 100.230 The carbonic acid, with the bases lime and magnesia, would yield: Woarnonatenorm imemayy. oe esse ee 76.82 Carbonate Ob magnesia. 25-4: 505.5 +25. 52--- -- 4.58 81.40 . _ The insoluble residue gave upon analysis: | Rillita ce: sovgeal 1 oe Say ee 13.447 ANNOOMMDE) oss oc esedhae Leake eee ee 3.120 . 16.567 These analyses show that the rock is a dolomitic limestone, rich in silica A12 DESCRIPTIVE GEOLOGY. The .12 per cent. of phosphoric acid present would seem to be derived from shells of the genus Obolella and other minute forms. The sandstones in the Ute Peak beds occur mostly in thin layers, usually granular, and carrying a considerable percentage of lime, and are found throughout the entire series, while the shales and slates appear, for the most part, to be confined to the lower horizons. As already mentioned, the argillaceous and arenaceous slates, which have been referred to the upper members of the Cambrian, occupy the cafiion-bottom. They are estimated at about 100 feet in thickness, and consist of exceedingly fine indurated clay-beds, inter- laminated with layers of sand material of a brown earthy color, closely resembling the beds from the same horizon in Ogden Cation. On the north side of the Muddy, no lateral cafion has cut through the slates, and there are found the Ute limestone and Cambrian quartzite forming a high cafion- wall, exposing a fine unbroken section, dipping about 16° to the westward. The two forks of Muddy Canon offer a striking difference in structural features; the cafion of the south fork trending approximately with the strike of the rocks, and presenting on one side the high wall of the Ute limestone and on the other the Cambrian quartzite, the intermediate slates being almost entirely eroded off the steep slope. On the other hand, the north fork, running at-right angles to the quartzite, cuts through 1,600 feet of the Cambrian rocks, forming a narrow impassable gorge, with pre- cipitous and almost perpendicular walls. CamBrian PratEau.—The large area of quartzite which underlies the Silurian limestone, and has been referred to the Cambrian series, occupies a very large superficial area. It extends from the northern limit of the map across Logan, Blacksmith’s, and Muddy Camnions, and as far south as Ogden River, occupying a belt of country from 6 to 8 miles in width. It forms a broad anticlinal fold, whose western side dips under the Ute limestone in the region of Logan and Blacksmith’s Cafions, with a low angle, increasing, however, toward the Muddy, where it reaches an inclination of 16°. The Bear Lake road, as shown on the map, appears to lie along the axis of the anticlinal fold, and here the quartzites are found quite horizontal, or else dipping under the influence of the eastern side of the fold 2° or 3° to the eastward. The eastern side of the fold is by no means as steep as the CAMBRIAN PLATEAU. 413 western, and the overlying limestones are found resting conformably upon the quartzites at the same angle of 2° and 3°. In the region of Blacksmith’s Fork, the beds lie horizontally in isolated hills, rising several hundred feet above the plateau level. An interesting feature in the scenery of the quartzite summit is formed by the picturesque falls and rapids found on the northern branch of Blacksmith’s Fork before it enters the main canton. There are several of these falls, the finest of which is about 30 feet in height, whose waters break over a ledge of quartzite, which is inclined 2° or 3° to the eastward, against the course of the stream, while rapids occur along the river between the more abrupt falls. The stream varies very considerably in width, running in narrow channels, and, in part, forming small lakes or ponds, surrounded by green meadows. _ The strike of the quartzite beds is approximately north 10° to 15° east. A thickness of from 1,500 to 1,600 feet is probably exposed beneath the Ute limestone, but the base is never reached. In lithological habit, these rocks present a close resemblance to the Cambrian quartzites, as seen in Ogden Canon and other localities throughout the Wahsatch Range. The different beds vary somewhat in texture, but are mostly fine-grained, of a steel-gray color and slightly vitreous lustre where not concealed by the discoloration of ferruginous material. The presence of iron in consider- able amounts would appear to be highly characteristic of the Cambrian formation. It occurs disseminated through the rock in thin seams or cracks, and in small coneretionary masses, usually, however, decomposed into yel- low ochreous earth. In the stream-beds of the north fork of the Muddy, and on the lower slopes of the ridges, were found fragments and rounded pebbles of specular iron; also, in the Cambrian quartzite on Mill Creek, which runs to Morgan Valley, similar fragments were found. It is not improbable that future explorations may discover iron masses of consider- able economic importance. — ; ‘In several localities in the Cambrian quartzite, but more especially in the region of Muddy Cation, there were observed certain peculiar markings and groovings, suggesting imperfect borings and tracks of worms, such as usually have been described as worm-burrowings of the genus Scolithus. _ They do not appear to be abundant, but where noticed were generally in a 414 DESCRIPTIVE GEOLOGY. vertical position, that is, at right angles to the bedding-planes of the rock. . On the Cambrian plateau, south of the Blacksmith’s Fork, extending to the divide between the Muddy and Beaver Creek, occur isolated patches of Tertiary sandstone. The largest body is some 4 or 5 miles in length, lying between two branches of the Blacksmith’s Fork, and rising about 500 feet above the level of the quartzite. Other smaller beds are found along the western base of the Bear River Plateau, which conceal the line of junc- tion between the quartzite and the overlying limestone, forming frequently low hills or mounds, and stretching up the slope of the ridge for 200 or 300 feet. The same formation may be traced in small remnants over a consid- erable part of the plateau, within the designated area, although to the north of Blacksmith’s Fork it was not recognized. These Tertiary beds have been referred to the Vermillion Creek series, partly from their close lithological resemblance, and partly from their apparent relation with the Tertiary series of the Bear River Plateau, although it is proper to state that no direct con- nection between these two formations was traced, and they may possibly be of later age. They generally consist of a coarse, sandy rock of loose, friable texture, colored bright red from the presence of a considerable amount of oxide of iron. ‘ The easterly-dipping beds of the Cambrian pass under the Bear River Plateau, and are concealed beneath the overlying beds of lime- stone. The arenaceous and argillaceous slates, which are so well shown on the western side of the axis in Muddy Canton, were nowhere observed on the eastern fold; the line of contact between the Cambrian and Silurian being very much obscured by remnants of Tertiary beds, and considerable accumulations of Quaternary detrital material, brought down from the pla- teau above. Bear River Plateau extends for nearly 25 miles in an unbroken line from the northern limit of the map, rising 2,000 to 2,500 feet above the Cambrian summit. All along its western face, there is exhibited an abrupt precipitous wall, cut by a few deep cafions, whose streams are branches of Blacksmith’s and the Muddy Fork. These canons, or rather gorges, are very narrow, and cut.deeply into the limestone down to the underlying CAMBRIAN PLATEAU. 415 Cambrian rocks. The most striking are perhaps those of the Blacksmith’s Fork, which present perpendicular walls nearly 2,000 feet in height, offering fine sections of the limestone. From all the structural observations made in the field, there can be scarcely any doubt but that this great limestone belt represents the Ute formation, already described as resting conformably upon the Cambrian rocks of the west side of the fold, and which here forms the eastern side of a broad anticlinal axis, the strata being inclined at an angle of only 2° or 3° to the eastward. On the summit of the plateau, this limestone is mostly concealed beneath the Tertiary sandstones of the Ver- million Creek beds, or loose, sandy Quaternary soil, and is only exposed here and there in a few isolated localities. No fossils were found in place along the edge of the cliffs, or in the cations, although it may be stated that only a cursory search was made, while a more careful examination may show the beds to be as rich in invertebrate remains as the formation on the opposite side of the fold. The thickness of this limestone is estimated as at least 2,000 feet. . Beaver Cafion lies entirely within the Cambrian quartzites. A variety of quartzite exposed here is of some special interest, as it differs from any beds observed in the region of the Muddy and Blacksmith’s Canons, but at the same time shows a close lithological resemblance with beds seen at other localities in the Wahsatch Range. It is characterized by purplish-gray color, vitreous lustre, and a tough, dense texture. The individual grains of quartz have a dark, smoky appearance, while the interstices between the grains are filled with crypto-crystalline, almost amorphous, quartz. Many of the beds develop a tendency to a schistose structure, containing interlaminated seams of thin, partially-foliated quartz, between layers of ‘coarser material. Under the microscope may be recognized a few minute plates of mica, while the quartz grains reveal large numbers of liquid-inclusions with mobile bub- bles. These purplish-gray rocks, by the absence of iron, present a marked difference from the white and brown quartzites of the Cambrian series. The reeorded dips in the cafion are all to the eastward. Some 2 or 3 miles : from the head of Beaver Canon occurs a large deposit of calcareous tufa, formed by an old thermal spring, which has now nearly ceased running. 416 DESCRIPTIVE GEOLOGY. The tufa is a compact, cream-colored rock, inclosing some minute shells and incrustations of stems and twigs. On the south fork of Ogden River, just above the junction of Beaver Creek, heavy beds of nearly horizontal dark limestones occur, which there form the abrupt cafion-walls, until concealed beneath the Vermillion Creek beds. No fossils were found in the limestones, but, from their.relative posi- tion, they have been referred, on stratigraphical grounds, with but little hesi- tation, to the Ute limestone. From the junction of Beaver Creek with Ogden River to the mouth of the upper cafion in Ogden Valley, the exposures are mostly in white or reddish-brown quartzites, whose walls rise between 1,000 and 1,500 feet above the stream-bed. The same purplish- -pray beds which form so prominent a feature in Beaver Canon occur here aks striking diago- nally across the cafion. The foot-hills along the east side of Ogden Valley, between the Upper Ogden Cafion and the base of Eyrie Peak, were not visited, but they pre- sent, from the valley, long, steep ridges, frequently broken by deep, narrow cafions, extending far back into the interior of the range. In crossing .the divide, between Ogden and Cache Valleys, quartzite beds are passed over for the greater part of the distance, which, on the summit of the pass, attain an altitude of about 1,000 feet above the Tertiaries of Ogden Valley. Eyrie Peak, which lies to the eastward of the pass, rises still higher, nearly 3,500 feet, commanding a broad view in all directions. It is composed entirely of quartzite from base to summit, whose beds dip appar- ently to the northeast at an angle of 18° to 25°, with a strike of north 30° west. The top of the peak is composed of dark brownish-white beds, car- rying considerable iron disseminated through them, and concentrated into thin seams or layers. Near the bottom of the series, the beds possess a decidedly bluish tinge, showing a marked resemblance to the purple beds of Beaver Cazion, with occasional layers of conglomerate made up of coarse — sand, carrying smooth, round pebbles. Throughout the series are frequently found intercalated seams of dark shales and fine sand beds. This entire series of beds has been referred provisionally to the Cambrian quartzites- partly on structural grounds, and in part from strong, well-marked petro, INTERIOR VALLEYS. A417 graphical resemblance, though their connection with well-defined Cambrian strata has not been clearly traced out. Inrerior VatLeys.—Of the great mountain-valleys which lie between the two crests of the northern portion of the Wahsatch Range, Cache Valley is the largest and most important. It occupies the great synclinal fold in the Wahsatch limestone already mentioned, and is overlaid by horizontal Tertiary beds of Pliocene age. They have been referred to the Humboldt Pliocene formation, inasmuch as they are probably of the same age as the beds which characterize such wide areas in the region of the Humboldt Valley in Nevada. They cover the greater portion of the southern end of the valley, except the broad fluviatile bottoms of the larger streams, and rest unconformably against the inclined strata of the Wahsatch limestone - on all sides of the valley. The drainage-channels on the west side and to the south, in the region of Saw Mill Caiion, cut through the Tertiary, offer- ing good exposures of a thickness at least of 350 feet of sandstones and limestones. The upper beds are friable sandstone, which wéathers readily. _A specimen subjected to chemical analysis yielded 94.44 per cent. of silica, the residue being chiefly iron and alumina, with considerable moisture. Below the red sandstones are found a series of fine-grained white and lavender-colored sands, interstratified with layers of calcareous sandstones. Near Wellsville occurs a body of soft compact sandstone, which is used as a building-stone by the inhabitants of the valley, as it is easily quarried and cut without difficulty. Other quarries have also been opened; and, from one near Mendon, a light porous rock was obtained, also much used in building. The beds of Mendon yielded a number of fresh-water shells, among which the genera Helix and Limnea are well represented. Prof. I’. B. Meek has described in his report a new species of the latter genus, found at Mendon, as Limnea King. In many localities, the Tertiary beds, especially among the steeper western foot-hills, are concealed by deposits of sand and coarse gravel, which belong to the Quaternary period. The terraced benches, which are so marked a feature on the western face of the Wahsatch, are also found along the foot-hills on both sides of Cache Valley, although not so broad as those observed in Salt Lake Valley. The entire southern portion of the former valley shows unmistakable signs 27DG 418 DESCRIPTIVE GEOLORY. of occupation by the waters of the ancient Lake Bonneville, which pene- trated Cache Valley by the “Gates” at its northern end, just beyond the limits of the OOO) 8 Copenhagen Valley, so named from a little Danish settlement of that name, which lies at the head of Box Elder Camion, has an elevation of about 5,000 feet above the sea-level, and 750 feet above the present level of Salt Lake. It was, therefore, covered by the waters of the ancient lake, although the terrace-lines are less conspicuous than in either Cache or Ogden Val- leys. A large portion of its area is covered with recent Quaternary deposits of very unequal thickness, with exposures showing clearly the fine white sands and conglomerates of the Tertiary beds, which have been, like those of the other lake-valleys of the Northern Wahsatch, referred to the Hum- boldt Pliocene. Ogden Valley, in its general features, is not unlike Cache Valley. It is, however, much smaller, measuring about five miles in width by six in length. The surface of the valley appears to have a much layger deposit of coarse Quaternary material than is found in Cache Valley, which may in part be owing to the quartzite slopes on the surround- ing mountains, which have sent down an immense amount of rubble and fragmentary débris covering the surface of the ground, so as to render it for the most part unavailable for agricultural purposes. Beneath these Quaternary deposits, however, especially on the north and east sides, may be seen, underlying the sandstones and limestones, fine conglomerates, which bear a marked resemblance to the beds of Cache Valley, though it is necessary to bear in mind that, owing to the close proximity of these beds to the high mountain-ranges, they have in each case a somewhat local character. These beds also have been referred to the Humboldt Pliocene, although it should be stated that they are too far removed from any well- defined Humboldt formations to trace any direct connection, and paleeonto- logical evidence is yet too meagre to throw any important light on the question. The lake-terraces can here also be traced with more or less dis- tinctness. The divide between Ogden and Morgan Valleys reaches an altitude of about 900 feet above the Weber River, measuring some 7 miles from valley to valley, with a width between the two high mountain- INTERIOR VALLEYS. 419 ridges on either side of 4 miles. In crossing from Huntsville to Mountain Green, but few outcrops are visible along the road, the hills being round and smooth, and covered with soil and vegetation. The rocks are chiefly sandstone, showing considerable variety in color and texture. The upper beds are in general more friable, possessing a reddish tint, many of them being fine conglomerates. The lower beds, though varying in physical habit, are much more compact, presenting under the hammer a decided | tendency to conchoidal fracture, and similar'to quartzose rocks which have a finely crystalline or amorphous base. Under the microscope, thin sec- tions reveal the presence of fragments of triclinic feldspar, hornblende, and mica, and a few dark grains, which are probably magnetite. Many of the beds resemble in lithological habit the compact gray sandstones, which are so characteristic of the Cretaceous rocks in the region of the Wahsatch. The entire series of beds, however, the upper members of which also occur in Morgan Valley, have been referred to the Vermillion Creek formation. 420 ; DESCRIPTIVE GEOLOGY. SECTION V. REGION NORTH OF SALT LAKE. BY ARNOLD HAGUE. — Promontory Upuirt.—To the west of the northern portion of the Wah- satch Range lies a broad Quaternary plain, in part occupied by the shallow waters of an arm of Salt Lake, known as Bear River Bay, and in part by the valley of the Bear and Malade Rivers. Along the shores of the bay, and in the deeper cuts of these rivers, are exposed the fine mud deposits of the Lower Quaternary, which, over the greater part of the surface, are concealed _by the more recent detrital material of the Upper Quaternary. Beyond the limits of the map, the valley of the Malade extends in a northerly direction, while Bear River, as already mentioned, has broken through the range at the ‘‘Gates”, coming from the region north of Cache Valley, in a general southwesterly course, after having flowed from the Uinta Range» _ through the Upper Bear River Valley, about 150 miles nearly due north. On the west side of the Malade River Valley, along the northern limits of the map, low rounded hills of limestone rise up above the Quaternary beds, presenting a broken undulating surface, and extending westward to the valley of Blue Creek. These limestone hills or ridges show a number of synclinal and anticlinal folds, with gentle dips, which can be traced from the Promontory Mountains nearly to Bear River. The first ridge to the eastward of Blue Creek has an inclination to the east, while the second ridge dips westward, forming a synclinal, followed by a second anticlinal fold to the eastward, the beds dipping under the valley, while in the small isolated hill to the west of Corinne, known as Little Mountain, the beds dip to the north at an angle of 18°. The northern end of these hills was not visited by our parties; but there would seem to be little doubt that they belong to the same horizon as the more southern hills, which have been referred to the Wahsatch limestone, from their close structural and litho- logical relations to the heavy limestone-beds of the Promontory Mountains. This range extends from the northern limit of the map about 45 miles to the southward, forming a rocky promontory, which divides the two northern PROMONTORY MOUNTAINS. 421 arms of Salt Lake, with a varying width from 4 to 7 miles, and reaching in its highest point 3,000 feet above the level of the lake. North of the railroad the range is comparatively low, with rounded outlines, the greater part of its sur- face being covered with loose soil and grass, and showing but few outcrops. _ The underlying formation, however, belongs to the Wahsatch limestone, and is evidently a continuation to the northward of the same beds which charac- _terize the more important portions of the range projecting into the lake. ' The railroad passes through a low depression in the range, which, on the summit, attains an altitude 4,943 feet above sea-level, or over 700 feet above the level of Salt Lake. The old Pliocene lake, at its highest elevation, unquestionably occupied this pass, isolating the main portion of the Prom- ontory Mountains, which formed an island of greater extent than either Stansbury or Antelope Island. This gap in the range, at its widest expanse, measures about three miles in a north and south direction, and everywhere shows the rounded forms and broad level benches produced by recent erosion and former occupation by the lake waters. On both the north and south sides of the gap, the upper ‘errace-lines of the old lake are quite marked, but perhaps less continuous than at other localities. All along the east and west sides of the Promontory Mountains, these old ter- races and beach-lines may be traced with more or less distinctness, indicated by loose deposits of sand and gravel, or by benches cut in the hard mass of limestone. The elevation of the highest of these terraces is approxi- mately 940 feet above the present level of the lake. To the south and west of the railroad, at Promontory Station, the range, which is quite nar- row, consists of a series of limestones, of a prevailing gray color, in the lower part of which are dark heavy beds of nearly black limestone, all dip- ping to the westward at an angle of 38°. About four miles south of Prom- ontory Station, the range widens rapidly to the westward, attaining a width _ of 6 to 7 miles, of which the western third is occupied by the same series - of limestones, which here rise with an easterly dip, and overlie a limited outcrop of Archzean schists. a ; These Archean rocks are exposed on the southwest corner of this pro- jection of the range, and consist of quartzites and mica-bearing schists, closely resembling those described in the Archzean bodies of the Wahsatch. The main crest to the east of this western projection is occupied by con- 422 DESCRIPTIVE GEOLOGY. formable strata dipping, as already mentioned, about 38° to the west. They are much contorted, and show more or less faulting, so that their thickness cannot be accurately determined. It is, however, not less than 3,800 feet. About the middle of the series, there is an included zone of yellowish- brown sandstone, more or less calcareous, within which are several beds of gray limestone. Its lower portion is sharply defined from the underlying — limestones; but, 300 feet above where it passes again into the limestones, it shades off gradually through shaly beds. The general strike of this por- tion of the range is north 28° east. Along the extreme eastern foot-hills, on the edge of the Lower Quater- nary plain, which borders the lake-shore, are outcrops of easterly-dipping beds, which evidently show a portion of the eastern half of an anticlinal fold, of which the main mass just spoken of is the western member. This anticlinal fold appears very distinctly in the group of hills about 8 miles south of Promontory Station, of which Benada Peak is the culminating point. Tere a distinct northern axis cuts the range, and south of that point the rocks dip to the eastward. Through the pass, about 14 miles north of Benada Peak, passes a synclinal axis quite parallel to the anticlinal, which lies 1 or 14 miles to the west of it. Here the easterly-dipping members of the western anticlinal and the westerly-dipping parts of the eastern, or second anticlinal, meet. The second anticlinal passes through Benada Peak itself, and, as has been said, to the south of that point, for about 12 miles down the range, the greater part of the limestones dip uniformly to the east, at angles varying from 20° to 40°. At Flat Rock Point, on the west side of the range, are found portions of the western members of this anticlinal fold, dipping at a gentle angle into the lake, and consisting, for the most part, of gray and drab limestones, among which are intercalated bands of yellowish- brown sandstone, similar to that described in the westerly-dipping mass south of Promontory Station. | From the westerly-dipping limestones, about 5 miles south of Promon- tory Station, near Antelope Springs, were obtained the following fossils: Productus Prattenianus, Spirvfer opimus, Athyris subtilita, Streptorhynchus (fragments) ; PROMONTORY MOUNTAINS. 423 while the limestones farther south afforded: Zaphrentis Stansburyi. Productus semireticulatus. These fossils are all clearly of Carboniferous age, though of themselves not distinctly characteristic, either of the Upper or Lower Coal-Measure limestones. The thickness of the series, and its relation to the underlying Archzeans, however, as well as its general lithological character, all serve to ally it rather to the latter division. mi About 14 miles south of Benada Peak, the Carboniferous limestones are found to abut unconformably upon a series of Archzean schists, which occupy the whole lower 7 or 8 miles of the range, with a strike north 30° to 35° west, and a dip to the northeast. The Archzean strata consist largely of siliceous schists and imperfectly-bedded hornblendic and micaceous gneisses, together with thick beds of quartzite and more or less interspersed argillaceous schists. Just west of the southernmost extremity of the range, the Archean rocks come nearly down to the water’s edge, presenting a cliff, some 50 feet in height, of dark argillaceous schist, which has apparently a dip of 25° to the west. Along the cracks and fissures, this rock appears to decompose readily, and is found to be coated with an efflorescent substance, which, when applied to the tongue, gives the characteristic astringent taste of alum. The fol- _ lowing analysis of this salt was made by Mr. R. W. Woodward: ANIUOTEIUTAL 3 2s cect le ie ae 11.26 IEGIBEIG CSAC 2.15 aS ee 0.35 Magnesia ..-.-- pie te allah 2h Meiet lor iyod omy 19.02 SOU ee mmr Gol Reheat 2.24 otassaie te Subs) 2 2 ek ey aed is ae PO ener Neh 0.28 Subohmmrctaetdes =. 52230 e224 Sh Dea Sey oer ae a 64.96 Ciiloninopee tee! Mach te eu Wan ha ae Behe 1.85 Orayreceite rane es FLT eS Lope Ch Rede st Sona cae Ue arth.» 0.04 100.00 The analysis of this alum gives no water of crystallization. 4294 DESCRIPTIVE GEOLOGY. Prof. J. Lawrence Smith has published an analysis of an alum from this locality,’ with the following results: AlumMaens Soe bos hos. 2 Lee eee eee 10.40 Meaonesiaa- 2.0.2 M0. Te. 1) eee 5.94 Manue@anese 200. se ee 2.12 Oxide of iron... --- Spice F Shot E ale foie Sc See ee ee 0.15 PGtassa 2 vce Cee ee ie a rae aN en 0.20 ° Water ...... RDM On Cr So et. 46.00 Sulphuric acid ‘>... Ge sess e se =e ee 35.85 100.66 In the last edition of his Mineralogy, Professor Dana has classed this alum under the name of Bosjemannite, a mangano-magnesium alum. The analysis made by Mr. Woodward, however, shows no manganese, but a very large percentage of magnesia, and contains all the impurities gathered with the alum at the locality, which appears to be more closely related to pickeringite, a magnesium alum mixed with some epsom salt, while the needle-shaped crystals, analyzed by Professor Smith, were not procured at Alum Bay, but were a product of recrystallization. Along the east side of the range, the cliffs in general come nearly to the water’s edge, and there occur a great number of alkaline and brack- — ish springs, which issue out of the limestone strata near the level of the lake. On the west side, the hills slope off more gently, and the lake- borders are occupied by a strip of Quaternary soil, which gradually widens toward the north. A few miles below Flat Rock Point is a fine spring of pure water. To the west of the railroad pass is a low north and south Quaternary valley, which is separated from the lake by a long low table-— land of black basalt, extending about 10 miles in a northwest direction, and abutting upon the lake, at its northern extremity, in an abrupt low preci- pice. A similar basalt table-land rises slightly out of the Quaternary plain, and forms the southern end of the Hansel Mountains, to the north of Mon- ument Station. 1Am. Jour. of Sci., 2d series, 18, 379. ARCHZAN ISLANDS. 495 _Istanps.—The Archean uplift of the Promontory Range is continued to the southwest in the rocky summits, which lie above the level of the lake, forming Frémont and Antelope Islands. A small outcrop of Archean gneisses is also found rising out of the mud plain at the Landing-rocks, to the west of Ogden, forming the extreme western point of the lake-shore line. Frémont’s Island is made up of beds of dark-green hornblendic and mica- ceous. gneisses, generally much contorted, in which the prevailing dip is about 40° to the west, but on the western shore presenting a bold escarpment toward the lake. The old terrace-lines are very distinctly marked, as upon most of the islands of the lake. Antelope or Church Island, as it is some- times called, is the largest of the rocky islands which dot the surface of Salt Lake, covering a superficial area of about 40 square miles. It has several fresh springs, and its slopes are covered with a good deal of grass, which have been used as common grazing-ground for the herds of sheep and cattle of the Mormon settlers. As seen from the shores of the lake near Farming- ton, in profile, the crest of the southern portion of the ridge is a perfectly horizontal line, evidently marking the level of one of the old lake-terraces. It is made up entirely of rocks of the Archzan series, mostly gneisses, with some quartzites and mica-slates. On the main peak is a thin stratum of not more than 20 feet of slates, which approach a limestone in composition These are the only calcareous beds that have been detected in the Archaean rocks of the Wahsatch Range. They stand in an almost vertical position, with a strike of north 45° west, and are enclosed on either side in gneissic rocks, which form the main ridge to the south with the same strike. An outlying spur to the west of the main ridge shows a secondary fold, whose axis has an easterly and westerly direction, the beds dipping over 7 0° to the south. Curtew VaiitEy.—To the west of the Promontory Mountains, the Rozel Hills and the southern end of the Hansel Mountains consist, as has . been seen, of low, flat tables of dark, compact basalt, forming part, doubt- less, of the same flow now separated by the Quaternary deposits of the valleys. 'To the west of the Hansel Mountains, the country north of the lake, as far as the Terrace Mountains, appears to be underlaid also by the basaltic formation, the southern extremity of the great outflow of basalt which covers an immense area to the north of the limits of the map. Much of the as here shown upon the map lies below the level of the upper 426 DESCRIPTIVE GHOLOGY. terrace-lines, and presents everywhere marked evidence of having been sub- merged within recent geological time. The greater part of this area is more or less concealed beneath loose sand and basaltic detrital material of the Upper Quaternary. Only here and there, the presence of the under- lying basalt is indicated by little hills and knolls which rise above the plain. North of the Terrace Mountains, the basalts reach a somewhat higher elevation, forming low, broad tables with isolated domes. Of these, Red Dome, just north of the railroad, is the most prominent, presenting a con- spicuous landmark in the region north of the lake. These basalts are char- acterized by a dense, fine-grained texture, but are occasionally quite porous, when they possess a reddish tinge, especially on the weathered surface, the color giving the name to the dome already mentioned. Wherever the slope of basalts was noted, it indicated a slight inclination to the southward, toward the desert. In a number of localities, at the head of the lake, salt springs occur on the desert, many of them quite cold and clear, all carrying con- siderable common salt in solution ; many of them, in fact, being dense brines. Between Red Dome and the Raft River Mountains lies an irregular mass of hills, which only in a few points attain an elevation of more than 1,000 feet above the desert-level. ‘The greater part of these hills are below the well-recognized level of the old lake, and, like the hills to the eastward, everywhere show evidences of the recent occupation of the country by the lake waters. They are made up of dark-gray limestone broken through and partly concealed by heavy outbursts of basalt. Nothing can be said definitely of the structure of the limestones of these hills, as they are much disturbed by the Tertiary volcanic rocks, or else concealed by the still later loose Quaternary gravel. No fossils were found which determined accurately the horizons of these limestones, but there can be little doubt that they belong to the upper members of the Wahsatch limestones, which characterize all the mountain-ranges north of the lake. On the west side of Duff Creek, basalts find their greatest development in broad, heavy, tabular masses, lying inclined at an angle of about 2° to the southeast, and presenting precipitous cliffs toward the creek. The rock is a compact black basalt, with a crypto-crystalline groundmass and uniform texture. On the basalt slopes west of Duff Creek, and on the south side facing the desert, the terrace-benches, which are so characteristic of the entire region, are TERRACE MOUNTAINS. 427 beautifully shown. Seven well-defined, sharply-cut benches, several feet wide, were counted, one above the other, on the sides of the hard rock. Probably no locality in the region of Salt Lake affords a better opportunity for observing the broader and more permanent lake-terraces which mark the changes of level of the earlier bodies of water. Terrace Mountarns.—In their physical aspect, the Terrace Mountains bear a marked resemblance to the other ranges of the Salt Lake Basin, especially to the Promontory Mountains on the opposite side of the lake. They measure about 20 miles in length by 4 to 6 in width, the culminating peak reaching 2,700 feet above the present water-level. Tangent Peak, the highest point in the mountains, affords on a clear day a most striking view of the arid gray desert and the blue lake stretching away to the southward and eastward as far as the eye canreach. The eastern horizon is bounded by a grand panoramic view, of over a hundred miles in length, of the Wahsatch Range, while to the westward the East Humboldt Range stands out in nearly equal distinctness, but witha more rugged and varied outline. The mass of these mountains, as far as visited, appears to be made up of beds of the _ Wahsatch limestone. The summit of Tangent Peak is occupied by a bluish- gray limestone, below which occurs a dark, siliceous, cherty band, in turn underlaid by dark-gray limestones. The recorded strike is north 16° east, with a gentle dip to the northwest. No fossils were found, except fragments of coral stems, too poor for identification. Just north of Tangent Peak, the spurs fall off somewhat abruptly, and a low saddle, with both east and west cafions, or valleys, separates the mountains into two distinct ridges. Both of these canons are marked by broad, shallow basins, with gentle slopes between the limestone ridges. In both valleys, there is a very con- siderable development of horizontal Tertiary beds, extending nearly to the summit of the divide, which have escaped erosion and concealment beneath the Quaternary deposits. These beds resemble the fine sands, reddish gravels, and marls which form the Humboldt Pliocene beds of Eastern Nevada, and have been referred to the same horizon. The terrace-lines, which form so characteristic a feature of the basin, are so prominent and well defined along the slopes and foot-hills as to have given the name to this range of mountains. They are remarkably well shown on the Tertiary strata, where seven broad, nearly level, benches may 428 DESCRIPTIVE GEOLOGY. be counted, beaches of the more constant shore-line, while several others, not so well preserved, have left more or less indication of the receding waters of the basin. Barometrical observations were made at our camp in the Ter- race Mountains, and from there careful instrumental determinations of the height of the upper beach-line. These observations were referred to our station-barometer at Matlin, and these again corrected by the railroad- levels as a base. This measurement agrees very closely with determina- tions made at Black Rock Point, where the position of the terrace was found, by a series of careful observations, to be 940 feet above the lake- level. South of the railroad, for 5 or 6 miles, the depressions of the Ter- race Mountains are in many places below the level of the old lake, the greater part of the range, like the Promontory, having stood as an island in the sea. In these low, narrow depressions, the action of the shallow water upon the shore is very clearly shown, with the beach-lines extending across the range from east to west. Considerable accumulations of Qua- ternary material skirt the base of the range, concealing the limestone slopes in many places for several hundred feet. It consists of beds of loose gravel and sand, and fine conglomerates, containing fragments of calcareous tufa, which also frequently serves as a cement, or binding material, for the con- glomerate. The two groups of hills which rise out of the desert to the southwest of the Terrace Mountains, known as the Rocky and Desert Hills, were not visited by our parties. They have, however, been referred pro- visionally to the Lower Coal-Measure formation, on grounds of general analogy with the structure of this region, which is supported by the meagre facts with regard to the rocks which compose them, which it has been pos- sible to obtain from those who have visited these almost inaccessible points. Rarr River Movntaiws.—In the southern end of the Raft River - Mountains, a very considerable body of granite forms the central mass of the range. It measures 10 or 12 miles in a north and south direction, and 6 to 8 miles in width at its broadest expanse, culminating in Cita- del Peak, a fine summit which rises nearly 2,500 feet above the level of the lake. On the south and west, it is covered by heavy beds of limestone, folding completely around its flanks, which have been referred to the Lower Coal-Measure formation; while on the east side it falls away gradually with easy slopes toward the valley of Clear Creek, until concealed by the a RAFT RIVER MOUNTAINS. | 429 recent Quaternary deposits. ‘The rock is a nearly structureless, medium- grained granite-mass, characterized by uniform texture and a pearl-gray color, and composed of the normal granitic constituents, quartz, feldspar, and mica. It decomposes readily; its surface being generally covered with detrital material, while the spurs and ridges everywhere present smooth, rounded outlines, with many fanciful forms of erosion. . _ The range to the north of the wagon-road was but cursorily examined. Next to the granite, to the north, are hard, compact, steel-gray slates, which pass into dark-bluish limestones, intercalated with cherty bands, in which no fossils were found. The main ridge to the north seems to be mainly com- posed of similar blue limestones, generally thinly bedded, witha large devel- opment of dark-colored argillaceous and calcareous shales, splitting into very thin laminze, having a north and south strike, and dipping to the eastward. A microscopical examination shows that the dark color of these slates is due to a mixture of opaque black particles, probably of carbonaceous material. A few fossiliferous beds were observed, from which were obtained an Avi- culopecten, whose species could not be determined. The western slopes of the range are covered high up on the flanks by heavy white beds, sloping gently toward the centre of the valley, composed of fine, white, pumiceous sands, loose sandstones, and fine conglomerates, which have been referred to the horizon of the Humboldt Pliocene, from. their general resemblance to these beds as developed in the valley of the Upper Humboldt. At the southernmost extremity of the mountains, and just below the _ granite body, occurs a somewhat isolated group of hills, which, in their geo- logical character, differ somewhat from the formation surrounding the granite to the west, but which have, nevertheless, been referred to the same horizon. _ Their structure is evidently somewhat complicated, and was not made out very clearly. The same dark, steel-gray slates are seen as in the pass, and would appear to be the underlying rock. Dark-brown quartzites carrying small amounts of carbonate of lime and dark bluish-gray limestones make up the series of the beds. These hills are traversed by dikes of fine-grained intrusive rocks, which, under the microscope, present an exceedingly fine erypto-crystalline base, filled with countless numbers of minute microlitic forms, fragments of triclinic feldspar, and a few grains of magnetite. Along the base of the higher ranges, and bordering the desert at irreg- 430 DESCRIPTIVE GEOLOGY. ular intervals, west of the Terrace Mountains, are small isolated buttes and knolls of Tertiary voleanic rock.” In exceptional instances, as at Desert Butte, they rise from 500 to 600 feet above the plain, but in general are small, low hills, mostly concealed by the Quaternary deposits. Several of the smaller outcrops occur along the south and southeast spurs of the Raft River Mountains, but occupy so small an area that they have not been des- ignated on the maps. So far as examined, they appear all to be rhyolites, with considerable variety in texture and aspect, but in general more allied to the compact, porcelain-like kinds than to the rough, porous types. The rhyolite of Desert Butte, which is situated near the wagon-road, some 5 miles to westward of the Raft River Mountains, may be considered as a typical variety. In its physical habit, it is a dense, compact rock, exhibit- ing to the naked eye almost a homogeneous groundmass, and breaking under the hammer with a sharp angular fracture. In color, the prevailing tint is a light reddish-gray, shading off into white or salmon. The rock would be very uniform in texture but for the occurrence of rough spheeru- litic bodies and the characteristic lithophyse. Narrow seams and lines of semi-transparent chalcedony traverse the rock in various directions. In a hand-specimen, the rhyolite somewhat resembles a quartz-porphyry, with small grains of brilliant white quartz and feldspar scattered through the groundmass; except that the minute feldspars have the characteristic lustre and habit of volcanic rocks. Under the microscope, the quartz-grains are seen to abound in glass-inclusions. Professor Zirkel has detected the presence of tridymite, occurring in hollows and cavities of the rock, and suggests that ‘it is a secondary product, as it is often seen overlying iron-ochre and earthy ferrite, which are themselves of later origin than the rhyolite. Well-marked terraces form a prominent and somewhat curious feature of the Desert Buttes. The broad terrace measures 6 to 8 feet in width, being nearly level, and about 125 feet below the summit. This same terrace may be traced with a pocket-level for a considerable distance along the shore of the northern bay of the old lake, extending up the valley, west of the Raft River Mount- ains. our distinct, plainly-marked terraces may be seen from this point, showing at favorable points level benches, 30 to 40 feet in width, cut in the solid rock, below which the slopes shelve off very abruptly. | : GREAT SALT LAKE. 431 SECTION VI. LAKE REGION. BY S. F. EMMONS. Great Sart Laxe.—The Great Salt Lake of Utah is a broad, shallow sheet of water, occupying the lowest portion of the Utah Basin, 80 miles in length in its greatest extension in a northwest and southeast direction, and about 32 miles wide at its greatest average lateral expansion. Its bottom is evidently even more level than the broad desert-valleys which surround it, since at its deepest points its waters do not reach a depth of 50 feet, while a very large proportion of its area, comprising broad belts along the shore- line and the partly-enclosed bays, have less than 10 feet of water. The line of deepest depression is that extending northwest from Black Rock Point, between Stansbury and Antelope Islands, and to the west of the Promontory Mountains. This valley averages about 40 feet in depth below the present surface of the lake, while in no other portion of the lake, except in the immediate vicinity of Frémont’s Island, are depressions of more than 20 feet found. It receives its supply of fresh water from four large streams, the Bear, Ogden, Weber, and Jordan Rivers, which, with a few minor mountain-streams from the western slopes, bring down the drainage of all the surface of the Wahsatch Range and the eastern portion of the Uinta Range, while a small but continuous supply of salt is furnished by the numerous springs which occur along its shores. | As it has no outlet, this great influx of fresh water would rapidly raise the level of the lake were it not for the enormous evaporation that takes place in this dry region, where the average difference in summer between the wet- and dry-bulb thermometers is from 20° to 30° (Fahren- heit). The level of the waters of the lake is, therefore, subject to changes depending on oscillations in climate and variations in the condensing power of the atmosphere from year to year. It might naturally be expected that there would also be some variation in the level of the lake at different sea- sons of the year, but it is probably slight, and no data have been obtained 432 DESCRIPTIVE GEOLOGY. with regard to it. Of the great climatic oscillations, traces are seen in the lake-terraces, which stretch along the flanks of the surrounding mountains, and show that at one period the waters of the lake were over 900 feet higher than at present. With regard to the changes in the height of the ~ water-line from year to year, which are dependent on the varying relation of atmospheric evaporation to condensation, it is impossible to obtain abso- lutely accurate data, since up to the year 1869 no fixed datum-point had been established by which this height could be determined. It is known, however, from information obtained from the Mormon settlers and others, with regard to the water-line on different shoal portions of the lake, that during the eight years preceding the date of our survey of the lake (1869), there had been a general rise of about 11 feet in the level of the waters of the lake. ‘The remarkable flatness of its immediate borders is well shown in the great increase of surface covered by the waters produced by this comparatively slight change of level. The superficial area of the lake, excluding the islands, as shown by this map, is 2,360 square miles, an increase of about 40 per cent., or 660 square miles, over that given by Stansbury’s map,' which is only 1,700 square miles. It is true that Stans- bury’s survey was made in 1849-50, or 11 years earlier than the time from which the rise of 11 feet is dated; but it is evident, from the depth of water found at given points along his shore-line, that the level of the surface in 1861 must have varied but little, if any, from that of 1849. One of the most striking peculiarities of this lake is the great density and pungent bitterness of its waters. This is practically shown by the fact _that the human body floats up entirely on the surface like a cork, and that the pain produced by water which enters the eye is almost blinding. It is generally stated by the Mormon settlers that during the early days of their” settlement they used to obtain one barrel of salt from three barrels of water. The water obtained by Stansbury in 1850 contained 22.4 per cent. of min- eral salts. In 1869, the solution had become much diluted by the addition of so great an amount of fresh water, and it contained, as will be seen, only 14.8 per cent. of solid matter. An analysis of several gallons of the water of Salt Lake, obtained by our parties in the summer of 1869 from near Black Rock Point, where the 1Stansbury’s Expedition to the Great Salt Lake, 1852. GREAT SALT LAKE. 433 influence of the fresh water from the tributary streams would not be felt, and made with the utmost care and thoroughness by Prof. O. D. Allen, of New Haven, gave the following results: One thousand (1,000) parts of water evaporated to dryness left a solid residuum of— aye I. IL Average. SARS Rts ee a 148.116 148.386 148.251 An analysis of this solid residuum gave: E 16 II. Average. Macmesiaws 222. - Bie 6.477 6.126 6.301 Himes ne May he Poe 8 0.369 Ont OBE Soman en te SFT Bika, 66.789 67.168 66.978 Potassar hoe aaah elt 2.949 2.854 ” 901 Sulphimdciaicid) eset 8.090 8.340 8.215 Cinlorimets ees ee oe. 84.053 83.839 83.946 3 } 168.698 Less oxygen of soda and magnesia -....--..- 18.758 149.940 Theoretically combining acids and bases, we have: CO lnlowileromsoaniiitees eee) e 2. S88 45 epee, a 118.628 OhlorMerotmaonesiume. - 42)... .. 22. sL2.+.26 6. 14.908 - Sulphatetofisodas 215.25.) - PATE al oth Sin Pe: Bes oe Goal DuulipbeiierOkipotassabss )2. 2.442 2). ee ee ee — -6.363- Suljonatevoiplmejerra1}-)4 $2... 222 Say. er Se ee ee 0.858 LBERUESP OL GINO eae ee ee ee 0.862 . 149.940 or, in 100 parts, maOhiomdctor sodium 20.5... 222.002 ve 79.11 Chloride of magnesium....--.---- pe See eres ee 9.95 Sullmiatenotmsoda, 200 5 Aa ge PS aa. 6.22 Sulphate of potassar- -=,--.-2--222: 5 Ube be ea Bs cesses 3.58 Srilphaterok mets: Sun hee eye a Sere SN 0.57 HW xGecstomehlonimel f2 42 wee sae tn see ee 2 0.57 100.00 28 DG 434 ; - DESCRIPTIVE GEOLOGY. A drop of the water, without concentration, gave spectra of potassa and lithia; a faint reaction for bromine and boracic acid was also obtained. In this connection, it is interesting to note an analysis of the surface- soil from a mud or alkali flat, not far from the lake-shores, between Salt Lake City and Black Rock Point. The material collected contained 16.40 per cent. of soluble matter, composed as follows: Callens 22.0) eee 6.16 6.28 Macnesium .o))0 1). eee eee eee Dee 2.16 Sodium — 4%. J. eee eee 29.62 29.45 Potassium: 20% 022 3 oe ee eee 6 OAG 0.46 Chilorines20 40% 3) eee pst Tae 57.97 57.83. Sulphuric acide 2S 2 eee eee aoe 3.44. Oxy genequiv.s Ose. 9s se eee 0.74 0.68 100.89 100.10 or, theoretically combined: Chloride: of sodium@e sees ase 71.43 71.05 Chioride‘of maemesium== == eae 8.80 8.55 Chloride of potassium. .-....--- a ERE 0.88 0.87 _ Chloride ohealcinm, 2s es552 =e 11.94 12.11 Sulphate of lime ....--..- Se ee 6.31 5.84. Excess. of Soci So aes eee BOP gale os 1.68 100.89 = 100.10 In composition, these salts show a remarkable analogy to those of the waters of Salt Lake, from which, at no very remote period, they must have proceeded. The relative proportions of chlorides of calcium and magnesium remain the same, but a portion of each has been replaced by the lime of the soil. It is noticeable that in this soil, as in that of the Great Desert, the alkaline chlorides are present in great abundance, but the alkaline sul- phates are wanting. It is interesting that in the waters of a lake containing so much mineral matter in solution, and which lies in a region of limestone rocks, so little lime should be found in solution as the above analysis shows. As the sulphates and carbonates of lime are, however, easily precipitated, it is probable that, in the solution presented by the waters of Salt Lake, they GREAT SALT LAKE. | 435 are unusually insoluble, and that those which are brought in by the trib- utary streams are almost immediately thrown down. That lime has been in solution in the waters is proved by the peculiar sands found on the beach at various points, notably at Black Rock Point and along the southern end of the Terrace Mountains. These sands are made up of little spherical grains of white, opaque carbonate of lime, up to one-tenth of an inch in diameter. An analysis made of them by Mr. R. W. Woodward gave the following results: Ferric oxide and alumina. . - - 2 be opnlelmae 0.25 0.29 JL AUTENS 5. cea dpe Sele le a BS ca) 51.44 MEISMNCSNG) 2 oie bee oe go oa ae ree 0.82 1.02 SOU Ma Wee Sp Se os foe Oar 0.73 IPOS ok cate hae 0.3 raw SU DINNING AVC Sr 0.52 OS Carlsomic acid eps. ye. be Be ee ek 40.74. 40.74 (CHOCHIING a8 ae a8 eels EG Oe trace trace WHS Abc eee LIGR A208 Insoluble residue........-.- aie ee 3.88 3.85 100.01 100.20 _ Under the microscope, they are seen to havea rudely concentric struct- ure, and may therefore be considered to be a concretion formed around some nucleus perhaps of organic origin, or perhaps some minute grain of siliceous sand. As has already been mentioned, similar deposits have been found in the Tertiary beds of the Green River Basin, compacted into a rock, and in some cases silicified. é The lake contains no fish, and was long supposed to be absolutely de- void of animal life, although the tributary streams abound in fresh-water fish, such as perch and trout, and the latter are even found in the Hot Spring Lake. Mr. Sereno Watson, of this Survey, has, however, discov- ered a minute crustacean which inhabits its waters, and which has been de- scribed by Prof. A. E. Verrill' as Artemia fertilis. The shores of the lake 1Am. Jour. of Sci., Nov., 1869. 436 DESCRIPTIVE GEOLOGY. are, moreover, covered in places, for a width of several inches, with the larvee and pupe of insects which live in its waters, among which have been described Ephydra gracilis, Packard. For the comparison of this great interior salt lake with those known in other parts of the world, the following table has been prepared, giving the analyses of the waters of some, whose physical conditions present points of resemblance with this, together with the composition of the water of the ocean, derived from a mean of nine analyses made of water taken from the Northern Atlantic and German Oceans, and one of the Mediterranean Sea: I 1a Til. IV. V oO : « - a cm 4} a} o Ct v Se a 4 4 a a. Ss 3 BS 3 Be Bie a8 FY ” Oke I Pe C= Pits) 4 ao a oO Os Es BS oO gs — oO ° n Q cas ® | ay ish ih) © » a) 8 nes Seu P=? 3 e Broil oe ee |e me b Oo Ss iC) a [2 D fo) a = P= Chloride of sodium. ...~.-.------.-000 wonnencnenno-- 11, 8628 6. 23 IQ. 05 12. 110 2. 6730 2. 9460 MAGNESIUM. ---.--.----2 see eee we eee ee 1. 4908 I. 03 0. 52 7. 822 ©. 3229 ©. 3223 HO) ASS UHH Ene eeo en Sca moc OFOmSo Os cOSSe0ss)|eseosnsacnnc|socossespsllcodaseasos I. 217 ©. 1290 0, 0505 CHOI le Sancsqaroecboonoos cootooonoSDoOsalasSmaa cad asa|lecobospanelasesoocons Bp Ales) \fanoemncooe sellomaccssoacssios aluminium. -\.. 2... - 9-0 one wen eee mone ee none e Paodecsnaa toceseross @ OHO |locconcons= sol|ssenoocsences + Bromide of ‘Soin «asi ciesie sales cielere siapels eects wt ctare cree ce ee ae ee ere Peer | een ©. 0417 0. 0558 magnesium)...--... 2-7. ce ae SoHE sae Sdecmeesocnd lasodassacctluasesneccss ©, 251 |.----- scoot [psoocosmessce: Sulphate of soda...-...........-- eosencaoess fonoo0 Doe ©. 9321 5 Sh secoddsacd| eopcaoanoods|looceeodsseeq]|assscsosontacs POMBE Sasso sesouosesotcossecesncenassase CHingiée), lampoadc eck las ansoecas| ooodeautccs|stoconecoseajucitseccenssea- WN ccooeosoossoosscony thocosossconsones o. 0858 0. 04 0. 18 0. 068 @. 1629 0. 1357 WHERE ES comp ococoenonsnesecchosoosoood|loococenseeciecooagcess GHD locoaocconcse ©. 1975 ©. 2480 Carbonate of lime =). <, és: asate ce a wfareieloe aresejerie eiateiere bois ol eater oiotats mice | hee mie ele ee I ete ee ee Sn | eer ee | eee eee ©. 0113 Otheringredicntst meee eee ree eee eee eee eee eee Gli =on0862 4|peeeeeee | aeeee eee OG) \|sancooresch 4 Fe,03=0.0004 Water oor serinee emcee ae Joie eeerancennece erences 85. 0060 gi. 36 79: 45 75-944 96. 4730 96. 2300 100. OOOO 100, 0O 100, 0O 100. COO 100. COCO | 100. 0000 Of these, the Sevier Lake lies in the Utah Basin, to the southward, within the limits of the ancient Lake Bonneville, being fed by a single river, the Sevier, which reaches it after a comparatively long course through a desert region. Its superficial area is only about a tenth of that of Salt Lake. The Oroomiah Sea of Northwestern Persia presents some remarkable ‘Wheeler, Expl. W. of 100th Merid., iii, 1875, 114. * Bischoff, Chem. Geol., ii, 1864, 59. * Bischoff, Chem. Geol., i, 1863, 313. * Bischoff, Chem. Geol., ii, 1864, 33. > Ramsay, Nature, vii, 513. GREAT SALT LAKE. 437 points of resemblance to Salt Lake. It is situated at 4,000 feet above sea- level, is 80 miles long, and 30 miles in average width. Its shores are very flat, and it is subject to annual variations of level of 3 to 6 feet. Its supply of salt is supposed by Edw. Hitchcock to be derived from Triassic sand- stones, as there are salt streams flowing into it from them. Salt Lake, on the other hand, is not connected, so far as known, with any salt deposits by its tributary streams, which have no perceptible salt taste. Deposits of -salt are known to exist, however, in rocks of the Jurassic age, which may _ have been connected with Lake Bonneville. The Dead Sea of Palestine is 60 miles long by 15 miles wide, and has an extreme depth of 1,800 feet, while its surface is over 1,300 feet below the level of the Mediterranean Sea. The depression occupied by the Dead Sea and the Lake of Tiberias is supposed to have been once occupied by the Mediterranean, and, having been cut off, to have reached its present con- centration of salts by evaporation. In this respect, it resembles Salt Lake, which is the concentration of Lake Bonneville. It is also subject to changes of level of 15 feet, and has extensive deposits of mineral salts on its borders, like those of the Great Desert. The water of Salt Lake differs from it principally in its smaller proportion of magnesia and lime. In its relative proportion of soda and magnesia, it Fesemihiec: more closely the composition of ocean salt than that of either of these two lakes. The two shore-lines on the east and west sides of Salt Lake present the greatest contrast in appearance. On the west, the shallow waters of the lake merge almost imperceptibly into the flat plains of the Great Desert, which will be described in a later section. On the east, green meadows, intersected by mountain-brooks, stretch up to the foot of the rugged slopes of the Wahsatch. From Ogden Point south to Salt Lake City, the immediate shores of the lake are occupied by varying widths of low marsh-land, which are continually being encroached upon by the rising waters of the lake. Along the flanks of the mountains are comparatively steep slopes of Quater- nary gravel and soil, which sometimes extend out in terrace-like ridges, composed, as far as can be seen, of loosely agglomerated sandstones and gravel conglomerates. ‘These are principally developed near Ogden City and to the south and west of the mouth of the Weber Camion, and represent a formation, probably of Pliocene age, which once occupied the valley. 438 DESCRIPTIVE GEOLOGY. At the point of the projecting spur of the Wahsatch, just north of Salt Lake City, a warm sulphur spring gushes out of the Wahsatch limestones, sending down a little stream, some 6 feet wide, of sulphurous waters, into - the little arm of the lake called Hot Spring Lake. These waters, like most of the springs around the lake, contain chloride of sodium as their principal mineral ingredient. Between this point and the city is another warm spring in the limestone, whose waters contain some sulphuretted hydrogen. At this spring are baths, much used by the inhabitants. The following analy-. sis of its water, made by Dr. C. T. Jackson, is exposed in the bathing estab- lishment: ‘Three ounces of water, evaporated to dryness, gave 8.25 grains of solid matter. Carbonates of lime and masmesia sss eee 0.240 Peroxide ofsiromseeee2 Besley Mem erer. Hi, ite 0.040 Lime 22). c3..0soRieee Sete ne ee 0545 Chlorine ~ -:2.22) 256 5 sie ee 3.454 Soda -. 22 Ree in ee ee ee 2.877 Macnesiai ete eee WOM eee mite als ke 3 0.370 Sulphumnte acrdyes aes ices 3.5 BU oe ey ee aa 0.703 ; nt B29 ‘Tt is slightly charged with sulphuretted hydrogen and carbonic acid.” It is interesting to note the occurrence of these hot springs with those at Ogden and in Bear River Valley, occupying a line just west of the foot of the mountains, which is approximately that of the great system of faults which have thrown down the western side of the range, and nearly parallel with the line of volcanic outbursts on the eastern flanks. Salt Lake City itself is situated upon the gently-sloping plains of Quaternary gravel, just at the base of one of the broader and more promi- nent, though by no means the highest, of the old lake-terraces. It is about 7 miles distant from the lake, which, owing to the flatness of the shores, cannot be seen from the level of the city. From the terrace above the city, however, a view is obtained to the westward over the lake to the mountain- JORDAN VALLEY. 439 ridges, which rib the desert beyond, while to the south lies outstretched the broad beautiful valley of the Jordan. ~ Jorpan VatLey.—Jordan Valley is a broad Quaternary plain from 15 to 20 miles wide, which, on, the eastern side, rises from the bed of the river in long, gentle slopes and gravel terraces, several hundred feet, toward the base of the mountains. In the alluvial bottoms of the streams, and in some cases on the gravelly benches, the Mormon settlers have cultivated their farms, utilizing the slope of the valley and the abundant supply of ‘water furnished by the streams issuing from the Wahsatch Mountains for irrigating the fields, which the almost rainless summers of this region would otherwise dry up. Along the mountain-flanks, the different lines of the _ old lake-terraces can be distinctly traced, the highest of which rises 940 feet above the present level of the lake. The depth of the Quaternary gravels cannot be definitely determined, but must be very considerable in the centre of the valley, as shown by the thickness exposed where the Jordan River cuts through the Traverse Mountains, which amounts to sev- eral hundred feet. At the mouths of some of the cafions, where the mount- ain-streams have cut deeply info these gravels, stratified beds of loose, coarse sandstones and conglomerates are seen, which doubtless represent the Pliocene valley deposit, perhaps contemporaneous with that of Cache Valley. So little definite data were obtained with regard to these deposits, however, that they have not been indicated upon the map. The best exposures of them in Jordan Valley are seen at the mouth of Parley’s Canon, where the erosion of the present stream has exposed a thickness of about 70 feet of Horizontal, coarse, reddish sandstones. From the lake-ter- races back of Salt Lake City was obtained the upper portion of the skull of a musk-ox, its horns and frontal bone well preserved and partially silici- fied, showing that the formation of these terraces was already in progress at the close of the Glacial period. On the west side of the Jordan, the slopes of the valley are more gentle and regular; but, owing to the smaller supply of water coming from the mountains on that side, there has been little cultivation of this portion of the valley, and it is principally used as a grazing-ground. . Traverse Mounraiys.—Jordan Valley is bounded on the south by a 440 DESCRIPTIVE GEOLOGY. low range of hills called the Traverse Mountains, which form a partial con- nection between the Wahsatch Range and the Oquirrh Mountains. These hills rise only about 2,000 feet above the valley, and show but few good — exposures of the rocks which compose them, their slope being generally covered with gravel and detrital material. They seem to be composed mainly of trachyte, the flows of which extend close up to the flanks of the bounding ranges, and on the western side extend along the foot-hills of the Oquirrh as far as the mouth of Bingliam Cation. It is probable that this trachyte-flow was preceded by an ejection of andesite, since among the specimens brought in from this range was one which a microscopic examination has proved to be andesite, though, owing to the fact that its locality cannot be well determined, this rock has not been indicated upon the map. It is a dark-gray rock, having a decidedly tra- chytic feel, the groundmass being very porous, and containing a few micro- scopical crystals of hornblende, with an occasional mica. Under the micro- scope, it is seen to be composed of plagioclase, with a little sanidin-feldspar, a large amount: of dark-brown hornblende in crystals, which show little alteration, and a small quantity of augite, while the groundmass, which is rich in gray glass, consists of an interwoven mass of microlites, which is characteristic of the andesites of the Wahsatch region. The trachyte of the eastern end of the Traverse Mountains is a dark bluish-gray, sometimes reddish, crystalline rock, made up of large crystals of sanidin-feldspar and mica, with such a small proportion of groundmass . that at a little distance it might be taken for granite. While the larger feldspars are almost all sanidin, a considerable amount of plagioclase- feldspar can also be detected in the mass. It is also rich in hornblende, which is comparatively unaltered. Under the microscope, the fresher feldspars are seen to have a zonal structure, and to be rich in glass- inclusions containing Jarge bubbles. Considerable greenish-yellow augite and apatite are also detected, but no quartz. The groundmas is made up of felsitic microlites and magnetite grains inclosed in a glassy base. Near the point of contact with the granite mass of Lone Peak, there is found a greenish-white, earthy, decomposed rock, in which the only traces of crystallization left are white irregular spots of partially kaolinized feld- UTAH LAKE VALLEY. 44] spar. Of the sedimentary rocks which underlie this trachyte flow, only a few exposures were found along the northern slopes of the eastern half of ‘the Traverse Mountains. They consist of white quartzites, and, in a cut made by the railroad not far from the point of the hills, of a blue quartzite having the external appearance of a limestone. Their structure-lines were too much obscured to afford indications of their age on stratigraphical grounds, but, from their lithological habit, they have been provisionally assigned to the Cambrian quartzites, which they most resemble. | The trachyte of the western portion of the Traverse Mountains is a reddish rock, containing large crystals of sanidin and considerable bronze- colored mica, together with some hornblende. The groundmass is very vesicular, and contains some glassy base. In Rose’s Cafion is found a light-. gray trachyte, having a laminated structure, rich in crystals of hornblende and mica, showing comparatively few macroscopical crystals of sanidin. While the dark trachytes of the range belong rather to the normal sanidin- trachyte group, this rock may be more properly classed among the horn- ‘blende-trachytes, and somewhat resembles the andesite above mentioned, which probably came from near the same locality. Near the mouth of Bingham Canon was found a rock which, in the field, was considered a rhyolite, consisting of a breccia-like felsitic groundmass, containing grains of free quartz; but, as the specimens obtained have been lost, the occurrence has not been colored upon the map. Urau Laxe Variry.—Utah Lake is a beautiful body of fresh water, ahout 20 miles long by 4 or 5 miles in width, which receives the drainage of the southern portion of the Wahsatch Mountains anda portion of that of the southwest slopes of the Uinta Range. It is nearly 300 feet above Salt Lake, into which its surplus waters flow through the Jordan River. Like the latter lake, its shores are very flat and shallow, especially along the eastern side, where the valley-slope from the foot-hills of the Wahsatch Range to the water’s edge is even less than in the Salt Lake Valley. The old lake- terraces form prominent lines along the faces of the mountains which sur- round it, and are especially developed at the gap in the Traverse Mountains through which the Jordan River flows, and where they show immense accu- mulations of fine gravel. The upper terrace-line, which could be distinctly 442 DESCRIPTIVE GEOLOGY. recognized on the soft slopes of the Traverse Mountains, was determined by barometrical measurement to be 87) feet above the level of Salt Lake. ) The Pelican Hills constitute a low, flat-topped ridge which borders Utah Lake on the west, made up of thinly-bedded gray and blue limestones, with intercalated lighter-colored arenaceous beds and quartzites, closely resem- bling those which form the summit of Timpanogos Peak, to which the few fossil remains obtained from them, consisting chiefly of Spirifers and Crinoid — stems, also ally them. . They probably represent the upper members of the Lower Coal-Measure group. The strata are nearly horizontal; on the east- ern slopes of the ridge having a slight inclination to the westward; while on the west side they dip nearly 10° to the eastward, showing a slight synclinal fold. This easterly dip is continued in the southern portion of the hills, beyond the limits of the map. From the comparatively horizontal position of the strata, it would seem that this mass must have been faulted up. See Sl OQUIRRH MOUNTAINS. 443 SECTION VII. REGION SOUTH OF SALT LAKE. BY S. F. EMMONS. Oqurrra Mountains.—The Oquirrh Mountains are a high, steep mass of hills lying to the westward of Jordan Valley, about thirty miles in length and from five to ten miles in width, whose summits rise from 5,000 to 6,000 feet above the surrounding plains. They are composed mainly of beds of Car- - boniferous limestones and quartzites, which the forces of contraction, acting almost equally in either direction, have compressed into aseries of complicated — folds, in which the prevalent strike, however, is in a northwesterly direction. The folding of these beds has been accompanied by a very considerable metamorphism and by the injection of porphyritic dikes, together with sub- sequent mineralization in the more disturbed districts. ' The southwestern portion of the range, to the west of the main ridge, isa quaquaversal uplift in the Wahsatch limestones, in the centre of which, at Ophir City, a fault- ing at right angles to the longer axis of the uplift has brought up the upper beds of the Cambrian. From Ophir City, as a centre, these limestone strata all dip away, steeply toward the west, more gently toward the north, . east, and south. The main crest of the range, between Tooelle and Lewiston Peaks, is the remnant of the flat arch of an anticlinal fold, which descends both to the north and to the south, resulting at the south point of the range in two minor synclinal folds, in Pole Cafion and in the cation south of Lewis- ton, and a similar synclinal fold to the north, in the region between Soldier Cation and Tooelle Canon. In the region between Tooelle Peak and Con- nor Peak, more particularly in Bingham Cafon, which is almost entirely in the beds of the Weber Quartzite, the structure-lines are much more diffi- cult to follow, and evidently the general system of folding observed in the southern portion is much complicated by minor folds; but its structure is in general that of a synclinal fold in these beds, while at the northern point 444 DESCRIPTIVE GEOLOGY. of* the range, beyond Connor Peak, the beds of the Lower Coal-Measure group are found to be pushed up and crumpled together in short, sharp folds, giving, in an east and west section across the northern point, no less than three small anticlinals, while the tendency of all the beds is to dip steeply beneath the waters of the lake. Kast Cafion is a deep, narrow gorge cut at right angles to the western anticlinal, or quaquaversal, already mentioned. At Ophir City, a steep wall of dark siliceous limestones rises perpendicularly on the south to a height of 2,000 or 38,000 feet, while in the opposite direction, about an eighth of a mile to the north of the cafion-bottom, a sheer wall of quartz- ite, from 300 to 400 feet in height, cuts off abruptly the tributary side- cations from the north. Beyond and above this wall of quartzite is an amphitheatre-like opening, shut in by a semicircular wall, rising in places to a height of 2,000 feet, formed of outwardly-dipping beds of limestone. The line of faulting, so distinctly shown by this quartzite wall, has a direc- tion of about north 30° east, and discloses a thickness of about 400 feet of compact reddish-white Cambrian quartzites. Above these are about 100 feet. of greenish-yellow clay-slates, in which were found numerous Trilo- bites and Primordial fossils, among which the following have been deter- mined by Messrs. Hall and Whitfield: | Ogyma producta. Ogygia parabola. Ogugia, new sp. Lingulepis, new sp. Kutorgina, new sp. Dikellocephalus, sp.? a Dikellocephalus, sp.? From their stratigraphical position, and their correspondence both in their horizon and fauna, with those found in the Wahsatch Mountains at City Creek, these beds evidently belong to the Potsdam group, although some of the above fossils have been assigned to the Quebee group by Messrs. Hall and Whitfield. In the limestones immediately above them, no fossils have, as yet, been found. But beyond the ridge to the OQUIRRH MOUNTAINS. 445 north, at a geological horizon of about 2,000 feet higher, are found abun- dant Sub-Carboniferous and Waverly forms.’ In the intermediate 2,000 feet, however, no considerable body of quartzite can be recognized which would lithologically correspond to the Ogden Quartzite. The limestones contain numerous siliceous and cherty bands, but do not differ essentially from those of the Wahsatch group. It therefore remains, in some measure, an open question whether the Silurian or Ute limestone is represented here, or whether this Cambrian quartzite, with its overlying shales, has been faulted up as a wedge-shaped mass, and the limestone beds here all belong to the Wahsatch limestone. On account of the decomposable nature of the shale bed which overlies the quartzite, it cannot be definitely determined whether, to the north of the fault-line, the overlying limestones are conformable or unconformable with the Cam- _brian beds. The dip of the quartzites at the line of fault is only about 10° to the northward. In the Miner’s Delight Mine, whose whole ore-body was at first within the shale belt, an incline which has been sunk in a northerly direction, at an angle of about 15°, steepening in depth to about 20°, has, at a short distance from the surface, passed out of the shales into solid limestone. The fact that this incline seems to dip steeper than the stratification-planes indicates that the quartzite and shales have been faulted -up as a wedge-shaped mass, otherwise it should have passed into quartzite instead of limestone beds. On this supposition, which is the one followed on the map, no lower beds are exposed in this cafion, with the exception of those brought up by the fault, than the Devonian limestone underlying the Waverly. At the mouth of East Cation, the limestones dip steeply to the west- ward, at an angle of 65°, striking nearly north and south. This dip is continued along the foot-hills of the range to the northward toward Dry Camton, the next little cation to the north; here the strike of the beds curves round somewhat to the east of north, while the dip of the beds shallows to 45°. In Dry Caiion, a considerable number of fossils of Sub-Carboniferous 1Dr. C. A. White describes an Olenellus Gilberti (Potsdam) from Ophir City, and Spivigera obmaxima, Euomphalus luxus, and a Conocardium ? (Sub-Carboniferous) from below Ophir City.—(Wheeler, Exp]. W. of 100th Merid., Vol. LV, Part I, 44 and 92 ct eq.) 446 : DESCRIPTIVE GEOLOGY. and Waverly types have been obtained by our parties, and, since the com- -pletion of our field-work, by Mr. J. E. Clayton. The vertical range of the fossils cbtained from this cafion, which have all a Sub-Carboniferous or Waverly aspect, shows a much greater development of these beds in the Oquirrh Mountains than in the Wahsatch. From the westerly-dipping beds near the mouth of the canon, in a blue limestone, were obtained the follow- ing Waverly forms: Streptorhynchus inflatus. Strophomena rhomboidalis.” Spirifer alba-pinensis. | Spirifer centronatus. Rhynchonella pustulosa. - Euomphalus Utahensis.’ Euomphalus (Straparollus) Ophirensis. Michelina, sp.? Zaphrentis, sp.% By Mr. J. E. Clayton, from the ridge above, between Dry Cafion and Kast Caiton, in a close-grained black !imestone, were obtained some of the same species, and: Proétus peroccidens. Orthis resupinata. Euomphalus latus var. laxus. From the northern side of Dry Cafion, at a horizon, according to Mr. Clayton, about 1,200 feet higher, he obtained: Trematopora. Fenestella. Polypora. While farther to the north, on the ridge toward Soldier Canon, and . still higher geologically, he found: : Productus levicostus, Productus elegans, Productus semireticulatus, Productus Flenvingi var. Burlingtonensis, CQUIRRH MOUNTAINS. 447 Spirifer striatus, Spirifer setiger, Spirifer Leidyi, Athyris subquadrata, which are regarded as Sub-Carboniferous. To the south of the mouth of East Cafion, the strike of the beds curves round to the east of south, and, at Lewiston Cation, is already nearly east and west, parallel with the canon. Lion Hill, as the ridge between Lewis- ton and East Cafions is called, is a flat-topped ridge, consisting of a half- dome of limestone strata, cut off on the north by the fault of Kast Canon, and sloping away with an ever-increasing dip east, south, and west. These beds are, toward the base, composed of dark, compact, fine-grained, more or less siliceous limestones, with some interstratified beds of shales and seams of black cherty material. On the flanks, toward Lewiston Cajon, there are found belts of a comparatively pure bluish limestone, which abound in remains of Spirifers, among which were recognized Spirifer opimus, the most abundant single species perhaps in this range. Between Lewiston and the southern point of thé mountains, the beds of the Wahsatch lime- stone dip gently to the south and west, rising slightly to the eastward, until, - in a line with the main crest of the ridge, they sink down again, passing under the shallow synclinal of Pole Canon. The section exposed in East Cation would be somewhat as follows: Passing up through the steeply-dipping beds at the mouth for a distance _ of nearly a mile, the inclination of the beds gradually: decreases, until, at Ophir City, they are on an east and west line, nearly horizontal; but have a slight inclination to the north and south. The cafion-walls are entirely in the limestones, the line of fault which has brought up the quartzite being _ to the north of the cafion. Above Ophir City, the beds are almost horizontal for some distance, and then slope off gradually to the east, the dip becoming _ steeper as one ascends the cafion until it reaches 45°. At the forks of the cafion, the limestones have a shaly appearance, owing to the frequence of thin interstratified seams of black chert. Above the forks, the dip shallows again, and near the head assumes a westerly inclination, forming a shallow synelinal, which can be traced to the south, following a line just west of 448 DESCRIPTIVE GEOLOGY. the main crest, while all the beds have a general inclination southward. About midway between Ophir City and the forks, a branch-canon from the south, by which the road to Lewiston passes, discloses a bed of soft black argillaceous shales, which follow the line of depression between the two canons. J'rom about this horizon, in Ophir Cafion, were obtained some specimens of Spirifer opimus. About a mile above this point were found, near the forks: Productus Prattenianus. Spirifer opimus. Naticopsis, new sp. From the head of the cation, near the divide, were obtained: Streptorhynchus robusta. Chonetes granulvfera. Spirifer opimus. Ehynchonella Osagensis. The crest of the range between East Cafion and North Canon is made up of limestone, with intercalated beds of sandstone and quartzite, resem- bling lithologically those of Timpanogos Peak, and abounding in excellent impressions of Productus Prattenianus and Spirifer opimus. ‘These beds all dip at a very slight angle to the westward; the main ridge, from here north to the head of Tooelle Cation, forming apparently the western member of an anticlinal fold. North Cafion cuts into the centre of this fold; but, as no fossils were obtained from this cafion, it is not known whether the Sub- Carboniferous and Devonian beds are here exposed or not. From beds on the same line of strike to the southward, near Camp Floyd, the following fossils were obtained by J. E. Clayton: Orthis carbonaria, Streptorhynchus crassus, Productus Prattenianus, Productus multistriatus, which, however, only indicate a Lower Coal-Measure horizon, and re-affirm what the stratification-lines have already shown, that the beds gradually sink as a whole to the south of Lewiston Peak. - OQUIRRH MOUNTAINS. 449 At the mouth of North Cafion, the quartzite beds of the Weber group are found striking northwest and dipping to the eastward; their contact-line with the trachyte body of the Traverse Mountains following approximately the line of the road from Rose Cation to Cedar Fort. Northward from Dry Canon, on the western side of the range, the anti- clinal fold gradually sinks under the plain, and to the north of Soldier Caton are found the lower beds of the Weber Quartzite, having a northwest strike, and dipping to the north and east. ‘There seems to be here an insensible eradation from the beds of the Wahsatch limestone, which are intercalated with quartzite beds, into the lower beds of the Weber Quartzite, which con- tain interstratified beds of limestone. In the quartzites on the foot-hills, between Stockton and Tooelle, is found an interesting occurrence of granite-porphyry, of which fragments are also found in the float coming down from Lewiston Canon. It is a coarsely crystalline, grayish rock, containing large crystals of orthoclase, up to three-quarters of an inch in length, in a semi-crystalline groundmass, composed of quartz, feldspar, hornblende, and black biotite. It is remark- able for the distinet crystallization and fresh, unaltered condition of its con- stituent members; both hornblendes and micas show very sharply-defined hexagonal outlines, while the orthoclase is clear and translucent, having a delicate rose hue. The rock contains besides considerable titanite, which may be seen in comparatively large well-defined crystals within the larger erystals of orthoclase. A few of the orthoclases show a tendency to a zonal alteration. Besides titanite, these crystals contain also small hexagonal flakes of mica, and occasional crystals of hornblende. The beds of the Weber Quartzite, as seen along the foot-hills from Stockton to Tooelle, are mainly composed of a close, somewhat vitreous rock, stained by oxide of iron, and breaking easily into small fragments, so that the slopes are so covered with débris as to conceal the structure-lines. At the mouth of Tooelle Canon, the quartzites are seen to have a strike nearly north and south, and to dip to the westward; the lower 1,000 feet being composed of a white compact quartzite. At the forks of Tooelle Camion are exposed heavy limestone beds, lying conformably under these quartzites, which correspond to the upper members of the Lower Coal- 29 DG ~ 450 DESCRIPTIVE GEOLOGY. Measure limestone, as seen along the main crest, on a line due south from this point. The beds at the bottom of the canon are massive and somewhat argillaceous limestones, from which were obtained the following Coal- Measure fossils: Fenestella. Productus semireticulatus. Productus Prattenianus. Spirifer cameratus. Spirifer opinus. The limestone beds north of the fork bend in strike somewhat to the east of north with a dip to the northwest, and belong to the northern end of the eastern anticlinal fold, where it, to use the expression of the English geologists, ‘noses under” the overlying quartzites. The eastern member of the North Camion fold, of which this-is the northern point, has a much steeper dip and is less well defined than the western, and it seems probable that the folding has been accompanied with some faulting which has lifted up the western member; this would account for the character of the main crest of the range between Tooelle and Connor Peak, whose beds are nearly horizontal, and resemble in that particular the structure of the ridge of Timpanogos Peak. Passing up the north fork of Tooelle Cation, the lime- stones soon disappear under quartzite beds; near the head of the cajion, already, a bed of yellowish-white quartzite seems to have a western dip, but this may be merely a local displacement. | On the divide between Tooelle and Bingham Cafons, occurs another body of granite-porphyry, somewhat similar to that already described on the western foot-hills. It is a light-green rock, in which the feldspar erys- tals are generally smaller and opaque, whereas, in the rock of the foot-hills, the feldspars are generally fresh and translucent. A few of the large trans- lucent feldspars can be seen in this rock also. Its groundmass contains a much larger proportion of hornblende, which is of a dark-green earthy color, and almost no mica. No titanite was detected in this rock. Under the microscope, the hornblendes present remarkable phenomena of alteration, being changed into three distinct products, magnetite, epidote, and a leek- OQUIRRH MOUNTAINS. 451 green fibrous mass, which will be found more fully described in Professor Zirkel’s Report, Vol. VI, Plate II, fig. 2 The mass of the range around Bingham Canon, and to the south as far as the mouth of North Caiion, is occupied by the Weber Quartz- ites. The structure of this portion of the range is very obscure, owing to the broken and metamorphosed nature of the beds and the complicated position of the folds. On the eastern foot-hills of the range, opposite Lewiston Peak, the eastern dip is seen in the limestones of the Lower Coal-Measures as they gradually sink to the southward: the axis of the North Canon fold passes through the low saddle on the spur to the south of the stream, showing that here, as in Tooelle Cation, the eastern mem- ber of the fold is much the more abrupt. North of the mouth of North Canon, the limestones pass by a gradual transition into the lower quartzites of the Weber group, which are seen striking northwest with a dip to the westward, forming the western end of the Traverse Mountains in contact with the trachyte body, and crossing the mouths of Rose and Butterfield Canons into Bingham Cajon. At the head of Butterfield and Bingham Cajfions, they form the main erest of the range. In the latter, the easterly dip shallows near the forks, and steepens again below, while at the extreme mouth of the cation the beds turn up steeply, and dip 60° to the west. The section exposed in Bingham Cajon, therefore, represents in general a synclinal fold, whose eastern member is short and abrupt; the whole series descends toward the north. In the north fork of Bingham Cafion, where the bedding of the quartzites is rendered more distinct by occasional interstratified calcareous - beds, the observed strike was north 35° east, with a dip 45° to the north- west; while on the spur to the east of this fork, the strata curve around and assume gradually an east and west strike, and dip to the north and east. In Bingham Canon itself, the quartzites are very much metamorphosed, broken, ‘and stained with iron, and rich in silver-bearing minerals. Owing to the irregularity of the folds, it is almost impossible to estimate the thickness of this development of quartzite. It can hardly be less than that found in the Wahsatch Range, however, and seems to be much greater. At the head of the south fork of Bingham Cafion is a diorite-dike, which 452 DESCRIPTIVE GEOLOGY. resembles very closely that seen on the northwest face of Twin Peak. It is a fine-grained, grayish rock, containing black and bronze-colored mica and dark-green hornblende, in a fine-grained groundmass, made up largely of quartz and plagioclase-feldspar. The microscope discloses the presence of apatite, and the fact that the laminee of mica are very much broken. ‘This dike has a general northwest trend with the strike of the beds. The sides of Bingham Canon, for a distance of several miles from its mouth, show the remains of gravel-terraces, made up of quartzite débris, which extend 50 to 100 feet above the bottom of the canon, and show that, as in the cafions of the Wahsatch, the waters of the ancient lake formerly extended up into this cation also. It was the finding of gold in these gravels that first directed the attention of the miners to the ore-beds in these mountains. In the quartzites of Bingham Caron, Mr. J. E. Clayton succeeded in finding some fossil remains, among which have been recognized Archeocidaris, new sp., Martinia lineata, Polypora, and columns of Crinoids. The sharp synclinal fold on the eastern foot-hills is continued to the north of Bingham Canon, and, at the eastern base of Connor Peak, quartzites are found striking north 15° east, and dipping about 25° to the westward. Some of the more thinly-bedded of these quartzites, of a compact cherty texture, show the effects of compression in the wavy undulating surface of the thinner sheets. Above these are red- dish and yellowish limy shales, overlaid by blue siliceous limestones, while the summit of the peak is occupied by beds of soft, earthy, blue limestone, in which were found Spirifer and Productus, but too poor for specific deter- mination. The dip of these upper beds is to the north and east. As palzeon- tological evidence in this region offers no means of distinguishing between the limestone of the Upper and Lower Coal-Measures, this body has been ascribed to the Upper Coal-Measure group on purely stratigraphical reasons, from the fact that the quartzites of Bingham Cafion apparently dip under the mass of Connor Peak. OQUIRRH MOUNTAINS. 453 Owing to want of time, the structure of the range north of Connor Peak was not satisfactorily made out. Enough was seen, however, to show that the beds of this portion of the range had been plicated into east and west folds, as if they had been crushed against some unyielding mass at the northern point of the range. At the extreme northwestern point, the beds dip 70° northwest, with a strike of north 45° east. These beds along the foot-hills are composed of white and iron-stained quartzites, which have been designated by the color of the Weber Quartzite, though they may only represent some of the inter- ealated siliceous beds in the upper part of the Wahsatch limestone. Fol- lowing the point of the mountain eastward, the beds assume a northeast strike, passing over a steep anticlinal fold. From the limestones exposed opposite Black Rock at 800 to 1,000 feet below the uppermost beds shown, though it was impossible to determine at what depth below the quartzites already mentioned, were obtained the following fossils, whose general aspect is rather that of the lower beds of the Lower Coal-Measure group: Productus semireticulatus. Productus Prattenianus. Streptorhynchus crenistria. Spirifer opimus. | Fenestella. Polypora. Trematopora. Within these limestones is an interesting bed of fine-grained white sandstone, of loose, friable texture, made up of rounded grains of limpid quartz, differing essentially from most of the siliceous beds, which are gen- erally compact and almost vitreous. Passing still to the eastward, two more short anticlinal folds are crossed, and at the northeastern point the lime- stone beds are overlaid by easterly-dipping quartzites, among which is one having the same curious cavities found in the quartzite beds of Weber Cation, which are doubtless the cavities left by some organic remains. A yellow sandstone is also found among the quartzites. The outlying hills 454 DESCRIPTIVE GEOLOGY. to the south are formed of the same quartzites, standing almost perpendic- ular. From the limestones of these eastern hills were obtained Chonetes granulifera. ~ Productus Nebrascensis. Productus longispinus. Martinia lineata. Athyris subtilita. In the steeply-dipping limestones at the northeastern point is an interest- ing cave, over 200 feet in length and in places as much as 25 feet high, whose walls and roof are covered with a sort of tufaceous conglomerate, made up of pebbles of dark-blue limestone, cemented by a white calcareous tufa, while a similar tufa covers the floor. These are the remnants of one of the lower lake-terraces. In them were found a few recent shells of the genus Ammicola. Along the steep front of the point of the mountains, which has an angle of slope of nearly 37°, the old lake-terraces can be traced with great distinct- ness, the upper one being marked by a line of calcareous tufa clinging to rock slopes. A careful measurement was made of the height of this terrace-line above the level of the present waters of the lake by a series of synchronous barometrical observations. The result gave 940 feet. The little islet about a mile from the shore, which gives the name to this point, is composed of limestone strata, lying nearly horizontal, whose weathered surfaces have become quite black. ToorLtLE AND Rusn Vauueys.—The broad plains to the west of the Oquirrh Mountains are divided by a low ridge, called the Stockton Hills, into two distinct valleys. Tooelle Valley, to the north, is a continuation of the present basin of Salt Lake, and on the borders of the lake consists largely of marsh-land and swamps, while along the stream-beds of the higher por- tions of the valley are considerable stretches of arable land occupied by the farms of Mormon settlers. On the flanks of the mountains, especially in the southern portion of the valley, the old lake-terraces are very distinctly marked, and at either end of the Stockton Hills form a broad, flat veee separating the two valleys. Rush Valley, as the northern portion which is cut off by these lake- es TOOELLE AND RUSH VALLEYS. 455 terraces is called, is in general a dry plain of Quaternary pravel and soil, supporting only a growth of sage-brush (Artemisia tridentata), but having . along the bottoms of a few streams, especially that of Clover Creek, some alluvial soil. Rush Lake, a little sheet of Water near the Stockton Hills, receives the surplus waters of the valley, and, though only existing as a lake since the time of the settlement of this region, its waters have already a slightly brackish taste. In the middle of the valley, near the southern limit of the map, is a low ridge, in which were fotind horizontal beds of a white limestone, with a silky texture. When treated by acid, this limestone leaves a pumiceous mass of glassy needles, which would indicate that it is a vol- .canie tufa which has been deposited under water and-become impregnated with carbonate of lime. ) Since the completion of the field-work of the Survey, it is reported that beds catrying coal have been discovered in the valley-slopes on the east side south of Rush Lake, where the Quaternary covering has been cut through by a stream-bed. From the description given of the beds, it is evident that they represent a southern extension of the beds of the Green River Eocene, which were discovered, also carrying coal, on the edge of the Great Desert, at the eastern foot of the Ombe Mountains, - The low ridge of the Stockton Hills, between these two valleys, is made up principally of quartzites of the Weber group, but shows at the south- eastern extremity a small development of limestone beds, which apparently form the northern point of the Ophir City anticlinal. Opposite the north- ern corner of Rush Lake tliese limestones strike northwest, dipping steeply to the southwest, and are overlaid in the hills farther west by quartzite beds, whose strike gradually changes to north and south, preserving a gen- eral westerly dip, as far as cari be detected under the accumulations of oravel and detrital material. . In the terrace-bench of the extreme eastern foot-hills of the Aqui Mount- ains, opposite the western end of the Stockton Hills, ridges of cherty white quartzite are seen striking a little west of north and dipping 75° to the west- ward. These are supposed to be a continuation of the beds of the Weber: Quartzite, with slightly inverted dip, inasmuch as the adjoining beds in the foot-hills of the Aqui Mountains; which have about the same strike and 456 DESCRIPTIVE GEOLOGY. dip, assume gradually an eastern dip as one penetrates the hills. These beds belong without doubt to the Wahsatch limestones, and the upright quartzite beds must therefore represent the base of the Weber Quartzites, turned up steeply against the flanks of the Aqui Mountains. 5; Aqut Mounrains.—Beyond Tooelle and Rush Valleys, to the west- ward, rises a second high mountain-ridge, having a north and south trend, parallel to the Oquirrh Mountains, known by the Indian name of Aqui or Onaqui. Its central portion, of which the culminating point, Bonneville Peak, rises nearly 7,000 feet above the level of Salt Lake, is a broad mountain mass, some 10 miles in width, cut by deep cafion-gorges, and covered with a considerable erowth of timber. To the north, it extends | in a sharp narrow ridge, of gradually-decreasing elevation, to the shores of Salt Lake, the continuation of its line of elevation being seen in Stansbury and Carrington Islands. To the south of the central mass, it is a rather flat-topped ridge, having an elevation of only about 4,500 feet above the adjoining valleys, which extends beyond the limits of the map, connecting with the group of hills that enclose Rush Valley on the south. The geological structure of this range, as well as could be determined by the limited observations made, is that of an anticlinal, whose axis, as far , as a few miles south of Bonneville Peak, has a due north and south trend, in a line with the main crest of the ridge, bending, south of this point, slightly to the eastward. Along this axis, in the central portion of the range, a line of fault has been developed, resulting in an upthrow of the western member of the fold, which reaches its maximum of not less than 10,000 feet at Bonneville Peak, and gradually decreases to the north and south as the axis of the anticlinal descends. The southern portion of the range, as seen on the map, is formed of limestones, having a gentle western dip, and striking diagonally acrogs the range a little to the west of north. The higher beds of these limestones contain many arenaceous and sometimes quartzite beds, and would appear to correspond to the alternating beds of the upper part of the Wahsatch limestone. Beyond the limits of the map, to the southward, are seen bodies of quartzite, apparently overlying these, which probably represent the Weber Quartzite. Toward Reynold’s Pass, the limestones become more AQUI MOUNTAINS. ADT massive and heavily bedded, still preserving a westerly dip of 15° to 20°. The few indistinct fossil remains found here are of Carboniferous types, while the thickness of limestone beds which can hardly be less than 5,000 feet, makes it evident that they must belong to the great Wahsatch belt. To the north of the pass, the hills are formed of the same limestone beds, but with an easterly dip, forming the other side of a broad anticlinal fold. These easterly-dipping limestones were traced to the summit of the first high peak north of Reynold’s Pass. The region between this peak and the head of South Willow Creek, on the eastern slopes of the range, was, how- ever, not explored. On the western flanks, a body of westerly-dipping quartzites comes in, some 4 or 5 miles north of Reynold’s Pass, and forms the main mass of the western ridge from here to a little distance beyond Grantville Peak. Here also the line of contact between the quartzites and limestones south of Bonneville Peak was not observed, and it is not known whether the latter wrap around the former with a western dip, as on the north end of the anticlinal, or are cut off by the fault, as the map would indicate. In ascending Bonneville Peak from the west, a body of white quartzites of not less than 6,000 feet in thickness is crossed, whose average dip is about 25° to the west, becoming somewhat less steep near the summit. The prevailing rock in these beds is a white, or yellowish-white, semi-granular quartzite. Occasional beds of conglomerate and one or two thin strata of a dark-green argillaceous rock, having an irregularly-laminated structure, with a development of minute spangles of white mica oa the laminated — surfaces, are found accompanying the quartzite. These imperfect mica- schists, and a bluish-purple quartzite, like that found east of Farmington, containing also the flattened pebbles observed in Ogden Canon, together with the general character of the quartzites, constitute a sufficiently close resemblance to the Cambrian formation of the Wahsatch to justify the . assigning them to this horizon, while the fact that no other quartzite body of such thickness is found underlying a limestone belt of over 5,000 feet precludes the possibility of any other supposition. It must be stated, how- ever, that in this range, as in the Oquirrh Mountains, it has not as yet been 458 DESCRIPTIVE GEOLOGY. possible to identify, either lithologically or paleontologically, the Ogden Quartzite or the Ute limestone, but the explorations have not been suff- ciently exhaustive to justify the conclusion that they are entirely wanting. The east face of the Bonneville Peak Ridge presents an almost perpen- dicular wall of qiiartzite from 2,000 to 3,000 feet in height. The deep cation under this peak at the head of South Willow Creek has the amphitheatre- like basin at its head, and the general shape in its upper part, of a glacier- canon. ‘This cafion was only explored in its lower portion, where a heavy body of blue limestone, covered at the foot-hills by a flow of trachyte, is exposed in section, with a strike a little west of north. These limestones are much metamorphosed aid dislocated, standing at such varying angles that it was difficult to determine their structure. But few imperfect casts of fossils were obtained from the lower beds exposed, among which the only one which has been specifically recognized is Zaphrentis muitilamella. Their general character, however, and the thickness and general habit of the limestones are sufficient to determine them as belonging to the Wahsatch group. Near the mouth of the cation, a body of trachyte is exposed, which has apparently poured out between the nearly upright beds of limestone, while flows of voleanic ash of red and gray color, containing pebbles and angular fragments of the lava, form the ridges on either side of the entrance, sloping 20° to the east, and apparently covering the flanks of the spurs to a considerable distance north and south. This rock is a light-gray hornblende-trachyte, containing abundant fine black needle-like crystals of hornblende, with some black biotite, but no distinct crystals of feldspar. The mass is quite porous and rough to the touch, and has a low specific gravity. Under the microscope, the grayish-white porous groundmass is found to be made up largely of feldspar crystals, in which plagioclases are comparatively frequent, with abundant biotite in remarkably perfect hexa- gons and rhombs, while no microscopical hornblende was seen. The ground- mass contains besides some apatite, and fine globulitic glass stains, which, on account of the colorless zone encircling them, might be mistaken for nosean. The limestone beds in the upper part of the cation have apparently a a ee ee ee ee. ee ee ee ee ee ee ee ee ee ee eS eo . ° AQUI MOUNTAINS. : 459 western dip, while in the narrow gorges a few miles from the mouth, the dip varies from perpendicular to 60° to 70° eastward. It may be supposed that the anticlinal axis here lies somewhat to the east of the main ridge, and that the break has followed a line a little to the west of it. Whether this suppo- sition be correct or not, it is evident that in this portion of the range the forces of contraction and dislocation have acted most powerfully. It is worthy of remark that the line of the southern general section on the map crosses the Wahsatch, Oquirrh, and Aqui Mountains approximately at the points of the most violent disturbances in the sedimentary beds, and where the develop- ment, both of the older granites and porphyries and of the younger volcanic rocks, has been most considerable; it also indicates, in the two former, the region of the greatest concentration of argentiferous minerals; in the latter, these have not yet been developed. On the western foot-hills of the range, the quartzites can be traced as far north as Hooper’s ranch, where they form an outlying hill, the northern point of which is formed of steeply-dipping limestone beds, having a strike somewhat to the east of north. ‘The limestone beds further north, on the west of Grantville Peak, were observed resting on the westerly-dipping quartzites, but their southern limit was not definitely determined. . Grantville Peak forms the crest of a sharp anticlinal fold, whose western member dips about 45° west, while the eastern beds are upturned at much steeper angles, assuming at the extreme foot-hills a perpendicular position like those on the east of Bonneville Peak. The lowest beds exposed here afe the same quartzites that were found at that peak, and likewise form the highest portion of the ridge. The purple quartzite with flattened pebbles is particularly noticeable, forming the surface of the saddle north of Grant- ville Peak, and of the eastern slopes, where the force of the strong west winds, blowing from the desert, has laid bare and polished its surface, and worn away the matrix of the rock, leaving the harder pebbles standing out in rounded knobs. The whole series from the Cambrian to the Lower Coal- Measure limestone have been indicated here, as there was no evidence of any faultmg. To the north, the beds sink, and the angle of dip becomes less steep; to the northeast of Grantville Peak, the outlying foot-hills show limestone beds dipping fromr 25° to 45° to the east and north, while the 460 DESCRIPTIVE GEOLOGY. narrow ridge which forms the extreme point of the range is made up of nearly horizontal beds of limestone, abruptly escarped on the west, but in which the dip seems to be rather west than east, though, in the little outly- ing limestone knob, called Pilot Rock, the beds have a well-defined dip of 20° to the south and east. All along both flanks of the northern portion of the range, particularly on the Skull Valley side, are numerous springs, some of fresh water carrying considerable lime, but many of them highly charged with chloride of sodium. On the steeper cliffs, the line of the old lake-terraces is marked by a deposit of calcareous tufa. IsLanps.—Stansbury Island was formerly connected with the mainland by a low beach-line, which is now in great measure covered with water. The island itself is a rugged mountain-ridge, with precipitous slopes, which, though only three miles in width at its greatest lateral extension, rises nearly 3,000 feet above the lake-level. It is formed mainly of beds of the Lower Coal-Measure limestones, which form a sharp anticlinal fold, dipping 75° in either direction, with a general north and south trend. These limestones abound in corals, among which has been recognized: | Zaphrentis Stansburyt. Zaphrentis multilamella. From a black limestone near the top of the peak was also obtained: - Euomphalus subplanus. | Underlying this black limestone is a bed of about 200 feet of lighter- colored siliceous rock. Along the flanks of the hills, especially on the eastern shore, is a considerable development of light-colored beds, consist- ing of sandstones and quartzites, which have been referred to the Weber Quartzite, as at Black Rock Point, though they may only represent the upper impure beds of the Wahsatch limestone. These beds are both compact and heavily bedded, and thinly laminated. On the southern portion of the eastern shore, they have a strike of north 18° east, showing a tendency to close around and cover this end of the anticlinal. The upper terrace-line on the island is marked by an abundant tufaceous deposit. In general, the geological structure of the island seems to resemble that of the Aqui Mountains, of which it forms a northern continuation en échelon, and perhaps may have a similar faulting, which has thrown up the western side of the fold. aa ISLANDS. AGL Carrington and Hat Islands evidently form part of the same uplift with Stansbury Island, and belong, like it, to the Lower Coal-Measure group. Associated with the limestones of Carrington Island is a considerable devel- opment of finely-laminated argillaceous slates, which contain little cubes of iron pyrites and some coarse conglomerates. The mass of Hat Island is principally made up of these slates and conglomerates. Between Hat Island and Frémont’s Island is, as has been seen, the deepest portion of the lake, the bottom being over forty feet below its present surface. 462 DESCRIPTIVE GEOLOGY: SECTION VIII DESERT REGION. BY S. F. EMMONS. Sxutt VALLEY is a broad arm of the Salt Lake Valley, lying to the west of the Aqui Mountains. In its northern portion, it scarcely rises above the level of the lake, and is occupied by a great extent of marshes, which, — for the greater part of the year, are almost impassable. Itrises gradually to the south to about opposite the southern end of the Cedar Mountains, where an almost imperceptible divide throws the drainage of the country beyond westward into the Great Desert.. This valley abounds in springs, which are most frequent along the eastern edge of its northern portion, where they are surrounded by very considerable extents of meadow-land, affording excellent winter-grazing for stock. In the southern portion of the valley, opposite Reynold’s Pass, is a group of springs, in the midst of a swampy tract, covered by coarse grass and reeds. Only one of these springs, how- ever, furnishes potable water, the others being too highly charged with mineral salts. The remaining dry portion is covered, as are all the valleys — of the plateau region, by a scattering growth of sage-brush and little clumps of the nutritious bunch-grass. On the slopes of the Aqui Mountains, at Reynold’s Pass, are great accumulations of fine quartz-sand, which have~ been blown in from the desert through the gap in the Cedar Mountains, and extend up many hundred feet on to the hills, choking up the bottoms of the smaller ravines. Crpar Movuntarns.—They consist of a low range of hills, scarcely rising more than 2,000 feet above the adjoining valley, whose long gentle slopes are well covered with detrital material, and support a scanty growth of sage-brush and juniper (Juniperus occidentalis), with near the summits a few stunted pines. Like all the desert ranges, of which they are a fair type, they afford a very scanty supply of water, which is only found in a few widely- ‘separated springs. ‘This fact, combined with the scanty data to be obtained, ; : j CEDAR MOUNTAINS. 463 owing to the absence of deep-cut canons or of extensive rock exposures, renders their exploration peculiarly unfruitful to the geologist. The extreme southern point of the Cedar Mountains, as represented on the map, is mostly covered by the broad, flat gravel-terraces of the ancient lake, out of which rise a few isolated hills of red iron-stained quartzites and limy shales, upturned at varying angles, but generally dipping to the north and. east. At White Rock Spring, the eastern foot-hills, forming a somewhat broken line of secondary elevation, are formed of beds of a coarse cherty limestone, abounding in cylindrical moulds of encrinites, like the calcareous quartzite found on Emma Hill in Little Cottonwood Cafion. These beds have a northwest strike, with a gentle dip to westward, and are succeeded higher on the foot-hills by limestone beds which are almost horizontal. They are partly covered by a flow of reddish breccia, which has occupied the stream-bottom between the spurs. The White Rocks themselves are three very sinetlar masses of grayish- white quartziferous trachyte, the largest, about 300 feet high, having a rudely conical shape, with perfectly smooth sides, without cleavage-planes or cracks, and so steep that it is difficult to ascend to their summit. This trachyte is a coarsely crystalline, almost granitoid rock, made up of large crystals of sanidin, in a few instances an inch in length, with rounded, eracked grains of quartz, occasional prisms of hornblende and flakes of black mica in a crypto-crystalline groundmass. The groundmass is quite porous, and shows many rounded cavities, from which the quartz-grains have fallen out. Under the microscope, it is seen to be made up of a crystalline aggre- gation of feldspar, quartz, and augite, the quartz being unusually rich in glass-inclusions. This rock resembles in every respect the quartziferous trachytes of the Elkhead Mountains, except that it contains microscopical quartz in the groundmass. For this reason, it has been classed by Pro- fessor Zirkel in his report as a rhyolite. . The broad, flat-topped crest of the hills at this point is noua by a flow of andesite, which extends for several miles to the northward, and forms an outlying hill to the west, which just rises above the accumulations of desert sand. In external habit, this andesite cannot be distinguished 464 DESCRIPTIVE GEOLOGY. from a basalt, flowing in thin sheets, with a rudely columnar structure, and becoming reddish-black upon its weathered surfaces. On the surfaces of fresh fracture, it shows a dark bluish-gray, somewhat porous groundmass, in which are imbedded crystals of augite and black mica, with occasional large crystals of plagioclase-feldspar. Under the microscope, it is seen to contain sanidin-feldspar, as well as plagioclase, some hornblende associated with the augite, and pale-gray glass. It has been classed, by Zirkel, with the augite-andesites, but, owing to the presence, unusual in these rocks, of mica and hornblende, it rather approaches the hornblende-andesites. It contains no olivine. An analysis made of this rock by R. W. Woodward shows more resemblance to the andesites proper than to the augite-andesites. The constituents are as follows: Silica» =,:)50 See ee te a iy, (ae Ee 60.71 Alamigia sees see babe tlelen ta sik ei ey Bey eee 16.00 Ferric oxide .:.)224. Sak ee 2.09 Ferrous oxide: Danie eee 3.87 Lime ... «:.. 22.350 si ee Se ee ent AG, Magnesia -.-.-..- air Sunt itches) pea eld int a page iene 38.07 Sodai « .'5 1st icy ee eee ee ee path a a A: Potassa:s 2). 0:94 BIS ae ee 3.78 Lithia: 2.0 [teehee ee BS Se ee es ee trace Carboni¢e acide! sche sae ae eee 1.01 Water . - .2s=:2. berate Meet Deke nee eee 1.48 99:92 To the north of White Rock Spring, limestones, generally lying at a shallow angle, form the main ridge as far as observed. Toward the north, opposite Hooper’s ranch, a low ridge to the eastward of the main ridge is formed of limestones and shales, having a western dip, and incrusted with calcareous tufas of the lake-terraces, from one of which issues a large spring of limy water. At the point where the road to Pilot Rock crosses the hills, both the eastern and western slopes of the range are covered by flows of dark, compact basalt, inclining with the spurs in either direction. On the crest, whence the basalt has been denuded off, are exposed beds of limestone and LAKESIDE MOUNTAINS. 465 siliceous shales, metamorphosed and blackened on the surface, in which are some indistinct impressions of encrinites and corals. On the western slopes, north of the pass, is a body of dark-blue limestone traversed by small veins of white calcite, also containing corals, which dips 85° to the eastward. To the east of the limestones, and overlying them, are reddish quartzites, whose structure, as well as could be ascertained from the few exposures to be seen under the accumulations of surface débris, is that of a synclinal descending toward the north. These have been referred to the Weber Quartzite group; the main body of the range being evidently in the Wah- satch limestone. : LaxesipE Mounrains.—A similar low ridge of hills, en echelon with the Cedar Mountains, lying along the western shores of Salt Lake, is known as the Lakeside Mountains. Its southern foot-hills are formed of similar quartzites, resting on strata of dark-blue limestone, also carrying crinoid remains, having a Coal-Measure aspect, which form the southern peak of the range, with a strike of northeast and a dip of 45° to the southeast. These limestones appar- ently form an anticlinal to the north, and are overlaid again by the quartzites at the low pass in the middle of the ridge. The northern portion of these hills, as far as could be learned by the isolated observations of our parties employed upon the survey of the lake, are composed of the same heavy dark lime- stones, with occasional lighter siliceous beds, in broken, confused masses, and have been referred to the Lower Coal-Measure group. The island called Strong’s Knob, which forms the northern continuation of this ridge, shows to the eastward almost perpendicular cliffs, several hundred feet in height, of dark-blue and black limestones, capped by a grayish limestone bed, containing corals, among which the following have been determined : Zaphrentis Stansburyt. Zaphrentis multilamella. The same black and gray limestones are observed in Gunnison’s Island, which is in the same line of elevation, and in Dolphin Island, opposite the Terrace Mountains. _ The desert ridge to the west of the Lakeside Hills is but little known by actual observation. Its northern point shows similar limestone beds to 30 DG 466 DESCRIPTIVE GEULOGY. those forming these islands, and has, like them, been considered to belong to the Lower Coal-Measure group, while the southern point is said to be formed of a vesicular basalt. Tue Great Desert.—To the west of Salt Lake and of the Cedar Mount- ains, stretches a wide desert plain, formerly the bottom of the broadest expanse of the ancient Lake Bonneville, and now known as the Great Desert. Over an extent of some 40 miles in width by over 80 in length, its surface is an almost absolute level, only broken by a few isolated ridges, forming rocky islands in the broad area. Its surface is covered by a deposit of the finest — silt and mud, the sediment of the ancient lake, and is almost absolutely bare of vegetation. When dry, this mud forms a hard level floor, almost like a pavement, but a comparatively slight fall of rain renders it so soft as to be practically impassable for horses or cattle. After a rain, the soluble salts, with which the soil is impregnated, are left in a thin film of white upon the surface, so that when looked upon from one of the bordering ranges at a time when the sun is near the horizon, so that its rays are reflected from the surface, the whole expanse seems to be covered by a mantle of pure white snow. Along the borders of the desert, these Lower Quaternary muds are covered by the more recent detritus of soil and gravel brought down from the neighboring mountain-ridges, and on its eastern side by the wind-blown sands, which have accumulated to great depths — along the flanks of the hills which form the first barrier to the currents brought along by the prevailing west winds that sweep its surface. The difference of level between the mud plain and the present surface of Salt Lake is so‘slight that its determination by barometrical measurements must be received with some reserve. The elevation of the southwestern ex- tremity, near Redding Spring, as determined by barometrical observations, is 4,256 feet, or 56 feet above Salt Lake; but it is probable that a rise of 20 or 30 feet in the waters of this lake would submerge almost. the entire surface of the Lower Quaternary deposits. As might naturally be expected from the composition of the mineral contents of the waters of Salt Lake, the salts which impregnate the soil of. the Desert consist mostly of chloride of sodium; the surface incrustations of this mineral are sometimes of sufficient thickness to-form beds, notably : . i ’ q ; r 2 , { ; THE GREAT DESERT. 467 at the eastern base of Pilot Peak, just beyond the western limit of Map III, where the accumulations of crystals of common salt cover the surface to a depth of several inches over an area of many square miles. Some of the ordinary surface incrustation was taken from the desert to the west of White Rock Pass in the Cedar Mountains, and subjected to chemical analysis. It contained 97.43 per cent. of soluble matter, which gave by analysis: Se re i Rey. 39.06 39.28 sh AROSE NS 8 aE So A ad a ee trace trace mere ee Hepiti Mite 38 one 0.10 0.09 Win Ouimepeeee er eee ene a 60.31 60.49 SullpmaGerd elds Nanas se yan = = Ss 0.18 0.17 99.65 100.03 or, combined theoretically: Ghiondesotesodmm 52222554. 5. 99.37 99.68 poulpphatenotalimer 86. Soe % ooo ee 0.24 0.22 JDBRGESS = 8 oe Claes etna eee BERENS ie SO,, 0.04 NaO, 0.09 99.65 99.99 A chemical examination was also made of the ordinary desert soil. The material analyzed was obtained from near the Dugway Station on the old Overland Stage Road, about 25 miles south of the limits of the map. That taken from the surface, an exceedingly fine, almost impalpable powder of a light brownish-gray color, known in the West as ‘alkali dust”, was treated with warm water; only 0.5 per cent. of the mass was found to be soluble. This gave, on analysis: IDIING, « cid. epics erie ce Re ea es an ana ee ar aa 31.22 30.87 NLS y/SAE CRNA eS ee ee earn en 1.84 2.41 S00 2a ee eee IE ANOS Sens Nth 9.54 9.20 SUL bOI: CGC] SR ae er ss eee ea 45.60 45.48 Chlorine a= set eee eee 9.78 10.81 —_>— —_—_—— 97.98 SIO ACs 468 DESCRIPTIVE GEOLOGY. which, theoretically combined, give: Sulphate of lime.....-.----- Be tamatet 75.85 14.93 Sulphate of magnesia... _. 2.22.22. 1.49 2.01 Chioride of sodium 2. 2-22. = - Bares 16.10 17.71 Chloride of magnesium =e eas se= ee 3.16 3.00 ixeess .6 220. bee Shane .. NaO,0.84 MgO,0.63 97.44 98.28 A quantity of the soil was taken at the same locality from a depth of 2 feet below the surface, which presented the same appearance and texture as the former, but yielded, after digestion with water for a considerable length of time, 4.83 per cent. of soluble salts of the following composition: Lime, 2.2 Slag eet 3.84 3.76. Mapnesiaa == eee CLUS EEO Niles LNA nen 7 Ut 0.63 Soda iat ieee Retort enc chs S456 ase Pothssan. 20.2 eee eee ee oy een trace _— trace | Sulphuric acid. = /42 522.50 222 22 oe 7.21 Chliorine®). 222. 5 ere ae Pees Se ASVH2IS 52.37 Oxyaeniequiv.S Ose ee ee ee eee 0.14 - 0.12 99.01 98.97 of which the theoretical composition would be: Chloride of odiums =n Gs =eeemeee - 86.61 86.33 Sulphate fof slimes) ee eee 9.32. alt, Sulphate of amaomesiqme) 37 =e eee eva 1.90 Sulphate: ot (sodlay yee ane ee teat 1.05 Hxcess of sodium ee © O06 S058 99.01 98.97 CHAP T HR FV. NEVADA PLATEAU. Section I.—IBENPAH MOUNTAINS TO RUBY VALLEY—IntTRopuctory— IBENPAH MOUNTAINS—WACHOE MOUNTAINS—ANTELOPE HILLS AND SCHELL CREEK RANGE—EGAN RANGE—RUBY GROUP—FRANKLIN BUTTES. Section I1.—OMBE MOUNTAINS TO EAST HUMBOLDT RANGE— OmpE MOUNTAINS — PEOQUOP AND TOANO PASSES—GosI-UTE RANGE— PEOQUOP RANGE—LITTLE CEDAR MOUNTAINS. SEction I!I.—GOOSE CREEK HILLS TO TUCUBITS MOUNTAINS—GoosE CREEK HILLS—TOANO GROUP—FOUNTAIN-HEAD HILLS—TUCUBITS MOUNTAINS. SEcrion IV.—EAST HUMBOLDT RANGE—REGION souTH oF FREMONT’S PASS— REGION NORTH OF FREMONT’S PASS—PLIOCENE AND QUATERNARY FORMA- TIONS—WHITE PINE MOUNTAINS. Section V.—DIAMOND AND PINON RANGES—DiAmMonp RANGE— PINON - RANGE—PALA0ZOIC FORMATIONS—VOLCANIC ROCKS—DIXIE GROUP REGION— PLIOCENE FORMATIONS—ROBERT’S PEAK—WAHWEAH MOUNTAINS. Section VI.—CORTEZ RANGE—TENABO PEAK REGION—AGATE PASS REGION— CORTEZ AND PAPoosrE PEAK REGION—PINE VALLEY PLIOCENE—REGION OF THE CLURO HILLS—PALISADE CANON REGION—REGION OF THE CARLIN PEAKS. SEcTION VII—REGION NORTH OF HUMBOLDT RIVER—Matiarp HitLts— BonrE VALLEY—EGYPTIAN AND Osino CaANons—ELKO AND RIVER RANGES— SEETOYA MOUNTAINS—NORTHERN CORTEZ RANGE—SQUAW VALLEY REGION— SHOSHONE MESA. : Section VIIL—SHOSHONE RANGE AND CARICO PEAK—NorTHERN SHO- SHONE RANGE—CARICO PEAK. 469 470 DESCRIPTIVE GEOLOGY. SECTION L. IBENPAH MOUNTAINS TO RUBY VALLEY. BY S. F. EMMONS. To the west of the Great Desert is a region of high narrow mount- ain-ridges, with a general trend of north and south, or else invariably a few degrees east of north and west of south. They are separated by broad, nearly level valleys, which present, but in a less pronounced man- ner, most of the arid desolate features of the Great Desert itself. These longitudinal valleys are, however, as compared with the Desert of Utah, relatively narrow, averaging, with a few marked exceptions, in general not more than 10 to 15 miles in width, but occupying a considerably higher level. Their elevation above the sea gradually increases to the west- ward from that of less than 4,300 feet of the Great Desert to over 6,000 feet, measured at the lowest point in the valleys near the centre of the region represented on Map IV. Of these valleys, Ruby Valley, along the east base of the Humboldt Range, is among the most elevated, retaining its high altitude for a distance of over 60 miles. From the desert westward, the mountain-ranges also increase in height and importance as far as the Kast Humboldt Range, a lofty mountain mass occupying the middle of the Nevada Plateau. This range now represents approximately the eastern boundary of all the westward-running waters of the Nevada Basin. To the west of this range, the valleys fall away gradually in altitude until, at the lowest levels of the Nevada Basin, they lie between 300 and 400 feet below the level of the Great Desert. The valleys west of the Humboldt Range contribute to the transverse drainage-system of the Humboldt River, their surfaces sloping upward from the river, both to the north and south, toward the east and west systems of divide, which correspond roughly with the north and south limits of the western half of the map. Many of the yal- leys, but more especially those east of the Humboldt Range, are regions of enclosed depressions, having no present outlet. In the bottoms of nearly every valley are either small lakes of fresh or slightly brackish water, fed NEVADA PLATEAU. ATI by the snows of the neighboring high peaks, or else arid alkaline plains, containing, during the early spring, shallow pools, but dry during the greater part of the year, and frequently covered with incrustations of various salts. The composition of many of these salines will be found scattered through this report when speaking of the locality where they are found. Although all these valleys are marked by the absence of any arbores- cent growth, they are for the most part, unlike the Salt Lake Desert, covered with some vegetation, either one or two species of grasses, or else a stunted development of shrubs and bushes. They present a monotonous, dreary aspect of a dull greenish-gray color, derived chiefly from the Artemisia tridentata, which usually stretches across the wide expanse of the valley. In their geological aspect, they appear equally monotonous, and a Ne description of one would, with but little variation, answer for the many. They are almost entirely covered by Quaternary deposits, made up of both coarse and fine detritus derived from the adjacent ranges, overlying and concealing, over the greater part of the area, the fine, impalpable, arenaceous clays and silts of the Lower Quatenary formation, which is usually only observed in the lowest portions of the valleys or along the banks of streams. Rarely, between the higher ranges, do formations older than the Quater- nary reach the surface, so regular are the upheavals of the older sedimentary beds and so great the accumulations of the overlying detrital matter. Taken together, the ranges of the Nevada Plateau present many fea- tures in common, especially as regards their topographical structure. As - already mentioned, their trend varies but little, showing, as compared with other mountain-systems in the world, aremarkable parallelism, over such wide areas, in the lines of upheaval of the sedimentary ridges. This regularity of structure would be still more apparent, even to the superficial observer, but for the great outflows of Tertiary volcanic rocks, which, occurring along — the old lines of upheaval, have spread out in all directions, concealing the older sedimentary strata. These ranges rise from 2,000 to 6,000 feet above the level of the adjacent valleys, presenting a mildly-serrated ridge, with culminating peaks every few miles. In width, they vary from 5 to 10 miles. In their transverse drainage-systems, and in their broader forms of erosions, making allowances for the differences in geological structure, they show 472 DESCRIPTIVE GEOLOGY. many features that are common to all the ranges of the Nevada Plateau. As regards their geological aspect, however, each mountain-range possesses much that is striking and distinctive, not only as related to their structural and dynamical features, but to the age of the beds exposed and their mode of occurrence. The salient features of each mountain-range will be given under the detailed description of each, beginning with those uplifted ridges that border upon the Great Desert, the Ibenpah and Ombe, and proceeding westward as far as. the Shoshone Range, which lies just to the east of Reese River. . a I tay : ; IsenrpaH Mounrains.—The first elevation to the west of the Desert, at the southern limit of the map, is that of the Ibenpah Mountains, a high commanding range, whose principal summits, just beyond the boundary of the map, attain a probable elevation of 10,000 feet or more. That portion of the mountains within the area of this exploration lies entirely in the Ter- ritory of Utah; the 114th meridian, the boundary-line between the State of Nevada and Utah, running through Deep Creek Valley, just west of the mountains. This higher portion of these mountains, beyond the southeast corner of the map, was not visited, but shows to the east of the crest a body of granite, overlaid by heavy limestone formations. These are seen at the gap through which passes the old overland stage-read, where they show an anticlinal structure, folding over the underlying granite core. The limestones are generally dark-colored, passing from gray to blue, and considerably meta- morphosed, while on the flanks toward the Desert they show some indis- tinct developments of arenaceous beds and quartzites. Mount Horeb, the extreme northern point of the range, is formed of earthy blue and black limestones, dipping 45° to the northeast. In none of the beds were any fossils found by our parties, but from their general lithological resemblance to the Wahsatch limestone, they have been referred to the Lower Coal-Measure horizon, while it is probable that in the lower exposures a careful search might reveal the Devonian and Silurian forma- tions. The lower portion of the eastern slopes of the range toward the Desert e IBENPAH MOUNTAINS. 473 are very long and gradual, occupying a width of 4 or 5 miles in a descent of less than 1,000 feet. On these slopes, the ancient lake-terraces can be traced, from a little distance, with great distinctness, but, owing to the low angle of the slopes, their actual level is difficult to determine at any one point. The highest terrace which could be distinctly recognized stands at an elevation of 800 feet above the desert-level, and is composed entirely of loose gravel material. The pebbles consist principally of limestone, with some mixture of quartzite and granite. In this upper terrace was found no tufa. At the level of 500 feet above the Desert is a very well-defined ter- race of calcareous tufa, filled with casts of recent fresh-water shells of the species common in the Lower Quaternary deposits of the Desert. Of this tufa, an analysis was made by Mr. R. W. Woodward, with the following result: : Sileai its: See es a 840.) 822 JEAN e aD eerie ah Shas ee eearemiy ies 46.38 46.50 ietonie Sic ee sees ees eres Scene Lig, t 3.54 Se, pAtlunmmittea were ee es ey Fa a 1.31 1.20 Soap ora ioe els a O48... 0.54 ofdssae spe tents late ae se en 122 0.21 OCanlhcinG 200. Seas ae ee ee 38.20 38.33 Bhesphouie acids 5: 55. 9 22 ).. trace trace Water........ ee 0 ey ei 1.71 1.62 100.24 100.14 (Silica combined, and as free sand.) A second prominent gravel terrace was found to be only 300 feet above the desert-level. Some ten or twelve distinct lines of intermediate terraces could be observed along the slopes of the range. These heights were all determined by barometrical measurements referred to station-observations at Redding Springs, a group of large pools of tolerably pure water, occupy- ing the edge of the Desert, just east of the stage-road at the base of the extreme eastern slopes of the Ibenpah Range. The valley of Deep Creek is traversed by a stream of Ales name, which takes its rise in the high peaks of the Ibenpah Mountains, to the south of AT4 DESCRIPTIVE GEOLOGY. the map, and flows north, through a gap in the limestone hills, out on to the Desert. In the neighborhood of the settlement, which has an elevation of 900 to 1,000 feet above the Great Desert, is considerable agricultural land, which has been occupied by Mormon settlers. As the stream approaches the Desert, its bed is cut deeper into the soft, muddy valley deposits, and its waters become impregnated with the soluble alkaline salts contained in the soil, which render it unfit to drink. In the spring and early summer, its waters form a shallow lake on the edges of the Desert, which, later in the season evaporating todryness, leave considerable deposits of alkaline salts. They form a thin, brittle crust, resting upon an exceed- ingly fine clay soil, largely derived from the neighboring rhyolites and Tertiary beds. A sample of this incrustation, mixed with some soil, yielded, upon being submitted to chemical analysis by Mr. R. W. Woodward, the — following result : . Do Cian s:s ce ee ree eee Sees eet 16.50 16.37 Soda; ~~. <.c.ne Sse tiie eee ee eee eee 26.47 26.39 Potassaleeeee Pees AoA Dine ces SCN ote Tate 2.55 2.51 Sulphuriciacid= =) Seeen eee eee ecm alae 11.91 Carbomicucid 94. as ee hates 1827 eo tee Chlorine. == 4-442 eee" cane ee: ise eee eee 220 23.14 Boravie acidiot <5. 5 ai See ane nee undet. undet. 99.04 98.68 with a theoretical combination of - SP z Sulphate of potassa.--.-- Ce tie, Oh a ae 4.71 4.63 Sulphate of, soda apes ara eee 17.54 17.37 Sesquicarbonate of soda .......:..-.---- 37.09 oneled Chloride of sodimm 9-2 saan 2 8825, 38.14 Excess-of soda....c. eee ee 1.45 Lad The deposit would appear to consist of an admixture of sesquicar- bonate of soda with a large percentage of alkaline sulphates, and common salt, the usual impurities of the trona of commerce. The large amount of potassic salt present is of considerable interest. The presence of boracic IBENPAH MOUNTAINS. AND .acid was clearly shown. It is probably combined with the excess of soda, as borax. Somewhat similar incrustations are found in the Nevada Basin, and usually in close relation with regions of rhyolitic outflows. It would seem of interest that the occurrence here in Deep Creek Valley has the same geological surroundings. To the west of the valley are long flat Tertiary ridges and narrow stream-beds cut through white beds of fine sands and marls, with some gravelly conglomerates. ‘These beds have a general lithological resem- blance to those of the Humboldt Pliocene, as developed in the valleys of the Upper Humboldt, containing, in particular, a bed of white, very fine- grained material, having a rough feel like a volcanic ash, which is almost identical with some beds found to the north of Toano, and have, therefore, been referred to that horizon, though, as far as our observations extended, no paleontological evidence of their age was obtained. The divide between Deep Creek and Gosi-Ute Valley is a low, rather flat-topped ridge, in which but few outcrops of underlying rocks were found. The evidence of fragments contained in the float shows that it is largely composed of eruptive rocks. These are mostly rhyolites. At one point, however, was obtained a rather singular rock, which has been colored as an andesite. On its weathered surface it has a light mauve color, and resem- bles a rhyolite, but in fresh fracture shows a dark-brown, compact, felsitic groundmass, in which are enclosed small white crystals of plagioclase feld- spar and frequent brown micas, together with hornblende and occasional rounded grains of cracked quartz. ‘The dark-green crystals of hornblende frequently show a zonal decomposition on the outer surfaces. The ground- mass is extremely homogeneous and almost half-glassy. The feldspars, as far as can be seen by the unaided eye, are mostly plagioclase ; while the quartz seems to be an entirely accessory constituent, and the rock has, therefore, been considered to hold the same relation to the normal andesite as the quartziferous trachytes do to the normal trachyte. . In the low hills to the north of Deep Creek Valley, and between it and the Desert, are occasional obscure outcrops of limestones, very much broken and dipping irregularly, associated with isolated flows ofrhyolite. 'Theaccu- 476 DESCRIPTIVE GEOLOGY. mulations of Quaternary detrital material are such that it was impossible to obtain any definite ideas of the structural relations of these beds. Wacuor Mounrains.—To the south of the Gosi-Ute and Peoquop. Ranges, rising out of the Gosi-Ute Desert, lie the Wachoe Mountains, an isolated body of hills of considerable geological interest. In ‘both their topographical and geological features they offer a striking contrast to the long, narrow, north and south lines of Palzeozoic ridges that characterize the surrounding ranges, and show instead an irregular group composed almost entirely of crystalline rocks, which include granites, later diorites, and quartz-porphyries, followed by andesites and rhyolites. Of this group, granite forms all the more elevated portions, and gives the character to the main topographical outlines, and is at the same time the geological nucleus around which, at the southeastern end, is found a body of limestone, while at its base is spread out over a considerable area one of the most interesting outbreaks of Tertiary volcanic rocks of Eastern Nevada. It is an irregular shaped mass some 8 or 9 miles in length, and across its broadest: expanse about 4 miles in width. From the westward, it rises somewhat abruptly, but with even slopes, nearly 2,000 feet above the Gosi-Ute Desert, while to the eastward it is more broken in outline, but falls away with gentler spurs toward the voleanic rocks below. In its physical habit, this granite is of. special interest, as it presents marked differences from all the isolated gran- itic bodies of the Raft River, Ombe, Gosi-Ute, and Peoquop Ranges, which have many points of resemblance, and would appear to belong to the same group. The Wachoe granite is a very compact dense mass, with a com- paratively uniform texture, weathering in rounded forms, but with regular monotonous outlines, all possessing the same gentle curves: it disintegrates slowly, the greater part of the hills showing but little soil and débris. Under the hammer, the rock breaks with great difficulty in irregular-shaped pieces, having a very uneven fracture. The minerals composing the rock show, as far as examined, no tendency to parallel arrangement, and have developed no regular lines of bedding. In color, it is dark reddish-gray, but with somewhat lighter tints on the northeastern spurs and foot-hills. In its mineralogical features, this rock presents many peculiarities, and is marked by a composition as striking as are its outward physical WACHOE MOUNTAINS. ATT characters, and equally at variance with that of most of the other larger granitic bodies, but more especially with those to the north and east. All the normal mineral constituents of common granite are here present, put not in the usual proportions. . Quartz, orthoclase, plagioclase, and mica are the essential ingredients; in addition to these, as subordinate minerals, may be observed hornblende and a few dark specks, probably specular iron but which it would be difficult by the unaided eye to determine, but for the fact that in thin sections, under the microscope, it has been detected inclosed in the larger feldspar crystals. The quartz is present in very small quantities and always in fine grains, with a slightly gray tint. Both mono- clinic and triclinic feldspars are present in considerable proportions; none of them have a brilliant color, but are more or less dull and opaque. A few of the larger crystals, which are frequently a half an inch in length, have a vitreous lustre. Mica plays an important part; it occurs in broad, shining plates, with a fresh, undecomposed appearance; there are also present some flakes of a bronze color, which are more or less altered. - Under the microscope, Zirkel has pointed out the presence of both titanite and apatite, the latter in short thick prisms, and carrying numerous liquid-inelusions, arranged in lines at right angles to the main axis of the crystals, as shown on Plate I, Fig. 8, accompanying his report. The liquid-inclusions of the quartz also carry minute crystals of chloride of sodium, while the larger feldspars hold specular iron. : ‘The Wachoe granite was subjected to chemical analysis by Professor Thomas M. Drown, of Lafayette College, Pennsylvania, with the following result : SLUNGE de Soin Lk el lee el a aera 55.53 ANCONOMMDANS Sc See eee eh 18.65 Memauspomdenme yoo. de eee Asis SSE 6.14 MEMO AMOUSHOSIGOS 2.0 si oo es eee a8 0.17 Winicperrenmernsets eS... wie les oe ee eee ee 5.62 Winierae sine state, 8 Se oe E es ed eae 3.37 POGUE neem are trace trace - Daly s? A 52 sir) ae 2s aes ee ae 8.22 8.13 Maonesiag Jie Pre Borers ieee ae 4.47 4.54 Soda ey eee ccf ee a ten Sie ea eee 3.14% 2 & Potassa:..19¢ S20 Sis ea aes ee L1G 2 eadaliG Waterand carbonicacid)s-2eneee a2) see 0.94 0.98 100.12 99.95 Specific gravity 2.5, 2.6. . It will be seen. that the analysis runs very high in silica; indeed, no basalt analysed from our collection gave so large a percentage. It is cor- _ respondingly low in its specific gravity. Along the east base of Pilot Peak, unrepresented on the map, occurs a small outflow of gray porous rhyolite. . In the Quaternary deposits that surround the Ombe Range, there is but little that is distinctive. On the-east side of Pilot Peak, beyond the long slopes of Upper Quaternary accumulations, occurs a broad level plain, PEOQUOP AND TOANO PASSES. 501 between 6 and 7 miles in width, composed of the Lower Quaternary fine clays and silts which characterize the Great Desert. In the dry season, over the greater part of this area, is found a heavy inerustation of quite pure common salt, derived from the beds below, which are evidently strongly impregnated, if, indeed, they do not carry a stratum of chloride of sodium. If necessary, there is no doubt but that this formation could be made to yield immense quantities of salt. From Pilot Peak, numerous streams run down beneath the débris of the slopes, coming to the surface near the plain in large springs. Many of them are quite fresh, but others, where the waters percolate through the Lower Quaternary strata before reaching the surface, are either brackish or highly charged with salt. At the Ombe Gap, north of the mountains, through which the railroad runs, occur alkaline deposits, consisting of an admixture of chloride of sodium -and sulphate of soda. Proquor AND Toano Passes.—Directly north of the Little Cedar Mountains, Peoquop and Gosi-Ute Ranges, and on a line nearly due east from the termination of the East Humboldt Archean mass, occurs an inter- esting break in the structure of the Paleozoic strata. The Carboniferous quartzites and limestones which form these narrow meridional uplifts are here thrown abruptly into a northeast and southwest direction, accompanied by considerable displacement, causing marked depressions and physical breaks in all three ranges, which may be easily recognized by reference to the geological maps. The railroad company have taken advantage of these gaps in constructing their line from the Salt Lake Basin to the headwaters of the Humboldt River. At Cedar Pass, the beds are much disturbed; at Peoquop Pass, the continuity of strata is broken, and a deep basin lying between the Peoquop Range and the Fountain Head Hills is occupied by Eocene Tertiary deposits; while, north of Toano Pass, the Carboniferous strata strike almost directly across the trend of the Gosi-Ute Range. The Tertiary deposits which occupy Peoquop Pass extend in an east and west line for a distance of 8 miles, and rest unconformably upon the steep flanks of both sides of the gap. ‘They strike northeast and southwest, and dip both to the north and south at angles varying from 6° to 15°. The railroad-cuts and stream-beds expose a series of fine carbonaceous 502 DESCRIPTIVE GEOLOGY. shales, marls, fine sandstones, and thin paper-shales. Thin, red, compact sandstones form the overlying beds, passing down into hard, red marls and shales, underneath which are more sandstones, banded red by oxide of iron, and in turn underlaid by finely-laminated gray shales, with thin beds of indurated clay. The peculiar carbonaceous zones, as well as the paper- shales, so closely relate these to the Elko shales that they have been referred to the Green River Eocene series. No organic remains of fish or insects, such as characterize the Elko beds, were obtained here, and the reference rests entirely upon lithological resemblances. Overlying the upturned Tertiary beds are others approximately hori- zontal, and made up largely of comminuted volcanic material. They appear to extend westward across the valley, and to form the divide between the. Gosi-Ute Desert and Thousand SpringValley, stretching south- ward as far as Toano Pass. At the pass, the depression is occupied ~ by the latter deposits, mainly lavender-colored pumice-like beds, exceed- ingly friable, but distinctly bedded, and composed largely of rhyolitic, sili- ceous, and feldspathic material, in which are some sandy, earthy seams re-arranged and deposited under water. The town of Toano lies directly upon these Pliocene strata, and the more favorable beds are used to advan- tage for building purposes. The rock appears to harden upon exposure. Gosi-Urre Ranez.—This range extends from Toano Pass southward to Mount Pisgah in an unbroken line of upheaval, with an almost true north and south trend. As thus limited, it measures about 65 miles in length, a narrow ridge scarcely averaging 6 miles in width. It presents the first long, continuous range west of the Great Desert, and forms the bound- ary of that great depression, its long slopes rising gradually above the plain on the eastern side, but falling away much more steeply on the other toward Gosi-Ute Valley, which lies 1,300 feet above the level of the desert. The range is one of extreme dryness and nearly barren of vegetation, there being but little soil either on the slopes or in the basins, while arborescent growth is confined to scattered dwarfed pines and stunted mountain-mahog- any (Cercocarpus ledifolius). Geologically, the Gosi-Ute Range is made up of granites, quartzites, and limestones; all the beds of the latter formations being referred to the GOSLUTE RANGE. 503 Carboniferous age. The granite formations of the range occupy a very small portion of the area, and were observed with certainty in but two localities, one a mere outcrop in Toano Pass, and the other a much larger body in Middle Pass. The Middle Pass granite is an irregular-shaped’ mass, and, like the granite from the Ombe Mountains, extends across the range from valley to valley. It lies depressed between two large quartzite masses, portions of the great quartzite formation of the range, referred to the Weber beds, which, within short distances, tower above the summit of the pass, both to the north and south, at least 1,500 or 2,000 feet. On the west side, the granite rises only from 500 to 600 feet above the Gosi-Ute Valley, has a smooth, rounded summit, and falls toward Tecoma Valley, 1,500 feet below, in long, gentle slopes. This granite is coarse-grained, with a loose friable texture and a light-gray color. The constituent minerals show no order in their arrangement, and the rock appears to possess a normal granitic structure. All the ridges, outlying masses, and drainage- basins have gently curved and rounded outlines, sub-aérial action develop- ing scarcely any sharp lines. The outcrop of granite mentioned as occur- ring in Toano Pass is found in the ravines north of the railroad, on the eastern slope, about two or three miles northeast from the town of Toano. So far as observed, it closely resembles the Middle Pass rock in physical habit and mode of disintegration, and is chiefly interesting from the indica- tion that it offers of a continuation northward of the same body of granite. Between Toano and Middle Pass, the range is formed of the Weber Quartzite and the overlying Upper Coal-Measure limestone. Directly north of Middle Pass, the highest hills are of quartzite, but beyond, the summits are all capped by the limestone. South of the Toano Pass, the high group of hills forming the east half of the range are also formed of heavy beds of bluish-gray limestone, dipping 30° to the east, and striking about north and south true. Near the west base of this series is a quartzite band, about 250 feet in thickness, which conformably underlies the main body of lime- stones. Underneath this again is a further development of limestone, whose thickness cannot be determined owing to the overlying Quaternary deposits. In the canon of Owl Valley, the rocks are mostly quartzite, apparently dip- ping east, and underlying the limestone body. 504 DESCRIPTIVE GEOLOGY. The quartzite mass, already referred to, north of Middle Pass, like the granite, stretches across the entire width of the range. It is distinctly bedded in heavy broad masses, striking north 34° east, with a dip to the southeast. This quartzite is mainly white, with bands showing both bluish and grayish tints, and also carries beds of almost black quartzite. It appears to be made up of both large and small quartz-grains, metamor- phosed and compressed into a dense compact rock. Many of the large grains are white and clear, while others appear to be flattened into thin flakes and sheets of quartz, with a decidedly schistose structure. Under the micro- scope may be seen minute flakes of white silvery mica, sometimes aggregated in layers; in the quartz are numerous fluid-inclusions. A small percentage of iron frequently colors the rock shades of brown and red. South of Middle Pass, for a long distance, quartzite forms the main ridge, with the limestone overlying upon the flanks. In the region of Pine Mountain, where best observed, the limestone, of a light bluish-gray color, occurs dipping steeply to the westward. Near the summit, the following Coal-Measure species were collected : Spirifer opimus. Athyris subtalita: At Lookout Mountain, the culminating point of the range, which at- tains an altitude of 9,645 feet above sea-level, occurs an immense develop- ment of limestone. ‘There are represented here between 3,000 and 4,000 feet of conformable strata, heavily-bedded, compact, blue limestone, with escarp- ments and walls varying from 30 to 100 feet in height. From Dondon Pass to the peak, the strata dip to the southward at an angle of 9°; along the main ridge of the peak the dip is 13°, and on the summit 9°. From the top of the mountain southward, there is a tendency to an anticlinal axis, and the beds which form the summit due west from Lookout Mountain dip sharply to the southwest. : The outlines of the limestone body to the northward and its exact rela- tions to the quartzite formation were not worked out. The limestone has, however, been referred to the Lower Coal-Measure series of the Wahsatch limestone, partly on account of its great thickness, partly from its litho- a ee PEOQUOP RANGE. Bay 0)5) logical resemblances, and in part to its relation to the other bodies of lime- stone in the adjacent regions. No organic remains that were capable of specific determination were collected; highly-altered specimens of Productus, associated with crinoidal stems, occur here, but of no special importance. Mount Pisgah is a sharp, narrow, somewhat isolated limestone ridge south of Dendon Pass, whose beds resemble in lithological character those of Lookout Peak; their structure being that of an anticlinal fold, with a north and south axis, whose eastern member has been partly eroded. On the western foot-hills is a development of finely-laminated slates consti- tuting part of the western fold, the entire structure being apparently in conformity: with that of Lookout Peak. Our examinations at this point were extremely brief, and no fossils were found. By reference to the lower section, upon the geological sheet, the position of Mount Pisgah and its anticlinal structure will be readily seen. Preoquop Rancr.—This range lies upon the west side of the Gosi-Ute Valley, and in many of its physical and geological features is almost a counterpart of the Gosi-Ute Range. As it rises, however, between two broad desert valleys of nearly equal elevation, it presents from the eastern side a much less bold and prominent appearance than does the Gosi-Ute Range. Its trend is almost due north and south, with a length of 52 miles, and is for the greater part of this distance even narrower than the range on the opposite side of the valley. It attains its culminating pomt in Spruce Mountain, which reaches an altitude of 10,400 feet above sea-level. Other prominent peaks are Grand Peak, 8,300 feet, at the southern end of the range, and at the northern extremity Orford Peak, 7,556 feet. This range is one of extreme dryness, only one creek of any consider- able leneth being known, and but few small obscure springs. As the strata along the northern end of the range for the most part dip easterly, there are along its eastern base numerous springs and ponds coming to the surface on the desert, just beyond where the strata pass under the valley-deposits. Along the great freight-road which runs from Toano southward, near the Peoquop foot-hills, a number of wells have been sunk in the desert Qua- ternary, yielding, after passing through sandstones, sandy shales, and clays, good water at a depth of 80 to 100 feet. 506 DESCRIPTIVE GEOLOGY. Geologically, the uplift embraces granites and Archean schists, with the southern portion of the range consisting of Carboniferous limestones referred to the Wahsatch beds, and the northern portion of the range made up of quartzites and overlying limestones, regarded as equivalent to the Weber Quartzite and the Upper Coal-Measure limestones. In the region of Spruce Mountain, subordinate intrusions of diorites and porphyries appear through the limestones, crumpling and displacing the strata and complicating its structure. ' In this range, granite is only known in one locality, at Holland Pass, and, like the similar occurrences in the Gosi-Ute and Ombe Mountains, occu- pies a low position or depression across the main trend of the uplift. At Holland Pass, the range reaches its narrowest dimensions, the granite appa- rently serving as a connecting link between two broader and more elevated masses of Paleozoic strata. It is barely two miles across the range from Gosi-Ute to Antelope Valley, with an elevation of not more than 500 feet above the Quaternary deposits. In its lithological character, as well as in its position, it closely resembles the granite bodies already mentioned in the Ombe Mountains and Gosi-Ute Range, which is all the more interesting, as it differs so widely from the granite mass of the Wachoe Mountains. In a narrow ravine, on the east side of Spruce Mountain, occur out- crops of mica schists and slates, which probably belong to the older crys- talline series. Their geological relations are quite obscure, and it would seem impossible, at least from present observations, to connect them with any series of beds in this region, as they are so isolated from other rocks of like character, and their outcrops cover such a limited area, but their physical and mineralogical habit is such as to suggest their Archean age. At the same time, it may be stated, that they seem to be more closely related to the crystalline schist series of the Humboldt Range, from which they are only separated by a broad open valley without any intervening uplift than to those of any other large body of crystalline rocks in Western Nevada. These schists and slates are all very distinctly bedded and finely laminated. A characteristic specimen in the collection of this slate represents a rock of a silvery-white color, and consisting of fine grains of white quartz and q PEOQUOP RANGE. 507 minute flakes of mica. The mica consists of both the dark magnesian biotite and white muscovite. Under the microscope, Zirkel detected numerous crystals of zircon, which he has shown to be so abundant in the Archzean series of gneisses and schists along the Fortieth Parallel; and the biotite plates, but not the white mica or quartz, contain exceedingly minute microscopical needles, which he suggests may possibly be referred to the same mineral. Other beds are somewhat coarser in texture, less compact on account of the quartz- grains being larger, and the dark mica more abundant, with broader plates, rocks more closely related to what are usually designated as schists. The observed area of these beds is exceedingly small, and has not been indicated on the geological map. It is possible that more careful field-study would discover anumber of such areas and would indicate clearly a much larger Archeean territory along the base of the mountain, and perhaps show an important Archzan foundation for the striking uplift of Palzeozoic strata. The entire northern end of the Peoquop Range would appear to con- sist of Weber Quartzite, overlaid by Upper Coal-Measure limestone. No estimate of the thickness of this quartzite was made, but it is at least several thousand feet, forming many of the higher summits and spurs. In places, it is capped by fragments of limestone, while, in others, the overlying rock may show a very great development. Directly south of Peoquop Pass rises a series of limestone hills with a strike varying from north 30° to 40° east, and dipping to the northwest at an angle of about 40°. There must be exposed here about 2,000 feet of limestones, which are conformably underlaid by heavy masses of quartzite, which are supposed to continue to the eastern foot-hills. ‘The same masses of limestone which dip northwest curve around, and form the hills on the west side of the range. In the limestones south of the pass, not far above the quartzites, were obtained Carboniferous fossils, among which were the following: Productus semireticulatus. Spirifer cameratus. Discina, sp. undet On the east side of the range, Squaw Creek from the summit to the 508 DESCRIPTIVE GEOLOGY. mouth of the canon passes through quartzite. On the summit of Orford Peak rests an isolated body of gray limestone from 150 to 200 feet in thickness, thinning out to the northeast, all but this small fragment having been eroded. Beneath this limestone occurs a thin bed of dark, steel-gray quartzite, which, in turn, is underlaid by a somewhat coarse conglomerate filled with flint nodules and pebbles, and resting directly upon the massive quartzite. These beds strike north 28° to 30° east, and dip at an angle of 30° to the northwest. . Large numbers of fossils were collected from this limestone, and the following species, among the Brachiopoda, have been recognized: Orthis carbonaria. Productus semireticulatus Productus punctatus. Productus Nebrascensis. Productus longispinus. Spirvfer cameratus. Athyris subtilita. Athyris. Roissyi. Associated with them are corals belonging to the genus Campophyllum. A characteristic feature of the Carboniferous limestone of the northern end of the range are the interstratified beds carrying nodular concretions and fragments of flint, and black bands of siliceous cherty rock, with an exceed- ingly fine-grained texture, and a rough irregular fracture. They usually are marked by narrow bands of chalcedony, and give, when treated with acid, a slight reaction for carbonate of lime. Directly north of Holland Pass occurs a body of Haein forming the higher summits of the range, which has been but little studied, and, although its relation to the great quartzite body has not been observed, it is provisionally regarded as underlying it, and has therefore been referred to the Lower Coal-Measure series of the Wahsatch limestone. A recorded strike on the summit gave north 30° west, with an easterly dip. South of Holland Pass, the range consists of nearly parallel ridges trending a few degrees west of north and east of south, that is, obliquely to the main trend of the uplift. * 7, PEOQUOP RANGE. 509 The formation, like that of the southern end of the Gosi-Ute Range, consists of limestone, and has, in like manner, been referred to the Lower Coal- Measure series. ‘The prevailing dip is westerly, and along the foot-hills, which rise above Gosi-Ute Valley, varies in angle from 8° to 40°. Heavily- bedded, dark-gray strata, many of them highly siliceous and seamed with calcite, characterize the hills; interstratified between them are frequent layers of calcareous and cherty shales and thin beds of quartzite. A highly siliceous limestone, from the slopes of Grand Peak, on being submitted to analysis, yielded Mr. B. E. Brewster the following: Insoles resiaire ye yeis 2 See ttyes Sir me ep ee Pa 34.912 Alumina Seer ee 0.386 Ferric oxide JASONS) 3 Se Bye MR EN he A fee de a 34.333 Meee sicnes ees este rete cone). CA EIN Een 2 Be 1.116 FC AE OMNC: ACI Clenae serene ERE NES a ole ak 27.769 os nonicnacide ne ahr etna eens Mite ol trace NWiabereerer meee are mle P kek hb inte te TP UERAE SNA) SENSE 1.249 99.765 This indicates a carbonate of lime with 2.34 per cent. of carbonate of magnesia. Of the 34.912 of insoluble residue, 31.51 per cent. consisted of silica, Organic remains of Brachiopoda, crinoidal columns, and fragments of stems and roots, highly metamorphosed, in general too poor for specific determinations, are abundant throughout the region, but only the two fol- lowing forms have been recognized : Athyris subtilita. Fusilina cylindrica. But for its intimate topographical and geological connection with the extreme southern end of the Peoquop uplift, Spruce Mountain, with its long ridge stretching to the northward, might almost be regarded as a separate range. As it is, the mountain, one of the loftiest in this region, presents, for a limestone summit, a striking appearance, rising steeply for nearly 4,000 feet above Butte Valley, and again falling away abruptly in the opposite direc- SOs DESCRIPTIVE GEOLOGY. tion. Like the lower end of the main range, it consists chiefly of heavy limestone strata, which have been referred to the Lower Coal-Measure group. In its geological features, Spruce Mountain shows a very com- plicated structure, but in general would appear to be an anticlinal fold, the eastern side forming a synclinal with the beds of the main range. The occurrence of mica slates and schists would indicate that the beds rested directly upon an Archean foundation, while the crumplings and plications of strata, with their local displacements, are rendered still more complex by the intrusion of both small and large bodies of diorite and feldspar-porphyry, the more prominent ones only being represented on the map. From these crystalline rocks, the Paleozoic strata incline in all directions, with abrupt changes in both dip and strike, showing that their present position is largely dependent upon the intrusive bodies. On the southern point of the high ridge, the strata strike northwest and southeast, and dip easterly. On the saddle between the peaks, a diorite body disturbs the original position of the beds; but, on the northern and higher peak, the beds strike north 8° to 12° west, apparently at a slight angle obliquely to the trend of the uplift. The dip is about 15° to the eastward. Northwest from here, and about 2,000 feet below the summit, occurs a large feldspar-porphyry body, to the west of which the strata mainly dip westerly, and from there northward to Blue Point Spring occur a number of minor folds and flexures. At Crawford Pass, a well-marked anticlinal fold in the hard siliceous limestone occupies the ridge, which is here not much more than 600 feet above the valleys. The axis of the fold strikes obliquely across the trend of the ridge, the beds upon each side dipping away at about an angle of 15°. No measurement of the thickness of the Spruce Mountain beds was made, but it would seem highly probable that there are at least between 2,000 and 3,000 feet of Wahsatch limestone represented. Lithologically, the formation shows the same habit as characterizes the beds in other places, that is, heavily-bedded limestones, more or less siliceous, with occasional layers of calcareous shales and fine bands of quartzite. On the west face of the mountain, cropping out in several localities, occurs a well-marked bed of hard, black slate, carrying cubes of pyrites. A recorded strike gave north 25° west. PEQUOP RANGE. 511 All the palzeontological evidence obtained would go to show that only the Lower Coal-Measures were represented. It is by no means improba- ble, however, that a further search of the lower horizons may prove the existence in the uplift of both the Sub-Carboniferous and Devonian members of the Wahsatch limestone. From the summit of Spruce Mountain, the following forms were col- lected : Productus costatus, Productus seméireticulatus, — Productus Nebrascensis, Eumetria punctulifera ; from the ridge north of Spruce Mountain, and from a number of other localities, were obtained : Productus Nebrascensis, Fusilina cylindrica, crinoidal columns of large size, small disks of pentangular columns, together with slender forms of an undetermined , Trematopora ; on the ridge near Blue Point Spring were found large numbers of Fusilina cylindrica. The Spruce Mountain diorites observed are usually small, irregular bodies or narrow dikes. On the summit between the two prominent peaks occurs one that may be considered typical. It is a fine-grained dark rock with no large crystals, but made up of long, slender, black hornblendes, with both monoclinic and triclinic feldspars; the latter evidently predomi- nating. The largest body of feldspar-porphyry is found on a saddle of the ridge northwest from the high peak. It is an exceedingly compact, tough rock, breaking with an angular fracture. In color, it is brownish- gray, spotted with incrustations derived from iron minerals, which give it a somewhat dirty appearance. Macroscopically, the only minerals that are distinguishable are a few rounded grains of translucent quartz and frag- ments of feldspar imbedded in a felsitic groundmass. Under the microscope,’ 512 DESCRIPTIVE GEOLOGY. the groundmass reveals no new constituents, but a purely spheerulitic structure, a detailed description of which will be found in Professor Zirkel’s -report, showing in an interesting manner a close analogy existing between these rocks and the Tertiary rhyolites. And yet while this microscopical analysis presents much that suggests such a comparison, no practiced field- lithologist would ever mistake it for a late eruptive rock. This region of Spruce Mountain forms a mining district, which, if not of great economic importance, possesses much that is of interest from a geological point of view, and worthy of detailed study. As the limestones have undergone considerable displacement and fracture, dependent upon the intrusion of crystalline rocks, so, in like manner, most of the ore-deposits show an intimate connection with both formations, usually occurring in the former, in close proximity with the latter. In places, they are found in seams and irregular breaks in the beds; at others, lying between the strata, and again as contact bodies between limestone and porphyry. All the ores would appear to be secondary products, such as carbonates and sulphates derived from the decomposition of galena and related minerals. Galena, although found in small masses, is not abundant; wulfenite occurs sin small quantities. | Lirtte Cepar Mountains. Ths group of mountains lies midway between the Peoquop and Humboldt Ranges, and may be considered as a continuation southward of the Fountain Head Hills, connected by Cedar Pass. They rise abruptly above the valleys, and form but a small group nearly 12 miles in length by about 10 in width; the highest summits attaining an altitude of between 2,000 and 2,500 feet above the valley. Albion Peak, the culminating point, lies 8,391 feet above sea-level. ‘The summits and higher slopes are well covered by a fair growth of coniferous trees, but the mountain mass is exceedingly dry, no stream being known, and probably not even a running spring. But little opportunity was afforded for its geological study with any detail, and only the main features were gathered. Hnough, however, was seen to recognize that the same geological horizons that are developed along the northern end of the Gosi-Ute and Peoquop Ranges re-appear here with the same characteristic structural and lithological behavior; that is, the LITTLE CEDAR MOUNTAINS. 513 range appears to be made up of beds of massive quartzite, occupying the central portion of the mountains overlaid by dark-blue limestones, the latter frequently appearing only in small patches on the flanks and ridges—frag- ments left by erosion. The general trend of the strata is north and south. _ Along the east flanks of the mountains, limestone is the prevailing forma- tion, dipping at varying angles from 10° to 22°, passing under the Qua- _ ternary valley, and apparently forming, with the west side of the Peoquop Range, a synclinal fold. Here were found crinoidal columns and fragments of bryozoans, together with Productus subhorridus. In a very similar limestone on the west side of the mountains, but dip- ping west at angles of 18° and 20°, were found the following Coal- les forms: Productus Prattenianus. Athyris subtilita. Syringopora multattenuata. Chaitetes, sp. undet. On the summit of the ridge just north of Albion Peak occurs a body of highly-altered limestone, which, but for a small amount of fine quartz- sand, has almost the theoretical composition of dolomite. It is a firm, com- pact rock, of a bluish-gray color. Mr. B. E. Brewster, on subjecting it to chemical fal ye found the following constituents : Silty pers. 0). ie ee eee ees 4 2A Alummumacameererric OXIde - 0.2 ....0. 2 0.274 ILMOR 5 obs 2 Sia A ee ee ete Ue pe ene 30.387 MAYORS), psc, 2 eee RIE tia le ke ag gs eer 20.069 Garhomiceaciae: 452. -. SE ae Sve Ma pee ua San Bee eee 45.726 EVRA RC Ie eoea rime ote pie tanya te yams eieaan Sie be ene a eR Yeu 1.708 - 100.278 33 D G 514 DESCRIPTIVE GEOLOGY. All the magnesia calculated as carbonate and the lime for the remain- ing carbonic acid gives: Carbonate of magnesia... 9.) 2 5- .eee 42.14 @Carbonate.ot Lime: Mass. ee eee eee eee 53.15 ixcess of limes: +22 eee Se ees Coming out at the base of the limestones, along the east side of the mountains, are a number of both hot and cold springs, running a large amount of bright clear water. They leave no saline incrustation, and to. the taste would seem to be comparatively free from mineral ingredients. GOOSE CREEK HILLS. 5lo SECTION III. - GOOSE CREEK HILLS TO TUCUBITS MOUNTAINS BY S. F. EMMONS. Goosr Creek Hitis.—This name hasbeen giventoa group of hills which lie directly north of the Ombe Mountains and form the southern continua- tion of a high range of mountains of the same name, extending north into Idaho, beyond the limits of the map. Immediately north of the hills, as represented on the map, extends a north and south ridge, having a general anticlinal structure, made up largely of white, close-grained quartzites, with blue and white, fine-grained, siliceous limestones. These rocks of the range show evidence of considerable metamorphic action and a large devel- opment of vein-material. The quartz veins have a general north and south trend, often being traceable for 6 or 7 miles, with a thickness of as much as 6 or 8 feet. In several localities upon the east side were found a new and undescribed species belonging to the genus Fusilina, associated with a poorly-preserved Productus, proving clearly the Carboniferous age of the limestone, while the quartzites have a general lithological resem- blance to those of the Weber formation. That portion of the hills which is included within the limits of the map is principally covered by rhyolite flows, beneath which are obscure outcrops of limestones, which have been referred to the Upper Coal-Measure group. The rhyolites present a great variety of texture and composition, and con- stitute a very interesting group of rocks. In an interior valley of the hills is an outcrop of granite-porphyry, showing a dome-shaped mass, only exposed in the lowest points of the valley. It is a greenish-gray rock, showing large erystals of pink-white orthoclase imbedded in a greenish-gray mass, made up of decomposed hornblendes in a gray felsitic groundmass. Under the microscope, the groundmuss is seen to be made up of hornblende, orthoclase, plagioclase, and quartz. The larger feldspars are altered into an opaque mass, in which, in some places, traces are seen of a former triclinic striation. *. 516 DESCRIPTIVE GEOLOGY. In some of the decomposed feldspars are colorless acicular crystals, which may be muscovite. The hornblende is remarkable for presenting, as a pro- duct of decomposition, black, opaque, angular grains like magnetite, which do not, however, occur in the fresher hornblendes. This body of granite- porphyry is immediately overlaid by calcareous shales. To the east of the valley is a broad, table-shaped ridge, made up of flows of rhyolite, showing great variety in structure and composition. The main flow is made up of a grayish-white rhyolite, which has a rough tra- chytic feel. It consists of a very porous felsitic groundmass, in which can be distinguished only a few scattered crystals of free quartz, and long, thin sections of tabular crystals of feldspar, often showing a very beautiful twin development. The groundmass, examined closely, has a porcelain-like appearance. Under the microscope, it is seen to be a mixture of transpar- ent polarizing particles and dull yellowish-gray bodies. Adjoining this rock on the east is a porphyritic rhyolite of reddish-purple color, still of somewhat porous texture, containing large crystals of quartz and sanidin, the former of which show frequently perfect pyramidal points; likewise no hornblende or mica. Under the microscope, the groundmass is seen to con- tain fibrous spheerulites, often as much as half a millimetre in diameter, which sometimes have a feldspar crystal in the centre. It also contains tridymite. To the eastward, these rhyolites pass into distinctly hyaline varieties, or pearlites. The first is a grayish porphyritic-looking rock, con- taining large grains of quartz the size of a pea, and very glassy sanidins, together with considerable hornblende and mica, in a gray pearlitic, and ‘somewhat granular groundmass. Under the microscope, the evoundmass is seen to be made up of imperfectly dihexahedral quartz, sanidin, plagio- clase, brown biotite, some yellowish-green augites, a few brown hornblendes and magnetite, together with pale yellow microlites, which are doubtless augitic. Both quartz and feldspars contain plentiful glass-inclusions. The mass between these ingredients shows an interesting arrangement of micro- lites, which appear to flow around the crystals, as will be seen in Volume VI, Plate X, fig. 2. The most remarkable of these hyaline rhyolites forms low rounded hills on the extreme eastern slopes, toward Surprise Valley. q é | ; TOANO GROUP. 517 It is a dark-gray, almost black, pearlitic mass, containing crystals of sanidin and quartz, with a large development of reddish spheerulitic grains, which, when broken, are seen to be made up of concentric layers of sphzrulitic material of a dull resinous lustre, often enclosing a nucleus of glass, quartz, and feldspar. Toano Grour.—To the west of the Goose Creek Hills is a broad valley, narrowing rapidly to the northward, called Desert Gap, through which runs Passage Creek, a stream carrying the drainage of Thousand Spring Valley and the mountains to the north out into the desert country. To the west of the gap, the Toano Group forms an irregular mass of hills, a continua- tion northward of the Gosi-Ute Range, and separated from it by a low broad pass, known as Toano Pass, through which the railroad runs. The Toano Pass cuts the range at a poimt where the axis of upheaval has suf- fered an abrupt curve. That part of the range south of the pass has a strike nearly true north and south, which it maintains up to the pass, north of which it forms roughly a semicircular ridge, the strike of the beds fol- lowing the curve of the ridge. Between this pass and Ives’ Pass, 5 or 6 miles to the northward, the hills form a somewhat isolated group, showing an interesting structure, with Fairview Peak both topographically and geologically the central point. On the northeast side of this ridge, the beds strike north 5° to 10° east, at Fairview Peak north 30° east; while on the west side they strike north- west. The beds form an anticlinal fold, the axis occurring in the Weber Quartzite along the south slope of the hills, conformably over which lie heavy beds of blue and gray limestone. The high hills north of Toano are formed for the first 1,200 or 1,500 feet of Weber Quartzite, and then 800 or 900 feet of limestone, the latter forming the summit of the ridge, and the north side of the anticlinal axis. Fragments of limestone, which represent the southern half of the anticlinal fold, are found along the extreme foot- hills of Toano Pass, with a steep dip, reaching in places 60°. It is evident that both sides of the anticlinal have suffered a fault, and that the southern member, including both quartzite and limestone, has been depressed several hundred feet. On the opposite side, the Coal-Measure limestone also shows 518 DESCRIPTIVE GEOLOGY. a fault of between 200 and 300 feet, and a ‘considerable compression of strata, the beds occurring along the inside of the curved ridge, where they — are found as a synclinal fold. By reference to the upper section at the foot of the geological sheet, this synclinal structure is shown, with the Weber Quartzite underlying the limestone. Interstratified in.the limestone near the summit of the ridge occurs a dark-brown cherty band. From this stratum, as well as both from the over- lying and underlying limestone, large numbers of organic remains may be obtained, but without any great variety of species. From the cherty band, the following Brachiopoda have been recognized: Productus Rogerst. Spiriferina pulchra. from the limestone, in addition to the above species : Productus Nebrascensis. Streptorhynchus crassus. Among Bryozoa, occurs an undetermined species of the genus Cascinmium. North of Ives’ Pass, the hills rise in rounded masses, stretching to the northward for 15 miles, before again disappearmg beneath the Quaternary deposits. The strata indicate considerable folding and crumpling, and the structure is much obscured. Just north of Ives’ Pass, the prevailing dip would seem to be to the eastward, while in the northern end it seems to be. - in the opposite direction. South of Montello Creek, along the foot-hills, the beds dip 3° east. The beds, so far as examined, are mainly limestones and calcareous shales, and have been referred to the Upper Coal-Measure series. No fossils were found in them. In these limestones are frequently seen beds and irregular bodies of bluish-black cherty matter, traversed by thin white seams of silica; the rock breaking with a rough, jagged frac- ture. Very similar rock appears to characterize the limestone in many localities, but its exact geological horizon was not clearly made out. _ On the western wall of the Desert Gap, at the extreme northern end of the map, is a development of a remarkably interesting rhyolite, of a deli- cate purplish-gray color, which, on the larger surfaces of fresh fracture, has a wavy, lace-like structure. It is full of druse-like cavities lined with THOUSAND SPRING VALLEY. - 519 minute erystals of quartz. The groundmass shows stripes and bands of darker and lighter material, which encircle in wavy lines these druses, and the sanidins and quartz. Small crystals of free quartz and feldspar are visible throughout the mass. Some portions of the rock abound in com- paratively large lithophysze, cavities which resemble bladder-like ‘swellings in the molten material of the rock, but which are generally regarded by microscopical geologists to result from a chemical and mechanical alteration of large spheerulites. Under the microscope, the stripes in the groundmass are seen to be made up of three characters of bands. The middle is of a grayish-yellow color composed of sphzrulites and small fibres. On either side are dull gray zones of fibrous, rather homogeneous material, bounding which are third zones of colorless crystalline aggregations. In a little group of hills to the west of the northern point of the Toano Group, which forms the southeastern border of Thousand Spring Valley, are similar shales and limestones, with an easterly dip. Here the develop- ment of limestone is heavily bedded, generally of a grayish-blue color, and seamed with white calcite. A very prominent zone of nearly black siliceous limestone has almost the hardness of quartz, although it effervesces freely with acids, leaving a black porous mass. Under the microscope, it is seen to contain crystals of white calcite and opaque black particles which are doubtless carbonaceous matter, to which the rock owes its dark color. These limestones have been assigned to the Upper Coal-Measure series, rather on account of their shaly character and relation to those of the Toano Group, than from any definite structural or paleontological resem- blance to this series. Thousand Spring Valley is a broad, shallow depression, covered with finely comminuted Quaternary material, which takes its name from the num- ber of small springs found along the bottom and adjoining the bed of Pass- age Creek, which is itself dry during portions of the year in the greater part of its course. These springs present a great range of temperature, from the boiling-point of the hot springs at the upper part of Passage _ Creek, to a temperature of near the freezing-point in little springs which. ooze out of the muddy bottom of Passage Creek, just north of the limits of the map. In the higher portions of the valley, along the borders of the 520 DESCRIPTIVE GEOLOGY bounding mountain-ridges, are considerable developments of white hori- zontal Tertiary beds, which have been referred to the Humboldt Pliocene. These find their greatest development in Holmes’ Creek Valley, just beyond the limits of the map, whose waters drain into the Snake River. On the low ridge which forms the divide between this valley and Thousand Spring Valley, the upper bed is a drab-white, earthy, impure limestone, full of den- dritic markings, and containing irregular-shaped cavities apparently left by no longer recognizable shells. As developed in Holmes’ Creek Valley, the Tertiary beds seem to be largely made up of fine volcanic and pum- iceous material. In this region, at least, their deposition seems to have been connected with a period of volcanic ejection of sand and ash. A peculiar castellated cliff on the east side‘of the valley, called Citadel Cliff, shows an exposure of a hundred feet or more of these beds, which are reg- ularly stratified and for the most part made up of fine, white, friable sand, containing many small transparent glass particles, with a development of beds of fine breccia material, in which are grains of pumice; the most notice- able bed has a thickness of about 5 feet of a reddish-brown, nearly com- pact, glassy rock, breaking with a conchoidal fracture, which is composed of crystals of feldspar and quartz in a groundmass of red and black vol- canic ash, consisting of thin splinters of obsidian partly fused together; under the microscope, the quartz is seen to have large glass-inclusions. The upper bed consists of a thickness of about 10 feet of soft, gravelly, cream- colored conglomerate. Within the beds is also a thin seam, a few inches thick, of a white, cherty material, banded with green, which breaks easily with a conchoidal fracture. Its hardness is less than that of quartz, and it probably contains a considerable mixture of felsitic material. A small coni- cal hill not far from Citadel Cliff was found to be capped by a black, glassy — obsidian. The hills betwen Holmes’ Creek Valley and Thousand Sore Valley, whose southern point extends into the region of the map, are made up of a body of limestone overlaid by quartzites dipping to the south and west, which have been referred respectively to the Lower Warbouiorope and. Weber Quartzite group. Fountain Heap Hitus.—To the west of Thousand Senne Valley, the FOUNTAIN HEAD HILLS. 521 low, crescent-shaped ridge of the northern portion of the Fountain Head Hills is made up of quartzite beds, which have been assigned to the Weber Quartzite. Owing to the gentle slopes of these hills and the low angle at which the rocks lie, no considerable section of the beds was obtained. In them is a large development of a peculiar quartzitic sandstone or grit, which is very persistent through the Northern Nevada region, and consid- ered characteristic of the horizon of the Weber Quartzite. - It is a more or less fine-grained, reddish-gray rock, made up of angular fragments of flint and chert of various colors, in which black and red generally predominate, with a matrix of a granular siliceous material, often stained by brown oxide of iron and containing a very large amount of limpid quartz. It has a pecu- liarly rough feel, suggesting a porous texture, almost like that of a volcanic rock. It effervesces slightly under acids, and, under the microscope, is seen to contain small crystals of calcite, the matrix being made up of crypto-crys- talline grains and rounded fragments of quartz. The structure of this ridge is, as far as can be seen, that of a gentle anticlinal, whose axis runs with the trend of the ridge. Southeast of the quartzite occurs a body of limestone, extending south- ward as far as Cedar Pass. It appears to be made up of long ridges, vary- ing much in direction, but with a general trend of northeast and southwest. One of the main ridges indicated a strike of north 25° to 30° east. The strata consist of heavy beds of grayish-blue earthy limestone, occasionally highly metamorphosed and in places impregnated with seams of white cal- cite. On Euclid Peak, the culminating point, the beds lie nearly hori- zontal, but have a slight western dip, and along their eastern base show outcrops of dark quartzite, which have been referred to the Weber forma- tion. Fragments of this quartzite may be traced cropping out above the Tertiary and Quaternary beds, along the foot-hills from Euclid Peak to Cedar Pass, where it rises in ridges several hundred feet in height. ‘Toward the pass, the structure is somewhat complicated, and the quartzite north of Indian Well, where the beds have undergone the greatest change in course, is seen striking north 60° to 65° west, with a dip of 12° to 15° E. Here the quartzite, a hard compact rock, is traversed, in a striking manner, by numerous narrow veins of pure quartz, but apparently of no economic 522 DESCRIPTIVE GEOLOGY. value. In the region of Independence Spring are a series of low quartzite hills, which, in passing north, are overlaid by patches and fragments of lime- stone, which dip generally to the northwest. As already mentioned, the quartzite has been referred to the Weber, and as the limestone, wherever observed, is seen invariably overlying it, the latter has all been placed in the Upper Coal-Measure series. Organic remains, generally too poorly. preserved for specific deienae nation, but which undoubtedly belong to Coal-Measure forms, are found in many localities. The following species have been determined: Productus subhorridus. aAthyris subtilita. North of Independence Spring were also found, not over 100 feet from the quartzite, undetermined species of Bryozoa, belonging to the genus Tre- matopora. Hast of Euclid Peak occurs a peculiar « eae st of volcanic rock, which, although not a typical trachyte, has been regarded as belonging to that group. It stands remote from all other trachytic bodies, the other acidic volcanic rocks of the region, so far as observed, belonging to the rhyolites. It forms a long north and south ridge inclined to the eastward, and is cut through by Peoquop Creek, offering a good exposure of the mass. It is an exceedingly dense, tough rock, breaking with difficulty. In color, it is yel- lowish-brown, derived from the decomposed earthy material which makes up the base. Macroscopically, in its mineralogical composition, it shows only well-developed monoclinic and triclinic feldspars; the latter, appar- ently predominating, are brilliant and characteristic. Hornblende, very much decomposed, may be recognized from its form. The rock carries small cavities and druses, many of them completely filled by secondary products, as calcite and chalcedony. A chemical analysis was made of this — rock by Mr. R. W. Woodward with the following result: Silica Wy i265 De Ee Be eee 67.81 67.60 Alumina) 2.) 20 ee eee Sees eer 15:83 15.74 Perrous oxide) >< St roe a eee 3.41 oa Lime TSE oS ae ee ei) dst Oates Lata 3.66 3.76 - TUCUBITS MOUNTAINS. 523 Magnesia EP ‘Sian, abies ra Se aed 1.36 1.39 Sodate i it ad “tae lege Sete eae ee nen eerie 5.10 O70 JE OIGS Eh ot is ee eet See eee 0.67 0.69 plentlina ete io pete ee oe ee peas iret trace trace Carbonic acid ....-.- Bee Pere SOs sits ues 0.49 | 0.49 Whether ae eer: eee cc ee a Bays) 1.75 99.88 99.96 Specific gravity 2.5-2.6. Tt will be seen that the rock stands rather high in silica for trachyte, but this is doubtless owing to the presence of the chalcedony. A marked feature is the large amount of soda and the correspondingly low percentage of potassa. The analysis would indicate a hornblende-oligoclase trachyte. To the west of the Fountain Head Hills is a north and south valley- like depression in the quartzite, in which the westward-flowing waters of the Humboldt River and the easterly-running streams at the head of Passage Creek take their rise, suggesting the name for this group of hills. It con- sists of a series of low rounded hills, whose underlying rocks are masked by surface-accumulations of gravel and débris. The few outcrops shown indi- cate that it is probably occupied by the beds of the Weber formation. Tucusits Mounrains.—The Tucubits or Wild Cat Mountains form a northern continuation of the East Humboldt line of elevation. They consist of a mass of easterly-dipping quartzites and limestones, which, toward the southern end, have been much faulted and dislocated, so that it has not always been possible to trace the direct continuance of the beds. In its northern portion, as represented on the map, where some of the peaks attain _ a considerable elevation, it is formed mainly of bodies of quartzite, contain- ing thin beds of curiously-banded cherty material, black and green in color, representing the horizon of the Weber Quartzite Along the western base are exposed heavy bodies of blue limestone, whose strike is somewhat to the west of the trend of the range; greater thicknesses are observed as one goes south, and they were principally studied in the section exposed by the catton of the Humboldt River called Emigrant Camon. ‘In the exposures along the western face of the range, particularly at 524 DESCRIPTIVE GEOLOGY. the head of the south branch of Forellen’ Creek, thicknesses of several thousand feet of limestones are found, generally dark bluish-gray, heavily bedded, and having a gentle dip of 20° to 25° to the eastward. No fossils were obtained, however, from these beds; but their general character is that of the Wabhsatch limestone. In the neighborhood of the mouth, or western end,- of Emigrant Cajion, the beds stand at a steeper angle, dipping in some cases 45° to the eastward, and have evidently been faulted, one line of fault being observed in a little side-ravine on the south side of the cafion, about a mile from its mouth, where the upthrow has been on the eastern side of the fault, and some of the eastern beds have been sharply bent downward at the line of fault. The line of this fault appears to be to the northeast. A short distance above this point a section is exposed of several hundred feet of shaly beds, from which issues a considerable body of hot water. ‘The beds shown here from the line of fault upward consist of 300 feet of light- gray limestone, overlaid by 100 feet of yellowish calcareous shales, above which are 150 feet of black, thinly-laminated, calcareous shales, abound ing in fossils; above the shaly beds are 200 feet of dark-gray limestones, followed by heavy beds of limestone about 1,500 feet thick, which could not be definitely determined on account of surface-accumulations. From the bed of black shales were obtained the following fossils, which have been con- sidered to represent the Upper Helderberg group: Ortlis multistriata. Orthis, n. sp. Spirifer Vanuxemi. Atrypa reticularis. Cryptonella, frag. Crania, undet. sp. The slopes of the cafion above the Hot Springs are in general too much covered by detritus to afford a continuous section. Only a general idea of the rocks can be obtained here, from which it is seen that at least 4,000 or 5,000 feet of limy beds are cut, which, toward the upper part, show a greater proportion of shales, and are generally of much lighter color. Near TUCUBITS MOUNTAINS. 525 the upper end of the cafion is an outcrop of about 500 feet of calcareous shales, having a purplish color on their weathered surface, overlaid by drab limestones, which, in turn, are overlaid by some blue siliceous limestones, carrying white seams of calcite containing crystals of pyrites. In the hills to the eastward, beyond the upper end of the cafion, as has already been seen, only quartzites are observed, which represent the Weber Quartzite. The limestones extend much farther eastward at the immediate line of the cation than they do either to the north or the south. In the low, rather broken hills which form the continuation of the range to the south of Emigrant Canon, distinct outcrops of compact white quartzite are found along the eastern slopes, dipping about 25° to the eastward and striking somewhat to the east of north. In general, but few exposures are found in these hills, but the surface is largely covered with débris of the peculiar dark-reddish quartzitic sandstone already observed in the Fountain Head Hills. Directly south of the Hot Springs is a bare limestone hill, showing about 500 feet in thickness, of earthy blue limestones, plentifully seamed with white calcite, somewhat arenaceous in the upper part, and the beds generally from 15 to 20 feet in thickness. This is underlaid by several hundred feet of darker-colored, sometimes black, limestones, which, in the lower part, are very siliceous. These beds dip about 20° to the southeast. No fossils were obtained from this outcrop of limestones. To the west of this hill, in a little ravine running northwest, just under the base of Tulasco Peak, was found exposed a series of thin-bedded limestones, from which were obtained a number of Coal-Measure fossils, whose aspect indicates a much higher horizon than the apparent position of the beds, which otherwise would have been supposed to be lower than the heavy-bedded limestones just mentioned. The bottom of the ravine is in dark-reddish limy shales. The lowest out- crop shown is 50 feet of white quartzite, overlaid by 100 feet of gray limestone with siliceous seams, above which 10 feet of a bluish-gray lime- stone carrying Fusulina, overlaid again by 30 feet of gray limestone with cherty seams, above which 50 feet of shaly limestone carrying corals, while on the hills above are, though not in direct contact, apparently con- formable beds of the quartzitic sandstones. ‘These beds all dip 35° to the | 526 DESCRIPTIVE GEOLOGY. eastward, with a strike of north 10° west. From them were obtained the following Coal-Measure fossils : Spirifer cameratus. Spirifer Kentuckensis. Athyris. subtilita. Rhynchonella, sp.? Pseudomonotis radialis. Pseudomonotis, sp.? - Dentaliwm Meekianum. Bellerophon carbonarius. Chetetes. Frenestella. Trematopora. The general aspect of these fossils, taken as a whole, together with. the lithological character of their beds, shows that they doubtless represent the extreme upper portion of the Wahsatch limestone. Their relative posi- tion with-regard to the Devonian beds exposed at the Hot Springs must be explained by a rather complicated system of faulting, which the character of the country and the limited time at our disposal did not permit us to work out in detail. Tulasco Peak itself and the hills to the southeast and west, though showing few outcrops, are evidently occupied by beds of the Weber Quartz- ite, associated with which in the southern end are some flows of a brecciated rhyolite. In some cases, these peculiar quartzitic sandstones are so full of limpid quartz that they may be almost confounded with the rhyolite. They are, in general, the same reddish, rough-feeling rocks observed in the Fount- . ain Head Hills, in which the proportion of granular matrix and of enclosed cherty fragments is very variable. The pores generally contain a great deal of brown hydrated oxide of iron, to which the color of the rock is some- what due. In the neighborhood of the rhyolite outflows are found rocks which are made up largely of the same cherty fragments of black and green colors, in which the rock has a more compact and almost felsitic structure, its granular character having disappeared, and there being a more consid- TUCUBITS MOUNTAINS. . 527 erable development of grains of limpid quartz. These greenish breccias gradually lose all appearance of a granular groundmass, the whole mass seeming to be more or less felsitic, and pass into a porphyritic rhyolite, having something of a brecciated structure, which is full of crystals of lim- pid quarts, and carries some few feldspar crystals. In this range, it has almost the appearance of a quartz-porphyry, and may possibly be of older age than the rhyolites, though, as will be seen later, the same association’ is found with well-defined Tertiary rhyolites, of whose age there can be no doubt. Out of the Tertiary plains, to the west of the Tucubits Mountains, rises a little group of hills called Forellen Buttes, which is composed of a some- what similar brecciated rhyolite, having a rather compact, grayish-drab, fel- sitic groundmass, in which are large crystals of sanidin and quartz. Under the microscope, this rhyolite is seen to be made up of three different mate- rials: first, broken crystals of sanidin and quartz, lying close together; sec- ond, fragments of dark-gray hornstone-rhyolite, rich in glass; and, third, bands of dull whitish rhyolite, enclosing angular fragments of quartz, which envelop the other ingredients in wavy lines. | 528 DESCRIPTIVE GEOLOGY. hie 2 LON Shy EAST HUMBOLDT RANGE. BY ARNOLD HAGUE. Recion soutH oF Friémont’s Pass.—The East Humboldt is not only the main range of Central Nevada, but is also the most prominent uplift lying between the Sierra Nevada of California upon the one side and the Wahsatch of Utah upon the other. It extends from the southern limit of the map northward to the Humboldt River, a distance of 80 miles. It is a bold, single ridge, having a trend of about north 18° to 20° east, with many rugged summits reaching over 10,000 feet above sea-level. Mount Bon- pland, the highest peak, a fine commanding point, at the northern end of the range, attains an elevation of 11,321 feet. The range, from its position and relative elevation, presents in its physical conditions much more of an alpine aspect, receiving at the same time a larger supply of moisture, in the form of both snow and rain, than any other of the Basin ranges. Its flora also suggests the higher elevations, the long slopes and glacier-carved cafion-basins being covered with scattered forests, including several varie- ties of pines and firs; Pinus flexilis would appear to be the prevailing spe- cies. The trees, however, are too short, being rarely over 50 feet in height, and too knotty to afford much valuable timber. In general terms, the geological structure of the Humboldt Range rep- resents a mass of Archean rocks, which acts as the axis of an anticlinal fold, striking obliquely across the range, from which are inclined the Devonian and Carboniferous strata, resting unconformably upon the granites and gneisses of the crystalline foundation. The southeast side of the fold extends from the region of Frémont’s Pass to Hasting’s Pass, and consists of a single series of limestones conformably underlaid by quartzites, the latter appearing along the western. base, while the entire summit and eastern face presents only heavy massive limestone. The eastern slope is -_P- -P) oF ; ; F . : a q . EAST HUMBOLDT RANGE. 529 broken by numerous canons, many of them quite remarkable, which show characteristically the mannerin which heavy bodies of limestone, when gently inclined, may be eroded into narrow, deep cations, with nearly precipitous. walls. The photograph, reproduced on Plate XVII, represents this type of structure, as seen in Blue Cafon, with nearly sheer cliffs from 1,400 to 1,800 feet in height, standing out boldly above the Quaternary plain. Wrapping around the granite mass, which occupies the whole of Fré- mont’s Pass, are found the limestone beds, forming the extreme northern extension of the main body. On the eastern foot-hills, about a mile and a half north of the pass, the limestones stand nearly vertical, and appear as a mere thin bed, which rapidly dies out against the granite to the north Coming south of the pass, the angle of inclination decreases from 50° to 40°, and falls off gradually to 22°, with a southeast dip. At the high peaks back of Cave Creek, a recorded dip gives 16° to the southeast, and still farther to the southward the bedsbecome nearly horizontal. They again rapidly rise in dip till, north of Hasting’s Pass, and west of Fort Ruby, they reach an angle ~ of 16° to 20°; this time, however, inclined to the northeast. It will be seen, therefore, that, while the general dip is eastward, there is a gentle north and south synclinal structure. About a mile south of Frémont’s Pass, these limestones rapidly thicken, and are underlaid by 800 to 1,000 feet of white to brownish-white, highly- laminated quartzite. It is usually a compact, highly vitreous rock, the brown color being derived from the presence of small amounts of iron scat- tered through it, or else occupying thin, narrow seams. This whole series, the quartzite and overlying limestone, is distinctly unconformable to the granites. Inthe cation next south of Frémont’s Pass is seen a good exhibi- tion of the conformable series, with the quartzites dipping 18° to 20° to the southeast. The transition from the quartzites to the limestones is made in a very short distance, without any noticeable interstratification of beds. The _ quartzites appear a little calcareous and the limestones somewhat siliceous, but the transition is made by a rapid passage from one to the other. The limestones are of a very light gray and grayish-buff, and these colors prevail for about 1,600 feet upward in the series, when the beds are usually of a dark-grayish hue, and the bedding much heavier than in the zones below. | 34D G 530 DESCRIPTIVE GEOLOGY. Thence to the top of the series limestone occupies the whole body, and here makes an exposure above the quartzite of not less than 6,000 feet. In this great thickness of limestone occur beds exhibiting considerable variety in texture and composition. In the lower part of the series, thin calcareous shales, more or less arenaceous, are a characteristic occurrence, while higher up more compact beds of argillaceous material are found inter- stratified in the limestone. Near the summit of the ridge, beds of highly metamorphosed dolomites occur, of a bluish-white color. Not far from one of the dolomitic zones, a bed of nearly white, sacchar- oidal limestone was observed,. altered into a coarse marble. It has been analyzed by Mr. B. EK. Brewster, with the following result: Alumina, and ferric Oxide. 25) e ere see 0.363 Lime". 2. 2/23: a Se ee 54.513 Magnesia . . =... 0. Stee ee eee ae ee 0.273 Soda... - eco. -cteed ec 5 see eee eee trace Carbonic acid... 32-2 > eee Be ego att 43.130 Phosphoric acid: | 2-252 eer eee eee 0.349 Water ..- 2.54.2: So ee ee ee 0.109 Insoluble residue. : . - 242232 5 ee eee ee L3At 100.084 Carbonate of. lime 2e 2 ot eee ee 97.345 Carbonate of magnesiqns ea) = =- See ee EO TS 97.918 Fragments of Coal-Measure fossils may be found scattered through the higher members of the series, but so far the lower members have yielded none. Stems of cyathophylloid corals, Bellerophon. sections, and poorly- preserved forms of Spirifer are abundant; but the only species obtained that could be identified were : Chonetes granulifera. Productus Nebrascensis. Fusilina cylindrica. CANON IN LIMESTONES_ EAST HUMBOLDT MTS_ NE VADA . EAST HUMBOLDT RANGE. ' 531 So thick a series of limestones overlying a pure quartzite can be noth- ing else than the Wahsatch limestone, and it is not surprising that the only fossils obtained are Coal-Measure forms, procured high up in the series. The quartzite is referred to the Ogden Devonian, and the section of beds seems to repeat that of the Pinon Range in the same latitude, with the exception that the limestone series is here continued much higher; the latter, in the Pifon Range, being eroded off down to the beds, which cor- respond to the Helderberg horizon in the New York State section, and which rise here in the Humboldt Range, 5,000 feet higher, embracing doubtless the narrow belt of Sub-Carboniferous and the enormous development of Lower Coal-Measure limestones. The lower section, C—D, at the bottom of the geological sheet, cuts the Humboldt Range at Frémont’s Pass, where only the upper members of the Wahsatch limestone are represented on the east side, lying steeply inclined against the granite. On the west slope, however, the Ogden Quartzite is shown resting next the granite, but without any overlying rock. It is noteworthy that in this heavy and elevated limestone mass run- ning streams are entirely wanting. The water, however, reaches the sur- face along the base of the range in numerous springs extending from Hast- ing’s to frémont’s Pass. These springs supply Ruby Lake. They are all clear, cold waters, with temperatures varying from 43° to 48°. Cave Spring, about 6 miles to the south of Frémont’s Pass, runs a considerable stream, coming out directly from the limestone through an opening suffi- ciently large to admit a man into an interior lake-chamber 10 by 12 feet and 10 feet in height. A narrow winding channel connects this chamber with still another and larger one beyond, with its limestone floor covered with water. It is worthy of exploration, but, so far as known, has never yet been visited. Not far north of Cave Spring occurs the only outburst of volcanic rocks observed in this portion of the range, and is of some special interest, as both macroscopically and microscopically it resembles a trachyte, and has been classed as such, although by no means a typical variety. Break- ing through the limestone, which is considerably shattered, it forms a low, regular hill of rough, gray rock with a medium compact texture. The 532 DESCRIPTIVE GEOLOGY. mineral constituents are well developed, and consist of both monoclinic and triclinic feldspars, hornblende, biotite, and quartz. Many of the plagio- clase crystals are quite large, and characterize the rock by their brilliant white faces. Thin flakes of black biotite are everywhere scattered through the groundmass, frequently adhering to the edges of the feldspars. The hornblende appears to be a deep dark green. Quartz-grains are rare, but are mainly in broken translucent masses; the rock forming no exception to most of the quartz-bearing trachytes in having the grains quite large, and in showing under a high power.no microscopical ones. Minute apatite crystals are seen under the microscope in great numbers. A marked pecu- liarity of this rock is its coarse crystalline groundmass, to which it doubtless owes the somewhat characteristic fracture. ReGion NorTH or Friémont’s Pass.\—The granite body which ends at Frémont’s Pass agrees in trend with the general course of the range, and extends northward for nearly 15 miles, finally falling away toward Ruby Valley. In the pass, the granite possesses usually a coarse crystalline text- ' ure, weathering readily into picturesque forms of domes and pillars, with great diversity of outline, the whole more or less covered by granitic detri- tus. The feldspar and quartz are intimately blended, giving the rock a white or yellowish-white color, while the mica, although aljvays present, varies greatly in amount. White Cloud Peak: is the culminating point of the granitic mass, and here possesses in general the characteristics of an eruptive granite; that is to say, there are no distinct lines of bedding that would ally it with the gneisses. - There are a series of divisional planes. which strike apparently with the range, and dip west, dividing the granite into broad tabular masses 40 or 50 and sometimes ‘80 feet in’ thickness. These planes, although traceable by the eye, when looked at in detail are obscure or wanting, yet there is a further indication of parallel structure in the granite, which appears in a hand-specimen by the arrangement of mica- flakes. The laminee of the mica are by no means all parallel, but there is, however, in certain strata a prevailing direction. Among feldspars, ortho- clase largely predominates, ‘although plagioclase is present. In the quartz, liquid-inclusions are almost entirely wanting. Apatite prisms occur very 1 From notes furnished by Mr. Clarence King. EAST HUMBOLDT RANGE. 933 plentifully, extending lengthwise with the direction of the mica; they are sometimes flattened, and are occasionally broken, appearing in disconnected sections. Hornblende is entirely wanting. ‘The most interesting charac- teristic is the microscopical crystals of zircon. A little way down from the summit on the west side of White Cloud Peak, a change takes place in the rock, and the granite becomes overlaid apparently unconformably by a series of quartzites and hornblendic schists, which occupy the range to the western foot-hills, sinking under the over- lying Pliocene beds. North of the granite body, these overlying schists ~ curve around and occupy the entire width of the range, which they con- tinue to do to its northern extremity, where it passes under the valley of the Humboldt River. They have a westerly dip, varying from 20° to 45°, and ‘toward the base of their series present a somewhat granitoid appearance. This immense thickness of eneisses and crystalline schists contains a few beds of white dolomitic limestone occurring in beds from 1 to 6 feet in thickness, separated from each other by micaceous quartzites and mica- schists. 'The whole limestone series has only been observed in one or two localities on the summit of the ridge, at Mount Bonpland and Clover Peak, and is altogether embraced within a band of less than 60 feet thick. Over the limestones are further micaceous schists, and above these, forming the summit of the series, is a heavy development of quartzite. ‘These quartzites form the summit of the ridges, which slope from Clover Peak westward. The erosion of glaciers has excavated deep U-shaped cafions, which have cut through the quartzite, leaving it standing upon the lateral ridges, and exposing the lower schist series in the bottoms of the cations. These quartzites are very well developed along the upper waters of Boulder Creek, and alsoin Clover Canon. On Plate XIX, this erosion of pure quartzite by glacial action is well shown, exhibiting the steep escarpments of the summit, the narrow lateral ridges, and the manner in which the brittle rock splits up with a sharp angular fracture. The quartzites of Clover Canon are either white or stained a light yel- lowish-brown by infiltrated oxide of iron. They consist mainly of white quartz, which is at times milky and at times translucent in the same speci- men. They also carry garnets up to the size of a large pea, numerous 534 DESCRIPTIVE GEOLOGY. white flakes of mica, which are, in general, disposed parallel to the bedding of the quartzite, and, as a microscopical constituent, fine black threads of hornblende and minute dislocated prisms of actinolite. The quartzites of Clover Canon represent the lowest part of the quartzitic series, and pos- sibly a lower series than those exposed on the west side of the mountain, west of Clover Peak. They are distinctly fissile, and split with very smooth faces, upon which are clearly seen striations not unlike the slickensides frequently observed in mines. The surfaces of these laminz are more or less discolored and spangled with plates of pure white mica. Occasionally rare small crystals of feldspar appear on these smooth brownish faces. The appearance of striation is in no way referable to the presence of mica, but is an actual rubbing and grooving of the surtace face from some early motion. In the quartzites of the entire group, this phenomenon is not uncommon, nor is it confined to the quartzites; but the mica-schists themselves show evidence of internal motion. Along the west side of the range, in the vicinity of Thompson’s Ranch, the quartzites are less milky and of a clearer gray tint; and although they still carry white mica, they have some black biotite. The same cleavage- faces are developed, but here they are decidedly corrugated and ribbed by. mica, which enters the face at a diagonal; the whole appearance is as if the cleavage-face had been developed obliquely to a zone of parallel mica flakes. Besides the white mica in these last quartzites, there is a considera- ble amount of finely fibrous green mineral, which, in localities, is more or less penetrated by half-decomposed and almost wholly-decomposed white mica. This green mineral is doubtless a chloritic decomposition-product of the mica. Such behavior of the mica in these quartzites is of interest as illustrating the transition from well-defined crystalline schists with a par- allel structure to granitoid forms, in which such structure is no longer observable. The lack of parallelism in the mica flakes, and the lack of continuity of the planes which carry mica, already suggest the granitoid structure. As in the Clover Cation quartzites, so here also is there an appear- ance of severe horizontal rubbing. The chloritic mineral, the mica, and the quartz, all show evidences of powerful attrition and pressure. No garnets are observed in the quartzites of the west side. Under the EAST HUMBOLDT RANGE. 535 microscope, the quartz proves to be rich in fluid-inclusions and empty cavi- ties. There are considerable zones, in which the quartz is a pure material, carrying neither mica nor garnet; but these zones rarely reach more than 20 or 30 feet in thickness, and are the exception rather than the rule. Beneath the quartzites is the narrow zone of dolomitic limestone already mentioned, and, under these, thin associated quartzites, and then the heavy mass of gneiss and gneissoid schist, which form the great bulk of the range. Of these, in the northern part of the range, there cannot be less than 5,500 or 6,000 feet. | In the region of Clover Peak, the gneisses are usually composed of quartz, orthoclase, brownish mica, and hornblende. They are varied by limited beds of dioritic schist, which are interesting from the number of minerals they contain. In them, plagioclase predominates over orthoclase, but both are always present. The mica is of a dark earthy brown, while the hornblende, always more abundant than the mica, is of a dark-green color. Titanic iron and apatite in unusually large quantities are present. Inclosed between the beds of gneiss, rich in orthoclase and poor in mica, are some sheets of pure amphibolite, noticeable as containing no foreign minerals, not even quartz. An unusually interesting gneiss is found under- neath the quartzite on the west slope of the range below Clover Peak. It is a fine-grained, brilliantly-colored gray rock, in which the white particles of quartz and black mica form a decidedly granitoid arrangement, but the rock at large has a very distinctly fissile structure, and cleaves easily in fine sheets of an inch or more in thickness. Besides the black mica, there is a large proportion of a brilliant coppery-bronze-colored variety; the rock is further distinguished by containing, as shown by the microscope, a con- siderable amount of fine zircon, and the rock is considerably stained by infiltrated oxide of iron. The gneisses in the region of the dolomitic lime- stones are more or less enriched by crystals of carbonate of lime. Besides these, in the remoter gneisses, there are calcareous passages, where the crys- tals are irregularly distributed, never enough to give a distinct character to the beds, but still enough to cause it to effervesce under treatment with acids. Garnet is confined to the quartzites and the lowest members of the gneiss. Quartz, with the exception of the dioritic beds, invariably predom- 536 DESCRIPTIVE GEOLOGY. inates over feldspar. In general, there is more orthoclase than plagioclase. The series is particularly instructive as illustrating the breaking-up of the schistose structure and assumption of granite forms by the development of large feldspars, and by the compression which has been brought to bear in the direction of the beds. There seems evidently to be some connection between these two phenomena; for wherever the parallel structure of the mica and hornblende is broken up into wrinkles and waves, there the feld- spars assume greater importance, and reach the size of large peas. The rock in such passages, in hand-specimens, is indistinguishable from a gran- ite; and between this and the schist with parallel mica, in which no crystals of quartz or feldspar interrupt the sheets of mica, there is every possible transition. 7 A very instructive exhibition of these changes is to be seen directly east of the summit of Mount Bonpland, where an abrupt precipice of not less than 1,000 feet falls off to the east. Across the face of this precipice may be traced the parallel layers of the gneiss, which vary in tint from a pale gray, almost white, to nearly black, according as the mica or horn- blende predominates. Across these planes of bedding is an irregular cloud- ing, which looks upon the surface of the precipice almost like the presence of irregular intruded masses. ‘Through these, however, the general lines and shades of the gneiss beds are seen to run; but the gneiss itself, within the limits of these vertical cloudings, has lost much of its schistose character, and is more granitic. The whole summit region is profoundly riven with vertical cracks par- allel to the trend of the range, but to what depth is unknown. They are, however, seen more or less distinctly throughout the whole of the eastern precipitous face of the northern part of the range. Owing, no doubt, to this series of vertical fissures, the summit rocks are very peculiarly weath- ered into a series of tall pinnacles 50 or 60 feet high, with large rounded tops like mushrooms, formed of beds which have more successfully resisted erosion. As already mentioned, this entire series is conformable, and dips to the west, and overlies the White Cloud Peak body of granite, but overlies it Plate XVIII 1. 40 Parallel U.S. Geol. Exp MVAd GHAOT)D UVAN — SLWN e LULOAN OH ~ NONV) WHlOV'TO EAST HUMBOLDT RANGE. 537 in an obscure manner, so that their relation is not clearly made out; their position, however, is unconformable. There is reason to believe that the gneiss of Sacred Pass is constantly descending in the series, so that the lowest members are reached at the southern end of the formation. The granite of White Cloud Peak bears a remarkable similarity to some of the well-known Laurentian rock-masses of the Appalachians, while the overlying schists and gneisses, with their limestones and heavy mica- bearing quartzites, have a noticeably close resemblance to the eastern Huron- ian. Thus isolated from al] other large Archean regions, and with only the general petrographical outlines to decide from, no definite reference of this interesting Archean body can at present be made; but since all its affinities lead toward the Huronian group, it is safest to refer it to that division. : als The summits of the Hast Humboldt Range, from White Cloud Peak to the northern end, all show abundant evidences of glaciation. Very consider- able glaciers existed in the elevated group south of Fort Halleck. From the region north of Lake Marian a fine view is obtained of the glacial canon which forms the south branch of the South Fork of the Humboldt River. The glacier here was 8 miles long, and its canon, presenting the character- istic U-shaped bottom, shows a depth of 2,500 to 3,000 feet. The whole range north of Frémont’s Pass contains along its summit a series of deeply- sculptured amphitheatres, with characteristic rounded bottoms, with roches moutonnées, and carries along the lines of present drainage an abundance of peculiar alpine glacial lakes. The rubbish of lateral moraines flanks the canons. The upper 50 miles of the range presents a pretty continuous field of glaciation. All the cations in the region of Clover Peak which descend to the west side of the range are cut at least 1,800 feet deep, and in many instances the glaciers flowed to the very edge of the plain. Upon the east side of the extreme north edge of the range, in the region of Mount Bonpland, the glaciers were short and steep, and have left abundant evidence of this in massive piles of terminal moraines. The evidence also is very convincing that since the Glacial Period erosion has been very insignificant. ~ On Plate 538 DESCRIPTIVE GEOLOGY. XVIII is shown one of the deeply-cut glacier-cafions which come down from Clover Peak. | A little north of where the main South Fork of the Humboldt River flows out of the East Humboldt Range, the Archzean mass makes out in a bold promontory, around whose base is wrapped a series of unconformable over- lying limestones. About a mile and a half north of the South Fork of the Humboldt, these beds have a north and south strike, and dip about 25° to the west. This position is held for nearly 3 miles to the north, when they describe a curve, and finally strike north 40° east, and dip northwest at about 20° to 25°. Nearly 4,000 feet of limestone are thus exposed, and at their base a varying amount of quartzites. At times, the Archzean comes directly in contact with the limestone, so that the intermediate quartzite, which has ~ -been referred to the Ogden group, is wanting, while in others, there is an exposure of 100 to 200 feet of quartzitic beds. The first 2,000 feet of lime- have prevailing light colors, and among the light-gray beds are many of a buff tone. Above these come the dense blue-black limestones, carrying a number of well-defined Coal-Measure forms, comprising the following species : Productus semireticulatus. Productus longispuus. Fusilina cylindrica. | Camarophoria. From its thickness, the character of the underlying quartzite, the pre- vailing buff hue of the lower members of the series, and the character of the organic remains,-there can be no hesitation in referring these beds to the Wahsatch limestone. | | Back of the Overland Ranch, in among the schists and granites, in a cafion just to the north of White Cloud Peak, there is a fragment of lime- stone devoid of fossils, and so deeply fractured and metamorphosed as to be little more than an irregular mass of blocks. It is doubtless an accidental fragment left by the general erosion, and indicates the fact that, prior to the upheaval, much of the crystalline schists were overlaid by the Wahsatch limestone. Along the foot-hills south of Camp Halleck, occupying a similar position and unconformably overlying the schists, is a little pointed a | EAST HUMBOLDT RANGE. 539 spur of limestone rising above the Quaternary of the valley. Upon the foot-hills, directly back of Camp Halleck, the limestones again recur, and here they wrap around a prominent mass of Archean, curving into Sacred Pass and skirting the crystalline rocks for a distance of 6 or 7 miles. There is here no underlying quartzite, but the limestone rests directly on the Archean, and has yielded, near the point of contact, the following Coal- Measure forms: . Syringopora multattenuata. Productus costatus. Athyris subtilita. The limestone is much shattered and decomposed. It is of a prevailing light color, is characterized by more or less earthy beds, and is doubtless a much higher member than the black limestones directly north of the South Fork. Further down the range, north of Sacred Pass, on the same spur, there are obscure outcrops of limestone seen under the rhyolite, and for the most part covered with glacial débris. Observed dips gave 35° and 40° west. No fossils were found, but they probably represent a northern extension of the Coal-Measure limestones already described. On the extreme northeast slope of the Archean mass south of Wells Station, on the Central Pacific Railraod, are a number of small isolated patches of limestone resting upon the crystalline rocks in a manner similar to those already mentioned on the western side of the range, and with the same lithological habit. Imperfect forms of Coal-Measure fossils, too poor for specific determination, were found imbedded in a light-gray rock, dipping 25° to the eastward. 3 North of the limestone in Sacred Pass, and extending northward until they rest against the Archean body is a group of rhyolites, which are chiefly a pale olive-green tufa, in which are large crystals of vitreous sanidin. Hast of Sacred Pass, the range is widened by the addition of an outlying mass, which projects southward as a promontory surrounded by ‘the Quaternary of the valley. Between the promontory and the main range in Clover Canon, the Archzan schists are broken through by a very peculiar black rhyolite, having a brilliant resinous lustre, and resembling externally many of the glassy andesites, except that it contains a very large 540 DESCRIPTIVE GEOLOGY. "proportion of rounded granules of quartz of an amber color, which are fissured into a perfect net-work by minute cracks. Both plagioclase and orthoclase occur, which, according to Zirkel, contain an enormous quantity of half-glassy inclusions. The quartz, on the other hand, contains no inclu- sions at all. It is remarkable that the rock also contains grass-green undichroitic augite and thick magnetite, but no biotite or hornblende. The groundmass is a brownish glass densely filled with both feldspar and augite microlites. This is another interesting instance of the remarkable associa- tion in one rock of free quartz, orthoclase, and augite, and especially so that they are found in an acid glass. . PLIOCENE AND QuATERNARY FoRMATIONS. —Throughout its while length, the Kast Humboldt Range is skirted on the west by Pliocene strata, extend- ing from the southern limit of the map northward to the Humboldt River. In Huntington Valley, they form a belt varying from one to two miles wide; but from the South Fork of the Humboldt to Trout Creek, the entire valley is filled with these strata, which, in the middle of the valley, are always horizontal, but have a slight dip of deposition along the foot-hills, away from the range, rarely amounting to more than 4° or 5°. These strata doubtless represent a lake-basin which filled the whole Huntington Valley, and the valley of the South Fork down to the gap, where the latter stream breaks through the Carboniferous limestones of the Elko Range. The Quaternary plain that occupies the depression east of the au boldt Range is divided into two valleys, known as Antelope and Ruby Valleys, separated by a low cross-ridge of limestones and basalts, extending from Spruce Mountain in a northwest direction to the Archean body of the Humboldt Range. Its highest summit in the region of Spruce Mountain barely rises 600 feet above the valley, while its western end falls away in low, rounded hills. No fossils were found in the limestone, but’ there can be little doubt that it belongs to the Wahsatch limestone. The basalts, fine- grained, black rocks, occur, breaking through the limestones in a number of places, and forming the summit for a considerable distance. In the south- west corner of Antelope Valley, between Eagle Lake and the main range, is found a large hot spring, so completely surrounded by the Quaternary deposits that it is difficult to recognize the formation through which it ‘qONVY LATOANOH ~ALIZIMVAD NVHVHOUV 40 HOaTHY i) JAD PLATE EAST HUMBOLDT RANGE. 5A1 breaks. It runs a considerable stream of clear water toward the lake, but leaves, upon evaporation, a thin crust of alkaline salts. This incrustation, upon being subjected to chemical aa by Mr. R. W. Woodward, yielded the following result: Sole, 0.11. e eee er 35.66 SOON «2 S25 one oh ce TNE ee eae O09) JE VUENO2) 42S SEE ooo eee eee hr 1.04 Carbonic acid... - - Ste oa 5 Och koe ee gt tee es eee ea 15.27 Carbonic acid (excess over monocarbonate).--..---. 3.35 Sap auinie selmaae ee ee ee ee 19.99 Chine 332 see 12d oo hes ee aaa 15.15 iipraplev AGI. 2 9.27 o oe Se fee ee re ee trace Fei CROIN@ IAG CCI es se ee ne trace ; , 100.25 Combining bases with acids, we have: Carbonate and sesquicarbonate oie sodases ee: Se 39.04 Dipomeraiesm@yeon ss se. 2 eo. ve le 33.88 Sulphate: Of -potassa-.-...-....-- BRE Segre 2k 1.94 Signe or commie 282.8 8.6 fst ea. o 24.96 Excess of sulphuric acid....-.-.--- ee ae Ae” 2 0.48 100.25 In Ruby Valley, near the northeast shore of Ruby Lake, another hot spring reaches the surface, which deposits upon evaporation a siliceous sinter, a product of much less common occurrence from hot springs in Nevada than are the salts of the alkalies. This incrustation yielded Mr. R. W. Woodward: Sic nn A LA oe ew Eee 88.79 Adiaanitia, 5 2.2252 Soper tee rer ee ewe oe 1 15 USN CHIL. SS a eee ene = etry are, cae trace ERO Le - oe: CS ee eine, SOR GLI rea 0.80 SOCIE enc. Oeste ee ae te ert tp ae ero We, 1.06 EOD SNP 3 ee ae ne eb eres E Peseta ao Veena O27 Vy Sym Sie tan ploy oT. EE ORS rece hs a thea Cae 100.00 542 DESCRIPTIVE GEOLOGY. Waite Pine Movntains.—This somewhat isolated group, lying about 60 miles to the southward of the limit of the map, may be regarded as a southern prolongation of the East Humboldt Range. In volume III,’ of this series will be found a geological sketch of that well-known mining region, accompanied by a geological map. Since its preparation, however, the district has again been visited, and a hasty examination made of the here-. tofore unvisited port’on on the west side of Pogonip Mountain, with the expectation, which was realized, of finding still lower formations than had previously been recognized. During this second visit, a large number of fossils were obtained from the different geological horizons represented, including several new species, as well as forms new to the locality. In the narrow longitudinal uplifts, lying between the Sierra Nevada and the Wahsatch Ranges, the greater number of which, in general terms, consist of single anticlinal or monoclinal folds, made up of quartzite and limestone formations of great thickness, it is exceptional to find exposed in any one region a wide geological horizon. But here, at White Pine, the mountains, which have an average width of 12 miles from valley to valley, are formed of three distinct north and south ridges, two of which are mono- clinal folds, with a sharp anticlinal lying between them, exposing, from the base of Pogonip Mountain on the western side, to the top of Mokomoke Ridge on the eastern side, strata from the Primordial shales to the Coal- Measure limestones. Granite crops out in-several small bodies along the base of Pogonip Ridge, but in only one locality was it observed in any large mass, where it occurs in a somewhat isolated hill as a coarse-grained hornblendic rock with a friable texture. At the northern end of the ridge, apparently uncon- formable with the granite, are obscure outcrops of mica slates and black arenaceous and argillaceous slates and shales, in turn overlaid by an unde- termined thickness of a compact vitreous steel-gray quartzite, closely resem- bling the Cambrian Quartzites of other Nevada localities. Above this quartzite, and forming the lower beds along the greater part of the ridge, occurs the Pogonip limestone, which extends to the top of Pogonip Moun- tain, with a thickness of from 3,000 to 4,000 feet of strata. They dip with ' Mining Industry, vol. iii, 409. WHITE PINE MOUNTAINS. 543 an angle of 24° to 30° eastward. The lower beds are a fine-grained, some- what siliceous, black limestone, varying considerably in compactness and bedding, and frequently passing into calcareous shales. Higher up in the series, they develop more of a dark-blue color, banded with layers of fine arenaceous limestones and occasional cherty bands a few inches in thickness. From the large number of organic remains obtained in the hurried study of these strata, it is evident. that the field is one that would well reward the paleontologist, who would make a careful search of the for- mation. - Messrs. Hall and Whitfield have described from these Pogonip lime- stone beds the following forms: Crepicephalus (Loganellus) Haguei, n. sp. . Crepicephalus (Bathyurus) angulatus, n. sp. Crepicephalus (Loganellus), sp. undet. Crepicephalus (Loganellus), sp. undet. Conocephalites (Pterocephalus) lateceps, n. sp. _ Dikellocephalus flabellifer, n. sp. Dikellocephalus quadriceps, n. sp. Piychaspis pustulosus, n. sp. Ptychaspis, n. sp. undescr. Chariocephalus tumifrons, n. sp. Agnostus communis, 0. sp. Lingulepis Mera. s Obolella, sp. undet. © Near the top of the Pogonip limestone, at the northern end of the ridge, were found the following forms, which have been referred to the Quebee group: | Ptychaspis pustulosus, n. sp. Bathyurus Pogonipensis, u. sp. Orthis Pogonipensis, n. sp. Strophomena Nemia, n. sp. Porambonites obscurus, n. sp. Raphistoma acuta, n. sp. Cyrtolites sinuatus, n. sp. 544 DESCRIPTIVE GEOLOGY. . The section given in volume III, from Treasure Peak to the summit of Mokomoke Ridge, presents the following beds: Feet 1. Dark bluish-gray compact limestone ........-..-..--.-.-.- Nelle ag ao 1,500 2. Thinly-laminated calcareous shales with interstratified reddish-gray bands.. 125 3. Siliceous limestone with lenticular masses and nodules of chert..-.....-.-- 100 4, Black koe shales, peers bedded, with seams of ituminous matter . 5 7 600 5. Black shales 1 more arenaceous gna te Vv with interstratified ‘thin beds of | crumbling sandstone =-~ 2 23 sities ae 2 Ones Sener eerie ee 6. Reddish-yellow sandstone, fine- santana even ONTO yee Saath ce UO 7. Light-yellow granular limestone, distinetly bedded, rich “apa enenre fossils. 1,500 — Upon Treasure Hill are exposed at least 1,500 feet of blue limestone, the upper 800 feet of which have been shown, by palzeontological evidence, to be of Devonian age, and the lower beds, although they have as yet yielded no organic remains, have been referred, in the absence of any direct evi- dence, to the same horizon, the Ogden Quartzite not coming to the surface along the base of the ridge. The species obtained from these Devonian strata range, according to Messrs. Hall and Whitfield, from the Upper Helderberg to the Chemung horizons of the New York section. From Treasure Hill were obtained: Cladopora prolijica. Diphyphyllum fasciculum. Acervulania pentagona. Ptychophyllum infundibuluun Naticopsis, sp. undet. | Orthoceras Kingi. Strophodonta canace. Productus subaculeatus. Atrypa reticularis. Lhynchonella Emmonst _Pentamerus, sp.? Spwifer argentarius. Cryptonella, sp.! . Orthas, sp.?; resembles O. resupinata. WHITE PINE MOUNTAINS. 545 Spirifer, sp.2; resembles S. striatus Paracyclas peroccidens. . Bellerophon neleus. Isoneina, sp.? The collection from Babylon Hill included: Syringopora Mocluri? Smithia Hennahu. Favosites, sp.? Atrypa reticularis. Rhynchonella Emmonst. Pentamerus, sp.? Orthoceras, sp.? Pterinea, sp.? . The only forms obtained from Mount Argyle belong to corals, and, although mostly fragments, Prof F. B. Meek has been able to specifically identify the following: Alveolites multiseptatus. Cladopora prolifica. Smithia Hennahia. Diphyphyllum fasciculum. From the Blue Ridge, near the top of the series, we have: Spirtfer Engelmanni. Productus subaculeatus. Pleurotomaria, sp.? _ In the calcareous shales, no fossils have as yet been found. The sili- ceous limestone which caps Telegraph Peak contains large numbers of stems of Crinoidea, especially abundant in a fine-grained, white, cherty band, from which was also obtained a dorsal valve of a new species: Spirifera alba-pinensis, H. & W. This fossil was taken from beds which evidently underlie strata of which there can be little doubt but that they belong to the horizon of the 35 DG 546 DESCRIPTIVE GEOLOGY. Genesee slate; and although this is the only locality from which it has as yet been recognized in Nevada, it is known in the Wahsatch Range asso- ciated with the interesting groups of fossils from Ogden and Logan Cations, which show close affinities with the Upper Devonian, and at the same time are allied to the Waverly group of Ohio. The black argillaceous shales which form so prominent a feature both in the geological and physical aspect of the district are but indistinctly recognized in other places, and without fossils. This may arise partly from the beds in neighboring ranges becoming more sandy or calcareous, thus losing their marked habit, and in part from offering exposures far less readily studied. There can be little doubt but that the horizon will be clearly identified at some future time. in other Paleozoic uplifts of the Great Basin. Here at White Pine, the black shales have been somewhat roughly separated into two groups, the lower more argillaceous, the upper arenaceous, but divided more sharply by the association of species. From the lower strata we have: Leiorhynchus quadricostatus. Aviculopecten catactus. Lunulicardium fragosum (Posidonomya?). Nuculites triangulus. Goniatites Kingit. _ Orthoceras cessator. From the upper beds we obtained: Streptorhynchus, sp.? Spirifer, sp.? (resembles S. disjuncta). Productus semireticulatus. This association of species from the lower beds with Leiorhynchus qua- dricostatus, a characteristic fossil from the Genesee slate, has naturally led Messrs. Hall and Whitfield to regard the horizon as Devonian, and the overlying upper series with the equally characteristic Spirifer resembling S. disjuncta as of Sub-Carboniferous age. . The sandstone beds are mostly barren of organic remains, their chief interest being derived from the number of impressions of stems and leaves — 4 } , EUREKA MINING DISTRICT. 5AT of Lepidodendron and Cordaites, vegetable remains being very rare in the Palzeozoic sandstones of Nevada. Associated with them occur some crinoidal stems similar to these observed in the siliceous limestone below. Next above the sandstone occurs the Carboniferous limestone of Mokomoke Ridge, highly fossiliferous and rich in well-known types of Coal-Measure forms of corals and Brachiopoda, so abundant in the ranges throughout the Great Basin. - These beds yielded: Diphyphyllum subcespitosum. Zaphrentis, sp.? Streptorhynchus crenistria. Productus semireticulatus. Productus Prattenianus. Productus longispinus. Productus, sp.? (resembles P. Worthent). Productus Nebrascensis. Productus costatus. Spirifer cameratus. Spirifer Rockymontanus. Spirifer planoconvexus. Spiriferina spinosa. Athyris subtilita. Athyris sinuata. Eumetria punctulifera. Terebratula, sp.? Evurexa Minine District.—At Eureka, northwest from White Pine, and in the next range to the westward, an exposure of Pogonip limestone is again seen, which forms the immense development of strata of Prospect Mountain, with the same lithological habit as at White Pine, and carrying throughout the greater part of the formation Primordial fossils, showing beyond doubt that the two series of beds are the same and equivalent to the Potsdam sandstone of Wisconsin. Our collections include the follow- ing new species: Crepicephalus (Loganellus) granulosus. Crepicephalus (Loganellus) maculosus. 548 DESCRIPTIVE GEOLOGY. 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 mmutissima. Leptena melita. The only other beds of the White Pine section definitely recognized at Kureka are the Coal-Measure limestones, also highly fossiliferous; many of the species being specifically identical with those from Mokomoke Ridge, although the beds are much darker and more compact than at White Pine. The list contains: Fusilina cylindrica. Trematopora, sp.? Chonetes glabra. Athyris subtilita. Productus semireticulatus. Productus costatus. Productus cora. Productus Nebrascensis. Machrocheilus, sp.? DIAMOND RANGE. HAD SECTION V. DIAMOND AND PINON RANGES. BY ARNOLD HAGUE. Diamonp Ranes.—This uplift lies next west of the Humboldt Range, on the west side of Huntington Valley. It is a long single ridge, of which only about 14 miles, at the northern end, comes within the limit of the map, the range terminating abruptly at Railroad Caiion, about latitude 40° 10.’ It rises from 2,000 to 2,500 feet above the adjoining valleys, of nearly equal elevation above sea-level, in a number of rounded limestone summits with somewhat steep slopes. But little opportunity was afforded for the study of the range, which was crossed at only two points, Chokup Pass, a mile below the boundary of the map, and at Railroad Canon. Structurally, this portion of the Diamond Range would appear to be an anticlinal ridge, with the strata trending obliquely across the topographical axis of the range; that is, striking northwest and southeast, both sides of the fold being largely made up of dark bluish-gray limestone. This limestone has been referred to the Lower Coal-Measure formation, the upper member of the Wahsatch group. At Chokup Pass, a depression in the ridge, the lime- stones are seen dipping both east and west at high angles, the axis of the fold occurring along the summit. In the limestone occurs a belt of coarse, although compact, brownish-yellow sandstone, not unlike the sandstone body at White Pine, which lies at the base of the Coal-Measure limestone. | It measures nearly 300 feet in thickness. No fossils were found. At Railroad Carion, the rocks, light cream-colored limestones dipping to the eastward, are much disturbed and plunge rapidly beneath the surface, where they are overflowed to the north by, large fields of basalt. On the eastern edge of the hills is an obscure dev elopment of yellowish-white rhyo- litic tufa, showing distinct strata-planes, and having feldspars greatly decom- posed. Quartz is rare, and, when present, is in large pieces penetrated by 550 : DESCRIPTIVE GEOLOGY. many cracks. There are a few flakes of black mica. This outburst of vol- ‘canic rocks occurs, like so many others in Nevada, at the end of a long ridge, where the sedimentary strata come to an abrupt termination by plunging suddenly downward, with the break, which is evidently a point of weakness, and one of least resistance, occupied by intrusive material. From this light-colored limestone were collected a number of fossils, types of Coal- Measure species, nearly all identical with forms found in the Carboniferous limestone of White Pine. The following have been identified : Chetetes, sp.? Streptorhynchus Crassus. Productus semireticulatus Productus Prattenianus. Productus costatus. Spirifer Rockymontanus. Spiriferina spinosa. From the southern end of the range, near Newark, in a bluish-gray limestone, were found: Chetetes, sp.? Campophyllum, sp.? Spwiferina spinosa. West of the Diamond Range, the Lower Quaternary plains occupy the central portion of the valley in a belt 4 or 5 miles in width. During the winter and early months of spring, they are usually covered by a few inches of water; but in summer, with the exception of small shallow ponds at the northern and lower end of the valley, they presenta hard level floor like the Great Desert. These Lower Quaternary deposits are strongly impregnated with common salt, and, upon the evaporation of the concentrated waters at the upper end of the valley, exhibit broad fields of salt incrustation, which have for several years been a source of revenue to those engaged in gather- ing it for the purposes of silver-extraction by amalgamation. As the strata upon both sides of the valley dip toward each other, it is not surprising that numerous springs, both hot and cold, should be found encircling the valley along the base of the limestone hills. 'The waters are } PINON RANGE. 551 usually free from saline ingredients. The temperature of several of the pools was taken, showing a variation from 51° to 109°. At the base of: the Pinon Range, on the line of the old Overland Stage Road, are found springs of clear but tepid waters highly charged with sulphur. Pinon Ranesz.’—The range of mountains which lies next west of the Diamond Range, and to the north is separated from the East Humboldt Range by the broad plain of Huntington Valley, derives its name from the very considerable growth of coniferous forests that are scattered over its summits and slopes. It extends from Dixie Pass, just north of the line of AQ)° 30’, where it terminates abruptly, southward to Swallow Canon, near the line of 39° 30’. The 116th meridian west. from Greenwich follows for a long distance the crest of its ridge. It is in general a well-defined single ridge, and for the greater part of its length barely averages six miles in width, having a varied broken outline, with isolated peaks rising between 3,000 and 4,000 feet above the valley, and then rapidly falling off into low depressions and easy passes. . ~Geologically, the Pinon Range presents several features which are of special interest, if not exceptional, in the structure of Great Basin ranges. Among these, the absence of granite throughout its entire length is worthy of remark, as but few ranges are seen in which granite or related rocks do not occupy more or less area, and to the influence of which the present structural features of the neighboring Palzeozoic formations may notin part be traced. But on the other hand there are seen here the entire conformable series rep- resented from the Cambrian schists and quartzites, through the great thick- ness of Silurian limestone, Ogden Quartzite, and nearly, if not quite, to the top of the Wahsatch limestone, lying highly inclined, and exposing about 14,000 feet of strata. In structure, we find, dipping both east and west, simple monoclinal ridges, gentle synclinal folds, and broad anticlinal axes. Everything later than the Wahsatch limestone appears to be wanting until Tertiary times, but of the latter deposits there have been recognized skirt- ing the older upheaval the non-conformable upturned Green River Eocene, with the later nearly horizontal Humboldt Pliocene beds. The volcanic 1Tn part from notes furnished by Mr. Clarence King. 552 DESCRIPTIVE GEOLOGY. activity of the Tertiary age is well shown in the broad areas of both acidic and basic rocks. | ~Parmozorc Formations or THE Prxon Rancr.—South of Dixie Pass, at its extreme northern end, the range rises in an elevated group of peaks, the highest of which has been called the Raven’s Nest. This is formed of a heavy body of grayish-blue limestones, with included strata of buff lime- stone, which trend diagonally across the Pifion Range, with a strike of about north 25° east and a dip of from 25° to 35° to the northwest. Directly north of the Railroad Mining District, the ends of this limestone belt are covered by an overflow of trachyte. At the east base of Raven’s Nest Peak, these beds are conformably underlaid by a thin bed of granular saccharoidal quartzite, which closely resembles the gray limestone above it, the one passing gradually into the other. The whole body of limestone is between 3,000 and 4,000 feet in thickness, and is made up of remarkably heavy beds. Toward the bottom, it is prominently siliceous, but toward the top is a very pure crystalline limestone, which has been much altered into marble, and, where unaltered, is reticulated with seams of calcite. This formation is overlaid by about 1,200 feet of finely-laminated and iron- stained quartzites. The material of this formation is exceedingly fine: it carries no conglomerates; it has no gritty grains, but shows throughout a uniform compact texture. West of Raven’s Nest Peak, it is much traversed by jointing planes, with a strike of northwest and southeast. It is altogether similar to the great quartzite formation which appears south of Pinto Peak in the region of Pinon Pass, and from the trend of the two bodies there is little doubt that they are the same. Directly south of Pinion Pass, the quartzite is overlaid by a heavy limestone, which contains Devonian fossils. West of Raven’s Nest Peak, the quartzite body is also overlaid by a high conical hill composed of heavy dark beds of limestone, conformable with the quartzite, and dipping west at about 40°. A few crinoidal stems were all the fossil remains found in this upper series of beds. Its thickness is entirely unknown, but there are exposed at least 4,000 feet of strata. How much more lies to the west under the Humboldt Pliocene is, of course, uncertain. From its position over the quartzite, from the heavy character of its PALHOZOIC FORMATIONS OF THE PINON RANGE. YI) dark-blue beds, and from the fact that a similar heavy body of limestone, above the quartzite at Pinon Pass, carries Devonian fossils, it has been re- ferred to the Wahsatch limestone. It must necessarily be either the Wah- satch limestone or the Upper Coal-Measures. The underlying quartzite is neither thick enough nor coarse enough to be referred to the Weber beds, and without doubt it could not be the Ute limestone, when still underlaid by so heavy a body of limestone as that of Raven's Nest Peak. Moreover, the quality of the quartzite separating these two limestone bodies is quite simi lar to that of the Ogden Quartzite, so clearly shown in Ogden Cation, Wah- satch Range. The thickness of 4,000 feet of underlying limestone is not too much for the Silurian and Primordial series; when we recall the thick- ness of the lower limestone, as seen at White Pine Mountains and at Rob- ert’s Peak. It is to be regretted that no organic remains were collected, in view of the fact that at Pogonip Mountain large collections of fossils were made throughout the series of nearly 4,000 feet of strata, the greater part of the beds yielding Primordial forms, overlaid by others carrying species identified as belonging to the Quebec formation. Lithologically, the upper limestones at Raven’s Nest do not resemble those of Moleen Peak, which carry, not far above the base of the series, Upper Coal-Measure fossils, and overlie the pebble-bearing, gritty, heavily- bedded quartzite. The character of this latter formation is maintained in Moleen Cafion, and differs entirely from the Ogden Quartzite, which, throughout Central Nevada, is uniformly fine-grained and finely bedded, and carries no conglomerates. | Underneath the heavy Silurian limestone, and under the thin bed of saccharoidal vitreous quartzite, there occurs a heavy red and chocolate-brown quartzite, which forms the summit of Pinto Peak, retaining its conformity with the overlying series, and on the south edge of the Pinto Peak Ridge approaching a horizontal position. These red quartzites to the north of Pinto Peak are underlaid by more or less of mica schists and quartzitic schists, which, from their position, inferior to the Silurian, and from their similarity to the Wahsatch Cam- brian, are referred to the Cambrian age. They are roughly estimated at 5,000 feet in thickness. The section here exposed, therefore, is a conform- yeh DESCRIPTIVE GEOLOGY. able series of about 14,000 feet in thickness, striking north 25° east, at an angle, diagonally to the north and south trend of the range, and composed in an ascending series of the following beds: 1. Heavy schists, grits, and quartzites (Cambrian)... ...-.- teres 5.000 feet. 2. Gray and bluish-gray limestones (Ute-Pogonip limestone) .... 3,500 to 4,000 feet. 3. Fine-grained and finely-laminated quartzites (Ogden Quartzite) . 1,200 feet. 4. Dark-blue limestone, with interstratified beds, toward the base of the series, of cream-colored and whitish limestone (Wah- satch limestone) ........ EE ea ee SES Se AREAS b 3,500 to 4,000 feet. No fossils were found in any of these beds except the crinoidal stems above mentioned, and the reference of their horizons is therefore made entirely from stratigraphical evidence, which, besides the great similarity to other sections, is in this case rendered quite certain by the continuity of the Ogden Quartzite to the southward in the range. It is not considered certain that the whole of the body laid down as Cambrian is really such. There are two zones of quartzite, one of a gray saccharoidal form, the other brownish and distinctly laminated, which, as described, immediately underlie the lower limestone. Underneath these, the mica schists and heavy red quartzites of Pinto Peak may possibly be unconformable with the Cambrian quartzites, and represent an Archzan centre. The relations between the two are obscure, but the observations in the field tended to show that the whole outcrop is, as colored on the map, Cambrian. The lower beds of the lime- — stone body, which has been designated on the geological sheet as Silurian, should probably have been referred to the Cambrian, so as to include in the latter formation those strata which contain Primordial forms. Trending southwest from Dixie Pass, the Ogden Quartzite becomes the foot-hill rock west of Pinto Peak, and, with slight interruptions where the Tertiary overlies it, may be traced upon a curved line of strike, until, in the region of Willow Creek, it trends south 50° east, and dips southwest. At Willow Creek, the range has developed a complete anticlinal, of which the _ central part is formed of the lower limestone, which dips at an angle of about 16° to the west and about 20° to the east. This is overlaid on both sides of the range by the Ogden Quartzite, which, farther south, arches over the Ute-Pogonip limestone, and forms the axis of the fold, overlaid again on each side by the Nevada Devonian, or lower members of the Wahsatch lime- PALHOZOIC FORMATIONS OF THE PINON RANGE. 555 stone. The limestone, which makes its appearance, conformably overlying the quartzite, just north of Willow Creek, and to the south of it, and again upon Hot Spring Creek, is similar in all respects to the limestone west of Raven’s Nest Peak, with the same predominance of earthy buff beds in the first 1,200 or 1,500 feet. The limestones from Willow Creek south do not rise so high in the series as at the north. Those at the north, upon purely structural grounds, from evidence obtained in so many other localities, are divided into the Devonian, Sub-Carboniferous, and Lower Coal- Measures ; or, in other words, all three divisions of the Wahsatch limestone. The Sub- Carboniferous, throughout our entire area, is such a narrow belt, that it is exceedingly difficult to recognize it; but, in sucha conformable deep-water series, it seems highly probable, with the Sub-Carboniferous probably occurring at White Pine, that it should be represented here. The line between the Devonian and Sub-Carboniferous is drawn quite sharply at Hamilton and Eberhardt in the White Pine Mountains, but cannot with equal certainty be laid down in the region of Raven’s Nest Peak. Farther to the southward in the range, evidence was obtained showing conclusively that about 1,200 feet of limestone, which overlie the Ogden Quartzite, con- tains organic remains, of which the Upper Helderberg marks the highest horizons. The occurrence of Devonian beds, as high as the Genesee slates, as well as the Upper Helderberg at White Pine, indicates that the summit of the Devonian series must be placed a few hundred feet above the Helderberg line. Accordingly, on the hills west of Raven’s Nest Peak, the hypothetical line separating the Devonian from the Sub-Car- boniferous is carried about 1,500 feet above the Ogden Quartzite. The geological section across the Pinon Range represented at the base of the geological map is made through the peak at the head of Pony Creek, and shows the flat anticlinal of Ogden Quartzite occupying the crest and higher summits, with the Devonian limestone dipping gently away both to the east and west. On the east side, the upper limestone beds are con- cealed by a heavy outburst of rhyolite, which extends to the plains, while on the west side the Humboldt Pliocene and Quaternary beds rest directly against the limestone. In the section, the Ute-Pogonip limestone and Cam- 556 DESCRIPTIVE GEOLOGY. brian beds are drawn as forming a part of the anticlinal fold, but covered by the great arch of Ogden Quartzite. This anticlinal axis, continuing southward, trends diagonally across the range at a strike of about south 25° east. The easterly-dipping limestones of the anticlinal, 4 miles north of Pinon Pass, are covered by the body of rhyolite already mentioned, but on the west side of the anticlinal, however, they dip uniformly to the southwest for about 2 miles, when they pass under the synclinal axis, and rise again to the west, having an easterly dip, and exposing the Ogden Quartzite along the west base of the range. In the basin of this synclinal, the Sub-Carboniferous and Lower Coal-Measure formations have been introduced upon the geological map. It should, however, be distinctly stated that no paleontological evidence for such an assignment was obtained, but it has been made for the same rea- son as already given for the great thickness of beds in the region of Raven's Nest Peak. Near Mineral Hill, on the west base of the range, the Ute- Pogonip limestone comes in below the Ogden Quartzite, extending south- ward for about 4 miles in low broken hills, until concealed beneath great flows of basalt. It forms the narrow entrance to Cave Cajon, where it appears in somewhat higher hills as a hard siliceous blue limestone, with a rough irregular fracture, and dipping under the overlying quartzite. The Ogden Quartzite is seen in low hills of exceedingly hard flinty rock of bluish and reddish tints and a vitreous lustre. Above the quartzite occurs the Devonian limestone, reaching to the summit of Fossil Pass, and form- ing the entire eastern slope. In color and texture, it resembles the lower members of the Wahsatch limestone already described, many of the beds possessing the characteristic buff color. The beds are slightly arenaceous, the siliceous grains being usually very fine, while certain layers are more or less dolomitic in composition. Under the microscope, the quartz-grains show frequent liquid-inclusions. The beds trend diagonally across the range, striking north 20° to 25° west, and dipping 28° to 30° to the east- ward. At Pine Nut Pass, 14 miles to the southward and near the southern end of the map, the structure is much the same, a simple monoclinal ridge dipping eastward; the section, however, exposing only the Ogden Quartzite PALHOZOIC FORMATIONS OF THE PINON RANGE. 5D7T and Devonian limestone. The former occurs as rolling foot-hills, overlaid: by ridges and walls of the latter, with a dip of 30°. As regards the paleontological evidences of the age of the Pifion Range, it may be said that from only one locality have organic remains been found in the lower body of limestone, and these were confined to stems of corals too poorly preserved for specific determination. They were found in a blue cherty bed near the entrance to Cave Camion, and, coming from the upper members, are of some special interest, as Prof. R. P. Whit- field regards them as belonging to the horizon of the Lower Helderberg of a the New York section. From several localities in the range, however, the j q F Wahsatch limestone has yielded fossils which have been referred to the Devonian age, the association of forms clearly indicating the Upper Hel- derberg beds. In one instance, there would appear to be a mingling of both , Lower and Upper Helderberg forms; but, according to Professor Whitfield, all the forms might possibly occur in the Devonian beds. With Lower Helderberg fossils near the top of the underlying limestone, and Upper Helderberg forms near the base of the overlying limestone, the paleonto- logical evidences certainly favor a conclusion that the Ogden Quartzite is the equivalent of the Oriskany sandstone in the New York section. | In the region of Hot Spring Creek, the limestone furnished the follow- ing forms: Dalmania, sp.? (closely resembles D. anchiops from the Schoharie Grit of New York). Edmondia Pinonensis (associated on the same block with Chonetes and Spirifer). Orthis oblata. Orthis, sp.? (resembles O. quadrans). Strophodonta, sp.? Spirifer Pinonensis. Spirifer, sp.? (resembles S. arenosa) Atrypa reticularis. Rhynchonella, sp.? - Several species of Brachiopoda, found in’ the above list, were also col- lected from the summit of Fossil Pass. 558 DESCRIPTIVE GEOLOGY. On the east side of the range, nearly due east from Chimney Station, were collected a number of fossils, chiefly corals, which, although they have not as yet been specifically identified, are closely related to Upper Helderberg forms. Among them were the following: Zaphrentis, sp.? (figured by Professor Meek). Fawosites, sp.? Cladopora, sp.? Spirifer, sp.? Mr. Henry Engelmann, who accompanied the expedition of Col. J. H. Simpson, obtained in Swallow Cajon, at the southern end of the Pinon Range, Devonian fossils, which Prof. F. B. Meek’ has described in a report accompanying that of Colonel Simpson. The list comprises: . Productus subaculeatus. Spirifer Utahensis. Spirifer Engelmann. Spirifer strigosus. Atrypa reticularis. Professor Meek regards the group as closely allied to forms found in the Hamilton series of New York in a very similar rock. All of these spe- cies have since been found by us in the Devonian limestone of White Pine. It is noteworthy, that while localities of Devonian fossils are as yet somewhat rare in the ranges of the Great Basin, and the Lower Coal-Meas- ure forms of the Wahsatch limestone so abundant, here, in the Pinon Range, the paleontological evidences of the Devonian age of the lower members of the series should be so clearly defined, and exposed in so many localities on both slopes of the range along a north and south line of nearly 60 miles. | Votcanic Rocks or THE PiXon Ranex.—Tertiary eruptive rocks are represented by trachytes, rhyolites, and basalts. From Dixie Pass south- Exploration across the Great Basin of Utah in 1859. Col. J. H. Simpson. Washington, 1876. , VOLCANIC ROCKS OF THE PINON RANGE. 559 ward, the stratified rocks are overlaid and cut off by irregular flows, which score the base of the range from its northern end to Pine Nut Pass. Not- withstanding these broad areas of volcanic rocks, it is noticeable that the Paleozoic ridge is never traversed by dikes or shattered by massive eruptions, forming prominent Tertiary peaks within the range; and although rhyolite hills in the region of Pinon Pass rise to considerable height, they lie to the eastward of the main uplift, and do not appear to have disturbed the broad anticlinal fold. From the region of Dixie Pass, the eastern foot-hills for about 12 miles are covered by successive outflows of trachyte, which, directly south of the pass, form rolling hills which abut against the ends of the Ute-Pogonip limestone, and trend southward until they flank the Cambrian quartzites, then continuing southward overflow the latter limestone on the east side of the anticlinal and also the Ogden Quartz- ite. This belt of trachyte widens out directly south of Dixie Valley for about six miles, and forms the material of a group of conical hills which, from their peculiar outlines, are conspicuous anywhere from the valley of Dixie Creek. | The overlying sheets and masses of trachyte, as well as all the promi- nent conical hills, are formed of a brownish and reddish-brown sanidin- trachyte, in which the characteristic vitreous crystals of sanidin are riven with a multitude of cracks like those in the typical trachyte of Washoe. The groundmass is very coarse and rough in texture, and is formed of sanidin and brown magnesian mica. In a number of places where erosion has laid bare the lower members of the outflow, there is seen a gray trachyte rich in hornblende, and carrying a high proportion of plagioclase. This has a distinct bedding and a decided dip to the east, or away from the flanks of the range. In these gray hornblendic trachytes, the base is more com- pacted, and the rock has far more the habit of bedded andesites. It is not unlike the rock of the cross-spur at Washoe, and only differs from it in having rather smaller feldspar crystals. Mica, although present, is always in less quantity than the hornblende, and forms large black crystals, with a tendency to decomposition into brown earthy material. The less altered crystals cleave with very smooth and brilliant black faces. It is interesting to observe here, as in so many other places, noticeably in 560 DESCRIPTIVE GEOLOGY. Washoe, this sequence of hornblendic trachyte, having affinities with andesite, followed by normal sanidin-trachyte. Hast of Pinto Peak, and a little to the north, in the middle of the trachytic zones are a series of north and south dikes of black vesicular basalt, which have small local outflows covering a group of hills with thin sheets. These basalts are poor in olivine and rich in acidic glass. They are also noticeable for the comparatively large size of the triclinic feldspars. The contact between the sanidin-trachytes and the rhyolites lying farther to the south was not actually observed; but, from the contour of the hills and the peculiar southward slope of the trachyte surface, it seems most probable that it passes under the rhyolite. The volcanic rocks in the region of Pinon Pass are a light earthy rhyolite, having a very trachytic texture, containing, in a micro-crystalline groundmass composed of quartz, sanidin, and biotite, numerous dihexahedral quartz-grains, earthy, half- decomposed orthoclase, and an unusually large proportion of biotite flakes. With the exception of the biotite, these minerals are not disseminated regu- larly through the mass, but occur in isolated bunches, ten or twelve large quartz-grains appearing together, and, in others, groups of broken crystals of orthoclase. It is one of the richest in biotite of any rhyolite in the collec- tion. But for the presence of quartz, both as a secreted mineral and in the ' groundmass, its general appearance and texture would unite it with the trachytes. About 12 miles farther to the southward, at the base of the range, occurs another rhyolitic outflow, which forms low broken hills in contact with the Devonian limestone. This rock isa half-glassy hyaline variety, of uniform texture, and of a dark-gray color, with large sanidin feldspars imbedded in the glassy groundmass. Like many others of the same class, it withstands atmospheric agencies remarkably well, but erosion-outlines are usually sharp and angular. Between these two bodies of rhyolite are found small isolated patches of basalt, occupying the same relation to the. Paleozoic strata as the rhyolitic masses. One occurs on the foot-hills near Fossil Pass, and is a hard, fine-grained, black rock. They appear simply as outlying bodies of the broad field of basalt, which borders the rhyolite east of Pinon Pass, and forms a continuous group of hills from the Pinon VOLCANIC ROCKS OF THE PINON RANGE. 561 Range to Railroad Cation in the Diamond Range, where it overflows the cream-colored Carboniferous limestone. These basalts connect the two ranges, completely encircling the northern end of-Diamond Valley. It would appear to be a common mode of occurrence for both rhyolites and - basalts, when coming to the surface along breaks in the sedimentary strata, or where the beds suddenly plunge downward beneath the surtace, to strike, in massive eruptions, diagonally across the intervening valley to the base of the next range, dividing the depression into separate basins. ‘The basalts of this long range of hills are rather uniform in character. Under the micro- scope, they appear to be unusually rich in grayish-black globulitic base. Augite is present in very fine grains, but the rock would appear to be remark- ably poor in olivine. On the west side of the Pinon Nange occurs a very interesting basaltic table, which extends along the base of the range for 10 miles, abutting against the Ogden Quartzite, and completely obscuring the Ute limestone below. Along its east side, toward the range, it presents a moderately steep cliff, or wall, the main body dipping very regularly to the westward at an angle of 3° toward the great basaltic flows of the Cortez Range on the opposite side of Garden Valley. The rock is distinctly bedded; deep black in color, and hard, but porous in texture. One other locality of rhyolite connected with the Pinon Range, and found on the east side, some 8 miles south of the limit of the map, deserves mention. It presents a nearly white groundmass studded with large irreeu- lar grains of quartz and broken tabular crystals of glassy feldspar. There _ may also be detected a few small flakes of dark biotite. The groundmass has a coarse crystalline structure, which at once suggests to the field- observer, upon superficial investigation, a granite-porphyry, and yet a closer examination, together with its geological position, shows that it ‘must be a Tertiary product. As rhyolite is sumply the modern Tertiary type of the older granite-porphyry, this structural relationship between the two rocks ‘is of interest. What adds greatly to this interest is, that. Professor Zirkel finds, after a microscopical analysis of the rock, the same close resemblances, but concludes that the rock is undoubtedly a rhyolite. Professor Zirkel also finds in this rock minute grains of garnet, an exceed- 36 DG : 562 _ DESCRIPTIVE GEOLOGY. ingly rare but not a unique occurrence, they having been observed in rhyo- lites from both Hungary and New Zealand.* . Dixie Group Recroy.—East of the foot-hills of the trachyte hills is an outcrop of uplifted Tertiary extending from Dixie Valley southward for 8 miles, and occupying a valley, or rather a lowridge, between the trachytes and a body of Lower Coal-Measure limestones. to the east. For the most part, they are finely-bedded calcareous shales and marls containing carbo- naceous seams and brown carbonaceous zones, which carry more or less coal. In the calcareous shales were noticed fragments of fossil fishes, but too obliterated for specific determination. They undoubtedly belong to the Elko shales, and are therefore referred to the Green River Eocene. They strike about north 20° east, and dip 30° to the east. This is the westernmost of the Green River outcrops, exposures of Eocene lacustrine deposits having never as yet been definitely recognized west of the Pinon Range. : To the east of this Hocene body, and penetrating it, lies a north and south ridge, detached from any mountain-range, about 8 miles in length, consisting of heavy beds of dark limestone, striking north 20° east, and dipping to the east. It contains the following Coal-Measure fossils: Pyoductus semireticulatus. Productus longispinus. ‘It is evidently a part of the Wahsatch limestone, and directly to be connected with the fragments of Wahsatch limestone of a corresponding dip and strike, which lie to the east of the anticlinal north of Pitton Pass. The strike and dip of this limited body of limestone, which overlies the Ogden Quartzite, and is itself masked by overlying rhyolites, would, if continued, bring the Devonian beds directly under the Green River Kocene, at the west base of the limestone ridge. There can be little doubt, in connection with the fossils, that this is really the upper part of the Wah- satch limestone, and is the equivalent of the heavy beds of limestone which overlie the Ogden Quartzite west of Raven’s Nest Peak; the rest of the 1 Microscopical Petrography, p. 195. PLIOCENE FORMATIONS. 563 easterly-dipping part of the anticlinal having been covered over first by the Eocene deposits, and then subsequently by trachytes. PurioceNEe Formations.—To the north, the eroded edges of the Gres River series are overlaid by the soft friable beds of the valley Tertiary of the Humboldt Pliocene, which here, as elsewhere, are approximately hori- zontal. They extend to Dixie Creek, where they are, for the most part, covered by Quaternary detrital matter, and at Dixie Pass entirely con- cealed by accumulations of both trachytes and rhyolites. From the pass to the neighborhood of Cave Creek, the western foot-hills are skirted by a continuous band of Pliocene Tertiary, consisting of remarkably fine calca- reous clays and sands. So much of the earlier rock of the range immedi- __ ately underlying these Pliocene beds is of limestone, that it is not surprising to find so general a calcareous character in the Pliocene strata. In the region of Pinion Pass, they are mostly calcareous, where the beds, for a thickness of from 80 to 100 feet, are of white compacted lime-rock, in which is mingled about 10 per cent. of siliceous sand. These Tertiary lime formations are very chalky in texture and appearance, and are evidently made up of exceedingly fine material; in places, they are also more or less impregnated with alkaline salts, as if the lake in which they formed had been saline. Carbonates and chlorides predominate, but there are, at least in two cases, a little sulphate of soda and lime. An analysis of this white lime-rock, from the Pine Valley Pliocene, by Mr. B. E. Brewster, yielded : ASiliGae ots Re ceyie oh) bot sotls 5 Gua see anes 12.07 Alumimay ere: ij bok 3 ee eee ee be. 1.28 INGO ORIG ye a ca tcla co 2 ee 0.57 ILNHNS «Gace shee sot ooeos seo ee nee ee 45.29 Maomesiag= S62 o-:- Be re eas acta wis Wien oa 1.86 Sala and (as. -0 0 090 @anbomicpaciduee yes ess ot ok eke 36.23 | Wade | er eile. (sade SORE en ees 2.65 564 DESCRIPTIVE GEOLOGY. Toward the northern part of theswange, in the region of Pinto and Raven’s Nest Peaks, a large amount of siliceous rock forms the foot-hills; the beds are in general more arenaceous, are far coarser, and carry thin sheets of pebbles. On the east side of the valley, and especially toward the northern end of the range, the Pliocene .strata are prominently terraced, but on the west side they slope gradually, becoming a sort of inclined table cut by shallow ravines. The depression of Dixie Pass represents a most remarkable point of dislocation. 'The Cambrian, Silurian, Devonian, and Carboniferous strata, all dipping west, come up to the pass from the south. The pass itself is obscured by trachytic and rhyolitic outflows, while on the hills to the north | the outcrops are those of the Upper Coal-Measure limestone and Weber Quartzite, all dipping to the east, or in an exactly opposite position to the rocks south of the pass. It seems not improbable that the anticlinal south of the pass has been depressed and moved to the eastward, and that the line of fault is now obscured by the Dixie Pass volcanic outflows. Rosert’s Peax.—Only the northernmost slopes of Robert's Peak come within the limit of the map; but the peak presents so much that is of interest that it will not be out of place to introduce here a few notes made during a hasty examination of the region. The mountain-group of which the peak forms the culminating point lies between the Pinon and Wah-weah Ranges, completely shutting in Keyes Valley to the north, and stands out promi- nently above the surrounding country, partly on account of its great, eleva- tion (10,136 feet) above sea-level, but in part also of its isolated position between two long, parallel ranges. ‘The group consists almost entirely of limestone; and, from the fossils obtained, it is evident that the beds belong to the lower limestone belt. No careful estimate of the thickness of strata _ could be made, as the structure, somewhat obscure, was not clearly seen, but there must be at least between 2,000 and 3,000 feet of conformable beds which lithologically closely resemble the Pogonip series, compact, dark limestones, more or less siliceous, with interstratified beds of calcare- ous shales, and thin, cherty layers. So far as examined, the beds are inclined uniformly to the eastward, with a varying dip, and a strike north- west and southeast. Along the northern slopes, recorded strikes give from > : , 4 qt q d : ROBERT'S PEAK. 56D north 20° to 25° west, with a dip from 40° to 50° to the eastward, while the southeast foot-hills indicate a strike of north 8° to 10° west, and a dip of 18° to 24° to the eastward. Organic remains were obtained from several Reais from the upper horizons on both the north and -south slopes, yielding forms which may range from the upper members of the Quebec group to the Lower Helder- berg of the Upper Silurian. Itis one of the few localities in Nevada along the line of the Fortieth Parallel Survey where es Silurian fossils have been found. ) . The list embraces the following : Cladopora, sp.?; resembles C. seriata. Orthis, sp.?; ae O. hybrida. Atrypa reticularis. Atrypa, sp.?; resembles A. nodostriata. Rhynchonella, sp.? Illenus, sp.? The lower beds were not examined, but it would seem highly probable that they may be found to contain forms characteristic of both the Quebec and Primordial horizons, as found at White Pine and Eureka. Overlying the Robert's Peak limestone, along the extreme northeastern foot-hills, occurs a dark-blue cherty quartzite, which, from its position and habit, has been referred to the Ogden Quartzite. It occupies but a limited area, being concealed both to the east and west by volcanic rocks, and derives its chief interest as indicating the relationship between the Robert’s Peak limestone and the Pifton uplift. ; Volcanic activity has had much to do in producing the displaced and shattered condition of the Robert’s Peak beds, which, both to the east and north, have been broken through and buried beneath large outflows of both trachytes and rhyolites, but chiefly by basalts. These intrusive rocks fre- - quently extend from the highest ridges down the long slopes of the mount- ain to the valleys below. ‘Trachytes are found breaking through the Ogden Quartzites, where they occur as a dark-gray, rough rock, carrying shat- tered crystals of sanidin and some dark mica. The trachytes are overlaid by basalts, which, to the north, are connected with the basaltic table 566 DESCRIPTIVE GEOLOGY. of the Piton Range, and southward with the great dome-shaped masses stretching from Robert's Peak to the Pition Range, forming a north and south line of eruption nearly 25 miles in length. Rhyolites skirt the northern foot-hills, connecting with those of the Wah-weah Range, but the most interesting occurrence is found near the summit, just north of the main peak, where it breaks out through the lime- stone in a rounded dome-shaped hill. Rocks of precisely similar character to this were nowhere observed throughout the Great Basin, and, although of volcanic origin, it presents, in the field, a somewhat slaty schistose structure rarely observed in rhyolites. The groundmass appears quite uniform in texture, and of a dark bluish-gray color. Large feldspars are rare. Well- developed hexagonal plates of biotite are abundant, associated with occa- sional dark hornblende crystals. But for the large amount of finely-dis- seminated quartz in the groundmass, the rock, like the rhyolite from the east side of the Pifion Range, would show a close relationship with the tra- chytes. In this connection, therefore, it is of special interest to know that - the microscopical analysis shows the same trachytic habit, but with many marked characteristics of rhyolite. Apatite may be detected in thin sec- tions under the microscope. . . Wau-wean Rance—This range extends from Garden Gate south- ward for nearly 30 miles, and forms the western border of Keyes Valley. It separates Keyes from Cortez Valley, the latter lying between 400 and 500 feet below the level of the former. Only about 8 miles of the extreme northern end of the range is represented within the limits of the map, which consists mainly of granite and quartzite. | Granite occurs a few miles below Garden Gate, on the western side of the range, where it rises abruptly above the long slopes of Quaternary deposits of Cortez Valley, and forms a broken irregular-shaped mass for some distance, reacliing an altitude nearly 1,000 feet above the plain. But little opportunity was afforded for studying this granite; it is, however, a medium-grained rock, resembling closely in its general outline the Mount Tenabo and Shoshone Wells body, and is probably simply an extension to the southward, with Garden Gate occupying a depression in the mass, which rises on both sides to a considerable elevation. Surrounding the ee ee ee eee ee ee eS LS eee lll WAH-WEAH RANGE. 567 granite on all sides, except toward the valley, occurs a heavy body of quartzite, which has been referred to the Ogden Devonian, although but little examined. Throughout Nevada, where large bodies of quartzite are found without any clue to their stratigraphical relations with an underlying or overlying limestone, the adjacent rocks being either granites or Tertiary volcanic outflows, it is exceedingly difficult, if not impossible, to definitely determine their true geological horizons. In many eases, lithological and structural resemblances will furnish a strong aid to such determinations, which, when followed up, will not infrequently throw the evidence in favor of one or the other of the great zones of quartzite; but unfortunately, in _ many cases, such resemblances are meagre, and the reference is made upon theoretical grounds, based upon slight evidence, or even personal impres- sions received in the field. ‘The relation of the quartzite of the Wah-weah Range to the heavy body of limestone of Robert’s Peak has not been worked out, but has been regarded as overlying it, and therefore has been referred, as already mentioned, to the Ogden formation. Geologically, the chief interest in the Wah-weah Range is found beyond the boundary of the map, where the quartzites give out, and are replaced by immense flows of trachyte and rhyolite, extending to the southern end of the range, and con- cealing the lower sedimentary strata. In one or two places, however, the. quartzite comes to the surface, indicating that the intrusive rocks follow, as is so often the case, the longitudinal axis of the Paleozoic uplift. - Trachyte-is the predominant rock, and forms the broad, table-like body which extends the width of the range. A number of small hills and peaks rise above the general level, and the mass is traversed by numerous deep eafions and ravines, exposing a great thickness of trachyte. It is, indeed, the largest body of trachyte observed in Central Nevada. Last of the Virginia Range, trachyte outbursts are usually confined to narrow dikes, isolated hills, or cappings of older beds; the broader areas of acidic rocks being mostly of the rhyolitic variety. It would appear, however, probable that many large fields of trachyte have been poured out, and have since been buried beneath extensive flows of both rhyolite and basalt. It is also worthy of note that this trachyte mass lies slightly inclined to the westward, or toward the lower valley. 568 DESCRIPTIVE GEOLOGY. Few localities afford a better opportunity for the study of the various modifications in form, texture, and mineral composition, of trachytes than the Wah-weah Range. There are represented here both the normal sanidin-trachytes and hornblende-oligoclase-trachytes. ‘The former, which are generally the younger, are rough, porous, light-gray rocks, rich in sanidin and brilliant flakes of biotite. In the latter, the groundmass is more compact, more homogeneous, darker in color, and rich in triclinic feld- spars, mostly oligoclase, associated with well-developed dark hornblendes. Between these two types are seen every variety, from those rich in either hornblende or mica to those in which both minerals would appear to oeeupy a very subordinate position. In one of the normal sanidin-trachytes, Professor Zirkel detected, under the microscope, the somewhat rare occur- rence of blue haiiyne. Associated in the same rock were also found minute forms of apatite. Quartz, which is a characteristic ingredient of rhyolite, also occurs in some trachytes, and Professor Zirkel has pointed out that the quartz of trachyte is almost always present, as a secreted mineral, in large macroscopical grains, while in rhyolites, in addition to the larger masses, it occurs in minute grains disseminated through the groundmass. Quartz-bearing trachytes are also well developed in the Wah-weah Range, -and would appear to form no exception to the general rule, the rock possess- ing all the habit of trachyte with the addition of large grains of clear, colorless quartz. In the same region are also found augite-trachytes, the groundmass of which presents. a dark-gray, uniform character, with a resinous, oily lustre, so marked in the augite-andesites. Scattered through this dark groundmass are numerous light-colored feldspars, which give the rock a decidedly porphyritic appearance. Brilliant striated plagioclase crystals are abundant. Apatite may be detected under the microscope, and the feldspars shown to contain some remarkable glass-inclusions. The rhyolites of the Wah-weah Range also play an important part in the volcanic activity, and are found skirting the hills both at the extreme northern and southern flanks, and also on the’summit of one of the higher points. They all possess the same general habit, a bluish-gray microfelsitie groundmass, characterized by large numbers of irregular black grains of quartz and broken crystals of sanidin. In some localities, mica forms a WAH-WEAH RANGE. 569... prominent ingredient. Like the trachytes, the rhyolites under the micro- scope show the presence of apatite. It will be seen that there are represented here a wide range of acidic types of volcanic rocks, embracing varieties from the extreme highly siliceous rhyolites, with their characteristic structure, through quartz-bearing trachytes, rough, light-gray, normal, sanidin-mica-trachytes, plagioclase- hornblende-trachytes, to the augitic varieties, which show a marked miner- alogical and physical resemblance to the rocks classed as augite-andesites. In Cortez Valley, just east of the Wah-weah Range, occurs an inter- esting shallow alkaline lake, which, during the autumnal months, becomes dry, depositing a considerable amount of sulphate of soda and common salt. A sample collected in the month of J uly from the northern end of the val- ley contained: Chloride of sodium wae e eee 5 afin ot OL pages RD are 78.31 Sulpietonamicadae oo sel. ees SS aad i 99.42 The aqueous solution was neutral. It contained, in addition to the substances quantatively determined, minute traces of lime, potassa, lithia, and boracic-acid. 570 DESCRIPTIVE GEOLOGY. SHC TON =v CORTEZ RANGE. BY S. F. EMMOXS. Tenaso Peak Recron.—The Cortez Range lies next west of the Pinon Range, and is separated from it by the narrow Pliocene basin of Pine Valley. It has a northeast and southwest trend; but, owing to the great accumulations of intrusive rocks, its boundaries are less clearly defined than are those com- posed mainly of sedimentary strata. To the south, the range terminates abruptly in Tenabo Peak, but to the north it stretches out in broad, irreg- ular fields of rhyolite. ‘The Cortez exhibits a marked contrast to the Pinon Range, the latter being formed of longitudinal uplifts of Palseozoic strata bordered by volcanic outflows, while the former, exposing but little of sand- stone and limestone, shows intense activity of igneous rocks, not only in the broad accumulations of volcanic material, but in the great variety of rocks represented from quartz-propylite to the latest flows of basalt. f Tenabo Peak, at the extreme southern end, stands out somewhat prominently from the rest of the range, separated by the marked depression. of Agate Pass. This peak, the highest in the range, has an elevation of 9,240 feet above sea-level, and rises boldly over 4,000 feet above the Qua- ternary plains of Crescent Valley. Tenabo, in the language of the Sho- shone Indians, is said to signify ‘“Lookout”, a very appropriate name, as the peak affords one of the broadest and most commanding views to be found in Central Nevada. The greater part of the mountain is made up of.a heavy body of granite, extending from the base up to within 900 or 1,000 feet of the summit, where it is overlaid by a limestone ‘body referred to the Upper Coal-Measure series. This granite also forms the lower 2,000 feet of the precipitous western wall of the mountain down to Shoshone Wells, stretch- ing westward so as to include the body making the divide between Cres- cent and Cortez Valleys. | Mill Creek and other lesser cations cut deeply into the formation, and TENABO PEAK. | yal expose numerous walls, which offer fine views of the granitic mass. The granite is characterized by its tough, dense appearance, with but little ten- deney to crumble or wear away by exfoliation. It varies very considerably in texture, from a fine to a medium-grained rock, and from a pearl-gray to a rather dark-gray color, due partly to the differences in texture and in part to the more or less quantity of dark mica present. The granite is made up of quartz, in translucent grains, usually quite small, both monoclinic and triclinic feldspars, and dark biotite plates. In the region of Shoshone Wells, the rock is perhaps somewhat lighter in color than the main body of Tenabo Peak, but otherwise shows but little difference. _ Between the forks of Upper Mill Creek, on the west side of Tevatna, occurs a rock-mass of later age than the granite just described, as it pene- trates the latter as an intrusive body, with sharp lines of contact. It may probably be best classed as a diorite, but at the same time it presents many features of a fine-grained granite which has broken through the older body. It is a compact, dense rock, breaking with great difficulty under the ham- mer, with an uneven surface and angular fracture, behaving like a fine granite, or, more accurately, like a rock in which fine quartz is a predomi- nant constituent of the groundmass. Few granites, however, possess so fine a texture as this rock, the groundmass being almost crypto-crystalline, with clearly-defined plagioclase and fibrous hornblende, while a more care- ful search indicates some orthoclase and quartz. The microscope reveals the presence of biotite in small flakes, and that the triclinic forms of feld- spar prevail over monoclinic.. So much hornblende with triclinic feldspar places the rock among the diorites, while on the other hand mica, asso- ciated with so considerable a proportion of quartz, would suggest a granite. It is of special interest that the diorite of the Agate Pass Region to the north also carries a large amount of quartz as an accessory constituent. Resting upon the granite, and forming the summit of the peak, oc- curs a body of limestone which dips with an angle of 30° to 35° to the eastward, and strikes south 10° east. The limestone extends but a short distance north of the summit, but thickens rapidly to the south. It is underlaid by a belt of pure white quartzite 420 feet in thickness, in turn underlaid by a second limestone formation. This quartzite has a saccha- 572 DESCRIPTIVE GEOLOGY. roidal granular texture, resembling many varieties of marble. In the quartz- grains may be seen under the microscope large numbers of fluid-inclusions. Interstratified.in the quartzite are thin seams or bands of black or steel- gray quartzite, with the lines of contact between the two kinds sharply defined. A precisely similar bed of white quartzite, interstratified in lime- stone, with the same lithological features, both above and below it, has not been recognized in any exposures of the great belts of limestones. It may, however, represent some of the coarse yellowish-brown sandstones, or pos- sibly some bed of arenaceous limestone, so frequently met with in other localities, notably the brown sandstone bed in the limestone of Chokup - Pass, Diamond Range. | The limestone has an even, fine-grained texture, and a gray to grayish- black color. Disseminated through it are thin flakes and minute particles of iron pyrites. A specimen taken from near the summit of Tenabo Peak has been submitted to analysis by Mr. B. E. Brewster, with the following result: Silica, (chiefly. (sandler ee eres 19.899 Silica: (soluble) S sawteer ee eee eee ee Rea 1.088 Jron pyrites*. 2 322s sao a ee eee 1.166 Alumina and temiccomiders= 4-69. ees 1.088 Time = ee ene ae CEE NES NS eet ee 39.765 Magnesia oo 2.5 Gee 2.799 Carbonic acid. 2). 32.85 02 5. ee eee Water and organic matter......-- Baresi ai See a OEY) 99.663 This gives : Carbonate-of lime.2 =e ee eee 67.545 Carbonate of magnesia.........- Spa eo ae 5.878 A minute quantity of the alkaline bases was detected, the spectro- scope indicating the presence of both soda and potassa. No direct stratigraphical evidence was obtained as to the age of the limestones, as they rest high up on the granite, cut off from all other sedi- _ AGATE PASS REGION. | 573 mentary formations, nor were fossils obtained. As heavy beds of quartzite and overlying limestone to the north of Agate Pass have been placed in the Weber Quartzite and Upper Coal-Measure limestone, the Tenabo Peak beds have also been provisionally referred to the horizon of the Upper Coal- Measures. fi In the cafion through which the road passes, just north of Shoshone Wells, an isolated patch of limestone is found, also resting upon the granite, and. dipping at a high angle to the northward, but which has not been indi- cated on the map. . In the Tenabo Peak limestone are a number of well-defined mineral veins, many of them. having been extensively worked. The ores are rich in silver sulphurets, but combined with zinc, lead, and other base metals, requiring expensive metallurgical processes. A description of the Cortez Mining District will be found in “Mining Industry”.* Agate Pass Recion.—The Agate Pass depression trends northwest and southeast at right angles to the general course of the range. ‘The western foot-hills of the range south of its mouth are formed of heavy-bedded dark- blue limestones, which are locally more or less changed into marbles and invariably crystalline, and, as far as observed, contain no fossils. They have a strike a little east of north, dipping eastward, or toward the cafion. The thickness exposed may be 1,200 or 1,500 feet. On the eastern edge of their outcrop, they abut against a mass of diorite, which fills the bot- tom of the caion for several miles, and extends northward, occupying the northwest foot-hills of the range for about 4 miles. This diorite is highly crystalline rock, containing very little groundmass, and is composed of well- preserved triclinic feldspar, green hornblende, abundant quartz, and a high proportion of brown biotite, but, as far as observed, no apatite. The crys- tals of triclinic feldspar are in some instances a quarter of an inch long, and the hornblendes sometimes reach an eighth of an inch in length. The feld- spars are more or less impurified by small inclusions of hornblende and mica, while the quartz crystals in general seem quite free from them. 1Mining Industry, vol. iii, 405. 2 From field-notes of Clarence King. 574 DESCRIPTIVE GEOLOGY. a Its chemical constituents, as determined by Mr. R. W. Woodward, are: SiliCawyey ee eee ok a ae ee 58.54 58.24 OMIM en esse. os, ae ee 16.68 16.85 errous Oxide... . 00. Ge 5.62 5.59 HEM Foes sk ee 6.00 5.92 M@onesia’.. 2020 5 9 sees Sa Se ea 5.33 Soda. S077 one ee 2.76 2.78 Potassa:- 2. 2 2 See 2.50 * 2.50 Water. . 0.2.0 222 eee 2a Ze 99.47 99.44 This diorite forms bold hills to the east of Agate Pass Road, through which are eroded gentle rounded cations. There is singularly little dioritic débris, almost all the disintegrating material being readily ground up into fine sand, so that few boulders of diorite are found on the surface. Directly to the east of the diorite is a very great thickness of siliceous and gritty beds, striking a little east of north, and dipping to the west, which in their composition and texture present a striking resemblance to the peculiar quartzitic sandstones already described from the Fountain Head Hills and Tucubits Mountains, though, in general, possessing a more massive habit. They consist chiefly of yellow and saffron-colored sand- rocks, containing a considerable proportion of broken feldspar crystals, with here and there sheets of siliceous cherty pebbles, black, red, and white, both angular and round. They contain also a small percentage of carbonate of lime, which is due to the presence of microscopic crystals of calcite. The | quartz-grains contain fluid-cavities with moving bubbles, and the feldspars are usually quite earthy and decomposed. A peculiar feature of this rock are the vugs lined with crystals of quartz and carbonate of lime. All the base of the rock is a fine clastic material, and a thin translucent chalcedony fills the interstices. Among the included pebbles and conglomerates are many of a small, brown hornstone or chert, which often occurs in the sili- ceous beds of the conglomerate, but havenowhere been found among the older rocks and clays. The angular condition of many of the included frag- ments is not surprising in view of the granite mass, directly to the north of AGATE PASS. 575 these quartzitic sandstones, which is of the older type, and in all probability Archean. The frequent outcroppings, through this deep sedimentary series, of granite and schist summits of the Archean age are sufficient to account for the presence of angular conglomerates in any of the subsequent rocks. _ The quartzite series and the before-mentioned limestone series dip toward each other at an angle of about 30°. Of the limestones, as has been seen, there are 1,500 feet exposed, and of the quartzites about 4,000. They represent the two sides of a synclinal, of which the western side has prob- ably been faulted downward, and the diorite then burst up through the fis- sure. The quartzitic series, from its character and thickness, has been referred to the Weber Quartzite, and the limestones to the Upper Coal- Measure group. There is nothing, however, to prove that these do not represent the upper members of the Wahsatch limestone, in which case it must be the rocks to the east side of the synclinal that are depressed. Be- sides the yellow conglomerate beds, near the summit of the quartzite series, is a bluish-gray quartzite, made up of very fine grains of quartz, with very little orthoclase and a few crystals of calcite. This is, however, a very unimportant member of the series. There is a very close resemblance between the yellow conglomerates and grits of this series and those under- lying the Upper Carboniferous limestone of Moleen Peak, which will be described in the next section. At the summit of Agate Pass, the quartzite series is cut through by innumerable basaltic dikes, and overflowed by sheets of fine black basalt, which flow down the eastern slope, and mask the whole range, from the region of Mount Tenabo to Wagon Cajion, a distance of 28 miles. As observed along Agate Pass, these basalts are of a fine doleritic type, con- sisting of plagioclase, augite, olivine, and rather coarse magnetite, between — which are small spots of dark bluish-gray globulitic base. There is consid- erable variety in these basalts, as to the coarseness of their crystalline ingre- dients, and the proportion of secreted crystals to the globulitic base. There are some specimens in the uppermost flows which are as fine-grained as hornstone, and have quite a resinous lustre in the fresh fracture. These contain a larger proportion of glassy matter, and their crystals are very minute. A characteristic of these basalts is the presence of a great quantity 576 DESCRIPTIVE GEOLOGY. of large cavities filled with agates and chalcedonies. They range from the size of a pea to a foot in diameter; and the surface of the flat slopes toward Pine Valley is literally covered with lenticular masses of chalcedony, which have weathered out from the easily disintegrated basalt. It is only rarely that these chalcedonies entirely fill the cavities in the basalt. They usually form a lining from half an inch to three or four inches in thickness, with a botryoidal surface toward the interior. They are both of uniform chalce- dony, and formed by repeated deposition of agate layers. On the lower sides of the cavity, there is found a considerable deposit of delessite, which sometimes plays a prominent part in the agate layers. The erosion subsequent to the outflow of these basaltic tables has been “comparatively limited: the ravines cut in'them are of sloping sides, and not usually over a couple of hundred feet deep. Everything points to a very slight erosion since the basaltic period, whereas it is equally evident that the whole range had been subjected to severe changes or modifications of form before the volcanic period. An obscure outcrop in the diorites of Agate Cation, which, by the presence of quartz, biotite, hornblende, and feldspar, seems to be related to the diorites, proves, on examination, to be a granite, containing titanite, resembling, in this particular, the Jurassic granites of the Sierra Nevada. The hornblendes are peculiarly cleavable, and the biotite is present in pro- portions smaller than in the neighboring diorite. The feldspars are highly altered, so that the proportion between orthoclase and plagioclase is not to be recognized. Professor Zirkel says:* “The product of this decomposition is curious, consisting of broader or narrower colorless, prismatic rays, which are either massed confusedly together like felt, or are heaped together in the form of stars and bunches, presenting a beautiful aggregate polarization.” The occurrence of this granite is very obscure. It is entirely surrounded with diorites, and may be either older or a Jurassic granite dike subsequent to the diorites. It is not to be connected with the heavy mass of granite which forms the north slope of the range about 4 miles northeast of Agate Pass. This is a broad mass of granite, extending 5 miles in a northeast and 1 Microscopical Petrography, vol. vi, 48. Re eet eel CORTEZ AND PAPPOOSE PEAK REGION. wire southwesi direction, and about 3 miles in width, which rises quite abruptly 4,000 feet from the plain. It is cut through by two sharp cafions, which ex- pose its structure very clearly. It presents singularly few dividing planes, and is remarkably solid, unbroken, and unseamed. It is composed of two feldspars, both entirely undecomposed, one of salmon-colored orthoclase, the other, a slender, white, triclinic feldspar, with quartz, which appears to be both translucent and of a milky whiteness, large white crystals of color- less orthoclase, long prisms of dark-green hornblende, and considerable bio- tite. There are not unfrequent veins and passages of granite, where all the constituents appear very large, the orthoclase reaching an inch and a half, and the quartz an inch in extent. The hornblende is here gathered into confused bunches of needles; and there is present a second mica, probably muscovite. The quartz contains fluid-inclusions: magnetic iron in small. quantity and a little apatite are also present. The rock presents every variety of texture, from large pegmatite occurrences down to a fine, com- pact, salmon-colored mass, in which all the ingredients are too fine to be detected by the naked eye, the rock having a felsitic appearance, clouded here and there by a mere dusting of very fine hornblende and mica. An analysis of a medium-grained variety of this granite was made by Prof. Thomas M. Drown, with the following result : Silieapeeeenenet eee Nh le ee Dogue be Ld 72.01 ANSORUOUUOE), 2. 522, Mn Ee eg es oe a a 14.75 Mernomsporidlenwee 221i) i) ea A eee ce et 2.35 iis MOUsKORIGe Ey AL welt ss Bet Peek 0.17 inte ees eG Pe ie ee Sid Sede ee 0.79 eemestammerrrt ey ete) 2 Sei hora veya 0.65 Sodas Aone: Pee ee trie te eh Grea GG Ose feb ek IPOTRSS2, = o's co ee eee meee eee are 4,49 rosa WOUD 5.0 2 ts ep i aR ee ek ea eae 0.61 100.03 Cortez anp Pappoose Pak Reeion.'—Directly to the south of this granite mass, and occupying the bold heights of Cortez Peak and the hill- 1Prom field-notes of Clarence King. 37 DG 578 DESCRIPTIVE GEOLOGY. tops to the north and south, forming a rude parallelogram, whose longer axis is with the range, about 8 miles in length, and whose shorter one is about 4 miles across the range, is a prominent occurrence of quartz-pro- pylite. The prevailing type of rock is a fine, gray base, in which large, green hornblendes and brownish-green triclinic feldspars are imbedded. It shades into salmon color and green, also into drab-gray and brownish-gray tones, and varies from a coarscly crystalline texture to a fine, almost felsitic groundmass. The feldspars are very dull, and the hornblende more or less decomposed. The groundmass presents a crystalline aggregation of opaque feldspars, resembling those of granite, half-altered hornblende payr- ticles, and quartz which cannot be recognized by the naked eye. Under the microscope, the frequent presence of these fine particles of quartz gives | a peculiar character to the section. The quartz contains numerous fluid- inclusions, among which some salt cubes were detected. The following note’ by Professor Zirkel is of interest: “The large feldspar crystals are dull, but they still show that ies have once been triclinic, the dimming lines, densely crowded together, crossing each other like lattice-work, or the bars of a grate, and leaving small, some- what clearer, fields between them. The best-preserved porphyritical horn- blendes are splendidly built up of long prismatic staffs, therein repeating the peculiarity which is shown as well in the quartzless propylites as in the older diorites. No dacitic hornblende has ever grown in such a manner. There is apatite and also some characteristi¢ titanite.” An incomplete analysis of this rock, made in Leipsic, gave: itl: in ene NE eo ose te cen OIG Alumina 22. 2! 225 SE ee 16.15 Ferrous oxid@: 222222 62 Se ee ee 3.64 Time... 2 Se 2.30 Magnesia. 2.2.2 0.53 Tonition® 22... 2. Re ee ee The same great sheets of basalt which wrap around the east base of the quartzite series continue to occupy the east slope of the range, and ' Microscopical Petrograpbhy, vol. vi, 119. CORTEZ AND PAPPOOSE PEAK REGION. 579 overflow the eastern boundary of the quartz-propylite mass. The rock is here, as at the head of Agate Pass, a very fine, green, more or less globu- litie dolerite. All this portion of the range is very much steeper on the northwest side, where the older rocks are found, than on the southeast, where the subsequent flows of volcanic rocks occur. With the granite, all the older rocks give out, and the range from Granite Cation north to beyond the Humboldt River is entirely made up of eruptive rocks. Skirting the northern edge of the granite outcrop, and overflowing the northern extremity of the quartz-propylite, is a considerable field of rhyolite, which occupies the summit and north slopes of the range, and is deeply cut by sharp narrow canons, which expose fine sections. These rhyolites, according to Zirkel,! are distinguished from the others in the collection in the following points: “Their feldspars are, for the most part, altered into a dull, half-kaolinic substance; they lack evidence of any tendency to develop fibrous sphzerolitic or axiolitic aggregations ; their groundmasses, which are in a very imperfect crystalline state, and are rich in ferrite, contain colorless feldspar-microlites, and they are absolutely free from biotite. Most of the rocks from this locality are rich in quartz, which is very pure, including only narrow lines of empty pores and beautiful iso- lated glass-inclusions.” . | In general appearance, the rock is of a buff, green, and purple color, and largely made up of a breccia, of which the fragments are apple- green, consisting of a very fine-grained, felsitic groundmass, containing a few decomposed feldspars and numerous large angular and rounded grains of quartz. These rounded grains of quartz are very peculiar, and possess the characteristic botryoidal surface of hyalite. or chalce- dony. The pellets are sometimes as large as a small pea. The paste in which these fragments of green rhyolites are imbedded is a rhyolite rich in kaolinized feldspars and angular grains of quartz, which are sometimes dihexahedral, and sometimes simply angular fragments. They are all sur- rounded by a fine glazing, so that the cavities out of which the quartz- grains fall present a smooth, pearly surface. It is noticeable that there are also in the purple paste rounded quartz pellets, like those in the green frag- * Microscopical Petrography, vol. vi, 194. 580 DESCRIPTIVE GEOLOGY. ments; and this is another instance in which marked peculiarities are pos- sessed in common by the breccia fragments and the including paste. - It seems to be a general rule in all the breccias that the paste and fragments are precisely of the same material. To the east, the rhyolites fall off in long spurs, and are overflowed by sheets of fine-grained basalt. In Wagon Cajon is a limited outcrop of reddish quartzitic sandstone, which is so similar to much of the rock in Agate Catton, while resembling that of the River Range, that it has been referred to the Weber Quartzite. It is overflowed by a rough, gray sanidin-trachyte consisting of small sani- dins, and laminz of more or less decomposed biotite. The microscope reveals a large proportion of small particles of hornblende, entering promi- nently into the constitution of the groundmass, which consists as well of dull feldspars, and tolerably well-preserved hornblende crystals whose color was originally green. Both in habit and mineralogical constitution, this rock shows close affinity to propylite, and would be so classed, but that the orthoclase predominates over the triclinic feldspar. ‘The peculiar look of the biotite which is noticeable in hand-specimens appears, under the microscope, to be due to the interposition, between the brown laminze of its transverse sections, of colorless muscovite. A little apatite also occurs. A somewhat fissile structure is given to the rock by the prominent, parallelism of the biotite. This body of trachyte forms a narrow zone about half a mile wide and four miles long, lying between the foot-hill rhyolites and the body of quartz-propylite which forms Pappoose Peak. The question of age between the trachyte and the rhyolite, in the hills lying to the west of it, is obscure, but it seems probable that the rhyolite is the younger. ‘The rhyolites of the foot-hills overlap the trachytes to the west and also the small body of quartzite which lies along the western edge of the quartz- propylite body, and connect with the rhyolites which surround the head of the valley, lying between Wagon Canon and the Cluro Hills. Beginning at Pappoose Peak, and extending along the middle of the range, across Wagon Cajon, and up nearly to the Humboldt River, is an irregular zone of quartz-propylite, probably part of the same eruption which occupies the crest of Cortez Peak, and which has been overflowed, to the south of Pappoose Peak, by the rhyolite body. It consists of a fine micro- | | : PAPPOOSE PEAK REGION. 581 crystalline groundmass of purplish-brown triclinic feldspar and green horn- blende, in which are porphyritically enclosed earthy kaolinized feldspars, less decomposed than those of Cortez Peak, aggregations of crystals of green hornblende, and a few dark-brown biotites.: Under the microscope, these latter contain between their laminz interposed layers of calcite crys- tals, and apatite occurs in the groundmass and in the biotite. This long ridge seems to be made up of repeated outflows, which have piled upon one another in thick masses, never showing the slightest tendency to overflow or spread out in thin sheets. The rock has the appéar- ance of having been erupted in an almost solid condition, and possesses no evidence of flow whatever, which is not the case in the Washoe propylites. The lower exposures contain no biotites, and the feldspars and hornblendes both more closely resemble the rock of Cortez Peak. The biotite-bearing member is probably the last outburst, and is not represented at Cortez Peak. As in the Cortez quartz-propylites, the quartz is never or rarely visible to the naked eye, but under the microscope is seen to form a prominent ele- ment in the groundmass. In the rocks of Pappoose Peak, it is the horn- blende that has suffered more decomposition than the feldspar, while at Cortez Peak the reverse is true. The actual proportion of biotite in the former rock is small, but its presence is conspicuous, because the flakes are very large, sometimes a quarter of an inch in diameter. The groundmass is also decidedly finer than at Cortez Peak. With these minor differences, the rocks are otherwise closely similar. Lying to the east of the quartz-propylite body is a large development of dacite, which extends south from Wagon Cafion 8 or 10 miles, and descends to Pine Valley on the east. ‘The prominent colors are dark-purple and dark-chocolate in the groundmass, in which are enclosed remarkably white, decomposed triclinic feldspars and numerous black, glittering quartz. Contained in the groundmass, and closely approximating to it in color and general appearance, are small angular fragments thickly scattered through the whole rock.- These fragments contain secreted crystals of hornblende, plagioclase, and quartz, which are generally smaller than those secreted from the groundmass, but in other respects identical. The rock is, therefore, a 582 DESCRIPTIVE GEOLOGY fine breccia, of which the included fragments are so small and similar to the paste that to the unaided eye it appears like one homogeneous rock. In certain of the larger feldspars, a metamorphism has taken place, resulting in a kaolin-like substance, penetrated in all directions by fine seams of chalce- dony. Further evidence of alteration is observable in the cloudings of rusty-brown which traverse the purple groundmass. This resultsno doubt — from the decomposition of the iron in the hornblendes, which conveys a stain to the plagioclases, and renders their edges and cracked portions a yel- lowish-brown. The mass possesses a general vertical structure, and never overflowed in tabular flows. This is common to all the dacites, whereas the andesite frequently overflows after the manner of the basalt, as at Washoe and Berkshire Caton, Virginia Range. Cropping through the dacite along the centre of the ridge is an Siecare mass of dark-brown andesite, possessing, in a remarkable degree, the same earthy, half-decomposed modification, as described in the neighboring dacite. This is probably the crest of a ridge of earlier origin than the dacite, and represents a limited area uncovered by erosion. The rock has somewhat of a resinous lustre, and its feldspars are decomposed, and show a zonal structure. Under the microscope, their twin striation is visible, and the 3 dark, yellow-brown crystals are seen to be augite, which brings this rock among the augite-andesites. The groundmass is much discolored, changing | from the prevailing chocolate color to a rusty, iron-red and pale, yellow- brown, and is seen under the microscope to have a gray, rather than the usual brown, glass, which is probably caused by its proportionately greater richness in augite. It contains no olivine nor quartz. Its chemical con- _ stituents, as determined by Mr. R. W. Woodward, are: Silica: 222 n- 2h oS ae ee a eee ae 61.64 Alwmiina,,..2.0)5)3:555 ee 2 ee eee ee 17.44 Betric¢: oxd¢ 2283 el i 0.82 Nerrous.oxide ..2 2243) -3)e oe ee Boe Manganous, oxide 4.02.53.) ee trace Tati. ge eget s “dy ag ie a a ea 5.86 PINE VALLEY PLIOCENE. 583 Sora wen ni a re SR ed bo ae 3.45 IPORERESE 2. CEE Dots aie ee rr 1.15 TUMEEDSD ooo oe gic ee er trace VW QIIGE clo aes ee Be eres eke 2.64 100.04 One specimen from this body contained some hornblende, which was apparently an accidental constituent. Pine VauuEy Puiocenr.'—In the eastern foot-hills of the range, at the east base of Cortez Peak, the basaltic field is overlaid by a comparatively thick deposit of lacustrine Pliocene, in all respects like the Humboldt Pliocene. The beds are largely arenaceous, though toward the top there are fine clays, and singular beds composed of carbonate of lime and car- bonate of soda in such proportions as almost to represent the composition of Gay-Lussite. There is no doubt that this formation formerly filled the entire area of Garden and Pine Valleys, and that the erosion of the drain- ing streams has worn away a broad depression through the middle, which has been filled with Lower Quaternary and Quaternary. On the east side of this. valley, about four or five miles north of Min- eral Hill, is an interesting exposure, where the Pliocene is worn into vertical bluffs 40 or 50 feet in height, of rounded and pinnacle-like shapes like the eastern bad-lands. The strata on this side are more calcareous than on the west, and contain beds which are almost limestone, but, as far as observed, are devoid of fossils. The locality is particularly interesting as showing the relations between Pliocene and the Lower Quaternary. Usually the Lower Quaternary, — as observed by us, has consisted of thin beds laid down conformably over the Pliocene, and occupying alkali flats, which, from their position in ° the very bottoms of the valleys, are not cut through and eroded by the streams. In this case, however, the main valley erosion took place, cutting out the broad valley bottom before the deposition of the lacustrine beds or Lower Quaternary, so that it occupies a position 40 or 50 feet below the top of the Pliocene, and skirts the base of the bad-lands, proving that the 1 From field notes of Clarence King. 584. ' DESCRIPTIVE GEOLOGY: Lower Quaternary, as laid down by us, is not necessarily the upper part of the Pliocene. BBR te | Region or THE CLuRo Hitts.—On the west of the northern portion of the range, a small, detached, outlying group of hills, called the Cluro Hills, rises out of the plain, edged by Quaternary on the east and by a series of flanking deposits of Pliocene on the west. The hills themselves are com- posed of syenite, granite, and a quartzite body which has been, for conven- ience, referred to the Weber group. These hills are of interest as showing the only true old syenites of the collection. This rock consists of a flesh- colored monoclinic feldspar and greenish hornblende. Under the microscope, the feldspars resemble the orthoclase of granite. The hornblende proves not to be made up of homogeneous individuals, but every one of an associa- tion of light-green rays or prisms. This polysynthetic arrangement sug- gests the hornblendes of propylites. The rock also contains microscopical quartz, and a little plagioclase feldspar, whose striation is, however, very indistinct. Both these minerals have been generally considered not to occur in syenites, and their presence in this rock could not be detected. but by the aid of the microscope. The granite of the Cluro Hills is similar to that already described in the Cortez Range. To the north of Wagon Cajon, dacite forms the main crest of the Cortez Range, to the west of which is a body of hornblende-andesite, whose outcrops are somewhat obscure, and only exposed by erosion. This dacite differs somewhat from that to the south of Wagon Cafion in being less of a brecciated mass, though it still includes some breccia fragments. It is of a purplish-green color, and contains large, opaque, triclinic feldspars, with a good deal of fresh, brownish hornblende, and some mica, in a micro-felsitic groundmass. The quartz crystals are not apparent to the naked eye, but * under the microscope can be easily distinguished. The feldspars contain inclusions of a yellowish-gray glass, which sometimes almost replace the entire felspathic substance. The hornblendes are frequently decomposed, being altered into a pale-green substance, which sometimes has a mixture of calcite, but the biotites are always fresh. The andesite which appears on the slopes of the range toward the Cluro Hills is a dark, even-grained PALISADE CANON REGION. 585 rock, containing but little hornblende. It seems, however, to be rather a hornblendic than an augitic andesite. It is full of very minute crystals of iron pyrites. ‘The feldspars are generally of the same color as the ground- mass, and can with difficulty be distinguished. The syenite body of the Cluro Hills is partly exposed in an outlying peak to the west of the main crest. Between it and the andesite body is a syenite-porphyry, which is practically only a porphyritic modification of the main body of the Cluro Hills, but the rock is rather darker in color and more fine-grained. It isa dark-green rock with small flesh-colored feldspars, green hornblendes, and small quartz crystals, porphyritically imbedded in a groundmass, which, under the microscope, is seen to be composed of crystalline grains of feldspar, quartz, and altered hornblende. The rock contains more plagioclase-feldspar than the syenite, and the crystals of both feldspars are evidently fragments. The rhyolite which covers the _ syenite on the west, at this point, has a peculiarly shaly habit, splitting into thin laminz only half an inch in thickness. It is stained by iron oxide on the surface, but, in the fresher fractures, shows a white, compact, felsitic groundmass containing only porphyritically imbedded crystals of quartz and feldspar. hy at, PatisaDE CaNon Recion.—In the neighborhood of Palisade Canin, the andesite core of the range has been overflowed and mostly con- cealed by a flow of trachyte, which, in its turn, is covered by extensive flows of rhyolite, which mask the greater portion of the range north of the river. Most of the cliffs which border the cafion west of Palisade Station are composed of a dark-gray sanidin-trachyte. This rock contains but very little plagioclase or macroscopical biotite. Under the microscope, the groundmass is seen to contain a large quantity of very fine laminz of mica, together with decomposed hornblendes, and some apatite, but no augite. It has also a good deal of magnetic iron, which is frequently decomposed into dendritic fibres of ferric oxide. Apparently inclosed in this trachyte, on the south bank of the river, at the mouth of a little side-cafion, is a hill a few hundred feet in height, containing a large mass of iron-ore, remarkably fine-grained, and having a thoroughly con- 586 DESCRIPTIVE GEOLOGY. choidal fracture. Ata little distance, it might be mistaken for a basaltic rock. An analysis of this ore, made by Mr. B. E. Brewster, gave the following results: | eric OxI0e.. 6 =. seen Done 84.217 Alumina ......::...0..s:6gS ee 0.178 Mancanous oxide... <2 02 See 1.454 Macnesia. 0. 20. i. — oe 0.472 Water... See usere wg synth shy Seek va ee bs Insoluble residues .< S4eee eee ee 12.518 otal uae ete er ee be Minin Se SE Sc 100.552 which would give a percentage of metallic iron 58.95. The occurrence of such a body of iron-ore in the midst of volcanic rocks is an interesting phe- nomenon, though it is probably too far from any source of fuel supply to be of practical value. It is, however, a remarkably pure ore, being entirely free from phosphorus or sulphur, though containing a rather high percent- age of silica. : It may possibly have some connection with a peculiar rock which is exposed under the trachyte body on the opposite side of the river, forming the cliffs of the west side of a ravine which enters the cation from the north. This has a very distinctly columnar structure, and is evidently of earlier age than any of the rocks around; but its relation to the other andesite bodies, on account of its isolated position, could not be determined. It is a heavy, fine-grained, crystalline rock, of a dark-gray color, whose constituents, with the exception of the plagioclase-feldspar, cannot be distinguished by the naked eye. Microscopic examination shows it to be a quartziferous augite- andesite, being made up of plagioclase, and a little sanidin-feldspar, augite, biotite, and some angular grains of quartz with glass-inclusions. Quartz crystals and some apatites are also found imbedded in the larger feld- spars. It contains no hornblende or olivine, nor has it any glassy or amorphous base. Its chemical composition, as determined by Mr. Rein- hard, at Leipsic, is: 3 REGION OF THE CARLIN PEAKS. 587 Since ey nee ye ee ee ee 62.71 AEM, . Obs eee oy Re ee 12-10 IFGIShG CHEGIS soi. Ee Soo ee eee ee 14.79 ITN® 2. oon ck ec oe Be ee ee 8.34 Ea me ilpunreneiny= epi Ss eS Dees Pe 1.31 SG oa 2 hace nee oe SI eee ee ae O73 IPQHASED LS aac aicle oR ee ee ee ee? 1.15 LOWS which is remarkable, not only for the high percentage of iron, but also for the absence of water and the small proportion of alkalies. The trachyte which forms the main body of the hills to the north of Palisade Cafion, and the narrow gorge at the lower end of this cafion, is a somewhat different rock from that found along the south banks of the river, and apparently of later origin. It is a light-gray, quite porous sanidin- trachyte, noticeable for the large earthy hornblende crystals, which occur in remarkably perfect hexagonal prisms, often as much as one-sixteenth of an inch in diameter. Casts of these crystals are found on the weathered surfaces of the rock, retaining perfectly the form of the original crystal. In general, the hornblendes are very much decomposed, and have imparted a somewhat reddish, rusty stain-to the groundmass. Under the microscope, the latter is seen to contain some glassy base and also a little tridymite. The decomposition of the hornblendes is also very peculiar, and has often proceeded so far that the interior core of the crystals has been removed, and in part replaced by groundmass-material. In one specimen of this trachyte from the south bank of the river were found a few yellowish-brown crystals of augite. : _ Reeion or THE Caruin Peaxs.—North of Palisade Cafon, for a dis- tance of about 20 miles, the surface of the Cortez Range is principally cov- ered by extensive flows of rhyolite. A few obscure outcrops of sediment- ary rocks show a pre-existing line of elevation, similar to that south of the river, whose form was probably determined prior to the volcanic period. These outcrops are, however, too isolated and indistinct to give any clue as to their structure, or any definite idea of the age of the rocks. The princi- D88 DESCRIPTIVE GEOLOGY. pal exposures are in the deep cafions at the base of Carlin Peaks, where is the greatest elevation of the range. Here, at the head of Annie Creek, was found a considerable body of siliceous and green argillaceous slates, enclosed in limestones having a westerly dip, while at the north of Carlin Peaks are also some few exposures of dark-blue and gray limestones, which are also seen at the gap of Maggie Creek, where, in direct contact with the rhyolite overflow, one bed of limestone has become marbleized. These sedimentary rocks, from which no palxontological evidence was obtained, have been re- ferred, on grounds of general probability, to the Lower Coal-Measure group. At Carlin Peaks, the range has a distinct double crest, of which the east- ern portion doubtless represents the original sedimentary elevation, while the western crest is formed by a body of andesite, whose general direction is suggested by the isolated exposures of andesite from a little north of Wagon Cafion to the western of the Carlin Peaks. The two more northern bodies of andesite, that where the Emigrant Road crosses the range and that of the western of the Carlin Peaks, differ from the andesite found in Palisade Caiion, in containing some augite, and in having a more glassy base. They resemble closely the augite-andesite of the Wachoe Mountains. That from the Emigrant Road is a quite porous rock, with prevailing plagioclase, considerable sanidin-feldspar, and dark-brown hornblende, with a good deal of yellowish, decomposed augite. Under the microscope, the groundmass is seen to have something of the microlitic structure peculiar to the augite-andesites, and many of the hornblendes are somewhat decom- posed, and have the characteristic black border. The andesite from the head of Annie Creek is less porous. It is a dark-gray compact rock, rich in hornblende, containing also a good deal of yellowish-brown augite and some apatite. Under the microscope, the feld- spars are seen to be mostly plagioclase, but with them are associated some schistiform, monoclinic feldspars and the groundmass to have the felt-like structure of augite-andesites. The feldspars are remarkable for containing inclusions of yellow glass, with a thick bubble, as shown in Vol. VI, Plate V, fig. 3. This andesite forms a considerable mountain mass, and rests directly on the slates and limestones, while its flanks are covered by flows — of rhyolite. REGION OF THE CARLIN PEAKS. 589 ‘The eastern of the Carlin Peaks is a high, flat, table-shaped mountain, made up of the typical red porphyritic rhyolite. The same character of rocks extends to the west of the upper part of Annie Creek, and covers the western slopes of the range where the Emigrant Road crosses it. Under it, near the river, is exposed an outlying portion of the trachyte body, and here the rhyolite itself very closely resembles the trachyte, but is distin- guished from it by its containing a considerable amount of free quartz. With its prevailing sanidin-feldspar, it has also some finely- striated triclinic feldspars and black hornblende, but no mica, in a reddish-brown micro- felsitic groundmass. The rhyolites which form the eastern slopes of the range north of Palisade Cajon, ift the neighborhood of the Emigrant Road, are grayish-red rocks, containing almost no macroscopical crystals, with the exception of a few sanidin and plagioclase-feldspars. ‘The microscope discloses no quartz, but shows that the groundmass has-a spheerulitic structure showing a radial fibration. ‘The numerous cavities are seen to be lined by a light-gray crust, made up of fine layers of different-colored hyalitic opaline material. 590 DESCRIPTIVE GEOLOGY. SECTION VII. REGION NORTH OF THE HUMBOLDT RIVER. BY S. F. EMMONS. Matuarp Hitus.—The Mallard Hills form the southern continuation of a high range to the northward, whence comes the principal supply of water to Bishop’s Creek, the main branch, properly speaking, of the Hum- boldt River. The higher portions of this range, as shown by the fragments in the wash of the streams, are formed of similar sedimentary materials to those of the Tucubits Mountains. The Mallard Hills, which are low, flat, rounded ridges, are made up almost entirely of flows of rhyolites, which are quite distinct in character from any observed in other portions of the region explored. 3 The rhyolite from Deer Cafion, the northern point of these hills, is a lavender-colored rock, which weathers into thin slabs, or lamine, generally from half an inch to an inch in thickness. It resembles in many respects the quartziferous trachytes of the Elk Head Mountains. In a light-gray felsitic groundmass, it contains large crystals of sanidin and rounded grains of quartz, often as large as a pea, which are cracked in the interior and are surrounded by a ring of altered groundmass; it has, however, no mica or hornblende. Under the microscope, the groundmass is seen to be made up of a distinct aggregation of colorless plates, and black and colorless grains, while the ring which surrounds the larger crystals is an extremely fine, granular modification of this groundmass. The rhyolites which form the main peak of these hills are generally of dark reddish-brown color. In some cases, they have the same laminated habit as those of Deer Canon, and, like them, have something of a trachytic look. They contain also large crystals of quartz and sanidin in a felsitic groundmass, and have likewise apparently no mica or hornblende. They are sometimes extremely porous, the druse-like cavities being lined with botryoidal concretions of black glass and of chalcedony. Under the micro- | MALLARD HILLS. — 591 scope, the rhyolitic character of these rocks is seen in the fact that the groundmass is spheerulitic. The larger sphzerulites consist usually of radiat- ing fibrous material grouped around a dark centre. In the valley to the north of these hills, whose waters run into the Snake River, ‘is a Tertiary deposit, in which were found curious menilite-like fragments of white porcelain-like material, having a somewhat vitreous lustre, which, by the naked eye, can be seen to be full of little needle- shaped fragments of black glass. In these, the microscope detects a tuface- ous structure and the remains of diatoms. Along the northern slopes of the hills, just beyond the limits of the map, are numerous warm springs. The ridge which runs northwest from the Mallard Hills, forming the north- eastern boundary of Bone Valley, is composed of the same dark Sovnatslhe red rock found in the main group. Bons Vauiey.—In Bone Valley, which forms an isolated interior basin, are deposits of white Tertiaries, which have been largely eroded away. On the surface of this valley were found a number of vertebra and fragments of the jaws of fossil horses, evidently originating in these Tertiary beds, and which determine their age as that of the Pliocene. These vertebrate remains were not found in place, but lying loose upon the surface of the valley; they were thoroughly petrified, but in general too imperfect for specific determination, although not water-worn, or showing any evidence of having been brought from a great distance; moreover, remains of light-colored limestone adhering to some of the specimens proved that they originated in the limestone beds of the Tertiary deposits of this enclosed valley. They were submitted to -Prof. Joseph Leidy, who pro- nounced them identical with those obtained from the Pliocene Tertiaries of the Niobrara River. Those which were recognized and Banned by him were: Protohippus perditus,' an extinct equine animal, represented, among the specimens collected, by a fragment of an upper jaw with two molars, frag- ments of the lower jaw with one molar each, fragments containing canine and incisors, some vertebre, the end of a humerus, a pastern, and a coronary bone; 1 Leidy, Extinct Mammalian Fauna, 1869, 275. 592 DESCRIPTIVE GEOLOGY. Merychippus mirabilis,’ another equine animal, represented by an upper molar tooth; and Cosoryxz,’ represented by a peculiar furcate fragment of a horn-core, supposed to belong to an extinct family of antelopes. The ridge to the west of Bone Valley is made up of quartzites and slates, striking a little north of east, and dipping about 25° to the eastward, on whose flanks along the southern portion are some conformable limestone beds. No fossils were obtained from any of the beds, but from their asso- ciation and position they have been assigned respectively to the Weber Quartzite and Upper Coal-Measure groups. pe E@yptian AND Osino CaXons.—The North Fork of the Humboldt, which here forms a considerable stream, takes its rise in the valley next west of Bone Valley, and, after leaving the open region of these two valleys, flows southward for 6 to 8 miles through a narrow caiion-like gorge called Egyp- tian Cafion. In this cafion is exposed a peculiar rock, which, from its posi- tion, is apparently older than the surrounding rhyolites. It has been colored on the map as an andesite, although Professor Zirkel has, from a study of the microscopical sections, classed it among the basalts. In physical habit, it resembles the andesites. Its manner of weathering is rather peculiar, showing a rudely columnar structure, in which the columns are of cylindrical rather than prismatic shapes, and have a tendency %o split into curved lam- inze or sherds, at right angles to the axis of the cylinder. This peculiar weathering produces singularly picturesque architectural forms on the cliffs of the rock, which frequently show resemblances to ruined columns and remains of ancient temples. The darker, more compact variety of the rock which is found at the lower end of the cafion is almost black, and shows only a few small crystals of feldspar in a semi-vitreous groundmass. . Under the microscope, the ground- mass is seen to be made up of a mixture of fine microlites and grains of plagioclase, and augite. It contains, however, no olivine. Another variety, which shows the prevailing character of the rock, has a dark brownish- gray groundmass, in which are imbedded large crystals, often half an inch in diameter, of sanidin, rounded, cracked quartz, and also microscopical 1Leidy, Extinct Mammalian Fauna, 1869. 2Tbid., 172. EGYPTIAN CANON. . 593 crystals of plagioclase and: augite. Both quartz and sanidins seem to be somewhat of an accessory ingredient like the quartz of the quartziferous trachytes. This rock likewise contains no olivine. Under the microscope, plagioclase is seen to be the predominating feldspar. The groundmass is a globulitic, half-glassy material, which contains peculiar crystalline products of secretion like those found in obsidians and artificial slags. The rock is also comparatively rich in apatite. ‘The peculiar products of devitrification seen in a thin section of vas rock will be found illustrated in Vol. VI, Plate XI, fig. 4. Below the narrower uaa of the cajion, need is cut through this dark, peculiar rock noticeable for its red, vitreous, weathered surfaces, spurs of reddish porphyritic rhyolite close into the river on either side for a few miles, and are succeeded by an open Quaternary valley, through which the North Fork flows in a broad, alluvial bottom as far as its junction with the main Humboldt. The hills to the east of this valley show a few out- crops of westerly-dipping quartzites, underlaid by limestones having a strike a little east of north, which were not closely examined, but have been referred to the Weber Quartzite and the Wahsatch limestone. They are covered high up on their flanks by the nearly horizontal white beds of the Humboldt Phocene, while to the north the sedimentary rocks are con- -cealed beneath the flows of rhyolite. _ The rhyolite of Peko Peak, ee adiginre the quartzite, has at first glance a strong resemblance to a sedimentary rock. It is, however, a distinctly eruptive body, but contains few crystals except those of quartz. It has a dull-gray, compact, felsitic groundmass, which in places encloses small fragments of green chalcedony, like those which make up the quartzitic sandstone already mentioned. In external appearance, it rather resembles an older eruptive rock. Under the microscope, it is seen to contain an enormous quantity of yellowish-brown grains of ferrite. _ A mesa-like ridge of the white beds of the Humboldt Pliocene sep- arates the lower part of the North Fork from the Elko Valley of the Hum- . boldt River. Out of this, southwest of Peko Peak, rises a low rounded hil! of white porphyritic rhyolite, whose groundmass has at times a somewhat earthy texture, but in general is very compact, almost like a porcelain. It abounds in small distinct crystals of quartz, which for the most part are 38 DG 594 DESCRIPTIVE GEOLOGY. smoky, and feldspar, with a small development of hornblende. The micro- scope also detects the presence of biotite, and shows that. the groundmass is made up mostly of axially fibrous strings. The rock contains few angu- lar fragments of quartzite. At the southern end of this ridge, in Osino Canon, is exposed a section of steeply-dipping quartzites and conglomerates, the latter showing the char- acteristic angular fragments of cherty material of the Weber Quartzite. Their general structure is that of a short synclinal fold, having a north and south axis, the beds being upturned at high angles. Within the quartzites are also some black, apparently carbonaceous seams. The outcrops are very irregular, and are masked on the south of the river by the rhyolite flows of Upriver Peak. On the north of the river, at the eastern end of the cafion, is a body of light-gray, very crystalline rhyolite, having almost a granitic structure, containing sanidin, quartz, and mica. . * In the broad valley of the Humboldt River, above Osino Cajion, are found in the dry season a number of saline incrustations, resting upon the fine impalpable Quaternary soil. From one of these deposits near Peko Station, a sufficient amount was collected for chemical investigation, the sample yielding 52 per cent.-of soluble alkaline salts. An analysis by Mr. R. W. Woodward gave the following: Soda: jo: hi ae eee aes He ote ag ee Sees 46.81. Sodium 2. 2. Seer E ee Rea eae cea rei ce a ae 220 -) Carbonic acid): 25322 oes se eee — 80.78 Carbonic acid (excess over monocarbonate).-....-.. 10.07 Sulphuric. acid’ s 52.2) Rt sis eee 2.59 Chlorine 2221s a ee ML So er 4.58 Boracie acid. 422 see ove (up. ie Chey eae 2.41 100.21 The theoretical combination would give: Carbonate of soda and excess of acid........-.-.- 83.57 Sulphate of sodas... 5c ee ee 4.60 Borate .of soda 2. 52st oie ea Sep Se 4.49 Chioride.of sodium... )_-. =a 7.55 100.21 ELKO AND RIVER RANGES. 595 Eiko and River Ranees.—From Osino Cafion to Moleen Canon, the Humboldt River runs through a wide bottom-land, which, to the southeast, extends close up to the foot-hills of the Elko Range, but on the northwest is bounded by low, bench-like spurs of the River Range. The beds which compose these spurs are almost entirely of volcanic ash, generally of white color, and containing enclosed fragments of rhyolite. They slope off gently toward the centre of the valley. Along the foot-hills of the River Range, under these volcanic beds, which belong to the Humboldt Pliocene, are found occasional outcrops of upturned beds of the Green River Eocene. . These are best seen near Penn Cafion, at the northern end of the valley, where attempts have been made to develop their included coal-seams. At the coal-mines, the strata dip 45° to the south, with a strike a little north of east. They consist of beds of white, earthy limestone from six inches to afoot in thickness, with white, finely-laminated, calcareous and arena- ceous shales, and seams of clay from two inches to a foot and a half in thickness. There have been found here three beds of coal: one of two feet in thickness, one of from five to six, and another of three. The coal is a very light lignite, black and lustrous, still retaining somewhat of a woody structure, and abounds in grains of yellow mellite. It is tolerably pure, and free from ash, but breaks up readily, on exposure to the air, mto _fine dust, and has thus far proved of little economical value. Adjoining the coal are beds of fine bituminous shales, which very closely resemble the brown paper-shales of the Green River series at Green River City in Wyoming. In them are found the same plentiful remains of fishes, and also occasional insects. Some of the shale beds have also abundant casts _of deciduous leaves remarkably well preserved. It was impossible to make an estimate of the aggregate thickness of these beds, as they are concealed beneath the white Pliocene beds, which often so closely approach them in lithological character that they cannot be easily distinguished. A roughly- measured thickness of 300 feet was obtained near the coal-mines, but, judg- ing from the position of the outcrops and the dip of the beds, it would seem‘ that as many thousand are probably represented. It is evident that these ; beds have suffered much more disturbance than those of the Green River Basin, since their angle of dip, which at the mines is 45°, shallows a little 596 DESCRIPTIVE GEOLOGY. eastward to 25°, and in the ravine below the mines is found to be 65°. 7 About four miles to the northeast of the coal-mines a, prospecting shaft has been sunk 100 feet, in a white, compact, fine-grained, volcanic ash, which doubtless represents one of the upper beds of the Humboldt Pliocene for- mation. The northeastern foot-hills of the range, toward the North Fork, are covered, as has been seen, by flows of red and white rhyolite. On the spurs to the north of the coal-mines are found a great variety of light- colored earthy rhyolites, from which one passes by insensible gradations, through compact, even-grained, structureless rocks, to the quartzitic sand- stones, which form the main body of the hills. The rhyolites have sometimes a porous earthy structure, sometimes a compact felsitic ground- mass, and enclose different-colored fragments of the same material, but show no distinct crystals, except very fine particles of quartz. The inter- mediate member is a compact felsitic rock, of a yellowish-white color, which, in the interior, is curiously striped by concentric bands of various colors, almost as fine and distinct as those of an agate. ‘The colors are very brilliant and well defined, ranging from a deep purple, through brick- red, into yellowish-white. Of these, Professor Zirkel remarks,’ “They are perfect likenesses of the felsitic tufas or clay-stones of the Lower Permian (Rothliegendes) in Germany, originating in the old felsite-porphyries; in every respect, the true precursors of the Tertiary rhyolites.” In close con- nection with these curiously-striped rocks ure found the fine-grained quartz- itic sandstones, full of grains and erypto-crystalline fragments of limpid | quartz and fine angular fragments of black and green chalcedony. It would seem therefore that these striped, compact rocks may represent here a tufa, which is contemporaneous with the Weber Quartzite; and the quartz- itic sandstones, in contact with it, have been more or less altered, while the rhyolitic tufas, which so closely resemble it, and which are undoubtedly of recent eruption, have followed the same channels, and carried with them fragments of the older adjoining rocks. On the western slopes of the northern point of the River Range are bodies of westerly-dipping limestones, overlying the quartzites, which, from their stratigraphical position, have been ‘Microscopical Petrography, 262. Le ee i ie, EE eee ] : ; ( 7 q } PENN CANON. 597 _ referred to the Upper Coal-Measure group, though no fossils were obtained from them. Their structure is shown in the upper section of the map. In Penn Canon, which is cut at right angles to the strike, nearly through the range, a thickness of some 3,000 to 4,000 feet of the beds of the Weber Quartzite is exposed. The structure is much obscured, but seems to be generally that of an anticlinal, whose eastern member is very steep and nearly perpendicular, while the main body of the range is formed of westerly- dipping beds, whose angle in the centre of the range is only about 10°, steepening to 25° on the extreme western foot-hills. The lowest beds ex- posed show a considerable thickness of black argillaceous shales and quartz- ites, which are overlaid by conglomerates, generally including a certain pro- portion of angular, cherty fragments, while the most prominent beds are the peculiar dark quartzitic sandstones already mentioned, which here are col- ored by hydrated oxide of iron. Microscopical examination shows that in both the quartzitic sandstones and conglomerates, the quartz-grains contain a great number of fluid-inclusions, and also small laminz of mica, some- times of distinctly hexagonal form. This fact also points to some pre- existing uplift of crystalline rocks, from whose débris these were formed, which is now worn away, or concealed beneath the later formations. In the upper portion of the series is an included bed of limestone, underlying the upper conglomerate. Immediately north of the cafon, the spurs are capped by a red porphy- ritic rhyolite of a type which is very widely spread throughout Nevada. It has a reddish-purple, compact, felsitic groundmass, and contains small. crys- tals of sanidin and quartz, with a little hornblende and occasional flakes of black mica. It has a peculiar irregular fracture, and in a hand-specimen, but for the presence of quartz, might be easily taken for a trachyte. ‘To the south of Penn Cafion, the range consists of low, rather broken hills, whose structure is masked by detrital material, but which, as far as observed, were composed principally of the greenish conglomerates and quartzite sandstones of the Weber group, having a prevailing dip of 10° to the westward. _ On the western slopes of the range, toward Susan Creek, are light- gray rhyolitic tufas, similar to those north of the coal-mines, being rather porous, and containing a few scattered crystals of feldspar and quartz in a 598 DESCRIPTIVE GEOLOGY. porous earthy groundmass. Associated with these are gray semi-vitreous thyolites, having a conchoidal fracture, which seem to be simply a more suddenly-cooled variety of the tufa. There also occurs here a dark-gray porphyritic rhyolite, having curious spherical balls, about an inch in diam- eter, of the same material, included in the mass, which is made up of distinct crystals of feldspar, quartz, and occasional hornblende and mica, in a com- pact, semi-vitreous groundmass. At the extremity of one of the western spurs, toward Susan Creek, is a flow of earthy, flesh-colored trachyte, which contains scattered crystals of sanidin and mica in a micro-crystalline feldspathic groundmass. This rock resembles the European domite. Under the microscope, it is seen to have a light globulitic glassy base, in which is no microscopical biotite, hornblende, augite, or apatite. It contains, however, granular aggregations of red isotrope garnet, an occurrence never before observed in any trachyte except that from the island of Ischia in Italy. It contains also tridymite, and occasional small blue grains of a hexagonal shape, which are considered by Zirkel as hatiyne.* A tributary to Susan Creek, which runs down from the western slopes of the River Range, exposes under these rhyolites and trachytes a body of augite-andesite. On its weathered surfaces, this rock is of . a greenish-eray color, but in fresh fracture almost black, having the resinous lustre peculiar to this type of rocks. In its half-glassy ground- mass,. one can distinguish crystals of feldspar and augite, the former being much more distinct on the weathered surfaces. By the aid of the microscope, magnetite grains are also found, but no olivine, and the groundmass is seen to be made up of yellowish-brown glass and the net- work of interwoven microlites peculiar to the augite-andesites. The glass- inclusions in the feldspars and augites are very abundant, and almost replace the original substance of the crystal, as will be seen by reference to Vol. VI, Plate XI, fig. 2, where a thin section of this rock, showing a feldspar crystal included in glass, is illustrated. A light-gray brecciated rhyolite, on the eastern slopes of the range, contains many fragments, which resemble the black and green jaspers of the conglomerate. It contains also fragments of rhyolite, while through 1 Microscopical Petrography, 151. 2 MOLEEN CANON. 599 the mass are well-defined crystals of black biotite, the whole enclosed in a subordinate felsitic groundmass full of crystals of quartz. In the southern half of the River Range, the geological axis has a direction apparently about northeast and southwest, and: south of the road from Elko the prevailing dip of the formation is to the eastward. Quartzites and conglomerates form the summit for some distance south of this point, showing occasional beds of limestone, while along the eastern slopes, toward Moleen Cajion, are found outcrops of light-colored earthy limestones overlying the quartzites conformably, which correspond to the Upper Coal-Measure limestones found at Moleen Peak, on the opposite side of the river. These are ex- posed in section at the entrance to the cation, where the dip, at first shallow, gradually rises to 45°. A thickness of nearly 2,000 feet of buff, earthy limestones, with some included conglomerates, is thus shown, though not in continuous section, many of the beds being obscured by débris. The strike of the upper beds is considerably to the east of north, but in the canon bends a little to the west of north, where the dip becomes steeper. In the Weber Quartzites, the river takes a sharp bend to the north, returning almost parallel to its course around a ridge of quartzite, whose beds stand almost vertical. In the upper portion of these quartzites can be recognized the peculiar greenish and purplish conglomerates made up of angular jasper pebbles in a somewhat calcareous matrix, which resemble the conglomerates found along the range to the north, but are less metamorphosed. Although there is a decided appearance of unconformity at this point between’ the quartzites and limestones, it is probably due to faulting. Underlying the quartzites, on the south side of the river, and dipping about 45° or 50° to the eastward, is a zone of mixed slaty limestones and heavy blue limestones, which extend as far west as Carlin. These beds have a strike a little east of north. One of the mud beds above the main mass of limestone, but still some distance below the Weber Quartzites, contains a carbonaceous zone, carrying an impure anthracite. — These Lower Coal-Measure limestones to the north of the river disap- pear beneath the horizontal Tertiaries of the Maggie Creek Valley. To the south, they are covered by extensive rhyolite flows, which cover the mountain-mass at the northern end of the Pinon Range north of Dixie’s e 600 DESCRIPTIVE GEOLOGY. Pass. The highest point of this mountain-mass, however, shows outcrops of the characteristic quartzitic sandstone of the Weber group, which here seem to be considerably metamorphosed, having a rough trachytic feel, and containing some crystals of quartz and a good deal of decomposed feld- spar. The surfaces of this quartzite show a great deal of slickenside-pol- ishing, evidence of a faulting, which the geological structure of the range renders necessary. The rhyolite, which is the red porphynitic variety already described as common through Nevada, forms flat, table-shaped ridges, which extend down to the banks of the Humboldt below Carlin, and to the eastward obscure the contact between the Weber Quartzites and the Upper Coal- Measure limestones. Moreen Peax.—The mass of Moleen Peak is made up of nearly hori- zontal limestones, having a dip of about 5° to 10° to the southeast, under- laid by quartzites, which have apparently been faulted up into their pres- ent position. Where the cafion of the South Fork of the Humboldt cuts through the Elko Range, it exposes about 1,800 feet of these limestones of a prevailing gray and light-blue hue, but with many beds toward the bottom of an earthy buff color, and near the top some prominent members of included quartzite. At the three different zones, representing about equal distances through the 1,800 feet, were found the following Coal-Measure fossils : . From bed No. 1: Productus subhorridus. . Productus symmetricus. From bed No. 2: Productus subhorridus. Athyris subtilita. Spurvfer cameratus. Zapnrentis Stansbury. From bed No. 3: Productus subhorridus. Productus semireticulatus. Productus Prattenianus. Productus symmetricus. MOLEEN PEAK. 601 Streptorhynchus crassus. Orthis carbonaria. Eumetria punctulifera. This limestone series is conformably underlaid along the north base by a series of quartzites and quartzitic conglomerates, carrying quartz and jasper pebbles, from the size of a filbert to that of an egg, resembling those exposed in Moleen Canon. Their bedding is broad and heavy, and the colors green, yellow, and purple; the general texture of the quartzite is very coarse, closely resembling that of the Weber group. Last of the cation of the South Fork, the same limestones continue for about 8 miles on their strike, showing a little Weber Quartzite on their north base near the cafion, and consider-— able development of quartzitic strata high up on the series along the south- east foot-hills. To the east of the Elko Range, the whole broad valley of the South _ Fork is a plain of horizontally-bedded Humboldt Pliocene, through which the narrow stream-beds are eroded. It is very difficult to get at the character of the beds, the best exposures being along the branches of the South Fork, where a couple of hundred feet of fine, siliceous, marly beds with occasional clay-seams occur. At the angle formed by Dixie Creek with the South Fork of the Humboldt, just southeast of Moleen Peak, there crops through the Tertiary plain a northeast ridge, or rather a low table of Carboniferous limestone of a prevailing light-blue color, banded with yellow and buff beds, like the neighboring limestones of Moleen Peak. This iso- lated outcrop is very much broken up, but possesses a general dip to the eastward, and is, without doubt, a fragment dislocated from the Moleen Peak mass. Opposite the town of Elko, the limestones break off suddenly, and a low depression in the Elko Range is filled with beds of the Humboldt Pliocene, which, on the eastern side, have been eroded away, exposing upturned strata of the Green River Kocene, the northwestern foot-hills flank- ing the pass on either side being made up of flows of red porphyritic rhyo- lite. The beds of the Green River Eocene as exposed here have a strike due north, and’ dip 35° to the eastward. They resemble closely those es, 602 DESCRIPTIVE GEOLOGY. exposed at the coal-mines in the northern end of the valley, consisting mostly of very thin shales, sometimes calcareous, sometimes made up entirely of quite siliceous material, often bituminous, and im some cases containing several thin seams of brown coal. The Pliocene beds which - overlie them non-conformably consist at the summit of the pass of white voleanic ash, very porous, and containing a good deal of fine black mica and hornblende. The northern end of the Elko Range is, as we have seen, made up of red, porphyritic rhyolites, which extend continuously to Upriver Peak. These rhyolite flows seem to be generally rather thin, but, with the exception of points already mentioned at Osino Cation and south of the Elko Pass, no underlying sedimentary rocks were found exposed in the range. Along the western flanks of these rhyolite ridges are numerous hot springs, the most remarkable of which is that two miles south of the town of Elko, where a public bath has been established. Owing to the peculiar taste of its waters, this spring has been designated the ‘Chicken Soup Spring”. Szetoya Movuntains.—The country represented on the northwest cor- ner of the map, west of the River Range, is a region which has been the scene of great volcanic activity in later Tertiary times, and in which the older formations are generally concealed beneath extensive flows of rhyolite, which now cover the greater part of the surface of the country. It is inter- sected by broad valleys, whose waters run alternately to the south into the Humboldt River or northward into the Snake, which have generally been filled by: Pliocene beds, composed largely of fine re-arranged volcanic material. ‘The depression occupied by the valley of Susan Creek and the north and south tributaries of the North Fork of the Humboldt presents a type of one of these Pliocene Valleys. The streams run in broad Qua- ternary bottoms of fine mud and silt, resulting from the decomposition of the soft Tertiaries, and support considerable growth of native grass, while on either side are mesa-like benches of Tertiary strata, which extend wp on to the flanks of the bounding ranges to a height of 600 to 800 feet above the valley-bottom, covered with a light gravelly soil, which only supports a scattered growth of sage-brush. : The southern portion of the Seetoya Range represents an uplift of sedi- NANNIP’S PBAK. 603 mentary rocks around a core of granite and granite-porphyry, which in Tertiary times has been deluged by flows of rhyolite to such an extent that but little can be seen at present of the original structure of the range. Nannie’s Peak, which is the central and most elevated point of this range, is a sharp, crescent-shaped ridge of granite, wrapped around by steeply- dipping beds of the Wahsatch limestone, which are intersected and covered by flows of rhyolite. The granite, though distinctly an eruptive rock, has remarkably regular cleavage or bedding-planes developed in the strike of _the ridge, whose summit is formed of projecting beds from 50-to 100 feet thick, dipping at an angle of 80° to the westward, in conformity with the overlying limestones on the western flanks. It also shows a tendency to split up into narrow bands from one to three inches in thickness, which have a general conformity with this larger system of bedding. The granite is a gray, coarsely crystalline rock, made up of quartz, plagioclase, and orthoclase, and large crystals of mica, but containing no hornblende. The orthoclase feldspar predominates over the plagioclase, and is generally decomposed and opaque, showing a zonal structure, while the latter remarkably is fresh and well preserved. Under the microscope, the quartz is seen to contain numerous fluid-inclusions, with well-defined salt cubes and sometimes grains of apatite. A tendency is observed, in the fine-grained aggregations of small quartz and -feldspar crystals, to form a groundmass. Its chemical composition, as determined by Prof. Thomas M. Drown, is: TSH Chin es ilehes Gu —, Se ahtiA e as Ns GOLaT AvITGRTENa, S Sins OS a ee ae de 15.27% Herrous Oxide. 2... ls. sh i eee. ZEOo Manganous oxide. ..-.-.-- Sahl cas La os coh 0.11 ASSES hig yak A oad Rua Sa ia i a GOs am ela ae RB ye ING esiern es Macmn mr tr ee eee oe a apaen 2 ONT OVO GLE Ti alsa pm SERS A 8s a, Sala a a i ea BE Potassa . - . - Bp a Saito, ag ud oa ele le a 4.58 TST CO YT geal ck RIP St 2 a I ig ile ian 0.52 604 DESCRIPTIVE GEOLOGY. In some places, where the granite splits into thin slabs only about an inch thick, a little microscopical hornblende is found, and the plagioclase seems’to predominate over the orthoclase. On the southwestern point of the peak, at the contact with the overly- ing limestones, is a small development of felsitic porphyry, enclosing a vein of red oxide of copper. It has a fine-grained grayish groundmass, enclos- ing crystals of feldspar and large proportion of hexagonal plates of black — mica and crystals of quartz. Under the microscope, the larger quartz erys- tals are seen to.contain only liquid-inclusions, in some of which are cubes of salt. In the groundmass, which is generally micro-erystalline, there is a tendency toward a spheerulitic formation, which is particularly observable around some of the small quartz crystals, which are surrounded by radiating felsitic fibres. On the western flanks of the peak, which are very steep, but well covered by detrital material, the limestones have a north and south strike, with a dip of 70° to 80° to the westward. Through them runs a curious dike or bed of rhyolite, which, on its weathered surface, at first glance has considerable resemblance to a felsite-porphyry. It is gen- erally of a yellowish-gray color, showing large crystals of mica, horn- blende, and quartz porphyritically imbedded in a dull, opaque, felsitic groundmass, whose fracture is very uneven and granitoid. In some cases, the groundmass has a greenish color, and is quite glassy, passing into a pearlite, and shows crystals of glassy sanidin. Under the micro- scope, the groundmass is seen to be distinctly sphzerulitic, but without axial — fibration. The limestones seem to close completely around the granite body, and are best seen in section on Coal Creek, where they have an east and west strike, with a dip of about 45° to the southward. A thickness of about 2,000 feet of limestones is here observed, the upper member of which is a con- glomerate, which may probably represent the lower bed of the Weber Quartzite. In the cafion of Coal Creek, about a mile from its mouth, is a considerable development of black shales, in which in the creek bottom was found an exposure of about 15 feet of black anthracitic material, eee ee eS Ss OL ee ee. Oe eee ; : SEETOYA MOUNTAINS. 605 forming in places an impure anthracite coal. The section exposed is as follows: Feet. Conglomerate. Blue limestone, with shales ................--.---. A ARSED SUSE iach Sisk PAR MS 2 100 Bluish-black, finely-divided, argillaceous shales Pe apeuaar et ta eeeoe Mave gs Onis winston 150 (OCAIESES IN Wee te Buedos ap edecee one 2 Sic HE EAD EO CHAIR Le eS IS ee Seta eI ae arte Paes 15 TP OD TRIMNOOS GOP ICS eh ON oe See eee ee ee eee cg ee ee 50 Gaptes lo. 6 oS eG HALE COG OSG SESS OIE a ten CON ec a ep ene See 100 ISIANGICRINGL GS BER SE Son can Se ene Sees eee Se his See cence Sect ey teers let gtayate 10 ASEM ACRES WPCC IODC eee. e SSE Ae GOES ee ae ea a eeepc vresk are 50 PevMOlo islnCaleareOus SlAlOSH= as t)2 fo- (05400425 + 22 Dead de gti s ened ete maceseeeee 200 Drab siliceous limestone, with shales............ Rifee Bova cect ei Gta: hike amines cote 200 Blue limestone, with seams of white calcite ............ 000.02 22sec ee ee eee eee 50 MUS by GUAT UZILC 5 sade. oes. eens SURE ARR abies REM eer ees Lewy ewer gare 50 Compact blue fossiliferous MmestOne. 2... 2 22 260s oe ee ce ee dee ele ale eet 100 Blue limestones and shales... -.........---.-- BP ayia Ae erica Ghee. cis Spe kate 200 Granite (unconformable). From the lower fossiliferous beds were obtained the following Coal- Measure fossils : ; Productus semireticulatus. Syringopora multattenuata. Cyathophylloid fragments. In these easterly-striking limestones, the same curious bed of rhyolite was observed as on the western slope. On the spur to the south of the mouth of Coal Creek is a body of gray trachyte, stained with streaks of iron oxide, which overlies a porphyritic decomposed rock resembling a rhyolite, but whose position would suggest that it may be an inter- ealated porphyry of Carboniferous age. If this be so, the interbedded rhyo- lites which encircle Nannie’s Peak should have the same origin. The trachyte is made up of sanidin and plagioclase-feldspar, with some little biotite, in a gray, somewhat porous, felsitic groundmass. Under the microscope, the groundmass is seen to be nearly colorless, and to contain feldspathic microlites, with very little ferrite, and also some little titanite. The porphyry or rhyolite has the same constituents as the trachyte, with addition of free quartz; but its groundmass has a peculiar half-glassy sphe- rulitic texture, as distinguished pony the granular semi-crystalline texture of that of the trachyte. 606 DESCRIPTIVE GEOLOGY. Maggie’s Peak is made up of a granite similar to that of Nannie’s Peak, but having a still more porphyritic texture. It has the same tend- ency to weather into thin slabs as that of Nannie’s Peak. It is a gray, rather fine-grained rock composed of mica and hornblende, and relatively little quartz, with both monoclinic and triclinic feldspars. This rock has been classed by Zirkel as granite-porphyry. It is associated with a well-defined ~ felsite porphyry, which closely resembles. a rhyolite in physical habit, having the same tendency to separate into thin slabs, but carried to a much greater extent than in the granite. In a white homogeneous ground- mass, it shows few crystals besides those of quartz, but under the micro- scope its groundmass is seen to be entirely crystalline, and the quartz to abound in fluid-inclusions, sufficient guarantees of its earlier origin. The rhyolites adjoining this porphyry, from which in the field it can be with diffeulty distinguished, are whitish and red compact rocks, containing like- wise only crystals of quartz. The exposed surfaces present beautiful botry- oidal secretions of hyalite and opaline chalcedony. . At the extreme southwestern point of the range is a body of gray sili- ceous limestone, forming an outlying ridge, through which Maggie Creek has cut a narrow cation. As far as observed, it was entirely barren of fos- sils, and, on account of its isolated position, no evidence was obtained as to its geological horizon. It has, however, been assigned, on general grounds, to the Lower Coal-Measure group. ) The valley of Maggie Creek, like that of Susan Creek, is covered by white Pliocene beds. At the head of the valley, the low divide between it and that © of the North Fork of the Humboldt is occupied by various flows of rhyolites, - some white earthy varieties and some dark obsidian-like pearlites containing | white feldspar crystals. - To the north of this divide, the range is continued by a higher ridge, en échelon with the Nannie’s Peak Ridge, which forms the eastern boundary of Independence Valley, and stretches northward beyond the limits of the map in a high important mountain mass. This portion of the Seetoya Mountains is made up of heavy bodies of quartzite, which have been considered to represent the Weber Quartzite in this region, inasmuch as they are both underlaid and overlaid by lime- stones. The structure of the ridge is that of an anticlinal fold, whose axis SEETOYA MOUNTAINS. 607 is a north and south line running along the western flanks of the ridge. A vertical displacement along this line has exposed, on the western spurs, heavy beds of limestone in a thickness of 4,000 to 5,000 feet, which are much contorted. At the northern end of the limestone body, the beds form the complete arch of a sharp anticlinal fold, which descends or “noses under” to the north. In the middle of the exposure, the western mem- ber has been broken down, the eastern member of the fold forming steep, rugged spurs under the highest point of the range, in which the limestone beds dip at first about 20° to the eastward, and gradually steepen to a perpendicular and even to a slightly western dip. At the southern point of the limestone exposure, in a little cation just north of Seetoya Peak, the dis- placement is a simple faulting of about 100 to 150 feet, which can be very 3 distinctly traced, where, in the upper portion of the limestone formation, a. thickness of about 150 feet of dark limestone is bounded below by a body of black shales, and above by a blue quartzite, which can be traced on two adjoining spurs, both dipping about 20° to the westward. ‘Although paleontological evidence is wanting, there is little doubt that these limestones belong to the Lower Coal-Measure group. The quartzites, which form the main crest of the ridge, consist mainly of white and blue sagcharoidal quartzites, containing a few thin beds of interstratified limestones. Their average dip is about 25° eastward, curv- ing in strike from a little east of north at the southern portion to a little west of north toward the northern limits of the map. They abound in " slickenside-surfaces, showing remarkably beautiful striation and polish. Along the eastern flanks of the ridge, overlying the quartzites, a few out- -. erops of limestone can be distinguished under the flows of rhyolite, which would represent the Upper Coal-Measure group. The lower portion of ‘the quartzite body, as it approaches the limestones, has a large proportion of limy strata and beds of calcareous shales, interstratified in the quartzites. On the western slopes of Seetoya Peak is a quartzitic conglomerate, which apparently forms a portion of the western fold, though, owing to the dis- placement and faulting, it was not possible to fix definitely its horizon. In a little cafion to the southwest of Seetoya Peak, the line of dis- placement is occupied by a dike of diorite or diabase cutting through the 608 DESCRIPTIVE GEOLOGY. ‘limestones, which are here exposed by the erosion of the ravine. The diorite is a fine-grained, dark-green variety, in which but few macro- scopical crystals can be distinguished. Itis made up mostly of plagioclase, mica, calcite, and a dark-green product of alteration, which Professor Zirkel thinks should be referred rather to augite than to hornblende, which would place the rock among the diabases, although, from a macroscopical examina- tion, it has been colored as a diorite. The line of the upper geological section at the bottom of the map cuts the range at Taylor’s Creek, show- ing this dike, and the fault on the western slopes. 'To the southwest of Tay- lor’s Creek, the low ridge which divides Independence Valley from Maggie Creek Valley is mostly occupied by flows of rhyolite, generally of white and red porphyritic varieties, which, as shown by the few outcrops and quartzite débris found in the ravines, have covered a pre-existing ridge of Weber — Quartzite. Nortuern Cortez Rancr.—That portion of the Cortez Range which bounds Maggie Creek on the west, and is connected by this ridge with the Seetoya Mountains, for the most part has not been covered by the rhyolite flows which have deluged this region. These hills are, however, remark- ably thickly covered by detrital material, and show very few outcrops. From the not always reliable inferences to be drawn, from fragments found in the ravines, the hills are mainly composed of quartzites, generally white, compact, and somewhat iron-stained varieties. At the Dalton Peaks are found almost the only good exposures of the sedimentary rocks, which make up the range. Here the eastern peak shows quartzites and siliceous shales, — through which runs a black cherty vein, striking due north, and dipping 25° to the eastward, while on the western peak are the peculiar greenish _ quartzitic conglomerates characteristic of the Weber Quartzite. These quartzites are very heavily bedded, and stand at a very steep angle, appa- rently with a slight dip to the westward. The structure here, then, as well as can be arrived at, is an anticlinal, whose western member is steeper, and has perhaps suffered displacement. In the valley of Boulder Creek, to the west of Dalton Peaks, at- White’s Ranch, is a little isolated hill of limestone, overlaid by a greenish- white quartzite, from which were obtained a collection of Lower Helder- ah sal el ; 4 4 NORTHERN CORTEZ RANGER: 609 berg fossils. ‘The limestone is dark, fine-grained, and rather siliceous, thinly _ bedded, and interstratified with light-reddish siliceous shales, about one- fourth inch in thickness, having some branching impressions like plant-roots. The beds from which the fossils were obtained are a series of thin-bedded limestones near the upper portion of the formation. The following species were determined by Messrs. Hall and Whitfield : Atrypa reticularis. Pentamerus galeatus. Strophodonta, sp. (ike S. punctulifera). Orthis, sp.? (allied to O. varica). Trematospwra. Celospira (new sp.). Rhynchonella, sp.? Favosites, sp.? (allied to I’. Helderbergia). Diphyphyllum (new sp.). Campophyllum, sp. ? A thickness of 500 to 700 feet of limestones is here exposed. Their general dip is to the eastward, the beds lying nearly horizontal at the west- ern face of the hill, and steepening in dip to the eastward. It would appear therefore as if this little body of limestone had been faulted up. The quartzites, which, from their stratigraphical position and general litholog- ical character, have been considered to represent the Ogden Quartzite, are found along the eastern and southern flanks of the hill, conformably overlying the limestones. They also crop on the western side of Boulder Creek, at the foot of the bluffs formed by the flows of rhyolite and basalt of the Shoshone Mesa. The immediate foot-hills of the Cortez Range, in the neighborhood of Boulder Creek Valley, are covered by thick deposits of Quaternary gravel and soil, so that the structural relations of the out- crops of the Silurian with the Weber Quartzites of Dalton Peaks could not be definitely established. From Dalton Peaks to Mount Neva, in the deeper ravines, are exposed frequent outcrops of quartzites having a general north and south strike, and the same lithological character with the Weber Quartzites of the Seetoya 39 DG 610 DESCRIPTIVE GEOLOGY. Range, which, though too isolated and obscure to show clearly their lines of structure, give sufficient evidence that the Mount Neva mass is a pre-. existing elevation of Weber Quartzite, continuous with that of the Dalton Peaks Ridge. Along the eastern flanks of this elevation, at Tuscarora, on the borders of Independence Valley, is a body of propylite, now largely covered by flows of rhyolite and Quaternary débris. Near the town of Tuscarora, the surface of this propylite is decomposed to a depth of 8 to 4 feet, and covered by as many feet of soil, which has been worked with considerable profit for placer gold. The propylite of Tuscarora has the characteristic physical habit of this rock, offering no prominent outcrops, and generally occupying a subordinate topographical position. It is a light ereenish-gray, porphyritical rock, having something of an earthy texture, ° showing macroscopical crystals of opaque, somewhat decomposed ortho- clase, and fresher plagioclase in a groundmass, which is characterized by a large admixture of light-green fibrous hornblende. There are also larger prismatic crystals of dark, fresh hornblende, usually characteristic of ande- site, in the rock, but not in sufficient quantity to form an important element in its composition. The microscope detects in it no augite or biotite. The two varieties of hornblende, the green and the dark-brown, may be seen in Vol. VI, Plate IV, fig. 4, which presents a thin section of this propylite with its characteristic groundmass. : Another darker green, somewhat decomposed, variety, obtained from under the Quaternary accumulation of the slopes, has been classed by Zirkel,' from his microscopic examination, as an andesite, with the remark, however, that it contains a great quantity of hornblendes in an advanced stage of alteration into epidote, a rare occurrence’ with andesites. These horn- blendes can be distinguished macroscopically in the feldspar crystals. The rock certainly has the physical habit and position of propylite rather than andesite. . A more well-defined andesite occurs on the foot-hills of the range, however, north of the town, where it has apparently poured out between the propylite and the underlying sedimentary rocks. It is a dark, com- 1 Microscopical Petrography, vol. vi, 130. NORTHERN CORTEZ RANGE 611 pact, heavy rock, having something of a columnar structure, of a dark reddish color on its weathered surfaces. Macroscopically, it shows only small plagioclase and black hornblende crystals in a dark-bluish, or sometimes greenish-gray, felsitic groundmass. Under the micro- scope, the hornblende has rather a greenish than the characteristic dark- brown color of andesite, and is somewhat fibrous. The groundmass is a yellowish-brown mass abounding in black trichites, containing some apatite, but neither augite, biotite, nor tridymite. ‘These three rocks, which are so closely connected geologically, have, in their mineralogical composition, therefore, a similar interchange of characteristics. The rhyolites which have covered these older volcanic rocks along the western borders of Independence Valley are generally white, decomposed varieties, which are almost amorphous, the only traces of crystals being white outlines of kaolinized feldspar. By the aid of the microscope, they are seen to have som2what of a trachytic appearance, the groundmass showing no tendency to fibration or fluidal structure, and the presence of some altered hornblende and biotite, together with a good deal of quartz, is detected. On the extreme foot-hills of the range, about four miles north of Tuscarora, is a bed of dark rhyolite, in some respects almost like an andesite. It contains, however, almost exclusively sanidin-feldspar in a dark, compact, felsitic groundmass, with mica in remarkably well-defined hexagonal prisms, anda little free quartz. In the ravine a few miles south of Tuscarora, a body of augite- andesite is exposed under the rhyolite flows. It has a dark-gray ground- mass, with somewhat of a resinous lustre, full of crystals of plagioclase and augite. The latter are remarkably well defined, while the plagioclases are seen to be full of fragments of yellowish glass. Under the microscope, the groundmass is seen to be made up of microlites in a glassy base of gray color, and to contain no olivine. The rhyolite adjoining this body of augite- andesite, and forming the foot-hills along the southern portion of Independ-. ence Valley, is a white porphyritic variety, containing a considerable development of mica, quartz, and sanidin in a somewhat decomposed felsitic groundmass. : The white amorphous rhyolites extend up on the eastern slopes of 612 DESCRIPTIVE GEOLOGY. Mount Neva to its very summit, and evidently cover most of the northern slopes toward the Owyhee Valley, though these were not examined by our parties. Doubtless, other outcrops of the older volcanic rocks might have been found by a more detailed search. Sufficient data were obtained, however, to show that this mountain mass consists mainly of a series of steeply upturned quartzites and slates, along whose eastern base there has been an outflow of propylite and andesite, the whole having been covered by thin flows of rhyolite, which have been sufficiently eroded in the deeper-cut ravines to expose the underlying sedimentary rocks. In the deep ravine on the western face of Mount Neva, a corisiderable thickness of quartzites and dark siliceous argillites, with cherty seams dipping steeply to the westward, was observed. Their general character resembles that of the quartzite body of the Seetoya Mountains on the east side of Independence Valley, being that of rather saccharoidal rocks, of a bluish- white color. One bed was noticeable for a wavy, vein-like, blue shading through the white mass, occasioned by accumulations of graphite in fine streaks through the rock. The lower end of the ravine is narrow and cafion- like, its walls being formed of a dark-gray pearlitic rhyolite, having an unusually massive structure, and a tendency to columnar weathering. It is very rich in sanidin and mica, and contains also some plagioclase and a considerable amount of free quartz. The glassy groundmass is of a gray color, as seen under the microscope, and full of microlites in a great variety of forms, but contains neither hornblende nor augite. Squaw Vattey Recion.—The region to the west of the northern por- tion of the Cortez Range consists of a series of low rolling hills and east and west valleys, formed by flows of rhyolite and basalt, in which, with the exception of the isolated outcrop near White’s Ranch, no sedimentary rocks were found. The valleys which occupy the lines of depression between these ridges are mostly filled with Quaternary débris, but in Squaw Valley and Rock Creek Valley there is a considerable development of stratified deposits composed largely of volcanic ash, which have been referred to the Humboldt Pliocene. The more northern line of elevation, that of Owyhee Bluffs, presents a rather more abr upt face to the south and long gentle slopes to the north, SQUAW VALLEY REGION, 6135 and forms the divide between the waters of the Humboldt and those of the Owyhee River. The view to the northward from the summit of Rose Mount- ain, the most northern point visited by us, extends out over an almost limitless plain, whose horizon is as level as that of the ocean. The rhyolite which forms the summit of Rose Mountain shows the appropriateness of the name which has been given to this rock, signifying ‘thin flowing”, since it is made up of sheets of lava only about an eighth of an inch in thickness. It is a red, compact, felsitic groundmass, containing only erystals of quartz, with an occasional development of sanidin-feldspar, the surface of each layer being colored by a red earthy coating, containing a few flattened erystals of feldspar. as considerable variety of rhyolites was found along the southern slopes of Rose Mountain. Among the most noticeable is a rhyolitic breccia, made up of pink and red angular fragments of earthy rhyolite, whose outline is generally rectangular, and which vary from half an inch to an inch or more in diameter. The banded structure of the rhyolite, from which these frag- ments are derived, gives to them the appearance of a structure like that of woody fibre, so that the rock has the appearance of a mosaic made of seg- | ments of wood. One variety of whitish, decomposed rhyolite is full of druse-like cavities, filled with prismatic. erystals of quartz. | Along the lower foot-hills is a development of dark pearlitic rhyolite, not ‘unlike that of Mount Neva, but less richin crystals. Quartz and sanidin are its prominent crystalline ingredients, bnt the microscope discloses also some green augite. In this rock are found fragmentary inclusions of a dark-. green, rather finely crystalline diabase, which is remarkably rich in olivine, and shows well-defined tabular crystals of plagioclase and pale-brown augite. Under the microscope, a little globulitic base is detected and some titanic iron. At Sunset Gap, in the eastern end of Squaw Valley, is‘a similar black pearlitic rhyolite, interstratified in a white porphyritic rhyolite containing small crystals of black hornblende and mica, with sanidin and a little quartz, in a white, rather earthy groundmass. The dark pearlitic rock contains, besides the sanidin, some little plagioclase and little green augite, but no — quartz, hornblende, or biotite. These rhyolites show a decided dip to the 614 DESCRIPTIVE GEOLOGY. eastward, and form north and south ridges, cropping out through the horizontal beds, which form the mesa-like benches through the middle of Squaw Valley: these are made up largely of re-arranged volcanic material, but along the eastern end of the valley contain also a considerable admix- ture of sedimentary débris from Mount Neva. In the western end of Squaw Valley is a broad expanse of bottom- land, which, at the entrance to the canon which Rock Creek cuts through the ridge south of Squaw Valley, is occupied by a shallow fresh-water lake. On the summit of the ridge south of Squaw Valley is found a erayish-red, banded rhyolite, in which the bands consist of alternately predominating portions of a reddish felsitic groundmass, and of aggregations of crystals of sanidin and quartz. The rock contains neither hornblende nor mica. Under the micro- scope, the groundmass is seen to have a very spherulitic structure and radial fibration, and to abound in ferritic microlites, to the predominance of which in the sphzerulites the reddish bands owe their color. The peculiar radial arrangement of the ferritic microlites is shown in the thin section of this rock, represented in Vol. VI, Plate VIII, fie. 3. The main body of this ridge is made up of the ordinary reddish por- phyritic rhyolite already described, which contains only a few crystals of quartz and sanidin, porphyritically imbedded in a red felsitic paste of peculiarly uneven fracture. The microscope discloses neither quartz, horn- blende, or mica. Through this ridge, Rock Creek has cut a narrow wind- ing cation for a distance of about 4 miles, but in Rock Creek Valley — runs in a broad Quaternary bottom, eroded out of the horizontal Pliocene beds. To the south of this valley, the rhyolites are covered by thin flows of of basalt, which form the surface of the broad table-shaped ridges of the Shoshone Mesa. . The hills to the west of Rock Creek Valley near the Warm Springs are composed of a peculiar decomposed rhyolite of a light pearl-gray color, which is almost identical in appearance with that which forms the little coni- cal hills rising out of the Shoshone Mesa near its southeastern edge. This rhyolite contains a large amount of small, gray, glassy sanidin crystals, and large cracked quartz-grains, but is almost devoid of hornblende and mica. It is remarkable for containing a large amount of tridymite. Near the | SHOSHONE MESA. 615 Warm Springs i is tse a small isolated remnant of basalt, which forms the foot-hills of this rhyolite ridge. SHosHonE Mrsa.—The Shoshone Mesa is one of ve most singular topographical features of the Fortieth Parallel region. From Rock Creek Valley, the country rises to the southward in broad and even slopes, keeping approximately the same angle for a distance of 15 or 20 miles, and form- ing an elevated plateau, bounded on its southern edge by perpendicular cliffs over 2,000 feet in height, which reach their greatest elevation at its extreme southern end, known as Stony Point. This elevation forms the southern of the three northeast and southwest ridges, or undulations, of the surface, which have -been covered by the volcanic flows of the northern region. Along the base of the cliffs, the lower thousand feet are seen to ate made up of rhyolites, generally of rather dark color, while the surface of the table is composed of flows of dark, compact basalt. These basaltic flows have evidently covered the pre-existing rhyolite ridge, and flowed around the higher hills, which now project above its surface... The rhyolite which forms the base of the cliffs on the southeast, toward Rock Creek, is” a dark-purple, thinly-banded rock, containing large crystals of sanidin and rounded quartz-grains in a compact, felsitic groundmass, which, under the microscope, does not show any signs of fibration except around the larger erystals. It constains a little plagioclase and considerable apatite, and the quartz-crystals are full of glass-inclusions, but the groundmass, although showing microscopically the fluidal structure peculiar to rhyolites, has rather a micro-crystalline development, and contains no micro-felsitic matter. — Associated with these, at one of the re-entering angles of the cliffs, is a peculiar dark pearlitic rhyolite abounding in large lithophysee an inch in diameter, which are generally hollow, and look like a clayey mass, formerly filled with gaseous matter, which has burst forth, leaving a hollow interior. The rock abounds in large crystals of sanidin and quartz enclosed in an almost black, pearlitic groundmass, which has become whitened in contact with the lithophyse. The centres of some of the lithophysee are still filled by erystals of quartz and feldspar. In some of the larger feldspars, grains 616 DESCRIPTIVE GEOLOGY. of mica can be detected macroscopically. Under the microscope, both mica, brown hornblende, and small dark-green augite grains can be distinguished. The gray, half-glassy groundmass contains sphzerulites as large as a walnut, which develop by decomposition a concentric-layer structure. The most advanced stage of this decomposition closely resembles the larger litho- physe, which would seem to sustain the opinion of J. Roth, that these lithophysee are nothing but mechanically and chemically altered larger 3 spheerulites. About a mile from the edge of the cliffs is a little group of projecting hills having a rude -semicircular shape, suggesting the form of an ancient crater, which ave composed of a light pearl-colored rhyolite similar to that found near the Warm Springs. Under the microscope, it is seen to be less distinctly crystalline than that which forms the base of the cliffs, and to containa large amount, of tridymite. It also contains long prismatic bodies, which are apparently altered biotite. . At the base of the cliffs, at Stony Point, is a rhyolite which resembles macroscopically the typical porphyritic rhyolite, already so often mentioned, though this has rather a brownish-red color. It contains only crystals of sanidin-feldspar, with some little plagioclase, in a compact felsitic eround- mass. ‘lhe monoclinic feldspars seem to be a good deal decomposed, and are somewhat stained with iron oxide. Dark particles, apparently of specular iron, can be distinguished macroscopically in the groundmass. Under the microscope, this rock, with the exception of the absence of quartz, resembles that found at the base of the cliffs further north. The groundmass is a micro-erystalline aggregation of colorless particles, with grains of black opacite and brownish ferrite. . The basalt which forms the summit of the plateau at Stony Point is a rather remarkable rock, having a light-brown color, through which are mottlings of a light-green material. The rock is a remarkably fine-grained variety, though somewhat vesicular, in which, by the unaided eye, no crys- talline ingredients, with the exception of a few isolated feldspars and occa- sional grains of quartz, can be distinguished. Under the microséope even, the constituents are so fine as to be somewhat confused and difficult to dis- tinguish. It is rather poor ‘in augite, and contains small reddish-brown SHOSHONE MESA. 617 grains of olivine, which can hardly be distinguished from the magnetite grains, which have also a reddish, decomposed surface. Between the crys- tals, particularly those of plagioclase, is an amorphous base of the usual basaltic character. ‘The quartz-grains are not seen under the microscope, and are quite an accidental occurrence, probably caught up by the basalt from the surrounding rhyolite. The main rock of the mesa is a normal dolerite, very porous, often . containing vesicules as large as a filbert, which are partially filled by carbon- ate of lime. It is a dark, rather coarse-grained rock, in which plagioclase, augite, and olivine can be distinguished by the naked eye, and, by the aid of the microscope, also magnetite and some apatite, with a little amorphous base. Chemical analysis detects the presence of titanic acid, so that some titanic iron is probably associated with the magnetite. The analysis was made by Mr. R. W. Woodward, and gives the following constituents: Diligent. oh aS alee aan oF ae ieee 48.40 48.38 Penman ek Ren he ce 17.95 18.95 OSS ORIG ee = a ae att 82998 Dale BEER OE Ox Sa er re 8.85 8.90 MianigAM@mspOXIGE 2.2 oe sla oS 5 os a9 |= trace trace TORERIVe 2 Se 10.05 10.32 MACTNOSG: - sR ee Se 6.99 7.02 epi es setae Sey ee oe eT a trace trace Sade) oS Sea ee ee ee eee 2.86 Dale JECOUBISSE IE a2 Sh 2 Se ee RS TO3si i l03 Mii rdCldee At a Gs a oe eR 0.24 0.24 WARDOMICRACIOuERt | Koo .e's Se veinis ced cee > 0.84. Ata VERS 2 SS ea ae es ee petae acs a Oro4: makes 99.83 100.78 618 DESCRIPTIVE GEOLOGY. Si Crt ON Vee SHOSHONE RANGE AND CARICO PEAK. BY ARNOLD HAGUE. SuosHone Raner.—The Shoshone Range rises from the valley of the Humboldt River in latitude 40° 40’, and extends in a southeast direction until it passes south of the southern limit of Map V, Its general course is about north 25° east or south 25° west. Only about 40 miles of the north- ern portion of the range come within the limits of Map IV, embraced in the present chapter. Directly south of the railroad, at the northernmost ex- tremity of the range, there occurs a large field of basalt, separated from the great Shoshone Mesa by the Humboldt Valley, which is here about 6 miles in width. This basalt flow extends south for about 16 miles, and consists of two gently-inclined tables, having a dip to the southeast, and separated from each other by a northeast and southwest valley, called Whirlwind Valley. These fields of basalt consist in general of fine-grained dolerite, made up of plagioclase, augite, olivine, and magnetite, with more or less of _ a gray globulitic base. Through these doleritic tables break out a great number of vertical dikes of fine-grained anamesitic basalt, containing a high proportion of brown glass, giving a very resinous lustre to the fresh frac- ture. In the gray dolerites, upon weathering, there is a noticeable tend- ency to the development of spherical forms. The ground is in some places strewn with basaltic balls a foot or more in diameter, with concentric shells weathering and peeling off under atmospheric agencies. On the face of the Whirlwind cliffs, overlooking the Reese River plains, these spherical forms are readily seen in the bluffs. There is also noticeable a rude columnar structure, which dies off into irregular jointing. These concentric balls seem to have something to do with the columnar forms, and they may possibly represent the remains of horizontal sections of the rude columns. The basalt here is covered with more or less hyaline incrustations, which SHOSHONE RANGE. 619 . are in some places a mere thin glaze, and in others a heavy coating nearly a quarter of an inch thick. _ Along the west and north margins of this field of basalt, there outcrops a line of quartzites and quartzitic shales, which form for 15 miles the foot- hills and base of the mountains. Their prevailing strike is a little west of true north, with a dip of about 35° to the east. They are mainly finely- laminated schists, which here and there in the lower horizons and at the base of the quartzitic series, apparently pass into blue quartzitic bands, with a little impure limestone. This quartzitic mass has great thickness, and, from the fact that, as developed to the southward, it is both underlaid and overlaid by limestone, has been referred to the Weber period. Further cor- roboration of this is the occurrence of a bed of impure anthracite in the lower siliceous zone, not far from Argenta, supposed to represent a horizon near the junction of the Weber Quartzite with the Lower Coal-Measure limestone. The north and south belt of upturned quartzites, lying along the west | side of the Whirlwind basalts, is about 2 miles wide. Continuing its | strike to the south, the quartzites are seen to wrap around the east side of a mass of granite, which rises above the quartzite in a high plateau, crowned by several prominent hills.. West of this granite, the quartzites for several miles are much broken, but appear to have a general dip to the west for about 4 miles west of the granite, when they curve into an. east dip again, making a low, obscure synclinal. That part of the range covered by the Whirlwind basalts is lower and less prominent than the mass immedi- | ately to the southwest, from which it is nearly separated by a deep bay of Quaternary accumulations. _ , South of this narrow neck, the range has its broadest expansion, reach- ing about 16 miles in a direction transverse to its trend. For about 20 miles in the direction of the trend, the range is oceupied by the quartzites already mentioned. They are covered along the east foot-hills by an overlying belt of rhyolite from 2 to 5 miles in width; and, west of Carico Lake, the entire range is overwhelmed by rhyolite. The granite mass, already mentioned, offers a good example of conoidal structure, on so large a scale that the rude layers might almost be mistaken for a sedimentary 620 - = DESCRIPTIVE GEOLOGY. bedding. Lithologically the granite is composed of quartz, both monoclinic and triclinic feldspars in almost equal proportion, magnesian mica, a great deal of hornblende, and a little apatite. Under the microscope, the ortho- clase is seen to contain fluid-inclusions. This rock seems almost to occupy an intermediate position between normal granites and diorites, which con- tain quartz, hornblende, triclinic feldspars, and, exceptionally, monoclinic forms. It is very similar to the granite from the region of Ravenswood Peak, and only differs from it by carrying a less proportion of mica and hornblende. Shoshone Peak, which here forms the culminating point of this por- tion of the range, is an immense outburst of gray and green dacite. It is the grandest and most elevated body of dacite to be found within the limits of the Fortieth Parallel Survey. Lithologically it is an interesting rock, from the large’size of its included quartz-grains, which are present in the form of irregular globes, sometimes exceeding an eighth of an inch in diameter, and sometimes as rude dihexahedral crystals. Under the microscope, they show numerous inclusions of nearly colorless glass with a dark bubble. The quartz also contains hornblende-microlites, a rare phenomenon in dacites. The — hornblende occurs as distinct green crystals, and as a fine earthy green element, intimately: mixed with plagioclase to form the groundmass. Much of the dacite consists of a well-individualized groundmass, with large, partially decomposed plagioclase-feldspars, artd pellucid grains of quartz, and small angular fragments of a finer-grained, less quartzitic dacite. ‘There are passages where these included fragments become so numerous as to give to it strictly the character of a breccia, and again there are considerable regions where, in hand-specimens, there will be only one or two included fragments, They are always sharply angular and always of dacite, as is proved under the microscope by the presence of hornblende in glass cavities of the quartz, The dacite contains well-defined vertiéal jointing planes, and, in some instances, betrays a rude columnar structure. Crown- ing as it does a group of considerable elevation, Shoshone Peak has acted as a condenser of the snows of the Glacial period, and there is ample evidence of the presence of actual glaciers, both in amphitheatre-structure and in actual glacial débris, as well as the striated surfaces at the base SHOSHONE RANGE. ile 621 of the peak. That these glaciers were exceedingly short is proved by the character of the canons a mile from the base of the peak, where, instead of the round ship-bottom curve, they are very sharp and V-shaped, and evidently the result of stream erosion. The dacite from Shoshone Peak has been analyzed by Mr. R. W. Woodward, who reports the following composition for the rock: STG ane AS OEE eWay hel 70.17 TOAD PAlonmmimaperpeeerncrier: Serial Leo Ld. 1458 14.90 Hemotsom@ereecumie 852.5... os. 4203 4.08 Sy imoanousmoxde ts: 5-82) scat leek trace trace Tene os ok 2.29 2.39 MRicMesit meee ete ares OR 9) 0.83 SOGIT 3 LA cS ie 3.25 3.24 IP OHSS oss cl Bie sie 5 Gahan ae Prine ieN. A B85 3.32 eines te ey, trace trace Iuoss by ignition... J. -. 2. Seeeeed 1.53 LIL 100.08 100.52 Specific gravity, 2.54, 2.65. In this rock, the percentage of silica comes within the limits of that found in rhyolites, and but little lower than the amount usually obtained in rhyolites of Central Nevada. It is of special interest to note that the amount of potassa slightly exceeds the soda, as it does in other dacites from Nevada, as well as in many from European localities. The percentage of lime, which is also low, is, however, higher than in the dacites analyzed from the Washoe region. A little northeast from Shoshone Peak, in the bottom of a deep canon, is a small inconspicuous outcrop of diorite. This diorite bears some slight resemblance to the later dacite, especially in the occurrence of the numerous large grains of pellucid quartz. The groundmass, however, is distinctly crystalline, with a compact texture, which acts under the hammer like the older rocks. TTriclinic forms of feldspar predominate, associated with some especially brilliant crthoclase crystals. In the groundmass are some minute 1 Microscopical Petrograpby, vol. vi, 136. 622 ¢ DESCRIPTIVE GEOLGGY. forms of hornblende and mica. In addition to the above, the microscope reveals the presence of titanite and apatite. These three rocks, the granite, diorite, and dacite, form actual outcrops through the quartzite. The granite is evidently earlier than the quartzite, since the beds rest their upturned edges against the granitic flanks, while the diorite and dacite have broken through the quartzites subsequently to their upheaval. | In general, the quartzites have a southerly and easterly dip, chiefly easterly; but between the granite and dacite there is what appears to be a local and limited fold, producing a westerly dip. In general, the entire mass may be considered as one member, having an easterly dip. The uppermost layers of the quartzite are very compact and dark, and bedded in thin sheets, passing into fine, fissile, and argillaceous slates, both of which pass upward through a gradual transition into beds of fine argillaceous limestone. Diligent search was made in these latter beds for fossils, but to no purpose. There occur curiously flattened lenticular concretions, which may possibly represent some remains of animal life, but no distinct forms could be recognized. These limestones are very slightly developed, nowhere exceeding two hun- dred feet in thickness. They have been supposed to represent the lower members of the Upper Coal-Measure limestone. They are best developed on the heights south of Shoshone Peak at the head of Trout Canon. Pass- ing down Trout Cation, an immense thickness of quartzites is seen, all con- formable and dipping to the east, and varying from thick heavy gray beds to thin black fine-grained flinty quartzites, having a peculiar sulphur-yellow stain. There is a strong tendency in these fine beds to shrink up, leaving _ irregular open cracks along the planes of deposition. Upon the outcrops of the siliceous schists on the ridges south of Sho- shone Peak, wherever the rock-masses are prominently exposed to the air and sun, they become coated with a film of black metallic oxides, iron and manganese, but chiefly iron, which is as brilliant as a graphitic polish. It closely resembles certain basalts observed in Arizona. It was especially noticeable that the polish was less on the north side of the outcrops than on the south. This may be due in part to the abrading force of the snow and ice particles driven by the north winds of winter. - Otherwise it would seem that the effect was purely a solar one, and it is difficult to understand SHOSHONE RANGE. 623 the transportation of metallic oxides through the rock simply by attraction of heat. The rhyolite, which scores the east base of the range, in the region of Shoshone Peak and to the southward, possesses a characteristic rhyolitic groundmass, with well-developed crystals of quartz and feldspar. In color, it exhibits various shades of lilac, light brown, and purple. The rock is full of seams, which give evidence of later solfataric action, and are stained with a slight deposition of sulphur and sulphate of lime. The quartz-grains in some localities are surrounded by a coating of maroon-colored ferruginous and siliceous material, which gives to the broken fragments of quartz the color of currant-jelly. In other localities, this coating is nearly black in | color. In places, the groundmass has a peculiar crushed sugary appearance, and the small interstices are filled with a clear siliceous binding material, probably chalcedonic in nature. In the large canon which leads up into the range from about 4 miles north of Carico Lake are obscure outcrops, which appear over quite a wide area of country, of earthy-white and cream-colored rhyolite, which - 1s composed of a homogeneous felsitic mass, containing no crystals, and revealing under the microscope scarcely any quartz or biotite. From the extreme fineness of the material and its earthy character, it would seem to be a tufa, and was probably ejected under a fresh-water lake, which for- merly filled Crescent and Carico Valleys. Nowhere else along the belt of: the Fortieth Parallel Survey has a tufa exactly similar been observed. It bears a close resemblance to some of the sandy beds of the Truckee Mio- -eene, which are rich in infusorie, but under the microscope, with crossed nicols, it is clearly seen to possess a crystalline groundmass. Some of the rhyolitic tufas of the Truckee Miocene are of mixed origin, being composed partly of ejected trachytic material and partly of lacustrine sands, and it is not improbable that this Shoshone rhyolite also carries some fine detrital matter. . It is characteristic of some of the finest-grained rhyolitic tufas that they show no planes of stratification, and indeed this is usually the case in the absence of much mica and hornblende. Where the tufas are chiefly felsitic, under certain circumstances of deposition they reach a con- siderable thickness, often not less than 50 or 80 feet, without showing any 624 DESCRIPTIVE GEOLOGY. traces of bedding; and it is possible that they are actual ejections of fine mud. The white rhyolite tufas of this portion of the range are so nearly on a common level, that one is inclined to refer them to lake origin. It is not often that two types of rhyolites so distinct in habit as these two varieties — can be observed so easily in the same locality. | The coarse porphyritic rhyolites which border the Shoshone Range extend eastward across the valley, and skirt the base of Carico and Railroad Peaks. In this way, rhyolitic formations completely encircle the northern end of Carico Valley and the southwestern end of Crescent Valley. Indeed, the two valleys are only separated by rhyolitic flows, which before the eruption formed evidently one long northeast and southwest depression. They are now connected by Rocky Pass, a narrow gap in the rhyolite, through which in wet seasons the drainage runs from Carico Lake into Crescent Valley and thence northward into the Humboldt River. Of the lithological character of the rhyolites bordering Carico and Railroad Peaks, little need be said, since they bear so close a resemblance to those already described, carrying in the same rough crumbling ground- mass, broken crystals of sanidin and large grains of quartz. North of - Railroad. Peak, the rhyolites attain a considerable elevation, reaching an altitude of 1,500 to 2,000 feet above the valley, which in their mode of occurrence present more the outlines of rugged granite forms than is usually seen in rhyolitic masses. Here they form numerous sharp cones and pin- nacles, with precipitous sides, and but little decomposed earthy débris. Carico anp Rarroap Praxs.—These somewhat isolated peaks belong geologically to the same uplift and the same formation, attaining elevations between 8,600 and 8,500 feet above sea-level. They appear in all respects quite similar, even in topographical details and modes of weathering. They form a broad mass, about 14 miles in width, of nearly pure white quartzite, — in places having a faint tinge of blue and in others a light brown. It pos- sesses a dull vitreous lustre, a saccharoidal texture, and conchoidal. fracture. The quartz-grains are visible to the unaided eye, and appear more or less rounded and with scarcely any base. Under the microscope, the quartz- grains reveal numerous liquid-inclusions with mobile bubbles. A specimén _ CARICO AND RAILROAD PEAKS. 625 of. pure white quartzite taken from near the summit of Carico Peak shows that it is made up largely of silica. It yielded: Stee Ene tek ee OT.E0 > 4 Water 222s. 22. Cee eGo eee Lee Get aaaae 0.28 97.88 aos bbe: other ingredients were alumina and iron. As to the geological ts horizon of these quartzites but little definite evidence was obtained, as they are either surrounded by volcanic material or Quaternary deposits, with no exposure of either an overlying or underlying limestone. It seems highly probable, however, that they belong to the same great series of quartzites _ that characterize the Shoshone and Toyabe Ranges, and have been referred to the Weber. Quartzite. . 40 DG | : : L CHAPTER V. NEVADA BASIN. SECTION I.—REGION EAST OF REESE RIVER—ToyYABE RANGE—SHOSHONE RANGE. SEoTion IIl.—_FROM REESE RIVER TO OSOBB VALLEY—Sovuturrn SHOo- SHONE RANGE—DESATOYA MOUNTAINS—AUGUSTA MOUNTAINS. ‘SEction Lil.—FISH CREEK AND BATTLE MOUNTAINS—FIsH CREEK MouN?- AINS—BATYTLE MOUNTAINS. ‘SECTION I1V.—HA VALLAH AND PAH-UTE RANGES—HAVALLAH RANGE—PAn- UTE RANGE. SECTION V.—WEST HUMBOLDT REGION—WeEst HumBotp1t RANGE—HILLS NORTH OF HUMBOLDT RIVER—HUMBOLDT VALLEY—CARSON DESERT. _SEecrion VI—MONTEZUMA RANGE AND KAWSOH MOUNTAINS—Monvte- ZUMA RANGE—KAWSOH MOUNTAINS. SEcTIon VIL—REGION OF THE MUD LAKES—Pau-Tson MounrTains—KAmMMA MountTains—BLAack Rock MOUNTAINS—GRANITE RANGE. SEcTION VIJL.—WINNEMUCCA LAKE REGION—Pau-Supre MouNnTAINS—SAH- WAVE MouNTAINS—TRUCKEE RANGE—LAKE RANGE. SEcTION IX.—TRUCKEE RIVER REGION—LoWER TRUCKEE VALLEY—VIR- GINIA RANGE—PEAVINE MOUNTAIN REGION. ou © ELON: st. REGION EAST OF REESE RIVER. BY ARNOLD HAGUE. Toyase Rance.—The main portion of the Toyabe Range lies to the southward of latitude 39° 30’, beyond the limit of Map V. As the range has been one of considerable economic interest from the large number of 627 628 DESCRIPTIVE GEOLOGY. mining developments centred there, a geological description of the most characteristic portion, extending from the town of Austin southward for 60 miles, was prepared, accompanied by a geological map, for ‘ Mining _ Industry ”. | From Austin northward, the range extends about 25 miles, with a trend nearly north and south true. In the extreme southeastern corner of the map are found the northern outlying portions of the granitic bodies, which play so important a part in the structure of the range to the south. North of the granitic bodies, the range is made up of quartzites, slates, and lime- stones, which have been referred to the Carboniferous age, represented by the Weber Quartzites, and the overlying Upper Coal-Measure series, while flanking the Paleozoic formations on the east side are broad accumulations of rhyolite, through which, in the deep cafions and open basins, may be recognized the soft, friable beds of the uplifted Truckee Miocene. The following description of the Austin body of granite is taken from the ‘Geology of the Toyabe Range”:! “The Austin body of granite, which is particularly interesting as being the principal ore-bearing body of the range, forms the core of the main ridge of the Toyabe, which is here com- paratively low for 5.miles south of Telegraph Pass. It is exposed mainly on the western slope of this ridge, where it is worn into the rounded spurs and open, shallow ravines, characteristic of an easily decomposed granite. This is a normal granite, consisting of quartz, feldspar, and mica; the feldspars of two varieties, a semi-translucent orthoclase, and an opaque, white variety, probably oligoclase; the mica, a dark magnesian variety ;. hornblende is found as an accessory ingredient, sometimes concentrated in bands or bunches. It forms the southern foot-hills of Telegraph Peak, underlying the metamorphic rocks, which are dark-blue siliceous limestone shales, dipping to the north and east at a low angle. At Telegraph Pass, it is exposed on the eastern slope of the ridge, where it is traversed by a dike, about 15 feet wide, of white granulitic rock, containing sparse crys- tals of mica, and black crystalline grains of tourmaline, concentrated in bunches throughout the mass. This dike has a northwest strike, which is — in the direction of the principal veins of this neighborhood.” 1Mining Industry, vol. iii, 328. TOYABE RANGE. 629 In speaking of the granite body on the eastern side of the Park Basin, the same report says: ‘Directly east of Austin, forming the eastern water- shed of the Park Basin, is a group of conical granite hills, having three principal peaks, rising about 1,800 feet above the neighboring valley, called the Park Mountains. Their entire mass appears to be of granite, which is in the main a compact, close-grained variety, in which the feldspars pre- dominate; these are of two varieties, a fresh-colored orthoclase, and a greenish-white, probably oligoclase, besides which the granite contains quartz and magnesian mica, with some small green crystals, probably horn- blende. A narrow dike is observable on the slope toward Park Creek, hay- ing a northwest trend, corresponding to that on the east of Telegraph Pass. The rock of this dike is a white granulite, containing no mica, ‘and the feld- spar partially kaolinized.” _ ; The range, for the first 6 or 8 miles north of the granitic body, forms a * comparatively low and irregular mass of hills, which rise gradually toward the north, culminating in the Dome Mountain. | The Dome is one of the most singular mountains in Central Nevada. It derives its name from the pecular outline of its summits, which form a _ broad, elevated mass, rising prominently above the surrounding country, with an elevation of over 11,000 feet above sea-level, while through the base it can hardly measure less than 10 miles in an east and west direction. 4 It is characterized by long, easy slopes to the westward, which are so gentle that one can ride to the summit from almost any point. To the eastward, the slopes are much steeper, and in places almost precipitous. The cafons are-deep, frequently opening out into broad basins or valleys, most of them being furnished with clear, running streams. Timber on the mountain slopes is both sparse and stunted. Throughout the summer months, all the clouds in the region seem to gather over the Dome, apparently attracted there, not only by the eleva- tion of the mountain, for there are others still higher, but by the immense “mountain mass. While in this region abundant opportunity was offered for watching these clouds, which collected daily around the Dome, precip- itating considerable quantities of moisture in the neighboring valleys, but leaving the country only a few miles distant in a dry and parched condi- 630 DESCRIPTIVE GEOLOGY. tion. Driven by the southwest winds, the clouds would pass from the Dome across Cortez Valley to Mount Tenabo, and from there on to the high peaks of the Humboldt Range. So far as examined, the Dome consists of nearly white quartzite beds. The rock is quite compact, with a slight arenaceous texture, has a vitreous lustre, and a brittle, splintery fracture. In places, it has more or less of a erayish tinge, and carries minute specks of oxide of iron, or ferruginous earth scattered through it. In the hand-specimen, the rock cannot be distinguished from that of Carico and Railroad Peaks, the microscopical analysis failing to detect any points of difference. Liquid-inclusions in the quartz-grains are abundant, and easily recognized under the microscope. The structure of this great quartzite body was not clearly ascertained, but it would seem most probable that it forms a broad anticlinal fold, with a low, gentle dip to the west, but inclined at a higher angle to the east. Overlying the Dome quartzites, on the east side, occur a series of | beds of siliceous and argillaceous slates, which pass up into compact gray limestones, considerably metaphorsed, and dipping to the eastward. It cannot be stated positively that the slate and limestone series overlie the quartzites conformably, although no apparent unconformity was ob-— served; and inasmuch as in the same range to the southward nearly iden- tical beds are seen resting conformably on massive beds of white and gray quartzites, it would seem more than probable that similar structural relations exist here in the region of the Dome. No fossils were found. North of the Dome, the beds sink rapidly downward, and, with the exception of a long tongue of quartzite extending nearly to Carico Valley, the entire region, like so many others where the Palzozoic beds suffer a sudden depression, is deluged with vast accumulations of rhyolite. These. rhyolites stretch westward to Reese River, rising in irregular- a hills between 1,000 and 1,500 feet above the valley. In the eroded basins and valleys worn out in the rhyolite, noticeably on Silver and Boone Creeks, the underlying beds of Truckee Miocene are well exposed. These beds consist almost completely of cream- and ash- colored strata, made up of extremely fine, impalpable powder, so fine that when crushed and agitated with water the liquid will remain turbid for days SHOSHONE RANGE. 631 before becoming perfectly free from sediment. The beds are very soft and friable, split easily into thin fissile plates, and emit a strong odor of clay. Much of the rock, however, shows no trace of bedding through thicknesses of 20 or 30 feet. The material of some of the coarser beds, examined under the microscope, reveals the volcanic nature of the beds, exhibiting particles of quartz, fragments of glassy feldspar, and black grains of hornblende or magnetic iron. A number of specimens treated with dilute acid gave no reaction, indicating the absence of soluble carbonates. In the beds are frequent bands, seams, or irregular aggregations of chalcedonic material of variegated and beautiful colors, which, withstand- ing atmospheric agencies much better than the friable material, protrude in a marked manner beyond the face of the bluffs. That these beds are of the nature of lacustrine deposits would seem evident, not only from their _ general appearance, but from the presence of vertebrate remains found exposed in the bluffs. The bones collected were of too fragmentary a nature to admit of specific deterniination or to throw any light upon the age of the beds. As already mentioned, the beds have been referred, like many other similar outcrops, to the Miocene Tertiary. It is evident that the beds are older than the great accumulations of rhyolite which have poured out and concealed them over wide areas. That they have been disturbed and up- turned since their deposition, probably by the intrusion of volcanic rocks, is shown in many localities, and that they underlie unconformably Pliocene strata which are later than the rhyolite masses is equally evident. In the extreme northern end of the quartzite body, near the head of Boone Creek, occur one or two local outbursts of propylite. In one instance, near the contact of propylite with the quartzite, a small dike of black vesic- ular basalt was observed, which formed a limited outflow, superimposed upon both the quartzites and propylites. SHosHone Rance.—The Shoshone Range, which trends about north 25° east, or south 25° west, lies for the greater part within the limit of Map V. The meridian of 114° 55’, which forms the eastern boundary of the map, cuts the range at the northern end through the great quartzitic series in the region of Shoshone Peak. This formation, referred to the hori- 632 DESCRIPTIVE GHOLOGY. zon of the Weber Quartzite, has already been described in its main struct- ural and lithological features, and the reasons assigned for regarding it as of Carboniferous age. Within the limits of this map, the western slope, which is traversed by numerous deep narrow cafions, exposing the same beds, all dipping at high angles to the eastward, forms for 10 or 12 miles the eastern side of Reese River Valley. To the southward, the ridge falls” away rapidly, causing a deep depression in the sedimentary strata, and in about latitude 40° 10’ passes under the great accumulation of rhyolite. At this point, the rhyolite, which has been traced along the eastern foot-hills, occupies the depression, stretching westward across the entire width of the range, and in Reese River Valley may be followed northward, flanking the older rocks, to within 3 miles of Trout Creek. Here, on the west side of the range, the rhyolites form a comparatively regular series of hills, with steep slopes, inclined to the westward, and broken through at intervals by drainage-courses. By reference to the geological map, it will be seen at a glance that the large body of quartzite to the north is sepa- rated from a smaller mass, which crops out through the general rhyolitic — accumulations to the south; the gap between the two bodies being only about 3 or 4 milesin width. That this depression occupied by rhyolite is not filled up by the mere flowing of rhyolitic material in a viscous state is easily — seen by the study of the topographical structure, but is rather a centre of massive eruption, the volcanic product seeking the surface along lines of greatest weakness in the older Paleozoic series. Between the two quartzite bodies, the rhyolite forms a high prominent peak, nearly 2,500 feet above the neighboring valleys, falling off with easy slopes toward Reese River, but somewhat steeper on the eastern side. On both the east and west slopes, the peak is penetrated by long deep cafions, with the broad basin-shaped valleys near the top, so characteristic of rhyo- lite mountains. The rock is similar to the rhyolites already described from the range, a gray and reddish-gray felsitic groundmass, with large trans- lucent fragments of quartz abundantly scattered through it. The smaller body of quartzite to the south follows the main trend of the range, rising above the rhyolite in a narrow ridge, about 7 or 8 miles in length. There SHOSHONE RANGE. 633 can be no doubt but that it belongs to the same horizon as the larger body, although, so far as examined, it carries less quartzitic schists, and the rock has a reddish-brown color and vitreous lustre. It dips to the eastward, the planes of bedding being distinctly marked. Under the microscope, all the quartzite bodies of this region, including those from Carico Peak, Dome Mountain in the Toyabe Range, and localities in the Shoshone Range, pre- sent the same detailed structure and appearance, so much so that they can scarcely be told the one from the other. Rhyolites score the ridge on three sides. They extend in low irregu- lar hills to the Reese River Canon, and toward the southeast connect the Shoshone with the Toyabe Range. These low hills hem in Carico Valley to the southwest. | Along the base of the Shoshone Range, in Reese River Valley, and nearly opposite the rhyolite spur from the Fish Creek Mountains, occur a number of hot and warm springs of considerable interest. ‘They are scat- tered over an area of several acres, and are mostly surrounded by fine light- — colored soil derived from the rhyolitic detritus, which near the edges of the pools, where it can obtain moisture, is frequently covered by a somewhat luxuriant growth of alkaline grasses. Each spring forms a basin of clear transparent water, varying in temperature, in the open pool, from 85° to 117°. When cool, the water is quite palatable, with only a slight taste of saline ingredients, and appears to deposit but a small quantity of mineral Inatter, . | To the southward, about one-half mile from the main group, occurs an isolated spring of clear water, which comes to the surface at the base of a low mound, or dome, of rhyolite. At the time of our visit, the water, which was in a slight state of ebullition from the escape of gases, indicated a tem- perature of 90°. Coating the rocky walls of the spring 6 inches below the surface of the water was a soft, pasty, light-gray mass, apparently formed by the decomposition of the rock by the carbonated thermal waters. A stick forced into this pasty mass penetrated it with ease to a depth of 18 to 20 inches before striking the hard rock. A large quantity of the materia! was collected for chemical examination. 634 DESCRIPTIVE GEOLOGY. The analysis was made by Mr. R. W. Woodward, who reported the following composition: Dilitae7 ssl kee ee 10.38 WCE ee oo ee oe a 48.98 IM@@nesia..... . 2.6: oo eae michs oan One Permic oxide .~ 5.2 1)... eee ee 0.44 Carbonic acid...) 2. 2222S eee 39.02 Sulphuric acid: /. 2.1222 ee eee eee ee 0.24 100.00 Combining acids with bases, we have: Carbonate of lhme.== ee 2 See one ees 87.18 Sulphate -~ 664 DESCRIPTIVE GEOLOGY. sanidins occur associated with some plagioclase. A specimen in the collec- tion from the summit of Mount Moses may be regarded as a typical one, not only of the Fish Creek Mountains, but of this portion of Central Ne- vada. 5 + i Ny a ba! i) | ‘ me caret ind Teer Ye a ie . { 4 ri " x r I a r +d oe re * Py / ad or : rity =4 Jee a s 7 i * ‘ 7 Ya cae 7 te i %, 1 Cor rap ee 7S mctpeeee / ; * ' THE CARSON DESERT. T47 ron Canadensis, Solidago occidentalis, Epipactis gigantea; Juncus Balticus, known as “‘wire-grass” and considered valuable for hay and pasturage, Juncus nodosus, Juncus xyphioides, Phragmitis communis, Poa tenuifolia, one of the most common bunch-grasses of Nevada, and Avena sativa, or com- mon oat, which, doubtless, escaped from some emigrant’s wagon. From the more or less alkaline shore, Mr. Watson obtained: Ranunculus cymba- ‘laria, Scirpus Kingvi, a new species of rush, Sporobolus asperfolias, found also on the sands of Mono Lake, and Brizopyrum spicatum, a very abundant salt-grass The water is highly charged with alkaline salts, and is so dense that the human body floats in it without exertion, and, after drying, the skin is left with a thin white coating. Wherever the water washes the shore, it leaves more or less residue upon evaporation. In the spring of the year, the water attains its highest level when there is but little deposit, and it gradually recedes until late in the autumn it reaches its greatest density, and there is left a very considerable amount of alkaline salts upon the shore. In the month of August, a quantity of this water was taken from the south side of the lake for the purposes of analysis. Prof. 0. D. Allen, who made the chemical examination, reports the following composition : Specific gravity, 1.0975. Fixed residue in 1,000 parts, 114.7. iM 1, 2s Average. Maenesiai 2 1.252 sose ee 0.0230 0.0230 0.0230 Sodiumeser 52. 228) al 42.5990 43.0780 42.8380 Ota SSIUIN eek ed Sk vay Sree 1.5460 1.6480 1.5970 @hionme 5-25 -= ea VS Sema 39.4100 39.3729 39.3914 Sulphate oo eee Sh a 0.0954 0.1002 0.0978 Sulphume-acid “222 be 2. 2 9.4350 9.4286 9.43038 Carbonic acid........------ 12.7440 12.5550 12.6490 Silicic ACen Seas Seren usc O20 50 Mors see 0.2050 Ox Gein reer ne Stet Fes 6.3465 112.5780 748 DESCRIPTIVE GEOLOGY. The combination of acids with bases gives: Chloride @Psodinum: 3.5.0 ee eee eee =.) 6494138 Sullphatevor soday- =: -.. =... /. <8 eee 13.7626 @arbonate of soda . sc... 2... 2-2 ae Ss Sulphiderof sodium 222. -<. 2. 3 pe eee 0.2384 Sulphate of potassa >. 22 3.2 — eee 3.6515 Carbonate of magnesia’: Ses. assess a= eae 0.0652 Silica. : SH t Bi t ‘ o “ =F ie) ae 2 a Z é ss 7 is re) be é w ie - % a i ; = ‘ =) LOWER TRUCKEE VALLEY. 819 desert like ordinary sands and gravels. They have not as yet been care- fully studied, and their specific characters are unknown. Another feature of the desert in the region of Wadsworth, where they never could have been brought by erosion, are large numbers of basaltic - bombs, characterized by their general spherical form, some of which are as vesicular as a pumice, the whole body of the bomb being made up of the _ thinnest possible basaltic skeleton. Others again consist of dense, compact rock. | A specimen of the tufa from the Truckee Valley has been chemically examined by Mr. R. W. Woodward, who reports as follows : PMN nec Cee ee eB 0.89 0.86 LAWNS 25 Se SS eae 3 7 7 r- E. , q f } 2 j — TRUCKEE CANON. 833 nently throughout the light-gray groundinass, while the microscope reveals augite, magnetite, and apatite. This occurrence of both sanidin and augite is to be specially noticed. Directly north of the Truckee Ferry lie some low purple hills, which consist also of sanidin-trachyte, with many small grains of magnetite, but no augite. It is an unusually dense, dark-colored trachyte, and the long sanidin crystals stand out very prominently. An analysis of this rock by Mr. R. W. Woodward yielded the fol- lowing: : (a Silicamemnnite amma mmr yd a 82 et 56.51 56.45 Marais are oe ee 1961 19854 Henncronidcnsa: 4 ye he vee cle: 5.10 4.95 Metros; Oxideny 2 a. eee ek ee ai oe 0.98 0.97 Mancamous oxide = =i 25 sie es gle) 0.11 0.11 JU ogy ce aa re LT an I 1.87 7.70 Magnesia .. - - - (dk eats Sete Ee a eee pee 2.66 2.66 Sod, 4.8 SL yee eae le eee 3.12 3.15 riPotassae 2 fe: Wes ase ae 3.67 3.84 1 Dict) GV gah a a es ae ar Merge RAE 4 ye eee Trace trace Waters" spor iosey cle ace ae ee 0.40 0.38 100.05 100.06 Specific gravity, 2.5, 2.6. Overlying these sanidin- -trachytes are horizontal beds of frachytic breccias of a very dark and basic appearance, which are in turn directly overflowed by dark-gray augite-trachytes, consisting, as shown by: the microscope, of sanidin, a little plagioclase, some brown hornblende, and a considerable portion of pale-green augite. Far richer in augite than the trachyte which underlies it, it approximates much more closely in its mode of jointing and weathering to the basalts, and presents a series of mural faces in all respects like the latter rock. , An analysis of this augite-trachyte was made by Mr. R. W. Woodward, who reported as follows: . Slice eat be ae hn ac ore gerd ttye: a vey suet Tye 50.36 50.03 JNU rib oe hee ek yan Pre aor eee ee 17.00 16.99 53 D G 834 DESCRIPTIVE GEOLOGY. Herric* Oxide meeerrnrte: mmr heen ecg vane 6.12 6.05 Ferroustoxidee sess Ot So. eee 3.84 3.86 Manganoustoxide= ©. < 222). eee 0.30 0.42 Time Serene eth SS 8 eee 8.85 8.81 iMeionesiaye see nS eee 3.02 2.98 Sodas wea rao 3.21 Doe POSS... 2... ... 2... See 15? Dppatl Water and carbonic acid........-.-.-.. 5.35 26. 100.00 100.00 Specific gravity, 2.6, 2.7. Trachytes of a similar composition form the detached hills between Wadsworth and Sheep Corral Canon. Here the rock is dark brown to nearly black; it overlies propylite and carries large crystals of both sanidin and augite associated with a little hornblende. Although different in text- ure from the heavy flows of augite-trachyte north of the Purple Hills, and showing considerable mineralogical distinctions, such as carrying conspicu- ous black hornblende crystals, the occasional occurrence of brown mica, and a large proportion of glass, these rocks are doubtless derived from a common source, and from their relations to the other trachytes are prnenly, also of the same age. In the open basin country just north of the Truckee Ferry are some hills of light-colored rhyolite presenting various shades of brown, yellow, reddish-yellow, light brick-red, and purple, the purple tints in general decid- edly predominating. All these colors, although very brilliant, occupy but small local patches in a prevailing white field of rhyolite. The purple and green masses seem to belong to an earlier eruption than the white. Directly over the white rhyolite lies a bed 150 feet thick, of dark trachytic breccia, which, in passing upward, becomes more and more solid and compact, merg- ing finally into a gray augite-trachyte. Indeed, this breccia is the first part of the augite-trachyte eruption. In a microfelsitic groundmass appear _well-developed crystals of sanidin, biotite, and occasional large clear grains of quartz. The latest flows of purple rhyolite are slightly brecciated, the fragments which they contain being of the same material as the rock itself. It is evident that these rhyolites pass under, and therefore antedate the TRUCKEE CANON. 835 augite-trachyte breccia beds and the compact gray augite-trachyte, which rise in the high bluff wall to the northward. The rhyolites themselves are penetrated by two sets of dikes, one of a nearly black, very compact augite- trachyte, which contains in the micro-crystalline groundmass crystals of one- half inch or more in length of sanidin. According to Professor Zirkel, the groundmass is a crystalline admixture of feldspar and pale brownish-yellow augite, many of the feldspars being striated, yet the prevailing forms are monoclinic. Short black lines of hornblende occur, although sparingly. No olivine was detected. So far as observed, these dikes all dip to the west and strike west of north. Where these black trachyte dikes break through the rhyolite, there are contact phenomena of exceeding interest, the latter, and in this instance older, rock being converted into a dark chocolate-brown glassy mass, in which only a few feldspars and biotite flakes still retain their integrity, the product having almost the habit of obsidian. From this extreme form, there is a gradation through 3 feet of less and less glassy product into the normal rhyolite of the adjoining region. Professor Zirkel’ has described with some detail the microscopical characteristics of these hyaline varieties, illustrat- ing in Plate VIII, fig. 4, a remarkable obsidian. But for the fact that on each side of these black trachyte dikes the glassy forms of rhyolite pass gradu- ally into the crystalline varieties, it might not seem conclusive that the dikes had been the agents of this glassy modification; but since the same phe- nomenon is repeated at the contact of several of them, it seems improbable that the form could have existed in the first instance, and the dikes have, by accident, followed the course of the glassy bands. This fusion of rhyolite into glass is no more remarkable in contact with the molten dikes of trachyte than is the fusion of trachytic mountain-points by lightning, and the two phenomena would appear to bear a close relation to each other. In this locality, therefore, occurs a marked exception to the law enunciated by von Richthofen of the sequence of rhyolites over trachytes, for here the trachytes have undoubtedly broken through in dikes and overflowed the earlier rhyo- lites, both in the form of breccia and compact material, in the instance of the gray tabular hills to the north. It is, however, a marked fact that while 1 Microscopical Petrography, vol. vi, 206. 836 DESCRIPTIVE GEOLOGY. these trachytes hold in time the period of the basalts, they show also an affinity with that group by the presence of augite. In a geological sense, though not petrographically, they may be considered as basalts with the olivine left out, and sanidin substituted for a portion of the plagioclase. Besides the dark trachyte-dikes above described, there is also another set, having a north and south strike and a nearly vertical position, but with very limited overflows. They consist of black vesicular basalts, and are characterized by frequent coatings of hyalite, varying from one-quarter of an inch in thickness down to a mere siliceous glaze. On the river-mesa, near the east end of the Truckee Canon, and east of the diorite outcrop, are four isolated hills of normal sanidin-trachyte, having a great similarity to the brown variety on the summit of Sheep Corral Cajfion. The large fields of basalt which lie to the south of the river and cap the higher summits have never been entered or examined by our parties, and it is quite probable that in the deeply eroded cafions may be found many outcrops of the earlier volcanic rocks. At the base of the range, just south of Wadsworth, partially buried by drifting sands and tufas, is a group of low hills, which cannot at first sight be distinguished from genuine basalts, yet which even in tne field present certain peculiarities of form and texture that distinguish them from the surrounding rocks. They are compact fine-grained rocks of a resinous lustre, and varying from black to grayish- black in color. Except minute feldspars, scarcely any mineral constituents can be determined by the naked eye. The value of methods brought to bear by the microscope in the analysis of rocks is well shown in the study of this group. Professor Zirkel! regards them as augite-andesites, and has given a detailed description of their structure and composition. Mineralog- ically they appear to hold both sanidin and plagioclase in equal propor- tions, but the minute crystals are mainly triclinic. Augite, however, greatly predominates over hornblende. A determination of silica in one of these rocks gave 59.99 per cent., an amount much too high for normal basalt, but within the limits admitted for augite-andesites. Geologically, their true 'Microscopical Petrography, vol. vi, 224. ls hah di, (ie je Fi le ae i! hah Pe ee =" | SHEEP CORRAL CANON. 837 relation to the neighboring basalts is not clearly made out, but it would seem most probable that they appear as dikes penetrating the genuine basalts. Some idea of the immense volume of the volcanic series is obtained from the study of so long and deep a cafion as this transverse valley of the Truckee. _ Upon either side, the hills rise from 1,200 to 3,000 feet. Much of this caiion-depth cannot be attributed to erosion, but certainly throughout the lower portion it would seem as if a very considerable part must have -been produced in this manner. The cajion therefore exhibits a deep cut across the Virginia Range, and it is somewhat remarkable that so little of the earlier formations have been exposed. A cut through the range in the region of Washoe must have exposed a very considerable amount of strati- fied rocks, and a large body of diorite. Here at the Truckee Cajon, there are but two small patches of diorite and a band of porphyry to represent the older rocks, all the rest being of Tertiary volcanic age, conveying some idea of the immense development of these comparatively recent outbursts. At the bend of the river, near Wadsworth, the Truckee having followed a course a little north of east through the cation, suddenly describes a semicircle having a diameter of 8 miles, and thence flows in a northwest ’ direction until it pours into Pyramid Lake. North from the intricate group of eruptive rocks along the Truckee Cafion, the Virginia Range is over- whelmed and masked by an immense flood of trachyte, which occupies nearly the entire distance to Mullen’s Gap, with the exception of a belt along the east flank extending from Sheep Corral Cafion for 10 miles to the northward. SHEEP CorRaL CaNon.—The walls of this cafion expose mainly heavy beds of dark-brown trachyte. Scattered through a glass-base are occasional erystals of sanidin and biotite, the microscope also revealing the presence of plagioclase, while within the glass-base various forms of devitrification have taken place, resulting in a variety of microscopic products, largely microlitic. Upon the summit-ridges, there is an unusual development of hyalite, covering many of the volcanic blocks to the thickness of one- quarter of an inch. Where the normal botryoidal hyalite is wanting, the blocks are inerusted with a thin film of siliceous material. The rock is also characterized by frequent cavities lined with crystalline sinter, which rises 838 DESCRIPTIVE GEOLOGY. in points one-sixteenth of an inch in height, and each point is crowned with a transparent globule of hyalite. A distinct horizontal bedding is frequently noticed in these trachytes. Their limit to the westward is not accurately known, but they are supposed to extend down to the valley west of Ormsby Peak. The gray, glassy augite-trachytes which break out aan the foot-hills just south of Sheep Corral Canon are supposed to be later than the sanidin- trachytes; a decision, however, which does not depend upon any super- - position, for they have not been seen in any immediate contact, but rather upon field impressions, and because the gray trachytes rise in bold hills with a much fresher and less weathered appearance. Dr. Anger, of Leipsic, who made an analysis of this augite-trachyte, found the following constituents : Silica... oS eee ud ONE nN Sh e 68.81 Adina, 22>: 2320 aie eee a URS att a aa 13.62 Ferrous oxide i206 oi ee ee cs trey os Rn eee 3.91 Time. 2° 2). oi on 4,30 Maonesia . 0 2 ee es oe ae ee a 214. Soda 2 2,5. 2 i Ss Se ae edie ee tne) 2.68 POtaS8ay » 2 2o oscar nea 2.56 Loss ‘by iemition =. 572. ik oper eu see eee 2.30 100.92 This rock stands over 18 per cent. richer in silica than the augite-tra- chyte from the hills back of the Truckee Ferry, and is unusually acidic for a rock so full of augite, having an amount of silica equal to that found in many varieties of rhyolite, while the Truckee Ferry Hills approach more nearly in chemical composition to basalt. The propylite at the entrance of Sheep Corral Camion is a gestae gray rock, closely resembling the typical body of Washoe, except that it carries a few grains of quartz. It is a dense, tough rock, with well-devel- oped feldspars and occasional hornblendes. The microscope reveals the presence of apatite and magnetite. BERKSHIRE CANON. 839 An analysis of this rock was made in the laboratory of Professor Wiede- mann, in Leipsic, with the following result: LSMIGS) ne ae aah iets fe on A 2h ee 64.62 JS TUCO, Baars Ui re ae Sab id SE as el 11.70 J NGESRS TG CSE ee ete i i re i ae a 8.39 J GRIEVE are Sos fins, Alp (enter gs Means gue ted go ald eae 8.96 NIG SSS GSI tk a pee arte hlcet oe tec le oe 1.18 SKDGIEs AAP ae ode se raw de da a elie ee Mea ce Seam 3.13 JEXOEYSISE) te Ba A ea auch I aR i Gi Cg 195 Bhosploricvacidy 2522202 1840 Dee Pee Verret OETA Ce Loss by ignition. -- - - a a ies fe ie i ge ag 1.02 100.95 Directly to the north of Sheep Corral Cation is observed the southern end of a bed of massive dacite, which occupies the extreme foot-hills of the range for about a mile, and then trends slightly into the range on a direc- tion about north 20° west. At the point where it trends into the range, the foot-hills are occupied by an outburst of rhyolite, which flanks the range for 8 miles along the Lower Truckee Valley, both rocks being well devel- oped in Berkshire Cafion, 3 miles to the northward. Berxsuire CaXon.—About 34 miles up Berkshire Cafion, from the mouth, there occurs a heavy mass of a somewhat peculiar rock, which has been recognized nowhere else within the limits of the Fortieth Parallel Survey, and which has been classed as melaphyr, from its close resemblance in micro- scopical habit to rocks thus designated in Germany. Of its age here in the Virginia Range nothing is definitely known, except that it underlies the propylite, the oldest of the Tertiary volcanic products. These melaphyrs extend from the head of the canon in a northwest direction about 4 miles, and to the west, north, and south are overlaid by the summit rocks already - described, and on the slopes of the range to the eastward are again concealed by propylites and andesites. They are, in general, deeply eroded in transverse ravines prior to the later outflows. In texture, they are extremely varied, passing from a fine-grained, compact, dark-green, or 840 : DESCRIPTIVE GEOLOGY. dark-brown rock, in which are no recognizable crystals, up to a coarse- grained mass, through which decomposed crystals of feldspar are very thickly scattered. The prevalent color is dark green, and in general the texture rather earthy. Under the microscope, Professor Zirkel found them to consist of triclinic feldspars, decomposed augite, a little hornblende, and considerable olivine. Many of the outcrops at the head of the cafion, near the summit of the melaphyr body, are characterized by green spots the size of a pea, partly formed of delessite, and partly of well-crystallized calcite. Nearly all the feldspars in the upper portion are more or less converted into carbonate of lime. There are present impure crystals of carbonate of lime half an inch long, rendered opaque by green earth and some small, gray grains, whose nature is not known, probably referable to augite. aie A little lower down the cafion occurs a chocolate-brown variety, in which the feldspars are mainly converted into carbonate of lime, but which is charac- terized by spherical amygdules from one-half inch downward until they are too small to be visible. The surface of these amygdules has a pitted appear- ance, like the smooth interior of certain empty cavities in basalt. They were evidently, in the first place, filled with green earth, which has been subse- quently more or less converted into calcite. Only a few feldspars are still preserved in anything like their original condition, and under the microscope these all appear to be triclinic. About a mile down from the head of the cation is the most altered zone in the melaphyr body. Here the entire mass is decomposed, and apparently consists of delessite and carbonate of lime, while the amygdules no longer show their spherical form, but are broken and run together until the rock is little more than a network of car- bonate of lime, rendered impure by streaks and grains of delessite, with a general filling of impure delessitic matter, in which are the faint traces of feldspar, and brown earthy material, probably representing the augites. In- this zone are found also large siliceous amygdules, which are in fact quartz geodes surrounded by a variable coating of carbonate of lime and green earth. In some instances, in the hollows of the calcareous amygdules, is a secondary growth of quartz crystals. . Descending the cafion, the first rock which is found to break through and overlie the melaphyrs is a pinkish-gray body, colored on the geologi- TT’ ae BERKSHIRE CANON. 841 cal map as a propylite. It consists of a micro-crystalline groundmass of feldspar and brown undecomposed hornblende, in which the feldspar largely predominates. In this groundmass are imbedded clear, undecom- posed, black and. brown hornblende, a few biotite flakes, and both ortho- clase and plagioclase, the latter slightly outnumbering the former. This rock, however, has much the habit of a trachyte, and in reality represents an intermediate condition, where, although plagioclase slightly predom- inates and carries the rock under the name of propylite, at the same time the proportion of orthoclase is so large as sensibly to affect its habit. Geologically it appears to be a trachyte, but lithologically a propylite. From its geological relations to the neighboring rocks, it was impossible to arrive at any definite conclusion as to its place in the volcanic series. It is younger than the melaphyrs, and older than the sanidin-trachyte which overflows it to the north, so that its position in time, so far as known, would coincide as well with propylite as with hornblende-plagioclase-trachyte. It builds up conical hills 600 feet in height, which show no bedding planes or other structural lines, and would: appear to be a dense homogeneous mass without indications of successive flow. | Just to the south of these propylite hills is a series of dikes of light greenish-gray rhyolite, which are seen to cut through the melaphyr and to overflow the base of the trachyte hills. This rhyolite is an extremely fine-grained rock, of a shaly structure, and is composed of a micro-crystalline groundmass, in which are observed a few partially decomposed orthoclase erystals and a little altered mica. A short distance farther down the cation, apparently breaking through the propylite body, is a broad dike, several hundred feet in width, of typi- cal hornblende-andesite. Brown, unaltered hornblende, prevailing plagio- clase, many crystals of sanidin, and a few biotite flakes are seen everywhere dispersed through the grayish-brown groundmass. Perhaps this rock should be classed with the above-described propylites, for it only differs from them mineralogically in the proportion of sanidin and an increase of horn- blende. It-is noticeable that the fragments of hornblende lie for the most part in parallel layers through the groundmass. Unlike the propylite, how- ever, it has the true geological habit of andesite, with the peculiar smooth, 842 DESCRIPTIVE GEOLOGY. flinty fracture. These two rocks together, although assigned in one case to propylite and in the other to andesite, have a strong affinity with the trachytes. | The andesite zone extends for about 6 miles north-and south, and is accompanied along its entire eastern edge by a belt of dacite. This dacite body averages about a mile in width, and consists of clouded masses of purple and bluish-gray rock. In general, the purple variety occurs in the most easterly beds, and seems to be the earliest of the dacite belt. It pre- sents sometimes a compact, fine-grained purple base, without any minerals recognizable to the naked eye, but under the microscope reveals the presence of triclinic feldspars and quartz grains. The main part, however, of the purple zone is a micro-crystalline base of feldspar and a decomposed brown mineral, probably hornblende. The feldspars themselves show every grade of passage into carbonate of lime. Breaking through this purple dacite are brecciated masses, which are characterized by a larger proportion of mica and quartz than is found in the earlier body. An obscure outcrop of gray brecciated propylite was observed, par- tially concealed by dacite, but no connection with any other rocks could be traced. Later than the purple breccias, a great outburst of pale-green dacite took place, in which also the feldspars have suffered considerable decompo- sition, resulting partly in carbonate of lime and partly in a soft kaolinized mass; but, where decomposition has not proceeded too far, they show, under the microscope, distinct striation. The quartz is in some instances crys- tallized in double pyramids, a not infrequent occurrence in dacites, and especially noticeable in the rock from Shoshone Peak, Shoshone Range. This green dacite extends south as far as Sheep Corral Cafion, where it is found to overlie a typical greenish-gray propylite already mentioned, but occupying too small an area to be represented on the geological map. Breaking through the purple dacite, and in some instances crossing in dikes through the green dacite, is a long and powerful outburst of rhyolite, which occupies the foot-hills from within a mile of Sheep Corral Canon to within 4 miles of Pyramid Lake. The main mass of the rhyolite in the region of Berkshire Canton comes up through a broad vein, making a dike nearly 400 feet in width, and overflowing the dacites, forms a bold group eee | BERKSHIRE CANON 843 of hills conspicuous from the surrounding country by their great variety of brilliant colors. They are white, salmon-color, yellow, pale green, pale lilac, gray, brown, olive, red, and deep purple, and present an equally varied texture., It is decidedly a massive outburst, and shows no tendency to bedding, the various colors appearing as cloudings in one mass, and by no means as a succession of ejections. In mineralogical composition, the variation seems quite as well marked. Near the top of the hills, it forms a pure white porcelainous rock of a fine microfelsitic groundmass, through which wind translucent siliceous bands, shading off into the more homo- geneous mass. ‘There are large areas which show no inclosed crystals. Following the samé mass, either north or south, it is found to contain clear, transparent grains of crystalline quartz, and some sanidin. Gradually the sanidin and quartz crowd together, and make up nearly the entire material of the rock, leaving but little space to be filled with felsitic grouwndmass In such instances, the sanidin is largely decomposed, while the quartz, sur- rounded by a thin coating of ferruginous material, has the color of garnet. Much of the quartz occurs in irregular fragments, having no crystalline boundaries, although in some a definite angle may occasionally be observed; but there are no such crystals as characterize the green dacites. In a salmon- colored rhyolite were noticed some large. cavities, in which were crystals of carbonate of lime imbedded between coatings of siliceous sinter. Occa- sionally can be noticed an appearance of fusion of the walls of the cavities, resulting in an obsidian-like substance. Besides this, there occur, in the sal- mon-colored rhyolites, passages of very fine, highly siliceous, jasper-like material. Decomposed spherulites abound, and it is not impossible that these larger cavities may have resulted from the destruction of groups of spheerulites, though they do not show the structure of lithophyse. Some of the largest of these jasper masses reach 5 and 6 inches in length, and contain minute snow-white globules of apparently colorless jasper, scattered irregularly through the red and green jasper bodies. The substitution of carbonate of lime in the place of feldspars, noticed in the earlier volcanic rocks, continues through the rhyolites. A few of the very clear and unde- composed orthoclase crystals possess the “labradorizing” quality, and are 844 DESCRIPTIVE GEOLOGY. conspicuous by the iridescent play of light, but hardly to the same extent as observed in the rhyolites of the Pah-Ute Range. Directly west of the highest point of the Berkshire Catton rhyolites occurs a small dike of black, compact basalt. There are then represented here in this section the exposures of seven types of eruptive rocks. Of these, melaphyrs are the earliest, followed by small outcrops of propylite, which, however, have a ‘trachytic affinity ; next the hornblende-andesite and the zone of purple and green dacites. As between the andesites and dacites, the evidence is not conclusive as to age. After the dacites come the trachytes, but the relation between the latter and the rhyolites was not observed here, although the sequence has been noted in too many other localities to leave any reasonable doubt as to their rela- tive positions. The rhyolites, however, are clearly later than the dacites, and the basalts later than the rhyolites. All these rocks, with the exception of basalt, have at some period been subjected to a uniform process of decom- position, in which the feldspars have been more or less replaced by carbon- ~ ate of lime, and, in the case of the melaphyrs, the olivine has been converted into a serpentineous product. That all these rocks have been suilgeateal to considerable sub-aérial action before the outbursts of basalt would seem highly probable. _ The section C—D, at the base of the geological sheet, crosses the Vir- ginia Range in the region of Berkshire Canon, and the intricate struct- ural relations of the different volcanic outbreaks are indicated as well as it is possible with the seale of the map and the geological data at hand. REGION WeEsT or Pyramip Laxe.—Opposite the southern end of Pyramid Lake, where the trachyte flow terminates, a broad sheet of tabular basalt, ris- ing in nearly perpendicular walls, forms the highest peaks, and caps all older voleanic flows, beyond which the hills fall away toward Mullen’s Gap. The gap cuts the Virginia Range at right angles to its trend, and, in a measure, isolates, topographically but not geologically, the northern end from the por- tion already described. On both sides of the gap, the hills rise gradually in a broken, irregular mass of ridges, cones, and pinnacles, of an interest- ing volcanic rock, presenting some peculiarities of habit. It is regarded as belonging to the quartz-propylites, and has been. represented as such on j 4 5 ; REGION WEST OF PYRAMID LAKE. 845 the geological maps, although microscopical analysis indicates that it is more closely allied to dacites, the quartz-bearing variety of the andesites. The rock has the characteristic greenish-gray groundmass of the typical Washoe propylite, with the same arrangement and structure of the plagio- clase and hornblende, and the same general field aspect. Its groundmass is ‘exceedingly fine-grained, through which are scattered many well-pre- served flesh-colored feldspars, occasionally one-half of an inch in length, and dark-green fragments of fibrous hornblende. Mica is present as sparse dark plates of biotite. Unlike the normal propylites of Washoe, the rock is characterized by the presence of a very considerable amount of translucent quartz-grains, all of them more or less cracked and fissured. Under the microscope, in thin sections, the quartz is shown to carry liquid-inclusions, which is a characteristic feature of quartz-propylites. A chemical analysis of this rock yielded Mr. R. W. Woodward the following result : Silicate Here: Perse a re Ie Oe 68.45 68.46 AN ITRVCCTUDG) Oe Ce alee se cae 16.97 16.85 EME OMSHOXUC Ce ptm ace Veale Sus oie cts ape 1.36 1.43 Monmeamous oxide 2: Sac. hee ek. 2 eo. trace _—_ trace Wine getters ia eae fre ac oy, EE ea 3.07 2.92 Wemeniaeomte steric = - oe, Rtn OE 005 Sadie. uot Ween tie i eo ee 3.60 3.60 | DEST ae ee ee eer ot Re AE es) ROS JL shal OME 0 ra Te le aes Ss gene trace trace B@arhomiciacida, .2Ps. ees cee tet los: S059) 0% O59 «WEY Gy Os ee ee Soeansleaosnepen 1.42 1.45 100.18 100.03 Specific eravity, 2.38, 2.44. | It is interesting to note the presence of carbonate of lime, as under the microscope may be detected minute crystals of calcite, derived from the decomposition of feldspars. nh As the area occupied by these quartz-propylites has not been carefully determined, it is possible that they may be represented on the geological 846 DESCRIPTIVE GEOLOGY. map as covering too broad a field, and that within the territory so colored other volcanic outbursts may be found. They occur, however, along the shore of Pyramid Lake on both sides of Mullen’s Gap, rising from 1,200 to 1,500 feet above the water-level. The only other volcanic rocks recog- nized in the region were rhyolites and basalts, both overlying the quartz- propylite, the former in low hills bordering the gap, and the latter capping the higher summits. | Geologically the most notable feature of these rhyolites is found in the great variety of structure which they present in such a comparatively lim- ited area. Rhyolites from the same ‘hill or outflow may show great differ- ences in color, texture, and superficial appearance, but, in general, are char- acterized, even over large regions, by much the same structural habit of the groundmass and arrangement of mineral constituents. There are found here in Mullen’s Gap rhyolites, having a microfelsitic eroundmass rich in secreted minerals, others in which the groundmass is distinctly lithoidal and homogeneous, associated with pearlites, pumicestones, light-colored tufas, and coarse rhyolitic breccias and ash. ‘The microfelsitic varieties, which have apparently broken through the quartz-propylites, have a purplish-gray color, a rough texture, and hackly fracture. Quartz and sanidin are the prevailing mineral secretions. ‘The rock shows a tendency to pass by gradual transitions into the lithoidal varieties, not unlike the rhyolites from the Sou Spring Hills, Pah-Ute Range, which they closely resemble in gen- eral habit. In this connection, it is interesting to note that the rhyolites from Mullen’s Gap, which are characterized by a lithoidal groundmass, possess a brilliant Indian-red color, also very similar to rocks described from the Sou Spring Hills, a similarity which is still further shown by the behavior of the well-defined fresh crystals of sanidin and the occasional particles of quartz. It would seem as if the segregated fragments of quartz in the microcrystalline and microfelsitic varieties had become dissolved in the magma, and, uniting with the ferritic material of the groundmass, had formed, during the period of solidification, a homogeneous, porcelain-like, red rock, which presented physically, although not chemically, a totally different product from the rough, purplish-gray types. The pumicestones and pearlites are remarkably light and porous, REGION WEST OF PYRAMID LAKE. 847 resembling those found in the southern end of the Montezuma Range and at Mono Lake. ‘They have the characteristic lavender and gray colors, a rough, fibrous texture, with a tendency to develop half-glassy rocks. Crys- tals of sanidin are abundant. Associated with these rocks are grayish-white and cream-colored tufas, made up of siliceous and feldspathic material, so extremely fine as to crumble into powder at the slightest blow. They are of interest as showing the intimate connection between the ejection of rhyo- litic products and the stratified lacustrine deposits, which, carrying remains of an extinct Tertiary fauna and flora, have necessarily been classed as of sedimentary origin. . There occurs here, on the north side of Mullen’s Gap, a small obscure mass of an uninteresting, dirty, ash-gray breccia, very little being known of its mode of occurrence or immediate associations, but a specimen of it was collected in the field solely as showing the great variety of rhyolitic material to be found at the locality. The inclosed brecciated fragments exhibit considerable variety, but are all apparently of a rhyolitic nature. Small sanidins are the only crystals observed macroscopically. In thin sections, under the microscope, this rock becomes one of great interest and importance, the gray brecciated fragments exhibiting peculiar phenomena, which Professor Zirkel! has described with considerable detail. Among the most striking features of the rock is the occurrence of liquid-inclusions in glass, and the presence also in the glass of minute crystals of apatite carry- ing glass, which also contains a fluid-inclusion. In Plate XII, fig. 1, accom- panying Professor Zirkel’s report, these phenomena are beautifully shown. Between Mullen’s Gap and the northern end of the Virginia Range, all the higher portions consist of broad, massive tables of black basalt, which incline gently to the eastward toward the lake or away from the granitic body of the Sierras, the volcanic masses evidently breaking out along the flanks of the older crystalline range. The deeply-eroded canons of the basalt have never been explored, and it is possible that there may be exposed in several of them some of the older volcanic rocks, especially as trachytes and rhyolites occur along the shore of Pyramid Lake and to the north of the basaltic table. 1 Microscopical Petrography, vol. vi, 265. 848 DESCRIPTIVE GEOLOGY. West of Black Mountain, at the head of Louis Valley, occurs a body of rhyolite, lying between the granite and the main mass of the Virginia Range, which has escaped the great flow of basalt. It is a reddish-gray rock, with a microfelsitic groundmass, and the characteristic banded struct- ure of rhyolites. Sanidin and mica are the prevailing constituents, the latter being remarkably well developed in minute flakes. Hornblende appears to be wanting. A thin section of this rock has been illustrated by Professor Zirkel, in Plate VI, fig. 4, accompanying his report, showing the marked manner in which the mica flakes have been broken and twisted. It is interesting to note that on the opposite side of the range, a little north of east, there crops out from beneath the basalt a very similar looking rock, having the banded fluidal structure of the groundmass remarkably well developed; indeed, there are few specimens in the collection that show this — structure aswell. The rock is more porous than the one from Louis Valley, and there is no macroscopical mica, but instead a few minute black horn- blendes. ; : : North of the basaltic body, the 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 La Hontan 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 proba- ble, however, that rhyolites are represented here; indeed, the entire group belongs to that class of rocks which stand on the border line between these two types of acidic rocks. They are characterized by reddish-brown and’ “pray colors, a decidedly crystalline texture, with the individual minerals 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, and about 4 miles northwest from Pyramid Lake, where it forms broad table- like masses. The prevailing color of its gtoundmass 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 PEAVINE MOUNTAIN REGION. 849 have a dull white color, quite unusual in rhyolites, and are frequently 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 by no means frequent, and resemble those usually found in that somewhat limited group known as quartz-trachytes; that is to say, they appear more like an acces- sory mineral than a primary constituent of the rock. They are quite clear and colorless, and apparently free from microscopical impurities. Under the microscope, minute crystals of apatite may be recognized. The pres- ence of quartz and the microscopical structure of the groundmass relate this rock to the rhyolites. Peavine. Mountaty Recron.—That portion of the Truckee Valley lying directly west of the Virginia Range is a broad open basin covered by a thick deposit of Quaternary sands and gravels obscuring all the Tertiary strata below; these appear, however, farther up the valley, just above the town of Reno, and extend thence westward to the California boundary. These Tertiary beds line the valley on both sides of the river, and form a distinct deposit. quite unlike those described from the Lower Truckee Valley. They lie inclined at angles varying from 10° to 15°, in general dipping to the southward away from Peavine Mountain, but considerably disturbed _ by local outbursts of voleanic rocks. Inasmuch ‘as the beds are so highly - inclined, and are older than many of the intrusive rocks of the region, they have been referred to the Miocene age, although they differ somewhat in lithological character from the Miocene strata of the Kawsoh Mountains and Montezuma Range, having much less volcanic material in their com- position. They consist mainly of sandstones, with interstratified beds of friable sands, clays, and thin shales of prevailing light colors. So far as | known, no-animal remains have'as yet been found in these beds, although stems, leaves, and partially carbonized vegetable matter are abundant in certain layers of shale. Perhaps the most characteristic feature of the basin, and one that suggests the Green River beds of the Elko region, is the presence of a number of seams of impure coal and carbonaceous shales. Outcrops of coal occur on both sides of the river north of the town of Verdi, b4 DG 850 DESCRIPTIVE GEOLOGY. dipping to the southward 10°. Another coal-seam has been opened a long time on Dog Creek, a short distance north of Crystal Peak, but, so far as known, none of the deposits have as yet proved of any economical import- ance. No accurate measurements of the thickness of these Tertiary strata — have been made, but there cannot be less than 500 or 600 feet of eon- formable beds. | A short distance south of the river, the Tertiary is hemmed in by masses of dark-gray sanidin-trachyte, to the south of which, in the region of Verdi, are outlying masses of Sierra granite. ie On the opposite side of the river, and lying just within the borders of the State of Nevada, is situated Peavine Mountain, an outlying ridge, or. rather peak, belonging properly to the Sierra Nevada Range of California. It stands somewhat isolated, forming a prominent landmark in the immediate region, partly on account of its commanding elevation, and partly from its striking outlines, which offer marked contrasts to the forms of Tertiary volcanic outbursts, which characterize the Virginia Range and the country . to the eastward. It attains an elevation of 8,217 feet above sea-level and about 3,700 feet above the river, rising in abrupt but long regular slopes to the summit. re Geologically, Peavine Mountain is formed of a series of highly altered quartzites and fine-grained feldspathic rocks, which have been referred to the Archeean series; but their definite relations to other crystalline rock- masses has not been made out, nor can they be referred to any beds of precisely similar petrographical habit. They ou at a highly inclined angle, with a strike varying from north 50° to 65° east, agreeing approxi- mately in strike with the Ar chean rocks of the West Humboldt and Pah- Ute Ranges, but quite at variance to the direction of the Mesozoic uplifts. The entire series of beds is characterized by a fine-grained texture, and all the beds seem more or less decomposed, the purer quartzites being pene- trated by fissures and cracks filled by ferruginous material. In the quartz- ites are also minute grains of magnetite and occasionally a little yellowish- green epidote. In the feldspathic beds, similar iron seams are even much more abundant, and many of the rocks are stained bright red from the discoloration produced by the ferruginous earth, rendering the lithological asi =i bee, hs GRANITE HILLS. | 851 study of the rocks quite difficult. On the north slope of Peavine Mountain, near the Bevelhymer ledge, occurs, intimately associated with the series just described, a rock which has a much fresher appearance, with the individual minerals more clearly defined. It is a compact dense rock, breaking with difficulty under the hammer, presenting a sharp angular | fracture. It carries considerable dull opaque orthoclase, a little plagioclase, with both hornblende and mica. It would seem to be related either to the diorites or syenites. On the north slopes of Peavine Mountain, the beds — are traversed by quartz veins. East of Peavine Mountain, a low group of voleanic hills, rising but a few hundred feet above the valley, stretches out toward the Virginia Range, and closely connects the intrusive rocks of those mountains ve the Sierra Nevada. Lithologically, these rocks present some features of interest, as they bear a close resemblance both to basalts and to augite-andesites, and, if classed with the latter, belong more to basalts than to normal andesite. They possess a bright fresh appearance, a conchoidal fracture, a grayish- black color, and a resinous lustre, characteristic of andesite Scarcely any crystals are of sufficient size to permit of determination by the unaided eye, yet the groundmass is brilliant with faces of feldspar crystals. Under the microscope, the feldspars are seen to be mainly triclinic forms associated with augite. It is evident that the rock is not a true basalt by the large - amount of silica present, a quantitative determination yielding 62.67 per cent., which is somewhat higher than is usually found in augite-andesite. As to the position of these rocks in regard to other ie outbursts, there 13 no evidence. : Granite Hitits.—Along the western one: of the map, lying between the Virginia Range and the California State boundary, oceurs a large area of granitic rocks. They extend from the southern limit of the map northward to Honey Lake Valley, a distance of 40) to 45 miles, with an undulating surface, not forming one continuous range, but broken into numerous ridges, separated by irregularly shaped valleys that are now filled by Quaternary deposits. These valleys everywhere show conclusive evidence that they are merely shallow. depressions in the great granite 852 -_ DESCRIPTIVE GEOLOGY. formation, and that the latter beds are composed simply of granitic detritus from the surrounding ridges. ‘To the eastward, this granitic group is topo- graphically closely connected with, but geologically quite distinct from, the Virginia Range, the volcanic outbursts of the latter resting as it were upon the flanks of the granitic body, although rising to a much higher elevation. In their physical attitude, the granite hills present but little that is of special interest, the ridges being long and narrow, of monotonous forms, and showing great uniformity of outline. State Line Peak is, however, an exception to this rule, rising grandly above the surrounding Conny nearly 4,000 feet above Honey Lake Valley. This granite may in general be characterized as a compact, dense, medium-grained rock of a prevailing dark-gray color. So far as observed, the rock-masses show no law in the arrangement of the mineral constitu- ents, which usually present a fresh undecomposed appearance. Both hornblende and triclinic feldspars seem to play an important part in the composition of the rock. ; In the ridge opposite Spanish Spring Valley occurs a rock iiieh may be properly classed as granite-porphyry, the groundmass being so exceed- _ ingly fine-grained that the individual minerals cannot be recognized by the unaided eye, but at the same time it carries well-developed crystals of all essential ingredients of granite. In the rock under examination, quartz, of all the normal constituents of granite, is the least readily recognized, although here and there are some well- defined clear grains. Both monoclinic and triclinic forms of feldspar are well developed, the latter frequently beauti- fully stratified. The biotite is in general much better crystallized than the hornblende, which is, however, thoroughly disseminated through the rock. Under the microscope, the rock reveals the presence of considerable apatite, and the quartz-grains seem poor in liquid-inclusions. Both of these obser-_ vations in the microscopical analysis are of “some interest, as Zirkel has shown them to-be characteristic of the later granites of Western Nevada. It may be added that this rock, in its physical habit, resembles closely the sur- rounding granite, but is Score waar more compact, from the character of the eroundmass. Just east of Spanish Spring Valley, the granite-porphyry is penetrated GRANITE HILLS. 868 by a narrow north and south dike of rhyolite, which, inasmuch as such dikes are of a somewhat rare occurrence in granitic bodies, requires a special detailed description. It is found just below the crest of the ridge, standing almost vertically, with the lines of contact between it and the granite-por- phyry sharply defined, and showing scarcely any indication of alterations or contact-products. A remarkable feature of this rock is its superficial resemblance to the main body of granite-porphyry, which, however, even a cursory examination dispels, revealing a fundamental difference in the structure of the two rocks. This rhyolite varies from light brown to a dark cream color, possesses a characteristic rough texture, and, under the hammer, breaks much more readily and with a totally different fracture from the granite-porphyry. Small but brilliant sanidin feldspars are the only min- eral secretions observable by the unaided eye, which are scattered through a microfelsitic groundmass. To the southward of the rhyolite is a dike of. black vesicular basalt, also standing at a high angle, and striking approxi- mately north and south. INO E.. Boece section of Syne ra formations, with the local groupings adopted by the Geological Exploration of the Fortieth, Parallel. In order to enable the reader to readily understand the local names of . the different series of strata used in the foregoing report, the following table has been prepared, in which are grouped together all the divisions of sedimentary rocks observed in the region explored, with the geological hori- zons to which they belong. ; The character and relative thickness of each group are deduced froth the most characteristic developments which have been studied; and as these are embraced in the wide region lying between the Great Plains and the Sierra Nevada, it will be readily understood that this table does not represent a section shown at any one point. The aggregate thickness given for each — of the larger subdivisions is estimated in general from the maximum develop- ments of the individual groups. | 854 ae 855 | QUATERNARY .. ; Upper Quaternary ........... | Gravels and loose detrital material. Lower Quaternary --......... | Fine muds and silts. Wyominz Con- if Y Pmerre } Coarse structureless conglomerate. 4 Niobrara Bee ee aad fing friable sandstones, and siliceous limestones ; | Pliocene nd orizontal where observed. i ATA oes rattan siliceons, fine-graineil, friable b2d3; frequently vol- = : | umboldt canic tufas; unilisturbed. ; : : 2 eye NORHMPATieeee me aw Swdstunes and limestones, loosely azglomerated; undis- sling turbed. = es) ie 5 eye . 5 A a ee = TURD oe oc ; Poss iferors limestones, gravels, and voleanic (palagonite) tufas; | S TERTIARY...... Let cree i -upturned. , | White River. ... | Fine light-colored sandstones, with clays interstratified. a i (ex : Coarse and fine pinkish sandstones, gravel conglomerates, and | Uinta...-..---+-.. § argillaceous beds. ae . ’ | Bridger § Drab thin-b>dded sandstones, and yreen marls, rich in verte- Bocene 4 Seca ache te brate remains; slight development of limestones. Paaas Thin calcareous shales, with fishes and insects; buff calcareous Green River ..... ; sandstones, and lignite toward the baso. eae . §Coars» pink and chocolate-colored sandstones with large de- na d 3 | Vermillion Creok. j volopmeit of Conglomerates. Coryphodon beds, = 32,000 + ft (Wakhsatch section). ‘|aRCHaAN.! 50000 + it. | development cf conl seams. Fossils marine and brackish {recs white and veidish sandstones, heavily bedded, with large water. Unconformable with foregoing series. | tect aera alle ee ee white sindstones, heavily bedded ; few coal seams; less CRETACEOUS =o iron than former; fo3sils marine. | @oularide ee ee nt yellow cats and marls, with thin sands’ones. ectnro a ACen G ues Pica oal. Wossiliferous. ——| (Ge a Sra ae Dakotarcys. esc. | Sandstones and characteris/ic conglomerate, * 30,000 ft MESOZOIC. © } DEVONIAN .. PALAOZOIC, } CAMBRIAN ..--. J Is {ra of Wahsatch. Clays and limestunes ; fossiliferous ; small \ In Novada. Heavy limestones, shales, and argillites; greater Al { development. ( ( Heavy - bedded, fossilif-) The Red Beds, which represent the en- | erous blue limestones, tire development of Triassic rocks | interstratified with eastof the Wahsatch, consist mainly | Star Peak........ 4 quartzitic schists and} ofcoarse, heavily-bedded sandstones, < | slates. ‘ of prevailing red color, sometimes : white or buff, with some clays, thin (v limestone beds, and frequent depos- ioinaito Quartzites, argillites, and its of gypsum. Almost barren of er eens Peter e porphyroids. ) fossils. ~ Red Beds Ne Permo-C irboniforous ees | ‘Clays ‘and argillaceous limestones, with ripple-marks. In general, licht-colored blue and drab limestonés, more or Tess siliceous, and passing in places into sandstones; generally fossiliferous. : CARBONIFEROUS wed - Weber Quartzite ........-.-- with local developments of interstratified calcareous and vi s:ndstones anil quartzites, frequently of reddish colors, argillaceous beds and conglomerates; non-fossiliferous. : Heavy-bedded blue and gray BeSOnes, anion Rome : «Far ; Wahsatch jnterstratified quartzites, more frequently in tho CO SUECMIDE COTO ee seeder limestone. upper part of the series. Lower beds siliceous ( Nevada Devonian ........... J : at times. Fossiliferous. Lower Coal Measures......-. \ u os5 “ ; b : White saccharoidal quartzite, pink tints; conglomerate with ogden Quartzite...--.....-.. { flattened pebbles. 1 SILURIAN ..-c-- | Ute-Pogonip limestone......-- } Compact blue limestone, with included argillites, passing into \ caleareous shales. More largely developed in Nevada, where (Pogonip essa st epee j the limestone carries primordial fossils at the base. some development of micaceous beds, and heavy dark-blue some white quartzites, more or less iron-stained, with argillites, Plagioclasé-hornblende granites, diorite-gneisses, argillites, [ TOONS AN oe Tea eet pipen Pal ee a te ; limestones, and quartzites. y ; ‘ § Coarse red orthoelase-mica granites, mica-gneisses, and schists. LHS DRENIEIOS eco ESE OE SELENE eee ; with deposits of ilmenite and graphite. CENERAL INDEX. {Small capitals denote headings of chapters, scctions, or sub-sections.] Abies amabilis ....-..-.... MB Ba esa R REE GSE Ab Or ncron Douglasii ..-...-..--..- Engelmanni grandis ......-....--- _Menziesii .-...---.---------« ggpcneonache dace INCREAS oes cigs Sgec ne Aone Seu ep scoop upon oss Activolite in quartzite, East Dumboldt Range .....-. Ada Spring, position ....-..-.-....-.-.-..-.--------- Agate Canon, Cortez Range, titanite in gianite .... Pass, Cortez Range, basalt .........-....----. : MIOTIUC eee cap racine ee ears a Weber Quartzite......... INC INTID PINSS) VRIO( CHI seeaescoeeod sso eececonds oles Age of augite-andesite. Beis cyanea israel : infasoniall silica: 222 .sec cases a certceee eae Red Creek Archean ......-. .------.-------- “Waachoe granite ....---. 2.5 ..-2-e see eee conan Albion Peak, Little Cedar Mounds altitude ...... Alnus koetersheiiere te cmc ccenct ence sem aineiels nae eae Aloha Peak, Pah-tson Mountains, basalt.........--. rbyolite.....-.-.. Alum on argillaceous schists.-...-.--.-----.-.------ American Fork Cafion, Wahsatch Range ...--....-. : diorite...-.-...-.. Qogesne see Miller Mine.-.-....-.........- Ogden Quartzite.........--.. a Amphibolite, Grand Encampment Mountain .......- Anaho Island, Pyramid Lake, trachyte..-...-.--.--. ASE of alum on argillaceous schists, Promontory Mountains, R. W. Woodward........-..- alum on argillaceous schists, Promontory 5 Mountains, J. L.Smith... ............. argillites, Star Peak, Tri jassic, West Humboldt Mountains, B. E. Erew- augite-andesite, Cedar Mountains R. W. Woodward...-...:-..-- Palisade Cation, Reinhard Wachoe Mountains, R. W. Woodward ........ basalt, Buffa’ o Peak, North Park, R. WwW. Waonvardt” mickeie mio rely coer ate * Diabase Hills, Truckee Range, R. = _ W. Woodward .................. : (nepheline), Navesink Peak, R. W. Woodward. Ombe Mountains, R. ae W. Woodward ...... : Stony Point, R. W. Woodward........-. 195 195 146 534 121 576 575: 573 BYE! 13 480 Ta 270 478 512 146 7eL 780 423 350 361 353 390 138 617 Analysisof bindheimite, Montezuma Mine, W. G. Mixtecs caaseoson sash toe hceeences cement of Wyoming Conglomerate, Con- crete Plateau, B. E. Brewster .....-.--- coal, Cooper Creck, Dr. F. A.Genth ....-- concretious in Colorado Cretacecus, B. E. LE KG(RDE Gasdgoccasataobs jadeubedeoony dacite, Cortez Ran ge, R. W. Woodward . ‘Shoshone Peak, It. W. Woodman diabase, Diabase Hills, Truckee Range, R.W. Woodwards.. 22-2255. .c2--- cece diorite, Agate Pass, R. W. Woodward .... feldspars in rhyolite, Pine Nut Caion, R. WieeWVOOCWiaAnd sence cease ene cea ' gabbro, Laramie Hills, R. W. Woodward . Chateau Richer, Canada, Dr. T.S. RIG, cSecendosoe eS HGSR ee OmEr Gay-Lussite, Soda Lakes, Carson Desert, OPDMATLEn G2 sis ee eee ar ee gneiss, Elk Mountain, R. W. Woodward . Little Snake River, R. W. Wood- (hornblendic), Ogden Caiion, Robert Bunsen .--.-..--.---- granite, Agate Ceiion, T. M. Drowr. ets. (Temple) Cottonwood Cafion, Wabhsatch, T. M. Drown....... Dale Creek, R. W. Woodward ..- Egan Cafion, T. M. Drown .....-. Granite Cziion, Laramie Hills, « R.W. Woodward ..-....-.-.--- Granite Peak, Pah-tson Mount- ains, T. M. Drown ............- Granite Range, T. M. Drown .... Iron Mountain, Laramie Hills, R. W. Woodward..-...--..--.-- Long’s Peak, Colorado Range, R. W. Woodward ..-..--..--..... Nannie’s Peak, Seetoya Mount- ‘ains, T. M. Drown .-....--..--- Wachoe Mountains, T. M. Drown West Humboldt Range, T. M. DOW oe ee compe neee oer green marl, Bridger Basin, GB E. Brewster gypsum, Jurassic, Ashley Criek, B. E. Brewster...-..-.--- “ ot Page. 7539 297 cgi S74 1 749, 750 103 140 Analysis of gypsum, Triassic, Ashley Creek, B. E. Brewster..-:-.-.-.----- Laramie Hills, B. E. Brewster. -..-.---.- ilmenite, Iron Mountain, O. D. Allen ..-.-.. R. H. Richards. - R.W.Woodward infusorial silica, Kawsoh Mountains, I. W. Woodward ......- Truckee Valley, R. W. Woodward. .......-.- iron ore, Palisade Caiion, B. LE. Brewster - iron-stone (clay), Elk Mountain, B. E. Brewster. -.-.----- PoE aes eee leucite rock, Leucite Hills, Wyoming, R. W.. Woodward. : 25:22. -s-stceces cecene limestone, (dolomitic), Archzan, Kinsley district, B. E. Brewster. ----. Carboniferous, Albion Peak, B.E. Brewster Granite Caiion, B. E. Brewster Horse Creek, B. E. Brewster .- Humboldt Pliocene, Pine Val- ley, B. E. Brewster ..---.---. Jurassic, eastera foothills, Col- . ~ orado Range, B. E. Brewster. ...-..--. Laramie Plains, B. E. Brewster ----..--. North Park, B. E: Brewster..-..-.--- LowerCoal-Measure, Kast Hum- boldt Range, B.E. Brewster. . Lower Coal-Measure, Grand Peak, B. E. Brewster. .--.--- Lower Coal-Measure, Mill Cai- on, Wabsatch, B.E. Brewster. Niobrara Pliocene, R.W.Wood- Oélitic, Green River Eocene, B. I. Brewster *.....------ rts Triassic, eastern foothills, Col- orado Range, B. E. Brewster ....-..... Duchesne Valley, Uinta Range, B. E. Brewster ..---:---- Truckee Valley, B. E. Brewster ..-..-.... West Humboldt Range,B.E.Brewster Truckee Miocene, Kawsoh Mountains, B. E. Brewster... Truckee Miocene, Valley Wells, Upper Coal-Measure, Parley’s Park, B. E. Brewster ........ Upper Coal-Measure, Tenabo _ Peak, B. E. Brewster ........ Upper Coal-Measure, Ute Peak, Uinta Range, B. E. Brewster. Upper Coal-Measure, Vermil- lion Creek, B. E. Brewster. - - INDEX. Page. 768 821 586 151 237 484 513 31 32 563 ‘167 114 373 572 288 274 Analysis of limestone, Upper Coal-Measure, Weber. Caiion, B. E. Brewster -.--. Ute, Ute Peak, Wahsatch Range, B. I. Brewster -.-.- paper-shales, Green RiverCity, Wyoming, B.E. Brewster_.-.---.--- Bo BEE ROT eiet porphyroid, Triassic, West Humboldt Range, B. E. Browster ..---...---------- propylite, Havallah Range, Dr. Walter Korman ..--.. Bee Soeon enone Ward oo ocho et nes ane een Storm Caiion, R. W. Woodward. (quartz), Cortez Peak, Prof. Wie- denian 2. se hacer ens Mullen’s Gap, R. W. Woodward.....-..-- quartzite; Cambrian, Big Cottonwood, | B. E. Brewster. -- Farmington, Wah- satch, B. E. Brew- 4 Riel. ce-e aaa Ogden, American Fork Cation, IB. W. Brewster. =: ---2---sco-5 Weber, Battle Mountains, Ne- vada, B. E. Brewster. Bear River, Utah, B. E. Brewster ...--..--.-- Big Cottonwood, Wah- satch, B. E. Brewster. La Motte Peak, Uinta Range, B. E. Brew- Lote ees ae Josie neeyee Point Carbon, Uinta Range, B. E. Brew- Stone aseee Bamps quartzitic schist, Star Peak Triassic, B. E. IBrewsten-2oreaseeree i o- peoee eee rhyolite, Bayless Caiion, Montezuma Range, R. W. Woodward... -- ‘s Black Caiion, Montezuma Range, R. W. Woodward .......-.. ads McKinney's Pass, Range, R. W. Woodward. .-... Mopupg Hills, West Humboldt | Range, R. W. Woodward...--. Mount Moses, Fish Creek Moun- tains, R. W. Woodward ....-... Sou Spring Hills, R. W. Wood- ward ...... sesh irecedssahueses sult incrustations, Antelope V alley Springs, R. W. Woodward ....-.... Buffalo Spring, O. D. Allene sees -teeere = Cortez Valley,.R. W. " Woodward ....-..... Grass Valley Spring, R. W. Woodward. -. Hardin City Flats, O. D: Allen.- 2: -2cs-5 Humboldt Valley, O. Pah-Ute 324 792 7144 Analysis of salt incrustations,Osobb Valley, R. W. Woodward Peko Station, R. W. Woodward .-......- Percy Station, R. W. Woodward ......... Quinn’s River Sink, OVD Allen’ =... .2:- Reese River Springs, R. W. Woodward... Ruby Valley Springs, R. W. Woodward.. Tiuckee Desert, O. D. ‘sands, Salt Lake Beach, R. W. Wood- WALA eae sence ene, ual eulete Seelam ats sandstone, bituminous, Wonsits Ridge, B. E. Brewster ..-. Antero Caton, B. I. Brewster .-.. Bridger Eocene, B. E. Brewster. Dakota Cretaceous, Laramie Hills, B. E. Brewster .--...-.- Dakota Cretaceous, St. Mary’s Peak, B. E. Brewster ...--.-- 3 Triassic, Duchesne Valley, Uinta, B, E. Brewster....---- Triassic, Weber Cafion, B. E. Brewster) 2-2 ai: ses0seccsse sinter, Steamboat Springs, R. W. Wood- WARS 565 Sonee cose ee aes sogereceee sass surface-soil, Jordan Valley, R. W. Wood- WALG focatiog tdcenceo sect ae Deep Creek Valley, R.,W. Woodward ..........- aes Great Desert, Dugway Sta- tion, R. W. Woodward..-.. Great Desert, White Rock : Pass, R. W. Woodward .... S Tertiary, Brown’s Park, B. E. Brewster... trachyte (augite), North Park, R. W. Woodward ......... Sheep Corral Cajion, Dr VAN CCR esas cee | Truckee Cziion, R. W. Woodward......-.:. Euclid Peak, R. W. Woodward. Pine Nut Caton, R. W. Wood- Wands see a oresmecicuscneee Provo and Silver Creek Divide, RW Woodward) 2255. ccos-6 Slater’s Fork, Elkhead Moun- tains, R. W. Woodward ...... - Truckee Cafion, R. W. Wood- OnbAllen) ois ces ses aeek seca OD B Adoni zeer sete cet tee tufa, Lake Bonneville, Redding Spring, Ry. Wo Woodward. - 2-1. -5-2------ 5 Lake La Hontan, Carson Desert, R. W. Woodward .. Pyramid Lake, R. W. Woodward .. INDEX. Page. Analysis of tufa, Lake La Hontan, Truckee Valley, R. WieaWOOdWwand ates ese eree aa eee eee 4 Medway Spring, Provo Valley, R. W. Woodward (palagonite,) Dyampang-Kulon, O. Prolssi.-s<.-tesec=n5 Galapagos Islands, Rob- ert Bunsen Hawes’ Station, Nevada, R. W. Woodward...-. Iceland, Robert Bunsen. water, Atlantic Ocean.......-...--..----- Dead Sea. .-..-.-- inate ceremecrins Hot-Spring, Salt Lake City, Dr. C. Ae lac RRO we assests cette se on Humboldt Lake, O. D. Allen..:.... Mediterranean Sea...., Oroomiah Sea, Persia ............. . Pyramid Lake, O. D. Allen ......-. SeviowlakesUitahieeeeses == eee ae Great Salt Lake, Utah, O. D. Al- Jen Sou Hot Springs, 0. D. Allen ...... Andesite (augite), age of .....-.- S aeeeasact ents hee > Annie Creek Antimony Cafion..........-. reraers Augusta Canons p22 s-- 55h Cedar Mountains....... ‘Jacob’s Promontory -..---.-- ---- Palisade Cafion (quartziferous) -. Peavine Mountain Sprivg Caion (mouth) Susan Creek ........---..---- Pee Truckee Cafion.....--.-.-.-...--. RUS CANOLAz EA ste eateries senses Augusta Cafion....-. Berkshire Cefion ..- Clan Alpine Caiion Crescent Peak.....-.--.------ eS Suereiet ee Deep Creek Valley . py ptian Cahoniee sac c ose eee Kamma Mountains ....-.--.-...--.-- North of Wagon Cafion.....-......--...-. quartz in Traverse Mountains. - Truckee Caiion..-.. Toscarora : West Humboldt Range.......--.-..-----. ANBIESIGeie ss scene ete ste tea ea eete Ole aecoe ore st Anita Peak, Elkhead Mountains, columnar basalt. . - magnetic attraction of basalt...--...-- fe Annie Creek, Cortez Range, augite-andesite. -....-.- Antoine’s Cation, Virginia Range, rhyolite .-... 2 tridymite in rhyolite.....-.-.-..- - ANTELOPE HILLS AND SCHELL CREEK MOUNTAINS... Antelope Island, limestopve in Archean .--..--....-- Peak, Montezuma Range, altitude -.-...-. Springs, Promontory Mountains..--....... Valley, Thermal Springs Antero Cation, Uinta Range, bituminous sandstone. - exposures of Mesozvic- 862 : Page. auteroCafion, Uinta Range, Weber Quartzite at head 301 Auticlinal axis of Bitter Creek Uplift....-...-..--.- 234 of Uinta Range-.....--.- 256, 257, 258, 267, 323 in Star Peak Triassic, Pah-Ute Range 710 Willow Creek Cafion, Pition Range 554 Authracite in Wahsatch limestone. .-...--..-...--. £99, 604,619 Antimony Czion, Augusta Mountains, augite-ande- BITCH ee wales ome ook Cat ere oiaeininte i onicinyanteloineletye wrens 654 Antler Peak, Battle Mountains, altitude.-......-.--- 666 Upper Coal-Measure limestone -.....-.. . 669 AQUI MOUNTAINS epee cee ities) min sieieniein = sie Terrace lines Archwan, Crawley Butie, North Park..-.. cyanite in ....--.-- dep eaedesssacacesoneses 270 Fault Cation, Wahsatch Range....-..--.-- 395 Frémont’s Island, Salt Lake.--..-.-...--. 425 Farmington, Wahsatch Range.....--.---. 377 GEOLOGY (of the Laramie Hills) .........- 7 gneiss, Landing Rocks, Salt Lake ..-..--. 425 Plessuresin. 4:22, ies series 379 Grand Encampment Czion........-..--.-. 137 Granite Mountain ...-.-.---.....-.-.----- 689 ‘granite, Pak-tson Mountains ....--..-.--. 776 Rawlings Peak .......---...----- 160 Scuthern Shoshone Range ...-..- 637 Kinsley District 483 IDS) IOVS osSee geeces sesss5° 814 Lone Peak, Wahsatch Range.--.--.--.--- 357 Medicine Bow Range : 97 Montezuma Range. --2---.-.-- 25. --------- 793 Ogden Cation, Wahsatch Range ... ...-.. 396 Point, Wahsatch Range ...-..-.--- 402 LEbya Se NEVES) 55 5ebSonenesocoansoous codecs 134 Péavine Meuntain 220-2 e- soc ene ee * 850 Pinion] Ranier seer ee tee e eis ss eee 504 Promontory Mountains ....-..--.:--.---- 421, 423 | Red Creek, Uinta Range ...--..- --- 202, 227, 268 Rocky Mountains, discussed ..-...-...--. 109, 141° ‘schists, Pah-tson Mountains...-......---. 175 Shoshone Range........-.-...- Ase 637 Trinity Cahon, Montezuma Range. 754 Truchec Range. ....--.- Seis Sette Ook £04, €06 Twin Peaks, Wahsatch Range ..-...-.... 358 | WintavRan'e Oren om seein seen eetse nic 198, 201 West Humboldt Range........-.--.-.---. 715, 717 Arena sativa.......-.- abe ie: pace eso pun me Sar anes TAT ATeentite!. not. acento Sheer nasi nein eee aes 731 Argillites under Archzan quartzites; Medicine Peak. 105 Arrow Peak: altitude... s-— 2 ssesot= scot oe eeeces 5 PAMtEMINAeEnUUIS). --s=-)eesnce eeeetdcontcod 435 Aptemisia) tridentatian ssa y-ace seen ences bieiee setae 793 Artesian boring at Rock Spring Station 234 ASHLEY CREEK BASIN .--.-- Booméeioscccsssse5 AIS BE 291 coal in Colorado Cretaceous .-...--. 294 Dakota couglomerate...--...--.-.-- 293 Fox Hill Cretaceous....-....-.-..- -s 295 gypsum in Triassic ...-......-----. 292 ID DULASSIC| a foc e yee 293 Park, Weber Quartzite ................--- 268 - Aspen Plateau, Vermillion Creek Eocene.-.......--- 337 Station, Colorado Cretaceous..-.....-.-..--.- 253, 326 Astor Pass, Virginia Range, trachyte .----...-...... 848 Augite-andesite, age of 480 Annie Creek..-..-.... o5 588 Antimony Cafion .-.......--..----. 654 INDEX. Page. Augite-andesite, Augusta Cafion.-...........-. Cerri iE | Cedar Mountains .-..-.-..-------.-- 463 Jacob's Promontory ....--.---.-.-- 641 * Palisade Cation (quartziferous) .-.-. 586 Peavine Mountains..............-- 85L Spring Canont ones. piece nanan 480 - Susan Cree eee ene eater 598 Truckee! Canonyess---1---eeese oe 830 Tuscarora ---......5...---..- 611 propylite, Silver Mountain ............ 832 trachyte, North Park...-.....-.--.--.- 124 Pilot; Butte c oseee sees 238. Angusta Cation, Augusta Mountains, andesite 653 ; augite-andesite 654 hornblende- - : 4 porphyry .-. “652 DONATING Fae eee lee 649 andesit@ess=-s senses eee eee 653, 654 RCIA ASB rae csc aes Soccer oes 649 GUN MOipacsce onanressesonaanccn 657 (ARNG = otc oooscesee -oeoseneso 651 hornblende-porphyry --.------- 651 OUPASSC 22s eee ee ase note 656 Thy olife spe sone eeees= eet 649, 655, 658 Star Peak Triassic..-....-..---- ‘681, €57 thickness of rbyolite flows G56 Authors, Allen, O. D., analyses.-........------------ 15, 443, 731, 743, 744, 747, 748, 749, 750, 773, 791, 792, 824 Anger, Dr., analysis --..----.-..--.-------- 8338 Bischoff, Gustav, cited.-..-..-.---.-------- 436 ‘Bradley; Hees, citedigs- tension eter ar 136 Brewster, B. E., analyses ..-...-.-..-----.-- 31, 32, 35, 36, 39, 41, 78, 115, 155, 212, 223, 242, 246, 247, 248, . 274, 288, 292, 295, 297, 299, 304, 306, 323, 324, 350, 366, 367, 373, 376, 380, 3&9, 390, 411, 467, 424, 509, 513, 530, 563, 572, 586, 669, 705, 720, 722, 723, 726, 767, 774, 821 Bunsen, Robert, analyses -.-..-- ---.------ -398, 770 = Clayton, J. E., cited.. ..--.---.----. 358, 365, 446, 448 Gone; E. Di eited 2222-5. - ones «---- 231, 241, 251 Drown, I’. M., analyses ....:. ...---------- 356, 477, : A 489, 577, €03, 715, 779, 798 Ehrenberg, C. G., cited .. 768, 820 Engelmann, Henry, cited .-..--.-...--..--- 348, 358 *Gabb, William I.. ciied 712, 725 Genth, F. A., analysis.-.-..-.------ enesiae oe 86 Grivnell, G. B., Paleontology of Black Hills 33 Hague, J. D., Comstock Lode -....--.-.----- £25 American Mining District... 729 mining’ in West Humboldt INFO G) Wee asec ASopeesoseee 730 terraces of Anaho Island .--. 824 Hall & Whitfield, cited ..-.-..-----.--- 365, 400, 444, 544, 546, 609, 657, 711, 712 Hayden, F. V.,¢oal reeks of Colorado....-- 63. : Palzozoic strata of Black TAGS ooh ec ee raciee 29 White River Tertiary...-.. 65 Hunt,'!: Sterry, avalysie......---.---.---.- 14 Hyatt, Alpheny, cited .-.-.....-........-.: enc 4. Jackson, C2 Le analysis ele saee nae 438 Dirstys) yoaveh CWE eso ne as Shosad Sess 33052 710 King, Clarence, notes ...-...--.-------- 330, 374, 532, 551, 573, 577, 583, 692, 713, 759, 824 geology of Washoe region. 825 Triassic in Oregon. -....-- 690 INDEX. 863 Page. Page. Authors, Korman, Walter, analysis .......... ...... 679 | Authors, Zirkel, F., haiiyne in trachyte ............. 568, 598 Leidy, Joseph, Niobrara Tertiary...-...... 591 hornblende in diorite ............ 646 Lesquerenx, Joseph, age of Carbon coal .. 147 propylite ......... 610 coal plants..-.... Sees: 146. hyalomelane tufa...............- 785 Meek, F. B., cited....... ener wetiark _. -- 62, 85, 121, inclusions in quartz ..........-.. 10 231, 328, 335, 336, 383, 388, 389)390, 405, liquid-inclusions in glass of rhy- - 411, 491, 545, 558, 646, 724, 728, 741, 767 OliGGSracten cece seen mooeeea cisions 847 Marsh, O. U., cited ....-..--..--..----- 52, 65, 67, 71, liquid-inclusions in quartz of dia 217, 225, 248, 262, 289, 296, poe 329, 741 DAS Maser e sae ete neecice acme 728 Marvine, A. R., cited......--.---.--+--e-- 29 liquid-inelusions in quartz of rhy- Newton, Henry, cited. .-.......-........-. 29 OllLOS ae wee ee ek ee oniactnence ae 482 Peale, A.C, cited =.-...5....2.-2.08-----5- 29 magnetite penetrated by mica... 136 Powell, J. W.. cited. .....-....- enanehee -- 196,199 melaphyGecceeeteresccene eeneces 840 Prolss, Otto, analysis..............---- oas0 7720 mica in Archean schist.......--- 776 Ramsey, A.C., cited ....-...............-- 436 micro- -granitic structure of feld- Reinhard, anatysis.....-.- 587 Spar-porphyry..--...-..--..--- 692 Richards, R. H., analysis .. 15 micro-structure of chalcedony. -- 784 Roth, J., lithophys~ ...........-.....----- 616 olivine in basalt......--...-...-. 764 Scheerer, gabbro of Norway .-..-.----.--- 14 trachyte........- thoes 169 Smith) (J. dus analysishesss-4es4---4-2-2---« 424 orthoclase in trachyte ..--.. .-.. 123 Stevenson, J. J., cited..........-..-.-.-.-. 63 PLOpY lite; “oy jate sce occe ec scles 662, 679 Varney, A.L., cited........... 52 quartz-propylite .......--..-.--- 578 Verrill, A. E., cited........... : 435 relation of rhyolite to granite-por- Watson, Sereno, cited -. 435, 746 phyry 561 White}; Geary cited ss eccer as de tsck sce 344, 445 rhyolite 579, 663 Ae GPG I Te) ooo bee oee geouen scebes ROOABB 597 _ ‘structure of orthoclase feldspar . 807 Whitney, J. D., Triassic in California ...-. 690 trachyte .......-- Si as ote 787 Wiedeman, Professor, analysis _ 839 tridymite in basalt ...-...-...... 172 Winchell, N. H., Black Hills............--. 29 tridymite in rhyolite ....-....... 430 Woodward, R. W., analyses ..-.10, 13, 14, 16, 17, 23, tourmaline in diorite....-.. eedas 658 70, 103, 125, 126, 140, 148, 176, 178, 237, 319, zeolite in rhyolite ....---......-. 643 320, 397, 423, 434, 435, 464, 473, 474, 481, 500, zircon in gneiss..-- .-----.----- 397, 507 522, 541, 569, 574, 582, 594, 617, 621, 634, 662, | Azurite ...........50----2 2-2 eee cee eee eens WL 664, 687, 695, 698, 701, 702, 707, 736, 745, 758, 5 763, 765, 768, 812, 819, 821, 823, 826, 833,845 | Bald Mountain, Uinta Range, altitude ........-...... 312 Wirisht) CoH e1ted tice. c= eet oe coc ee ose 771 | Ball Rocks, Grass Canon, obsidian ....... + 784 Zirkel, F. (alteration of feldspar in granite. - 576 | Barrel Springs, Green River Eocene 214 alteration of hornblende in gran- Basalt, Agate Pass -----..--.-..---....-......-..--.. 579, ite-porphyry .......---.-..---- 450 Aloha Peak.-......- Beene s8og2=2ess00eKs 781 andesite Sanwa me ee eee hes 827 Anit» Peak, (columnar).......--..20-------+- 179 augite-andesite - - 480, 421, 836 Basalt Peak, Pah-tson Mountains....-....... 785 basaltic. Ceeeeee eae eee 592, 666, 730 Bastion Mountain 177 carbonic-acid inclusions in quartz 675 Battle Mountains.........-...- 672 > contortions of mica slates ....... 848 Berkshire Cafion. .........---.--------------- £44 Devonian slates..--....- Leoseess 603 Black Mountain ...--.-......-....--..--..--. 847 diabase reese haere ween ecer ace 810 Wom DSi setae ee tee eee cnet cee secre 819 different forms of inclusions in breaking through diabase............-..-.--- R12 quartz and felcspar ...-....-.-. 26 RAN Ciee Bsa coosseoce oodene 677 - diorite of Quenast ..-........... 805 | granite-porphyry -......-.-. 853 feldspar inrhyolite........-..-.. 702 Thy Oller ace ewes ass clnea= 698 feldspar-porphyry and gavel Buffalo Peak, North Park.........-...--..--. 126 Comparedec ses = seem ese acige == 512 Cedar Mountains .........--...-.---.-------- 464 deleiiieyputasy ler eesa- =a eee ' 596 Clan Alpine Cafion .....-.. .-..--....--.---- 650 ferritic necdles as coloring mat- columnar structure .......... auodeeuvandade ds 180 ter of rhyolites................ 734 craters, Humboldt Valley 714 OO Wad cena aesen6 aodespesseen 14 Diabase Hills, Truckee Range. .-..--...--.... 812 glass-inc!usions in feldspar...... 340 Egyptian Cafion .......--.-....--------.- --- 592 glassy structure of rhyolit s.... 499, 835 Fossil Pass, Pifion Range ......-......---.--. 560 globulitic devitrification ..-:.... 813 GandeniVialleycesiem- ssesia2 sniccisciecteiscicm e's 815 | Big Thompson Creek, course of.:-..- soate sons Bie Montezuma Range .......---.--.-.--- 757, 758, 760, 763 fall ofee5 tee oeeee Moore’s Fork, Yampa River....-......--.---- 1¢4 ; Mesozoic strata Mountain Wells Station ..........-...--.---. 704 | Bindheimite ......:..-... Speen eeeee Navesink Peak, Elkhead Mouutains -.....--. 178 | Bingham Cafion, diorite ....--......-....---.------- (nepheline,) sanidin in, the Rampart oadaceos 180 ecauitesnrorinay Ombe Mountains :. .-.. 2-2 tae oe wena = 499, 500 phyoliteresss-se-tee over rhyolite ei-tectcenuc ses odesdees=gacncecs 795 Weber Quartzite in crater-cones ...-.-.-.--=----- 765 | Bird bones, Vermillion Creek Eocene ........--..--- DEO SiG TM = 5 sao nosss0 case conseane tonabeoesaas 730, 765 | Bishop’s Mountain, Wyoming Conglomerate ....---: period, erosion since..-----.-----.----------. 576 | Bitter Creek Uplift, anticlinal axis .... .......----- QUEWA WT o.oo sc osonoo osoncoanéoconsoogsescocs 617 | Bituminous sandstone, Fox Hill Cretaceous.....---. Railroad! Cations. 2-5 scm snlenenine ence salar 549 Triassic ......- RedsDome se 5-2 s2s-ca--eee ne 426 | Black Butte ( Nevada), Jurassic........ Rozel Hills .... 424 syenite...... - Ruby Group.........-..-...-... 4£0 (Wyoming), altitude ...........-.....- sand sculpture on V2 metamorphosed sandstone Snowstorm Ledge, Black Rock Mountains. -.- 795 Station, Laramie Cretaceous ... ...--- Spaulding’s Pass, Pah-Ute Range.........--. 709 Vermillion Creek Eocene.-.-.- splerival forms im eee. seeeeeneeeme eee seer 618 Cafion, Montezuma Range, basalt .....--.---. Stonysointe sos peeeeeaeeeeeceee 616 Mountain, Virginia Range, basalt ..-.......-. Table Mountain, Pah-Ute Range .. 103 quartz, coloring matter of Truckee Canon Aasjscwe eee cseceee cesar 828, 831, 836 Rock Point, cave in limestone .-----.--. fated Ran pep atten) eine 810, 811, 828, 831, 836, 844 Lower Coal-Measure limestone. -. ‘walls: North, Park: cstuco. esos see oe eae 126 terrace-linests..260.-6 ee ascesecee West Humboldt Range ......-.-....--..-.-:. 729 BLACK Reck MOUNTAINS ........------------------- Wrhirlwind Walley: 22.2 <5-.ensceee stir semeiete 618 Heed Se onise sue aaeeseee ; White miverc 2 ot wesete aw cctcecls 184 dolerite: :. i322 ee access - Bastion Mountain, Elkhead Mountains 177 geological structure...-.. BATILE MOUNTAING: 22015-10272 - ces ao eee henna = 666 IMMUNE Ace ees scence basalt....-......:..- eee SE CARE i712 palagonite tufa........-.. (HOW) sonosshdeodosuecdusososusos 672 phy olitelees ss aneeeeaeeeae geological SUPE Baas oni 667 Point, Oquirrh Mountains .....-...... Tivolite aise er oseeea nodes 671) || Black's Fork, Triassie.-.-..--- <--.--2-------..--055 : Upper Coal-Measure limestone.. 670 - Upper Coal-Measure limestone -.....-- ‘Battila Stevensontes-c.- + - seen ease eee eee tee 146 Weber Quartzite ........--.---------- Bear Ridge, Fox Hill Crétaceous.........:..---.---- 185 | Blacksmith’s Tork, cafion cf ..-..-.-----.----------- Bear River City, brackish-water beds ......-..-...-. 327 falls of..* Cretaceous age of ..-..-..:......-.. Shit G dey seasee mercateaeconsasoecdod agessos Fox Hill Cretaceous 327 | Blue Point Spring, Peoquop Range Green River Bgcene! PACRBRAG SIS OB Wail Sto MO VON bin Ze SoRernoomce cosaoo pCoaeso seen cemodans Plates yao eee neces 414 | Bonnevillo Peak, Aqui Mountains, altitude. sobeus=So5 iron in Cambrian....-.------ eee, 413 Cambrian EAs Vermillion Creek Eocene. Hes aeesn ee 415° WiGySchives eaecors ybyolttetta srs e- sesso eee «See eciseiee cites 337 -. fault in Cambrian. Wyoming Conglomerate ...-...-....-.- = 324 | Boone Creek, rhyolite.....-....--.. Lege AS oA cates Beaver Cefion, Cambrian quartzite ....-.....- Pee 415 | Bosjemannite ....-.....-..-.------ ------------------ Lake, Upper Coz]-Mgasure limestone. - 305 | Boulder Creek, Lower Helderberg fossils - . 7 Bee-Hives, rhyolite tufa .......--.-.-...-..-2- -----6 489 Ogden Quartzite .-....--.-. awes Bellevue Peak, garnet in gneiss. .........---.-------. 108 Pogonip limestone -~--..--- - Benada Peak, Promontory Rango, altitude 4¢2 | ‘Bournonite.....-------.--.--- --+---------- - Bennett’s Peak, diorite schist...-......--...- 100 | Box Elder Cation, Wahsateh Range, Cambrian: .-... IBERESHIRE| CANONS. ooo ee seer se nseae ee sen ee £39 . Silurian -...-.- ENGNG senecudestaassoooDe 841° ’ Creek (Or OE section of Jurassic ..- ‘ ERED aeenerencosceeacaepaceeee cess a44 Triassic. .... dacitec.d-/as ere saeco eee 842 Peak, Wahsatch limestone melapbyr..-.-.. rookie cae sea 839 IRWGION} sacs eee eee eae eee Cee eaase propylite)..(. fsck ann. eee " 840, 842 | Brackish-water beds, Bear River City WV OMG eae Sobabsncsesossages ozo 841,842 |. BRIDGER BASIN ...--...----------= s-eeee ene ee ene ee tiaehy ter. 2225.58 es aoe Seeraeine 841 IORI A gaan osaose seco cso soseeace seeeee Berry Creek, Uinta Range, Weber Quartzite..-..--. 321 ChunchButtes) -=-eceeemece eee Big Cottonwood Cafion, Cambrian, thickness of .... 366 described granite evoen- see neaaesee ese 360 erosion Of ..-..-.---- ---------- aeons 457 456, 457 630 424 608 609 609 731 ~ 403 403 38. 34 404 403 327 238 244 245 204 x17 — oe) INDEX. Bridger Eocene, fauna of.........-......-----2s2++s Carrington Island, Salt Lake........-.------ a Haystack Mountain Carr Statiow, Colorado, Coal strata....- daBSonade moss agatesin.,-.-.--..----..----- White River Miccene thickness of...--......-..---- CARSON DD RSHRT act aor oscste peace ane cee ee Pass, Fox Hill Cretaceous............--... 159 Lake La Hontan terraces REGION. .------ 222-222. eee - 156 _Lower Quaternary..... ...........- Brisopyrum spicatum 3 747 Truckee Miocene Brown's ParK AND YAMPA VALUEY..-...-----.----- 222 | Cascades in Provo Cafion ......-.--.2---eececees-eee Eihot iG l2) 285 poeene cee ce ceereceecece 222 | Cathedral Bluffs, seciion of Vermillion Creek Eocene. described ....-.....----2---..--.--- . 196,222 | Castle Peak, Wachoe Mountains; quartz-porphyry .. feng ihiny envi any ecommerce seis) 223 Wahsatch lime- Ona Oc Gonace neonabeeee a 201, 202, 272, 282 BLOnee see ee Tertiary, Pliocene fossils -......-... 224 | Cave in Wahsatch Wee Black Reck Point..... thickness of......-...-.... 223 | Cave Spring, East Humboldt Range.........-....--. ; Yampa Valley ............ 224 | Cedar Mountain, diorite schist LEO) TEGES (9 PLU) .congocesonoocOneppEDaEe See seeaen TSW NORDAR MOUNTAINS tico cu. nee oscoscoecele Sees be Brush Creek, Medicine Bow Range, horntlende & augite-andesite SOME cutdodabee euadseack ssseaaEeTeese 100 Ten Gea OIG. Seay Uinta Range, Colorado Cretaceous. .-.. 296 | Central Peak, altitude .......... Buffalo Peak, West Humboldt Range, altitude ...... 713 | Cercocarpus ledifolius......----.----++-+eeeeeeeerees North Park, described .---............ LOM OT USIte ets eee eee eR a eee ae ne ee aoe Burro Peak, Weber Quartzite -........ wpagacoocooss 259 | Chalk Bluffs, described......-----.---eeeeeeseeeeeede Chalk Creek, Colorado Cretaceous Cache-la-poudre River, course of........-.--c--.-.-- g ChalybeaterSpringsmeenescae csc seiee ein ese eere = 143, Cache Valley, Humboldt Pliocene. .................. 406, 417 | Changes cf level in Salt Lake ..........-.-. ascooncs sandstone for building -.......---... 417 | Chataya Peak, Pah-Ute Range, altitude........-.... tergace:lnes),. oo 2enshieee sees Seasiens 417 diorite .......... Call’s Fort, Wahsatch Range, Ute limestone........ 405 mica-diorite .... CAMBRIAN Formation, Big Cottonwood Cafion...... 366 | Chervkee Butte, Medicine Bow Range, granite Beuver Canon .--....--.-...- 415 gray gneiss.... Bonneville Peak....-........ 457 ° rounded quartz Bex Elder Caiion............ 408 in granite... Cambrian Plateau........... 413 Ridge, Green River Hocene............ as City Creek Cafion........... 377, | Cheyenne, altitude m2 - 22) 2st eee =e ee en ann conglomerate in .......-.. 399, 457, 459 Pass, Carboniferous limestone ........... Hean Canon\.-22---2--2---2 + 488 | Chicken Soup Spring, Elko Valley ........-...--.--- Grantville Peak, anticlinal .. 459 | Chlorite in gneiss, Deer Mountain ...-...-.....----- Muddy Caiion, shales......-- 409, 412 Elk Mountain.-...--....----..--. Binonyhangeeesse- 2 --n-oe 553 Park Range Pogonip Ridge, White Pine. - 542 | Chokup Pass, Diamond Range Schell Creek Mountains ..... 425 | Chrysocolla....-..-.. AOS os Hees Witmtaan severe serene eee 199 | Chugwater, described......-......-..--.-----.------ CAMBRIAN BEATE AUaac ceiestismceencecec-curiesnece ene 412 * section of Triassic ... ...--...--------- Camel Peak, Elkhead Mountains, red gneiss ..-.-... 140,175 | Church Buttes, Bridger Eocene........-.-.--..---.- : brachyt@\eme- sce = 172 | Cinnam onum Mississippiense..--.-----.------------ Camp Floyd, Carboniferous fossils 8 | Citadel Peak, Raft River Mountains....+........... Cafion of Yampa Fiver ..-..-...--.---- City Creek, Wahsatch Range, Potsdam ..-.......-.. Canion-within-cafion structure.....-...-. tridymite in trachyte IWARBON BASING. sohacecne bee ee cete sate ce ismnisinieiniee Vermillion Creek ; age of coal rocks.......-.------------ Eocene ..-..------- AUHEGWS o n €09 TUG) omaanc obacronScbeodboserccepscesacec 263 Trigonia quadrangularis 91 PRION YR SUAS) o = oe seal eee alee eee eee 249 Trypodendron impressus ........---..- Seer 242 Uintacyon edax. .... .-.....--.- dencsnennas = 249 = INDEX. 873 ; Page. Page Fossils, Uintavrinus socialis...... Sceiaered Sales Nerslaere 296 | FRONT RANGE, Wahsatch .....-....2.-- 0s APC ACIS 393 Uintatherium robustum ..............-..-.. 2498 PHncoldssnl Cretaceousessssecceoe ene cece condeoeeeincne 332 AM bOMnIsMuCanls eerie aeee eee oreo istareeeae 249 Gabbrowilmenitenmiee see eeeces een eeeee eee eee 14 Unio belliplicatus..........-.-. Raise Nene is 328 ILA MEADE) BUI) os sasoeesoreonoo-o Insoles 13 iUnionHaydeniteses-eestesssese in Ong ie Galen asersasmcttenrsets.(5 5155s ae eee eee ee aMlalnes 731 Unio tellinoides 215 | Garden-Gate, Wah-weab Rango......-.....-.-.---00 566 lWiniohvetustiusieeseeenceeeceeee es Be sae eee 328 \ Willen WERE iaeeeeseoccscoaeicerctnaporson acc 561 Wiva pans 740 sHiamibtoners witelcseees sa aes ans sla~einincsco canes cos 491 thickness of... 74] Hum’s Hill, Fox Hill Cretaceous.............---.--. 241 Lake La Hontan terraces ......-. 741, 742 Hansel Mountains \basalte.coscsse--.- das so2- =e oo ean ose beiea ree aware esepiseee garnet in Archeean.......-... 109 Thy Olite ses cpe sealer eee glacial erosion........-..---.. 96 breccia gold in Archean ............. 109 salt on rhyolite hornblende-gneiss .......----- 99 | Morgan Peak, Wahsatch Range, Wahsatch lime- limestone in Archwan.-.....-. 107 stone : : Medicine Bow Peak, altitude. 94 | Morgan Valley, Humboldt Pliocene. .... eee eres manetite in Archean ....... 108 trachyites.- sseneoseeeeeeeae aie a pyrites in Archean .......... 108 Vermillion Creek Eocene........... red jasper conglomerate in Moss agates in Bridger Eocene ..............----.--- Archean jeer «pape case Fs 106 Niobrara Pliocene ..-..---4-2--..----< timber line ................... 97 | Mountain Dell Pass, Dakota conglomerate. .......:.. River nc ceo ces keniee ee oo eonen 142 Wells Station, Pah Ute Range, basalt....-. Butte, Aspen Plateau, Cretaceous...--..... 330 | Mount Agassiz, Uinta Range, altitude of ..........-. Peak, argilliteunder quartzite ............. 105 : Weber Quartzite..... cyanite in quartzite ......--.-.----.. 1.04) | Mio UNTWAUR Y JEG 1S tere eee eee ete ee ete 3 compressed pebbles in quartzite ..... 104 PHY OMS: <2 a- wasn same eee «ee 5 Medway Hot Springs, Provo Valley 318 Bonpland, East Humboldt Range, altitude. -. Melaphyr, Berkshire Cafion ......-...--. 839 structure of gneiss. ....-......-.. Melrose Mountain, Wachoe Mountains, diorite...... 478 Clark, Jaltitudeiofe ses -sse-isseece sees see eee Menilites in Tertiary .-----.-0-.----sec.nceen- seen 591 Corson, Wyoming Conglomerate...-....---- Mesozoic strata, Big Thompson Cafion.............- : 57 Davidson, altitude of..-......--------------- Rarkis\S tationges-sree- eee eis 54 NGioLite sce eeeeeecere me eee es Sentinel Hill, North Park .....-.... 117 Horeb, Ibenpah Mountains, Wahsatch lime- Metamorphism in Koipato Triassic..........-..----- 718 SONG Kes ceets oles eames Gaeemnee tees ereee sandstone, Black Butte........... 232 Lander, altitude of Mica-diopite, Chatayar bed eames eee emerenesaeieee ens 700 Lena, Uinta Range, Weber Quartzite....... ’ schist in Archzean, Colorado Range..-.--.-----. 25 Moses, Fish Creek Mountains, altitude...... Medicine Bow Range ...-.. 105 rhyolite...... Pahkeah Peak.........---- 776 Nebo, Wahsatch Range, altitude............ Shoshone Range .......... 637 : structure ...-...... Cambrian, Egan Cafion .............. 488 Neva, Cortez Range, rhyolite..-.....-...--. Spruce Mountain s-eeeee=-s-= ase 506 Weber Quartzite...... Microlites\imiquartzpe-sseee ee esee sees eceeeeee 676 Pisgah, Toano Range, anticlinal structure -. Microscope, value in determining rocks ...-....-.-.- 756 Richthoten, Colorado Range, altitude ....... Mill Cation, Wahsatch Range, Ogden Quartzite...... 377 described ..... Creek Cation, Wahsatch Range, Weber Quartzite. 368 rhyolite. ....-. Laramie Plains coalineys Hill Cretaceous 85 Steele Ridge, Fox Hill Cretaceous........... Miller Mine, American Fork Caton, Wahsatch Range 353 Wéry; altitude - 21, 97, 195 Roberts Peak ..----------------- 564 Pioneer Hollow, coal in Fox Hill Cretaceous. -------- 252 CWhitoubinole aes seeeceeen cece ee 543 Pisolite .....---------2- 22: -- <2 522-8202 ern 796 Ridge, White Pine, Cambrian 542 Plant remains in Carboniferous sandstone .---.----- 546 Braniteleeseeeahe===e= 542 Plate I. Horse-Shoe Curve, Green River, de- Porphyroids, West Humboldt Range ---..----------- 721 scribed .-.-.------------------------ 193, 267 | Porphyry-dikes, Colorado Range ....---.------------ 25 II. Summit Valley, Uinta Range, de- (feldspar), delessite in .--..--.------------ 828 scribed .--..---.-------------------- 196 Franklin Buttes ..-..--- 492 Til. Junction of Yampa and Green Rivers Granite Mountain 691 Cescribed.--..---------------------- 196 Montezuma Range 756 IV. Brown’s Park from cation of Lodore Ravenswood Peak 638 Gescribedes ssn 2-2 emai = ae 222 Seetoya Mountains 604, 606 Y. Tertiary Bluffs, Green River City, de- Spruce Mountain Bee 10; DIL SCribed).4=-- 2-02 =2s-es-e----=-5--=" 240 Truckee Cafion ....--.--------- 828 VI. Tertiary columns, Green River City, (hornblende), Augusta Mountains -...---- 651 described. sas. -cee--e-s--=\ Sonssoe 156 SABEWA Vit MOUNTAINS) 2 oie dae eecinn se einjiecioe omen ve 803 Salt-cubes in quartz of granite 10, 160, 603, 738 granite-porphyry .-----...-- 492 Salt-fields east of Pilot Peak ..-.......:...-..------< 501 Diamond: Valleyenc-s.-n-c-e sso -e etee ee 550 Osobb Valley.-.-..-.- sadsorecgnctanoacssae 707 Salt Lake, changes of level.-.........-- 432 City, position --.....-...-- 438 Thermal Springs 374 composition of water......--..--..--.---- 433 density of water --- 2-2. s2s-<-.s-<+c-e~-5 432 MPO AMF oe = are stale eve oe eicisiciee ete eo ateleteete 435 Valley, dryness of.................---...- 431 TAIN NG). procamonooceee MOoSSesOOS 439 Salt on rbyolite, Mopung Hills.........-.....-..---- 735 STpama, LENG GIES Goss os senor oescost eo doeasocc 50L Saint Cassiam fossils ene ee~ emcee sels sme ==lelsn ca =e 723 Saint Mary’s Station, Laramie Cretaceous. -..-.-...- 148 Sanders Peak, Laramie Hills, altitude of.----..-..-. 5 Sand-dunes in North Park ........-..-.---.--.------ 119 Sand-sculpture on basalt ...........----..---.------- 772 (EN) > — «Soe Amodeccoc se eroseoson 160 conglomerates... o-s6 == oes e = = 159 Sandstone for building, Cache Valley Tertiary. -..-- 417 Fort Benton group, Rock (COrGB) Gamer ae SoSee seen 89 Sanidin in basalt, Fish Creek Mountains...-.....--.- 656 nepheline-basalt, the Rampart ..-.-... ere 180 Santa Clara Peak, West Humboldt Range, limestone. 727 Sarcobatus vermiculatus .--...--.-.---.-..-.-.------ 790 Saurian teeth in Colorado Cretaceous ......-.--.---- 84 Savory Creek, North Park Tertiary........--..--.-- 165 Seoomys LESAN) «sa See ee seeeceo bec ansorosedacca 164 Saw-mill Creek, Uinta Range, Jurassic.......--..--- 257 884 INDEX . Page. Page. Schell Creek Mountains, Cambrian ..--....-.------- 485 | Shoshone Range, rhyolite. ..-.--.-.--------.-------- 623, 632 Scirpus Kingit ¢-- 22. 22202. coe ee eei emer nm 747 Weber Quartzite 619, 622, 631 Section A—B, Map I, described ......---.-------.--- 50 Springs, Augusta Mountains, Jurassic --- 656 II, described .--..--...---------. 229 | Signal Peak, Havallah Range, altitude ..........-... 673 DVaerdescribediee pease =a a= 608 Laramie HiJls, gneiss.-.-----...-.----- il iV, described sere eee eee ee 709, 802 section of Palzozoic-.-. 30 C—D, Map I, described 55, 129 zircon in gneiss .-.----- 11 described seese aie s- 222-6 oe 280 | Silicified wood, Niobrara Pliocene. .........-.--.---- 71 IV, described ...-....---- 483, 505, 531,555 | Silurian in*Box Elder Cafion -.---..---.-.---.-..-.-- 403 Ve described psn. -- == seria am a= 644, 844 | Silver Creek, Toyabe Range, rhyolite -.............. 630 (generalized) of sedimentary rocks of For- Wahsatch Range, tridymite in trachyte 320 tiethyParalle less seten a= melee ell 855 | Simpson’s Ridge, altitude....-....-.........-.---..-- * 144 of Archzan, Red Creek..-..-.-------------- 269 anticlinallt:52<3 =7a.cc0eee sce eee 144 Colorado Cretaceous... - 44,156, 264 section of Fox Hill Cretaceons. ---- 144 Dakota Cretaceous .--.------------------- 40, 264 | Skelligs Ridge, Elkhead Mountains, trachyte 171 Fox Hill Cretaceous .--.--------------- 144, 154,155 | SkuLL VALLEY ....------:--...-....- J: 2eR tS neaeaen 462 Green River Eocene......---------------- 219, 221 | Siater’s Fork, Elkhead Mountains, Laramie Creta- DMLASSi Cs ee essere a Sepesaetedoes 38, 80, 264, 293, 390 COONS’. jaded cence ce eo etaa ee ae ae eee eee 188 Laramie Cretaceous .-.-.-------~_-- 61, 145, 158,188 | Slater’s Fork, Elkhead Mountains, olivine in trachyte 176 Mesozoic strata.-.......---.--------:----- 91,275.) Smilax prandifoliaies.s—.t= 2 eee = eee eee eee 147 Palzozoic strata -.-30, 343, 346, 385, 398, 405, 544, 555 | Snowstorm Hill, Oquirrh Mountains, Carboniferous PrIASS1Otheearitee ronnie eee 34, 265, 292, 303 fossil. 0s. SS ise Soe aoe ee ae ee 446 Truckee Miocene, Fossil Hill....-.-...-.- 766 | Soapstone Caiion, Uinta Range 315 Upper Coal-Measures ....--.-..--- ------ 291,599 | Soda Lakes, Carson Desert, described ...-.....--..-- 746 Vermillion Creek Eocene....-.--.---.---- 212, 274 ; Gay-Lussite in-........- 749 Wahsatch limestone, Coal Creek .......--. 604 Lifevin Sane a2, Ree 749 Weber Quartzite, Weber Caiion ..-.-...-. 387 | Soil, Reese River Valley, composition of -.----....-- 635 Ridge, Yampa Plateau, anticlinal.......-..-- 285 | Soldier Caiion, Oquirrh Mountains, Weber Quartzite 449 Permo-Carboniferous 285 | Solidago occidentalis 747 SEETOY AS MOUNTAINS (acces = 6 22> =e e aaa enone 602: | ‘Sotr HOT SPRINGS .2¢ =< -s2-..-.--..-- 313 Crescent Peak, Elkhead Mountains. ....-. 171 Star Peake = seas cee 651, 657, 682, €93, 718, 723, 732 divide between Provo and Silver Creeks. 319 Uinta Range, described...-....-.....----.- 200 Dixie Valley.cs0 5 Be see fessagescesctet ie 559 thickness of. 5 200 Hast Cation Creek .....-.-.--....-.-..--.- 381 Upper Yampa River--2--- 2-522. enn 184 East Humboldt Range. -.:....-.----..---- 531 Valley of Burnt Fork.......--.....-.- ee 209 Elkhead Mountains .................-..-- 169, 176 WampagValley-cn ap eet een ee cease nee R24 Euclid Peak, Fountain Head Hills ....-... 522) |) Lridymite in thyolitess---eess=sese eee sees 430, 485, 516, 830 Hantz Peak, Elkhead Mountains. ........ 173 trachyteen-=--eee ese 317, 320, 375, 382, 384, 598 Frat ynenins cea. ee sees Scaisasoaee seieeees 568, 593 | Trinity Cabon, Montezuma Range, Archeen schists - 754 - hornblende prevaiting over sanidin....-.. 559 Peak, Montezuma Range, altitude of....-..-- 751 JACOD SHeLOMONtOLy..- ase - secon eee se 642 | Trona, an article of commerce.--........------------ 748 Kawsolt Mountaims:.-.-2<:22----2--- 6-5) 412 ||) PRUCKEX) (CANON ase oes eee eee ee PAS ScR Sa SSACO SSeS 827 Kimball's Parley suPark esi. o-e-e =e 384 GIG @seeans, coscoshossabaqeseneo 827 likewhyolites-aeteece act ceeeece coe 700 augite-andesite........-....- Snonee 830 Morgan aWalleys ss cccc see sree en otoeecee ae 381 Dasalt ooo aa ccies eee eeeeee 828, 831, 36 Palisade Caion, Cortez Range ..-..-...--. 585, 587 columuar structurein rhyolite. .... 830 Parkview Peak, North Park.............. 122 Giorite cs 2 5 ajesiasecsssee eases se 832 Pine Nut Caiion, Pah-Ute Range..:.... -. 700 feldspat-porphyry ------ .---- 828 Purple Hills, Virginia Range ..-e-.-----.- 833 Humboldt Pliocene se &31 (quartz), Cave Creek, East Humboldt Range 532 propylie a. seo eee ‘ 827, 831 Havallah Range .....-......--25; 684 rhyolite 5.3s) 2 eee 831, 834 Steves Ridge, Elkhead Mountains 170 trachy to foothillisection=).-ce asec seer 368 Fox Hill Cretaceous .-.. 276 PWN soc sssoneceenso Jsenmaios 355, 357, 360 Laramie Cretaceous. .--. 276 granite-porphyry.--...--. ..-.-.- 361 . Permo-Carboniferous .-. 275 EQUI AO) VERN Sapp pasccomnesoccéacd on 378 section of Mesozoic -.--. 275 Daurentiall 2s2ee- ces ana ose eee 377 Vertebrate remains in Truckee Miocene 631 physical description of..-..-..... 340 , VIRGINIA RANGE S222 ccceacscone ce ease econo 824 ; relation to Uinta Range.......--. 316 aNdesites. st aee cece Souleeelosesen 830, 841 section of Palzozoic strata. ..343, 346, 385, Astor Pass, trachyte.-..-.... pees . 348 398, 405 augite-andesite ..........--.--.---- 830 staurolite in Archwan.........--- 358 basalisee-e erence 810, 811, 828, 831, 836, 844 syenite-porphyry ---.--.......-.- 560, 365 Berkshire Cafion.....-. Sateen cers 839 thickness of Cambrian. ...- ase ae 366, 398 GaGiies ses seseces cseement cee -. 839, 842 conformable strata . .341, 370, 412 diorite.-...... F 832 Jturenians-s246 = eee 378 geological structure SERB) ; Ogden quartzite -.....- 364, 400 ° melaphyr -.....- ty a oe ne SS ae 839 : Wahsatch limestone.375, 3&6, 400 Mullon’siGap!st--caasicos oe cosacee B44 : Ute limestone... .-.364, 399, 410 PLOpPita wate eae ee ene -. 838, 840 trachyte...... 316, 317, 318, 375, 381, 382, 384 Purple; Hille cso eeeeeaeee cer see 833 - Ute limestone....-...- 364, 377, 399, 405, 410 quartz-propylite -...-...-..-..-.--. 844 Waverly beds 365, 400, 406 Ty OlIGO ee eeyeee eee 831, 834, 841, 846, 847 | WAH-WEAH RANGE...........-.------------ ose -566 Sheep Corral Cafion................ 837 praniteysis-a5--e sees Fasc 566 trachytemaesces-eecer ane 832, 833, 837, 841, 848 quartz-trachyte ..... Aeasnoss2005t 568 breaking through rhyolite. 835 trachyte..---.. eee at amen aemeete Lt 567 Mruekee| Canons 22. -2-easeneeeee ee B27 1) WASHAKIE BASIN a= seeiiiae samen tenis miasteeleeiimette eters 207 VOLCANIC REGION SOUTH OF TRINITY PEAK... 759 Bridger Hocene\..----s2seen- 5-52 a 215 Rocks, Green River Basin................ 236 erosion eee s2h)s care sabebetee ees 210 Niortht Paice seen eee eee aeee = 119 Laramie Cretaceous. .-.....--..- a5 208 - PinonyRansenpereese ni acsceseeere 558 Mountain, Wyoming Conglomerate ..... 209 Watch Hill, Elkhead Mountains, dolerite ..-.....-.. 177 W/ACHOT MODN TAINS Sepa ee eee eeee eee eeeeeeeeee 476 | Waverly limestone, Dry Cafion...........--..------- 446 ; age of granite....... d 478 Little Cottonwood. --. : 35 augite-andesite 480 hogant@anony -as4--e5 ee ee 40 - Page. Waverly limestone, Ogden Caiion...-----..---.----- 400 Vigne (CANON T.o syecoocebaos see sor Osdessh OEE Sonoee 384 Jurassic section..-....--.-.-----..--. 390 Permo-Carboniferous section. .-.-..--. 389 ALTIASSIO/SCCUIOM «=o a-'- ape sla =e 390 Upper Coal-Measures .-....---------- 388 Weber Quartzite section~............ 387 quartzite, Agate Pass, Cortez Range........ 574 Antero Creek, Uinta Range....-.. 301 Ashley Park, Uinta Range .....-. 268 Berry Creek, Uinta Range - ..---- 321 Bingham Cafion, Oquirrh Moun- : LOMO AS Ker Racsoasoocemscce erent 451 Black’s Fork, Uinta Range -- . -- 255 Burro Peak, Uinta Range ......-- 259 Clayton’s Peak, Wahsatch Range 373 Dalton Peaks, Cortez Range - .-... 608 i fossils in t..... ......-<...-...290, 323, 452 Fountain Head Hills .... ......-. 521 Gilbert’s Peak, Uinta Range -.---. 258 Gosi-Uite Range .:.. ......--...-. 503 Junction Peak, Uinta Range.-.w.. | 281 Kamas Creek, Uinta Range ...-.-. 316 Leidy’s Peak, Uinta Range. -...-. 260 Mill Creek Cafion ..... Svtodneseno 368 Mount Agassiz, Uinta Range. ..-- 322 _Lena, Uinta Range ees 239 Neva, Cortez Range....--- 610, 612 Osino Cafion...... Crean o eae 594 Peoquop Range .......-.--5..---. 507 Pinon Range ...-..----+:---....2 600 AIV OUP EUAN 2 Cleretoe = cintaler=imtael eine) 596 © Shoshone Range 619, 622, 631 Soldier Cation, Oquirrh Mountains 449 LOCK COMPU S eae serene ase ea 445 Tokewanna Peak....... ........- 256 Uinta Range discussed ........--. 199 thickness in .199, 256, 287, 323 Ute Peak, Uinta Range. ..-.....-. 288 Wagon Caiion, Cortez Range ..-.. 580 Whirlpool Cation, Green River .-. 286, River, thickness of Colorado Cretaceous. .--. 334 Dakota Cretaceous ....-- 333 WESTERN UINTA RANGE....-..---.--- 311 WEsT HUMBOLDT RANGE : - 3 andesite 716 715, 717 R9 Coyote Canon........ pase 719, 721 diabasoizsassese oes ates 716, 727 erosion in Buffalo Caijon -.- 728 geological structure of ..714, 716, 736 Fg 13) fo Jos SAE ee i ee 715 PTAaANitesos-pace esas eee 714 _Jurassic limestono .......-. 727, 732 Koipato Triassic. -.:716, 719, 728, 733 thickness. 719 porphyroids =< -- 222 - == 721 Prince Royal Caiion.....--. 727 Star Cafion........- AbEESEeo 719 Peak, -2s22 247 64, 71 72 205, 258 316 247 189 308 290, 294 246 221 277 209 285 731 196 287 279 Rv Macmnamas ee INDEX. | Page. | ald : \ : Yampa Peak, Upper Coal-Measures, cafion in....... 579); MampanVialley uLiinssiGr aaneeees se eteee aaemetaeeeee 4 Plateau, Section Ridge ...... OAS ee Seas 285 pri hes ‘ ‘ ‘ structure Of-ess-aeceeeeeeo eee ee 284 ; Manks Peaks aes 284 | Z-contortion in Wahsatch limestone .......--.------ 386, 400 Wyoming Conglomerate .-.. ....-.. 285 | Zenobia Peak, Escalante Hills, Uinta Range ....-... 287 Valley, Brown’s Park, Tertiary.----..-.-- 224 | Zirconia, estimation of, by R. W. Woodward ...-.... 397 Dakota Cretaceous. -- 184 | Zircon in Archean gneiss --. - 11, 101, 379, 397, 506, 533, 535 Fox Hill Cretaceous .-.-- 278 : =: SpBStrocds | 98, ae 488 Laramie Cretaceous........-...----- 278 | Zirke!, F. (See Authors.) ; ms i : nepheline-basalt ..........-.-.-.---- 186 Mount --.-...- ---2 22 seeeee core ce eee e ene eee ee 130, 136 , , nS 6 ‘ ; ~ “ . < ks * * > i 2 8324