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Home , Abiathar Peak, Absaroka Range, Beartooth Mountains, Index Peak (Wyoming), Specimen Ridge, Yellowstone River

DESCRIPTION OF THE ABSAROKA QUADRANGLE.

GEOGRAPHY AND TOPOGRAPHY. presenting an imposing panorama of high sierras streams, fed from the snow fields and lakes of the ferromagnesian minerals, chiefly hornblende and dotted over with snow fields, rising 3000 feet higher alpine ridges, flow southward and empty mica. Over large areas some of the rock masses The area of country mapped and described in above the level of . Index into the main stream. are distinctly bedded, while in others this folio includes the Ishawooa and Crandall Peak, the highest point in the northern Absarokas, Coniferous forests cloth the greater part of the indications of structure appear to be anTstruV-0 attains 11,740 feet and stands out conspicuously T-, . i . tureofthe quadrangles, each 30' by 30' in extent, , at least that portion included wanting. Jkviaences ot movement in rocks. and is situated in the northwestern extent an as a slender pinnacle, seen far and wide and easily within the Yellowstone Park and Yel­ the material and of the rearrangement part of the State of , the recognized by its graceful outlines. A few moun­ lowstone Park Forest Reservation. of the constituent minerals abound, such as northern line of the Crandall quadrangle coin­ tain trails, seldom used, lead over into the Park, Interspersed through these denser areas of forest the distortion of the individual crystals and the ciding with the boundary between Wyoming and but until recent years the Absarokas presented occur numerous gently inclined slopes, barren gnarled and twisted appearance of the segregated . The Ishawooa quadrangle lies between an unbroken barrier to travel along the entire of arborescent growth, while open glades abound patches of quartz, feldspar, and mica. Frequently parallels 109° 30' and 110° and meridians 44° and eastern side of the Park. For railway or wagon everywhere. Isolated peaks and broken crests of the effect of lateral compression is clearly brought 44° 30', the Crandall quadrangle lying directly traffic the best natural route across the crest of the main elevated ridges stand out above timber out by minute faulting and folding. Evidences to the north of it. Their combined area com­ the mountains from the Yellowstone follows Soda line, with only here and there a scattered and of metamorphism, caused by movement accom­ prises 1706 square miles. The eastern boundary Butte Creek to Cook City in Montana, just beyond stunted growth of weather-beaten trees. Along panied by pressure, may be seen all along the of the Yellowstone National Park, as defined in the boundaries of the area mapped, and thence the western side of the range, toward the Park, southern slopes and in the walls of the lateral the statute establishing the Park, lies 10 miles down Clark Fork Valley to the open plain. A the slopes are generally forest clad, but eastward canyons. The stream bed of Clark Fork, which east of Yellowstone Lake, a line nearly coincident striking feature of this region is the many deeply the timber becomes less and less dense and bare flows easterly along the base of the range and with the meridian of 110°. Along this line the trenched canyons, which in some instances have ridges are more and more apparent, with the serves as a well-defined line of demarcation Park adjoins for its entire length the country penetrated the to a depth of 4000 and 5000 lower slopes covered by luxuriant grasses. If between the and the Absa­ described in this folio. feet, presenting narrow defiles with somber, rug­ the lower eastern slopes are excluded, together rokas, lies wholly in Archean rocks. Just below The Absaroka district derives its name from ged cliffs of varied form and outline. with the barren area around Sunlight Basin, the mouth of Crandall Creek the river falls away the Absaroka Mountains, the prominent physical The main watershed of the plateau follows a about 80 per cent of the forest reserve is forest rapidly and enters an imposing gorge known as feature of the region. Beyond the Park limits the sinuous course with sweeping curves, maintain­ covered. The somber, black Pinus murrayana Clark Fork Canyon. A partial view of the can­ Yellowstone Park Forest Reservation ing, in general, a north-south direction. is the prevailing tree of the Absaroka Range. yon is shown in fig. 4 of the page of illustrations, embraces most of the range, having TimberYellowstone AtA thei northerni endici ot the range thei Watershed. Associated with it, but generally found at higher a reproduction of a photograph taken from a been, set, aside-JIT) by President -J ? HarrisonIT Reservation. divide lies wholly east of the Park, altitudes, occur considerable bodies of Pinus flex- commanding knoll, looking westward up the val­ under the act of March 3, 1891, as the first forest and Hurricane Ridge draining toward Clark Fork. ilis, and upon still higher ridges and exposed ley. It represents a narrow defile, with nearly reserve established by the General Government Continuing southward the watershed sweeps far slopes the variety P. albicaulis, with its smooth perpendicular walls rising in places over 1200 feet in the . As this reserve sur­ to the west, and, entering the Park, curves in white bark. The balsam, Abies subalpina, and above the stream. Occasionally benches and rounds the Park on the east and south, and stands and out along the crowning crest of the ridge spruce, Picea engelmanni, occur over all parts of shelves carved in hard gneisses parallel with the so closely identified with it, the Secretary of the that rises abruptly above Yellowstone Lake. It the range, but nowhere grow to any great height canyon break the abrupt rock face. The canyon Interior has placed it under the supervision of again curves eastward, encircling in its winding or size, although many of the trees appear uncom­ walls stand out in buttresses of grand ruggedness, the Park Superintendent, the Park rules applying course a large area of country which sends its monly graceful in the more open basins and shel­ piled one above another in^a most impressive man­ to the entire area. The boundaries of the reser­ waters through Thorofare Creek into the Upper tered park-like areas. Of all trees the Douglas ner. The canyon affords an exceptionally fine vation, as defined in the proclamation of the Yellowstone. Above the junction of the two fir, Pseudotsuga taxifolia, is the most stately and opportunity for a study of the Archean rocks and President, are laid down upon the folio sheets. streams the Thorofare drains more country than vigorous in its growth, developing a dark, rugged their forms of erosion in recent canyon cutting, With the exception of a relatively small area in the Yellowstone, while the amount of water car­ bark and towering above all its companions of the gorge being of much later origin than the the northeast corner of the Crandall quadrangle, ried by each is about the same. the forest, but it is found only in small numbers Archean platform of the broad valley above. this entire region of country may be Absaroka Three main streams Clark Fork, Stinking- scattered over widely separated areas. Nowhere considered as belonging to the Ran«e- water, and Shoshone rivers carry off the waters in the Absarokas can timber be said to be of SEDIMENTARY ROCKS. Absaroka Range. The Absarokas, so called from the east side. Clark Fork and its superior quality, but at some future time, if judi­ Back from the brink of Clark Fork Canyon the Drainage. from the Indian name of the Crow nation, extend two principal tributaries, Sunlight and ciously cut, it may meet all the requirements for Archean rocks stretch away in rounded hills and in a north-south direction for over 80 miles. Crandall creeks, drain all the northeastern portion local consumption. For maintaining and regulat­ mounds, dotted over with lakes and ponds of With an average width of nearly 50 miles, they of the country, being fed by numerous mountain ing the water supply of the Absarokas these for­ glacial origin. Upon the uneven and deeply stretch eastward beyond the limits of the area torrents both from the high plateaus of the ests are of incalculable value. But little land in eroded surface of this Archean conti- Paleozoic , mapped, while westward long, rugged ridges fall Absarokas and from the southern slopes of the the Absarokas is available for the purposes of nental land mass there was deposited away toward and Lake. At Beartooth Range. All the central portion of agriculture. The canyon bottoms consist for the unconformably a series of sediments andclays- the southern end the range, which is made up of the Absarokas drains eastward by the Stinking- most part of narrow, rocky defiles piled up with consisting of , , and clays, enormous outflows of volcanic material, is struc­ water, a clear, sparkling river flowing through a bowlders and without any covering of soil. In which were laid down partly as coarse material turally so closely connected with the picturesque valley hemmed in by rugged walls. broad, open valleys patches of rich in shallow waters as inshore deposits and partly Plateau and Owl Mountains that no well-defined Stinkingwater is one of the oldest geographical meadow lands border the streams, but, SSg and as finer sediments, mainly clays and muds, accu­ line of demarcation can be drawn. On the other names in the State of Wyoming, dating back to owing to the elevation of the country mulated as offshore deposits in more tranquil and hand, at the northern end the broad valley of the days of those gallant explorers, Lewis and and the consequent severity of the climate, only deeper seas. These overlying sediments represent, Clark Fork of the Yellowstone sharply separates Clark. In those days it was designated by the isolated areas, are suitable for the cultivation of so far as known, a great thickness of conformable the range from the Beartooth Mountains, the river fur trappers the River by the Stinkingwater a cereals. Many of the intermontane valleys and Paleozoic rocks, extending from the basal beds of flowing closely under the cliffs that mark the hot sulphurous spring well known as a landmark gently inclined lava slopes, notably Shoshone middle Cambrian age through the Silurian and northern escarpments of this vast pile of lavas. near where the river leaves the high mountain for Valley and Sunlight Basin, afford excellent graz­ Devonian and well on into limestones of the Car­ The Absarokas present a -broad, deeply eroded the open plain. The trappers are said to have ing lands capable of furnishing pasturage for boniferous period. On the south side of Clark plateau rather than a sharply outlined ridge, with taken the name from the Indians. The Shoshone thousands of cattle and horses. Fork Valley these Paleozoic rocks are well shown irregular lateral spurs putting out from the crest River drains all the southern portion of the in a long line of cliffs which border the valley for GEOLOGY. of a high well-defined watershed. Along the Absarokas represented on the map. It rises on its entire length, extending from far east side this mass of lava rises out of the plain the Wind River Plateau close by , Arcliean rocks. Crystalline granites, schists, to the east of Russell Peak. It is this line from an elevation of about 5000 feet, while on near the sources of the Yellowstone. It enters and gneisses represent the oldest rock masses in of cliffs which defines the northern mural face of the west slope the adjacent level is clearly indi­ the Ishawooa quadrangle at the southwest corner this region. They are regarded as con- Cr stalline the Absaroka Range, its present configuration cated by Yellowstone Lake and the wide bottom and flows northeasterly through the most impos­ stituting a part of the earliest rock gSJjJfand being in great part due to the action of glacial of the Upper Yellowstone, which may be taken ing and profound gorge in the mountains, the formations of the crust of the earth, gneiss- ice in its movement down the valley. The sedi­ as 8000 feet. Along the northern portion of the summit of Needle Mountain rising with precipi­ and, like similar crystalline masses elsewhere in mentary beds lie inclined to the southward at Absarokas the western base is defined by the tous slopes over 5000 feet above the bed of the Montana and Wyoming, are supposed to be of slight angles, varying from 1° to 5°, dipping valley of , with an approximate ele­ stream. After leaving the rugged canyon, the Archean age. In the area of country described away from the Archean mass of the Beartooth vation of 7000 feet above sea level. river meanders through a broad plain, dotted in this folio these Archean rocks are found only Mountains and passing beneath the accumulation Excessive denudation has carved this broad with meadows and patches of agricultural lands. in the northeastern portion of the Crandall quad­ of Tertiary lavas of the Absaroka Range. plateau-like body into a complex mass of rough Sheer cliffs of basalt and breccia, in places expos­ rangle, where they constitute the massive body of After these Paleozoic rocks were lifted above and rugged peaks and of jagged and ing nearly 3000 feet of vertical section, border the Beartooth Mountains. They are entirely the sea, erosion, cutting very irregularly upon the ' 11broken pinnacled 11 mountains inter- i remnantsPeaks and of both sides of the valley for many miles. Finally, unknown in the Absaroka Range, although other sediments, carried away varying thick­ spersed between long, crenulated but­ just beyond the eastern limit of the area mapped, exposures of the Archean occur at short distances nesses of strata, leaving rocks of very iowed°by tresses with bold escarpments rising above the the Shoshone joins the Stinkingwater, and thence, to the eastward, notably at Cedar Mountain, and different ages exposed at the surface. general level of the surrounding country. Gen­ through the Bighorn, pours into the broad Yel­ to the southward they come to the surface, occu­ These in turn were again protected from atmos­ tly inclined tables, in many instances inaccessible lowstone in Montana. pying large areas in the Owl Mountains. The pheric agencies by the pouring out of the more by reason of their abrupt encircling walls, every­ Only a. small portion of the Beartooth Moun­ Beartooth Mountains, at least so much of them as recent breccias and lavas, which in places rest where characterize the larger physical features of tains, which form one of the most prominent comes within the Crandall quadrangle, consist directly upon the Cambrian rocks and in others the range. The higher peaks and castellated physical features of this part of the Beartooth almost wholly of mica-gneiss, amphibolites, and rest upon the Silurian, Devonian, or Carbon­ remnants of table-lands do not follow in definite country, comes within the Absaroka Mountains- schists, distinctly light in color,, well shown in iferous. The most complete exposure of the trend, but lie scattered over the entire region. district. The entire crest of this range and all the sheer cliffs exposed along the mountain slopes Paleozoic beds is shown at Hunter Peak, lying Needle Mountain, situated in the southeast corner the higher summits are situated in Montana, and and in the polished glaciated hills rising above in the angle between Crandall Creek and Clark of this dissected plateau, and and Dead some of them stand among the loftiest peaks to the valley of Clark Fork. Fork Valley. They attain a thickness of about Indian peaks, near the eastern boundary, attain be found in the State. Beartooth Butte, with an In mineral composition, texture, and physical 2000 feet. Here the beds rise boldly above the elevations of over 12,000 feet above sea level. altitude of 10,500 feet above sea level, is the features the Archean rocks exhibit constant vari­ stream, with the Cambrian sandstones at the base Numerous peaks with commanding outlooks highest point of the mountains in Wyoming. The ations and modifications. Much of the rock struc­ and the Carboniferous limestones forming the reach altitudes of more than 11,000 feet. Several slopes of the range fall away in broken, accidented ture consists of a mingling of both coarse and fine summit of the mountain. At numerous places of the more prominent points lie within the Park, hills and ridges toward Clark Fork. Numerous quartz and feldspar, with varying proportions of along this northern escarpment deep lateral can- yons, carrying streams coming down from the . Each is distinguished' by its own pecu- mottled limestone presents one of the most char­ Throughout this entire series not a fossil was Absarokas, break through the lavas and cut into liar fossil fauna; at the same time each is equally acteristic topographic features to be found in the procured that could be called characteristic of

the underlying sedimentary rocks, in which case well defined by lithological characters. The entire Paleozoic series,' and nowhere is Mottled__ _ . the Silurian period. Nothing indicat-. the strata are frequently seen exposed for several Flathead and the Gallatin are usually found asso­ it better displayed than along Clark »mestone- ing even a possible grouping of forms c^acter- istic fossils. miles up the valley, notably along the different ciated, but with varying thicknesses of the basal Fork Valley, extending for miles as a bold escarp­ was obtained. In fact, with the upper tributaries of Crandall Creek. beds. In this way they are exposed all along the ment difficult to scale. It is massively bedded, beds of the Gallatin formation, which carry In fig. 5 of the page of illustrations will be northern escarpment of the Absarokas from Soda and its prominence is in great part due to the organic remains regarded as belonging to the top found a reproduction from a photograph of a Butte to Sunlight Creek. Just east of the limit crumbling away of fissile beds beneath the escarp­ of the Cambrian series, the fossiliferous strata characteristic view of the sedimentary cliffs. of the area mapped they stand out in a most ment and the erosion of shaly ones above, expos­ suddenly cease. In the Jefferson formation only Along the base of the cliffs the contact Sedlmentai. imposing manner, appearing as isolated limestone ing the hard, resistant surface that forms the top partial and most fragmentary proof of the exist­ between the crystalline and sedimen- cliffs- tables resting upon an Archean platform. The of the mottled limestone. It occurs as a dark- ence of a fauna remains. This is true for the tary rocks is largely concealed by forest growth, total thickness assigned to the Cambrian rocks brown crystalline ledge, its mottled appearance entire region of the Absarokas. Such partially but the irregular broken line between the light- is 1100 feet; at least that seems to be their being due to the cherty character of the dark-gray preserved fossils as were obtained in the lower colored limestone strata and the somber lavas is broadest development where best exposed and and brown lenticular patches scattered through beds assigned to the Jefferson indicate the exist­ sharply defined. Persistency in the continuity of where their summit is most clearly defined. Upon it. The weathered surfaces are invariably rough ence of species that possess a wide vertical range certain beds is also well shown in the illustration paleontological evidence the Flathead formation and rugged, with narrow seams of indurated clays and might occur high in the Cambrian or near by the conspicuous bluffs of Cambrian limestones, corresponds to and has been correlated with the and flinty aggregations disseminated through the the base of the Silurian. In the same way, at and by the inclined benches carved out of the middle Cambrian, while the Gallatin has been beds and standing out from the main mass of the other localities the species procured from near, interbedded clays and shales. This line of cliffs assigned to the upper Cambrian. Excellent limestone. No well-preserved fossils have been the summit of the terrane are such as possess a is maintained for over 25 miles, stretching from localities for the study of these rocks may be obtained from the mottled limestone, conse­ wide vertical range and might be found as low as the Snowy Range eastward to the outlet of Sun­ found near the entrance of Republic Creek, on quently no evidence based upon paleontological the Silurian, but at the same time are known to light Basin, beyond the limits of the area mapped. the ridge between Crandall and Closed creeks, facts determines the precise age of the bed. occur elsewhere with typical Devonian species. North of the river Paleozoic rocks are known and at Beartooth Butte. Provisionally it has been placed at the base For these reasons it is frequently impossible to in only two localities, resting upon the Archean Flathead formation. This formation, which is of the Gallatin formation, the few trilobitic frag­ determine either the base or the summit of the

slopesA of Beartooth Mountain, ' and of _Paleozoic exposed in a number of localities throughout ments found indicating a facies more closely allied formation with any degree of precision. these the picturesque mass of Bear- JJc&S£rth northern "Wyoming and central Montana, derives to the Gallatin than to the Flathead fauna. DEVONIAN. tooth Butte is the more prominent. Fork' its name from Flathead Pass, in the Bridger Immediately above the mottled limestone the The second locality is the angle between Bear- Range, in the latter State. The Flathead forma­ fossiliferous belt of the formation is foreshadowed Rocks of the Devonian period in the Absarokas

tooth Creek and Clark Fork Canyon, where a tion in the Absarokas has been divided into three by > the fissile nature of the argillaceous. Fossiliferous .... consist mainly of limestone, and may usually be slightly inclined limestone table is found. In series dependent upon lithological distinctions and calcareous shales, passing upward belt- readily identified wherever the overlying Carbon­ both these areas the uppermost rocks consist of persistent over wide areas: (1) quartzite and into more and more massive limestone and hold­ iferous strata are exposed. As yet no subdivi­ Cambrian strata, all later beds having been , (2) shales, and (3) limestones. It can ing interstratified shaly layers and beds of sions of the Devonian have been worked out upon removed by erosion. The only other locality in not be affirmed positively that the brecciated .material. These limestones are usually lithological grounds, and the organic remains, the Absaroka district where Paleozoic rocks lowest members of the Flathead are highly crystalline, varying in color, but with a while characteristic, are meager in species, with stone. occur is Sunlight Basin. Here there is a broad, exposed along the Absarokai escarp­ prevailing yellowish-brown tint, becoming decid­ an apparent vertical range throughout the entire plateau-like mass of nearly horizontal rocks, con­ ment, for there is no evidence as to the thickness edly darker toward the top. Fragmentary thickness of 250 feet assigned to them. They sisting of Devonian and Carboniferous strata. The of the quartzites and sandstones, but it is certain remains of fossils are occasionally found through­ have been correlated with the Three Forks for­ underlying rocks are, so far as known, nowhere that wherever they occur next to the gneiss and out the limestone beds, although well-preserved mation, the designation given to the Devonian exposed. The relation between the sedimentary schist they consist, as already mentioned, of detri­ species are only found either immediately over strata exposed at the three forks of the Missouri rocks and the Tertiary lavas is well shown, the tal material derived from the ancient Archean the mottled limestone or in bluish-gray limestone River in Montana, where they carry a small and latter filling up all the uneven surfaces in the land mass. For the most part the lowest beds at the summit of the strata. Such species as have varied typical Devonian fauna. Without any sedimentary beds and in places rising high above consist of coarse quartz grains compacted into been determined clearly show the existence of a apparent interruption in the continuity of oceanic the level of the limestone plateau. The Paleozoic sandstone or quartzite, the degree of hardness characteristic upper Cambrian life, the non-fossil- sediments, the brown and dark-gray limestones of cliffs of the Absaroka continue westward into being dependent mainly upon the amount of pres­ iferous mottled limestone lying between two the Silurian pass upward into bluish-gray beds Yellowstone Park, where they present much the sure they have undergone. Beds which in places sharply defined faunas and separating the middle holding Devonian fossils, which are regarded as same physical features of sedimentation, and consist of loose and friable material, disintegrating from the upper Cambrian. The thickness of the representing the base of the Three Forks terrane. where they have been studied and compared with readily, are continued elsewhere as firm and dense Gallatin formation has been estimated approxi­ Three Forks limestone. The bluish-gray lime­ other localities of similar rocks in the Park. rocks weathering in solid blocks. Varying mately at 400 feet, with a development of the stones at the base alternate with shaly beds and Identical geological horizons have been correlated, amounts of oxide of iron tinge the beds either mottled limestone varying from 100 to 150 feet. fine clays, the latter also occasionally and in consequence the same nomenclature has red or yellow, the iron frequently serving as the carrying organic remains. These pass Bmelfonef,y SILURIAN. jI A v JJ J T x shaly beds, been adopted for the Absaroka country. cementing agent for the more compact beds. In upward into bedded limestones, gener- ««i«"« The basal sediments are mainly siliceous, pass­ some instances this produces a banded structure, Rocks assigned to this period in the Absarokas ally of light tints of purple and blue, ing gradually up through transition beds into which not only affords an excellent means of consist mainly of limestones, showing, as regards with intercalated thin layers of indurated earthy nearly pure limestones. From this determining the slight angle of inclination of the angle of deposition, conformity of sedimentation sandy material. Recurring alternations abound, point to the top of the series of beds theCharacterasedime°n- of strata but serves as a base line for the measure­ with the underlying Cambrian strata. Viewed in but with limestone as the prevailing rock. In exposed limestones form the great block ment of the thickness of deposits. in a broad way, they present similar physical places near the top of the formation the shaly of sediments. Some beds are highly arenaceous, Passing upward the siliceous material becomes conditions in lithological habit across the entire beds exhibit bright red and orange tints, but this others carry a large amount of argillaceous mate­ finer and is mingled with more and more mica­ width of the Absaroka Range from Lamar River is by no means a safe guide in tracing the strata, rial, while still others hold enough ferruginous ceous and argillaceous material, the latter derived to Sunlight Creek, but in detail they show con­ as in many other places these highly colored matter to impart a distinct character to the strata. from the decomposition of feldspars in the crys­ siderable variation in bedding, crystallization, and layers appear to be wanting. Over wide areas Brecciated, nodular, and cherty deposits, persistent talline rocks. > It is the alteration of these latter position. No divisions of the Silurian into epochs there are slight evidences of organic remains, con­ variations in color, and the tendency of impure sediments under pressure that has has yet been made, the entire formation being sisting mainly of coralline fragments too poor for argillaceous beds to take on a shaly structure caused the shale formation. Gradually designated the Jefferson limestone, a name derived specific identification. Such typical Devonian over large areas, make it possible to divide this the beds become more and more calcareous, until from the mountain range in Montana where the fossils as Atrypa reticularis and Spirifera engel- great development of sediments into a series of they pass over into nearly pure limestones, form­ beds are well exposed. Along Clark Fork Val­ manni determine with certainty the geological formations recognized solely by their physical ing the third division already enumerated. ley the Jefferson limestone stands out conspicu­ horizon of the Three Forks formation. Localities features. In many instances the geological posi­ From the coming in of the first limestone to ously as one of the sedimentary walls that make yielding small groupings of a Devonian marine tion of these formations may be determined with­ the top of the Flathead formation the sediments up the grand escarpment rising above the river. fauna may be found at near the out the aid of paleontological evidence. consist mainly of limestone, separable As already mentioned, the broad bench usually eastern boundary of the Yellowstone Park, at . -,. . -i. Limestones. into beds of varying condition 01 sedi­ found above the mottled limestone is carved in Mount Miller just north of the Park, and again CAMBRIAN. mentation or mode of weathering. In some shaly beds, but the next cliff back from the valley on Little Sunlight Creek in bright-colored shales Resting directly upon the uneven surface of instances they are divided by narrow shale beds. presents a fairly continuous wall of Silurian rocks. below Carboniferous beds. the Archean mass comes a series of beds made Grains of glauconite not infrequently impart a Jefferson limestone. In general the ledges con­ up of coarse and fine material consisting of both greenish tinge to limestone belts, which may be sist of massive beds of highly crystalline, bluish- CARBONIFEROUS.

angular and rounded grains of quartz, mingled traced for long distances. At a number of black or ogray J limestone,1 but not Highly . ., crys= Rocks of the Carboniferous period fall readily with fragmentary pieces of the underlying crys­ localities along the northern escarpment of the infrequently all traces of bedding are {SSi|eo?lulsl1gray " into two sharply defined formations based upon talline rock. This detrital material was all Absarokas the Flathead formation affords a few obliterated until the coming in of inter limestone. lithological distinctions indicating derived from the disintegration, under atmos­ characteristic fossils. The widely distributed stratified bands of yellowish-brown arenaceous marked changes in conditions of sedi­ pheric agencies, of the granites, schists, and species Ptychoparia antiquata occurs on the broad deposits. The beds near the base are for the mentation, the lower formation being gneisses, and everywhere represents a beach accu­ Cambrian tables TOO feet above the Archean most part dark and somber in color, growing calcareous, the upper one siliceous. They have mulation deposited on a steadily but slowly platform of Clark Fork Canyon. Near the same lighter toward the top of the series, becoming been designated the Madison limestone and the receding land surface. It represents the basal horizon at several localities in the neighborhood occasionally almost creamy white in the bright Quadrant quartzite. Nowhere within the Absa­ member of the Cambrian period, so far of Sunlight Creek gray limestones carry HyolitJies glare of the sun. Seams of white calcite often roka district are the Quadrant quartzites exposed, as it is exposed in this part of the Basalher of mem-the" primordialis. Both these species characterize traverse the Jefferson beds. Under the blows of although only a short distance eastward they are country. The beds pass upward into the middle Cambrian strata in the Yellowstone the hammer the dark-colored beds frequently shown on Dead Indian Ridge in strong force, fine-grained sandstone carrying more and more Park. give off a strong fetid odor, which is rather char­ several hundred feet in thickness. In the Absa­ calcareous material, until they become nearly Crallatin limestone. Directly overlying the acteristic of this horizon. It is difficult to give roka Range the sediments of the Paleozoic ocean pure limestones, retaining this character to the thinly bedded limestone of the Flathead comes even a rough estimate of the thickness of these have undergone so much erosion that not only summit of the beds assigned to this period. the Gallatin limestone, the name for the terrane Silurian beds, owing to the lack of recognized has the Quadrant quartzite been removed but Rocks of the Cambrian period have been being appropriately derived from the range of lithological limits and the absence of well-pre­ with it also a very considerable thickness of the divided into two sharply defined series, based mountains where it occurs especially well devel­ served fossils to define its boundaries. From our Madison limestone. Along the northern face of primarily upon their organic remains. Twoshar , oped. In the Absaroka Range the Gallatin lime­ present knowledge the thickness is estimated at the range Carboniferous rocks are for the most The underlying series of beds, recog- JfSSbS? stone may be divided into two distinct broad about 300 feet. part wanting, but are well shown capping nized as representing a single epoch, has beds' beds separated by calcareous shale, the lower No positive evidence based upon paleontolog­ Hunter Peak and along the bottoms of several been designated the Flathead formation, while known as the mottled limestone and the upper ical data has been obtained which determines of the deeply trenched lateral cannons. The the overlying terrane is known as the Gallatin generally designated the fossiliferous belt. The the geological position of the Jefferson beds. most impressive exposure of the Carboniferous

J*. occurs in Sunlight Basin, where there is a broad nearly 600 feet. These sandstones are every­ the sea, and coincident with it a denudation of changed to marble, the clays baked to argillites, body of Madison limestone nearly 1000 feet in where capped by breccias. The region presents the new continental area took place, accompanied and the Montana sandstones compressed to com­ thickness. The narrow defile of the main Sun­ a depressed area occupied by sedimentary beds by deposition of fresh sediments, unconformable pact indurated quartzites. light Creek presents nearly vertical walls of encircled by lavas rising for 2000 feet above the to the uplifted Laramie. In this connection it The breccias and lava flows were thrown out similar strata on both sides of the stream. lowland. A small area of sandstone lies higher may be stated that the Laramie, with its marine from numerous vents and centers of volcanic Madison limestone. The Madison limestone up the river, near the junction of the Stinking- and brackish faunas, along the east base of the activity, now for the most part obliter- Brecclas and takes its name from a prominent range of moun­ water with Wapiti River. In Shoshone Valley Absarokas attains an elevation of about 6000 ated by the piling up of successive Iavaflows- tains in central Montana, just west of Yellowstone the Montana stretches along the stream bottom, feet. On Big Game Ridge, to the west of layers of later material. Gradual transitions in Park. Within the Park the Madison maintains only here and there exposed beneath the coarse the volcanic plateau, the sandstones have been mineral composition, texture, and mode of occur­ a thickness of quite 1600 feet, but the Absarokas gravels of the flood plain and the still higher uplifted to nearly 10,000 feet above sea level. rence of the ejected lavas may be found, but, offer no point where the summit of the formation detrital material upon the hill slopes. Neither Pinyon conglomerate. Between the blocking taken as a whole, the Absaroka Range presents can be determined. By gradual transition the valley affords suitable opportunity for a study of out of the mountains composed of sedimentary an elevated volcanic region showing from north Three Forks formation passes into a p.nel these sandstones, no good vertical sections being rocks at the close of the Laramie and the pouring to south great uniformity in its geological fea­ finely crystalline gray limestone, in Styifme-' exposed. Either the beds are dislocated and out of enormous masses of igneous rocks, there tures. It consists essentially of a broad dissected places more or less cherty, which in disturbed by intrusions of igneous rocks or the were deposited at a number of localities beds plateau, greatly eroded and deeply trenched by a certain localities consists of irregular nodular surface of the country is covered by Pleistocene of coarse conglomerate. They are not exposed system of canyons exposing from 2000 to 5000 bands, but this latter feature is not maintained deposits. within the Absarokas, but are found just west feet of nearly horizontal or only slightly inclined over any wide area. Viewed in a broad way, Montana formation. This formation embraces of the range high up on the mountains, resting breccias and basalt sheets. Above the canyon this great development of limestone is dark bluish both the Pierre shale and the Fox Hills sandstone, unconformably upon the tilted and eroded walls the bare, rough ridges frequently rise gray at the base, coarsely crystalline, and thinly it being impossible in northeastern Laramie sandstones. They consist of nearly hori­ beyond timber line for 1000 or 2000 feet more, bedded. It passes gradually upward into light Wyoming to distinguish between the amfpox HIM zontal beds designated the Pinyon conglomerate, offering additional sections across the accumulated colored masses, rough and rugged in texture and two subdivisions frequently so well the name being derived from the mountain where material. It has been found possible to divide less finely bedded. The upper portions consist defined elsewhere. Here the Montana was essen­ they occur admirably exposed, on the divide this enormous bulk of breccias and of light bluish-gray beds, in places nearly white. tially a sandstone-making epoch, although by no between and Gravel creeks, in the lavas ejected from many widely dis- The characteristic weathering with a tendency to means uniform in its sedimentation and varying Yellowstone Park. Nearly all of this material tributed fissures and orifices into six produce rounded forms, together with the light greatly in its mode of bedding. The sandstones consists of rounded, smoothly worn well-defined groups, dependent upon the relative coloring, renders it possible to recognize the are usually white or yellowish gray and occasion­ -Lpebbles mingledo with sand and ogravel, wornsmoothly pebbles age of eruption. They represent as many dis­ upper members of the Madisqn limestone upon ally brown, due to varying amounts of iron It has accumulated to a thickness of l?dgaenddwith tinct periods or volcanic chapters in the long far-away ridges, all the more readily as it not deposited with the quartzitic material. They are nearly 600 feet, and indicates clearly graveh geological history of the range. Beginning with infrequently forms the summit of prominent more or less impure, with recurring alternations the shallow water inshore deposit. The Pinyon the earliest in order of eruption, they have been peaks and the capping rock of long lines of cliffs. of interbedded dark clays and shales, the latter conglomerates stretch southward in patches designated as follows: early acid breccia, early In detail it is by no means easy to correlate or occurring as lenticular bodies far more strongly in the Wind River Mountains, and under the basic breccia, early basalt sheets, late acid breccia, compare individual beds from widely separated developed in certain localities than in others. breccias of the Wind River Plateau. This for­ late basic breccia, late basalt sheets. areas, in spite of the marked uniformity of sedi­ Good exposures of such black and gray shales are mation, while unrepresented in the Absarokas, The acid and basic breccias pass into each mentation when the limestone formation is con­ seen on Bobcat Creek, where it leaves the moun­ is mentioned here on account of its importance in other by gradual transition products of interme­ sidered as a unit. tains and enters the valley of . the geological history of the region. It was laid diate mineral and chemical composition. The acid As previously pointed out, the line of demar­ In the absence of a fossil flora and fauna the down after a very considerable erosion of the rocks are so designated because they contain a cation between the Devonian and Carboniferous beds are only provisionally assigned to the Mon­ Laramie, and probably before the eruption of relatively large amount of silicic acid, together is drawn upon paleontological evidence Madison tana. Black argillaceous shales carrying organic the greater part of the volcanic material, since it with a high percentage of alkalies. When there based upon the earliest appearance of fauna- matter accompanied by fragmentary plant remains, contains no fragments of the Absaroka breccias. is an excess of silicic acid and the rock is com­ organic remains usually assigned to the latter such as stems, twigs, and partial impressions of On the other hand, the basic breccias cap the con­ pletely crystallized, it is usually accompanied by period. A study of these fossils shows that the leaves, have been found, but all too poor for glomerates of Pinyon Peak and have served as a free quartz. Basic rocks, in distinction from acid Madison limestone throughout its entire develop­ specific identification. Marine Cretaceous inver­ protection against the wearing away of the more ones, carry less silicic acid, but contain a corres­ ment belongs to the lower Carboniferous, without tebrate fossils also occur sparingly, but their easily eroded beds. Provisionally they have been pondingly large amount of the bases iron, mag­ any distinct foreshadowing of a higher or coal- specific characters could not be made out. It is assigned to the Eocene period, being subsequent nesia, and lime. With this increase of the bases measure fauna. About 80 species have been possible that some of these higher sandstones to the Laramie movement. Possibly they were there is usually a development of what is called determined and described from this terrane. All should be assigned more properly to the Laramie synchronous with some portion of the uptilted ferromagnesian minerals hornblende, pyroxene, the fossil collections obtained from the Carbonif­ formation. Livingston formation in Montana, which, from its and mica. Under the discussion of each type of erous were submitted to Mr. George H. Grirty, Laramie formation. Sandstones of this epoch somewhat meager fossil flora, is supposed to be breccia there will be found a detailed account of who regards the. Madison limestone as a paleonto­ are not definitely known in the Absaroka district, more closely allied to Cretaceous than to Tertiary its mineral composition. logical unit corresponding closely to the Choteau- but a short distance east of the southern half the time. In any case they represent the latest sedi­ Early acid breccias. The oldest volcanic lavas Waverly division of the Mississippi Basin. Nearly Ishawooa quadrangle they occur over large ments laid down in this region before the pouring found in the Absaroka Range comprise a series one-half of the fossils have been specifically areas, conformably overlying the Montana. It is out of the breccias. Their geological position of eruptiveA rocks made up-1- almost Agglomer-. , identified with forms occurring in the Waverly not always easy to discriminate between the two and relations to both the uplifted Laramie sand­ entirely of fragmental material consist- S£d£2?d limestone, and about one-quarter of them are formations. The Laramie is far less uniform in stone and the overlying breccias may be seen in ing of agglomerates, silts, muds, and tuffs' described for the first time from the Madison its sedimentation and the beds are less pure sand­ the generalized section of the igneous rocks of tuffs, designated early acid breccia. In color they limestone. Fourteen species are found throughout stones. It is characterized by terrestrial vegeta­ the Yellowstone Park given in folio 30 of this present usually light tints, varying from grayish the entire 1600 feet of beds assigned to the Madi­ tion found also elsewhere in the Rocky Mountains series. white to lavender. Occasionally they are green­ son, and are for the most part characteristic of and known as the Laramie flora. It is a forma­ IGNEOUS ROCKS. ish brown, due in part to the decomposition of the lower Carboniferous elsewhere. In the tion of great economic importance, as nearly all the ferromagnesian minerals. The color is con­ Absarokas all evidence of life in the Paleozoic marketable coals found in northern Wyoming and POST-LABAMEE VOLCANIC EPOCH. stantly changing, dependent upon the texture of sea ends with the limestone-making epoch of the Montana occur in the Laramie sandstone. Near Closely associated with the post-Laramie move­ the material and the degree of decomposition Madison. the close of the epoch evidences of shallow ment, but followed by a long period of erosion of of the included minerals. In mineral composi­ water, cross bedding, and frequent fluctuations The entire series of Paleozoic sediments exposed the Mesozoic land area,7 there occurred Volcanic , , tion they vary considerably, but con­ in the range is shown in the columnar section, of sea level foreshadow marked changes in the the first of those volcanic eruptions eruPtions- sist mainly of hornblende-andesites and andesitt" atTd hornblende-mica-andesites. Flakes of mica-ande." which represents a thickness of 3200 feet. At geological development of the pre-existing conti­ along the Absaroka Range which subsequently, sites. the base of the section 'TOO feet is assigned to the nental area. in Tertiary time, submerged all the surrounding dark-brown biotite abound through the Flathead, which is about the average thickness of country. This eruptive material, forcing its way greater part of these breccias. Some of the most POST-LARAMIE MOVEMENT. the formation. At the top 1600 feet is given to upward, followed lines of least resistance along siliceous varieties carry phenocrysts of quartz, and the Madison limestone. Nowhere within the With the close of the Laramie formation the or near planes of faulting, or wherever strain had in sufficient quantity to place the rock under the limits of the area mapped does the Madison attain deposition of conformable Paleozoic and Mesozoic been greatest upon the weakened or crumpled head of dacite or quartz-bearing andesite. Occa­ so broad a development, but only a short distance sediments ceased. Oscillations of sea level took strata. It continued to pour forth during a long sionally the more basic varieties carry a larger beyond the borders of the Crandall quadrangle it place, the accumulating sediments being laid period, lasting, with intervals of comparative rest, amount of ferromagnesian minerals, when some is estimated to measure that amount. down partly in shallow and partly in deep waters. throughout Eocene and a great part of Neocene form of pyroxene is usually found accompanying In this region no unconformity of beds by depo­ time. Evidence of partial cessation of activities the hornblende. These latter rocks show transi­ CRETACEOUS. sition has been recognized, and in this sense they is seen at one or two places in the erosion of lavas tions into the overlying basic breccia, but in most Rocks of Mesozoic age occupy but limited spaces may be said to be conformable throughout from before the. pouring out of fresh masses. In cases the contrast between the two forms of acid in the Absaroka district. All sediments of the middle Cambrian time to the summit of the other localities seasons of volcanic inactivity are and basic rocks is sharply drawn, by topographic Juratrias and of the larger part of the Laramie, although evidence of this continuity is recorded by fossil flora representing vigorous configuration as well as by color. Cretaceous period are unknown. Only andaiar|er wanting in the immediate country represented by growths of forest trees and plants which were A characteristic feature of these early acid beds assigned to the Montana formation J|c*^|n^ the Absaroka folio. The entire region was again repeatedly submerged by renewed outbursts of breccias, but one by no means confined to them, of the upper Cretaceous are exposed, elevated above the sea. In the Absaroka Range muds and tuffs. is the occurrence at several localities of numerous all intermediate sediments, if ever present in this the great Paleozoic sedimentary beds The Absaroka Range was built up by the slow angular fragments of gneisses and schists, evi­ region, being submerged beneath accumulations were tilted up at low angles, with more withVisioca- accumulation of volcanic breccias with interbed­ dently brought up from below at the time the of breccias and basaltic flows. Such exposures of or ,less dislocation,,. , . ^but thei region. is. so tion. ded basaltic flows, which buried every­ breccia was thrown out by explosive action. the Montana as occur are found along the eastern submerged beneath more recent volcanic outflows thing beneath them to a depth of In the country embraced within the Absaroka base of the range, where they come to the surface that very little of the structural features can be several thousand feet. Volcanic ag­ Range the early acid breccias are known only in from beneath the volcanic lavas, or in the deeply made but. Profound orogenic movements took glomerates, silts, and tuffs, and extrusive lavas, the northwest corner of the Crandall quadrangle. trenched canyons of the Stinking water and Sho- place, and the entire region became one of moun­ or those that have poured out and cooled near They are found all along the west wall of shone rivers. Along the Stinking water Canyon tain building accompanied by folding and faulting. the surface, make up by far the greater part of Republic Creek, in the bottom of the deep can­ the stream has cut its way through breccias and All evidence tends to show that this uplifting the range. Other rocks playing any part in the yon formed by the junction of Timber and Closed agglomerate, but where it leaves the narrow defile was contemporaneous in all the ranges. For this building up of the mountains have already been creeks, and again at the head of Cache Creek and enters the more open country, sandstones of reason, and on account of its great geological described under the head of Paleozoic and Meso­ Valley. In the first two localities they rest the Cretaceous period come to the surface upon importance, this uplift has been named the post- zoic sediments. In close proximity to the lavas directly upon the Paleozoic limestones, and are both sides of the river, on the north side extend­ Laramie movement. With this elevation a greatly these latter rocks have been more or less altered clearly shown to be the earliest eruptions of a ing back in bluffs and benches to a height of enlarged continental land mass was raised above by heat and pressure ; the limestones have been vast pile of lava. In the valley of" Republic Absaroka 3.

-r-V ^*«ifc>- Creek they present a mass of rudely bedded, present a rough and ropy surface, like recent vol­ grained, with but few well-developed megascopic of light-colored occur in the dark breccia coarse breccias, dipping to the south, away from canic scoria, piled up in a most irregular way. The constituents, mainly augite, olivine, and plagio- along the escarpment of Trident Plateau and on the slightly inclined limestones. cementing material was thrown out in a liquid clase. In chemical composition they the east slope of Overlook Mountain. In the Absaroka Range, but within the Park, state, carrying with it angular and subangular show within certain limits considerable of0tne°eariyn Late basic breccia. Overlying the late acid . . .. _. - basalt sheets. the early acid breccias are shown for several miles fragments of the earlier lava. The great bulk of variation, with corresponding change breccias comes a second series of basic breccias, along the bottom of Cache Creek Valley, the result the breccia shows indistinct bedding. A tumul­ in mineral development. Many of these flows of the deep trenching of the canyon. Above tuous piling up of large masses of agglomerate, covering large areas are decidedly feldspar basalt, them lie the basic breccias, capping the high ridges the result of violent explosive action, from widely being rich in alkalies and carrying both leucite and on both sides of the stream. To the east rocks distributed fissures and vents, forms a character­ orthoclase, and are the extrusive members of the resembling the acid breccias are exposed at one istic feature of these breccias. Not infrequently absarokite group described later under the head­ or two localities. They are shown near the head they contain enormous andesitic and basaltic ing "Intrusive rocks." Leucite has been deter­ of Lodge Pole Creek and on Dry Creek, but they bowlders measuring 5 or 6 feet in length, and mined from a number of localities in sufficient are basic in character and are so intermingled occasionally double that size. The interbedded amount to form a characteristic feature of several with the undoubted basic breccias that they have sheets are usually fine-grained, dark rocks, like basaltic outflows. Phenocrysts of plagioclase and not been discriminated from them upon the map. normal basalts elsewhere. Some of them are pyroxene are frequently well developed in the Similar rocks occur in Sunlight Basin beneath a highly feldspathic and carry phenocrysts of horn­ feldspar basalts. Basalts cap many of the higher great accumulation of basic breccia. In general blende, pyroxene, and orthoclase feldspar. peaks and ridges, presenting to the eye for long where both series of breccias occur together they Through the central portion of the Absarokas distances broad, plateau-like summits with pre­ are easily recognized by their strong contrast of these early basic breccias stretch across the entire cipitous walls on all sides. These basalt tables color, by differences in their forms of erosion, and width of the range, from the broad open valley on are remnants of much broader fields. Many of by their marked unconformity, the earlier breccias the east to the shores of Yellowstone Lake on the them in cooling have developed fine showing evidences of extensive erosion before the west. They may be well studied by following examples of columnar structure, the Columnarstructure of pouring out of the later and more basic rocks. In up the valley of the Stinkingwater from the pillars«n oi» ibasalt i extendingT across thei the basalt. some instances there appear to be tran- Transition entrance of the canyon, thence up Middle Creek entire thickness of the flow and standing out in FlG. 1. DARK BRECCIA OF PYROXENE-ANDESITE AND BASALT RESTING sition rocks, passing over from one rocks* and across Signal Hills to the terrace bluffs the canyon walls in a most impressive manner. UPON AN ABRUPT HILL SLOPE OF LIGHT-COLORED HORNBLENDE- series to the other without any marked physical known as Signal Point, near the southeast corner Perhaps the grandest display of this structure is ANDESITE BRECCIA. or mineralogical break. of the lake. Along this line the continuity of shown at the head of Mole Creek in the bold agglomerates, and andesitic sheets, closely resem­ In a few localities the finer beds seem to be the early basic breccias is broken only at one or escarpment under Sheep Mesa, where the smooth bling the earlier deposits of erupted material. In made up of the mingling of material from both two points by overlying basalts and by flows of jet-black basaltic columns spread out with a mineral composition this second series . T . -i i i i Hornblend types of rock, as if the beds had been formed of rhyolite which skirt the foothills above the lake radial, fan-like structure. Here the columns and 01 basic rocks is nearly f identical with andesite,pyroxene-and the finer material from areas both of acid and of shore. The red, ropy, irregular breccias are well surrounding basalts are glassy and show abun­ the early basic breccia, consisting of basic rock washed down into depressions and shown along the Stinkingwater River from the dant evidence of being part of a surface outflow. hornblende - pyroxene - audesite and and basalts. irregular basins. entrance of the canyon to its junction with Fish- Over large areas the basaltic flows are wanting. pyroxene - andesitej ., tree. iroin» -,horn­ As shown in the Absaroka Range and west­ hawk Creek. Impressive mural faces are dis­ They do not occur capping the breccias in the blende and basalts. Hornblende-bearing rocks ward along the Yellowstone Valley, the acid played in the south face of Saddle Mountain and northeastern portion of the Absarokas, nor on do not appear to characterize large areas, but at breccia appears to have been thrown out from on the south walls of Castor and Pollux peaks, the southwestern slopes of the range draining certain outflows at widely separated localities numerous and independent centers of eruption, towering above Little Lamar Valley. One of the toward Yellowstone Lake. Within the Yellow- they abound with many well-developed individual none of which heaped up any very great mass of most accessible places for the study of these stone Park these basalts are well shown in the crystals. Pyroxene-andesite, with both augite lava. But from all of such centers they were the breccias is along Clark Fork Valley, where they abrupt precipices of Mirror Plateau, facing Lamar and hypersthene, is evidently the predominating earliest eruptions forced to the surface. Early rest directly upon the Paleozoic sedimentary Valley. From here they stretch southeastward rock, although normal olivine-bearing basalts acid breccias are exposed only in limited areas, rocks, as shown in fig. 5 of the accompanying across the crest of the range between Lamar and occur in both the coarse and the fine volcanic due mainly to vast accumulations of still later page of illustrations. Stinkingwater rivers, and are admirably exposed ejectamenta. The two basic breccias are singu­ lavas. In no instance do they attain any great Fantastic and ever-changing forms of rock on Wapiti Ridge and in the massive walls on larly alike in their mode of occurrence. Appar­ elevation, the exposures being due to extensive sculpture, the results of erosion upon volcanic both sides of Shoshone River. They extend over ently the conditions governing their eruptions erosion and characteristic trenching of narrow tuffs and loose agglomerate, characterize k a broad belt of country, with a general northwest- were much the same. In the early breccias the gorges. Induration of these breccias may be seen the early basic breccia, but are by no sculPture- southeast trend. outflows are more frequently ropy and scoria- in several localities, but it is by no means a charac­ means confined to eruptions of any one period. Late acid breccia. These breccias do not play ceous, without bedding. In the later the material teristic feature. Occasionally dikes of pyroxene- They abound high up on canyon walls wherever an important part in that portion of the range thrown out ordinarily consists of coarse angular andesite have been observed cutting acid breccias, layers of more or less indurated rock or basaltic lying within the Absaroka district, but westward, fragmental material near the sources of erup­ presenting additional evidence as to the relative bowlders rest upon friable material. They are inside the Park line, they present an imposing tion, diminishing in size with distance from the age of the two types of rocks. usually carved out of the rock along edges of appearance. Unlike the early acid breccias, they vent. Nowhere can the contact between the late JEarly basic breccias. Overlying the early acid cliff furrowed by frequent shallow drainage are not so deeply buried beneath later erupted acid and basic breccias be better studied than in breccias occurs a vast accumulation of volcanic channels. Many of these slender vertical rock masses, but form the summits of several peaks the open basin of Mountain Creek, along the material with occasional interbedded columns stand closely packed together, recalling and elevated ridges, and are spread out in thin eastern slopes of Overlook and Chaos mountains. flows of basalt, the entire mass near the in some ways the so-called " fossil forests " found sheets over the earlier basalt tables. They are The bottom of the basin and lower slopes are withinter= orifices. oi ejection. . -,being . piledMI up to, a in this region. The famous Hoodoo Basin at the found only along the western borders of both the formed of acid breccia, while the ridges jutting height of nearly 5000 feet. They cover head of the Lamar River, frequently visited by Crandall and the Ishawooa quadrangles, occurring out from the main crest of the range consist of a far more extensive area than any other group tourists to the Yellowstone Park, is the most as the eastern extension of more massive bodies. dark-brown breccia superimposed upon the early into which the lavas have been divided, stretching notable locality for these grotesque figures. They They may be seen high up on the ridges near the flows. The overlying rocks weather in rounded, from the northern limit of the range southward are also admirably shown in the lower portion of sources of Middle Creek, in the bottom of the dome-like forms,) the erupted material being firmly beyond the boundaries of the Ishawooa quad­ Stinkingwater Canyon and along the west side of broad basin of Mountain Creek, and on the slopes cemented in a compact mass, but furrowed at rangle. All the northern portion of the Absaroka Wapiti River. of Overlook Mountain. They closely resemble frequent intervals by shallow drainage channels. Range is made up of these breccias, which extend Early basalt sheets. Next in order, and directly the early acid breccia, consisting of Wherever the late acid breccias are wanting Hornblende- westward over the northeast corner of the Park. resting upon the uneven surfaces of the early hornblende - mica - andesite and horn- mica-andes* the basic breccias have spread out upon the basalt Like the early acid breccias, they consist of both basic breccias, comes a succession of blende-andesite, in places carrying con- hornblende- sheets and over wide areas form the summits of coarse and fine material, showing marked differ­ basalt flows which in places near their Successionofubasait° siderable pyroxene-andesite, together with Pyrox= many high ridges and elevated plateaus. In some flows. J-