DESCRIPTION OF THE DEVILS TOWER QUADRANGLE

By INT. H, Barton and C. C. O'Harra.

GEOGRAPHY. margin of the higher levels of the Great Plains, and owing to the steeper dip of the strata, it narrows of small streams. On the top of the plateau rise presents cliffs and steep slopes descending a thou­ to a ridge having a steep western face. This ridge the Missouri Buttes a mass of igneous rock, form­ Position and extent. The Devils Tower quad­ sand feet into the drainage basin of Cheyenne is interrupted by water gaps of all the larger ing a small group of prominent summits, of which rangle embraces the quarter of a square degree River, one of the most important branches of the streams .in the southeastern and eastern portion of the highest reaches an altitude of 5372 feet. The which lies between the parallels 44° 30' and 45° Missouri. From this basin northward there is a the hills, which rise in the high limestone plateau, most notable feature in the region is Devils Tower, north latitude and meridians 104° 30' and 105° succession of other basins with relatively low inter­ cross the region of crystalline rocks, and flow which rises on one of the ridges west of Belle west longitude. It measures approximately 34^ vening divides, which do not attain the high level through canyons in the flanking rocks of the Fourche River. It has a towerlike form (see figs. miles from north to south.and 25 miles from east of the Great Plains to the south. eastern side of Cheyenne River. All around the 1 and 2), nearly circular, and is about 100 feet in to west, and its area is very nearly 850 square Drainage. The northern portion of the Great Black Hills the limestone plateau slopes outward, diameter at the top. Its sides are nearly vertical miles. It comprises a portion of the northeastern Plains above described is drained by the middle but near its base there is a low ridge of Minne- and it attains an altitude of 5117 feet, or about part of Crook County, Wyo. Its north limit is branches of Missouri River, of which the larger kahta limestone with a steep infacing escarpment 600 feet above the sandstone platform from which the Wyoming-Montana State line. The southeast­ members are Yellowstone, Powder, Little Missouri, from 40 to 50 feet high, surmounted by a bare, it rises. Its height above the river a short distance ern two-thirds of the quadrangle lies on the north- Grand, Cannonball, Owl, Cheyenne, Bad, and White rocky incline which descends several hundred feet east of its base is a little less than 1250 feet. era extension of the Black Hills uplift and its rivers. On the summit of Pine Ridge not far south into the Red Valley. This minor escarpment and Features pertaining to the Great Plains. The northwestern portion extends onto the Great Plains. of the escarpment is Niobrara River, which rises in slope are at intervals sharply notched by canyons, southwestward dip of the uppermost sandstones of It embraces a portion of the Belle Fourche and the midst of the plains some distance east of the which on each stream form a characteristic narrows the Black Hills series carries them beneath soft Little Missouri valleys, including the head of the north end of the Laramie Mountains. To the south or "gate." shales, and in the northwestern third of the quad­ latter. Being a part of the Black Hills and the are the Rio Grande, Platte River with two large The Red Valley. The Red Valley is a wide rangle there is a wide area underlain by soft rocks Great Plains, this quadrangle exhibits many fea­ branches heading far back in the Rocky Mountains, depression that extends continuously around the presenting characteristic topography of the Great tures of both, and a general account of these prov­ arid Arkansas River, which crosses the plains to the hills, with long, high limestone slopes on the Plains. The valleys are wide and most of the inces will be given before the detailed description southeast and affords an outlet for the drainage from inner side and the steep hogback ridge already slopes are gentle or not high. Here and there a of the quadrangle is presented. a large watershed of mountains and plains. Between mentioned on the outer side. This valley is in harder bed gives rise to a low escarpment, or ridge, * the Rio Grande and the Arkansas are Cimarron many places 2 miles wide, though it is much nar­ but it is an insignificant feature as compared with GREAT PLAINS PROVINCE. River and numerous smaller streams heading in the rower where the strata dip steeply. It is one of the higher ridges and mountains of the adjacent General features, The Great Plains province western portion of the plains. Between Arkansas the most conspicuous features of the region, owing Black Hills. The elevation of the plains portion is that part of the continental slope which extends and Platte rivers is Republican River, rising near in no small degree to the red color of its soil and of the Devils Tower quadrangle ranges from 3500 from the foot of the Rocky Mountains eastward the one hundred and fifth meridian, and an extended the absence of trees, the main forests of the Black to 4600 feet in greater part, with a general down­ to the valley of the Mississippi, where it merges system of local drainage in eastern Kansas and Hills ending at the margin of the limestone slopes. ward slope to the north and east. The principal into the prairies on the north and the low plains Nebraska. As a rule the larger streams flowing out of the hills stream is Little Missouri River, which rises in the adjoining the Gulf coast and the Mississippi cross it without material deflection, between divides southwest corner of the quadrangle and flows north­ THE BLACK HILLS. embayment on the south. The plains present wide most of which are so low as to give the valley the ward for the first 15 miles and then northeastward, areas of tabular surfaces traversed by broad, shal­ General feat ares. In western South Dakota and appearance of being continuous, but in its middle its course being closely parallel to the strike of low valleys of large rivers that rise mainly in the eastern Wyoming a small group of mountains eastern section it is extensively choked with Olig- the rocks. Its valley is wide and flat bottomed for Rocky Mountains, and are more or less deeply known as the Black Hills rises several thousand ocene deposits. the greater part of its length, with a declivity of cut by narrower valleys of the lateral drainage. feet above the plains. Having abundant rainfall, it The hogback rim. The hogback range consti­ about 20 feet a mile in its upper portion and of Smooth surfaces and eastward-sloping plains are constitutes, through its vegetation and streams, an tuting the outer rim of the hills is for the most 10 to 12 feet a mile in its course northeastward. the characteristic features, but in portions of the oasis in the semiarid region. The hills are carved part a single-crested ridge of hard sandstone, vary­ From the east the Little Missouri receives numerous province there are buttes, extended escarpments, from a dome-shaped uplift of the earth's crust, and ing in prominence and in steepness of slope. At branches, usually dry the greater part of the year, and local areas of badlands. Wide districts of consist largely of rocks which are older than those the north and south and locally along the middle which rise in the shale and sandstone slopes of the' sand hills surmount the plains in some localities, forming the surface of the Great Plains and which western section it spreads out into long, sloping Black Hills. Elkhorn Creek is the largest affluent notably in northwestern Nebraska, where sand contain valuable minerals. The length of the more plateaus. It nearly everywhere presents a steep from the east, but Hulett and T. L. creeks and dunes occupy an area of several thousand square elevated area is about 100 miles, and its greatest face toward the Red Valley, above which the crest Government Canyon have drainage basins 10 to 20: miles. width is 50 miles. The hills rise abruptly from the line rises several hundred feet, but on the outer square miles in area. From the west the Little The province is developed on a great thickness plains, although the flanking ridges are of moderate side it slopes more or less steeply down to the Missouri receives a stream known as North Fork, of soft rocks, sands, clays, and loams, in general elevation. The salient features are an encircling plains that extend far out from the Black Hills which gathers water from an extensive shale region spread in thin but extensive beds sloping gently hogback ridge, constituting the outer rim of the in every direction. The hogback rim is crossed in the northwest corner of the quadrangle. Thomp­ eastward with the slope of the plains. These hills; next, a continuous depression, the Red Valley, by numerous gaps or canyons, which divide it son and Prairie creeks ar^smaller affluents, usually- deposits lie on relatively smooth surfaces of the which extends completely around the uplift; then a into level-topped ridges of various lengths. At containing a small amount of water. Cabin Creek older rocks. The materials of the formations were limestone plateau with infacing escarpment; and the southern margin of the hills Cheyenne River rises in the plains near the southwest corner of the derived mainly from the west and were deposited, finally a central area of high ridges culminating in has cut a tortuous valley through the ridge for sev­ quadrangle, but flows across the sandstone hogback layer by layer, either by streams on their flood the precipitous crags of Harney Peak at an altitude eral miles, and the Belle Fourche does the same range and empties into the Belle Fourche. plains or in lakes and, during earlier times, in the of 7216 feet. Two branches of Cheyenne River toward the north end of the uplift. sea, Aside from a very few local flexures, the nearly surround the hills and receive many tribu­ GEOLOGY. GEOGRAPHIC FEATURES OF THE QUADRANGLE. region has not been subjected to folding, but has taries from them. DESCRIPTION OE THE KOCKS. been broadly uplifted and depressed successively. The central area. The central area of the Black Features pertaining to the Black Hills. The During earlier epochs the surface was even smoother Hills comprises an elevated basin, eroded in crys­ Devils Tower quadrangle presents some characteris­ The strata coming to the surface in the Devils than at present. Owing to the great breadth of the talline schists and granite, in which scattered rocky tic features of the Black Hills topography, mainly of Tower quadrangle have a thickness of about 4800 plains and their relatively gentle declivity, general ridges and groups of mountains are separated by the sloping plateau of the flanking sandstone ridges. feet. The rocks are mainly sedimentary, compris­ erosion has progressed slowly notwithstanding the parklike valleys. The wider valleys are above the This is deeply cut by the valley of Belle Fourche ing sandstones and shales, with smaller amounts of softness of the formations; and as at times of freshet heads of canyons of greater or less size, which River and its numerous side branches. A short limestone, gravel, and sand. They range in age many of the rivers bring out of the mountains a become deeper and steeper sided as they extend distance east of the southeast corner of the quad­ from Triassic to Quaternary. Their general charac­ larger load of sediment than they carry to the outward to the northeast, east, and south. rangle are the steep slopes of the Bear Lodge Range, teristics, thicknesses, etc., are given in the columnar Mississippi, they are now locally building up their The limestone plateau'. The limestone plateau a local uplift rising considerably above the general section sheet. Igneous rocks traverse the sedimen­ valleys rather than deepening them. forms an interior highland belt around the central northwestern slope of the Black Hills. In this tary members, but they are of relatively slight Altitudes and slopes. The Great Plains province hills, rising considerably above the greater part of area are the highest lands of the region, the alti­ extent. While the Spearfish red shale is the lowest as a whole descends to the east about 10 feet in each the area of crystalline rocks. Its western portion is tude being 5800 feet in the southeast corner of the formation exposed, the region is underlain by about mile from altitudes approaching 6000 feet at the much more extensive than its eastern, and is broad quadrangle. There is a rapid descent of both 1500 feet of older sedimentary rocks lying on foot of the Rocky Mountains to about 1000 feet and flat, sloping gently downward near its outer ridges and valleys to Belle Fourche River, on which schists and granites, as shown in the structure above sea near Mississippi River. The altitudes margin, but being level near its eastern, inner side, the altitudes are 3940 feet at the southern margin sections. These formations appear in the higher and the rates of slope vary considerably in different which presents a line of cliffs many miles long and of the quadrangle and 3640 feet at the eastern portions of the Black Hills uplift southeast of this districts, particularly to the north, along the mid­ often rising 800 feet above the central valleys. It margin. In the pdrtion of the quadrangle east of quadrangle and are described in other folios. Some dle course of Missouri River, where the general attains altitudes of slightly more than 7000 feet, in the river there are long sloping ridges and outlying further references to them are given in the section level has been greatly reduced. West of Denver the places almost equaling Harney Peak in height, and plateaus, the latter capped by masses of Lakota or on "Underground waters," page 9. central plains rise to an altitude of 6200 feet at the forms the main divide of the Black Hills. The overlying sandstones. West of the river there is Sedimentary Rocks. foot of the Rocky Mountains, and maintain this streams which flow down its western slope are rapid rise, to a general plateau, capped by this elevation far to the north along the foot of the Lar- affluents of Beaver Creek to the southwest and of same sandstone. It has an altitude of about 4500 TRIASSIC SYSTEM. amie Mountains. High altitudes are also attained the Belle Fourche to the northwest. Rising in feet at the south and 4300 feet at the north, SPEARFISH FORMATION. in Pine Ridge, a great escarpment that extends shallow, parklike valleys on the plateau, they sink constituting the divide between Belle Fourche and Relations and character. The oldest exposed from near the north end of theLaramie Mountains into deep canyons with precipitous walls of lime­ Little Missouri rivers. The front of this plateau sedimentary rocks in the Devils Tower quadrangle eastward through Wyoming, across the northwest stone, in places many hundred feet high. The is deeply incised by numerous canyons, and it rises are the red beds of the Spearfish formation. The corner of Nebraska, and for many miles into south­ limestone plateau, extending southward, swings irregularly from the Belle Fourche in long slopes entire thickness of the formation is not revealed, ern South Dakota. Pine Kidge marks the northern around to the eastern side of the hills, where, interrupted by many local breaks due to the cutting but the upper members are extensively exhibited Feet. in nearly horizontal position along Belle Fourche been discovered in the Spearfish formation, and eastern part and near Miller Creek in the southern Shales, partly concealed______25 River and the lower courses of the tributary its precise age is unknown. From the fact that part of the quadrangle, the lowest beds, for a Massive brownish sandstone______6 streams, particularly in Red and Barlow canyons it lies between supposed Permian below and marine thickness of 20 to 30 feet or more, are of pink or Shales, partly concealed______35 Nonfossiliferous limestone____.______3 and along Blacktail, Whitetail, and Lytle creeks. Jurassic above, it has been regarded as Triassic in red color. In Bush Canyon they are pink, but on Reddish shales, largely concealed______60 The most complete exposures in this quadrangle age, but it may prove to be Permian, at least in Miller Creek they are distinctly red. These red Massive reddish-yellow sandstone, thin bedded at beds resemble the red shales of the Spearfish for­ the top.__.____-.______62 are in the Belle Fourche Valley near the mouth part. The planation unconformity by which it is Thin sandstones and shales______6 of Barlow Canyon, midway between Hulett and separated from the Sundance formation represents mation, but their position above the prominent Gray shales, largely concealed______. ______14 Devils Tower. The thickness of" the Spearfish all of earlier Jurassic and probably part at least of underlying sandstone indicates their true relation. Heavy gray sandstone______8 Gray and drab shales_____.______14 strata exposed here is approximately 200 feet. Triassic time. Several beds of massive, platy, or shaly limestones, Massive sandstone______2 In the disturbed area near the head of Lytle varying considerably in character in different local­ Gray sandy shales and thin sandstones______25 JURASSIC SYSTEM. ities, occur in the shales. North of lower Miller Massive sandstones______4 Creek, in the southeast corner of the quadrangle, Thin sandstones and shales______16 SUNDANCE FORMATION. the thickness of the exposed beds is apparently Creek some of these limestones contain numerous Greenish-purple shales, lying on red beds__ ___ 5 greater than at the mouth of Barlow Canyon, but General relations. The Sundance formation is clay-lime concretions, or nodules. Nearly all the 366 limestones contain considerable sand, and on well- the variableness of the dips and the wooded con­ exposed in a wide area in the southeastern portion Section of lower part of Sundance formation on east bank of dition of the area prevent accurate determination. of the quadrangle. The upper and middle beds weathered outcrops, where percolating water has the Belle Fourche at Hulett. had opportunity to dissolve out the lime, the sandy Feet. Between Hulett and Devils Tower the formation are characterized by gently sloping hillsides and Yellow, massive, highly ripple-marked sandstone, outcrops extensively in slopes, but there are cliffs broadly undulating or flat surfaces. A heavy residue as a rule masks the original nature of the slight reddish tinge______45 where the formation is cut by the river or is pro­ massive sandstone in the lower beds gives rise to rock. The limestones are more resistant than the Soft, yellow sand stone ______10 Very soft, greenish shale with local thin sandstones 24 tected by the massive sandstone of the overlying extensive terraces near the base of the slopes and to inclosing shales, so that in many places they out­ Massive but soft, yellow sandstone______8 Sundance formation. Along the smaller valleys small canyons along many of the streams. This crop prominently on the slopes, but very few of the Flaggy yellowish-gray sandstone with scattered exposures are sufficiently clear to admit of accurate lamellibranchs and brachiopods.______3 the exposures are for the most part in steep can­ formation affords the chief grazing lands of the Greenish shales______.___ 12 yon walls, the bright-red color of which is in region east of Little Missouri River. measurement, and it is not everywhere practicable Buff sandy shales with a few lamellibranchs and striking contrast to the somber tint of the Sun- Rocks. The formation consists mainly of shales, to determine the nature of the rocks from the brachiopods ______1 Thin, papery gray shales___---__-______3 dance slopes above. partly sandy, and sandstones, and has an average weathered materials. The thicknesses vary from a Gray sandstones with chalcedonic pebbles in upper The formation consists largely of a mixture of thickness of about 340 feet. It comprises several few inches to 10 feet, but mostly from 5 to 6 feet, part ______1 and the beds are from 5 to 40 feet or more apart. Thin purplish-white soft shales______-J fine clay and sand in somewhat variable propor­ members which are persistent throughout the Gray sandstone______-J tions, but the sand is in few places, if anywhere, in region, as well as most other portions of the Most of them are highly fossiliferous, especially in Fine white shale much resembling fire clay, lying on sufficient amount to give the rock the nature of a Black Hills uplift. There are basal shales, as a the upper portion of the formation, but some fossil­ red beds______4 sandstone. At many horizons fresh surfaces show rule from 75 to 90 feet thick; buff sandstone, iferous layers occur throughout. The fossiliferous 112 an indistinct nodular structure, due to incipient mostly massive, 40 to 60 feet; and at the top 150 slabs are conspicuous features on the surface, as are Section of upper beds of Sundance formation on Cabin concretionary development. to 200 feet of shales. The latter are in most also the weathered individual fossils, particularly Creek, near southern edge of Devils Tower quadrangle. Feet. The color of the beds varies between light pink places of reddish color in their lower portion. Belemnites, which is in places very abundant. Morrison shale. and Indian red, the deeper shades predominating Limestones, nowhere more than a few feet in thick­ Locally this fossil occurs in profusion among the Massive yellow sandstone, very soft (Unkpapa?)_ 12 Thin gray and purple shales with a few lime-clay in fresh exposures. Here and there green laminse ness and in many places very fossiliferous, occur other fossils of the massive limestones, but its chief nodules_.______20 are observed, but these, although sharply outlined, abundantly in the upper part of the formation. occurrence seems to be in thin, highly sandy beds Flaggy yellowish sandstone______2 and in nodular limy layers. Many of the fossilif­ Yellowish-gray sandy shales with some lime clay are in few places more than an inch or two thick. With the exception of one sandstone bed at the nodules and many small, irregular fragments of Several thin beds of gypsum, most of them less top, the sandy beds are mostly in the lower part. erous layers show abrupt vertical passage into rion- chalcedonic material______18 than 2 feet thick, occur near the top of the forma­ The shales which so greatly predominate in the fossiliferous layers, even where no lithologic break Slabby sandstone______4 Purple and gray sandy shales with some lime-clay tion, interbedded with soft shales. Gypsum of formation vary somewhat in purity, and at many of any character is recognized. concretions ______16 secondary deposition occurs in thin seams and nar­ places in the lower part of the formation they are Local sections. The following detailed sections Massive, highly fossiliferous sandy limestone.___ 4 row veins. The line of demarcation between the sandy. Because of their softness they are as a rule show the thickness and the composition of the beds Concealed below. Spearfish and overlying Sundance beds is distinct, poorly exposed. The sandstone at the top of the in this formation: 76 owing mainly to the great difference in color, but formation is yellowish and probably represents the Section of Sundance formation 2 miles north-northwest of Fossils. Fossils are abundant in the Sundance there is no marked evidence of erosional uncon­ Unkpapa sandstone of the eastern portion of Hulett. beds, particularly in the limestone layers in the Feet. formity between them, although they are separated the Black Hills. It is massive, but extremely Morrison shale. upper shales, but some occur in the basal shales by a long hiatus. soft, and on this account is nowhere well exposed. Massive yellow sandstone, very soft (Unkpapa?)__ 30 also. The most characteristic species is Belemnites The formation is nearly horizontal in much of The greatest thickness observed is 40 feet, midway Shales, partly concealed______25 densus, represented by hard, dark-colored, cigar- Highly fossiliferous limestone______6 the outcrop area, but there is a prevailing low dip between Devils Tower and the Missouri Buttes. Shales in talus.______10 shaped bodies varying in size from an inch or less to the north-northwest. The highest exposure is The thickness at other localities is given in the Fossiliferous limestone, containing beleuinites, etc , to 4 inches in length and having a radiated struc­ but chiefly concealed______10 in the southeast corner of the quadrangle, at an subjoined sections. Highly fossiliferous limestone, many oysters, few ture when seen in transverse section. In many altitude of more than 5000 feet, due to uplift by The most conspicuous member of the formation is belemnites, occasional limestone pebbles 2 or 3 places these weather out on the surface and are a the igneous intrusions of the central Bear Lodge a bed of sandstone, about 40 feet thick, which lies inches in diameter.______8 conspicuous feature in most of the upper shale out­ Chiefly concealed, but many fragments of limestone area. The lowest exposure is on Buck Creek at near the bottom. It consists of a massive bed of conglomerate ______8 crops. In the upper shales there also occur the the eastern edge of the quadrangle, at 3600 medium-coarse-grained rock. In places, on weath­ Highly fossiliferous limestone with few lime-clay following species: Ostrea strigilecula, Avicula wyo- pebbles ______6 feet above sea level. Throughout the greater part ering, it exhibits a flaggy structure, and some layers Yellowish-gray shales not well exposed, but evi­ mingensis, Camptonectes bellistriatus, Astarte fra- of its outcrop area along Belle Fourche River the are ripple-marked. O wing to its hardness and nearly dently containing several layers of belemnites 12 gilis, Trapezium beliefour chensis, Pleuromya newtoni, formation preserves a fairly uniform level, reach­ horizontal position it gives rise to prominent benches, Greenish yellow shales with lime-clay nodules____ 5 Tancredia inornatar T. corbuliformis, T. bulbosa, T. Highly fossiliferous blue slabby limestone____ 2 ing in general a height of about 4000 feet. It or terraces, and outlying buttes terminated by ver­ Chiefly concealed apparently nearly all shales, but postica, Dosinia jurassica, Saxicava jurassica, Car- passes beneath the Sundance formation and the tical cliffs, all along the Belle Fourche Valley. It with some thin, highly fossiliferous limestones. dioceras cordiforme, and Pentacrinus asteriscus. Belemnites apparently in great abundance. One alluvium of the river bottom at a point about 2 is one of the best exposed beds in the quadrangle, fragment of ammonite found______50 Here and there layers of limestone and sandstone miles from the southern limit of the quadrangle. appearing as a rim rock along all the streams Massive reddish-yellow sandstone______40 in the lower shales carry Ostrea strigilecula, Camp­ There is but little variation in the stratigraphy of entering Belle Fourche River from the east and Greenish-gray arenaceous shale, grayish white in lower part______80 tonectes bellistriatus, Pseudomonotis (Eumicrotis) the formation, and the following section, made on outcropping in the lower course of most of the Flaggy grayish-white sandstone___.______2 curia, Psammobiaprematura, and Belemnites densus. the southeastern side of the base of Devils Tower, streams entering from the west. The color varies, Gray arenaceous shale, lying on red beds______3 The character of this fauna, and especially of the is representative: fresh surfaces being in general light pink or gray, 297 ammonite Cardioceras cordiforme, indicates a hori­ Section of Spearjish formation on Belle Fourche River at while exposed surfaces show some shade of red, Section of Sundance formation on north side of Bush Canyon zon in the lower part of the upper Jurassic, corres­ base of Devils Tower. yellow, or buff. There is a gertain regularity in 3 miles north of Hulett. ponding to a part of the European Oxfordian. Feet. the areal distribution of the colors. In the south­ Feet. The Sundance formation is approximately equiv­ Red shales, mostly concealed___. __. _____ 25 Morrison shale. Gypsum in 1- and 2-foot beds with thin red shales eastern part of the quadrangle, along the upper Massive yellow sandstone, very soft (Unkpapa ?)_ 30 alent to the Ellis formation of Montana and the between.__j______portions of Whitetail, Blacktail, and Lytle creeks Drab soft shales______8 Yellowstone Park region. Fossiliferous sandy limestone, platy to nodular____ 1 Red shales, nodular and sandy in upper part _____ 10 and their tributaries, the red is pronounced. In Massive and nearly uniform bed of red sandy shale 30 Gray soft shales______5 CRETACEOUS SYSTEM. Very soft, thin, red clay shales.______12 the vicinity of Devils Tower the red color softens Fossiliferous arenaceous limestone, platy,_____ 1 Soft, red shales with some arenaceous layers ______10 to a reddish yellow, or buff, and north, northeast, Shale, mostly concealed______20 MORRISON SHALE. Massive red sandstone layer ______4 Massive gray arenaceous limestone, fossiliferous in Very soft, thin, red shales, slightly green at top ___ and northwest of Hulett the reddish tinge is almost upper part______4 Character and outcrops. The slopes of the Sun- Red sandy bed with little clay______wholly lacking. West and south of the tower and Shale, mostly concealed______._____ 18 dance formation are in most places continued Fossiliferous arenaceous limestone ______4 Very soft, red shales, slightly nodular ______especially along Miller Creek, light yellow prevails. upward by those of the overlying shales of the Massive red sandstone______.______Shale, chiefly concealed, but contains at least three Arenaceous red shales, inclined to nodular _:.______Shales, in part sandy, varying from 70 to 90 limestone layers, each being sandy in lower part. Morrison formation, which rise to the base of the The limestones divide the concealed rocks into Very soft, very thin red shales ______feet in thickness, lie below the massive sandstone cliifs of Lakota sandstone. The outcrop zone of Thin arenaceous red shales______three nearly equal portions____ '.'. ______92 Very soft, very thin red shales ______and constitute the basal member of the formation. Fossiliferous arenaceous limeston e ______4 the Morrison is narrow, extending along the west Rather hard arenaceous red clay shales, slightly In many places layers of sandstone are included Purple and green shales, about_____-____- 40 side of the Belle Fourche Valley and around the Massive yellow sandstone______40 green near the top______among these shales, but with one exception they higher sandstone ridges in the southeast corner of Massive red sandstone layer ______Greenish-gray.shales with thin sandstones, lying on Arenaceous red clay shales, nodular.______are rather soft or flaggy and inconspicuous. The red beds,______.______80 the quadrangle. Owing to the low dips and deeply Gypsum, thin seam one-eighth inch thick. exception referred to is in the vicinity of Devils 347 incised creek valleys, the outcrop is very sinuous, Soft, thin, red shales ______Arenaceous red shales ___.______----______-___-___ Tower, where midway in the shales there is a bed Section of Sundance formation north of Lytle Creek, 4 miles especially on the west side of the river. Arenaceous red clay shales, riodular______.______of massive, sparingly fossiliferous quartzitic sand­ east-southeast of Devils Tower. The formation consists chiefly of massive shale. Massive arenaceous red shales______stone 4 to 8 feet thick. The best exposures of this Feet. The prevailing color on weathered slopes is greenish Thin red shales______...______Morrison shale. quartzitic sandstone are along the roadside imme­ Massive yellow sandstone, very soft (Unkpapa ?), gray or yellowish gray, but pink and purple tints diately north and northwest of Devils Tower. about______10 are not uncommon, and in a few places, particularly Shales, partly concealed______24 Age. Throughout the Black Hills uplift the The thick mass of shales constituting the middle Fossiliferous sandy limestone______3 north of Hulett, between Bush Canyon and Burnt Spearfish deposits are distinctly separated from and upper part of the formation is mainly of dark Shales covered by talus______5 Hollow, the lower beds are red. Some exposures the Permian (?) Minnekahta limestone below by Flaggy nonfossiliferous limestone______, 4 greenish gray color and over 200 feet thick. In Shales, partly concealed______30 show decidedly darker shades, and in a few places an abrupt change of material. No fossils have portions of the area, as along Bush Canyon in the Massive gray sandstone______.______5 the upper beds are black and somewhat carbona- ceous. These were carefully examined for coal, but Section of Morrison formation on north side of Sourdough Local sections. The following sections of the Feet. Greek, 6 miles north of Hulett. Massive yellowish sandstone.-..--___.__..____ 5 none was found. Thin layers of lime-clay nodules Feet. Lakota have been measured: Yellowish-gray shales, darker near the top, lying on are common, and some of these in the southeastern Shales, yellow at top, red at bottom, underlying Lakota sandstone ______50 Section of Lakota sandstone in Burnt Hollow. portion of the quadrangle coalesce into fairly defi­ Lakota sandstone______18 100 Black shales______. 14 Feet. nite bands of soft impure limestone. Sandstones Black shale with 4-inch sandstone near top; slight Fuson shale. Section of Fuson formation 2i miles northwest of Hulett, are present, but in few places do they become con­ purple or pink tinge throughout and rather Massive, gray, cross-bedded sandstone______2 between Bush Canyon and Moore Canyon. prominent near the middle______17 Shaly sandstone ______7 Feet. spicuous. An 8-foot bed was observed in Barlow Black shale______26 Massive cross-bedded sandstone, much iron stained- 10 Shales and concealed, at base of cliff of Dakota Canyon 30 feet above the bottom of the formation. Slightly sandy, green soft shale, some lime near the Flaggy sandstone with iron concretions______4 sandstone______12 The thickness of the formation at this place is 85 base ______10 Massive,cross-bedded,yellowish-gray sandstone with Sandstone ______4 White sandstone-______2 few iron concretions______8 Shales ______6 feet. About 3^ miles north-northwest of Hulett, Green shale__-_____.______5 Shaly sandstone with considerable iron.____-_._____ 3 Sandstone ______2 between Bush Canyon and Burnt Hollow, a 1-foot White sandstone, carbonaceous fragments.______2 Massive gray sandstone______3 Shales and concealed to top of Lakota sandstone. __ 85 Gray and reddish shales, lying on Sundance forma- Shaly sandstone, considerable iron near bottom____ 4 bed of sandstone was observed 70 feet below the tion____.______.______. 40 Flaggy sandstone______2 109 top, followed 20 feet lower by a 2-foot bed. The Gray sandy shale.______3 134 Massive sandstone, lying on Morrison formation__ 1 Section of Fuson formation on north side of Burnt Hollow total thickness of the formation at this place is near its head. about 150 feet. Near the head of Bush Canyon a /Section of Morrison formation on north side of Deer Creek 47 Feet. near eastern border of Demls Tower quadrangle. Sandy shale, very dark near the top, gray below, 2-foot bed of sandstone occurs 20 feet above the Section of Lakota sandstone on north side of Sourdough overlain by Dakota sandstone______16 bottom of the formation, and above this for several Feet. Creek. Flaggy sandstones with some iron concretions.____ 4 Lakota sandstone. Feet. Dark-gray shales______12 feet there are chalcedonic nodules and a few chal- Dark-purple shale, weathers to light purple____ 9 Massive yellowish-gray sandstone, overlain by Fuson Massive sandstone ----_------_---____--_____-____ 2 cedonized fragments of saurian limb bones and Massive sandstone______1 formation______10 Gray sandy shales, lying on Lakota sandstone___ 22 vertebra?. The thickness of the formation varies Purple shale______10 Soft, purplish gray, shaly sand stone ____.______1 Concealed ______8 Flaggy purplish sandstone with several bands of 56 considerably. The greatest thickness observed, Purplish-gray shale____---_-______12 iron oxide______^______14 Section of Fuson formation on Sourdough Creek north- 160 feet, is on Miller Creek near the southern Dark-purplish shale____-____--___-_____-.______20 Massive sandstone______1 Very dark shale______14 northwest of Hulett. border of the quadrangle, 4J miles east of the Shaly sandstone______1 Feet. Gray shale______17 Massive, soft sandstone, lying on Morrison formation 3 Flaggy sandstones and sandy shales, overlain by Belle Fourche. The thinnest section observed was Concealed, but contains some sand______24 Dakota sandstone______32 30 Green and purple shale______6 Grayish-black shales_-__--__--_--___--__-____-____ 10 40 feet, in Barlow Canyon due north of Devils Sandy shale______4 Fossil plants. The formation contains some pet­ Flaggy sandstone______4 Tower. Very white sandstone weathering to a dirty, velvety Purple sandy shales, lying on Lakota formation____ 5 Local sections. The formation is fairly well brown ______1 rified wood, but much less than in the eastern Grayish-white shales______-____--__--______5 51 exposed in many places and several detailed sec­ Green shales______.______2 slopes of the Black Hills. A small amount was tions were obtained. They are as follows: Purple shales______6 found 2-| miles northwest of Hulett and also 4 Fossils and age. Some of the sandy clays of the Grayish green shales with some lime nodules, lying miles east of Devils Tower. Larger quantities, Fuson formation contain fossil plants, mostly ferns Section of Morrison formation on north side of Moore Can­ on Sundance formation______16 yon 2| miles northwest of Hulett. with many good-sized pieces, were observed in a and conifers, which have been collected extensively Feet. 155 Grayish-purple shales, underlying Lakota sand­ rather small area in Barlow Canyon due north of in the neighboring Aladdin quadrangle. The spe­ stone ______20 the Missouri Buttes. In most portions of the Black cies are numerous and their age is Lower Cretaceous. Dark-purple shales______36 Fossils and age, The Morrison shale contains Yellowish, slightly sandy shales______._-______4 many large bones, and in other areas it has yielded Hills cycads have been obtained from the sandstone DAKOTA SANDSTONE. Clay, nodular layer___.______1 a varied vertebrate fauna, consisting of many genera horizon containing the fossil tree trunks. When Dark greenish-gray shales______10 growing the cycad consisted of an oval trunk Distribution. The Dakota sandstone is a con­ Clay, nodular layer______1 of dinosaurs, some of which are of huge size, and Purple shales______6 of primitive forms of small mammals. This fauna, extending a short distance out of the ground, spicuous member of the Cretaceous series, capping Dark gray shales with lime-clay nodules__.___ 2 with leaves on long stems growing out of its sur­ the hogback range and in most places presenting Drab shales______8 which is often called the Atlantosaurus fauna, is Very soft sandy shales, lying on Sundance formation 8 thought by some paleontologists to be of early face. The fossil cycad ordinarily consists of the high cliffs along its eastern margin and in the can­ petrified trunk, which shows the deep scars of yon walls. It rises gradually on the northwesterly 96 Cretaceous age and by others is assigned to the late former sockets of the leaf stems. Some of the dip from the slopes of the overlying shales in the Section of Morrison formation at southern edge of Devils Jurassic. The invertebrate fossils are all fresh­ Tower quadrangle, 21 miles west of the Belle Fourche. water forms which furnish no positive evidence as shales which are here and there included in the hills east of the Little Missouri Valley, and its Feet. Lakota formation contain other fossil plants, main outcrop zone is an elevated table-land, termi­ Lakota s&nd stone. to age. mostly ferns and conifers, representing numerous nating on the east in high cliffs from which the Purple, gray, and yellowish fine shales with one or LAKOTA SANDSTONE. two thin sandstones...__.______60 species of Lower Cretaceous age. Large collections land drops rapidly to the bottom of the Belle Flaggy to massive white sandstone______4 of these have been made in the Hay Creek coal Fourche Valley about 500 feet below. Most of . Purple and green shales with occasional limestone General relations. The Lakota formation out­ nodules, lying on Sundance formation_____ 60 crops in a narrow zone along the higher slopes field. these cliffs consist of Dakota, sandstone at the top and Lakota sandstone below, surmounting long 124 west of the Belle Fourche and constitutes portions FUSON FORMATION. slopes of Morrison and Sundance shales. The Section of Morrison formation in the northwestern portion of several high ridges on the divides in the south­ of T 52, R. 64. east corner of the quadrangle. It consists mainly General character and relations. The Fuson Dakota outcrop west of this valley varies in width Feet. formation consists mainly of clay or shale with from 1 to 8 miles in greater part, being widest in Argillaceous limestone..,______2 of light-colored, coarse-grained, massive sandstone Concealed ______3 which gives rise to cliffs, many of which are of thin sandstones, lying between the massive sand­ the slopes adjoining Elkhorn Creek and Govern­ Argillaceous limestone-.______1 considerable prominence. These cliffs surmount stones of the Lakota and Dakota formations. It ment Canyon, along which the formation is exposed Grayish clay shales__ __..______12 nearly to the Little Missouri. Numerous canyons Argillaceous limestone..______1 the rounded slopes of Sundance and Morrison is as a rule not well exposed on the slopes, but Yellowish-gray shales______6 shales and form the beginning of the ascent to the locally, where the cliffs are perpendicular, it is opening to the east cut deeply into the formation Argillaceous liniestone______-___-___-_-______1 exhibited. Its outcrop area follows the very irreg­ and give to its eastern margin a most irregular out­ Greenish shales______40 plateau surface of the Dakota sandstone. On the Argillaceous limestone-____--_____-__--_-______$ west side of the Belle Fourche they follow a very ular course of the margin of the Dakota sandstone, line. Small -areas of the formation are revealed by Greenish shales______30 irregular course, extending eastward on the divides but outliers appear along the divides adjoining several valleys in the Graneros shale area near the between the creeks and receding to the west in the Elkhorn and Tie creeks and Government Canyon. Little Missouri Valley, notably on Hulett, Poison, This is believed to be nearly the full thickness valleys. Here and there outliers are isolated from In the southeast corner of the quadrangle the sand­ Broncho John, and Gaff creeks. Small outliers at this place, although the upper and lower contacts the main mass of the formation, rising in buttes of stones of the formation are of more than usual of the sandstone cap the higher portions of several, are not clearly exposed. various shapes and sizes. prominence, and this in connection with the high ridges lying between Whitetail and Miller Thickness and rocks. The Lakota sandstone of wooded condition of the region renders the sep­ creeks a few miles southeast of the Belle Fourche. Section of Morrison formation 4 miles east-southeast of Character. The formation is chiefly a massive, Devils Tower, north of Lytle Creek. the Devils Tower quadrangle, as in other portions aration of the Lakota and the Fuson in this vicinr Feet. of the Black Hills uplift, shows considerable resem­ ity a matter of uncertainty. Sandstones appear in hard, cross-bedded sandstone of medium-sized grain. Rough nodular layer of impure fire clay, overlain by blance to the Dakota, It is, however, not so con­ nearly every exposure of the formation, and in gen­ In places deposits of shale are included, especially Lakota sandstone______. 2 Green shale______.______... 12 tinuously massive, and although hard in some eral in this area the Fuson is much more sandy in the 'lower portion and where the formation Sandy fire clay______.__ 1 localities, it is generally softer than the Dakota than in other parts of the Black Hills uplift, where expands in thickness. They vary from nearly Green shale, locally with purple tinge______-___- 70 pure clay to mixtures of sand and clay. In the Lime-clay shale.______6 and forms a less marked feature in the topography. it contains much soft shale and fire" clay. The Fine green and drab shale______12 The thickness of the Lakota varies considerably thickness varies from 50 to 100 feet, but some of high vertical walls of Government Canyon the Green shale with some lime-clay nodules.______16 and in many places it is difficult to separate it from the measurements are indefinite on account of the shales and thin-bedded sandstones are of sufficient Limestone, slightly argillaceous, lying on Sundance formation______6 the overlying Fuson beds. Near the head of changeable nature of the various beds. importance to mask in considerable measure the general massive nature of the formation. The 125 Burnt Hollow it is apparently only 25 feet thick, Local features. The following sections illustrate and near the head of Deer Creek and on Sour­ the principal stratigraphic features of the formation thickness varies from 70 feet near the head of Burnt Section of Morrison formation near head of Burnt Hollow, Hollow to 160 feet in Barlow Canyon. The sand­ 4 miles northwest of Hulett. dough Creek it is 30 feet thick. The latter thickness at a number of representative exposures: Feet. stones are light gray on fresh fracture, but all prom­ was observed on Cabin Creek 2^ miles west of the Section of Fuson formation north of Cabin Creek, 2£ miles Lakota sandstone. inent cliffs show a light brown or yellowish brown Very black shales, rather fine; on weathered sur­ Belle Fourche, while on the same creek 4 miles west of the Belle Fourche. face much resemble a coal outcrop, but no coal Feet. on exposed surfaces. The shales range from dull west of the river it is 60 feet thick, consisting of Black shale, overlain by Dakota sandstone__ __ 10 is present. (This may possibly represent the hori­ 20 feet of reddish flaggy sandstone underlain by Sandy shale and concealed______.____- 10 gray to intense black and in a few places carbon­ zon of the Aladdin coal.)______10 Flaggy to massive sandstone ______^______4 Gray shales______32 40 feet of nearly white massive sandstone. Near ized fragments of plants were found. This phase Sandstone -___-_-______.._-___-____---____----_-_-__ 1 Shales, thin sandstones, and concealed______30 is best shown in Government Canyon, where the the southern limit of the quadrangle, 4 miles east Massive sandstones______-__-______- 2 Shales with poorly preserved plant impressions____ 3 carbonaceous material makes up a very considera­ Interbedded shales and thin sandstones, lying on of the Belle Fourche, it is 60 feet thick and consists Sandy shales and concealed______10 Shaly sandstone______6 Sundance formation______18 ble portion of one or two of the beds. entirely of a white massive sandstone. Midway Black carbonaceous shales.______6 64 between Devils Tower and the Missouri Buttes, Yellowish-gray sandy shales.______8 Local sections. The principal features of the and south of the Missouri Buttes near the head Purple shales______5 formation at several localities are shown by the Section of Morrison formation a short distance east of the Yellowish sandy shales, lying on Lakota sandstone. 4 preceding. of Lake Creek, the thickness is 40 feet; 3^ miles subjoined sections. The first is on the north side Feet. northwest of Hulett, on Left Creek 3 miles south- 95 of Barlow Canyon just across from the foot of the Very black shales, as in preceding section_____ 10 Brownish-gray and purple shales______14 southwest of the Missouri Buttes, and in Barlow Section of Fuson formation north of Cabin Creek, 4 miles steep road leading up to the Missouri Buttes: west of the Belle Fourche. Sandstone ______.______2 Canvon northeast of the buttes it is 50 feet. The Section of Dakota sandstone in Barlow Canyon. Brownish-red shales.______'_ 8 «/ Feet. Black shale______---__-__-.___--___----_-_____ 40 best detailed section was obtained on the north side Yellowish-gray sandy shales, darker near top, over­ Feet. Thin sandstone to top of hill (approximate top of Light-gray shale, lying on Sundance formation-____ 36 lain by Dakota sandstone ______~ _ _ 36 of Burnt Hollow near its head, where the thickness Massive yellowish sandstone__--____--- _____ 3 formation) __,.______30 110 is 47 feet, as shown in the accompanying section. Yellowish sandy shales______6 Flaggy to massive sandstone______10 Devils Tower. Feet. altitude of about 4400 feet is attained. On the than half a mile. In the northern half the dip is exposed along the prominent ridge west of the Shaly sandstone______.______._ 28 Massive sandstone______4 west slope of the Missouri Buttes the formation low and in consequence the outcrop is considerably margin of the alluvium of North Fork of the Little Shaly sandstone______8 rises locally to an altitude of nearly 5000 feet. wider. From Mud Creek to the mouth of North Missouri between Prickly Pear and Battle creeks. Massive sandstone______.______6 Concealed slope______10 The lower shale. The lower Graneros shale Fork of Little Missouri Biver the Mowry beds The general lithologic features are clearly exposed, Massive sandstone.______6 occupies a much dissected belt of considerable width give rise to a ridge of moderate prominence on the but the measurements of thickness may be some­ Shaly sandstone and concealed.______22 in the west-central and northern portions of the west side of the Little Missouri, and this feature what in error on account of irregularity of dip. Massive, highly cross-bedded, grayish-brown sand­ stone, lying on Fuson formation ______36 quadrangle. The member enters the area from the also extends northeastward from North Fork to Since the section does not include the portions con­ 160 south as a narrow band, for here the dips are rela­ the northeast corner of the quadrangle. There are cealed by and lying east of the alluvium, it would tively steep. After crossing Cabin Creek at a point several outliers of the member on the high ridges seem that if the measurements are approximately The next section was measured 1 mile east of the several miles west of the Belle Fourche, the dip between the Little Missouri and Belle Fourche correct the full thickness in this locality might preceding, on the same side of the canyon: rapidly decreases and the outcrop zone extends valleys. Three of them cap portions of the high reach considerably more than 1000 feet. Section of Dakota sandstone in Barlow Canyon. northward and then northeastward, with gradual divide between Poison Creek and the head of Elk- Partial section of upper Graneros shale between Prickly Feet. increase of width, South of Mud Creek the out­ horn Creek north-northwest of the Missouri Buttes. Pear and Battle creeks. Concealed slope. ______20 crop lies wholly to the east of the Little Missouri, The fourth is of small size and lies along the gran­ Feet. Massive sandstone, slightly flaggy at bottom. ___ 65 Black shales with bands of lime-clay concretions Shale and concealed.-______40 but northeast of that creek the western boundary ite outcrop west of the main peak of the Missouri about every 8 or 10 feet______75 Massive sandstone with iron oxide near bottom____ 8 extends west of the river and rises above the valley Buttes; here the beds are steeply upturned. Highly fossiliferous lime-clay concretions and black Concealed slope______5 shales alternating in beds from 4 to 8 feet thick_ 60 Massive sandstone, lying on Fuson formation___ 8 alluvium. The area thus situated on the west side The thickness of the Mowry beds is nearly con­ Black shale______.______60 of the valley gradually grows wider toward the stant, several measurements giving 115 to 125 feet. Thin sandstone lenses____..--_---______1 146 Black shale with a few bands of sandy septarian northeast. The material is a compact shale of dark color, concretions _ _ __.______200± The following section is shown on the north side The rock is a fissile shale of dark-gray or containing large numbers of detached fish scales. Black shale______100± of Burnt Hollow, near its head: intensely black color. Small deposits of sandstone These scales are found in all portions of the mem­ Large septarian concretions, sandy and fossiliferous. 12 Black shale_____.______-.______40 Section of Dakota sandstone in Burnt Hollow. and sandy shales occur near the bottom, and here ber, but vary in abundance. In places they are Concretions ______12 and there iron-charged concretions 1 to 2 feet in closely packed together, while in some beds they Black shale with scattered bands of sandy septa­ Feet. rian concretions______300± Soft flaggy sandstone at top of formation__ ___ 20 diameter are scattered through the middle and upper are somewhat widely scattered. In general they Massive yellowish:gray sandstone______5 portions, but they show at few places, except in the 860db Shaly sandstone______5 are sprinkled singly over the shale surfaces, in the GREENHORN FORMATION. Massive sandstone______1 extensive exposures, and are nowhere abundant. proportion of one to four scales in 6 square inches. Shaly sandstone.______-______- 4 They not uncommonly are inclosed by a shell of They range mostly from one-half to three-fourths The Greenhorn formation is not so clearly defined Massive sandstone______...______3 Flaggy and shaly sandstone.______cone-in-cone structure 2 to 6 inches thick. Owing of an inch in diameter. in the Devils Tower quadrangle as in other portions Limonitic band of sandstone____--____--___-______to the extremely soft nature of the shales the small In the hand specimen of fresh rock the shale of the Black Hills uplift. It consists of alternating Sandy shales______Massive gray sandstone with iron oxide at bottom. streams have cut deep gullies, so that the resulting differs little in general appearance from that of the beds of lime-clay concretions and black shales, the Shaly sandstone with iron-oxide bands______topography is for the most part one of innumerable lower Graneros except in fissility, the lower beds shales being almost identical in general appearance Thin gray shales______..______small hills and ridges or badlands over which travel being thin and papery, while the Mowry scale with the Carlile and upper Graneros shales and Massive sandstone______Flaggy sandstone______is difficult. The thickness of the shale varies con­ shales are thicker or more slabby and considerably the concretions not differing greatly from those Grray shales______siderably, but is prevailingly greater in the central harder. Owing to the fact that the Mowry beds of the Carlile. The concretions are of sufficient Soft black shales______Massive sandstorie______and northern portions of the quadrangle. On the are much harder than the adjoining shales, they importance, however, to give a perceptible topo­ Sandy shales______...______.___ southern border it is 120 feet. In Barnard Can­ give rise to hills and ridges of moderate prominence. graphic effect, and with careful observations, in the Massive yellowish-gray sandstone, lying on Fuson yon due north of Devils Tower it is 150 feet. On They afford a fairly firm hold for tree roots, and absence of good exposures, the general position of formation ______T. L. Creek it is a little more than 200 feet, but as a result the Mowry hills are generally well cov­ these beds may be traced over the gently undulat­ 70 the full thickness is not revealed. It can not, ered with pines and scrub oaks. The shales are ing surface. The concretions vary from a few The following section is near the mouth of Gov­ however, be much greater than 200 feet. Near dark gray or decidedly black when fresh, but, inches to several feet in diameter, the usual size ernment Canyon, 3 miles above the mouth of the the head of the intervening Elkhorn Creek, where unlike the other Graneros shales, weather through being 1 to 4 feet. They have a bluish-gray color creek and 3 miles west of the eastern edge of the the shale is crossed by contour line 4150, its drab to a distinct light gray, and this light color, and are spherical or ellipsoidal in shape. Here and quadrangle: thickness is 180 feet. The amount on Hulett together with the wooded hills and ridges, causes there they show a well-developed septarian charac­ Section of Dakota sandstone near mouth of Government Creek 3 miles above its mouth is at least 190 feet, the Mowry outcrop to be very conspicuous. The ter, and a fair proportion contain fossils, chiefly Ino­ Canyon. but, as on T. L. and Tie creeks, the full thickness contact of the Mowry beds with the underlying ceramus labiatuSj a fossil which is characteristic of Feet. Flaggy sandstone at top of formation______16 was not observed at points where satisfactory meas­ sandstone is in most places distinct, but the con­ this formation. The thickness of the formation Massive sandstone....______6 urements could be made. The lithologic nature of tact with the overlying upper Graneros shale is as varies between 60 and 80 feet, but its stratigraphic Dark sandy shale.-______15 Iron concretionary band__--______-_.___--______1 the member is nearly constant throughout the a rule concealed by the mingled shales of the two limits are somewhat indistinct. The accompany­ Highly carbonaceous black shale ______10 quadrangle. members. One exceptional local feature consists ing section, as measured between Prickly Pear Massive sandstone______14 Sandstone member. The sandstone lying on the in the prominent exposure near the west end of the and Battle creeks, amounts to 78 feet. The Flaggy to massive sandstone-___---__---.-____-__ 8 Grayish shaly sandstone with iron concretions.__ 4 basal black shales is most extensively developed in area that lies between Poison Creek and the head-of thickness midway between Mud and Driscoll creeks Flaggy to massive sandstone with iron concretions the area drained by Hulett, T. L., and adjacent Hulett Creek, where the Mowry beds are tinged is 60 feet. The outcrop of the formation occupies near the bottom______10 Dark-gray carbonaceous shale____.___--.______5 creeks. Its outcrop extends along the east side of with red oxide of iron and from a distance present a narrow north-south zone that extends across the Shaly sandstone______6 the Little Missouri Valley as far as Mud Creek, a most unusual bright-reddish tint, unlike the com­ western part of the quadrangle, in the northwest Flaggy to massive sandstone__.______4 where it crosses the river under the alluvium; mon light gray. Without close examination the corner being deflected somewhat toward the north­ Iron concretionary band______1 o o «/ Shaly to flaggy sandstone______5 thence northeastward it appears at intervals a short rock at this place might be mistaken for the mass­ east and widening considerably on account of Massive sandstone______4 distance west of the stream. It crosses Cabin Creek ive Graneros sandstone. change in strike and dip. Shaly sandstone with iron concretions.______12 in a zone which is rather narrow, but to the north, Flaggy sandstone______7 Upper shale. The soft shale constituting the Section of Greenhorn formation between Prickly Pear and Yellow sandy shale with iron concretions.______8 in the vicinity of Yeast's ranch, it extends some upper member of the Graneros formation is widely Battle creeks. Shaly carbonaceous sandstone, lying on Fuson for­ distance eastward up the shale slopes and caps sev­ exposed in the north-central portion of the quad­ Feet. mation ______4 eral outlying knobs. Extensive outlying areas cap rangle. This is due chiefly to the low, undulating Large septarian lime concretions (1 to 6 feet in 140 diameter) with Inoceramus______15 the irregular ridges adjoining and at the heads of dip in the area northwest of Little Missouri River, Black shale______8 Fossils and age. In this region the Dakota has T. L., Elkhorn, and Hulett creeks, and smaller out­ where the outcrop of the upper shale, partially Shale with smaller lime concretions______2 Black shale______30 yielded no satisfactory fossils, but in other portions liers occur west and northwest of the Missouri concealed by a broad veneer of alluvium, occupies Shale with lime concretions______1 of the Black Hills it has been found to contain Buttes and cap Strawberry Hill and the ridge next many square miles of low, rolling grazing land. Black shale______12 remains of dicotyledonous plants of later Cretaceous north. , . Shale with large lime concretions, at supposed base In the vicinity of Mud Creek the dip is steeper and of formation______.______10 age. The rock is a massive sandstone of medium to the outcrop zone narrows to less than half a mile. 78 coarse grain and in a few places it becomes a con­ GRANEROS SHALE. It maintains approximately this width southward glomerate. The conglomeratic character is well to a point beyond Poison Creek, where the dip CARLILE SHALE. Components. The Graneros formation in this developed in the two areas west and northwest of the lowers and the outcrop widens considerably. Near The outcrop zone of the Carlile shale extends quadrangle consists of four distinct members the Missouri Buttes. The rock in the outcrops nearest Yeast's ranch it becomes much constricted again on north and south in a narrow band lying entirely in lower black shale, a massive sandstone, the Mowry the buttes consists largely of pebbles about the size account of steepening dip, and continues southward range 67. From Cabin Creek to Mud Creek the beds, and the upper shale the total thickness being of a pea, while in the larger area 2 or 3 miles away across Cabin Creek and beyond the quadrangle width is only a few hundred yards, but it increases about 1250 feet. These divisions are clearly denned many of the pebbles are 1 inch in diameter and boundary as a rather narrow belt. to the north, being about a mile north of Gammon lithologically and widely exposed. They are also there are some reaching 2, 3, or even 4 inches. This member consists of dark-gray to black Creek. In places the formation rises in knobs and distinct topographically, the massive sandstone and The thickness of the sandstone varies from 8 feet, shale interbedded with lime concretions, of which ridges on the divides, especially on a prominent the overlying Mowry beds rising in ridges of mod­ as the approximately general amount south of many are traversed by cracks filled with calcite. point known as Blackbank Hill, which it caps. erate prominence from valleys of the adjoining Poison Creek, to 50 feet in the area south and west Most of the concretions near the bottom con­ The greater part of the outcrop is on gentle grass- shales. The massive sandstone is apparently iden­ of Elkhorn Creek. Northeast of Hulett's ranch it tain much iron and disintegrate readily into dark- covered slopes, and only one good section was tical with the petroleum-bearing sandstone of the varies from 25 to 40 feet. East of Hulett Creek the brown or black chips that lie thickly strewn over obtained, at a point midway between Mud and Newcastle quadrangle. sandstone is much the same as the Dakota sandstone the weathered surfaces in many places. Perhaps Driscoll creeks, where the thickness is 620 feet. Distribution. The Graneros outcrop extends in general appearance, and outcrops in many prom­ the most distinctive concretionary layer of the mem­ The formation is made up of three fairly distinct along the west slope of the hogback range in a inent cliffs. North and south of this locality the ber is one lying near the top. The concretions of divisions. The upper division is about 300 feet zone which is narrow at the south but broadens sandstone is much less distinct topographically and this layer contain considerable sand and many of thick and is nearly all shale; few concretions are toward the north, reaching a width of 12 miles in over considerable areas is not clearly exposed. them carry Prionocyclus, Inoceramus, and /S'caphites. present and these occur at indefinite horizons. the north-central portion of the quadrangle. The Mowry member. The main outcrop zone of the The thickness of the upper Graneros shale mid­ The middle division is 125 feet thick and consists greater part of the valley of the Little Missouri is Mowry member lies immediately west of the sand­ way between Mud and Driscoll creeks west of Little of concretions and shale, the concretions being of excavated in its shales. The formation extends far stone described in the preceding paragraphs and, Missouri River is approximately 850 feet. Farther considerable size and in sufficient number to leave eastward on some of the hogback ridges on the like it, follows the general course of Little Mis­ north the amount appears to be greater, but the an impress on the topography in favorable local­ west side of the Belle Fourche Valley, where it souri Valley. In the southern half of the quad­ measurements were less definite. In the accom­ ities. The lower division is 200 feet thick and, like rises in elevations of considerable prominence. The rangle, where the strata dip rather steeply, the panying section the measurements were qbtained the upper division, is chiefly shale, only a few con­ largest of these is Strawberry Hill, in which an outcrop is narrow, in few places reaching more by estimate for that part of the formation which is cretions being observed. The middle series much resembles the Greenhorn formation, but lacks the become nearly pure limestone. The best illustra­ tions of the quadrangle. The largest is on the high gin of the extensive zone of intrusions that extends distinctive Inoceramus. tion of this is 4 miles north of Yeast's ranch, where flat east of Poison Creek. The deposit here consists across the northern portion of the Black Hills A section measured between Mud and Driscoll well-rounded concretions of nearly pure, bluish-gray of only a thin sheet of white clay and nodular argil­ uplift. Most of these rocks in this quadrangle creeks is as follows: limestone 1 to 5 feet in diameter lie in considerable laceous limestone, poorly exposed. The greatest have been intruded as laccoliths between strata Section of Carlile shale near Mud Creek. numbers along the outcrop. The beds at this place thickness is near the south end of the area, where ranging in age from Spearfish to lower Benton, the Feet. dip 80° W. Highly fossiliferous concretions may the amount is 8 feet. The deposit lies unconform- intrusions being at progressively higher horizons Fine light-gray shale______70 Yellow and dark-gray shale______80 be found a short distance above and below the ably upon the massive Graneros sandstone in the to the northwest. The most notable igneous Light-gray septarian lime concretions (4 to 6 feet horizon of these large concretions. Much of the central and southern parts of the area and upon masses constitute Devils Tower and the Missouri in diameter) in dark, somewhat fossiliferous shale, shale in the lower part of the formation weathers to the Mowry beds in the northern part. A similar Buttes; others occur on branches of Lytle Creek, much carbonate of lime in veins______6 Yellowish-gray shale with a few concretions 1 foot a dull gray, but the upper beds remain black. All but smaller deposit lies on a high ridge in the in the southeast corner of the quadrangle, and a in diameter near the bottom-__.______12 of the shale produces a decided gumbo soil, nearly southeast corner of the quadrangle 1 mile north small laccolith is revealed in Barlow Canyon. Fine black shale with a few septarian concretions 1 foot in diameter______25 all of which is covered by an excellent growth of of the southern boundary and 2^ miles west of the The early Eocene age of these intrusions is indi­ Large septarian concretions in black shale ; a few grasses. eastern boundary. This deposit is mostly con­ cated by the fact that they intersect or are asso­ fossils in the concretions.______12 The greatest thickness of Pierre shale within the cealed, its presence being detected only by stray ciated with the uplift of strata as late in age as Very fine black shale with a few small concretions. 90 Grayish-black shale with abundant somewhat fos­ quadrangle is in the northwest corner. Opportu­ bits of white nodular limestone scattered over the later Cretaceous, while in places they are over­ siliferous iron-stained lime concretions in lower nities for measurement are not favorable, owing surface. Another more important area lies just lapped by Oligocene deposits. part (Inoceramus, Prionocyclus, and here and to the very low dip, but the thickness appears to be northwest of the Missouri Buttes. The southern there a baculite). This series forms a slight PHONOLITE PORPHYRY OF DEVILS TOWER. ridge__.______125 more than 1500 feet. edge begins 150 yards from the base of the north­ Grayish-black shales with a few sandy litne concre­ In the numerous concretions which occur in the western butte and, curving southward, extends to Occurrence. The mass of igneous rock known tions______200 Pierre shale at various horizons there are in many a point within 250 yards of the lake at the head of as Devils Tower is one of the most conspicuous 620 places large numbers of very distinctive fossils, Lake Creek. From this edge the area extends and notable features in the Black Hills province. Correlation. This formation is correlated with especially in the upper beds. The more abundant westward and northwestward one-half mile or more. Characteristic views of the steep-sided shaft, which the Carlile shale of other portions of the Black are of the following species: Baculites compressus, Exposures are not good on the side next the buttes, rises 600 feet from a rounded ridge of sedimentary Hills uplift by continuity of outcrop, by its occur­ Inoceramus sagensis, Nautilus delcayi, Placenticeras but along the western edge from 20 to 30 feet of rocks, 600 feet high, on the west bank of the Belle rence between distinctive Niobrara beds above and placenta, Heteroceras nebrascense, and here and there the deposit are shown in several places. The Fourche, are given in figs. 1 and 2 on the colum­ Greenhorn below, and by its fossils, especially Lucina occidentalis. material is the usual fine, massive, creamy-white nar section sheet. Its nearly flat top is elliptical Prionocyclus woolgari. calcareous clay with thin bands or bunches of in outline, with a north-south diameter of over FOX HILLS SANDSTONE. argillaceous limestones. There is some indication 100 feet and an east-west diameter of about 60 NIOBRARA FORMATION. Along the western-southwestern border of the that a considerable area in addition to that mapped feet. Its sides are strongly fluted by the great The outcrop of the Niobrara formation lies next quadrangle the Pierre shale is overlain by buff sand­ lies beneath the heavy grass-covered porphyry talus columns of the igneous rock and are nearly per­ west of that of the Carlile shale, extending north stones which appear to represent the Fox Hills northwest and north of the northwestern butte. pendicular, except near the top, where there is and south in a narrow zone across the western formation, but positive evidence of their age was The thickness can not be determined with accu­ some rounding, and near the bottom, where there portion of the quadrangle. Its greatest thickness, not obtained. The rocks are in general massive racy, but the deposit appears to have a dip of 5° or is considerable outward flare. The base is hidden which appears to be between Mud and Driscoll but extremely soft and in few places well exposed. more and there is a vertical distance of about 160 by a talus of huge masses of broken columns lying creeks, is not more than 120 feet. The width of They grade into Pierre shales through a few feet of feet between the lowest exposure on the west side upon a platform of the lower buff sandstone of the the outcrop in the northwestern part of the quad­ sandy shale. Some indurated beds are present, but of the area and the highest exposure near the Sundance formation. Lower down are slopes of rangle is nearly one-fourth mile. In the southern they do not seem to have any wide distribution. On buttes. The Tertiary lies upon the Graneros Spearfish red beds, which present high eastward- half of the quadrangle the thickness is less and the the north side of Good Lad Creek, northwest of sandstone at the west, but toward the south end facing cliffs on the bank of the Belle Fourche. dip greater, so that the outcrop narrows to only 40 Yeast's ranch, a rather concretionary sandstone it rests upon the Mowry beds, while nearer the All the strata lie nearly horizontal, with a slight to 50 yards. Not far from the southern limit of appears in one or two places about 80 feet above the lake it appears to extend onto the lower shale of downward deflection toward the center of the the quadrangle the outcrop becomes indistinct, and Pierre. This and the beds intervening down to the Graneros formation. One-half mile west of igneous mass. In the narrow ridges northwest on the slopes north and south of Cabin Creek it the Pierre were carefully searched for fossils, but the Missouri Buttes area there is another very of the tower part of the beds are somewhat tilted is wholly concealed beneath local wash. West of none were found. Three miles southwest of Yeast's small area. Between the two occur scattered frag­ in various directions, but apparently this is due to Blackbank Hill, in the northern part of the quad­ ranch a 1-foot bed of sandy limestone was observed ments of Tertiary limestone, remnants of a connec­ undermining by erosion in the adjacent gulches. rangle, the thickness seems to be less than 80 feet, near the bottom of the formation. This likewise tion which existed between tne deposits at no dis­ Columnar structure and talus. The great columns but the measurements are not conclusive. The contained no fossils. One sandstone of more than tant time. of which the tower consists are mostly pentagonal lithologic character of the Niobrara in this quad­ usual hardness and persistence caps a number of the Correlation. No fossils were found in the Ter­ in shape, but some are four or six sided. The rangle is identical with that which is so uniformly higher hills near the western border of the quad­ tiary deposits, and there is no basis for correlating average diameter is 6 feet and in general the peculiar to it throughout the Black Hills region rangle between Prairie and Good Lad creeks. In them with beds in other regions. They may columns taper slightly toward the top. In places that is, it consists of soft, light-gray, slabby shales, places it reaches a thickness of 30 feet and is highly belong to the White River formation, which several columns unite in their upper portion to weathering to creamy yellow and chalky gray, cross-bedded, and in one locality, 2| miles south of extends high on the eastern slope of the Black form a large fluted column. The columns are finely dotted with white specks and carrying thin, the point where Prairie Creek enters the quadrangle, Hills. not perpendicular, but slope inward toward the irregular aggregates of Ostrea congesta. it contains turtle bones and bones of some other top, the angle being 4° to 5° on the west side and QUATERNARY SYSTEM. In old exposures the yellow color is very con­ vertebrate, some fossil wood, and here and there 10° to 12° on the east side. They are not much spicuous and characteristic. For this reason the Inoceramus. Thin beds of hard rock are included Terrace deposits. High terrace deposits, prod­ jointed, but are marked horizontally by faint ridges Niobrara, notwithstanding its thinness and soft­ at intervals below this fossiliferous stratum for a ucts of an earlier drainage system, are present in or swellings, which give the rock some appearance ness, is a particularly important guide to the strat- hundred feet or more. various places in the quadrangle. Their thickness of bedding, especially toward the top of the tower. igraphic succession in the western half of the Concretions are present in this formation and in is nowhere great and in some areas the deposits Near the top there is much cross jointing and quadrangle. at least two places they have the distinctive form consist of isolated bowlders and pebbles scattered more or less decomposed rock which crumbles Section of Niobrara formation midway between Mud and of "log concretions." These were best observed on over the surface. A number of areas are shown into rounded fragments. The color at the top is Driscoll creeks. a little knoll soitth of the Little Missouri, 200 yards on the geologic map, but these do not fully repre-' brownish, mottled with dirty yellowish green, due Feet. Pierre shale. west of the north-south wagon road 2 miles west of sent the original extent of the deposits. Much of to lichens. In the lower quarter or third of the Creamy-yellow shales______12 Yeast's ranch. The log concretions are near the the northwest corner of the quadrangle seems to tower the columns bend outward and merge rather Grayish-yellow and dark-gray shales.______14 bottom of the formation, in a soft sandstone which have been once covered by the bowlder deposits, abruptly into massive rock which toward the base Very deep creamy-yellow, soft shales with a few thin layers of Ostrea congesta, lying on Carlile forma­ differs but little from the concretionary material, as evidenced by scattered bowlders or pebbles which shows but little trace of columnar structure. This tion______94 except that the latter is harder. Some of the concre­ remain in many places; only the thicker and larger massive rock circles the tower as a bench, extend­ 120 tions are spherical, as usual, but most of them are areas were mapped. The deposits lie chiefly west ing out 30 to 40 feet. It is strongly jointed, in Section of Niobrara formation 1 mile east of bench mark 4036, elongated and a number present excellent cylindrical and northwest of the Little Missouri, although a part into irregular prismatic forms and in part into west of Little Missouri River, nearly due west of Hulett. forms. They are gray and some are slightly iron few of small extent occur near and east of the Belle rough, coarse layers. On the southwest face the Feet. stained, but in geoeral not more so than ordinary Fourche. long columns curve outward over the massive basal Pierre shale. Grayish-yellow soft shales______20 weathered sandstone of the region. The matrix Alluvium. Alluvial deposits cover areas of portion and lie nearly horizontal. The rugged pile Very deep creamy-yellow, soft shales with some thin sandstone is brownish yellow. It is extremely soft moderate extent in the Devils Tower quadrangle. of talus extends high up the lower slopes of the Ostrea bands one-half to 1 inch thick_-____.____ 50 Belle Fourche River and its tributaries are bor­ massive bench at the base of the tower and also far Yellowish-gray, soft shales with few Cte£rea______14 and the wind has carved it in an interesting manner. About 5 miles north-northwest of this dered by alluvial flats of considerable width, but down the adjoining slopes of the sedimentary rocks. 84 locality there is another but less important exposure the widest are along and to the west and northwest In places it rises as a low ridge a short distance PIERRE SHALE. of log concretions, about 350 feet above the bottom of the Little Missouri. These deposits, which con­ from the base of the tower, the fragments falling The Pierre shale is extensively exposed along or of the formation. The concretions in general vary sist chiefly of loam and fine sand, pass insensibly from the higher cliffs having bounded some dis­ near the western edge of the quadrangle, occupy­ much in shape. Some are 1 or 2 inches in diam­ into the more recent wash along the upper courses tance away. At one point on the platform a short ing a broad area in its northwest corner and con­ eter and 1 to 5 feet in length; others are 4 to 5 feet of the many smaller streams. They are of local distance south of the tower there is a low hill of tinuing northwestward far beyond the boundary. in diameter and 15 to 20 feet in length. The origin, having been derived from the neighboring porphyry showing a surface of 30 or 40 feet of South of Mud Creek, where the dips are steeper, the spherical forms reach as much as 5 feet in diam­ outcropping rocks. Along the upper Little Mis­ massive rock which may possibly be in place, while outcrop narrows to a width of 1^ to 2 miles. eter. Some are sharply conical and others roughly souri the light-colored sands from the sandstone a low cliff of massive porphyry a few rods south­ Like several of the formations already described, nodular as if several had been joined together. highlands to the west have mingled with the clay east of the base of the tower strongly suggests the Pierre is largely soft dark-gray shale. It con­ As a rule they weather free from the matrix, but from the shales of the formations below. igneous rock in place. tains lime-clay concretions at many horizons, but Laccolithic intrusion. There is no conclusive some blend into hard, slabby sandstone. Igneous Rocks. these are of secondary importance. In much of the The greatest thickness of the Fox Hills sandstone evidence as to the former extent of the Devils GENERAL RELATIONS. lower part they are small, contain much oxide of included in the quadrangle is apparently about 400 Tower rock and location of its vent. The vertical iron, and readily break up into reddish-brown chips to 450 feet. The sedimentary rocks of the Devils Tower columns indicate that the tower does not represent which cover the weathered slopes much as do the quadrangle are intersected by several masses of the conduit of a flow to higher levels, and for this TERTIARY SYSTEM. somewhat darker pieces of the upper Graneros shale. igneous rock which were intruded between the reason it is believed that the mass is the remains of Higher in the formation the concretions are larger Deposits. The Tertiary is represented by small strata in early Eocene time. These igneous rocks a laccolith which was originally much larger than and some of them, by decrease in clay admixture, outliers in the southeastern and south-central por­ outcrop in detached areas at the northwestern mar­ the tower. It is evident that much of the lacco- Devils Tower. 6 lith has been eroded, but the originalTform and Lake Creek. The highest butte is on the north­ a little less yellow in color. The outlines remaining flint, and coarse pegmatite. The most conspicuous extent can only be conjectured. There is no evi­ west corner and rises to an altitude of 5372 feet; show that this mineral occurred in irregular rounded fragments are of granite in rounded and angular dence but that the vent is under the tower or the the next in height, on the northeast corner, has an grains; it may have been a feldspathoid. masses, varying in size from small grains to bowl­ The groundmass is very much altered. There are talus, for the materials of the associated agglomer­ altitude of 5218 feet; the other two are about 200 numerous very small feldspar laths in subparallel posi­ ders 1 to 2 feet in diameter. The rounded masses ate are of local origin and no dikes appear in the feet lower. The butte on the northeast corner is tion and some small rectangular areas, many of which have a somewhat faceted character. A bowlder of surrounding area. It has been suggested by Jaggar separated from its neighbor on the west by a deep are altered and which may represent either a feldspar fossiliferous Pahasapa limestone a foot in diameter that the tower is a remnant of the southeast end of saddle, but the depressions between the others are or a nephelite. The greater part of the groundmass, was noted, incased in a shell half an inch thick a laccolith extending from the Missouri Buttes, but more shallow. The buttes and the adjoining ridge however, is of a brownish, nearly isotropic alteration which could be easily stripped and appeared to be this idea involves an improbable amount of erosion consist of phonolite, but in the saddle on the north substance, and in this, besides the phenocrysts men­ due to calcination. Some of the sandstone grains tioned above, are a great many patches of radiating and numerous other complexities. side the rock is possibly not continuous. All the crystals, which were probably originally segirite. have a crust about them, suggesting fusion. The Petrographic description. The rock from Devils adjoining slopes consist of talus, which is narrow Titanite and magnetite occur as accessory minerals, and shales in the agglomerate are carbonaceous and Tower has been described as phonolite by Pirsson to the south, west, and east, but extends down the analcite, calcite, kaolin, and chlorite are secondary. comprise two varieties, one breaking into small (Am. Jour. Sci., 3d ser., vol. 47, 1894, pp. 341- gentle declivity over half a mile to the north and The rock, in the specimen examined, is too much blocks of dark-gray color and the other into soft, 344) and as sanidine trachyte by Caswell (Geology northwest. In the depression between the two decomposed to permit satisfactory determination. It coaly flakes. Shales of this character occur at of the Black Hills, 1880). It is here called phono­ western buttes there is a low ridge of phonolite may have been originally an segirite-syenite porphyry, intervals in the formations from the Minnelusa to or possibly a phonolite. lite porphyry in recognition of its porphyritic tex­ which may possibly be a dike, but its relations are the later Cretaceous. ture. The following petrographic description is by not exposed. PHONOLITE OF LYTLE CREEK. Monzonite. Half a mile west of the Missouri Albert Johannsen : Structure Columnar structure, so strongly exhib­ In the valley of Lytle Creek, in the southeast Buttes there is a small area of granular rock the corner of the quadrangle, there are several areas of Megascopically the rock is coarsely porphyritic and is ited in Devils Tower, is much less developed in the structural relations of which are not exposed. It medium gray in color. It consists of large, white or Missouri Buttes, but columns appear at some of the phonolite which project from the northwestern mar­ appears in the slopes of lower Graneros shale colorless, short, thick crystals of feldspar and minute, exposures, standing at various steep angles, and on gin of the Bear Lodge instrusions. They cut the north of the lake and extends northward about 50 dark-green pyroxenes, in a gray, aphanitic groundmass. the northeastern butte they lie nearly horizontal Sundance and Spearfish beds, following the strata yards to a point at which it disappears beneath a The felspar crystals vary from one-eighth to one-half with their pentagonal ends projecting from the face to some extent, but also cutting across them, although small area of Mowry beds and a wide area of inch in diameter, although most of them are somewhat of the cliff. the latter feature may be due to dikes. This phono­ Tertiary deposits. Its greatest width is 20 yards. less than one-fourth inch. lite was described by W. S. Tangier Smith in the Under the microscope the phenocrysts are found to The buttes are interpreted as the remains of a One massive pile of the rock is 12 feet long, 10 be feldspar, pyroxene, apatite, and a very little mag­ a laccolith or series of laccoliths, of irregular oval Aladdin folio (No. 128), substantially as follows: feet wide, and 8 feet high. It is separated from the netite and titanite. They vary greatly in size and are form. Apparently the magma rose through a vent The rock is mostly massive and of a moderately light- igneous rocks of the buttes by slopes of lower somewhat less in amount than the groundmass. No neph- or vents, lying beneath the present igneous masses. gray to dark-gray color, in general with a slight greenish Graneros shale. Probably this body is a remnant elite phenocrysts are found. The feldspar, a soda-rich The intrusive rock appears to lie upon a platform tinge. It is porphyritic, containing coarse tabular san­ of agglomerate from which all the finer materials orthoclase, is in general fairly fresh, though somewhat of nearly level Dakota sandstone, but on its west idine crystals, many of which have a length of 3 cm. or have been removed by erosion, but there is a possi­ altered along cleavage cracks to kaolin and isotropic side the lower Graneros shale and an outlier more. Besides sanidine (or perhaps soda orthoclase), bility that it may be a separate intrusion. zeolites. The pyroxene, varying from perhaps one-fourth the phenocrysts comprise anorthoclase, augite, and to one-half as much in amount as the feldspar, occurs in of Tertiary rocks are overlapped by the talus. segirite-augite, locally with augite centers or segirite According to Mr. Johannsen the rock has the short, thick crystals, is very fresh, and almost invariably Probably here the igneous rock is in contact with rims, or both. An altered and undeterminable feld­ following petrographic character: shows zonal structure. It is green in color and as a rule the shale. At a few points the sedimentary beds spathoid or group of feldspathoidal minerals, melanite- darkest around the edges. The centers are augite and have dips of 10° or more, but it is not apparent garnet, magnetite, titanite, apatite, and here and there Megascopically it is a dark granular rock, showing the outer zones are segirite. The apatite phenocrysts are that these steeper dips are due to the intrusion. zircon, also occur as phenocrysts. Feldspar or the feld­ rather large pink feldspar crystals, a greenish femic short, thick, colorless prisms or hexagonal basal sections. mineral, and a little quartz. Microscopically the texture Petrography. The rock from the Missouri Buttes spathoid is most common, though locally segirite-augite Magnetite occurs only in a few irregular grains, and is most abundant. Brownish or brownish-yellow mel- is hypidiomorphic granular. The constituents are feld­ is of a rather dark-green color and subordinate por­ titanite, in rectangular or lozenge-shaped crystals, most anite is common in some places; magnetite is in general spar, considerably less quartz, and still less altered bio­ of which are twinned, is rare. Apatite is present in phyritic texture. A representative sample from the unimportant; while titanite and apatite are common tite, with accessory rutile and apatite and secondary small amount as an accessory. northwest side of the northwestern butte is described accessories in most of the rock. sericite, epidote, chlorite, iron oxide, and calcite. The The groundmass consists of small orthoclase laths in by Mr. Johannsen as follows: The groundmass of this phonolite is invariably fine chief feldspar is oligoclase, which is considerably greater subparallel position and shreds and needles of segirite, grained, in some places granular, more commonly tra- in amount than microcline. There is still less ortho­ with small clouded crystals and anhedrons between. The rock has a very fine aphanitic groundmass, full chytic, and for the most part showing flow structure. clase. Both the microcline and the orthoclase are fresh, These clouded spaces are for the most part indeterminate; of small lath-shaped white feldspar phenocrysts from It is composed mainly of alkali-feldspar laths, together but the oligoclase is much clouded with many minute some of them are clear and colorless and definitely alkali one-sixteenth to one-fourth inch in length and a few with more or less segirite or segirite-augite, or both, shreds of sericite and a little chlorite and epidote. feldspar, but about half of them are brownish and small dark pyroxene prisms. Under the microscope locally augite, one or more feldspathoids, in many places clouded. It is probable that they were, in part, orig­ the texture is seen to be porphyritic, the phenocrysts a small amount of magnetite, and here and there a little Missouri Buttes. The exposures of agglomerate inally nephelite, but, if so, that mineral is now entirely exceeding the groundmass in amount. The phenocrysts garnet. As a rule, only one feldspathoid was noted, in the Missouri Buttes are on the eastern and south­ altered in the specimens examined. Pirsson describes vary greatly in size and are in subparallel position. most commonly a second generation of the one occurring eastern sides of the igneous area. Apparently the some fresh nephelite and an altered mineral of the soda- They are all short, broad laths, are very regular in among the phenocrysts. Nephelite occurs in the ground- rock underlies the phonolite for some distance, but lite group in the material he examined. Scattered shape, and consist of feldspar, nephelite, and pyroxene. mass of some of the rock, being locally abundant, in the relations are not exposed. It carries much through the groundmass, in some of the rock, is magnet­ The feldspar is a soda-rich orthoclase. Nephelite is clear, colorless, short, hexagonal prisms. ite in exceedingly small cubes. There is much secondary about equal in amount and occurs in similar form. Both coarse material, consisting largely of fragments of material calcite, kaolin, chlorite, analcite, and an the feldspar and nephelite are considerably altered to LAMPROPHYRE DIKES. pink granite and sandstones of various kinds in a anisotropic zeolite. Very commonly a calcite center is analcite in cracks and patches. The pyroxene is very On one of the spurs of the ridge of Lakota sand­ vesicular or highly porous matrix, the porosity surrounded by an analcite rim, the whole being a cavity much less in amount than either the feldspar or nephe­ stone in the northwest corner of T. 52, R. 64, the being due to the leaching out of secondary min­ filling . Some of these secondary products have definitely lite and is segirite-augite or segirite. Apatite occurs as erals. Mr. Jaggar reports that, on microscopic been derived from the feldspars, as is shown by the fact an accessory in the form of long, thin needles with lon­ Morrison shale is traversed by three narrow per­ that the decomposition has taken place along cleavage gitudinal inclusions. Magnetite occurs sparingly in the pendicular dikes of lamprophyre. These clikes run examination, the matrix N. 80° W., but are exposed for only a few yards. cracks. segirite in the form of irregular grains. shows small angular fragments, reaching a maximum of No chemical analysis was made of this rock, but the The groundmass consists of a felt of very minute The largest is 5 feet wide and about 4 rods distant 1 to 2 mm. in diameter, of quartz, orthoclase, micro­ specimen analyzed by Pirsson from the same locality needles of segirite with interspaces of orthoclase and a from the other two. These are each about 1 foot cline, pieces of fine-grained porphyry with segirine, showed the following composition : very cloudy brownish is6tropic substance, probably a wide and separated by a foot of shale, which is not magnetite, and calcite in an earthy-brown groundmass. zeolite derived from nephelite. The character of the This groundmass, when examined under a high power, Analysis of phonolite porphyry from Devils Tower. groundmass is the same as in the rock from Devils visibly altered and shows but slight disturbance. According to Mr. Johannsen is seen to consist of a nearly isotropic base with specks SiO ______- __ -- _ ... _ - __ - __ -- __ 61.08 Tower. The phenocrysts are, however, more numerous of brown iron oxide. Here and there transparent por­ A18 O,_ - __ __.__.__. 18.71 and more uniform in size, and nephelite occurs as well the dikes consist of a dark-green, rusty-looking rock tions of the base show a faint felty polarization. Ferro- Pe2 O8 ______- _ _-______1.91 as feldspar. PeO _ __.____- _ - __ - _ _- ______.___ .63 with an aphanitic groundmass containing a few small magnesian constituents in general are not preserved; Mgo ______----____-______^______.08 black phenocrysts. The microscope shows the texture there are one or two doubtful cases that may be idio- SYENITE PORPHYRY OP BARLOW CANYON. CaO ______- ____ - ______1.58 to be obscurely porphyritic. There are numerous long, morphic outlines of an original hornblende or augite Na2 O _____.____..__ __^. ______8.68 thin laths, a few of them rounded or irregular, grading K2 0 ____._._.._...... _..:____.___.___.._.._____ 4.63 Occurrence and relations. In the bottom of crystal, preserved by paramorphic masses of calcite. H 2 O (ign.)____-_-______2.21 Barlow Canyon, 2^ miles northeast of the Mis­ into a slightly anisotropic, very clouded, and much altered groundmass, whose original character is now ______.18 souri Buttes, there is a small exposure of igne­ STEUCTUEAL GEOLOGY. 80 S ------Trace. indeterminate. The phenocrysts consist of long laths of Cl .______--______-- _ .___.___ _ _.-__ __ .12 ous rock. It appears in a small cliff about 250 various sizes of pale-green diopside, crystals and irreg­ Structure of the Black Hills uplift. The Black MnO-- ______--_--.______Trace. yards long north of the road. The rock is intruded ular grains of magnetite, and vrather large prisms of BaO ______- - --______.05 Hills uplift, if not eroded, would present an irreg- immediately below the massive sandstone in the perfectly fresh apatite. Eed iron oxide occurs in con­ lar dome at the north end of the anticlinal axis that lower portion of the Sundance formation, and this siderable amount in irregular patches, and there is a very extends northward from the Laramie Range of the O Cl. .03 little pyrite. bed is domed over the laccolith with dips of 7° to .Rocky Mountains. A diagram of the dome, illus­ According to the quantitative system the rock of the 10° on the west side and 5° on the east side. The AGGLOMERATE. trated by contours on the surface of the Minne- above analysis is a nordmarkose containing 10.5 per cent base is not exposed. The sedimentary rocks show of normative nephelite. As it is probable that the Associated with the. intrusions of Devils Tower kahta limestone, will be found in the Aladdin folio specimens collected did not contain much nephelite, no marked evidence of alteration, and the disturb­ and the Missouri Buttes are masses of agglomerate (No. 128). The dome is elongated to the south possibly the rock may be more correctly described as ance is confined to the immediate vicinity of the consisting of fragments of rocks of various kinds and northwest, has steep slopes on the sides, is segirite-syenite porphyry. laccolith. included in an apparently igneous matrix. nearly flat on top, and is subordinately fluted to a Petrography. Mr. Johannsen describes the Bar­ Devils Tower. The exposures near Devils Tower PHONOLITE OF THE MISSOURI BUTTES. minor extent. The greatest vertical displacement low Canyon rock as follows: are at the edge of the main talus slope on the west- of the strata, as indicated by the height at which Occurrence. The Missouri Buttes, which rise southwest side of the tower, jdn. a small, elliptical the granite floor is now found, amounts to about prominently above the plateau of Dakota sandstone It is pinkish brown in color and consists of numerous small white and pink feldspar and very few biotite grassy hill encircled by talus. This hill is about 9000 feet. The subordinate flexures in the dome on the divide between the Belle Fourche and Little phenocrysts in an aphanitic groundmass which greatly 150 yards long a'nd trends to the west-southwest. are mainly along the eastern side of the uplift, the Missouri valleys, 3 miles northwest of Devils Tower, exceeds the phenocrysts in amount. It consists of agglomerate, which does not appear most notable ones being in the ridge of Minne- consist of phonolite. There are four principal Under the microscope, in the siagle specimen exam­ elsewhere in the vicinity, although it may underlie kahta limestone just west of Hot Springs, which peaks, rising from 500 to 800 feet above the adjacent ined, the phenocrysts are not everywhere definitely some of the talus. According to T. A. Jaggar, jr., may be regarded as a bifurcation of the southern plateau, which is somewhat higher than the top of determinable. An untwinned alkali feldspar and a who described this rock in the Twenty-first Annual edge of the dome. Another anticline of consider­ Devils Tower. The buttes are on the four corners little segirite or segirite-augite occur, with a small amount of biotite. Besides the fresh phenocrysts, Report, the matrix appears to be a decomposed able prominence occurs 3 miles east of Hot Springs. of an approximately rectangular ridge about a mile there are areas which are entirely altered to an almost porphyry, and the rocks included comprise irregular The subordinate flexures are characterized by steeper in diameter, the eastern side of which is cut away isotropic mineral which was not determined and which fragments of granite, limestone, sandstone, quartz- dips on their western side and gentler dips to the by a deep draw at the head of the east prong of is very similar in appearance to the groundmass, though ite, purplish rhyolite, slate or schist, black shale, east. They merge into the general dome to the north and run out with declining pitch to the south. southeast 25°. Another sharp fold of similar char­ receiving only fine sediment and substances in mulated in thin layers to a thickness of 700 feet, On the western side of the main uplift there is a acter is south of Cabin Creek, on the southern solution. The older formations exposed by the as is now attested by the formation, and it is so marked local steepening of dips and at the north boundary of the quadrangle. This is a northeast- Black Hills uplift were laid down from seas which uniformly of a deep-red tint that this is undoubt­ an abrupt deflection of the dome to the northwest, southwest anticlinal ridge of considerable extent, covered a large portion of west-central United edly the original color. This color is present not which is one of its most notable irregularities. the major portion of which, however, lies beyond States, for many of the rocks are continuous over only throughout the extent of the formation but To the south the dome is separated from a small the quadrangle. The northwesterly dip in this ridge a vast area. The land surfaces were probably large also through its entire thickness, as shown by deep local anticline, which is the extension of the Lara- is 12° to 30°, the southwesterly dip 20°. Farther islands of an archipelago, which was in a general borings, and therefore is not due to later or surface mie Range uplift, by a shallow syncline extending north, near the head of Poison Creek, there is a way coextensive with the present Rocky Mountain oxidation. Either the original material of the northwest and southeast. In the northern Black small, rather steep dome, and still farther north, province, but the peripheral shores are not even sediments was red or it was colored during deposi­ Hills there are numerous local domes and flexures, along Hulett Creek, an elongated but lower dome approximately determined for any one epoch, and tion by the precipitation of iron oxide. At various due mainly to laccolithic igneous intrusions, of is exposed. In irregular areas along Elkhorn Creek the relations of land and sea varied greatly from times the accumulation of clay was interrupted which the most prominent is that of the Bear and Government Canyon, as well as in smaller time to time. The strata brought to view by the by chemical precipitation of comparatively pure Lodge Range, but no similar features are indicated isolated areas on the neighboring minor streams, Black Hills uplift record many local variations in gypsum in beds ranging in thickness from a few by the structure of the southern hills. local doming is observed, and to this may be attrib­ the ancient geography and topography of the inches to 30 feet and free from mechanical sediment. Faults are of rare occurrence, and none have uted in considerable measure the large undulating continent. It is believed that these beds are the products of been detected which amount to more than a few exposures in this portion of the quadrangle. The Cambrian submergence. One of the great events evaporation during an epoch of little or no rainfall feet of vertical displacement, except where some of Dakota sandstone is domed in many places. This of early North American geologic history was the and consequently of temporarily suspended erosion; the igneous masses have dislocated the strata and is noticed particularly on Poison Creek, on Hulett wide expansion of an interior sea over the west- otherwise it is difficult to understand their nearly elevated them unevenly. Creek, on Tie Creek, on lower Elkhorn Creek, on central region. The submergence reached the general purity. It has been supposed that the Structure sections. The sections on the structure- Broncho John and neighboring creeks, in the vicin­ Rocky Mountain province in Cambrian time, and Spearfish red beds are Triassic, but there fe no section sheet represent the strata as they would ity of Strawberry Hill near the head of Sourdough for a while the central portion of the Black Hills direct evidence that they are of this age, and they appear in the sides of a deep trench cut across Creek, and east, northeast, and south of Govern­ remained as one of the islands rising above the may be Permian. Their deposition appears to the country. Their position with reference to the ment Canyon. With the exception of the Poison waters. From the ancient crystalline rocks streams have been followed by extensive uplift, without map is on the line at the upper edge of the blank Creek and Hulett Creek domes, where the westerly and waves gathered and concentrated sands and local structural deformation but with some pla- space. The vertical and horizontal scales are the dip reaches 15° or more, the dip is at few places pebbles, which were deposited as a widespread sheet nation and occasional channeling, which represents same, so that the actual form and slope of the land more than 5° or 6° and may be calculated with fair of sandstone and conglomerate on sea beaches, a portion of Triassic-Jurassic time of unknown and the actual but generalized relations of the accuracy from the topography and the areal distri­ partly in shallow waters offshore and partly in duration. It was succeeded by the deposition of rocks are shown, the structure where buried being- bution of the various formations, the thickness of estuaries. Abutting against the irregular surface later Jurassic sediments. inferred from the position and thickness of the each being given. There is a slight syncline 2 miles of the crystalline rocks which formed the shore are Jurassic sea. In the Black Hills region the strata observed at the surface. south-southeast of Anchor Reservoir, and another sediments containing much local material. Subse­ Jurassic was a period of varying conditions, shallow Structure of the Devils Tower quadrangle. The 2 miles north of Deer Creek near the eastern edge quently, the altitude being reduced by erosion and and deep marine waters alternating. The materials principal structural features of this quadrangle are of the quadrangle. the area possibly lessened by submergence, the are nearly all fine grained and indicate waters with­ illustrated by the five structure sections on the In the vicinity of the Belle Fourche Valley the islands yielded the finer grained muds now repre­ out strong currents. In the southeastern Black structure-section sheet. The quadrangle embraces dips are mostly very low. North of Devils Tower sented by the shales that occur in the upper portion Hills region some of the earliest deposits are thin a portion of the northwestern margin of the Black the valley crosses the slope of a low dome, which of the Cambrian in some areas. In many regions masses of coarse sandstone, indicating shore condi­ Hills uplift, with rocks dipping to the west and causes the Spearfish red beds to rise to a moderate the land surface of crystalline rocks was buried tions, but generally there is shale lying directly on northwest. There are several local irregularities height in the slopes. This dome rises to the south­ beneath the sediments. the Spearfish red beds. Upon this shale is ripple- in the rnonoclinal structure, consisting mainly of east mainly as a part of the Bear Lodge uplift, and Ordovician-Devonian conditions. From the close marked sandstone, evidently laid down in shallow variations of strike and pitch and a few low sub­ with gradual increase in rate of slope approaches the of Cambrian to the beginning of Carboniferous time water and probably the product of a time when ordinate flexures. The rate of slope in the eastern great laccolith of the Warren Peaks area, which lies the Black Hills area presents a scanty geologic record, sedimentation was in excess of submergence, if half of the quadrangle generally varies from 50 to a short distance southeast of the southeast corner of the Ordovician, Silurian, and Devonian being absent not during an arrest of submergence. The red 100 feet to the mile, but to the west and northwest this quadrangle. This steeper dip is a marked in the south and only a portion of the Ordovician color of the upper part of the medial sandy series the amount is much greater. West of a diagonal feature on the upper part of Lytle Creek, where the being present in the north. This is probably in some portions of the Black Hills appears to show line passing from the northwest to the southeast Spearfish red beds and adjoining formations rise because there was an extensive but very shallow a transient return to arid conditions similar to those corner of the quadrangle, the strike is north and abruptly in the vicinity of the igneous intrusions, sea, or land so low as to leave no noticeable evi­ under which the Spearfish formation was laid down. south; east of that line it is northeast and south­ as shown in section E-E of the structure-section dence of erosion. Whether it remained land or An extensive marine fauna and the limestone west. Near the Belle Fourche Valley the change sheet. There is no evidence of uplift connected sea, or alternated from one to the other condition, layers in the upper shale of the Sundance formation in strike is gradual, but in the Little Missouri Val­ with the igneous masses of Devils Tower and the the region shows no evidence of having undergone indicate that deeper water followed. After this ley the change takes place abruptly near the mouth Missouri Buttes, and only a slight local doming in any considerable uplift or depression until early stage widespread uplift gave rise to fresh-water of Prairie Creek. The low dips which prevail in the immediate vicinity of the intrusion in Barlow in Carboniferous time, when there was a decided bodies. The first product was the thick body of the region east of Little Missouri River give place Canyon. subsidence, which established relatively deep-water fine sand of the Unkpapa sandstone, now a promi­ and marine conditions, not only over the Black nent feature along the eastern side of the Black within a short distance to steep dips west of that GEOLOGIC HISTOEY. stream, in the southwestern quarter of the quad­ Hills area, but generally throughout the Rock} Hills, but thinner or absent elsewhere. rangle. The steep dips occur in a zone of north­ General sedimentary record. The rocks appear­ Mountain province. Cretaceous seas. During the Cretaceous period erly strike nearly to the mouth of Prairie Creek, ing at the surface within the limits of the Devils Carboniferous sea. Under the marine condi­ deposits of various kinds, but generally uniform beyond which they diminish considerably in Tower quadrangle are of sedimentary origin that tions of early Carboniferous time there were laid over wide areas, gathered in a great series, begin­ amount, in the region adjacent to North Fork of is, they were deposited by water. They consist of down calcareous sediments which are now rep­ ning with such as are characteristic of shallow seas the Little Missouri and Thompson Creek. At sandstone, shale, limestone, sand, loam, and gravels, resented by several hundred feet of nearly pure and estuaries along a coastal plain, passing into North Fork the dip of the Niobrara beds is 15° all presenting more or less variety in composition limestone, the greater part of which is known as sediments from deeper marine waters, and changing W., but, entering the zone of steep dips 1 mile and appearance. The principal materials of which the Pahasapa limestone. As no coarse deposits toward the end to fresh-water sands and clays with farther south, it increases to 60°. Midway between they are composed were originally gravel, sand, or occur, it is probable that no crystalline rocks were marsh vegetation. The earliest of these deposits, Driscoll and Mud creeks it is 40° in the Niobrara mud, derived from the waste of older rocks, or then exposed above water in this region, although beginning possibly in late Jurassic time, consti­ and 30° in the Greenhorn. About 4^ miles north chemical precipitates from salty waters. elsewhere the limestone, or its stratigraphic equiva­ tute the Morrison formation, a widespread mantle of Yeast's ranch the dip increases to 80°, but 2 These rocks afford a record of physical geography lent, was deposited immediately upon them. In of sandy shales, which is absent to the southeast, miles farther south decreases to 22°. Two miles from Triassic (?) time to the present, and other sed­ the middle part of the Carboniferous the c,ondi- although probably originally deposited there to a south of Yeast's ranch it increases to 45°; farther iments which underlie them extend the record tions were so changed that fine sand was brought greater or less thickness and then removed by south it decreases again to 10°, but increases to 20° back into the Cambrian period. The composition, into the region in large amount and deposited in erosion in consequence of the uplift which initiated at Cabin Creek. The dip in the extreme southwest appearance, and relations of the strata indicate in thick but regular beds, apparently with much cal­ the next epoch. The extent of this degradation is corner of the quadrangle is practically zero. Two some measure the conditions under which they were careous precipitate and more or less ferruginous not known, but it has given rise to a general ero- miles to the north-northeast it is 4°, 2 miles west deposited. Sandstones ripple-marked by waters material. The presence of the iron is indicated by sional unconformity at the base of the Lakota of Yeast's ranch it is 2°, and 2^ miles north west of and cross-bedded by currents and shales cracked the color of many beds of the Minnelusa forma­ sandstone, the next succeeding deposit. The mate­ this ranch it is 5° to 6°. On the western bound­ by drying on mud flats are deposited in shallow tion. Minnelusa deposition is believed to have rials of this formation consist mainly of coarse sands ary of the quadrangle, midway between Good Lad water; pure limestones suggest clear, open seas been followed by an uplift, which appears to have spread by strong currents in beds 30 to 40 feet and Prairie creeks, the beds are horizontal. Far­ and scarcity of land-derived sediment. The fossils resulted in ponding saline water in lakes, in which thick, but include several thin partings of clay ther north along the western boundary and east­ which the strata contain may belong to species accumulated the bright-red sands and sandy muds and local accumulations of vegetal material. Next ward through Blackbank Hill most of the area known to inhabit waters that are fresh, brackish or of the Opeche formation. The Minnekahta lime­ there was deposited a thin calcareous series, repre­ drained by Battle, Prickly Pear, Thompson, Sage, salt, warm or cold, muddy or clear. The character stone, which is the next in sequence, was deposited sented by the Minnewaste limestone, but apparently and Flat creeks has a dip of less than 5°. of the adjacent land may be shown by the character from sea water, and its fossils show with a fair it was laid down only in a local basin in the Due north of the gap between the two northern of the sediments derived from its waste. The degree of certainty that it is a representative of the southern portion of the Black Hills. Over this was peaks of the Missouri Buttes, near the head of the quartz sand and pebbles of coarse sandstones and latest Carboniferous (Permian) time. It was laid spread a thin but widely extended sheet of clay of steep gulch leading northward to Barlow Canyon, conglomerates, such as are found in the Lakota down in thin layers, to a thickness now repre­ the Fuson formation. After the deposition of this there is a small anticline showing a dip of 5° to 7° formation, had their original source in the crys­ sented by only 40 feet of limestone. The very great clay there was a return to shallow waters and east and west. The sharpest anticline of the quad­ talline rocks, but have been repeatedly redistributed uniformity of this formation over the entire Black strong currents, as in Lakota time, and coarse sands rangle is three-fourths of a mile southwest of the lake by streams and concentrated by wave action on Hills area is an impressive feature, probably indic­ of the Dakota formation were accumulated. At near Missouri Buttes. So far as can be observed, beaqhes. Red shales and sandstones, such as make ative of widespread submergence. the beginning of the Benton there was everywhere this disturbance affects a very small area a few up the "Red Beds," as a rule result directly from Red gypsiferous sediments. At the close of the in the region a rapid change of sediment from sand hundred yards long at the most but in view of the revival of erosion on a land surface long epoch represented by the Minnekahta limestone to clay. the proximity of the locality to the Missouri Buttes exposed to rock decay and oxidation and hence there was a resumption of red-bed deposition, and During the great later Cretaceous submergence its significance is perhaps greater than the area of covered by deep residual soil. Limestones, on the the great mass of red sandy clay of the Spearfish marine conditions prevailed, throughout the Ben- disturbance might seem to imply. The axis of the other hand, if deposited near the shore, indicate formation was accumulated. This material prob­ ton, Niobrara, and Pierre epochs, and several anticline trends approximately northeast and south­ that the land was low and that its streams were too ably was laid down in vast salt lakes that resulted thousand feet of clay were deposited. In Benton west, the dip to .the northwest being 35° and to the sluggish to carry off coarse sediments, the sea from extensive uplift and aridity.' The mud accu­ time there were occasional deposits of sand, mostly Devils Tower.

1 8

in the later part of the epoch and general over have developed in the soft deposits, and canyons of on its removal clay and sand remain, often forming a sandy loam of good texture. Owing to the the greater part of the Black Hills region. moderate extent and depth in the harder rocks. a deep soil. If the calcareous cement is present in meander of the river from one side of the valley One earlier deposit was local and produced the Later erosion has progressed with but little deposi­ small proportion only, it is often leached out far to the other, the alluvial tracts are cut into areas as lenses of sandstone which now underlie Mowry tion, but in some cases, with the shifting of chan­ below the surface, the rock retaining its form but a rule less than half a mile square. In a few places beds at various localities in this quadrangle nels, there have been accumulations of local becoming soft and porous, as in the Minnelusa crops are raised in this valley. Small alluvial areas and elsewhere. Another marked episode was that deposits on small terraces at various levels. sandstone. If, as on the limestone plateaus, the lie along Miller, Lytle, Blacktail, and some of the which resulted in the general deposition of the thin calcareous material forms the greater part of the other creeks emptying into the Belle Fourche. In Greenhorn limestone in the middle of the Benton ECONOMIC GEOLOGY. rock, the insoluble portions collect on the surface all of these areas the soil is of excellent quality, sediments. The clay of Benton time was followed MINERAL RESOURCES. as a mantle, varying in thickness with the charac­ and water for irrigation is, either available or could by several hundred feet of impure chalk, now con­ ter of the limestone, being thin where the latter is be easily stored in the many side draws or by dam­ COAL. stituting the Niobrara formation, and this in turn pure, but very thick in many places where the ming the streams. by over 1200 feet of Pierre shale, deposited under At several localities on the northwestern slope of rock contains much insoluble matter. The amount WATER SUPPLY. very uniform conditions. The retreat of the Cre­ the Black Hills coal deposits occur in the base of of soil remaining on the rocks depends on erosion, SUEFACE WATER. taceous sea corresponds with the Fox Hills epoch, the Lakota formation, but no coal has been observed for on many slopes the erosion is sufficient to during which sands were spread in an extensive at this horizon in the Devils Tower quadrangle. remove the soil as rapidly as it forms, leaving bare The average annual rainfall in the Devils Tower sheet over the clay beds, and resulted in the devel­ The Lakota outcrop extending across the quad­ rock surfaces. Crystalline schists and granitic quadrangle is probably somewhat less than 15 opment of extensive bodies of brackish or fresh rangle has been examined for coal at many local­ rocks are decomposed mostly by hydration of a inches, but the amount of rain falling on the ele­ water, which received the sands, clays, and marsh ities, but as the base of the formation is commonly portion of their contained feldspar, and the result vated Bear Lodge Mountains to the southeast is deposits of the Laramie. Whether the two last- hidden by talus from the sandstone cliffs above, it is usually a mixture of clay, quartz grains, mica, considerably more than this. A part of the pre­ named groups of sediments were deposited over is seldom possible to ascertain whether or not and other materials. Shales are disintegrated in cipitation is in the form of snow, and the remainder any of the area now occupied by the Black Hills coal is present. Moreover, coal often crumbles or consequence of changes of temperature, by frost falls mostly in heavy showers of short duration, is not definitely known, but it is possible that they burns away at the outcrop and the overlying and by water, thus by softening and washing during the spring and early summer months. were, as they are upturned around two sides of the sandstone sinks down, leaving no surface indi­ giving rise to soils. If they are sandy, sandy soils The Bear Lodge Mountains, which extend to a uplift. cation of the presence of a coal bed. At many result, and if they are composed of relatively pure high altitude, catch many showers that do not Early Tertiary mountain growth. The Black localities in the quadrangle the Lakota sandstone clay a very clayey soil is the product. The char­ fall on the adjacent plains and have also a greatly Hills dome developed early in Tertiary time or is exposed lying directly upon the Morrison shale, acter of the soil thus derived from the various geo­ increased snowfall. As most of the surface of the possibly in latest Cretaceous time to a moderate apparently in regular succession, indicating that no logic formations being known, their distribution country has a thin soil and only small areas pre­ height, and the larger topographic outlines of the coal is present, but there is a possibility that local may be approximately determined from the map sent porous rocks, the water of rains and melting region were established before the Oligocene epoch, basins occur. Several attempts have been made showing the areal geology, which thus serves also snow runs off rapidly, usually in freshets that fol­ the dome being truncated and its larger old valleys to prospect for coal in the basal Graneros shale, as a soil map. It must be borne in mind that low storms or the rapid melting of snow, the latter excavated in part to their present depths. This is because it is similar to the black shales often some of-the geologic formations present alterna­ taking place during warm spells in the spring. In indicated by the occurrence in them of White River observed in association with coal, but there is not tions of beds of various materials; for instance, consequence of these conditions there is but little (Oligocene) deposits, even in some of the deeper the slightest likelihood that any coal will be found shales and sandstones alternating with limestone. running water in the region during the greater part portions. Where the great mass of eroded material at this horizon, although some of the shale is suf­ These give abrupt transitions in the character of of the year. Springs are few and of small volume was carried is not known, for in the lower lands to ficiently carbonaceous to burn for a few minutes. their disintegration products, soils which differ in the lower lands. the east and southeast there are no early Eocene widely in composition and agricultural capabilities A large amount of run-off in this region could deposits nearer than those of the Gulf coast and BUILDING STONE. occurring in narrow zones side by side. The only be saved by dams and made available for irriga­ Mississippi embayment and those of the Denver Large amounts of stone suitable for building are areas in which the boundaries between different tion. There are suitable dam sites at many local­ Basin. available from the Lakota and Dakota sandstones, varieties of soil do not coincide with the boundaries ities, especially in the higher slopes. As the Oligocene fresh-water deposits. Oligocene depos­ but they have not as yet been utilized to any great of the rock formations are in the river bottoms, in evaporation in the region is about 6 feet each its were laid down by streams and in local lakes extent. Stone also occurs in the Sundance and sand dunes, in the areas of high-level gravels, in year, a large amount of water would have to be or bayous, and finally covered the country to a Fuson formations, and the sandstones and concre­ the smaller valleys, and upon steep slopes, where impounded to compensate for this loss. There are level now far up the flanks of the Black Hills. tions in the Graneros, and overlying formations can soils derived from rocks higher up the slope have many excellent dam sites along the creeks flowing; Erosion has removed them from most of the higher be used for rough work. Portions of the Dakota washed down and mingled with or covered the into the Belle Fourche; but, to judge by the results regions where they existed, especially along the sandstone are massive, fine grained, even textured, soils derived from the rocks below. Soils of this obtained with a number of dams in the plains western side of the hills, but in the vicinity of and of a pleasant light-buff to gray tint, similar to class are known as overplaced soils, and a special region farther northeast, more or less water can be Lead small outliers remain at an altitude of over the stone worked extensively in Buffalo Gap. At map of large scale would be required to show their held in almost all portions of the area. 5200 feet, and on the north end of the Bear Lodge present the region is too far from railroads for this distribution. Belle Fourche River carries a large volume of Mountains they are a thousand feet higher. In stone to be profitably worked for shipment. The Distribution. The arable lands of the Devils water at times of freshet, but is a very insignificant many places on the slopes of the uplift there is igneous rocks of Devils Tower and the Missouri Tower quadrangle are irregularly distributed and stream during the dry periods of midsummer. Its clear evidence of superimposition of drainage, due Buttes are so hard that there would be great dif­ occur in several formations. The most extensive normal flow varies from about 2 to 15 second-feet, to a former capping of Oligocene formations. ficulty in dressing them, but they could be crushed areas available for farms are in the alluvial deposits so far as observed, and occasionally portions of its Later Tertiary mountain growth. After the for road metal if there were any demand for it. along Little Missouri and Belle Fourche rivers and course go dry. It drains a large area in the plains Oligocene epoch the dome was raised several hun­ some of their branches. Many areas which have of east-central Wyoming, and the total volume of dred feet higher and was more extensively eroded. CLAYS. naturally fertile soils are not situated favorably for water which it carries in a year is very great. It No representatives of the succeeding Loup Fork Many of the shales above the Dakota sandstone farming, notably those which are at altitudes so receives numerous tributaries from the western and group the Arikaree and Ogalalla formations- are sufficiently soft to be classed as clays, and por­ high that frosts are prevalent. Scanty rainfall is northern sides of the Black Hills, including some have been discovered in the immediate vicinity of tions of the Fuson, Morrison, and Sundance the principal handicap in the greater part of the streams of considerable volume. Its waters are not the Black Hills but they are extensively developed formations could be used as clays. There is, how­ area, especially in localities where there is not used to any extent for irrigation because of the dif­ in Pine Ridge to the south and remain on the high ever, no local demand for this material. Sandy sufficient running water for irrigation. ficulty of maintaining head-gates and ditches dur­ buttes to the north, in the northwest corner of clays suitable for brickmaking occur along many The Spearfish formation is mostly bare of soil in ing freshets. Its course is winding, and although South Dakota. There was probably slow but con­ of the alluvial flats and they haV-e been utilized for the small areas in which it outcrops in this quad­ there are alluvial flats within most of its bends, tinuous uplift during the Loup Fork epoch, and this purpose to a small extent at one or two points. rangle. Extensive exposures of the Sundance these are cut into small areas by the meanders, materials were contributed by the higher slopes of A peculiar absorbent clay, known as bentonite, formation are chiefly in high ridges and slopes, which in their outer curves as a rule impinge on the Black Hills at that time, but whether the for­ occurs in the Graneros shale, but it has not been where ordinarily the soil is thin. Much of the the steep slopes of the valley. mations ever were deposited in the immediate worked in this region. formation consists of clay, and it lies in general upon Little Missouri River rises in the southeast cor­ vicinity of the hills has not been ascertained. dry slopes where the rainfall is seldom sufficient ner of the quadrangle and flows northward to the Quaternary uplift and erosion. During the GYPSUM. for raising crops. The Lakota and Dakota sand­ north line of T. 55 and thence northeastward to early portion of the Quaternary period there was Several thin beds of gypsum are present near the stones, although having considerable extent, yield the northeast corner of the quadrangle. Ordi­ widespread denudation of the preceding deposits, top of the Spearfish formation, but their thickness relatively barren soils and are for the most part so narily it carries but a small volume of water, but and many of the old valleys were revived, with in few places exceeds 2 feet and they are interbed- dry and so situated topographically that they are it is subject to freshets in which the flow often much rearrangement of the drainage, which on the ded with soft shale. Plaster of Paris is prepared not favorable for farming. The soils in the exten­ is large. ' In dry weather the only branches from eastern side of the Black Hills was caused mainly from gypsum by calcining it to drive off part of sive shale areas in the western and northern which it receives running water are Prairie Creek by increased tilting to the northeast. This rear­ the chemically combined water, and then pulver­ portions of the quadrangle are mainly thin and and North Fork of Little Missouri River, both very rangement has caused several streams superimposed izing it. The material is of no value, however, contain a large amount of clay. They could be small streams. The flow in the river is sustained upon the Oligocene deposits to cut across old unless near to market. tilled on nearly all the lower slopes, however, if mainly by small seeps and springs in its bottom. divides, in some places connecting a valley with properly irrigated. The sandstones in the south­ Lytle Creek rises on the northwestern slope of the SOILS. its next neighbor to the north. Such streams flow western portion of the quadrangle disintegrate into Bear Lodge Mountains and flows northwestward, southeastward for some distance in pre-Oligocene Derivation. The soils in this region are closely excellent soils, but the land is not suitably sit­ reaching the Belle Fourche a short distance east of valleys and then turn abruptly northward into related to the underlying rocks, from which they uated for farming. Most of the wide alluvial bot­ Devils Tower. Its small flow is sustained mainly canyons of post-Oligocene age, leaving elevated are residual products of decay and disintegration, tom lands along Little Missouri River have rich by springs which rise at intervals along its bed. saddles which mark the southeastward course of except where they are formed as alluvial deposits and sandy loams, but in some portions of the area Blacktail Creek drains an inconsiderable area the old valleys. Some of the offsetting in the in the larger valleys or are spread by winds. In the percentage of clay is so large that "gumbo" along the western slope of the Bear Lodge Moun­ present drainage has been largely increased by the process of disintegration residual soil develops results. There are many areas along the Little tains and flows in small volume to the Belle early Quaternary erosion and recent stream more or less rapidly on the several rocks of the Missouri and its larger branches thai? could be Fourche, which it joins half a mile southeast of robbing. region according to the character of the cement farmed advantageously if they were irrigated. At Jffulett. There was apparently still further uplift in late holding the particles together. Siliceous cement many localities water could be =held in reservoirs Miller Creek, another small tributary reaching Quaternary time, for the present valleys, below the dissolves most slowly, and rocks in which it is pres­ which would afford a supply for the irrigation of the Belle Fourche in the northeastern portion of level of the earlier Quaternary high-level deposits, ent, such as quartzite and sandstones, are extremely areas of moderate size. The alluvial flats along T. 52, rises on the east slope of the Bear Lodge seem to be cut deeper than they would be in durable and produce but a scanty soil. Calcareous the Belle Fourche are in general well adapted for Mountains. There are numerous springs along the simply grading their profiles to the level of Mis­ cement, on the other hand, is more readily dissolved agriculture. At a few localities there is a pre­ valley of this creek, which are important factors an souri and Cheyenne rivers. Wide, shallow valleys by water containing carbonic and other acids, and dominance of: sand, but in most places the soil is sustaining the flow...... 9

Except Blacktail, Lytle, and Miller creeks, the those of the Minnelusa, Lakota, and Dakota forma­ its outcrops this formation appears to consist of abandoned in the red beds, which were entered at 400 many small branches flowing into the Belle tions. The water thus absorbed by the sandstones very porous sandstone, likely to imbibe much sur­ feet. Probably it penetrated the Opeche red sand­ Fourche are dry in summer or carry only a very passes far beneath the surface as the water-bearing face water and to constitute a water-bearing stratum stones and was discontinued very near the top of small volume of water, mainly in scattered pools. beds descend on the slopes of the uplift. available for deep wells. The numerous springs the upper sandstone of the Minnelusa formation. All the ordinary streams in the western and north­ Dakota-Lakota sandstones. The Dakota and which emerge in places from the upper sandstone It is unfortunate that this bed was not entered and ern portions of the quadrangle have very .scanty Lakota sandstones are the principal formations in furnish a further indication of its. properties in this tested as to its water content. water supplies, and in dry weather many of them which water supplies are to be expected in the regard. The formation was penetrated by a deep Pahasapa limestone. As shown on the structure- contain no water at all. Thompson Creek is an western and northern, or plains portion, of the boring at Cambria and found to consist there of a section sheet, the Devils Tower quadrangle is under­ exception, for ordinarily it carries a small amount Devils Tower quadrangle. As shown on the struc­ very fine-textured rock, with the sand grains so lain by the Pahasapa limestone, but, except in the of water, mostly in pools with feeble overflow from ture-section sheet, they pass beneath the overlying closely cemented by lime that the interstices were vicinity of the Bear Lodge uplift, this formation one to another. shales with varying dips that carry them to a depth filled up, without leaving room for much water. lies at great depth. A large supply of water was of about 3,700 feet along the western margin of the The rock appears to be of much coarser grain and obtained from it in a deep boring at Cambria, and UNDERGROUND WATERS. quadrangle. The depth to the top of the Dakota less calcareous to the north, especially the upper possibly the water-bearing stratum continues to this Source. Throughout the quadrangle there are sandstone is indicated approximately on the artesian bed of white sandstone, which would probably region. Its depth in the Belle Fourche Valley prospects of water supplies from wells of greater or water sheet. In various portions of the country yield flowing water in portions of the northern ranges from 900 to 1100 feet, but toward the less depth. The series of formations, as shown surrounding the Black Hills the Dakota-Lakota Black Hills region. This upper sandstone lies at a northwest greatly increases, so that the formation in the columnar section, includes several beds sandstones have been penetrated by wells, most of moderate depth along the Belle Fourche and the lies far below the surface in the western and north­ of water-bearing sandstone which receive water which obtain flows of greater or less volume and of larger confluent valleys in the southeast corner of ern portions of the quadrangle. at the surface in the higher ridges and slopes satisfactory quality. The nearest wells to the Dev­ the quadrangle. The depth to its top is shown on Deadwood^sandstone. Below the Pahasapa lime­ of the Black Hills. These sandstones are carried ils Tower quadrangle are those in the vicinity the artesian water sheet, from which it will be seen stone is a series of shales and sandstones which underground in the general outward dip on the of Belle Fourche, a short distance to the east. that along the Belle Fourche Valley from bench probably contain a water supply, but in this quad­ flanks of the hills, and within a short distance, owing Undoubtedly the same water-bearing sandstones mark 3870, near Devils Tower, nearly to the north rangle they are too deeply buried beneath the sur­ to the relative steepness of the dip, attain consid­ underlie the.western and northern portions of this side of Burnt Hollow the sandstone could be reached face to be reached by ordinary boring operations. erable depth. In most of the area water-bearing quadrangle, and they will probably yield flowing by borings less than 600 feet deep, probably about TIMBER, beds at one horizon or another lie at a depth that wells in the lower lands in the valleys of the Little 500 feet in T. 54 N. Above bench mark 3870 and is within reach of the well borer. As the region is Missouri and its larger tributaries, as shown on the near the eastern margin of the quadrangle the There is little merchantable timber in the Devils semiarid, with surface waters inadequate or of bad artesian water sheet. depth gradually increases to 750 feet or more. Tower quadrangle, but portions of the area contain quality in most localities, there is considerable need Formations between the Lakota and Minnelusa. Along Lytle Creek the depth varies from 550 feet abundant supplies for firewood and other local use. for underground waters. The principal water­ In the Morrison and Sundance shales, underlying near its mouth to about 700 feet between bench Scattered pines grow along the slopes of most of bearing strata rise to the surface on the slopes of the Lakota sandstone, there are no prospects for marks 4146 and 4402 and 600 feet as the Bear the canyons on either side of the Belle Fourche the Black Hills in regular succession, as already water, although the sandstone layer in the lower Lodge uplift is approached, in the southeast corner Valley and in moderately large bodies on the described. They outcrop in wide zones encircling portion of the Sundance formation may contain a of the quadrangle. higher ridges in the southeast corner of the quad­ the uplift, and receive a large amount of water not small amount. The great mass of gypsiferous red As the sandstone rises high on the slopes of the rangle. Along the Belle Fourche there is an only from the rainfall on their surface but from shale of the Spearfish and Opeche formations is Black Hills, if it contains water the pressure or almost continuous border of cottonwoods, many streams which at many points sink into them also not water bearing. The Minnekahta limestone head should be sufficient to afford a flow in all the of them attaining large size. In the plains region wholly or in part in crossing their outcrops. The is too dense to carry water, notwithstanding the deeper valleys in the southeastern portion of the of the western and northern portions of the quad­ sinking of the streams in this manner is observed fact that in some places it is cavernous. Devils Tower quadrangle. rangle wood is very scarce. The ridge due to the in almost every valley leading out of the central Minnelusa formation. As shown on the struc­ The only attempt to obtain deep-seated waters outcrop of the Mowry beds is covered thinly with area. Few of the streams carry into Cheyenne ture-section sheet, the quadrangle is underlain by in the vicinity of this quadrangle was in a deep small pines, but farther west, in the wide shale out­ River more than a small portion of the original the Minnelusa formation, which lies at great depth boring made at Aladdin several years ago. This crops, there are no trees, except a cottonwood here run-off of their drainage basins, for much of it 'sinks in the western and northern portions of the area boring reached a depth of 1150 feet, but it was and there along the streams. underground in crossing the sandstones, particularly but rises nearer to the surface to the southeast. In a practically dry hole. It is stated to have been January, 1906. Devils Tower.