the mountain sides. We can only account for them on the supposition that as the anticlinal crest was slowly emerging from the sea, the myriad sources of our great rivers were seeking their natural channels, and that these branches or tributaries began this erosive action long before the great thoroughfares, the valleys of the Mississippi and the Missouri, were marked out. The erosion would go on as the mountains continued slowly rising at an almost imperceptible rate, and in process of time the stupendous channels which every where meet us along the immediate sides of the mountains would be formed. If we examine the barometrical profiles, already referred to, we see at a glance that in traversing the country from the Mississippi to the foot of the mountains the ascent is very gradual, but increases as we approach the upheaved ridges. In an equal proportion will the rapidity and consequently the erosive power of the streams be increased so that we may readily account for those grand displays of the erosive action of water which occur so frequently along the mountain sides. Eastward from the mountains, beyond this immediate influence, the descent is so gradual that the Missouri flows quietly along over its yielding alluvial bed, transporting its sediments to the Gulf of Mexico. That the progressive elevation of the country continued up to our present period, or at least until near the time of the deposition of the most recent superficial deposits, we think we have evidence derived from the terraces, which are seen all along the streams. The elevation of these terraces increases as we approach the sources of the rivers, averaging from a few feet to 150 or 200 feet in height. This subject will be discussed more fully in a future article. We conclude, therefore, that the barometrical profiles, constructed from explorations across our continent, and geological data, indicate a long-continued quiet expansion of the earth's crust, commencing toward the close of the Cretaceous epoch and extending even to our present period; that near the close of the accumulation of the Tertiary lignite deposits, the crust of the earth had reached its utmost tension, the long lines of fractures had commenced, and the anticlinal crests of the mountain ranges were marked out. In a previous paper in this Journal, we remarked that there is no unconformability in any of the fossiliferous sedimentary strata in the Northwest, from the Potsdam sandstone to the summits of the true lignite Tertiary. We believe, therefore, that the elevated ridges which form the nuclei of the mountain ranges began to emerge above the surface of the surrounding country near the close of the Eocene period. We think also that the evidence is clear that there were periods of subsidence and repose; but the thought which we wish to illustrate is, that there was a slow, long-continued, quiet, upward tendency which began near the close of the Cretaceous epoch and culminated in the present configuration of the western portion of our continent near the commencement of our present period. WASHINGTON, D. C., January 1, 1862. ART. XXXIV.—REMARKS ON THE GEOLOGICAL FORMATIONS ALONG THE EASTERN MARGINS OF THE ROCKY MOUNTAINS.* BY F. V. HAYDEN. [From the American Journal of Science, May, 1868.] On several former occasions I have described the different geological periods represented by the rocks uplifted along the margins of the Rocky Mountains and especially along the eastern slope. Examinations over a great extent of country in considerable detail, from latitude 49° south nearly to the Arkansas River, have shown me that quite marked lithological and paleontological changes occur in them all as we proceed from the north southward. It is the purpose of this article to note this fact somewhat more in detail than hitherto. Beginning with the nucleus of the Rocky Mountains at any point along the eastern range, we find it composed of massive granite rocks, mostly red feldspathic, but not unfrequently gray or other shades of color; then a series of metamorphic rocks (as they are usually called, though no doubt all the granites should be included with them), syenites, diorites, clay, mica, and hornblende slates, and igneous rocks of various kinds here and there. Proceeding outward, we find the Silurian period represented by the Potsdam sandstone, Devonian wanting, then Carboniferous, Red Beds (Triassic ?), Jurassic, Creta*This article refers only to the eastern ranges of the Rocky Mountains, extending south to the Arkansas. The same remarks may or may not apply to other portions. ceous, and Tertiary, all connected together in the regular order of sequence, and all but the most recent Tertiary in strict conformity. The Tertiary deposits do not exhibit any marked change either in their mineral or fossil contents from the northern portion of our domain to the Arkansas, but the Cretaceous beds present several quite imarked changes. Nos.* 5 and 4 maintain their peculiar characters as shown on the Upper Missouri, wherever they are exposed all along the eastern slope, except that they contain comparatively few fossils, yet a few characteristic species are found wherever these beds are seen, which identify them. On the Missouri River, No. 3 attains a great thickness, 400 to 600 feet, presenting massive escarpments of yellow chalk, and it can be traced all the way across the prairie country lying between 98° and 100° longitude. At Forts Hayes and Wallace on the Union Pacific Railway, Eastern Division, there are massive beds of this chalk which is sawed into building blocks with a common saw, and in many instances it is nearly as white as our chalk of commerce and might be used for the same purposes. The two characteristic species of fossils of this division are found everywhere, Ostrea congesta and Inoceramus problematicus. All along the slope of the mountains No. 3 still retains its chalky nature, but becomes quite shaly, none of the layers ever becoming more than one or two inches in thickness. This is the case at the sources of the Missouri along the Bighorn and Wind River Mountains also, from the South Pass to Pike's Peak, and on the western slope wherever this bed is exposed. Near Denver, at Marshall's coal-mine, No. 3 has been changed by heat into a grayish compact limestone, quite hard and brittle in its fracture, which makes an excellent flux in smelting ores. But this change is local, for 16 miles north of this point it presents the same laminated character. It seems that No. 3 loses its massive chalky character, by which it first attracted attention on the Missouri River, in its westward extension, so that along the margins of the mountains, except in one locality, it cannot prove of any economical value, while between 98° and 100° longitude it becomes very useful not only for lime, but also for building purposes. No. 2, like Nos. 4 and 5, retains its dark plastic clay character everywhere that it has been observed, but, like the others, it is not nearly as well developed in Colorado as on the Upper Missouri. Near Fort Benton it attains a thickness of 200 to 400 feet, while in Colorado it is not more than 50 to 150 feet. Between longitude 96 and 99° No. 1 retains its deep rustred sandy characters with dicotyledonous leaves from the Missouri River to the Arkansas, but nowhere along the margins of the mountains from latitude 49° to Pike's Peak have I ever seen any well-defined palæontological proof of its existence. Near Fort Benton are a series of Cretaceous beds containing some seams of impure lignite and numerous species of fossils, not one of which is identical with those so abundant in Nos. 4 and 5 lower down on the Missouri. These beds have been placed provisionally in the general section as a portion of No. 1, but the region about Fort Benton needs a more careful examination before any positive conclusions can be arrived at. Around the Black Hills is a bed of massive siliceous rocks, some layers forming a pudding stone, which in some localities takes the name of fortification rocks. These hold a position between No. 2 Cretaceous and the Jurassic marls. The same are seen along the margin of the Bighorn Mountains, in which I observed a bed of impure lignite, an abundance of silicified wood, and some uncharacteristic Saurian bones. From the Wind River Mountains to Pike's Peak these same siliceous and pebble cemented rocks occur holding the same geological position, forming, as it were, beds of transition between the Cretaceous and the Jurassic periods. I have carefully examined these rocks for hundreds of miles and have never yet detected any organic remains, animal or vegetable, in them. The Jurassic beds, as revealed along the mountains, possess peculiar and marked lithological characters, so that having identified them by the fossils in one locality we can trace them over great areas. They were first shown to exist in the West in the form of a zone engirdling the Black Hills. They here attain a thickness from 200 to 300 feet at least, and from the beds in this locality alone have fossils enough been collected of such unmistakable Jurassic types as to prove their existence beyond a doubt. But these beds have also been shown, since they were first made known in the Black Hills, to be exposed along the margins of the Bighorn and Wind River Mountains near Red Buttes, on North Platte, and in numerous localities in the Laramie Plains, and westward to Fort Bridger. So numerous are the species now known from the West and so close are the affinities of most of them to well-known Jurassic types that it is not necessary for me in this place to detail the evidence in support of that statement. It is sufficient to remark that the Jurassic system is quite plainly represented along the margins of the different ranges of mountains north of latitude 42°, but proceeding southward from Deer Creek on the North Platte, the Jurassic beds diminish in force until near Cache la Poudre it becomes doubtful whether they are represented at all' * The different divisions of the Cretaceous period, as shown on the Missouri River, have received geographical names, as Fort Benton Group, &c., but I use the old divisions by figures for brevity. At this point there is a thin bed, perhaps 20 to 50 feet in thickness, of greenish-gray arenaceous marl overlying the Red Beds, which seem to occupy the place of the Jurassic. This seems to thin out more and more as we proceed southward toward the Arkansas. From Deer Creek 100 miles north of Fort Laramie to Denver, a distance of 400 miles, I have searched in vain for any organic remains in the rocks which appear to represent the Jurassic period of the Black Hills, Bighorn and Wind River Mountains. In the Red Beds or supposed Triassic no organic remains have been found north of the Arkansas, and they do not differ much lithologically in their southward extension, except that they seem to be much thicker and more gypsiferous northward. In the far north the Carboniferous rocks are in many localities 500 to 1,500 feet in thickness, and even as far south as the Red Buttes the massive beds of limestone, with true Carboniferous fossils, are exposed 500 to 1,000 feet thick, and are quite distinct from the red or variegated beds. But as we proceed southward from this point the Carboniferous limestones seem to lose their usual lithological characters and the Red Beds prevail. At the head of Pole Creek on the eastern margin and in the Laramie Plains west, the Carboniferous rocks are mostly of a red arenaceous character, with a few layers 2 to 10 feet in thickness of whitish or yellowish limestone. From these limestones I collected Productus Prattenianus, Athyris subtilita, and other well-known Carboniferous forms. Above these Red Beds, which contain intercalated layers of limestone, is a considerable thickness of purely red arenaceous beds, but in studying all these rocks with some care from Pole Creek nearly to Pike's Peak, I could not separate the Red Beds from the Carboniferous by any break in continuity, and I was rather inclined to the opinion that inasmuch as a large portion of the gypsiferous or variegated beds could be shown to be Carboniferous, they might possibly all be included in that period. The Potsdam sandstone, the only portion of the Silurian era ever detected along the eastern slope of the Rocky Mountains north of the Arkansas, seems to fade out entirely south of the Red Buttes on the North Platte. It is well defined around the Black Hills, Bighorn, and Wind River Mountains. Near the Red Buttes there is a bed of siliceous pudding stone resting on the metamorphic rocks which may be the Potsdam in its southern extension, but south of Fort Laramie to Pike's Peak it is somewhat doubtful whether any trace of it exists. If it occurs at all it a very thin layer, for the most part concealed. So far as I could determine, the Carboniferous rocks rest directly (though not conforming) upon the metamorphic rocks. There is also some change in the nuclei of the mountain ranges southward. At the north the feldspathic and the gray granites prevail, but southward the syenites and igneous rocks form the central portions of the mountains almost entirely. It is rare to see true granite. The above remarks, founded on observations that have been made over a very great extent of country through a period of many years, lead me to the following conclusions: 1st. That all the formations of the West undergo more or less change both in their mineral and fossil contents in their extension toward the west and south. They all seem to reach their culmination not far from the central portion of the great area drained by the Missouri, and lose to a great extent their distinctive characters beyond its limits. 2d. The Potsdam sandstone and the Jurassic beds present more remarkable changes than any of the others. While north both these formations are well marked, both lithologically and paleontologically in their southward extension they gradually fade out, so that south of Fort Laramie to Pike's Peak it becomes a matter of doubt whether · they exist at all. The inference therefore is that these groups of rocks are not well defined, if they occur at all south of the Arkansas. In support of this statement is the fact that although this southern region has been traversed in every direction by multitudes of explorers for thirty years past, among whom have been geologists of high reputation, yet south of latitude 40° not a single animal fossil has ever been detected with Jurassic affinities, and it is quite doubtful whether any have been found with Triassic or Permian relations;* even the few plants that have been found are doubtful in their affinities and are regarded as probably Cretaceous or Permian. I have made these remarks from the fact that all the observations that have been made by explorers in the West during the past will, ere many years, be put to the rigid test of a most careful scrutiny, and an error by whomsoever made, though sustained by the highest authority in the land, will fall to the ground before the light of true science as the dead bark from a tree. The ease with which the Rocky Mountain region can soon be reached, in a few years, when our great national highways are completed to the Pacific, will induce the best geologists in this country and in Europe to visit them, and the many intricate problems of Rocky Mountain geology must be solved. * I do not wish to be understood as saying that the Jurassic rocks do not occur, south of the Arkansas, as well as the Permian and Triassic, for there is ample room for their fullest development, but no evidence has ever yet been obtained of its (Jurassic) existence, although the country has been so long traversed by explorers. The evidence, so far as it goes, would seem to be against its occurrence at all. The great school of mines, which will no doubt be soon established in the heart of the mining districts of the Rocky Mountains, must gather around it able men who will either sustain or reject the observations of other investigators who have examined the country under less favorable auspices. THE PRIMORDIAL SANDSTONE OF THE ROCKY MOUNTAINS IN THE NORTHWESTERN TERRITORIES ON THE UNITED STATES. BY DR. F. V. HAYDEN. [From the American Journal of Science and Arts, vol. xxxiii, Jan., 1862.] We have attempted in this paper to present as clear and connected an account as the known facts will permit, of the Primordial rocks west of the Mississippi, more especially those of the northwest, west of longitude 960. The Potsdam sandstone of the New York series is the division of the Primordial zone of Barrande, mainly represented in the Rocky Mountain district, and is that part alluded to unless otherwise mentioned. In speaking of the geographical distribution of the Potsdam sandstone reference will be made to localities to the eastward where it has furnished most abundant and satisfactory testimony in regard to its age. We will, in the first place, present more in detail such facts as we have been able to obtain by personal observation in the field, and by the aid of these and the statements of reliable explorers we hope to give some idea of the geographical extension of this wide-spread formation in the West. Our first knowledge of Primordial rocks west of the Missouri River was obtained in the summer of 1857, during the exploration of the Black Hills of Nebraska, by an expedition under the command of Lieut. G. K. Warren, Topographical Engineers. The more important facts, with the determination of the fossils, were published by Mr. Meek and the writer in March, 1858.* By reference to the general map of the country west of the Mississippi, recently published under the auspices of the War Department, we find that the Black Hills lie between the 43d and 45th degrees of latitude, and the 103d and 104th degrees of longitude, and occupy an area about 80 miles in length, and from 30 to 50 in width. According to Lieutenant Warren the shape of the mass is elliptical and the major axis trends about 20° west of north. The base of these hills is about 2,500 to 3,000 feet, and the highest peaks 6,700 feet above the ocean. The entire range is clasped, as it were, by the North and South Branches of the Shyenne River, the most important stream in this region. The North Branch passes along the north side of the range, receiving most of its waters from it, but taking its rise far to the westward near the sources of Powder River, in the "divide," between the waters of the Yellowstone and those of the Missouri. The South Branch also rises in the same "divide," flows along the southern base of this range, receiving the waters of numerous tributaries which have their sources in it. Again, by referring to the map above alluded to, we ascertain that the Black Hills form the most eastern outlier of the great Rocky Mountain Range as well as the first point where rocks older than the Carboniferous are exposed to the eye after leaving the Missouri westward. These hills would seem to constitute an independent elevation, so far are they removed from other ranges, were it not for a low anticlinal which may be traced across the plain country southward, connecting them with the Laramie Mountains near Laramie Peak. The central portion is composed of red feldspathic granite and stratified Azoic rocks, and resting unconformably upon, and forming a zone or belt around the ellipsoidal nucleus, are a series of variable, reddish ferruginous sandstones, which by their organic remains furnish the most reliable evidence that they belong to the Potsdam period. As observed in and around the Black Hills, the Potsdam sandstone presents a great variety of lithological characters. In many localities it is composed of a conglomerate of more or less water-worn pebbles, mostly whitish crystalline quartz, but representing to a greater or less extent the different varieties of the changed rocks beneath. The pebbles vary in size from an eighth of an inch to four inches in diameter cemented together with a silico-calcareous paste. Some of the pebbles are scarcely worn, while others are quite smooth. At the locality where the following section was taken, the sandstone is of a gray color tinged with red at the base, but ascending it becomes more Proceedings of the Academy Nat. Sci., Pa., March, 1858. * ferruginous until its color is a dark dull red, and its texture a coarse-grained friable sandstone with many quartzose and micaceous particles and some calcareous matter. Seams two to four inches in thickness are very nearly composed of shells of the genera Lingula, Obolella, &c., which, though quite fragile in their nature, are so well preserved as to be easily identified. The following section taken near the central portion of the Black Hills exhibits Carboniferous rocks and the Potsdam sandstone conforming to each other, but the latter resting discordantly upon the Azoic stratified and granitic rocks. 1. A hard, compact, fine-grained yellowish limestone of an excellent quality, 3. Variegated sandstone, of a gray and ferruginous red color, composed chiefly 4. Stratified Azoic rocks standing in a vertical position for the most part. Feet. 50 40 50 to 80 Leaving the Black Hills in a direction a little west of south, we follow an anticlinal valley to the Laramie Mountains with which the Black Hills seem thus obscurely connected. The evidence, so far as it goes, appears to indicate that the same force which elevated the one raised the other, and that the events were synchronous. We do not observe the lower rocks after leaving the Black Hills until we reach the source of the Niobrara River, where we find a series of horizontal strata resting upon the vertical edges of Azoic clay slates and schists, which from their lithological characters and position doubtless belong to the age of the Potsdam sandstone, though no organic remains could be found. The following section shows the descending order of the beds. 3. Sandstone, dull reddish ferruginous, like bed 1, above 4. A series of strata more or less inclined, composed of gneiss with silvery mica in large plates, micaceous and talcose slates, white quartz, &c. Feet. 22 5 37 We have no doubt that the Potsdam sandstone occurs in the form of an outcropping belt all along the Laramie range of mountains, though, after a thorough search we were unable to discover any organic remains. Having once fixed the position and age of a formation, as the Potsdam sandstone is established in the Black Hills, we may rely with considerable confidence upon the physical characters and stratigraphical position to determine the age of rocks in the same district of country. We have on these grounds regarded certain rocks along the Laramie Range as of this age. In the first ridge of elevation west of the trading post on La Prele Creek, about 60 miles northwest of Fort Laramie, is a series of rocky layers 50 feet in thickness, reposing unconformably upon red feldspathic granites, mica schists, and clay slates. The lower portion is a fine-grained subcrystalline quartzose rock, partially metamorphosed, passing up into a friable sandstone arranged in thin layers, with the lamina quite oblique, overlaid by a considerable thickness of conglomerate. The dip is about 20° east. Resting upon these supposed Potsdam rocks at this point and inclining at about the same angle are layers of limestone, containing numerous fossils which prove them to belong to the Carboniferous age. Again, further southward along the same range, near the source of the Chugwater River we find the same limestones well developed, containing some Carboniferous fossils, and underneath them and inclining in the same direction is a group of strata of a brick-red color, more or less changed by heat, holding the position of the Potsdam sandstone in other localities. In some places these rocks are so metamorphosed by heat from beneath as to appear like a red feldspathic granite, and in others, like a reddened granular sandstone containing numerous unchanged masses of quartz. At the Shyenne Pass, we observed the well-known Carboniferous rocks, inclining about 130. Beneath them is a considerable thickness of red marls and laminated sandstone, and still farther down and inclining 260 is a quartzose sandstone, full of water-worn pebbles, passing down into layers which at a distance look like indurated clay, but which, on closer examination, proved to be an aggregation of quartz and feldspar crystals cemented with a calcareous paste. At another locality we have the following characters: (1) a grayish quartzose sandstone, 12 inches; then descending, (2) laminated granitoid rock, 2 feet; (3) compact reddish ferruginous granitoid mate |