brilliant red Triassic strata. The difficulty of drawing any line between Triassic and Jurassic formations in that region is again acknowledged on these maps, the lower red series being doubtfully assigned to the older, and the upper variegated deposits to the latter system.

Cretaceous rocks are abundantly developed, and cover a vast extent of territory. In particular, they spread over the wide plateaux between the San Juan and Gunnison Rivers, and form the platform on which the enormous volcanic outbursts have been piled up from the West Elk Mountains southward into New Mexico. It is more easy to trace on these maps, too, the area respectively occupied by the Laramie, Wasatch, Green River, Bridger, and Uintah formations which represent Post Cretaceous and Tertiary times. Glacier moraines, lake deposits, drifts, sand-dunes, and recent alluvia, all find adequate expression on the maps. Especial care, too, seems to have been bestowed upon the eruptive rocks which form so important and interesting a feature of Colorado geology. The more characteristic varieties are represented by distinct shades of crimson or orange, and they have been mapped in such a way as to convey at a glance, and even without the aid of sections, a tolerable clear notion of the volcanic phenomena of the region. On the one hand we see the great lava-sheets capping the mesas and spreading far over the plateaux; on the other, we notice the great centres of volcanic activity, with their abundant flows, dikes, and breccias.

Two sheets of sections, drawn across all the more interesting and important portions of the geology, complete the vast fund of information given by the maps; while, that nothing may be wanting to enable readers to realize what has been done by the survey, and the conditions under which it has been accomplished, two large sheets of sketches are given, which most vividly represent the forms of the mountains, plateaux, mesas, and river channels as seen from various commanding heights.

Dr. Hayden, with whose personal supervision this great work has been accomplished, has increased tenfold the obligations under which he has laid geologists all over the world for the number and value of his contributions to geology. He now furnishes us with new light whereby to read his former researches and those of his able colleagues. May we venture to hope that he may find leisure to confer yet one further benefit before the progress of his survey plunges him into a new whirl of work? If he could be prevailed upon to sketch out a plan for digesting the materials of his published annual reports, he could doubtless find among his staff some competent writer who, under his guidance, could produce a well-arranged systematic guide-book or text-book to complete the value of the work of his survey. Such a book of reference as would give a reader who has never had access to the annual reports a clear and comprehensive view of Colorado geology would be of great service.

These remarks may be fitly closed with an expression of the warmest admiration of the liberal spirit in which the United States Government has conducted these surveys of the Territories and has published their results. This costly atlas has been distributed gratuitously all over Europe. That this is a wise policy cannot be doubted. Whether actuated or not by a desire to diffuse scientific information, the authorities at Washington do well to make as widely known as possible the geological structure and economic resources of their country. They cast their bread upon the waters and the harvest comes to them in the form of eager, active emigrants from all parts of Europe.

The Bulletin of the Survey has now reached the close of the fourth volume, which contains 37 articles and about 900 octavo pages. The tenth annual report embraces 550 closely printed pages, octavo, with 80 plates, maps, sections, &c. About 50 of the plates illustrate the remarkable cliff-dwellings which were found by the members of the Survey along the cañons of the streams of Southern Colorado and New Mexico. Volume IV, quarto, on the Miocene and Pliocene vertebrates of the West, by E. D. Cope, and Volume XII, by Dr. Joseph Leidy, on the Rhizopods, are far advanced, and will be ready for distribution in the spring. The eleventh annual report is in press; about 300 pages already in type. This volume will be issued early in the spring.

The members of the Survey are now all in the office from their fieldwork, and busily engaged in elaborating their field-notes. The materials for the twelfth annual are very ample and of great interest. Very respectfully, your obedient servant,

Hon. CARL SCHURZ,

Secretary of the Interior.

F. V. HAYDEN, United States Geologist.

APPENDIX.

The following articles on the geology of the Rocky Mountain region were published in the American Journal of Science, New Haven, Conn., several years ago, and are now entirely out of print. Inasmuch as they contain some views that have either been absorbed or overlooked by modern geologists, they are reprinted in this connection. There are some views that, if written at this time, might be restricted or modified, but in the main they are correct. The articles are reprinted without any alteration.

SOME REMARKS IN REGARD TO THE PERIOD OF ELEVATION OF THOSE RANGES OF THE ROCKY MOUNTAINS NEAR THE SOURCES OF THE MISSOURI RIVER AND ITS TRIBUTARIES.

BY DR. F. V. HAYDEN.*

[From the American Journal of Science, vol. xxxiii, May, 1862.]

The object of the present article is to show, as nearly as can be done from known geological data, the period of the elevation of a portion of the Rocky Mountains. My observations have been more especially confined to the ranges from which the Missouri and Yellowstone Rivers, with their numerous tributaries, take their rise, though I feel confident that principles which will apply to mountains occupying so large an area will also be applicable to the whole Rocky Mountain district. It will be impossible, at this time, to mention in detail all the facts in support of my statements, and therefore I shall assume that the reader has examined the previous papers of my associate, Mr. Meek, and myself. During the coming year I hope to prepare a series of articles for this journal which will have a more or less direct bearing on the physical geography of this region and the influences which gave to it its present configuration. Some erroneous statements, growing out of our limited knowledge of the structure of these mountain chains, may be made, but these, when known, will be corrected. Geology is a progressive science, and even our best efforts are but approximations to truth rather than the truth itself.

The evidence seems to me to be clear that the great subterranean forces that elevated the western portion of our continent were called into operation toward the close of the Cretaceous epoch, and that the gradual quiet rising continued, without a general bursting of the earth's crust, until after the accumulation of the Tertiary lignite deposits, or at least the greater part of them; also, that after the fracture of the surface commenced and those great crust movements began to display themselves, the whole country continued rising, or at least, though there may have been periods of subsidence or repose, there was a general upward tendency, which has continued even up to our present period. I hope hereafter to illustrate the correctness of these statements by all the facts that have been obtained in my past explorations as well as by those I may secure in the future.

Let us, in the first place, examine some of the barometrical profiles across the country from the Mississippi River to the Pacific coast, constructed under the direction of the War Department. Previously, however, to this examination we may make the statement that west of longitude 98° the surface of the country may be separated into two divisions, mountain and plain, and that a combination of the two compose the Rocky * For most important information I would direct attention to second series of this journal, articles xiii, xxxix, vol. iii, 1847, article xxxiv, vol. xii, 1849, and articles xxiv, xxv, vol. xxii, 1856, by Prof. J. D. Dana, in which, it seems to me, will be found the most profound, far-reaching generalizations in regard to the physical geography and geology of the West and other portions of our country which have ever been given to the public. The origin and character of those subterranean forces which have produced such important results in the West are fully discussed in those papers.

Mountain district. After leaving the Mississippi the intervening country westward to the upheaved ridges is an apparently level or undulating plain, with no disturbance of the strata of the underlying formations until we come in close proximity to some of the mountain elevations. Reaching the base of the elevated ridges which form the mountain crests, we at once commence a rugged and abrupt ascent.

If we look at the profile constructed by Governor Stevens, from Saint Paul, Minn., latitude 44° 58' and longitude 92° 58', to the Pacific coast, we shall find that the starting point is 828 feet above the ocean-level. Near Fort Union, at the junction of the waters of the Yellowstone and Missouri, 670 miles westward, the height above the ocean-level has increased to 2,010 feet, or 1,182 feet higher than Saint Paul. We thus see that the average ascent of the country between these two points is not quite two feet to the mile. From Fort Union to the valley of Dearborn River, just under the base of the elevated ridges of the principal eastern range, we find the distance to be 448 miles and the height above the ocean 2,081 feet greater then that at Fort Union, or the average rate of ascent increased to nearly five feet per mile. Over this vast extent of country extends an almost limitless prairie, apparently level, with no forests or groves, with no timber except that which skirts the streams. There is in this great distance a gradual increase in the inclination of the strata proportioned to the increase of the ascent, but no marked disturbance of the beds until we arrive in close proximity to the mountain elevations. There are a few local fractures of the earth's crust caused by the elevation of the Bear's Paw, Little Rocky Mountain, &c., around which the sedimentary rocks are more or less disturbed, but all these lesser mountains are more or less remotely connected with the main chain. After passing the highest point of the principal range, along this line, which is near Cadotte's Pass, we commence our descent toward the Pacific very much as we ascended the eastern slope, but over a much more rugged route. We find a continued series of more or less parallel ridges of elevation until we approach the coast for a distance of from 400 to 600 miles. From Fort Walla Walla to the ocean, however, the average descent is a little less than one foot to the mile.

Again, if we examine the profile constructed by Frémont, commencing at the mouth of the Kansas River, we find that the initial point is 690 feet above the ocean. Proceeding westward, the average grade for the first 300 miles is between 4 and 5 feet per mile. Thence to Fort Laramie the ascent, as stated by Frémont, is 8 feet to the mile, and from Fort Laramie to Hot Spring Gate, although still passing over prairie country, the average grade of ascent is given by the same explorer as 45 feet per mile. Over this entire route, however, loaded wagons have been transported with ease. When we reach the foot of the mountains in this direction, the lofty elevated ridges seem to rise abruptly out of the prairie, averaging from 1,000 to 6,000 feet in height above the surrounding country. From thence to the Pacific coast we pass over a continued series of elevations which taken in the aggregate seem to trend nearly northwest and southeast, but which, when examined in detail, often present no definite direction or continuous line of fracture. This mountain region is composed of a series of these ridges forming a belt or zone 400 to 800 miles in width from east to west, interspersed with beautiful valleys through which wind streams of clear water. So numerous are the profiles which have now been made across the continent by different explorers that it is hardly necessary to describe each one, since what we have already said indicates the object in view.

We have said that the western portion of our continent, especially if we look only at the easterly slope, may very properly be divided into mountain and prairie. It is true that in Kansas and Iowa, groves of timber of considerable size are seen, but they form rather the exception than the rule. Along the eastern slope there is a belt of country 300 to 600 miles in width, where, for the most part, the only timber to be seen is a thin fringe bordering the streams. Even in the eastern portion of the main range the timber is not luxuriant, like that so common along the coast of Oregon and California. The pine trees are seldom more than 3 feet in diameter.

Again, we may divide the mountains or elevated ridges which form the different ranges into two kinds, viz, those with long extended lines of fracture, with a granitic nucleus and a comparatively regular outline, and those which appear to be composed of a series of cones or peaks more or less intimately connected, exceedingly irregular in their outline and of eruptive origin. Of the first class, the Black Hills, Bighorn, Laramie, and Wind River Mountains are good examples, while the Wahsatch, Green River, Teton Ranges, and many others west of the dividing crest might be cited as illustrations of the second class. From all the information within our reach we have inferred that after passing the eastern slope the mountain ranges of eruptive origin are far the most numerous. We also know from personal observation that the main range of the Rocky Mountains and the subordinate ridges on either side, near the headwaters of the two principal branches, the Yellowstone and Missouri, are of similar origin and present similar rugged features.

We may now return to the Cretaceous period. In a previous paper in this journal,*

* Vol. xxxi, March, 1861.

we remarked that there were no indications in the geological formations of that portion of the West over which we have traversed of long-continued deep-water deposits until we pass up into the Cretaceous epoch. The lower portion of No. 1, or the Dakota Group, which ushered in the Cretaceous epoch in this portion of the West, is composed of coarse sand, pebbles, &c., with ripple marks, oblique laminæ, and with other indications of shallow water and change of currents. The same characters are seen throughout the formation wherever it is exhibited. We also know from the numerous impressions of leaves, and some beds of impure lignite, that dry land could not have been far distant. But as we pass up through Nos. 2, 3, and 4, whatever changes of land may have occurred in the mean time, we think there were periods at least when the sea was of considerable depth and suffered a quiet deposition to go on. We infer this from the fine and homogeneous character of the sediments. Throughout No. 4 we have a fine plastic clay which continues up into No. 5, when a gradual change takes place from the introduction of yellowish ferruginous matter, and a slow increase of sandy sediments. Toward the middle of No. 5 the sand begins to predominate until the upper part becomes a coarse ferruginous sandstone, with all the indications of shallow-water deposits. We know, also, from fragments of wood and impressions of leaves which have been found quite widely distributed in the upper part of No. 5, that dry land could not have been far away. We also infer from the character of the molluscan remains that the great Cretaceous sea which had so long spread its vast waters over this region was becoming shallow, and that a new epoch was approaching. As we arise in No. 4, and pass up into No. 5, there is an evident increase in the number of gasteropoda, indicating shoal waters. We have already remarked their peculiar Tertiary aspect, which seemed to point directly to that epoch, showing that it was not far distant. We may now ask the cause of this apparent approach to land, as foreshadowed by the lithological as well as the paleontological characters of the Upper Cretaceous formation No. 5. We think that the facts indicate that during the deposition of this formation the western portion of the continent was slowly rising above the ocean level, the waters on the one side receding toward the Pacific, and on the other toward the Atlantic, introducing the great Tertiary epoch which had already been foretold in the Cretaceous. At the commencement of the Tertiary period, throughout the central portions of the continent, lakes, estuaries, &c., more or less salt, at length becoming brackish, and finally fresh water, existed, and a new flora and fauna were introduced. The subterranean expansive power which was quietly lifting up the country still continued, although no bursting of the earth's crust had commenced. These brackish water-deposits, which appear to mark the dawn of the Tertiary period in the West, are distributed quite widely over the central portions of the Rocky Mountain district, and then, by a general subsidence or a vast increase of fresh water, the true lignite deposits spread themselves over large areas and probably covered much of the country now occupied by the mountain ranges, and were doubtless more or less intimately connected with the Tertiary beds on the Pacific coast. What barriers separated them from the Tertiary formations along the Pacific it is impossible from our present limited knowledge of the geology of the intermediate region to determine.

We have remarked that the probable period of the bursting of the earth's crust which resulted in the formation of those abrupt mountain crests or ridges, occurred somewhere near the close of the accumulation of the true lignite deposits. We believe this for the following reasons: Whenever we observe the lignite beds in the vicinity of the mountain ranges we find them more or less inclined in the same direction with the older fossiliferous rocks, though, as a general rule, dipping at a smaller angle, because more remote from the axis of the disturbing power. Of course, as the land was slowly elevated toward the surface of the waters, the newer Tertiary beds would be subjected to the erosive action of water first, and thus continuing downward, as the mass was slowly rising, until the granitic nucleus was exposed. The Tertiary rocks, being composed for the most part of loose, yielding material, sands, clays and lignites, would be worn away from the surface for some distance from the axis of elevation. Although the lignite Tertiary beds are developed in full force all along the base of the larger ranges of mountains, it is not unlikely that some of these ridges formed barriers or lofty shores to these great Tertiary lakes. It would seem as if this country during the Tertiary period was not unlike the Undine region of the north, so called by the geographer Nicollet on account of the great number of fresh-water lakes distributed over that district.

Near the Black Hills these beds are worn away from the immediate base of the mountains, and it is doubtful from any proofs that we can now obtain whether the Tertiary lake extended over the country at that time occupied by the Black Hills. West of this range, the lignite Tertiary beds incline from the western slope 5 to 10 degrees. All along the Bighorn Mountains, the same features, only more strongly marked, are seen. These beds often lie quite high upon the slopes of the mountains, conforming to the Cretaceous rocks and sometimes inclining at a high angle. Between the western extremity of the Bighorn Range and the Sweet Water Mountains on the North Platte

they are more disturbed than at any other locality. The lignite Tertiary strata are nearly vertical and the hard layers of sandstone or limestone extend in long projecting lines across the country, while the intermediate yielding beds of clay, sand, and lignite are smoothed and leveled by atmospheric agencies and clothed with a thick turf of grass. All along the Laramie Range, from the Red Buttes to Deer Creek, until the lignite beds are concealed by the White River Group, the same features are seen, though the strata incline less, being more remote from the anticlinal crest. On both sides of the Wind River Mountains the same phenomena occur, and other examples might be cited pointing to the same conclusions, but enough has been said to show that it is probable that the lignite Tertiary beds partook of the same movements that have elevated the older fossiliferous rocks. We therefore infer that the fracture of the earth's crust in this portion of the West, by which the nucleus of the mountains was revealed, occurred near the time of the accumulation of the lignite deposits or at the close of that epoch.

Again, although there is not a strict unconformability between the true lignite beds and the Wind River Group, the latter incline in the same direction, only at a much smaller angle. Near the source of Wind River the Wind River Group rests directly upon Cretaceous formation No. 2. At this point the Cretaceous rocks incline from 100 to 25°, while the Wind River beds dip from 10 to 5°. As we ascend the valley of Wind River towards its source, we pass, for a long distance, the steeply inclined Cretaceous and Jurassic rocks, along the margins of the mountains on our left hand, while on our right, but a few hundred yards distant, the naked, almost vertical walls of the lower portion of the Wind River Group* are seen, the strata, however, seldom inclining more than one degree.

The same examples may be observed on the west side of the Wind River Mountains, where the Wind River beds lie high upon the sides of the western slope in a very slightly inclined position and in some localities covering the very summit, showing clearly that even the dividing crest of the mountains was beneath the waters during the deposition of this group. Along the margins of both the Wind River and the Bighorn Mountains these beds seem to have risen in an undisturbed or in a nearly horizontal condition. We have already expressed the opinion in a previous paper,† that the Wind River Group was intermediate in age between the lignite Tertiary and the White River beds, and in point of time filled up a chronological chasm. We have inferred this from the fact that these beds seem to possess paleontological and lithological characters intermediate between the two. They contain casts of a species of Vivipara which is undistinguishable from V. trochiformis, and fragments of a Trionyx apparently the same with that occurring in the lignite beds, also fragments of a Testudo which, so far as we can determine, is identical with the T. Nebrascensis of the White River beds. If we look also at the composition of the Wind River beds, we find that their light color, indurated arenaceous and argillaceous character, and their general appearance after erosion, favor the correctness of the inference in regard to their intermediate position. From the facts before us in regard to this group, we conclude that even after the crust broke, the country continued slowly rising while the Wind River deposits were accumulating, and that the upper portions when not eroded away were elevated high upon the sides of the mountains in a nearly horizontal position.

Again, the White River beds hold a similar position with reference to the lignite formations as the Wind River Group. They are seldom disturbed, and only in a few instances do they incline as much as 50. They, however, occur high up on the mountain slopes along both sides of the Laramie Range, showing that they partook of the gradual elevation of the country, after the crust was broken and the mountain district began to approach its present configuration. On the west side of the Black Hills, where the White River beds probably began their origin, we find only the lower strata of this group, usually reposing directly upon Cretaceous rocks, though in a few localities upon lignite formations. But as we descend south and southwestward, these lower beds disappear and more recent ones take their place, until they pass into the Pliocene sands of the Loup River Group, and then, in turn, still farther southward, are lost in the Loess or yellow marl deposits. We can only account for these phenomena on the supposition that this great Tertiary fresh-water lake had its commence- * ment in the White River Valley, and as the Black Hills, and of course the whole Rocky Mountain district, arose slowly toward its present elevation, the waters gradually receded southward and southwestward, and then more recent beds continued to be accumulated, until this formation spread itself over the vast area which it now occnpies. We thus think that, by means of these Cretaceous and Tertiary deposits of the West, we can yet trace step by step the progress of that grand development which has given the present geographical conformation to the West, and originated the. fountains from which flow those mighty rivers which may well be called the commercial arteries of the American continent.

Another illustration of the gradual and long-continued rise of the country may be found in the immense chasms or cañons which have been formed by the streams along

* Same as the Wahsatch Group, 1878.
See this Journal, vol. xxxi, March, 1861.