waters at temperatures of from 46° to 70° Centigrade; the presence of apophyllite, natrolite and stilbite in the lacustrine tertiary limestones of Auvergne; apophyllite incrusting fossil wood, and chabazite crystals lining shells in a recent deposit in Iceland. The association of such hydrated silicates with orthoclase, as already noticed (§ 13) and as described by Scheerer, where natrolite and orthoclase envelop each other, showing their contemporaneous formation, with many other facts of a similar kind, lead to the conjecture that orthoclase, like beryl and quartz, and perhaps some other constituents of granitic veins, may have crystallized in many cases at temperatures much lower than those determined by Sorby, and that the conditions of their production include a considerable range of temperature, a conclusion which is, however, probably true to some extent, of zeolites also.

It is proposed to continue the subject of granitic veins, and in a third part of this paper to give some facts in the history of the veinstones of Laurentian rocks.

[To be continued.]

ART. XXIX.-On the Geology of the Eastern Uintah Mountains; by Professor O. C. MARSH, of Yale College.

ONE of the Expeditions in the Rocky Mountain region, made by the Yale College Scientific party during the past season, had for its special object the study of the vertebrate remains of the Tertiary deposits known to exist in the Green River Valley, but never carefully examined. During this investigation, while endeavoring to reach the junction of the Green and White Rivers, in Utah, the party passed along the base of the Eastern Uintah Mountains, as well as over portions of the range; and as nearly all of this region was entirely unexplored, it is desirable to note its more important geological features.

The route pursued by our party on this expedition was from Fort Bridger, in Wyoming, southeast by way of Henry's Fork to the Green River; thence down the eastern side of the river to the great bend near the mouth of the Vermilion. Then crossing to the western side, and passing over the eastern spurs and foothills of the Uintah Mountains, we proceeded southward to the mouth of the White River. After continuing up this stream for about twenty miles, we returned directly to the Green River, then proceeded to Fort Uintah, and from there struck northward over the Uintah range to Henry's Fork, and back to Fort Bridger by our former route. As the country traversed is entirely impassable for wagons, and it was only with considerable difficulty that a way for our pack-animals could be found,

our geological observations were necessarily confined mainly to the immediate route pursued, and even then, in the limited time at our command, could not be systematically conducted. The region passed over, however, proved to be one of the most interesting fields for geological research yet discovered in this country, and hence the results obtained, although fragmentary, will add something to the previous knowledge of Rocky Mountain structure.

Fort Bridger, in Wyoming, from which the Yale party started on their expedition in September last, is situated at the northern base of the Uintah Mountains, about 7000 feet above the sea. The surrounding plain is part of a great basin of denudation, washed out of light-colored clays and soft sandstones of Tertiary age, the deposits in one of the great fresh-water lakes, that replaced the Cretaceous sea from which the mass of the Rocky Mountains emerged. Remnants of the strata removed may be seen at various points around; some in the shape of flat, isolated buttes, and others forming benches, resting horizontally against the sides of the mountains. These fragments serve to show the great original thickness of this lake deposit, which cannot, apparently, have been less than 1500 feet, and may have been much greater. A few miles to the southeast, these soft strata have still further escaped denudation, and are weathered out into fantastic, conical forms, resembling those of the "Mauvaises Terres" formation of Nebraska and Dakota. These bluffs are known in this region as the "Grizzly Buttes," and through them lay our route to the Green River.

A careful examination of this "Bad Land" district soon indicated that a fossil, vertebrate fauna of peculiar interest was here entombed; one apparently older and quite distinct from that preserved in the great Miocene lake-basin east of the Rocky Mountains, which we had recently explored. In the latter deposit, the remains of ruminating mammals were especially numerous, while the entire absence of fishes, and of reptiles, with the exception of a single species of tortoise, was a well marked feature. Here, however, reptilian life had evidently been abundant, and was represented by all its principal forms. Crocodilians, tortoises, lizards, serpents, and fishes had swarmed in the waters of this tropical lake; while Tapiroid mammals, with many smaller quadrupeds, had lived near its borders. Their remains had long been weathering out of the "Grizzly Buttes,' which offered so inviting a field, that we devoted a fortnight to their exploration, and were rewarded by the discovery of a large number of extinct vertebrates new to science, which will be described by the writer at an early day.

Proceeding eastward along Cottonwood Creek, and over the divide to Henry's Fork, we found the same Tertiary deposits on

either side, still nearly horizontal, and in places beautifully variegated by layers of light green clays, alternating with others of various shades of brown. In addition to the numerous vertebrate remains, a few fresh-water mollusca were observed, especially on Henry's Fork, the more common being Planorbis spectabilis Meek, abundant in some of the harder layers, and Helix altispira Meek. Farther down the stream, and about fifteen miles from its mouth, several seams of lignite were noticed on the right bank. In the intervening shale were some thin layers of black hornstone, and others containing great numbers of shells, principally Unios and Melanias. One of the latter was apparently identical with the species described by Professor Hall in Fremont's Report (page 308), as Cerithium tenerum, which, however, with its associate fossils, is clearly a fresh-water type. A few feet under the lignite, were layers of shale full of Cypris, with here and there cycloidal fish-scales and coprolites.

A few miles below, a red sandstone dipping slightly to the N.W. makes its appearance on the left bank, beneath the lightcolored Tertiary deposits, and farther down, curves upward into a sharp ridge, of highly inclined strata, through which the stream has obliquely cut its way. On the southern side, these beds form a wall of sandstone, nearly perpendicular, resembling strongly the famous "Teufels Mauer" in the Hartz. This ridge, one of the typical foot-hills of the Uintah range, makes a sigmoid curve along the base of the mountains, from which its strata dip away at various angles. The different colored sandstones which compose it are evidently of Mesozoic age, and probably Cretaceous, as they have below them, farther down the stream, calcareous beds containing undoubted Jurassic fossils. These are in turn underlaid by sandstones, which are probably Triassic, and these again by well marked Carboniferous strata, near the junction of Henry's Fork with the Green River.

At this point the Green River leaves the great Tertiary basin which it drains for 200 miles or more, and cuts through the eastern Uintah Mountains by a succession of narrow cañons, with walls of older rocks, whose exact age can be determined only by a systematic study. In continuing our course down the east side of the river, we passed over several high ridges, composed mainly of hard reddish sandstones and quartzites, more or less metamorphosed, and apparently without fossils. The general inclination of these beds, which are of great thickness, was to the N.E., or away from the Uintah mountain nucleus, but the dip varied greatly at different points. Ripplemarks and oblique lamination showed them to be shallow water deposits, and a subsequent examination of apparently a portion of the same series, on the western side of the river, rendered it probable that a part of them at least are of Silurian age.

On reaching "Brown's Hole," a narrow valley about thirty miles in length, through which the river flows, a series of more recent beds was met with, that are well developed to the southward, where they have played an important part in shaping the present topography of the country. These strata, which are several hundred feet in thickness, lie nearly horizontal, and are mainly composed of conglomerates, and very soft, white, friable sandstones, which at some localities pass into thinly laminated, calcareous shales. At one point on the right bank of the river, a thin seam of lignite was observed in the white sandstone, and about ten miles below, in a high bluff on the opposite side, some of the calcareous layers had all the physical characters of white chalk, although apparently without the same organic structure. As no fossils were detected in these beds, except some obscure remains of plants, their exact age is a matter of some doubt. That they are Tertiary, however, is rendered probable by the fact that, farther down the river, they are seen to rest unconformably on the upturned edges of Cretaceous rocks.

Finding it impossible to proceed with our pack-animals down the river on the east side, we crossed just above the mouth of the Vermilion, and proceeded in a southwesterly course, by a difficult pass, over the eastern extension of the Uintahs. In ascending the mountains from the river we first found a great development of red and purple grits and sandstones, apparently the same as those seen on the eastern side above, but here dipping about 15° to the S.W. Above these strata, and perhaps ten miles to the south, we passed over a series of bright red, thickly bedded sandstones, having the same general inclination, and at least 1000 feet in thickness. In these beds, also, no fossils were detected during the hasty examination we were obliged to make. Resting conformably on this sandstone, was a bed of gray, siliceous limestone, at least 100 feet in thickness, which formed the summits of several of the smaller elevations between the main Uintah range and the Green River, and by its denudation had strewn the region to the southward with its waterworn fragments. This rock, fortunately, contained a few fossils, the most characteristic of which were specimens of Productus, Spirifer cameratus Morton, Athyris subtilita Hall, Hemipronites crassus M. and H., a species of Zaphrentis, apparently Z. Stansburyi Hall, with fragments of Fenestella and Phillipsia. These remains clearly indicate the Carboniferous age of the limestone, and, indirectly, throw considerable light on the strata beneath it.

Continuing our journey southward, for fifteen miles or more across an elevated plateau, we came suddenly to the overhanging edge of a great basin, which afforded a most striking illustration of the vast amount of erosion to which this region has been subjected since the mountains attained their present eleva

tion. From the base of the Uintahs, as far south as the eye could reach, the soft beds of the more recent formations had been washed away to a depth of one or two thousand feet, leaving at the bottom of the great depression the bare, upturned edges of the variegated Mesozoic strata on which they had rested. The flanks of the adjacent mountains were gashed by deep cañons leading into the basin, showing the source from which the denuding agent came. Our course lay through this basin, and descending with great difficulty by an obscure Indian trail, we passed on, through dry cañons and over steep intervening ridges to Brush Creek, a small stream which now helps to drain this region into the Green River. The rim of this great basin where we descended was composed of nearly horizontal beds of conglomerate, underlaid by light colored clays and sandstones, resting unconformably on the edges of an extensive series of red and yellow sandstones and shales, which dip to the south away from the mountains, but in places have been much curved and folded. The upper, horizontal beds, apparently Tertiary deposits, were evidently identical with those observed on the Green River at "Brown's Hole;" and that valley, as well as this lower basin, owes its present size, if not its origin, to the readiness with which these strata are eroded.

Near Brush Creek, and about six miles from Green River, a seam of bituminous coal was discovered in the side of a dry gorge, which cuts through a high ridge of sandstones and shales. This seam was about a foot in thickness, and indications of others were seen at various points in the basin. The strata containing the coal where first seen dip about 65° to the north, and form part of a denuded anticlinal. The weathering of the thickly bedded sandstone above the coal had developed huge concretionary masses, some of them fifteen feet in diameter, which projected from the cliff, or had fallen into the ravine. below. As the age of the coal deposits of the Rocky Mountain region has of late been much discussed, a careful examination was made of the series of strata containing the present bed, and their Cretaceous age established beyond a doubt. In a stratum of yellow calcareous shale which overlies the coal series conformably, a thin layer was found full of Ostrea congesta Conrad, a typical Cretaceous fossil; and just above, a new and very interesting crinoid, allied apparently to the Marsupites of the English Chalk. In the shales directly below the coal bed, cycloidal fish scales and coprolites were abundant; and lower down, remains of Turtles of Cretaceous types, and teeth of a Dinosaurian reptile, resembling those of Megalosaurus, were also discovered. After passing out of the deeper portion of this basin on our way southward, and proceeding about ten miles beyond a small stream, which on the Government maps is called Ashley's Fork,