The inclined sandstone at the base of the Rocky Mountains we found much wider and its summits incomparably more elevated than our previous opinions, or a distant view had led us to expect. This extensive range, rising abruptly from the plain, skirts the base of the mountain like a vast rampart, and from a person standing near it, intercepts the view of the still more grand and imposing features of the granite ridge beyond. It consists of rocks in which the comminuted fragments of primitive aggregates are intermixed with the reliquiae of the animals of a former world, known to us only by the monuments which these remains exhibit. The stratifications, with which this rugged and precipitous wall of sandstone is distinctly seamed, penetrate the mass with various degrees of obliquity; not unfrequently the laminae are entirely vertical, as if the whole had receded from its original position, and these immense rocky masses, had, by the operation of some powerful agent, bten broken off from their former continuity, with the strata now found in a horizontal position in the plains.

It is difficult, when contemplating the present appearance and situation ol these rocks, to prevent the imagination from wandering back to that remote unascertained period, when the billows of the primeval ocean lashed the base of the Rocky Mountains, and deposited, during a succession of ages, that vast accumulation of rounded fragments of rocks alternating with beds of animal remains, which now extend without interruption from the base of this range to the summits of the AUeghanies; and endeavouring to form some conception of that subsequent catastrophe which has so changed the relative elevation of the two great formations that the margin of the secondary has been broken off and thrown into an inclined or vertical position.

The valley between this parapet of sand-rock and the first granitic ridge is near a mile wide. It is ornamented with numerous isolated columnar rocks, often of a snowy whiteness, standing like pyramids and obelisks, interspersed among mounds and hillocks, which seem to have resulted from the disintegration of similar masses.

The range of sandstone appears to have been originally of uniform elevation and uninterrupted continuity, stretching along the base of the mountains from north to south, but it has been divided transversely by the bed of the Platte, and all the larger rivers in their descent to the plains.

From our camp, we had expected to be able to ascend the most distant sumniits then in sight, and return the same evening, but night overtook us and we found ourselves scarcely arrived at the base of the mountain. The lowest part of the sandstone stratum, exposed at the western declivities of the hills, and in the points nearest the granite, contains extensive beds of coarse conglomerate or pudding-stone, often of a reddish colour. The more compact parts of the rock present remains of terebraiulge and other submarine animals. Among these, few are entire or in good preservation. We observed here, several singular, scorpion-like animals, inha-

biting under stones and dried bison's dung. They have a formidable appearance, and run actively. They belong to the class Arachnides, genus Galeodes, which has been heretofore observed only in warm climates; not one was known to inhabit this continent.

About the sandstone ledges we collected a geraniumf intermediate between the crane's bill and herb robert, the beautiful calochortus,- [C. elegans Ph.] and a few other valuable plants.

The Platte at the foot of the mountains is twenty-five yards wide, having an average depth of about three feet; its water clear and cool, and its current rapid. Its descent for twenty miles below cannot be less than eight feet per mile. Its valley is narrow and serpentine, bounded by steep and elevated hills, embosoming innumerable little lawns often of a semicircular form, ornamented by the narrow margin of shrubbery along the Platte.

The narrow valley, which intervenes between the ridges

Genus Gaieodes, Oliv.

1. G.paUipes. Say. Hairy; mandibles horizontal; fingers regularly arquated; abdomen subdepressed, livid.

Description. Body, pale yellowisb brown, hairy.yeef, paler; whitish, first pair smallest, fourth pair largest, and longest; abdomen, livid, hairy, subdepesed; palpi, more robust than the three anterior pairs of legs, of subequal diameter, but rather thicker towards the tip, more hairy than the feet; pyes and tubercfe blackish; mandibles, dilated with numerous rigid setoe; and with parallel setae projected over the fingers; Jiiiiers, regularly arquated, reddish brown at tip, and with a reddish brown line above and beneath; within armed with many robust teeth; thorax, with a deep sinus at the anterior angles.

5. G. subulatn, hairy; mandibles, horizontal; thumb nearly rectilinear; destitude of teeth.

This species has the strongest resemblance to the preceding, both in form, maguitnte, and colouring, but the superior finger of the mandibles is unarmed and rectilinear, or very slightly flexuous; the inferior finger is arquated, with about two robust teeth.

f G. coespitose, sub-erect, pubescent, sparingly branched above. Radical leaves reniform deeply 5-7 cleft. The flower is a little larger than that of G. robertianum, and similarly coloured, having whiti-h lines towards the base of the corrolla We also saw here the Campanula decipiens. Pers. L>simac!iia ciliala, Ph. Troximon glaucum, A", with two or three belonging to genera with which we were unacquainted.

of sandstone before mentioned, is a little more fertile than the plains along the river. It is covered with fine and short grasses, and varied with here and there a copse of small oaks or hazles. There are also some columnar masses of white sandstone, twenty or thirty feet high, standing remote from each other, having the debris around their bases covered with shrubby oaks.

We observed here the obscure wren, a bird more closely related to the great Carolina wren of Wilson than any other we have seen; but the characters drawn from the primaries, and from the marking of the tail sufficiently distinguish it from that species. The bill is somewhat longer, and the general tint of the plumage of a much more sombre hue. It frequents the arid country in the vicinity of the mountains, and is often seen hopping about upon the branches and singularly compressed semi- procumbent trunks, of a species of juniper.

The bill of this species approaches the form which characterizes the genus Certhia in which Wilson has placed its kindred species, the Carolina wren.

On the morning of the 7th of July, the party remaining in the encampment of the preceding day. Dr. James and Mr. Peale, accompanied by two riflemen, were sent out to examine the mountains. These appeared most acces-

Genus Troglodytes- Cuv.

T. obsoleta. Sat. Above, dusky-brownisli, slightly undulated with pale, tinted with dull ferruginous on the top of the head and superior portion of the back; sides of the head dull whitish, with a broad brown line passing through the eye to the origin ol'the neck; primaries plain, beingentirely destitute of undulations or spots: feathers ofthe tail-coverts pale, each with four or five fuscous bands; chin, neck beneath, and breast whitish, each feather marked by a longitudinal line of light brown; belly white, flanks a little tinged with ferruginous; inferior tail-coverts white, each feather bifasciate with black brown; tail simple, broadly tipped with ferruginous yellow, and with black before the tip; the remaining portion colour of the wings and obsoletely banded; these bands are more distinct on the two middle feathers which are destitute of the black and yellowish termination; exterior plume marked by four yellowish white spots on the exterior web, and by two larger ones on the inner web; the tip ig dusky.

Length six incbes; bill from the corner of the mouth rather more than one inch.

sible on the north side of the river, which was opposite our encampment. The river was here about four feet deep, and the strength of the current such as to render it impossible for a man to keep on his feet, in the deepest part of the stream. As some of the party destined for the mountains could not swim, it was thought hazardous for them to attempt to cross by fording. To obviate this difficulty two men were sent with a long rope, which they were directed to stretch across the river, making the ends fast on either shore. This was readily accomplished, one of the men swimming across with an end of the rope in his teeth. By the aid of this the detachment were enabled to keep their feet in crossing, though with extreme difficulty as the bed of the river was uneven and rocky. They all however arrived in safety on the left bank about sunrise.

After passing the region of inclined sandstone, which is about two miles in width, they began to rise upon what may be considered the base of the mountain. As the day advanced the heat became oppressive, and they found themselves somewhat exhausted, before they had crossed the sandstone hills, which appeared so inconsiderable from our encampment, that the labour of crossing them had been almost forgotten in estimating the toils of the day. The first range of primitive rocks they found far more abrupt and rugged than the sandstone hills they had already passed. Its sides are destitute of vegetation, except a few priclcly pears and yuccas, with here and there a stinted oak or juniper, and so steep that great exertion as well as the utmost caution are necessary in ascending.

The rock is an aggregate of feldspar and hornblend, approaching in character some of the common varieties of Sienite. On the eastern side, where the feldspar is in the greatest proportion, it is flesh-coloured and its structure crystalline, the fractured surface of the mass being uneven like that of coarse granite; advancing towards the west, horn-

blend was found more and more predominant, and so arranged as to have, in the mass, a laminated appearance. The natural fissures or cleavages between the laminae run nearly in a perpendicular direction, giving the rock the columnar structure of trap, or greenstone. As they proceeded, a few interesting insects and plants occurred to reward their labors. But these impenetrable and naked rocks are the abodes of few living beings either animal or vegetable. In the crevices where a scanty soil has accumulated, is here and there planted, a hardy evergreen, whose short and gnarled trunk, and recurved inflexible branches, seem to proclaim the storms it has withstood, and the centuries during which it has vegetated.

The design of the party had been to cross the first rnge of the mountains and gain the valley of the Platte beyond, but this they found themselves unable to accomplish. After climbing successively to the summit of several ridges, whieh they had supposed to be the top of the mountain, they still found others beyond higher and more rugged. They therefore relinquished the intention of crossing, and began to look for the best way to descend to the bed of the river, which lay on their left hand. Here they halted to rest fur a few moments, and exposed a thermometer in the shade of a large rock. The mercury fell to 72; in camp, at the same hour, it stood at 86°. They were so much elevated above the river, that although they could sec it plainly, it appeared like a small brook of two or ihrve yards in width, white with foam and spray caused by the impetuosity of its current and the roughness of its channel. They could distinguish two principal branches of the Platte, one coming from the northwest, the othrr from ;he south. A little below the confluence of these brarchts iht liver turns abruptly to S. E., bursting through a ch:ism in a v:Ast ni'iral pn cipice of naked colun.nar rocks.

About noon the detichment tommencid their descent, which cost them no less exertion than their ascent in the

morning. Their fatigue was aggravated by thirst, as they met with no water nor any shade except that of projecting rocks in the higher parts of the mountain. They chose a different route from that which they had taken in ascending, intending to descend to the river, with the hope of being able to travel along its bed. They were obliged to assist each other in lowering themselves down precipices, which they would have found it impossible to pass singly. On the southern declivity of the mountain they met with a few ripe currants, but these were hard and juiceless, of a sweetish taste, and aggravated instead of alleviating their thirst, and were probably the cause of a violent headach with which several of the party were affected soon after eating them. There were also found a few large and delicious raspberries, of a species approaching the flowering raspberry, [Rubus odoratus but Avith smaller leaves and a more branching stem.