Our camp was immediately in front of the chasm, through which the Platte issues from the mountains. A little to the south is a commanding eminence, from which the view of the chasm was taken.[139]
{188} CHAPTER IX {VII}
Sandstone Formation at the Base of the Rocky Mountains—The Platte within the Mountains—Granitic Mountains Between the Platte and Arkansa—Castle Rock—Birds—Plants.
The district occupied by the inclined sandstone, at the base of the mountains, we found much wider, and the rocky summits incomparably more elevated, than from a remote view we had supposed.
July 6. This extensive range, rising abruptly from the plain, skirts the base of the mountains like an immense rampart, and to a spectator placed near it, intercepts the view of the still more grand and imposing features of the granitic ridge beyond. It is made up of rocks composed of the broken down and comminuted fragments of preexisting aggregates embosoming reliquæ of the animals of a former world, known to us only by the monuments which these remains exhibit. Though rugged and precipitous, its elevation is small, when compared to that of the stupendous Andes, which rise above it far into the regions of perpetual winter. The stratifications with which it is distinctly seamed, penetrate the mass with various degrees of obliquity, sometimes running perpendicularly to the horizon; seeming unequivocally to prove, that the whole has receded from its original position, and that these immense rocky masses have, by the operation of some powerful agent, been broken off from their original continuity with the strata now found in a horizontal position in the plains.
It is difficult, when contemplating the present appearance and situation of these rocks, to prevent the {189} imagination from wandering back to that remote period, when the billows of an ocean lashed the base of the Andes, depositing, during a succession of ages, that vast accumulation of rounded fragments of rocks, alternating with beds of animal remains, which now extends without interruption from the base of this range to the summits of the Alleghany mountains; and endeavouring to form some idea of that great subsequent catastrophe, by which this secondary formation has so changed its elevation, in relation to the primitive, that its margin has been broken off and thrown into an inclined or vertical position.
The valley which intervenes between this huge parapet of sand-rock and the first range of the primitive is nearly a mile in width; it is ornamented with numerous insulated columnar rocks, sometimes 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. This range of sandstone would appear to have been originally of uniform elevation and uninterrupted continuity, running along the base of the mountains from north to south; but it has been cut through by the bed of the Platte, and all the larger streams in their descent to the plains.
From our camp, we had expected to be able to ascend the most distant summits then in sight, and return the same evening; but night overtook us, and we found ourselves scarcely arrived at the base of the mountain.[140] The lower part of the sandstone stratum, being exposed at the western declivities of the hills, and in the parts nearest the granite, contains extensive beds of coarse conglomeratic, or pudding-stone, often of a reddish colour. The more compact parts of the rock contain the remains of terebratulæ, and other submarine animals. Among these, few are entire or in good preservation. We observed here several singular scorpion-like, spider-formed {190} animals, inhabiting under stones and dried bisons' dung. They have a formidable appearance, and run actively. They belong to the class arachnoides, genus galeodes, which has been heretofore observed only in warm climates; not one was known to inhabit this continent.[141]
About the sandstone ledges we collected a geranium[142] intermediate between the crane's-bill and herb-robert, the beautiful calochortus (C. elegans, Ph.) and a few other valuable plants.