GEOLOGY. 97 
A white, fine-grained, non-fossiliferous limestone on the Little Arkansas, and a red ferrugi- 
nous endis: out of which Pawnee rock is formed, have a horizontal Mei The 
latter is again imd on Coon creek, and, according to a specimen brought to me by Captain 
Gunnison, it extends up to the Republican fork of the Kansas river. It supports a loose con- 
glomerate of quartzose rocks, which is seen to extend some thirty miles along the Arkansas west 
of Fort Atkinson. It is very probable that these strata belong to the chalk formation, which, 
going westward, we find distinctly represented by several kinds of limestone strata ; the first, 
about ninety miles from the fort, is a soft, argillaceous, yellowish limestone, with inoceramus. 
It seems to have a slight dip to the southwest. About thirty miles farther west, we meet with 
another limestone of the cretaceous period, It is a gray rock, a little harder than the preceding 
one, and is replete with inoceramus mytiloides. The row of low hills which, in these localities, 
stand at a short distance from, and extend along the road, consist of this limestone. "These 
hills show lines which mark the banks of an ancient sea ; they lie in one and the same horizontal 
plane, in whatever direction these hills may run. 
View of the limestone hills of the valley of the Upper Arkansas: the broken line, a----- a, showing the positions of ancient shores.* 
* Note by Lieut. Beckwith, 
The old shore-lines existing in the vicinity of the Great Salt Lake present an interesting study. Some of them are elevated 
but a few feet (from five to twenty) above the present level of the lake, and are as distinct and as well defined and preserved as its 
present beaches; and Stansbury speaks, in the Report of bis Exploration, pages 158-160, of drift-wood still existing upon those 
having an elevation of five feet above the lake, which unmistakably indicates the remarkably recent recession of the waters 
which formed them, whilst their magnitude and smoothly-worn forms as unmistakably indicate the levels which the waters 
maintained, at their respective formations, for very ecc den periods. 
In the Tuilla valley, at the south end of the lake, they are so remarkably distinct eae eter ci in form and position, that one 
of them, on which we travelled in crossing that valley on the 7th of May, attracted th of the least informed teamsters 
of our party—to whom it appeared artificial. Its elevation we judged to be twenty feet above the present level of the lake. It 
is also twelve or fifteen feet above the plain to the south of it, and is several miles long; but it is narrow, only affording a fine 
roadway, and is crescent-formed, and terminates to the west as though it had once formed a cape, projecting into the lake from 
the mountains on the east—in miniature, perhaps, not unlike the strip of land dividing the sea of Azoff from the Putrid sea. 
cross-range of mountains, with passages at either end, however, leading over quite as remarkable beaches into what is known, to 
the Mormons, as Rush valley, in which there are still small lakes or ponds, once, doubtless, forming part of the Great Salt Lake. 
The recessions of the waters of the /ake from the beaches at these comparatively slight elevations, took place, beyond all doubt, 
within a very modern geological period; and the volume of the water of the lake at each subsidence—by whatever cause pro- 
duced, and whether by gradual or spasmodic action—seems as plainly to have been diminished; for its present volume is not 
sufficient to form a lake of even two or three feet in depth, over the area indicated by these shores, and, if existing, would be 
annually dried up during the summer. 
These banks—which so clearly seem to have been formed and left dry within a period so recent that it would seem impossible 
for the waters which formed them to have escaped into the sea, either by great convulsions, opening passages for them, or by the 
gradual breaking of the distant shore (rim of the Basin) and draining them off, without having left abundant records of the 
escaping waters, as legible at least as the old shóres they formed—are not peculiar to the vicinity of this lake of the Basin, but 
were observed near the lakes in Franklin valley, and will probably be found near other lakes, and in the numerous small basins 
which, united, form the Great Basin. : 
But high above these diminutive banks of recent date, on the mountains to the east, south, and west, and on the islands of the 
Gaeat Salt Lake, formations are seen, p apparently, a uniform elevation as far as the eye can extend—formations on a 
magnificent scale, which, hastily examined, seem no less unmistakably than the former to indicate their shore origin. They 
are elevated from two or three hundred to six or eight hundred feet above the present lake; and if upon a thorough examina- 
tion they prove to be ancient shores, they will perhaps afford (being easily traced on the numerous mountains of the Basin) 
by the breaking or wearing away of the rim of the Basin—of the existence of which at any time, in the form of continuous elevated 
tain cháítis, there seems at present but little veoneiuedaucton eg an erm of the main sea, Which, with the continent, 
h tad i y these shores. 
13 b 
