GEOLOGICAL SURVEY OF THE TERRITORIES. 19 



and usually retains no snow on its summit after May. One fact is quite 

 clearly shown, along the immediate base of the mountains from the 

 Chugwater to the Bitter Cottonwood, that when a flexure in a mountain 

 range occurs, a portion of the foot-hills and ridges have suffered very 

 little erosion, and can be studied in their full development. For a dis- 

 tance of fifteen miles north of the Chugwater the local erosion from the 

 mountains was very limited, while from Laramie Eiver to the Bitter Cot- 

 tonwood, about fifteen to twenty miles, the erosion has been tremendous. 

 This difference can be accounted for, perhaps, from the fact that the 

 passage of the waters from the mountains was through the anticlinal 

 and synclinal valleys which extend nearly north, and swept over the 

 plains between the Cottonwood and the Laramie Bivers. Long parallel 

 benches, with remarkably regular, table-like surfaces, extend down from 

 the base of the mountains between the valleys of the streams. Their uni- 

 formity over such large areas ^s a striking feature in the landscape. 

 North of the Cottonwood these long benches have a singularly regular 

 series of side furrows, which extend for miles, and give to the surface 

 the appearance of the sea swept by a gentle breeze. We have not before 

 observed this feature, so well marked, although the parallel benches are 

 not uncommon. 



On the morning of the 14th we left Cottonwood Creek for the La 

 Bonte. The wagon-road, although several miles from the Platte Eiver, 

 is still ten to fifteen miles distant from the foot of the mountains. The 

 "White Biver tertiary beds prevail, for the most part, and here and there 

 are high hills, or' " buttes," of marls and sandstones, weathering into the 

 castellated forms, before described, but to a limited extent. Still, these 

 beds continue to possess a thickness sufficient to conceal the underlying 

 older formations. Between the Cottonwood and Horseshoe Creeks these 

 deposits are overlaid by a heavy thickness of local drift, and jut up 

 against the granites until we come to the immediate valley of the 

 Horseshoe, where it emerges from the foot-hills. Here is a singular val- 

 ley of erosion on the south side. A small branch flows into the Horse- 

 shoe, uncovering the ridges of carboniferous limestones and red beds, 

 over an area of about a mile in length and half a mile in width ; still, 

 on the opposite or north side of the Horseshoe, the drift juts full against 

 the granite sides. This example shows clearly, that even where they 

 cannot be seen at the present time these sedimentary ridges exist in 

 greater or less force all along the mountain flanks. There is no water 

 in this little branch for a great portion of the year, yet all the superficial 

 drift or White Biver sediments have been washed out, leaving the skele- 

 ton-like ridges of the older rocks. In one place the limestones rest 

 directly on the granites. The dip of the ridges is about 60°, and they are 

 two hundred to two hundred and fifty feet in height above the bed of 

 Horseshoe Creek. That the Jurassic and cretaceous beds exist all along 

 here we cannot doubt, but they are entirely concealed. The valley of 

 the Horseshoe is about three miles wide from bluff to bluff. The cream- 

 colored marls lie close up to the granite rocks. We have usually observed 

 that the sediments of the later tertiary strata were coarser the nearer 

 we approach the base of the mountains 5 but this does not seem to be 

 the rule. In some localities the finest marls and sands rest directly 

 upon the metamorphic rocks or fill up the inequalities in the surface far 

 up among the foot-hills nearly to the crest. This range of mountains, 

 however, seems to have formed a well-defined shore line for the lake, for 

 we can find no evidence that the waters passed the divide in the Laramie 

 Plains, although they washed the flanks far up toward the summit. 



From the north side of the Horseshoe Creek we have the most im- 



