90 REPOET UNITED STATES GEOLOGICAL SURVEY. 



tion, and transportation can be admirably studied. A large portion of 

 the lower country east of the anticlinal fold was at one time higher, but 

 was gradually reduced by the persistent abrasion and removal of por- 

 tions of its strata. 



EVIDENCE OF FORMER GLACIERS. 



In the Wind River Range the most complete evidence of extensive 

 glaciers formerly existing there was obtained. Many of the small val- 

 leys and canons at the southern end of the mountains show accumula- 

 tions of glacial drift. In the immediate vicinity of Camp Stambaugh 

 we find the gravel and drift adjoining small streams to be composed of 

 rocks with which their drainage has at present no connection. Near the 

 post there occurs, within the metamorphic area, a local deposit over 70 

 feet hi depth, consisting entirely of drift material. It is located along 

 the sides of a narrow gulch, and contains gravel and bowlders from the 

 size of a pea to such weighing half a ton. As will be seen subsequently, 

 we have evidence farther south which permits us to regard this as a 

 ground moraine. On the western slope of the range evidence of former 

 glaciers can be obtained as soon as we reach high elevations. Near 

 timber-line we find numerous small, shallow lakes. Not unfrequently 

 these are surrounded on three sides by morainal deposits. The most 

 striking examples of extensive glaciers that I had occasion to observe 

 we found between the headwaters of the Sandy's and Muddy Creek. 

 While riding through the dense timber there we encountered huge masses 

 of exposed rocks in situ. Intervening spaces between them were filled 

 with shallow ponds or swamps, showing the fact that the depressions 

 containing them were mostly excavations directly in the solid rock. 

 Wherever such rocks were exposed they showed a very remarkable 

 smoothness, resembling the famous u roches moutonnees" in shape. 

 Grooving and striation covered them, leading from the more elevated 

 points to the lower ones. In a number of instances we found the polish 

 of these rocks to be absolutely mirror-like. This condition continued 

 until we reached timber-line. There the constant weathering action has 

 loosened enormous masses of rock, which, falling down, have in part 

 obscured the effects of glaciers. Following down the course of an ancient 

 glacier west of Muddy Creek, we observed with much interest the defin- 

 ite traces it has left. Originating along the steep walls of a semicircular 

 depression, the glacier first moved through a narrow, shallow valley. 

 Touching rocky walls on either side, it swept these perfectly clean, 

 smoothing and polishing the granites wherever it came in contact with 

 them. As the valley widened the glacier spread laterally, until the 

 width became so considerable that lateral moraines were deposited. 

 Shallow, basin-shaped excavations, oval in form, were worn down into 

 the hard rock. Most of them are now filled with small sheets of water. 

 From there the ice moved downward along a steep incline, pushing before 

 it enormous masses of bowlders, in the form of terminal moraines. At 

 present these extend for several miles into the low country beyond the 

 western base of the range. Their width amounts to about a mile and a 

 half, and their thickness may be estimated at a maximum of 800 to 900 

 feet. As the climatal conditions caused a recession of the glacier, smaller 

 moraines, composed not unfrequently of material taken from the older 

 ones, remained to mark the gradual decrease of the moving mass of ice. 

 This feature becomes more noticeable as we retrace our steps to the 

 small lakes found high up in the mountains. In several instances termi- 

 inal moraines have formed dams across shallow depressions which now 



