DEPOSITS ON TWO MEDICINE RlDGE G93 



stones are rare among the stones scattered over the mesa top and also in 

 the upper part of the 150-foot section. Farther down the slope, how- 

 ever, they become more numerous and show less effects of weathering. 

 It is probable that the calcareous cement of the conglomerate was de- 

 rived from solution of the limestones in the upper part of the deposit. 

 This exposure faces the mountain slope at a distance of something over 

 a mile. Between the two the ridge has been lowered and narrowed by 

 erosion. This lower part is densely timbered and was not examined. 

 From this narrowed divide the valley between the high mesa and the 

 much higher mountain slope deepens rapidly northward to a level 1,000 

 feet below the top of the former. The composition of the deposit, its 

 topographic situation relative to the mountains, to the present drainage 

 lines and to the deposits made by the glaciers of the Wisconsin stage, the 

 modification by weathering, and the cementation to a heavy bed of con- 

 glomerate all indicate that we have here a glacial deposit of relatively 

 great age. If all the dissection of the Blackfoot peneplain was accom- 

 plished in the interval between deposition of the high level and the low 

 level drifts, the earlier glacial extension antedated the Wisconsin glacia- 

 tion by a very long time. 



North of this drift-capped ridge are numerous much lower hills and 

 ridges of sandstone and shale. On one of those examined a few pebbles 

 of quartzite and diorite were found, but on the others there was no evi- 

 dence of this older drift. Among these hills flow tributaries of South 

 Fork of Cut Bank Creek. One of these. Lake Creek, heads in glacial 

 cirques in the mountains, and, stretching eastward on either side of the 

 valley, are the finely developed moraines of a glacier of the Wisconsin 

 stage.. At its greatest extension Lake Creek glacier had a length of 

 about 10 miles. At points equally distant from the mountain front the 

 crests of these moraines of Lake Creek glacier stand 500 feet lower than 

 the top of the high drift-capped mesa, and the bed of the stream between 

 them is 300 feet still lower. 



Deposits on Cut Bank Ridge 



Between the South and North forks of Cut Bank Creek is a ridge of 

 Cretaceous shale whose crest 1 mile from the mountain front has an ele- 

 vation 6,300 feet above the sea. Standing on this crest one looks down 

 1,000 feet to the stream on the south and 1,200 feet to bottom of the 

 valley on the north. Both slopes are steep, that on the north being par- 

 ticularly precipitous, that on the south much less so. Sliale is exposed 

 to within 100 feet of the top near the west end of the highest part of the 



