694 W. C. ALDEN PRE-WISCONSIN GLACIAL DKIFT IN MONTANA 



crest. Here there is an abrupt drop in the crest line, and from this point 

 to the mountain the crest is narrow, lower, and composed of shale. The 

 highest part of the ridge is capped with till and gravelly drift, which is 

 exposed at several points in fresh scarps due to landslides. The litho- 

 logical composition is the same as on Two Medicine Eidge and many of 

 the green argillite fragments show glacial striations. This rock is very 

 dense, fine grained, and so dijSicultly soluble as scarcely to be etched at 

 all even after very long exposure to the weather. Some of the limestone 

 blocks are 6 to 8 feet in length. The top of this ridge is broad, smooth, 

 and gently sloping. The north slope is heavily timbered and there has 

 been much slumping of the drift on the underlying shale, so that the 

 upper limit reached by the North Fork glacier during the later extension 

 of the ice has not been accurately determined. Judging from the condi- 

 tion on the opposite side of the valley, the surface of the later ice was at 

 least 200 feet below the top of this ridge. 



Between 4: and 5 miles east of the mountain the crest drops 300 or 400 

 feet to a sag. Through this sag the ice of the N"orth Fork glacier of the 

 Wisconsin stage appears to have extended nearly or quite to contact with 

 that of the South Fork glacier. Beyond the sag the crest rises again 200 

 to 300 feet, maintains its height for about a mile, and again drops to a 

 much lower level, over which the later ice spread morainal deposits. 

 Two miles farther southeast the ridge, here of sandstone, rises again 

 above the later drift and extends thence eastward with even, flat top, 2 

 miles to the point where it is cut by the post-glacial gorge of the South 

 Fork of Cut Bank Creek. East of this creek the ridge continues toward 

 Browning, but is still lower and was overridden by the later ice. Both 

 the isolated mesa-like parts of the ridge are capped with coarse gravel, 

 largely quartzite, evidently to be correlated with the drift farther west 

 and on Two Medicine Eidge, although here no till and no striated pebbles 

 were observed. 



Deposits on Milk Eiver Eidge 



On the north side of the valley of l^ovth Fork of Cut Bank Creek is 

 another great ridge of Cretaceous shales and sandstones left from the 

 erosion of the Blackfoot peneplain. This is known as Milk Eiver Eidge 

 from the fact that tributaries of that stream head on its north slope. 

 Down the great trough between Milk Eiver and Cut Bank ridges Cut 

 Bank glacier extended at the Wisconsin stage of glaciation, attaining a 

 length of 12 miles east of the mountain front. Climbing 1,600 feet from 

 the valley bottom to the point where Milk Eiver Eidge joins the moun- 

 tain front, one finds the deposits much disturbed by landslides, but it 



