704 W. C. ALDEN PRE-WISCONSIN GLACIAL DRIFT IN MONTANA 



gravel mesa to the east stood at least 200 feet above the limit of the later 

 ice. From its elevation and its isolated jDosition it seems to me that the 

 drift capping of this ridge is to be correlated with that on the mesa to 

 the east as a remnant of the pre-Wisconsin glacial drift. 



Deposits in the A^icinitt of Belly Eiver 



Crossing the ridge between Chief Mountain and the main front of the 

 mountain on the west, we descend the slope of Belly Eiver Valley by the 

 old Indian trail. At about 6,300 feet above sealevel we passed from the 

 talus-covered slope of Cretaceous shale out along the crest of a scarp 

 produced by landsliding. This exposure showed the flattened top of the 

 ridge, between elevations 6,000 and 6,300 feet above the sea — that is, 

 between 1,300 and 1,600 feet above Belly Eiver — to be composed of 

 glacial drift. On the following day Mr. Thomas made a more careful 

 examination, and he described the deposit as glacial till and gravel, 

 composed principally of limestone and quartzite from the Altyn forma- 

 tion, with subordinate amounts of red and green argillite, some Creta- 

 ceous sandstone, and a few clay ironstones. Much of the material is 

 glaciated, the argillites showing striations most frequently. On a point 

 nearer the mountain beside the new trail is an exposure of a similar 

 deposit at about the same elevation. 



Crossing to the west side of the valley, we climbed the heavily wooded 

 slope. Between 5,750 and 5,950 feet above the sea, or between 1,000 and 

 1,200 feet above the valley bottom, we found a bare scarp face, the mar- 

 ginal slope of a shoulder standing out on the slope. The material ex- 

 posed in this scarp is glacial till. All the pre-Cambrian formations are 

 represented in the pebbles and boulders of this drift, limestones from 

 the Altyn and Siyeh formations of the adjacent mountains, red and white 

 quartzite, diorite, and amygdaloidal trap. Many of the argillite pebbles, 

 especially, are well striated. Numerous blocks of tillite conglomerate 

 were observed, but no ledges were seen projecting in place. Above the 

 scarp the bench rises westward to the base of the cliff of pre-Cambrian 

 rock, but with a slope much less steep than the general slope of the valley 

 wall below. A similar bench, but somewhat less well marked, occurs to 

 the north just across the ravine. No exposures were seen to show 

 whether or not this bench is on a deposit of till. Seen from the east 

 side of the bottom of the valiey, the two appear to be parts of one bench, 

 cut through by a broad sag, in the bottom of which is a sharp V-shaped 

 ravine which drains two glacial cirques in the mountain slope above. 

 This relation, taken together with the form of the bench and the char- 



