700 W. C. ALDEX PHE-WISCONSlN GLACIAL DRIFT IN MONTANA 



continue to the front of Point Mountain, but after reaching this high 

 altitude the crest drops abruptly to a notch 200 feet or more in depth, 

 beyond which it again rises to Point Mountain. This sharp, highest 

 part of the crest of Boulder Eidge consists of chipstone of limestone, 

 white quartzite, and red and green argillite, such as compose Point 

 Mountain. Xo fragments of diorite were noted. The material does not 

 look like glacial drift but like talus, and its character and relation leads 

 to the suggestion that here is the last remnant of a disintegrated salient 

 of Point Mountain, which at the time of the deposition of this high level 

 drift extended 1% miles farther to the northwestward than it does at 

 present. The material is from the pre-Cambrian formations, which in 

 the nearest part of Point Mountain lie at elevations more than 800 feet 

 higlier than does this remnant. This relationship indicates either that 

 the pre-Cambrian rock of this remnant was let down from a higher ele- 

 vation by gradual slumping or washing away of the underlying Creta- 

 ceous shale, or that, owing to a slight anticlinal fold, it originally stood 

 lower at this point than it does in Point Mountain, I14 miles away, 

 where the rock is now inclined upward in the direction of the remnant 

 in question. Owing to similarity in component material of the older 

 and younger drift and to the slumped and wooded condition of the 

 slopes, it is difficult to determine just how high on the flanks of Boulder 

 Eidge the ice of Boulder Creek and Swiftcurrent glaciers extended at 

 the AYisconsin stage of glaciation. It seems clear, however, that the 

 later ice did not overtop the ridge, and that the drift capping the crest 

 of the rido-e is that of a much earlier stasre of s^laciation. 



Deposits on Swiftcueeent Eidge 



The companion ridge to that just described stands between Swift- 

 current A^alley on the south and South Fork of Kennedy Creek on the 

 north. A subordinate part of this ridge extends northward at right 

 angles to the main ridge from Swiftcurrent Valley and forms the divide 

 between Saint Mary Valley on the east and South Fork of Kennedy 

 Creek on the west. The subordinate ridge, which rises 650 to 850 feet 

 above the bottom of the valley on the east, appears to have been over- 

 topped by Saint Mary glacier of the Wisconsin stage, inasmuch as mo- 

 rainal deposits are found along its crest. The summit of the main 

 ridge, which trends in a general east-west direction, appears not to have 

 been overtopped by the later ice moving down the valleys of either Swift- 

 current Creek or South Fork of Kennedy Creek. For 2 14 miles the top 

 of this ridge is very even (plate 40, figure 1), with a width of 90 to 120 



