DRIFT ON THE BLACKFOOT PENEPLAIN 



537 



boulders are exclusively from the mountain rocks, mostly quartzite and 

 red and green argillite, with some of diorite and some from the limestones' 

 which Willis called the Siyeh and Altyn limestones. Many of the pebbles 

 of the last mentioned, in the upper part of the section, are rotted to a 

 loose, buff powder, as the result of solution. In places streaks of the 

 stratified sand are cemented to hard sandstone, and below the upper 5 

 feet the till is cemented to a hard tillite by the calcium carbonate rede- 

 posited by the downward percolating waters. 



Examination showed also that the flat top, on that part of the Hudson 

 Bay divide between a point south of Spider Lake and the gap south of 

 Galbraith's ranch, well above the marginal moraine of Saint Mary Gla- 



Figure 3. — View looking Eastward from a Point about J f Miles North of Duck Lake 



Showing relations of the terminal moraine of Saint Mary Glacier, of Wisconsin stage 

 of glaciation, to the north slope of the Hudson Bay Divide, on whose top lies pre- Wis- 

 consin glacial drift. (From photograph.) 



cier, is capped in the western part by 15 to 25 feet or more of glacial till. 

 and farther east by thin, gravelly drift containing striated pebbles of 

 greenish argillite (plate 15, figure 1). The superficial deposits on that 

 part east of the gap south of Galbraith's ranch was not carefully exam- 

 ined. The top of the ridge where capped with this drift declines eastward 

 in 5 miles from 5,300 feet above tide to 5,100 feet. The marginal mo- 

 raine of Saint Mary Glacier, looping back to the northwest on the north 

 side of Goose Lake (plate 13), crosses the highest pail of the ridge at the 

 west end, doubles sharply back to an east-north easterly (rend, and grad- 

 ually descends the steep north slope of the ridge until it lies on the plain 

 several hundred feet below the drift on the top of (he divide (figure ^). 

 It is thus clear that the latter deposit is not referable to the Wisconsin 

 stage of glaciation. The elevation of (he top of the ridge correlates it 

 with that part of Saint Mary Ridge between Duck Lake and Divide 

 Mountain as a remnant of the highesl plain. 



