DEPOSITS ON SAINT MARY RIDGE 097 



lower lake and the lower part of the upper lake on the east is an iiiulu- 

 lating tract about a mile in width composed of small hills and ridges of 

 shale mantled with drift and standing 100 to 300 feet above the lake 

 levels. From this a steep slope, most of which is heavily timbered, rises 

 to the crest of a broad ridge known as Saint Mary Ridge. The crest of 

 this ridge gradually lowers in elevation from south to north. It is 

 highest between 2 and 3 miles north of Divide Mountain, there standing 

 about 6,100 feet above scale vel. In the interval between tliis highest part 

 and the mountain there is a broad sag in the crest line where the top of 

 the ridge is 300 feet lower. Where highest the top of Saint Mary Kidge 

 stands over 1,600 feet above the level of the upper lake. From this high- 

 est part the northward decline carries the crest line down to a level 

 which, east of the foot of the lower lake, between 9 and 10 miles to the 

 northward, is about 1,100 feet above the water in this lake and 5,500 feet 

 above tidewater. Duck Lake lies in a big sag in the upland, so that the 

 crest of the ridge may be said to curve eastward on the south side of the 

 lake. The top of Saint Mary Ridge is broad and smooth. From this 

 the i^lain slopes gradually to the eastward. Much of this surface has 

 been lowered by erosion by the headwaters of tributaries of Milk River, 

 but in the interstream areas the higher tracts still represent the Black- 

 foot peneplain. 



Beyond the broad sag, in which lies Duck Lake, the Hudson Bay 

 divide continues as a broad high ridge similar to and really a part of 

 Saint Mary Ridge. This part of the ridge, which consists of Cretaceous 

 sandstones and shales, has iiot been examined. The ridge east of Saint 

 Mary Lake has not been thoroughly examined, but what was seen by Mr. 

 Thomas and the writer is significant in connection with this question of 

 pre-Wisconsin glaciation. 



On the steep west slope of Saint Mary Ridge there has been consider- 

 able landsliding on the shale, which probably forms the bulk of the ridge. 

 At a few places near the top of the slope this slumping has produced 

 fresh scarps, giving excellent exposures of the material capping the ridge. 

 Following the trail southeastward from the foot of Upper Saint Mary 

 Lake for about II/2 miles and then climbing the wooded slope, we 

 reached one of these scarps between 1,100 and 1,400 feet above the lake. 

 The exposure has a height of nearly 300 feet and a length of 500 feet or 

 more. The upper 30 to 50 feet (A) of the section is grayish glacial 

 till, in which the pebbles and boulders are of red and green argillite, 

 quartzite, gray siliceous limestone from the Siyeh formation, diorite, and 

 some buff limestone from the Altyn formation. It looks as though most 

 of the Altyn limestone pebbles had been removed by solution and frag- 



