570 PRE-WISCONSIN GLACIAL DRIPT IN MONTANA 



bined mountain glaciers onto the Blackfoot peneplain must have been 

 quite as favorable as were those in the area of the Two Medicine Glacier 

 at the Wisconsin stage. The latter piedmont glacier extended about 38 

 miles from the mountain front. 



11. It is not certain that there is pre- Wisconsin drift of the Keewatin 

 Glacier in any of the valleys within 30 or 40 miles north of the 49th 

 parallel, so that it is not known that the streams had cut to anything like 

 their present levels before the earlier giaciation. There is, however, 

 unmodified glacial till in the valleys farther north which may be as old 

 as the high-level mountain drift, showing that the streams had there cut 

 down nearly to their present levels before the time of the earlier giacia- 

 tion. 



12. It is believed to be the uppermost drift of the Keewatin ice-sheet, 

 that of the Wisconsin stage, which extends to the limit of continental 

 giaciation in this area, and there overlaps till deposited by the mountain 

 glaciers. 



13. The mountain drift, which was seen to be overlapped by the drift 

 of the Keewatin ice-sheet in the valleys of Saint Mary and Belly rivers 

 and farther north, is characterized by uneroded moraines just beyond the 

 limit of the drift of the Keewatin ice and is regarded as deposited at the 

 same, Wisconsin, stage of giaciation. Dawson referred this drift and the 

 moraines to his "Albertan" stage. 



14. It is quite possible that there is pre-Wisconsin mountain drift in 

 the valley of Oldman Eiver or farther north, and that this grades east- 

 ward into "quartzite gravels," such as those underlying the lower boulder- 

 clay of the Keewatin ice-sheet at Lethbridge. Dawson states that Mc- 

 Connell observed this relation farther north on Bow Eiver, and from this 

 relation he inferred the early deposition of the mountain drift. We did 

 not, however, observe such a relation, and we feel quite safe in the corre- 

 lation indicated above in paragraph 13. 



15. We are inclined to think that a part at least, if not all, of the so- 

 called "Saskatchewan" gravel exposed at intervals along the valleys in 

 southwestern Alberta is an interglacial deposit derived by erosion from 

 the pre-Wisconsin mountain drift, which, near the boundary line and to 

 the south, was originally confined very largely to the high-level plains, 

 but which farther north mantled the slopes and lower surfaces that had 

 been reduced by degradation prior to the early advance of the mountain 

 glaciers. 



16. If the name ''Albertan" is to be used, we think it should be applied 

 to the pre-Wisconsin mountain drift on the remnants of the highest plain, 

 the Blackfoot peneplain, as best preserved in the Browning, Montana, 



