562 PRE-WISCONSIN GLACIAL DRIFT IN MONTANA 



Wisconsin mountain till may have been deposited in valley bottoms, al- 

 though in the Browning and adjacent quadrangles it is confined to the 

 high-level tracts. We are inclined to think, however, that the mountain 

 till which we found overlapped by till of the Keewatin ice on South Fork 

 of Oldman Eiver and on Drywood Fork of Waterton Eiver is to be corre- 

 lated with the moraines of the mountain glaciers farther west, and that 

 it is of Wisconsin age. As has already been indicated, this certainly 

 seems to be the case in the valleys of Belly and Saint Mary rivers near 

 the 49th parallel. 



The "quartzite gravels" in southern Alberta are largely concentrated 

 along what appear to be pre- Wisconsin drainage lines. So far as we have 

 seen them, these gravels are not exposed continuously for any considerable 

 distance in the bluffs along the present courses of the streams, unless it 

 be at Lethbridge, nor even in numerous consecutive, interrupted sections. 

 It rather seems as though they are exposed only at places where the 

 present streams have cut across older stream channels. Where the gravels 

 appear in one section, neighboring sections above and below may show no 

 such gravels, even where the stream has cut entirely through the drift 

 deposits and into the underlying Cretaceous or Tertiary shales and sand- 

 stones. 



On almost all those parts of the Browning and Blackfoot quadrangles 

 which were overrun by neither the Keewatin ice-sheet nor the later moun- 

 tain glaciers, and which have been degraded from the high levels of the 

 Blackfoot and second peneplains, quartzite gravels are sprinkled on slopes 

 and lowlands. The stones do not form thick deposits, but in many places 

 are set almost closely enough to form a cobblestone pavement, and along 

 the present stream courses they are concentrated to beds which are in 

 places several feet in thickness. 



It is clear from the relations that these quartzite pebbles and boulders 

 have been let down during the process of degradation of the area from the 

 high-level plains, where the evidence of pre-Wisconsin mountain glacia- 

 tion is found. In their present positions, therefore, they are to be re- 

 garded as interglacial gravels, excepting where they have been rehandled 

 and redeposited by the streams since the last extension of the mountain 

 glaciers. 



On the basis of these observations, we venture to express the opinion 

 that part at least, if not all, of the so-called "Saskatchewan" gravel ex- 

 posed at intervals along the valleys in southwestern Alberta are inter- 

 glacial deposits derived by erosion from the pre-Wisconsin mountain 

 drift, which, near the boundary line and to the south, was originally con- 

 fined very largely to the high-level plains, but which farther north man- 



