RELATIONS OF EARLIER AND LATER DRIFT 557 



not differentiated the earlier mountain drift, Calhoun concluded that 

 there was no great difference in age between the drift of the mountain 

 valley glaciers and the continental drift which overlapped it. 



The topographic relations in and near the Browning quadrangle show 

 indisputably that the last great extension of the mountain glaciers oc- 

 curred long after the deposition of the earlier mountain drift on the 

 Blackfoot peneplain. Great valleys cut in this peneplain confined and 

 directed the flow of the last ice-tongues projecting beyond the mountain 

 front. Even with the checks noted above, which curb any tendency to 

 refer all the dissection of the Blackfoot peneplain to time since the 

 earliest mountain glaciation, yet it seems to us clear that the interval 

 between the deposition of the high-level drift and the valley drift must 

 have been very considerable. The moraines of the valley glaciers are very 

 finely developed, showing in many places a sag-and-swell or kame-and- 

 kettle topography, dotted with lakelets and wholly unmodified by erosion. 

 These moraines are quite as well preserved as the famous "kettle mo- 

 raine" of the Mississippi Valley, and we think can not be referred to 

 deposition prior to the Wisconsin stage. 



We did not differentiate any pre-Wisconsin mountain drift at any 

 place excepting where it is preserved on the remnants of the high-level 

 plains. In these places the areal and topographic relations are such as to 

 render the differentiation unquestionable. Farther north, however, as we 

 have indicated, the high-level tracts were probably largely cut away, even 

 at the time of the early glaciation, and they have now wholly disappeared. 

 This being the case, it is to be expected that with increasing distance 

 northward from the boundary line the ratio of lowland to highland on 

 which this early mountain drift was deposited must have gradually in- 

 creased. All that part of southern Alberta from Oldman River south- 

 ward to the boundary, excepting a narrow belt bordering the mountain 

 front, is covered with drift from the Keewatin ice-sheet, and almost the 

 only exposures of any considerable thickness of drift in this area are those 

 afforded by the bluffs which form the steep sides of the narrow trench- 

 like valleys cut by the streams in the undulating plain. Tt is thus to be 

 expected that the evidence of an early mountain glaciation would be 

 found, if at all, in this part of the region only in the valleys. 



As stated above, we think that the drift of the mountain glaciers which 

 we saw overlapped by drift of the Keewatin ice on Saint Mary and Belly 

 rivers, within 10 miles of the boundary, must surely have been deposited 

 by the valley glaciers of the last great extension. We do not know of any 

 evidence clearly indicating that this drift is older. Calhoun cites 17 one 



17 Professional Paper No. 50, p. 49, flg. 31. 



