556 PRE-WISCONSIN GLACIAL DRIFT IN MONTANA 



eastward), and there found reason to believe that the Saskatchewan gravels 

 of the plains represent and gradually pass into a 'western boulder-clay,' in 

 approaching the mountains. This observation has remained unpublished, but 

 now appears to be well established, and it follows from it, taken in connection 

 with the facts already summarized, that there are no less than three distinct 

 boulder-clays in the region here treated of, the oldest or 'western' boulder-clay 

 being followed in time by that previously named the 'lower' boulder-clay, 

 which is in turn distinctly separated from the 'upper' boulder-clay over a 

 considerable part of the district, at least by interglacial deposits." 



And again: 15 



"As implied in Mr. McConnell's summary of the Bow River section, just 

 given, it may, I believe,'now be stated with certainty that the earliest sign of 

 glacial conditions met with in southwestern Alberta is found in the evidence of 

 the extension of glaciers from the Rocky Mountains to a certain distance 

 beyond the base of that range. These may have reached nearly to Calgary, in 

 Bow Valley, which has the largest drainage basin in the mountains, but were 

 much less considerable farther south. A boulder-clay was at this early time 

 laid down in connection with these glaciers, probably in part as a subglacial 

 deposit, in part along their retreating fronts as a fluvio-glacial deposit The 

 latter as it is followed eastward gradually changes into the typical Saskatche- 

 wan gravels, in places associated with silty or sandy beds. All the drift 

 material of this stage is either local or derived from the Rocky Mountain side, 

 and it is probable that the boulder-clay of this time is actually connected with 

 the mass of the moraine ridges and hills of Bow Valley and those found 

 fringing the mountains in places farther to the south." 



We agree with Dawson in the statement that "the earliest sign of 

 glacial conditions met with in southwestern Alberta is found in the evi- 

 dence of the extension of glaciers from the Eocky Mountains to a certain 

 distance beyond the base of that range." We, however, find the best evi- 

 dence of this is the drift on the remnants of the high-level plains in the 

 vicinity of Belly River and in the Browning quadrangle. Evidently there 

 are in the region at least four drift sheets instead of three, two deposited 

 by the continental ice, of which the best evidence is found in the region 

 of Lethbridge, and two deposited by mountain glaciers, of which the best 

 evidence is found in the region south of that studied by Dawson and 

 McConnell. 



In Saint Mary River Valley, a short distance south of the boundary, 

 and in Belly River Valley at a point west of Mountain View, about 10 

 miles north of the boundary, we found the drift of the mountain glaciers, 

 whose surface is characterized by such youthful topography, extending 

 down the valleys underneath the drift of the continental sheet. This 

 relation was also observed and described by Calhoun. 16 Although he had 



15 Op. ctt, p. 59. 



16 Professional Paper No. 50, 1906, pp. 46-49. 



