RELATIONS OF THE "SASKATCHEWAN^ GRAVEL 561 



the moraines, to be a deposit of these glaciers. The lower gravels in this case 

 and in that of Pincher Creek are obviously due to preglacial streams flowing 

 from the mountains, and, although the name Saskatchewan gravels may be 

 applied to them, they here evidently antedate the eastern gravelly representa- 

 tive of the Rocky Mountains or earliest boulder-clay. Further to the east, 

 where this boulder-clay gradually passes into such gravels, there is no means 

 of distinguishing between wholly preglacial beds and those which may have 

 been formed during the main period of the Rocky Mountain glaciers. Many 

 exposures of the Saskatchewan gravels may include both, and this without 

 necessitating the supposition of any great chronologic break." 



From the observations of Dawson and McConnell and from those of 

 ourselves, it is clear that gravels exclusively from the Eocky Mountains, 

 mostly quartzite, underlie the lower till of the Keewatin ice-sheet near 

 Lethbridge, underlie the drift at a point on Belly Eiver and at the con- 

 fluence of North and Middle forks of Oldman Eiver, where only one 

 boulder-clay of the Keewatin ice-sheet, presumably the upper, is exposed, 

 underlie mountain till at points where it is overlapped by drift of the 

 Keewatin Glacier on Saint Mary Eiver and on South Fork of Oldman 

 Eiver, and underlie mountain till beyond the limit of the drift of the 

 Keewatin ice on South Fork of Oldman Eiver and on Mill Creek. From 

 these relations it might be concluded that the "quartzite gravel" is wholly 

 a preglacial deposit. 



As shown from quotations given, Dawson did regard the "quartzite 

 gravel," where underlying mountain till, as preglacial, although he in- 

 cluded it under the name "Saskatchewan." He states, however, 20 that 

 from his studies on Bow Eiver, McConnell ''found reason to believe that 

 the Saskatchewan gravels of the plains represent and gradually pass into 

 a 'western boulder-clay' in approaching the mountains." Inasmuch as 

 the gravels in the Lethbridge region underlie the lower boulder-clay of the 

 Keewatin ice-sheet, he concluded that the mountain till was older than 

 both deposits of the continental ice-sheet. 



Our own studies in southern Alberta were not sufficiently exhaustive to 

 warrant expressing an opinion as to the correctness of the theory that the 

 same gravels which underlie the lower till of the Keewatin ice-sheet at 

 Lethbridge grade westward into mountain till. It is quite possible that 

 there is in places such a gradation, and that the mountain till into which 

 such gravels grade, in valleys as far north as Bow River, or even on Old- 

 man Eiver, is really older than the lower boulder-clay of the Keewatin 

 ice-sheet. We ourselves saw no ground for such a conclusion in the ex- 

 posures which we examined. It is quite possible that this far north pre- 



30 Bull. Geol. Soc. Am., vol. 7. pp. 88, •".'.»; quoted on p. 568 of the preaenl paper. 

 XXXVIII— Bull. Geol. Soc. Am., Vol. 24, 1012 



