DEDUCTIONS FROM RELATIONS OF THE DRIFT 547 



such contemporaneous continental and mountain glaciation did occur at 

 the Wisconsin stage, it is a rational inference that the deposition of the 

 pre-Wisconsin mountain drift was approximately contemporaneous with 

 that of the pre-Wisconsin continental drift which has been observed in 

 the region. 



If we judged from the topographic relations of the high-level drift to 

 the valley drift in the Browning ^quadrangle, we might conclude at once 

 that the interval of erosion between the formation of the two deposits was 

 very long, and that the pre-Wisconsin drifts were correspondingly old. 



This conclusion, however, requires some further qualification than that 

 already deduced from the comparison of the relations of the high-level 

 drift and that of Two Medicine Glacier presented above. 



No pre-Wisconsin drift of the continental ice-sheet has been observed 

 by the writers south of or near to the International Boundary.* Calhoun 7 

 observed drift outside the terminal moraine of the continental glacier 

 farther south, which suggested an earlier stage of glaciation, but he 

 found very little evidence which he thought supported the theory. On 

 page 49, Professional Paper 50, he describes a section observed by him 

 on Saint Mary Eiver, north of Sloans Eaneh, a few miles north of the 

 boundary, and which he illustrated by a figure, reproduced here as figure 

 6. Of this Calhoun stated (loc. cit.) : 



"This section furnishd the only discovered evidence of two distinct glacial 

 epochs. As no other section was found showing like or similar phenomena, 

 little stress is laid upon this." 



It seems to the present writers, however, that this section merits some 

 consideration because of its similarity to sections observed by them, and 

 earlier by Dawson and McConnell, on Belly Eiver in the vicinity of Leth- 

 bridge, Alberta, and because we have now clear evidence of an earlier 

 extension of the mountain glaciers. 



The writers examined numerous exposures on Saint Mary Eiver both 

 above and below Sloans Eanch, but this section, if still preserved, is evi- 

 dently one of those which we did not examine. This section is particu- 

 larly interesting because, if the lower bed of northeastern drift (B) is in 

 reality unmodified pre-Wisconsin glacial till deposited in situ by the 

 Keewatin ice-sheet, it means that Saint Mary Valley had at the time of 

 that glacial extension been cut down approximately to its present depth, 

 more than 1,000 feet below the level of the pre-Wisconsin mountain drift 

 on Hudson Bay Divide, 8 or 10 miles to the southward, and more than 



* See statement at end of paper of a recent discovery of Buch i drift, 

 7 Professional Paper No. 50, U. S. Geological Survey, p. 55. 



