SUMMARY AND DISCUSSION. 63 



glacier may still have continued to hold some importance in the foot- 

 hill region, but the abundant supply of well rounded gravels, with other 

 circumstances, renders it probable that the Rocky Mountain glaciers 

 generally had become strictly local and relatively insignificant. 



If it may thus be assumed that the higher terraces and traveled gravels 

 of the Porcupines are approximately contemporaneous with the upper 

 boulder-clay, all the lower and later terraces and gravel plains may be 

 regarded as marking stages in the subsidence of this water-level from its 

 maximum height of 5,300 feet. These, it has already been noted, are 

 usually not strongly impressed, and there is no evidence that the subsi- 

 dence was arrested long, except at one stage, which is that spoken of in 

 the report of 1882-'84 as being at about 4,200 feet. Further examina- 

 tion appears to show that the terraces referable to this particular stage 

 slope up gradual^ in the foothills and on approaching the mountains 

 to a maximum height of about 4,500 feet, from which it may be argued 

 that from the last mentioned height the water lowered its level gradually 

 to one of about 4,200 feet, while new material was constantly being 

 washed down by rivers from the mountains. A later and still lower, 

 though less important, period of arrest seems to be marked by the gravel 

 plain near Macleod at about 3,200 feet. 



The first mentioned line of relative stability appears to be equally well 

 marked in the southern portion of the region, about Waterton lake and 

 the Oldman river, and in the northern, in the Bow valley, leading to the 

 suggestion that the irregular uplift of the earlier stages of recovery had 

 been succeeded along the base of the mountains by one in which further 

 change of level occurred throughout uniformly, as compared with the 

 actual heights of the surface found in the same region today, or with 

 isobases changed in direction and parallel to the trend of the mountains. 

 This later uplift may have continued, with the stranding of large boulders 

 near the water-line from time to time, until this part of the plains rea*ched 

 its present condition and slope. 



There is, however, some good evidence to show that in postglacial times 

 a renewed or continued southern uplift took place. This is derived from 

 the changes in the course of streams and slopes of their valleys, but can- 

 not be entered into in this paper.* 



In this connection I may digress so far as to mention that there is a 

 somewhat notable correspondence between the higher levels of terraces 

 on both sides of the Rocky mountains and continental watershed. It is 

 found in the southern part of the interior plateau of British Columbia 



* Report of Progress, Geol. Survey of Canada, 1882-'84, p. 150 C ; Annual Report, Geol. Survey of 

 Cananda, vol. i (n. s.), p. 75 C ; Physiographical Geology of the Rocky Mountain region in Canada, 

 Trans. Royal Soe. Canada,vol. viii, sec. 4, p. 63. 



IX— Bull. Geol. Soc. Am., Vol. 7, 1895. 



