GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. I09 



has been made entirely since the withdrawal of the ice from that part of the 

 valley, then the rate of cutting would be over an inch a year, which is probably 

 too fast for even water at high velocity, charged with glacial sediment and oper- 

 ating upon rather soft rock. This seems especially true when we consider that 

 the supply of water is much reduced, or possibly entirely shut off during the 

 greater part of the year. It is very probable, however, that the narrow gorge may 

 have been largely formed subglacially, while the glacier extended far down the 

 valley. Schist layers upon edge do not well record ice action, but even if such 

 evidence of glaciation was present it may have been destroyed by subsequent 

 weathering. It must be noted that the time of retreat determined as above 

 would represent only a minimum value and the rate of movement per annum 

 for a definite distance would represent a maximum. 



CHAPTER VIII. 



SUMMARY AND CONCLUSIONS. 



In the closing chapter it is desired to give a concise statement of the most 

 important results secured in the two seasons' work and the conclusions reached. 

 The writer desires further to express for the benefit of those who may be interested 

 his conviction concerning some of the theoretic questions that have arisen in 

 connection with the study of these Canadian glaciers. 



I. Physiographic Changes in the Region. 



a. Mesozoic peneplain. From the close of the Archsan to the end of the 

 Laramie, conditions were ver}' favorable for the accumulation of sedimentary 

 deposits in the region now covered by the Canadian Rockies and Selkirks. 

 Strata belonging to the Palaeozoic and Mesozoic eras of the world's history reached 

 the extraordinary thickness, according to the work of Dawson and McConnell, 

 of 50,000 to 60,000 feet. Much of this was brought above sea-leverduring the 

 Mesozoic era and further sedimentation ceased except in certain restricted 

 regions in the eastern part of the area,where conditions were still favorable for 

 marine or fresh- water accumulations. During countless ages of exposure 

 to the manifold atmospheric agencies there was developed a broad Mesozoic 

 peneplain, extending in a direction to the west of north and sloping east- 

 ward and westward, determining the general direction of flow of the drainage 

 streams. It was during this stage, probably, that the mountains suffered 

 their greatest denudation, rather than since. The great Laramide revolu- 

 tion of the western United States and Canada completed the fonnation of 

 these mountains, the pressure coming from the west in the region under con- 

 sideration, and producing a series of parallel folds and troughs, with numerous 

 overthrust faults, all having a north-northwest to south-southeast trend. The 

 upheaval was slow enough so that many of the original drainage streams were 

 able to maintain their general direction of flow, cutting their way continuously 



