GLACIATION OF NORTH CENTRAL CANADA I 53 



period of this advance of the ice would seem to correspond to 

 the Kansan epoch, as at present understood by American geolo- 

 gists. This till is very similar to that below it, but the material 

 of which it is composed is more highly oxidized and decayed, 

 and fragments of soft, brittle rocks, such as lignite, are much less 

 common in it than in the lower till. 



Both during the Kansan and sub-Aftonian epochs, extragla- 

 cial lakes of greater or less size doubtless existed, and any 

 material brought down into them by the glaciers would doubtless 

 have been scattered over their floors or along their sides. Thus 

 bowlders were probably carried some distance beyond the 

 extreme limits to which the glaciers themselves reached, as, for 

 instance, on some of the terraces near, and at the foot of the 

 Rocky Mountains where Dr. Dawson has recorded the occurrence 

 of numerous transported bowlders. Where these lakes existed 

 terminal moraines would also not be found, and thus the absence 

 of terminal moraines may often be explained in places where we 

 should otherwise expect to find them. 



Striae have not been recognized in this western district, for 

 the soft Cretaceous rocks are not suitable for their preservation, 

 but the older and harder rocks, nearer the center of the glaciated 

 area, are everywhere scored with glacial markings. Around the 

 periphery of this area underlain by harder rocks I have not been 

 able to recognize more than one set of striae referable to the 

 Keewatin ice-sheet or rather more than one direction of stria- 

 tion, but nearer the glacial center several sets may be distinctly 

 seen. Along the Doobaunt River above the Forks the oldest of 

 these point southward, probably running outwards from a center 

 between Doobaunt and Back rivers. These I have associated 

 with the earlier stages of the Keewatin glacier, though I have no 

 direct evidence to offer on that point, except that they are the 

 earliest of four different and distinct sets of glacial striae. 



The accomplished geologists who have worked in the United 

 States, near the headwaters of the Mississippi River, have found 

 that there was an extended epoch of deglaciation after the depo- 

 sition of the Kansan till, and I would assign to this interglacial 



