Records of ancient Ice- Work. 155 



Former Glaciation. 



In common with other jiarts of the coast region, the Taku 

 basin shoAVS signs of intense glaciation from the westward- 

 moving portion of the Cordilleran ice sheet. Evidence of this 

 in the way of glacial deposits is wanting along the lower portion 

 of the river, while the polished and striated rock surfaces so 

 abundant there may be due to the action of a glacier occupying 

 simply the river valley. The evidence of an ice sheet becomes 

 more abundant, however, toward the upper part of the basin. 

 Thus, on a spur of the high plateau east of the forks of Taku 

 river, bowlder clay and stratified gravels were seen 3,100 feet 

 above the river. The movement of the ice in the greater por- 

 tion of the Taku basin was apparently in the same direction as 

 the present drainage. The high broad valleys of the upper 

 Taku branches are deeply filled with a mantle of bowlder clay 

 and gravel. In most cases this is spread out in a comparatively 

 even layer over the surface, but also many narrow ridges occur 

 from ten to fifty feet in height, with the longer axes in the direc- 

 tion of the present valleys. These, however, probably mark -a 

 phase of deposition by a greatly diminished and waning ice 

 sheet, so that they afford little if any indication of the direction 

 of ice movement during the maximum glaciation. A much 

 better indication is afforded by the transportation of bowlders. 

 From the head of canoe navigation on the Taku to a point 

 nearl}^ half way across to Ahklen valley, increasing numbers of 

 bowlders were observed composed of a peculiar granite contain- 

 ing large porphyritic crystals of black hornblende. At this 

 point their source was found in a range of hills composed of the 

 same granite, and no bowlders of this rock were seen to the 

 northeastward. At the summit of the divide but little evidence 

 was seen which would indicate the direction of the ice move- 

 ment, though it seems probable that it was toward the north- 

 west, as it certainly was in Ahklen valley. 



Some deposits of true bowlder clay occur at various points 

 along the lake, and a single occurrence was noted on the Teslin 

 river about five miles from its mouth. Among the many lakes 

 in the upper part of the valley are ridges and mounds of 

 rounded bowlders and gravel, which, with terraces of the same 

 material about the head of Ahklen, were evidently deposited by 



