30 Notes on some Evidences of 



proximate cause of a lake-basin are extremely rare, if any 

 at all exist ; while numerous instances have been given of 

 Scottish lochs having been scooped out by the erosive power 

 of glacial ice in unbroken strata. It does not appear probable 

 that the origin of the Livingstone Creek old lake-beds is to 

 be ascribed to any pre-giacial earth movements. 



2. That they were scooped out by the erosive action of 

 glaciers is more in accordance with the observed facts. The 

 seeming difficulty in the apparent want of sufficient slope in 

 the valley may be answered by the well-known fact, "that 

 the slope of the upper surface of a plastic or fluid substance 

 determines the rate of the flow, and not that of the under 

 surface ; since, if ice were accumulated over a region so that 

 the upper surface had the requisite slope, there would be 

 motion in the mass in the direction of this slope whatever 

 the bottom of the slope might be. At the same time the 

 slope of the land at the bottom or the courses of the valleys 

 would determine to some extent the movement of the 

 bottom."* In this case there would in all probability be 

 a sufficient slope to allow of a proper down-thrust of the 

 glacier mass at each of the localities previously referred to, 

 and the consequent rasping and carving-out of the lake-beds 

 by the harder rock fragments in the glacier bottom. I am 

 sensible of the difficulties which beset the theory of glacier 

 excavation on mechanical and physical principles'!", but the 

 facts observed in the Dry Gully area can be more satisfac- 

 torily explained by the theory than by any other means. 



3. Should, however, the slope be considered insufficient 

 for erosion of the hollows, there are not wanting evidences 

 that the filling up was accelerated by the building up of 

 terminal moraines, where subsidiary lateral glaciers joined 

 the medial valley glacier. The heavy materials deposited 

 at the junction of New Rush, Jim-and-Jack, Dry Gully, and 

 Wilson's Creek are striking evidences of such. Objections 

 may be raised to the cross markings or striae on the sample 

 of volcanic rock produced in illustration of the evidences 

 referred to in this paper, that "the scratches take such 

 a variety of directions, and occur in a manner that hardly 

 appears reconcilable with the idea that they were caused by 

 the passage of other materials under the grinding power of 

 ice;" but we must remember that, "as water is always 



* Text Book of Geology : Dana,, p. 224. 



f Mechanics of Glaciers : Eev. A. Irving, B.A., Q.J.G.S., No. 153, p. 73. 



