40 THE ICE AGE IN CANADA. 



Though the boulder-clay often presents a somewhat 

 widely extended and uniform sheet, yet it may be stated 

 to fill up all small valleys and depressions, to be confined 

 chiefly to the lower grounds, and to be thin or absent on 

 ridges and rising grounds. The boulders which it contains 

 are also by no means uniformly dispersed. Where it is 

 cut through by rivers, or denuded by the action of the 

 sea, ridges of boulders often appear to be included in it. 

 Those on the Ottawa referred to in the " Geology of 

 Canada," p. 895, are very good illustrations, and I have 

 observed the same fact on the Lower St. Lawrence and on 

 the coast of Nova Scotia. It is also observable that these 

 lines and groups of boulders are often not of local 

 material, but of rocks from distant localities, and that a 

 number of the same kind seem often to have been 

 deposited together in one group. 



Loose boulders are often found upon the surface, and 

 sometimes in great numbers. In some instances these 

 may represent beds of boulder-clay removed by denuda- 

 tion. In other cases they may have been derived from 

 the overlying members of the formation, or may have 

 been deposited 011 the surface in the later Pleistocene 

 subsidence, without any covering of clay or gravel. In 

 "Acadian Geology," p. 64, I have illustrated the manner 

 in which large stones, sometimes eight feet or more in 

 diameter, are moved by the coasi ice and sometimes 

 deposited on the surface of soft mud, and I have had 

 occasion to verify the observations of the same kind made 

 by Admiral Bay field, and quoted by Sir C. Lyell in the 

 " Principles of Geology." Lastly, on certain high grounds 

 there are large loose boulders, which have probably been 

 moved to their present positions by means of land ice or 

 glaciers. 



