60 THE ICE AGE IN CANADA. 



sand was deposited. It is usually, indeed, in this position 

 that the greater part of the shells of our Post-pliocene 

 beds occur ; the Saxicava sand being generally somewhat 

 barren, or containing only a few shallow-water species, 

 while the Leda clay is usually also somewhat scantily 

 supplied with shells, except toward its upper layers. 

 Hence it is somewhat difficult to refer a large part of the 

 shells to either deposit. I have, however, usually 

 regarded the richly fossiliferous deposit as belonging to 

 the Leda clay ; and where, as sometimes happens, the 

 clay itself is absent and merely a thin layer rich in 

 fossils separates the Saxicava sand from the boulder-clay, 

 I have regarded this layer as the representative of the 

 Leda clay. Where, on the other hand, the Leda clay is 

 thick and well developed, it admits of sub-division into a 

 lower Leda clay, unfossiliferous or with only shells of Leda 

 glacialis and Macoma Groznlandica, and an upper Leda 

 day, usually more sandy and holding a rich boreal fauna 

 identical with that of the northern part of the gulf and 

 river St. Lawrence at present. 



The Saxicava sand, in typical localities, consists of 

 yellow or brownish quartzose sand, derived probably from 

 the waste of the Potsdam sandstone and Laurentian 

 gneiss, and stratified. It often contains layers of gravel, 

 and sometimes is represented altogether by coarse gravels. 

 It is somewhat irregular in its distribution, forming banks 

 and mounds, partly no doubt in consequence of original 

 irregularities of deposit, and partly from subsequent 

 denudation. In some outlying localities it is liable to be 

 confounded with the modern river sands and gravels. 

 Large travelled boulders often occur in it ; but it rarely 

 contains glaciated stones, the stones and pebbles seen in 

 it being usually well rounded. 



