No. 1.] DAWSON— POST-PLIOCENE. 37 



levels nearer the sea, just as a similar deposit still continues in 

 the Gulf of St. Lawrence. On the whole, then, while we regard 

 this as one bed stratigraphically, we may be prepared to find that 

 in the lower levels the upper layers of it may be somewhat more 

 modern than those portions of the deposit occurring on higher 

 ground and farther from the sea. 



Where the Leda clay rests on marine Boulder-clay, the change 

 of the deposits implies a diminution of ice-transport relatively to 

 deposition of fine sediment from water ; and with this more 

 favourable circumstances for marine animals. This may have 

 arisen from geographical changes diminishing the supply of ice 

 from local glaciers, or obstructing the access of heavy icebergs 

 from the Arctic regions. At the present time, for example, the 

 action of the heaviest ber^'s is limited to the outer coasts of La- 

 brador and Newfoundland, and a deposit resembling the Leda 

 clay is forming in the Gulf of St. Lawrence ; but a subsidence 

 which would determine the Arctic current and the trains of 

 heavy bergs into the Gulf, would bring with it the conditions 

 for the formation of a Boulder-clay, more especially if there were 

 glaciers on the Laurentide hills to the north. Where the Leda 

 clay rests on Boulder-clay, which may be supposed to be of terres- 

 trial origin, subsidence is of course implied ; and it is interesting 

 to observe that the conditions thus required are the reverse of 

 each other. In other words, elevation of land or sea bottom 

 would be required to enable Leda clay to take the place of marine 

 Boulder-clay, but depression of the land would be necessary to 

 enable Leda clay to replace the moraine of a glacier. I cannot 

 say, however, that I know any case in Canada where I can cer- 

 tainly affirm that this last change has occurred ; though on the 

 north shore of the St. Lawrence there are cases in which the Leda 

 clay rests directly on striated surfaces which might be attributed 

 to glaciers ; just as in the West the Erie clay occupies this posi- 

 tion. 



3. The Saxicava Sand. 



When this deposit rests upon the Leda clay, as is not unfre- 

 qucntly the case, the contact may be of either of two kinds. In 

 some instances the surface of the clay has experienced much 

 denudation, being cut into deep trenches, and the sand rests 

 abruptly upon it. In other cases there is a transition from one 

 deposit to the other, the clay becoming sandy and gradually pass- 



