[COLEMAN] GLACIAL HISTORY 37 



on the land and carry with them the debris acquired in their journey 

 over land. On the other hand, the apparently local origin of the 

 stones in the till seems to harmonise better with the idea of a thin 

 ice sheet covering the low ground. The evidence at hand seems in- 

 sufficient to decide finally between the two explanations. 



No striated surfaces were found on the island, but the soft sand- 

 stones of the glaciated lower levels were not well adapted to retain 

 such markings. In this respect the contrast is great with Prince 

 Edward Island, where Chalmers has reported many striated surfaces, 

 some of which he attributes to land ice and others to floating ice. 



Both islands differ greatly from most other parts of eastern Can- 

 ada in the small amount of glaciation they display, and in the frequent 

 occurrence of residual soils passing down into rock in place. They 

 were evidently little affected by the passage of land ice over them, if 

 this ever really happened; and one would be tempted to account for 

 the undoubted till deposits as the work of icebergs floating from the 

 margin of the main sheet, if it were not the fact that the till and the 

 striated stones contained in it are usually of local materials. If the 

 ice sheet was so thin that low hills of 250 feet were not covered during 

 its advance one can hardly imagine it capable of depositing boulder 

 clay up to 105 feet. Is it possible that the thin edge of the continental 

 ice was afloat, like the Ross Barrier ice of Antarctica, when the sea 

 stood 75, or perhaps 150 feet higher than at present, and that the 

 sandy till with its enclosed bits of sandstone was gathered from rocks 

 on the bottom nearby and left when the ice grounded on the present 

 lowlands of the islands, then shoals covered by shallow water ? 



The facts are apparently contradictory and are not easily ac- 

 counted for by the action of land ice as illustrated in Quebec or Ontario; 

 so that some modification of the glacial machinery, as generally 

 imagined, seems to be necessary. 



To an observer from Ontario, all the glacial deposits seen in the 

 east, both on the mainland and on the islands, seem much more 

 weathered and ancient than the glacial deposits north of Lake Ontario, 

 and it may be that they were formed during an earlier and much more 

 extensive glaciation than that of the Wisconsin sheet. 



