30 THE CANADIAN NATURALIST. [Vol. Vl. 



another must have terminated at tlie borders of the two lakes 

 above mentioned. 



On a still larger scale the N. W. and S. E. striation appears in 

 the valley of the Ottawa, and farther west between the head of 

 Lake Ontario and Lake Huron. In these places there is no 

 elevation capable of giving rise to local glaciers, and therefore, as 

 in New England and Nova Scotia, we must ascribe the glacia- 

 tion either to general ice-laden currents from the North-west, or 

 to the great continental glacier imagined by some geologists. 



A most important observation bearing on this subject appears 

 in the Report of Mr. R. Bell, in the region of Lake Nipigon, 

 North of Lake Superior. He observed there the prevailing 

 South-west striation, but with a more westerly trend than usual. 

 Crossing this, however, there was a southerly and S. E. set of 

 striae which were observed to be older than the South-west striae. 

 In some other parts of Canada these striae seem to be newer than 

 the others, but there would be nothing improbable in their occur- 

 ing both at the beginning and end of the Boulder-clay period. 



In summing up this subject, I think it may be affirmed that 

 when the striation and transfer of materials have obviously been 

 from N.E. to S.W., in the direction of the Arctic current, and 

 more especially when marine remains occur in the drift, we may 

 infer that floatins; ice and marine currents have been the efficient 

 agents. Where the striation has a local character, depending 

 upon existing mountains and valleys, we may on the other hand 

 infer the action of land ice. For many minor effects of striation, 

 and of heaping up of moraine-like ridges, we may refer to the pre- 

 sence of lake or coast ice as the land was rising or subsiding. 

 This we now see producing such effects, and I think it has not 

 been sufficiently taken into the account. 



As to the St. Lawrence valley, it is evident that its condition 

 during the deposit of the Boulder-clay must have been that of a 

 part of a wide sound or inland sea extending across the continent, 

 and that local glaciers may have descended into it from the high 

 lands on the north and possibly also on the south. During this 

 state of the valley great quantities of boulders were brought down 

 into it, especially from the Laurentide hills, and were drifted 

 along the valley, principally to the south-west. Extensive erosion 

 also took place by the combined action of frost, rain, melting 

 snows, and the arctic current and the waves, and thus was fur- 

 nished the finer material of the Boulder-clay. 



