The Drift or Boulder Formation. 329 



the summits of the hills. Sometimes two sets of striae may be 

 seen on the same surface, crossing each other at a small angle ; 

 but in such instances, all the Hues belonging to each will be 

 parallel. The hard parts of the rock are ground down to the 

 same level with the soft, as if they had been rasped with a file of 

 steel ; and further, thousands of boulders may be seen thrown out 

 of new excavations, which are covered with similar scratches. 



It is generally believed that in each section of the country 

 the direction of the glacial striae is the same as that in which the 

 boulders of the neighborhood have proceeded. Dr. Bigsby, a 

 gentleman who travelled over a large portion of British No'^th 

 America some years ago, states, in a paper read before the Geolo- 

 gical Society of London in 1851, that boulders have been carried 

 from the Mountain of Montreal up the valley of the St. Lawrence. 

 " It is curious," he says, "to trace the well marked an gitic trap 

 of Montreal, stretching up the St. Lawrence, and occurring at 

 successive distances, until the last bit I observed was on the 

 Genesee River, on the south shore of Lake Ontario, 270 miles to 

 the south-west. The boulders of this rock are, however, in far 

 greater quantity on the southern levels between Montreal and 

 Lake Champlain."* 



On the map which accompanies Dr. Bigsby's paper, he has laid 

 down a line extendmg from the rear of the Island of Montreal, 

 across the Isle Perrot, through the northern part of the State of 

 New York, the Thousand Islands, and Lake Ontario, to Rochester, 

 as the direction in which the boulders have travelled. We are 

 not aware that this line was drawn with reference to any glacial 

 strige observed by him ; but very recently, in the cutting of the 

 Grand Trunk Railway on the Isle Perrot, we had an opportunity 

 of observing the strige where the Potsdam sandstone has been 

 laid bare. Their course is there about north-east and south- 

 west, which corresponds very nearly with the line on the map' 

 Another proof that the course of the drift was up the St. Law- 

 rence, may be seen, we think, at the north-west corner of the 

 Mountain of Montreal, at Cote St. Antoine, where a long ridge of 

 drift runs south-west, pointing in the direction of Lachine and 

 Caughnawaga. This line would be about parallel with the other, 

 but several miles further south. It is found that where a moun- 

 tain of rock like that at Montreal stands alone in the midst of a 



*Bigsby on Canadian Erratics — Quarterly Journal of the Geologieal 

 Society, vol. 8, page 234. 



