SOME LOCAL DETAILS. 201 



terraces. The highest terrace holds littoral marine shells, 

 which also occur on a little plateau at a height of 560 

 feet. On the highest of these, on the west side of the 

 mountain, over Cote des Neiges village, there is a beach 

 with marine shells, and on the summit of the mountain, 

 at a height of about 750 feet, there are rounded surfaces, 

 possibly polished by floating ice at the time of greatest 

 depression, though no striation remains, and large Lauren- 

 tian boulders, which must have been carried probably a 

 hundred miles from the Laurentian regions to the N.E., 

 and over the deep intervening valley of the St. Lawrence.* 



I have already, in the earlier part of this section, noticed 

 the striation on rock surfaces at Montreal, and may merely 

 add that it is often very perfect, and must have been pro- 

 duced by a force acting up the St. Lawrence valley from 

 the north-east, and planing all the spurs of the mountain 

 on that side, while leaving the mountain itself as a bare 

 and rugged unglaciated escarpment. In the streets of 

 Montreal the true boulder-clay is often exposed in excava- 

 tions, and is seen to contain great numbers of glaciated 

 stones, most of which are of the hardened Lower Silurian 

 shales and limestones of the base of the mountain ; and, 

 though no marine shells have been found, the sub-aquatic 

 origin of the mass is evidenced by its gray unoxidised 

 character, and by the fact that many of the striated stones 

 at once fall to pieces when exposed to the frost, so that 

 they cannot possibly have been glaciated by a sub-aerial 

 glacier. 



At the Glen brick- work, near Montreal, the Leda clay 

 and underlying deposits have been excavated to a consid- 



* Lyell ("Travels in North America," vol. 2, p. 140) very well 

 describes the Pleistocene of the vicinity of Montreal. 



