SOME LOCAL DETAILS. 201 



teiTiiees. The liiuliest terrace holds littoral marine shells, 

 whicli also oecnr on a little plateau at a hei<i;ht of 5G0 

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

 mountain, over Cote des Xei,t>es village, there is a be.ich 

 with marine shells, and on tiie summit of tht; mountain, 

 at a height of al)0ut T^O feet, there are rounded surfaces, 

 possiljly poHshed liy floating ice at the time of greatest 

 depression, though no strialion remains, and large Lauren- 

 tian lioulders, which nnist ha\'e l)een carried probably a 

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

 and over the deep intervening valley of tiie 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 iiave been pro- 

 duced l)y 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 escari»ment. In the streets of 

 Montreal the true l)oulder-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 l»een fouiul, the sub-acpiatic 

 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 i)ieces when exposed to the frost, so that 

 riiey cannot possibly have been glaciated by a sub-aerial 

 glacier. 



At the (Jlen brick-work, near Montreal, the Leda clay 

 and underlying deposits have been excavated to a cousid- 



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

 describes the Pleistocene of the vicinity of Montreal. -^ 



