198 THE ICE AGE IN CANADA. 



The Montreal mountain, like other isolated trappean 

 hills in the great plain of the lower St. Lawrence, presents 

 a steep, craggy front to the north-east, and a long slope or 

 tail to the south-west ; and in front of its north-east side 

 is a bare, rocky plateau of great extent, and at a height of 

 about 200 feet above the river. This plateau must have 

 been produced by marine denudation of the solid mass of 

 the mountain in the Pleistocene period, and proves an 

 astonishing amount of this kind of erosive action in hard 

 limestones interleaved with trap dykes, and which have 

 been ground and polished with ice at the same time that 

 the plateau was cut into the hill. By ice, also, must the 

 dShris produced by this enormous erosion have been 

 removed, and piled along the more sheltered sides of the 

 hill in the boulder-clay. 



With regard to the crag-and-tail attitude of Montreal 

 mountain, I have to observe that in large masses of this 

 kind reaching to a considerable height, and rising above 

 the Pleistocene sea, the north-east, or exposed, side has 

 been cut into steep cliffs, but in smaller projections of the 

 surface over which the ice could grind, the exposed side is 

 smoothed, or "moutonnee," and the sheltered side is 

 angular. A little reflection must show that this must 

 be the necessary action of a sea burdened with heavy 

 floating ice. 



These facts have been well illustrated in the extensive 

 limestone quarries lying on the plateau already referred 

 to behind the city of Montreal, and north-east of the 

 Montreal mountain. At this place the surface of the 

 limestone has been polished and striated, the direction of 

 the striae ranging from K 50° E. to K 70° E. Not only 

 has the surface been intensely glaciated, but ledges of 

 rock of great size have been lifted up and pushed to the S.W. 



