and on the Modern Deposits of its Valley. 461 



weight." As they appear also above the surface in the shallow parts 

 of the river, Mr. Logan is of opinion that the bed of it likewise teems 

 with them. Their position has been frequently observed to be 

 changed, both in the St. Lawrence and on its banks, at the breaking 

 up of the ice in the spring. Mr. Logan examined, in the autumn of 

 1841, the boulders between Montreal and Lachine, a distance of nine 

 miles, and again in the spring of the present year (1842), when he 

 missed some which had particularly attracted his attention ; but he 

 adds, he may, from not having mapped their position, have inad- 

 vertently passed them over. The author then offers some remarks 

 on the power of ice in moving or traasporting boulders along the 

 river, and furrowing the surface of the fixed rocks, as well as along 

 the shores j but he is of opinion that the distance is limited to which 

 they may in the latter position be conveyed annually. 



It is not only on the immediate banks of the St. Lawrence that 

 boulders abound, as they are spread more or less over the whole island 

 of Montreal, and the plains on the opposite side of the river. Mr. 

 Logan states that he had not examined their position with sufficient 

 accuracy to offer an opinion respecting the causes of their distribu- 

 tion, but they appeared to him to be more abundant in the upper than 

 the lower part of the island, and they are stated to cease altogether 

 not many miles below it ; but their size is not less at the limit of 

 their range than elsewhere. 



2. Landslip. — The country for a considerable distance on both 

 sides of the St. Lawrence, between Montreal and Quebec, is very 

 level, and is generally covered to some depth by a highly levigated 

 deposit composed of clay, sand, and calcareous matter resting on 

 black shale and black and grey limestone belonging to the Silurian 

 system. This flat region or trough is bounded on the north-west by 

 granitic and syenitic hills about 500 feet in altitude ; and on the 

 south-east by an undulating picturesque tract, composed of a hard 

 quartzose conglomerate, which crops out from beneath the limestone, 

 and is succeeded by pyritiferous clay-slate. The cleavage of this 

 formation is stated to be from N.E. toS.W., or parallel to the general 

 strike of the beds. 



Between Montreal and Lake St. Peter, the banks of the St. Law- 

 rence have generally a height of twenty or thirty feet above the level 

 of the water, but the plains near the margin of the river are occa- 

 sionally so low as to permit the formation of marshes, and on the 

 southern side the general surface does not apparently attain the same 

 altitude as on the north-western. On this side, at a distance varying 

 from one to six miles from the St. Lawrence, there is a sudden rise 

 of 1 00 feet, forming the boundary of a terrace which extends to the 

 granitic hills, where a second rise takes place of 200 or 300 feet. 

 The terrace, composed of soft materials, has a very even surface over 

 a great area, being only modified by the protrusion, at a few places, 

 of the Silurian limestone. It is however intersected by the rivers 

 which flow from the granitic range, and which, dashing down from the 

 hills, cut at once into the terrace, nearly to the level of the St. Law- 

 rence. The banks of these tributaries are liable to landslips, and an 



