LOGAN ON THE PACKING OF ICE IN THE ST. LAWRENCE. 4-27 



projecting materials that present themselves to its grasp, the ice 

 must seize a multitude of the loose boulders below ; and not only- 

 will these be carried away, occasionally to very considerable di- 

 stances, when it breaks up in the spring, but firmly set in their gla- 

 cial matrix, they will, when in the course of the movements that 

 occur, such masses as hold them are forced over shallow places, act 

 as gravers to register in parallel grooves on the face of such rocks 

 as they encounter, a memento of their progress as they pass alonor. 



The boulders in the middle of the river may at once be occasion- 

 ally carried to considerable distances ; but it can scarcely be so with 

 such as are stationed at or near the borders. For though these may 

 become packed and imbedded in marginal ice, and by the force of 

 a general movement or shove, as it is termed by the inhabitants, be 

 driven obliquely up the bank, as soon as this ceases they will there 

 be left ; and as these general movements occur only three or four 

 times during a season, and are never of long continuance, and even 

 where the marginal ice is driven up the bank the friction it suffers 

 soon causes succeeding portions to pile over one another, it is evi- 

 dent the boulders would not be carried by it to any very great 

 distance. When a break-up occurs in the spring, it is the great body 

 of ice in the middle of the river that is carried away, which, separa- 

 ting from the grounded portion on the margin, leaves this to be melted 

 down by the increasing temperature of the season. The movements 

 of succeeding winters may push marginal boulders farther and far- 

 ther on, but they must at the same time have a tendency to carry all 

 within a certain range gradually nearer to the bank, and at last place 

 them in a position at the very limit of their influence. And it is 

 certainly the case, that in the neighbourhood of Montreal there are 

 in many places along the borders of the river collections of boulders 

 sufficiently great to induce the supposition that their presence may 

 be accounted for in this manner. 



It is not however only on the immediate banks of the St. Law- 

 rence that boulders abound. They are more or less spread over the 

 whole island of Montreal, and over the plains on the opposite side 

 of the river. I do not pretend to have ascertained their distribution 

 with the precision necessary to permit the expression of an opinion 

 as to the causes which placed them, but I may state that they ap- 

 peared to me more abundant in the upper part of the island than in 

 the lower, and that proceeding down the valley of the St. Lawrence 

 they ceased altogether not many miles below the island in question : 

 and it may be further remarked, that they did not seem of less 

 weight at the limit of their range than elsewhere. 



The country to a considerable distance on both banks of the St. 

 Lawrence, from Montreal to Lake St. Peter and even to Quebec, is 

 very level, and it is in general covered with a deep and highly levi- 

 gated deposit of argillaceous, arenaceous and calcareous matter, the 

 constituents of which vary in their proportions in different localities. 

 This deposit rests upon a shallow trough of black shale and black 

 and grey limestone, the fossils of which are palteozoic, and resemble 

 those figured as belonging to the Lower Silurian rocks of Britain. 



