404 Newer Pliocene and Post Pliocene Deposits 



In this bottom we have in Craig Street, and toward the Tanneries, 

 river gravel, occasionally with fresh-water shells. In some places 

 the river has probably cut through the boulder clay quite to the 

 underlying rock, but in other places this is not the case. In the 

 bottom of one of the most advanced coffer-dams of the Victoria 

 Bridge, I observed a great depth of the original boulder clay, 

 on which the river had made no impression. The mud brought 

 Tip by the dredging machines from the current immediately below 

 Montreal, and from some parts of Lake St. Peter, is evidently the 

 undisturbed marine clay. In the former place I found in it one 

 of its characteristic fossil shells, Tellina groenlandica. 



All the beds above referred to belong to the close of the ter- 

 tiary period, and they are all marine ; but they may have been 

 deposited at distant intervals of time, and in waters of very va- 

 rious depth and area. The climates and other physical conditions 

 appertaining to the times of their deposition, may have been dif- 

 ferent from each other and from that which now prevails. On 

 these subjects the best evidence that we can obtain is that of 

 fossil remains. We may therefore proceed to consider these, as 

 they exist in different localities and at different levels; and first 

 with reference to the lower level referred to, that of the plain or 

 terrace at the height of 100 to 120 feet above the river. 



At and near the Tanneries, shells are found in superficial sand, 

 and also in tenacious gray and reddish clay underlying it. In the 

 former and at the surface of the latter, the prevailing shell is 

 Saxicava rugosa, along with which Sir C. Lyell mentions My- 

 tilus edulis, which I have not yet seen at this place. These may 

 be regarded as in this latitude littoral or shallow water shells. 

 In the clay the only abundant shell is Nucula (Leda) Portlandica. 

 This, judging from the habits of its modern congeners, must be a 

 deep sea shell, inhabiting quiet muddy bottoms at from 10 to 50 

 fathoms in depth, or perhaps still lower.* 



At this place then there appears to have been a shallow water 

 or littoral deposit, superimposed on one that must have ben de- 

 posited in deeper water. Under both is the boulder clay. 



In the grounds of McGill College, the excavations for the main 

 pipe of the water work, have exposed an interesting section of 



* Living specimens of Nucula tenuis and Yoldia lucida have been 

 dredged from a depth of 200 fathoms on the coast of Norway by M'Andrew 

 & Barrett. 



