Of the Vicinity of Montreal. 413 



been considering, had previously to the beginning of the Post 

 Pliocene period sunk below the waves. Its subsidence must have 

 been very slow, to give time for the accumulation of so thick a 

 bed of travelled stones and clay; and that its re- elevation was 

 also slow is evidenced by the cliffs cut by the waves, the beds of 

 clay and sand deposited, and the multitudes of shellfish which 

 lived and died during the process. 



These stupendous changes of level, however slow, must have 

 caused great vicissitudes of climate, and must seriously have af- 

 fected animal and vegetable life, both on the land and in the sea. 

 If, as seems probable, before the great boulder period subsidence, 

 the land had attained its present extent and elevation, the climate 

 might have resembled that which now prevails. As the land 

 sunk, its climate would become less extreme, but of lower mean 

 temperature, and the opening up of easier access to the arctic 

 currents might greatly reduce the temperature of the sea. This 

 would be especially the case, if, as seems probable, tbe loss of land 

 was greater in the south, and extensive tracts remained above 

 water in the north, producing quantities of drift ice. 



The fossils correspond with such views. All the species, so far as 

 determined, except one or two, are still living, and most of them 

 in this latitude, though there is a prevalence of the more northern 

 forms, and an absence of many species now extending as far north 

 on the American coast. - This conclusion was announced by Sir 

 C. Lyell as far back as 1839, and it is confirmed by the species 

 since found, which are stated by Dr. Gould of Boston, to form on 

 the whole, a sub-arctic assemblage. Sir C Lyell says, (Geol. 

 Trans., 1839) "It is very probable that in the period immediately 

 antecedent to the present, the climate of Canada was even more 

 excessive than it is now, and that the shells resembled still more 

 closely that small assemblage now found in high northern lati- 

 tudes." Dr. Gould, in a letter to the author, says in reference to 

 tbe group of additional species lately discovered : " Its character is 

 sub-arctic, like that of Behring's Straits, Kamtschatka and Green- 

 land." This character of the fauna corresponds with the indi- 

 cations of ice afforded by the presence of boulders, with the low 

 mean temperature likely to result from a great depression of the 

 land, and with the southward extension of the Arctic Ocean, and 

 the great facilities thus afforded for the migrations of Arctic species 

 both in longitude and latitude. On the other hand the resem- 

 blance of this fossil fauna to that of the American seas in modern 



