THE TERTIARY TO THE MODERN PERIOD. 



233 



glacialis, the most exclusively arctic shell of these de- 

 posits. In other words, I regard the plants above men- 

 tioned as probably belonging to the period of greatest re- 

 frigeration of which we have any evidence, of course not 

 including that mythical period of universal incasement in 

 ice, of which, as I have elsewhere endeavoured to show, 

 in so far as Canada is concerned, there is no evidence 

 whatever.* 



The facts above stated in reference to Post-pliocene 

 plants concur, with all the other evidence I have been 

 able to obtain, in the conclusion that the refrigeration of 

 Canada in the Post-pliocene period consisted of a diminu- 

 tion of the summer heat, and was of no greater amount 

 than that fairly attributable to the great depression of the 

 land and the different distribution of the ice-bearing 

 arctic current. 



In connection with the plants above noticed, it is in- 

 teresting to observe that at Green's Creek, at Pakenham 

 Mills, at Montreal, and at Clarenceville on Lake Cham- 

 plain, species of Canadian Puhnonata have been found in 

 deposits of the same age with those containing the plants. 

 The species which have been noticed belong to the genera 

 Lymnea and Planorhis. 



The Glacial age was, fortunately, not of very long du- 

 ration, though its length has been much exaggerated by 

 certain schools of geologists, f It passed away, and a re- 

 turning cosmic spring gladdened the earth, and was ush- 

 ered in by a time of great rainfall and consequent denu- 

 dation and deposit, which has been styled the '* Pluvial 

 Period." The remains of the Pliocene forests then re- 

 turned — with somewhat diminished numbers of species — 



* Notes on Post-Pliocene of Canada, " Canadian Naturalist," 1872. 



f This I have long maintained on grounds connected with Pleistocene 

 fossils, amount of denudation and deposit, &c., and I am glad to see that 

 Prestwich, the best English authority on such subjects, has recently an- 

 nounced similar conclusions, based on independent reasons. 



