12 THE ICE AGE IN CANADA. 



heat, advantages which must have existed to a less extent 

 in western Europe.* 



" It is farther to be observed that such subsidence and 

 elevation would necessarily afford great facilities for the 

 migration of arctic marine animals, and that the differ- 

 ence between modern and pleistocene faunas must be 

 greatest in those localities to which the animals of 

 temperate regions could most readily migrate after the 

 change of temperature had occurred." 



In an address delivered in 1864 f as retiring president 

 of the Natural History Society of Montreal, the relative 

 importance of land-ice and sea-borne ice is referred to in 

 the following terms, in connection with the then recent 

 appearance of Logan's " General Eeport on the Geology of 

 Canada," published in 1863 : — 



" There is another subject of great geological importance 

 on which the publication of this report enables strong 

 ground to be taken. I refer to the conditions under 

 which the hoidder-drift of Canada was deposited. It 

 has been customary to refer this to the action of ice-laden 

 seas and currents, on a continent first subsiding^ and then 

 re-elevated. But this opinion has recently been giving 

 way before a re-assertion of the doctrine that land- 

 glaciers have been the principal agents in the distribution 

 of the boulder-drift, and in the erosions with which it was 

 accompanied. I confess that I have steadily rejected this 

 last doctrine ; being convinced that insuperable physical 



* One cannot be too emphatic in insisting on the fact that, in North 

 America, throughout geological time, movements of subsidence which 

 threw open the interior plains to the arctic currents produced refriger- 

 ation, while those that produced a great mediterranean sea, open to 

 the south and closed on the north, introduced mild climates. 



t Canadian Naturalist, 1864. 



