80 THE POST-PLIOCENE PERIOD. 



American and European climates so characteristic of the time. The 

 climate of western Europe, in short, would, under such a state of 

 things, be greatly reduced in mean temperature : the climate of 

 America would suffer a smaller reduction of its mean temperature, 

 but would be much less extreme than at present ; the general effect 

 being the establishment of a more equable but lower temperature 

 throughout the northern hemisphere. It is perhaps necessary to add, 

 that the existence on the land, during this period of depression, of 

 large elephantine mammals in northern latitudes, as, for instance, the 

 mammoth and mastodon, does not contradict this conclusion. W e 

 know that these creatures were clothed in a manner to fit them for a 

 cool climate, and an equable rather than a high temperature was 

 probably most conducive to their welfare, while the more extreme 

 climate consequent on the present elevation and distribution of the 

 land may have led to their extinction. 



The establishment of the present distribution of land and water, 

 giving to America its extreme climate, leaving its seas cool, and 

 throwing on the coasts of Europe the heated water of the tropics, 

 would thus affect but slightly the marine life of the American coast, 

 but very materially that of Europe, producing the result already 

 referred to in the above pages, that the Canadian Post-pliocene 

 fauna differs comparatively little from that now existing in the 

 Gulf of St Lawrence ; though in so far as any difference subsists, it 

 is in the direction of an Arctic character. The changes that have 

 occurred were perhaps all the less that so soon as the Laurentide Hills 

 to the north of the St Lawrence valley emerged from the sea, the 

 coasts to the south of these hills would be effectually protected from 

 the heavy northern ice-drifts and from the Arctic currents, and would 

 have the benefit of the full action of the summer 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 difference between the Modem and 

 Post-pliocene faunas must be greatest in those localities to which 

 the forms of temperate regions could most readily migrate after the 

 change of temperature had occurred. 



It has been fully shown by many previous writers on this subject, 

 that the causes above referred to are sufficient to account for all the 

 local and minor phenomena of the stratified and unstratified drifts, 

 and for the driftage of boulders and other materials, and the erosion 

 that accompanied its deposition. Into these subjects I do not propose 

 to enter; my object in these remarks being merely to give the reasons 



