20 THE POST-PLIOCENE. 



indicated by fossil shells, was much more severe than at present, com- 

 paratively little change has occurred in our American seas. I have 

 more fully illustrated this difference in my Notes on the Post-plio- 

 cene Geology of Canada, and have shown that it is to be explained 

 principally by the distribution of the marine currents. Crosskey and 

 others have recently directed attention to it in England, but it receives 

 less attention than it deserves, in consequence of the tendency to seek, 

 for causes of an extreme and general glaciation of the northern hemi- 

 sphere. It should, however, be regarded as of the utmost importance 

 as indicating the value of that different distribution of land and water 

 so much insisted on by S'w C. Lyell as a cause of change of climate, 

 and to which I still think, as in 18G8, that the cold of the glacial 

 period is mainly referable. 



In any case, I still fail to find, either in the Acadian Provinces or 

 in Canada proper, any indication of a great continental glacier. What 

 I do find is the evidence of great depression of the land, accompanied 

 with a reduction of the mean temperature to such an extent that the 

 hills remaining above water were occupied Avith local glaciers, and 

 formed areas of denudation, while tho lower lands, traversed by 

 northern cuiTcnts of ice-cold water, bore floating ice throughout the 

 year, and this was steadily pushed by the lower currents from the 

 north-east ; while in periods of extreme submergence there was a drift, 

 perhaps caused by prevailing winds, from the north-west. In these 

 circumstances the boulder clay and the lower part of the Leda clay 

 were formed, and are consequently non-fossiliferous, or liold only a 

 few Arctic shells, lie-elevation brought shallowness, and consequently 

 warmer water, and eventually land surfaces, and introduced the 

 modern climate. 



Whatever the cause of this submergence, the fact of its occurrence 

 is proved by the marine clays and the high-level sea-beaches. Mr 

 Richardson of the Geological Survey has found these terraces 1225 

 feet above the sea on the coast of Newfoundland, and the evidence of 

 travelled stones would take the sea to the tops of the highest hills in 

 Eastern America, GUOO feet above the sea. The drift phenomena of 

 the western plains and the Rocky Mountains imply subsidence there to 

 the extent of at least 4400 ft.* Now, the existing climates of the North 

 Atlantic, as compared with those of the Post-pliocene, point precisely 

 to the natural effects of such a submergence, while the action of local 

 glaciers, of pack and pan ice, and of drifting bergs, as now actually 

 observed, would, if intensified, as they must have been by the causes 

 supposed, give all the observed effects of glaciation. There is there- 

 * (.!. .M. Dawson, Report on 49th Parallel. 



