414 THE CANADIAN NATURALIST. [Vol. 



VI. 



ice, and that in these hills there might be glaciers of greater or 

 less extent. Further it should be understood that I regard the 

 boulder clays of the St. Lawrence valley as of different ages, 

 ranging from the early post-pliocene to that at present forming 

 in the gulf of St. Lawrence. Further, that this boulder clay 

 shows in every place where I have been able to examine it, 

 evidence of sub-aquatic accumulation, in the presence of marine 

 shells or in the unweathered state of the rocks and minerals en- 

 closed in it, conditions which, in my view, preclude any reference 

 of it to glacier action, except possibly in some cases to that of 

 glaciers stretching from the land over the margin of the sea, and 

 forming under water a deposit equivalent in character to the 

 ' boue glaciare' of the bottom of the Swiss glaciers. But such a 

 deposit must have been local, and would not be easily distin- 

 guishable from the marine boulder clay. I have not had oppor- 

 tunities to study the boulder clay of Scotland, which in character 

 and relations so closely resembles that of Canada, but I confess 

 several of the facts stated by Scottish Geologists lead me to infer 

 that much of what they regard as of sub-aerial origin must really 

 be marine, though whether deposited by ice-bergs or by the 

 fronts of glaciers terminating in the sea, I do not pretend to 

 determine. It must however be observed that the antecedent 

 probability of a glaciated condition is much greater in the case of 

 Scotland than in that of Canada, from the high northern latitude 

 of the former, its more hilly character, and the circumstance that 

 its present exemption from glaciers is due to what may be termed 

 exceptional and accidental geographical conditions; more espe- 

 cially to the distribution of the waters of the Gulf stream, which 

 might be changed by a comparatively small subsidence in Central 

 America. To assume the former existence of irlaciers in a 

 country in north latitude 66°, and with its highest hills, under 

 the present exceptionally favourable conditions, snow-capped dur- 

 ing most of the year, is a very different thing from assuming a 

 covering of continental ice over wide plains more than ten degrees 

 farther south, and in which, even under very unfavourable geo- 

 graphical accidents, no snow can endure the summer sun, even in 

 mountains several thousand feet high. Were the plains of North 

 America submerged and invaded by the cold Arctic currents, the 

 Gulf stream being at the same time turned into the Pacific, the 

 temperature of the remaining North American land would be 

 greatly diminished ; but under these circumstances the climate 



