THE GREAT ICE AGE 365 



exemption from glaciers is due to what may be termed excep- 

 tional and accidental geographical conditions ; more especially 

 to the distribution of the waters of the Gulf Stream, which 

 might be changed by a comparatively small subsidence in Cen- 

 tral America. To assume the former existence of glaciers in a 

 country in north latitude 56, and with its highest hills, under 

 the present exceptionally favourable conditions, snow-capped 

 during 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 unfavour- 

 able geographical 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 of Scotland would necessarily be 

 reduced to the same condition with that of South Greenland 

 or Northern Labrador. As we know such a submergence of 

 America to have occurred in the Pleistocene period, it does not 

 seem necessary to have recourse to any other cause for either 

 side of the Atlantic. It would, however, be a very interesting 

 point to determine, whether in the Pleistocene period the 

 greatest submergence of America coincided with the greatest 

 submergence of Europe, or otherwise. It is quite possible 

 that more accurate information on this point might remove 

 some present difficulties. I think it much to be desired that 

 the many able observers now engaged on the Pleistocene of 

 Europe, would at least keep before their minds the probable 

 effects of the geographical conditions above referred to, and 

 inquire whether a due consideration of these would not allow 

 them to dispense altogether with the somewhat extravagant 

 theories of glaciation now agitated. 



The preceding pages give the substance of my conclusions 



