ADDRESS. 29 



on the frozen surface. In reasoning on the extent of ice action, and 

 especially of glaciers in the Pleistocene age, it is necessary to keep thia 

 fully in view. Now in the formation of glaciers at present — and it 

 would seem also in any conceivable former state of the earth — it is neces- 

 sary that extensive evaporation should conspire with great condensation 

 of water in the solid form. Such conditions exist in mountainous 

 regions sufficiently near to the sea, as in Greenland, Norway, the Alps, and 

 the Himalayas ; but they do not exist in low arctic lands like Siberia or 

 Grinnel-land nor in inland mountains. It follows that land glaciation 

 has narrow limits, and that we cannot assume the possibility of great 

 confluent or continental glaciers covering the interior of wide tracts of 

 land. No imaginable increase of cold could render this possible, inas- 

 much as there could not be a sufficient influx of vapour to produce the 

 necessary condensation ; and the greater the cold, the less would be the 

 evaporation. On the other hand, any increase of heat would be felt 

 more rapidly in the thawing and evaporation of land ice and snow than 

 on the surface of the sea. 



Applying these very simple geographical truths to the North Atlantic 

 continents, it is easy to perceive that no amount of refrigeration could 

 produce a continental glacier, because there could not be sufficient eva- 

 poration and precipitation to afford the necessary snow in the interior. 

 The case of Greenland is often referred to, but this is the case of a high 

 mass of cold land with sea, mostly open, on both sides of it, giving, there- 

 fore, the conditions most favourable to precipitation of snow. If Green- 

 laud were less elevated, or if there were dry plains around it, the case 

 would be quite different, as Nares has well shown by his observations on 

 the summer verdure of Grinnel-land, which, in the immediate vicinity of 

 North Greenland, presents very different conditions as to glaciation and 

 climate.' If the plains were submerged, and the Arctic currents allowed 

 free access to the interior of the continent of America, it is conceivable 

 that the mountainous regions remaining out of water would be covered with 

 snow and ice, and there is the best evidence that this actually occurred 

 in the Glacial period ; but with the plains out of water this would be im- 

 possible.* We see evidence of this at the present day in the fact that in 

 unusually cold winters the great precipitation of snow takes place south of 

 Canada, leaving the north comparatively bare, while as the temperature 

 becomes milder the area of snow-deposit moves farther to the north. 

 Thus a greater extension of the Atlantic, and especially of its cold ice- 

 laden arctic currents, becomes the most potent cause of a glacial age. 



I have long maintained these conclusions on general geographical 

 grounds, as well as on the evidence afforded by the Pleistocene deposits of 

 Canada; and in an address the theme of which is the ocean I may be excused 

 for continuing to regard the supposed terminal moraines of great continental 



' These views have been admirably illustrated by Von Wceickoff in the paper 

 already referred to and in previous geographical papers. 



