ADDRESS. 27 



Glacial period which is beat known to us, and is more immediately con- 

 nected with the early history of man and the modern animals, it may bo 

 proper to make a few general statements bearing on the relative import- 

 ance of sea-borne and land ice in producing those remarkable phenomena 

 attributable to ice action in this period. In considering this question it 

 must be borne in mind that the greater masses of floating ice are pro- 

 duced at the seaward extremities of land glaciers, and that the heavy 

 field-ice of the Arctic regions is not so much a result of the direct freez- 

 ing of the surface of the sea as of the accumulation of snow precipitated 

 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 this 

 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 ^olid 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 Jess 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 i^ easy to perceii^e that no amount of refrigeration could 

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

 poration and precipitation to aflbrd 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- 

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

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

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

 North Greenland, presents very difierent conditions as to glaciation and 

 climate.* If the plains wei^e 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 



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

 already referred it and in previous geographical papers. 



