No. 3.] MEMOIR ON GLACIERS. 183 



16. Astronomical changes do not affect this result. With a 

 great eccentricity of the orbit and the winter in aphelion the 

 colder winters and hotter summers would produce more power- 

 ful monsoons, while on the opposite condition the interior of the 

 continents would have warmer winters and cooler summers and 

 weaker monsoons. In either case the conditions for continental 

 glaciers would not be improved. 



17. These considerations show that general coverings of ice 

 stretching from the Pole to perhaps 45^ are impossible. Under 

 conditions of submergence of the plains the sea must keep open, 

 in order to afford material for snow on the remaining high 

 lands, and with large continental plains the climate will be too 

 dry for glaciers. Thus there must always be seas free from ice, 

 or continental plains free of ice, and under most supposable 

 conditions there must be both. 



Applying these very simple geographical truths to the North 

 American continent, it is easy to perceive that no amount of 

 refrigeration could produce a Continental glacier, because there 

 could not be sufl&cient evaporation 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, therefore, the con- 

 ditions most favourable to precipitation of snow. If Greenland 

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

 would be quite different ; as Nares has well shown in the case of 

 Grinnel land, which in the immediate vicinity of Greenland pre- 

 sents 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 con- 

 ceivable that the mountainous reiiions remaininij out of water 

 should 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, there could never have been a suffi- 

 ciency of snow to cause any general glaciation of the interior. 

 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 further to the north. 



The writer of this note has always maintained these conclu- 

 sions on general geographical grounds, as well ;is on the evidence 



