APPENDIX. 405 



least 10° Fahr. than that of Northern Asia, where the amount of 

 snowfall is very slight, and rapidly disappears during the short 

 arctic summer. If there be, as some persons believe, a large 

 tract of continental land surrounding the south pole, I should 

 expect to find that the great accumulations of snow and ice are 

 confined to the coast regions. In that case the mean tempera- 

 ture of the region within the antarctic circle would probably be 

 lower than it would be in the supposition, which appears to me 

 more probable, that the lands hitherto seen belong to scattered 

 mountainous islands. If, from any combination of causes, one 

 pole of the earth has ever been brought to a mean temperature 

 much lower than that now experienced, I should expect to find 

 that the phenomena of glaciation would be exhibited towards 

 the equatorial limit of the cold zone, rather than in the portions 

 near the pole. The formation of land-ice depends on the 

 condensation of vapour, and before air-currents could reach the 

 centre of an area of extreme cold the contained vapour would 

 have been condensed. This consideration alone suffices, to my 

 mind, to make the supposition of a polar ice-cap in the highest 

 degree improbable. 



Mr. Wallace (" Island Life," p. 142) cites, as conclusive evidence 

 of the effect of winter in aphelion in producing glaciation, the 

 facts, to which attention was first directed by Darwin, as to the 

 depression of the line of perjjetual snow, and the consequent 

 extension of great glaciers, on the west coast of Southern Chili. 

 I have adverted to this subject in the text (p. 229), and I may 

 further remark that if winter in aphelion be the cause of the 

 depression of the snow-line in latitude 41° S., it can scarcely 

 fail to produce some similar effect in latitude 34° S. Yet we 

 find on the southern limit the snow-line much lower, and at the 

 northern much higher, than it has ever been observed in 

 corresponding latitudes in the northern hemisphere, the line 

 being depressed by more than 8000 feet within a distance of 

 only seven degrees of latitude. The explanation, as I have 

 ventured to maintain, is altogether to be found in the extra- 

 ordinary rainfall of Southern Chili ; and to the same cause we 

 must attribute the fact that, in spite of the greater distance of 

 the sun, the winter temperature is higher than in most places in 

 corresponding latitudes in the northern hemisphere. At Ancud 

 in Chiloe, in latitude 41° 46', the temperature of the coldest 



