CHAP. VTTi THE CAUSES OF GLACIAL EPOCHS 135 



SO little snow falls that it is quickly melted by the return- 

 ing sun, there is nothing to prevent the summer being hot 

 and the earth producing a luxuriant vegetation. As an 

 example of this we have great forests in the extreme north 

 of Asia and America where the winters are colder and the 

 summers shorter than in Greenland in Lat. G2° N., or than 

 in Heard Island and South Georgia, both in Lat. SS"" S. in 

 the Southern Ocean, and almost wholly covered with per- 

 petual snow and ice. At the " Jardin '' on the Mount 

 Blanc range, above the line of perpetual snow, a thermo- 

 meter in an exposed situation marked - 6° F. as the lowest 

 winter temperature : while in many parts of Siberia mer- 

 cury freezes during several weeks in winter, showing a 

 temperature below — 40° F. ; yet here the summers are 

 hot, all the snuw disappears, and there is a luxuriant 

 vegetation. Even in the very highest latitudes reached 

 by our last Arctic Expedition there is very little perpetual 

 snow or ice, for Captain Nares tells us that north of Haye's 

 Sound, in Lat. 79° N., the mountains were remarkably free 

 from ice-cap, while extensive tracts of land were free 

 from snow during summer, and covered with a rich vege- 

 tation with abundance of bright flowers. The reason of 

 this is evidently the scanty snow-fall, which rendered it 

 sometimes difficult to obtain enough to form shelter-banks 

 around the ships ; and this was north of 80° N. Lat., where 

 the sun was absent for 142 days. 



Perpetual Snow Nowhere Exists on Loiuland Areas. — It is 

 a very remarkable and most suggestive fact, that nowhere 

 in the world at the present time are there any extensive 

 lowlands covered with perpetual snow. The Tundras of 

 Siberia and the barren grounds of N. America are all 

 clothed with some kind of summer vegetation ; ^ and it is 



errors within the whole range of geological climatology." The temperature 

 of the snow itself is, he says, one of the main factors. {Climate and 

 Cosmology y p. 85.) But surely the temperature of the snow must depend 

 on the temperature of the air through which it falls. 



^ In an account of Prof. Nordenskj old's recent expedition round the 

 northern coast of Asia, given in Nature, November 20th, 1879, we have 

 the following passage, fully supporting the statement in the text. *' Along 

 the whole coast, from the White Sea to Behring's Straits, no glacier was 

 seen. During autumn the Siberian coast is nearly free of ice and snow. 

 Theiie are no mountains covered all the year round with snow, although 



