CHAP. VIII THE CAUSES OF GLACIAL EPOCHS 147 



equator from sunrise to sunset, if none were cut off by the 

 atmosphere, would melt 3J inches of ice, or 100 feet in a 

 year. The quantity received between latitude 60° and 80°, 

 which is that of Greenland, is, according to Meech, one-half 

 that received at the equator. The heat received by 

 Greenland from the sun, if none were cut off by the 

 atmosphere, would therefore melt fifty feet of ice per 

 annum, or fifty times the amount of snow wdiich falls on 

 that continent. What then cuts off the ninety-eight per 

 cent, of the sun's heat ? " The only possible answer is, 

 that it is the clouds and fog during a great part of the 

 summer, and reflection from the surface of the snow and ice 

 when these are absent. 



South Temperate America as Illustrating the Influence of 

 Astronomical Causes on Climate. — Those persons who still 

 doubt the effect of winter in aphelion with a high degree 

 of excentricity in producing glaciation, should consider how 

 the condition of south temperate America at the present 

 day is explicable if they reject this agency. The line of 

 perpetual snow in the Southern Andes is so low as 6,000 

 feet in the same latitude as the Pyrenees ; in the latitude 

 of the Swiss Alps mountains only 6,200 feet high produce 

 immense glaciers which descend to the sea-level; while in 

 the latitude of Cumberland mountains only from 3,000 to 

 4,000 feet high have every valley filled with streams of ice 

 descending to the sea-coast and giving off abundance of 

 huge icebergs.^ Here w^e have exactly the condition of 

 things to which England and Western Europe were sub- 

 jected during the latter portion of the glacial epoch, wdien 

 every valley in Wales, Cumberland, and Scotland had its 

 glacier ; and to what can this state of things be imputed 

 if not to the fact that there is now a moderate amount of 

 excentricity, and the winter of the southern hemisphere is 

 in aphelion? The mere geographical position of the 

 southern extremity of America does not seem especially 

 favourable to the production of such a state of glaciation. 

 The land narrows from the tropics southvv^ards and termin- 

 ates altogether in about the latitude of Edinburgh ; the 



^ See Darwin's Naturalist's Voyage Hound the Vv^orld, 2nd Edition, pp. 

 244-251. 



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