Dr. J. Croll—On the Cause of the Glacial Epoch. 67 
more than fifty times the amount of heat required to melt all the 
snow and ice formed on it, and yet that country is buried under ice. 
The annual precipitation on Greenland in the form of snow and rain, 
according to Dr. Rink, amounts to only 12 inches, and two inches of 
this he considers is never melted, but is carried away in the form of 
icebergs. The quantity of heat received at the equator from sun-rise 
to sunset, if none were cut off by the atmosphere, would melt 3} 
inches of ice, or 100 feet 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 50 feet of ice per annum, or 50 times the 
amount of snow which falls on that continent. What then cuts off 
the 98 per cent. of the sun’s heat? Is it clouds and fog? If so, 
why do not these, according to Mr. Hill’s theory, supply sufficient 
‘heat to melt the small quantity of snow which falls on Greenland ? 
And if the heat is not cut off, and far more than sufficient to melt the 
ice reaches the ground, why is not the ice melted ? 
Take another example. South Georgia in the latitude of England 
is covered with snow and ice down almost to the sea-shore during 
the whole summer, and yet the amount of heat which that island 
receives is sufficient to melt 62 feet of ice. Why then are not the 
snow and ice melted? Suppose the snowfall there were ten times 
greater than that of Greenland, which it evidently is not, yet this 
would not amount to one-sixth part of what the sun’s heat could 
melt. What then cuts off the 80 per cent. of the sun’s heat? It 
cannot, according to Mr. Hill, be either clouds or fogs, and if the 
heat is not cut off, the question returns, why are not the snow and 
ice melted? There is still another thing to be explained. The snow 
falls in that region in the very middle of summer, but snow would 
not fall unless the temperature was near the freezing-point. Why 
then have we such a low midsummer temperature, notwithstanding 
the fact that the sun is in perihelion at that season ? 
There is another class of facts utterly at variance with Mr. Hill’s 
fundamental proposition. The lofty peaks of the Himalayas, the 
Andes, and other mountain ranges are covered with perpetual snow. 
There comparatively few of the sun’s rays are cut off, and yet the 
snow is perennial. Few, I suppose, would admit that at these great 
elevations more than 50 per cent. of the sun’s heat could be cut off. 
But if 50 per cent. reached the snow, this would be sufficient to melt 
50 feet of ice, and this no doubt is more than ten times the quantity 
which actually requires to be melted. Why then does not the heat 
melt the snow ? 
T have little doubt that if Mr. Hill will ponder over the subject, 
so as to find out a satisfactory answer to the foregoing queries, be 
will satisfy himself that the causes to which I attribute the Glacial 
Epoch are not so impotent as he has been led to suppose. 
