in Geological Climatology. 259 
case undoubtedly descend to a lower level on the dry than 
on the moist side. Melting would certainly take place at a 
greater elevation on the moist than on the dry side ; and this 
is what would mainly determine the position of the snow-line. 
The annual precipitation on Greenland, as we have seen, is 
very small, scarcely one half that of the driest parts of 
Great Britain. This region is covered with snow and ice, 
not because the quantity of snow falling on it is great, but 
because the quantity melted is small ; and the reason why the 
snow does not melt is not that the amount of heat received 
during the year is unequal to the work of melting the ice, 
but that, mainly through the dryness of the air, the snow is 
prevented from rising to the melting-point. The very cause 
which prevents a heavy snowfall protects the little which does 
fall from disappearing. The same remarks apply to the Ant- 
arctic regions. 
In South Georgia and Fuego, where clouds and dense fogs 
prevail during nearly the whole year, the permanent snow 
and ice are due to a different cause. Here the snowfall is 
great, and the amount of heat cut off enormous; but this 
alone would not account for the non-disappearance of the 
snow and ice; for, notwithstanding this, the heat received 
is certainly more than sufficient to melt all the snow which 
falls, great as that amount may be. The real cause is that 
the heat received is not sufficiently intense to raise the tem- 
perature to the melting-point. More heat is actually received 
by the snow than is required to melt it ; but it is dissipated 
and lost before it can manage to raise the temperature of the 
snow to the melting-point; consequently the snow is not 
melted. Here snow falls in the very middle of summer; 
but snow would not fall unless the temperature were near the 
freezing-point. 
Foregoing principles applied to the case of the Glacial 
Epoch. — Let us now apply the foregoing principles to the 
case of the glacial epoch. As winter then occurred in 
aphelion during a high state of eccentricity, that season 
would be much longer and colder than at present. Snow in 
temperate regions would then fall in place of rain ; and 
although the snowfall during the winter might not be great, 
yet, as the temperature would be far below the freezing-point, 
what fell would not melt. As heat, which produces evapora- 
tion, is just as essential to the accumulation of snow and ice 
as is cold, which produces condensation, after the sun had 
passed the vernal equinox and summer was approaching, the 
consequent rise of temperature would be accompanied by an 
increase in the snowfall. A melting of the snow would also 
U2 b 
