144 
ISLAND LIFE. 
[part I. 
state of almost perpetual glaciation of much of the land would 
result, notwithstanding that the whole *earth should theoretically 
be at a somewhat higher temperature. Two main causes would 
bring about this glaciation. A very large area of elevated land 
in high latitudes would act as a powerful condenser of the 
enormous quantity of vapour produced by the whole of the 
equatorial and much of the temperate regions being areas of 
evaporation, and thus a greater accumulation of snow and ice 
would take place around both poles than would be possible 
under any other conditions. In the second place there would 
be little or no check to this accumulation of ice, because, owing 
to the quantity of land around the polar areas, warm oceanic 
currents could not reach them, while the warm winds would 
necessarily bring so much moisture that they would help on 
instead of checking the process of ice-accumulation. If we 
suppose the continents to be of the same total area and to have 
the same extent and altitude of mountain ranges as the present 
ones, these mountains must necessarily offer an almost continu- 
ous barrier to the vapour-bearing winds from the south, and the 
result would probably be that three-fourths of the land would 
be in the ice-clad condition of Greenland, while a comparatively 
narrow belt of the more southern lowlands would alone afford 
habitable surfaces or produce any woody vegetation. 
Notwithstanding, therefore, the criticism above referred to, 
I believe that Sir Charles Lyell was substantially right, and 
that the two ideal maps given in the Principles of Geology (11th 
ed. Yol. i. p. 270), if somewhat modified so as to allow a freer 
passage of currents in the tropics, do really exhibit a condition 
of the earth which, by geographical changes alone, would bring 
about a perpetual summer or an almost universal winter. But 
we have seen in our sixth chapter that there is the strongest 
cumulative evidence, almost amounting to demonstration, that 
for all known geological periods our continents and oceans have 
occupied the same general position they do now, and that no 
such radical changes in the distribution of sea and land as 
imagined by way of hypothesis by Sir Charles Lyell, have ever 
occurred. Such an hypothesis, however, is not without its 
use in our present inquiry, for if we obtain thereby a clear 
