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 b}^ 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. Vol. 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 



