RECENT ADVANCES IN GEOLOGY. 467 
it would if, as in the Drift Epoch, it were submerged to the 
depth of at least two thousand feet. In the Great Year of 
astronomers, the southern pole, after having passed through 
its great winter solstice, is now entering upon its summer 
climate. 
Lyell has conjectured that these phenomena are due to a 
different distribution of land and water, combined with a 
different distribution of oceanie currents; but with an ex- 
panse of land occupying almost the whole of the northern 
hemisphere, and with the Gulf-stream diffusing its warm 
breath over the western coast of Europe, and the Japan Cur- 
rent over the western coast of America, we find that the 
domain of ice and snow remains fixed ; and we can conceive 
of no conditions, dependent upon these causes, whereby the 
Cinnamonium should again flourish at Bellingham Bay, or 
the Sequoia on the Greenland coast. 
Others have inferred that these great cycles of warmth 
and cold may be due to the increased or diminished heat 
transmitted from the interior of the earth. If we adopt the 
theory of a cooling globe, there must have lapsed a very 
considerable period between the time when it passed from 
‘an incandescent state and when it became fitted for the sus- 
tenance of organic forms. Sir William Thompson, basing 
his observations on the well known laws of heat and conser- 
vation of energy, infers that it has only been habitable 
within the last one hundred millions of years. It is, then, 
if his estimates be true, that within this interval we are to 
include all the changes in the organic world — the flor: and 
faunz which have successively come into being, and have 
successively displaced each other. 
n the process of solidification the earth is supposed long 
ago to have arrived at that stage when the radiation from the 
cooling surface is no greater than that derived from the sun, 
and therefore, a stable temperature has been established. 
We would infer, then, that any violent reaction of the inte- 
rior upon the external crust, would affect more sensibly the 
