i88i.] 
Scepticism in Geology . 
335 
their brightness, and being surrounded with atmospheres, we 
do not possess much information as to their surfaces ; but it 
is believed that their mountains are relatively very much 
higher than those of the Earth, and it has been calculated 
that some exist in Venus between 20 and 30 miles high. 
If we could remove the waters of the ocean, and the sedi- 
mentary and other stratified deposits, the valleys of our globe 
would be some 6 miles deeper and the mountains correspond- 
ingly higher than at present. I believe that such inequalities 
are sufficient to account for the evidences of great heat and 
great cold in the earlier periods of geological history. The 
high or low degrees of temperature in any latitude is greatly 
a question of the depths of the valleys or the heights of the 
mountains, as demonstrated by the fa Ct that, even in tropical 
regions, high mountains are perpetually covered with snow. 
It is not necessary, therefore, to imagine the existence of 
periods in which extreme heat or extreme cold alternately 
ruled upon the Earth. The great depths of the valleys and 
the great heights of the mountains in former ages will also 
help to explain the alternate depositions of coal, clay, gravel, 
sand, &c., which have taken place over the same areas. In 
such a condition of high mountain and deep valley in con- 
nection with the development of water, the deeper valleys 
would be liable, at intervals, to be overwhelmed by the 
breaking away of the waters of lakes or seas which existed 
at higher elevations. It has been supposed that, when the 
vegetation of the coal-measures was in the course of growth, 
the air was hotter and moister than at present. The pre- 
sence of deep valleys in which such growth was favoured 
would account for such local condition of the atmosphere 
without the necessity for imagining a period of tropical heat 
over the entire globe. This greater contrast between valley 
and mountain would also account for the transport of large 
blocks of rock and other evidences of “ glaciation” described 
by geologists. Curiously enough the belief in a. “ great ice 
age ” is not unfrequently entertained in connection with the 
theory of radiation into space consequent upon the cooling- 
down of the Earth from a red-hot molten condition ; as if 
such mechanical radiation had unaccountably stopped for a 
period and afterwards as unaccountably again commenced ! 
With Immanuel Kant and Laplace I believe that the various 
substances of which the Earth is constituted once existed 
in a gaseous state, but with Lyell I see no reason to doubt 
that the forces by which the transformations have been made 
are the same in kind and degree as those which are now in 
operation. 
