The Evolutio/i of Clvnatcs. — Maxson, 163 
form, moist, and highly torrid chmate was estal)Hshed, and 
types of Hfe developed, culminating in the Carboniferous age. 
The crust evidently cooled sufficiently to permit the de- 
markation of the continental and ocean areas, but the cooling 
did not necessarily proceed to that point which upheaved the 
massive mountain ranges, nor greatly depressed the ocean 
areas. Apparently an era of low, flat continents and shallow 
hot seas followed. 
The life of that period abundantly shows this condition 
from one polar circle to the other, and the prevailing tempera- 
ture is recorded in the fossil life of the Palaeozoic and Mesozoic 
eras. 
The greater part of the vapors and gases existing previously 
in the atmosphere were condensed, and existed upon the sur- 
face, the vapors as heated oceans, and the gases in various 
combinations of the mineral and life kingdoms. Now, in the 
oceans thus formed and further enlarged, there was stored up 
a vast quantity of the original earth heat, by reason of the 
high specific heat of water; from which it could not be ex- 
hausted until after the cooling of those portions of the surface 
having a lower specific heat. In this process of exhaustion of 
this heat, it must have maintained the cloud shield, largely 
shutting out solar heat until the effective remnant of earth 
heat w^as exhausted. Not until the bottoms of the oceans 
were subjected to a degree of cold approximating that to 
which the continental areas were exposed could the whole 
crust be cooled uniformly and attain its present rigidity and 
stability. 
Moreover, in cooling the exposure of one pole to glacial 
and the other to temperate or sub-tropical conditions, as 
argued by Dr. Croll, would have subjected our planet to very 
peculiar "cooling strains," as they are termed by foundry- 
men. Whereas the slow and uniform cooling, as herein de- 
scribed, is productive of maximum thickness, strength and 
imiformity of crust.* 
*There is evidently cause why the denser crust materials should 
have been concentrated in the southern hemisphere. This is in a 
measure foreign to the present discussion, but two reasons may be sug- 
gested, (i) The direction of motion of the solar system in space, and 
(2) the greater amount of solar energy received by the northern hemi- 
sphere. 
