1 66 The American Geologist. seFJtomber, isyy 
sea level, and by the local escape of earth heat; elevated equa- 
torial or temperature areas were under this interpretation as 
much exposed to glaciation as polar lands. By reason of the 
high specific heat of water, this isotherm also reached conti- 
nental areas prior to reaching ocean areas. 
The crust beneath the ocean, having been protected from 
loss of heat by the superincumbent water, shrunk approxi- 
mately to its present shape subsequent to those more exposed 
portions forming continental areas. The ocean bottoms must 
also have been fractured, as continental areas had previously 
been. In this way very considerable increments of earth heat 
may have been set free after glaciation had commenced. This 
process which is entirely in consonance with known laws, 
might result in increasing the depth of glaciation, or even in 
re-establishing it after partial recedence. 
There would also result a complicated series of crust move- 
ments as the continents were relieved of pressure by the 
melting of the ice caps* and the ocean bottoms subjected to 
increased pressure by the restoration of water to the oceans.^ 
Thus the same forces which, even before the eras we have 
been considering, must have built up upon the surface of the 
globe mineral forms of surpassing beauty, largely to be de- 
stroyed and ground down, to give place to vegetable and 
animal forms of wonderful development — these same forces 
were called upon to well nigh obliterate every living individual 
of both kingdoms. The efficiency of their work is attested in 
every zone of life from the equator to the polar regions. 
The continued exhaustion of earth heat in the oceans and 
beneath them was doubtless accomplished by the same means 
as before, and this exhaustion resulted in the preservation of 
those conditions most favorable to glaciation — namely light 
cloud formations but sufificiently dense to intercept much solar 
*The Great Ice Age, 3rd Edition, pp. 292-3. 
fit will again be noted that the isotherms inside of the particular 
one receiving equal amounts of earth and solar heat were chiefly 
maintained by earth heat, and therefore largely independent of equa- 
torial or polar exposure to solar heat. Consequently, their intersec- 
tions were upon different lines from those isotherms exterior to the 
one above specified; these latter ones were mainly dependent upon solar 
heat. It will also be observed that much of the solar heat reaching 
the lower, denser regions of the atmosphere, is trapped or selectively 
absorbed, and is therefore capable of establishing and maintaining 
higher temperatures than in the upper atmosphere. 
