164 The Ametican Geologist. September, \m.\ 
At the expiration of another succeeding period of time, 
the spheroidal isotherm having a temperature of say 60° Fahr., 
similarly shrunk to the surface of the earth, and a correspond- 
ing uniformly temperate climate was established. 
The further cooling of the crust caused its shrinkage, and 
a consequent greater upheaval of the lighter areas most ex- 
posed to loss of heat, the continents. This further shrinkage 
caused the strata formed during the previous eras to be up- 
heaved and fractured, and the lines of demarkation between 
oceans and continents were thus more strongly accentuated. 
The life developed in the interim evidences an approach to 
that of the present temperate zones, and its wide distribution 
indicates the complete control of the climates of the globe by 
internal heat. The isothermal lines were entirely at variance 
with those established by solar heat, therefore the functions of 
solar heat were principally conservative of those operating on 
the surface during this period also. 
The extreme and uniform distribution of fur or hair-covered 
animals and of the deciduous and coniferous trees of the 
Cenozoic era, mark further the control of a source of heat 
more uniformly distributed than solar heat could possibly be. 
For reasons previously given, this isotherm also reached con- 
tinental areas earlier than ocean areas. When the mean tem- 
perature of the land was 60° the tepid oceans must have had 
a higher mean temperature due to the high specific heat of 
water and to increments of earth heat received from the crust. 
Whenever the isothermal shell of 32° Fahr. shrunk so as to 
reach the more elevated portions of the continental areas, a 
snow line was established independent of the influences now 
establishing and maintaining such snow line. The resulting 
glaciation was controlled by the same general laws that now 
exist, only the distribution of heat being independent of lati- 
tude, and mainly dependent upon altitude above sea level, 
glaciation was as likely to occur in equatorial as in polar lati- 
tudes; the only requirement was the existence of land at an 
elevation above the isothermal shell of 32° Fahr. 
The moment a snowflake reached the earth which succes- 
sive escapes of the waning earth heat were unable to melt, the 
