1 68 Tlie America?i Geologist. septcmbor. i899 
its period of existence in unmistakable terms, all shrouded 
from the direct action of solar heat, and all evidencing- by the 
life produced, the stifling, smothered character of the climate. 
During each era glacial conditions could exist locally just as 
glacial conditions now locally exist in the temperate and trop- 
ical zones; during each they could fluctuate as the fading 
earth heat fluctuated in its outbursts from the forming crust. 
These fluctuations, towards the last, would tend to cause those 
puzzling "interglacial periods" to the east of the narrow A\- 
lantic, but less manifest to the east of the broad Pacific. 
That solar heat was shut out from the surface of the earth 
during the Ice age is geologically recorded in the glaciation of 
the temperate zones over continental areas, where solar energy 
has removed glacial conditions, and established in their stead 
a mean annual temperature of 40° Fahr., and in the torrid zone, 
it has removed glacial conditions and established a mean an- 
nual temperature of 76° Fahr., where snow never falls. 
Consecpiently, it appears that in a heated globe, constituted 
and circumstanced as the earth, exposed to two sources of 
heat, internal heat and solar heat, before its climates or surface 
temperatures can pass under the control of solar heat climatic 
changes must be independent of latitude and the continental 
areas must be glaciated. 
Chapter VI. 
The Development of Solar Climates. 
In the foregoing chapters, the development of preglacial 
climates has been briefly traced from a condition of ultra torrid 
temperature gradually chilling down through a series of 
climates, each colder than the preceding and each independent 
of latitude; the last of the series being the Ice age, during 
which glacial conditions were vastly more extended and lower 
in temperate and tropical latitudes than they are now. It 
therefore becomes necessary to explain the development of ex- 
isting conditions from those prevalent at the culmination of 
the Ice age. Since this development has been and is a progres- 
sive one, it must be interpreted through laws now active, and 
the interpretation should correctly indicate the state towards 
which this advance is tending. 
