CLIMATES OF GEOLOGIC TIME—SCHUCHERT. Sisk 
On the other hand, a great deal has been written about the supply 
and consumption of the carbonic acid of the air as the primary cause 
for the storage of warmth by the atmospheric blanket. A greater 
supply of carbon dioxide is said to cause increase of temperature, and 
a marked subtraction of it will bring on a glacial climate. This aspect 
of the climatic problem is altogether too large and important to be 
entered upon here. It is permissible to state, however, that the glacial 
climates are irregular in their geologic appearance, are variable lati- 
tudinally, as is seen in the geographic distribution of the tillites be- 
tween the poles and the equatorial region, and finally that they appear 
in geologic time as if suddenly introduced. These differences do not 
seem to the writer to be conditioned in the main by a greater or smaller 
amount of carbon dioxide in the atmosphere, for if this gas is so strong 
a controlling factor, it would seem that at least the glacial climates 
should not be of such quick development. On the other hand, an 
enormous amount of carbon dioxide was consumed in the vast lime- 
stones and coals of the Cretacic, with no glacial climate as a result; 
though it must be admitted that the great limestone and vaster coal 
accumulations of the Pennsylvanic were quickly followed by the 
Permic glaciation. Again it may be stated that the Pleistocene cold 
period was preceded in the Miocene and Pliocene by far smaller areas 
of known accumulations of limestone and coal than during either the 
Pennsylvanic or Cretacic, and yet a severe glacial climate followed. 
Briefly, then, we may conclude that the markedly varying climates 
of the past seem to be due primarily to periodic changes in the topo- 
eraphic form of the earth’s surface, plus variations in the amount of 
heat stored by the oceans. The causation for the warmer interglacial 
climates is the most difficult of all to explain, and it is here that factors 
other than those mentioned may enter. 
Granting all this, there still seems to lie back of all these theories a 
greater question connected with the major changes in paleomete- 
orology. This is: What is it that forces the earth’s topography to 
change with varying intensity at irregularly rhythmic intervals? 
This difficult and elusive problem the older geologists solved with a 
great deal of assurance by saying that such change was due to a cool- 
ing earth, resulting in periodic shrinkage; but the amount of shrinkage 
that would necessarily have taken place to account for all the wrin- 
klings and overthrustings of the earth’s crust during geologic time 
would be far greater than that which has apparently occurred. 
Further, a cooling earth is yet to be demonstrated. Again, some 
paleogeographers seem to see a periodic heaping up of the oceanic 
waters in the equatorial region and a pulsatory flowing away later 
toward the poles. If these observations are not misleading, are we 
not forced to conclude that the earth’s shape changes periodically in 
response to gravitative forces that alter the body form ? 
