HYPOTHESIS OF CAUSE OF, GLACIAL. PERIODS 779 
affected was essentially a non-reactive one. Of course the reac- 
tive factor was never really absent, for the formation and solu- 
tion of carbonates was always in progress. In this case it is 
merely supposed to be the minor rather than the major factor. 
It is inferred, therefore, that a higher stage of permanent deple- 
tion of the atmosphere was reached before glaciation ensued 
through coal formation than would have been the case had the 
glaciation been produced by the formation of carbonates. To 
this, in a measure at least, is attributed the conditions which 
made it possible for the glaciation to affect lower latitudes in 
Permo-Carboniferous times than they did in Pleistocene times. 
As before noted, the Permo-Carboniferous glaciation extended 
20° nearer to the equator than the Pleistocene. 
The locahzation of the Permo-Carboniferous glaciation. —It 
remains to consider the remarkable localization of this ancient 
glaciation. Thegeneral principles involved are assumed to have 
been the same as those already applied to tne Pleistocene prob- 
lem, but the geographic factors were quite different, and it is 
here that the lack of complete data is most keenly felt. In 
Pleistocene times, as also at present, certain great geographical 
features are thought to have given a pronouncedly oblique 
circulation to the air currents of the northern hemisphere. In 
the southern hemisphere at present a much greater approach to 
symmetrical circulation prevails because great oblique features 
are absent. It is postulated that the configuration of Permo-Car- 
boniferous lands and oceans was such as to seriously disturb the 
symmetry of the atmospheric and oceanic circulation of that 
hemisphere, and to give it peculiar form and special intensity. 
The geographic features of the Permo-Carboniferous period.—The 
assigned changes introduced by the development of Gondwana 
land have been mentioned. These are thought to have pro- 
longed the Asiatic continent southeasterly to Australia, and 
probably to New Zealand, and perhaps to the Antarctic land. 
This prolongation, taken with its backward projection across 
Asia and Europe, constituted an oblique feature of great exten- 
sion. It also interposed a barrier which very notably modified 
