YMPOTHESTS-OF CAUSE*OF (GLACIAL, PERIODS TG, 
distribution of the Glossopteris flora. It will be quite conserva- 
tive to assume that this involved a land connection between 
India and Australia, and probably New Zealand, the connection 
presumably lying along the submerged platform which even to 
this day stretches southeasterly from Asia to the islands in 
question with slight interruptions. It is not improbable that 
between India and South Africa at least a partial bridge was 
formed by the elevation of the submerged plateau on which 
Madagascar and the Seychelles rest, together with the tract 
now accentuated by the Maldive islands. 
A connection with South America (where the Glossopteris 
flora also appeared — southern Brazil and Argentina) involving 
the least radical departure from modern configuration, may have 
been made via New Zealand and the Antarctic continent. This, 
I believe, also best satisfies the general tenor of paleontological 
evidence. 
If the geographic changes were confined to such connections 
and extensions of land as these, and to such moderate eleva- 
tions as the nature of the glacial beds and the associated deposits 
seem to imply, and to such changes in the northern hemisphere 
as can fairly be assigned to the Permo-Carboniferous period, 
there does not seem to be adequate ground for attributing a very 
exceptional depletion of the atmosphere to land-contact alone, 
or chiefly, though it may have made some notable contribution 
in that direction. 
Effects of atmospheric depletion by coal deposition—We there- 
fore turn to coal-formation as the effective alternative. There 
are no reliable estimates of the total carbon in the coal and 
carbonaceous deposits of the Carboniferous period, but such 
approximations as have been made seem to show that it equals 
several times the present atmospheric content, and that its 
extraction superadded to the increasing formation of carbonates 
resulting from the rising land would have been competent to 
reduce to the point of glaciation an atmosphere three or four times 
as rich in carbon dioxide as the present ; in other words, such 
an atmosphere as the sub-Carboniferous climate seems to imply. 
