— 389 — 
bonation of the oceanic currents, and the effects of great changes 
in the direction (1) of these currents. 
A discussion of these hypotheses to account for the Gondwana 
glaciation would go beyond the limits of this report, and it is not 
possible here to more than mention a few of the most important 
facts specially relating to any of them. The extension of the Gan- 
gamopteris flora into South America, and the very certain deductions 
as to climate indicated thereby go far to relieveus from the neces- 
sity of assuming any great shifting of the earth’s axis, if indeed 
the variation in the northward extension of the glacial action may 
not wholly be explained by continental configuration and changes 
In ocean currents. 
There is much to be said in support of zonal climatic refri- 
geration as the result of the atmosphere in carbonic acid. The 
conditions of deposition of the red beds, often accompanied by great 
precipitation of gypsum and other salts, at the close of the Carbo- 
niferous, and particularly in the Permian, and earliest Trias, cons- 
titute a strong argument in support of this theory, which is, in 
my opinion by far the best geological explanation yet offered for 
the extinction of the great cosmopolitan Carboniferous flora and 
the overwhelming changes in terrestrial plant life that mark the 
relatively short passage from the upper Stephanian to the beginning 
of the Trias. If, in this connection, we bear in mind that the 
continental surfaces in the Northern Hemisphere were low and 
approaching nearer and nearer to base level during Permo-Carbo- 
niferous time, so that climatic zones would be less strongly marked 
in the northern regions, it is not difficult to see how, on the 
higher land masses of Gondwana-land, not only would the mean 
temperature be lower, but the seasonal differences would be in far 
stronger contrast. Increased elevation of the land would, naturally, 
under conditions of carbonic acid reduction, not only exaggerate 
the differences between the climate of the low northern and of 
the high southern continental areas, but it would also greatly 
exaggerate the seasonal differences. 
We are acustomed, for very good reasons, to regard the cos- 
mopolitan Northern Permo-Carboniferous flora as having developed 
(1) Chamberlin, Science, n.s,, vol XXIII, 1906, p- 930. The full publication of the pro- 
ositions very briefly outlined in Professor Chamberlin’s abstract has not yet appeared. 
tis therefore impossible to give his theory due consideration at this time. 
