286 REVIEWS 
of a glacial zone above us, while the latter are but details of the border 
ground of common ice precipitation. . 
The author confesses to uncertainty regarding the cause of the 
Permian and Pleistocene glaciations, but he takes only three sentences 
to do up “the recently elaborated hypothesis that glaciation may be 
brought about through the temporary reduction of the amount of carbon 
in the earth’s atmosphere.” He says this theory “leaves unexplained 
the shortly succeeding ice advances between whose dates no corre- 
sponding appreciable reduction in the carbon is registered by tock- 
making in the earth’s crust.”” Something no doubt is to be allowed for 
infelicity in phrasing when one is giving so short a shrift to a theory, 
but the author seems to lack a close acquaintance with the view he rejects. 
There are different views in which carbon dioxide plays a part, but 
there is only one that has been “elaborated” in a geological sense. 
This view makes a radical distinction between a glacial period and 
its oscillations, as also between fundamental agencies that may bring 
on a glacial period and auxiliary agencies that can only impose oscilla- 
tions on it. The glacial period in this view persists through the whole 
series of oscillations, and the fundamental agencies continue in effect 
and action throughout. The fundamental agency assigned by this 
hypothesis is world-wide diastrophism which acts on the atmosphere 
by the increased contact it gives, and leads to its depletion; it also acts 
physically and mechanically. The chief auxiliary agency assigned to 
the production of oscillations is the ocean which holds 90 per cent 
or more of all the free and semi-free carbon dioxide on the face of the 
globe. The ocean alternately absorbs and gives forth carbon dioxide as 
set forth in detail by the author of this view. It is misleading to say that 
this hypothesis “leaves unexplained” the glacial oscillations, for it 
not only offers an elaborate explanation but is without a rival in the 
explicitness with which it draws forth and lays emphasis on the char- 
acter of these oscillations, particularly that singular combination of 
subequal ice advances with continually shortening  time-intervals 
between them. The author was of course altogether at liberty to say 
that in his judgment the explanation is inadequate or incompetent, but 
readers will hardly commend his precision of statement when he tells 
them that it leaves unexplained the oscillations when in fact it offers 
the most explicit explanation yet put in print, except perhaps that of 
Croll on quite a different line. 
In summarizing the geomorphology of south Brazil the author 
brings out clearly the two distinct topographic units, the tableland, or 
