248 The American Geologist. October, 1902. 
country of Brazil, he did not see, "a single phenomenon in the 
way of boulders, gravels, clays, soils, surfaces, or topography 
that could be attributed to glaciation." 
On the other hand Prof. T. G. Bonney * refers to the 
glaciers on Mount Kenia as significant. To quote his own 
words : "The extension of the glaciers on Mount Kenya 
(19,500 feet) is especially interesting, because its position 
(almost on the equator) suggests a possible refrigeration of 
the earth as a whole, rather than that of its hemispheres 
alternately." He adds in a foot note, however, that Dr. J. \V. 
Gregory, the explorer of Kenia, was more favorable to the idea 
that the refrigeration was produced by an uprising of the 
region, and not by any general climatal change. 
A paper by L^pham, t recently published, elaborates to 
some length the "evidences of epeirogenic movements caus- 
ing and terminating the Ice-age." 
The paper by T. C. Chamberlin for which reference has 
been given, on ''An Attempt to Frame a Working Hypothesis 
of the Cause of Glacial Periods on an Atmospheric Basis," 
is one of the most recent, and at the same time, perhaps, 
the most logical and profound of those that have been writ- 
ten. This hypothesis accounts admirably for the cause of 
the variations of climate, producing epochs of glaciation 
during Pleistocene time, by variations of the amount of carbon 
dioxide contained in the atmosphere. It has been calculated 
by the Swedish physicist Dr. Arrhenius (1896) that were the 
present content of COo in the atmosphere to be reduced to an 
amount ranging from 55% to 67% the average temperature 
would fall 4 or 5 degrees C, and thus produce a glacial epoch ; 
on the other hand an increase of the COo by two or three times 
the present amount would raise the average temperature 
sufficiently to produce a mild climate in high latitudes. 
Upon such a foundation for his theory, Professor 
Chamberlin has rigorously analyzed and discussed, so far as 
present knowledge permits, the rational causes of CO^. 
depletion in the atmosphere, with its subsequent restoration 
thereto; and further the competency of such to produce oscil- 
lations of glaciation in accordance with the tiixie limits set for 
*"Ice-\Vork Present and Past." 1896. 
tBuIl. Geol. Soc. Am. 1899. 
