The Evolution of Climates. — Ma /i son. loi 
equator) suggests a possible refrigeration of the earth as a 
whole rather than of its hemisphere independently."* 
This conclusion applies also to all evidences of glacial ac- 
tion in sub-tropical and tropical latitudes. 
g. A Combinatioti of {8) A Coincidence of an Aphelion Winter 
with a Period of Maximum Ecce?itricity, and (2) Changes 
in the Elevation of Land and Consequent Variations 
i?i the Distribution of Land and Water. 
The ninth theory has been maintained by one of the great- 
est English naturalists, Dr. Alfred Russell Wallace. He com- 
bines the theory of Dr. CroU with that of Sir Charles Lyell, 
and very ably presents his views in "Island Life." 
The strongest support that has been given to any of the 
foregoing theories is contributed by the arguments and deduc- 
tions of Dr. CroU and Dr. Wallace; yet they have failed to ef- 
fect conviction for, in a recent work, Dr. Joseph LeConte, after 
reviewing the various theories as to the cause of the Ice age, 
uses this expression: "This seems to be by far the most proba- 
ble yet presented."! 
With a full knowledge of the general and special literature 
on the subject and after a comprehensive review Dr. T. G. 
Bonney says: 
"It follows from what has been said above, that the low 
temperature which undoubtedly prevailed during the Glacial 
epoch has not yet received any satisfactory explanation. 
Each one that has been proposed is either inadequate or 
attended by grave difficulties. It is therefore probable that 
some factor which is essential for the complete solution of the 
problem is as yet undiscovered, or at any rate, the importa/ice 
of one which is already known Jias not been didy recognised. '''\ 
Dr. Jas. Geikie, after summing up all the evidence and re- 
viewing all the theories, admits that no satisfactory solution has 
been ofifered: 
"Geologists are justly jealous of attempts to account for 
the facts of their science by reference to causes other than 
*Ice Work, Present and Past, p. 242. Appleton's, 1896. 
t Elements of Geology, 2nd Edition, page 578. 
Jlce Work, Present and Past, p. 260. (Appleton's 1896). Italicised 
by the present writer. 
