90 J. Croll—Examination of Wallace’s Modification of the 
at least in so far as the disappearance of the ice in Arctic 
regions is concerne 
To narrow the field of inquiry, and bring more prominently 
before the mind the real question at issue, I shall state the 
main points on which Mr. Wallace and I appear to agree. 
Points of agreement.—1. Mr. Wallace agrees with me that a 
high state of eccentricity could never directly produce a glacial 
condition of climate ; that the Glacial epoch was the result, not 
of a high state of eccentricity, but of a combination of physical 
— — into operation by means of this high. state. 
rees with me also in regard to what these physical 
agencies really were ; for the agencies to which he refers in his. 
‘Island Life* are almost identically ie which I have ad- 
vanced in ‘Climate and Time elsew 
3. Mr. Wallace agrees wits me in repend to the mutual 
reactions of the physical agents. He maintains with me that 
actions, and says that seo “produce a maximum of effect 
which, without their aid, would be altogether unattainable.” 
4. As has already been shown, we agree as to the ne- 
cessity of —_ geographical conditions for the production 
of the Glacial epoch. For although that epoch was mainly 
brought sei by the physical agencies, yet these agencies 
could not have produced the required effect unless the neces- 
sary geographical conditions - sky supplied, these belts 
necessary for their effective operat 
5. Mr. Wallace admits, of course, that the necessary geo- 
graphical conditions existed during the Glacial epoch; for, 
unless this had been the case, no glacial epoch could have oc- 
curred. Therefore all that was required to produce glaciation 
was an amount of eccentricity sufficient to set the pea 
conditions ete ocintents all that was te required to bring 
about the Glacial epoch was the operation of - physical 
agencies. The overlooking of this fact has led to much con- 
fasion: For example, 210,000 years ago, rik winter in 
aphelion, “the problem to be solved,” says Mr. Wallace, “is, 
whether the snow that fell in winter would accumulate to such 
an extent that it would not be melted in summer, and so go on 
increasing year by year till it covered the whole of Scotland, 
Ireland and Wales, and much of England. Dr. Croll and Dr- 
Geikie answer without hesitation that it would. Sir Charles 
