92 J. Croll—Examination of Wallace's Modification of the 
barrier had extended from the British Isles, across the Far6e 
Islands and Iceland to Greenland, cutting off from Northern 
Europe the warm waters of the Atlantic, including the Gulf- 
tream. ‘The result,” he says, “would almost certainly be 
that snow would accumulate on the high mountains of Scandi- 
navia till they became glaciated to as great an extent as Green- 
land.”’ 
It would be easy to multiply cases of this kind where a dis- 
tribution of land and water different from the present might 
have been more favorable to glaciation than the present; but 
the question is, Did any such difference favoring glaciation 
actually exist during the Glacial epoch? I have never been 
able to find any evidence that it did. Many a change in geo- 
graphical conditions has taken place during Tertiary times, 
some of which were doubtless favorable to glaciation; but have 
we any evidence that during the Glacial epoch the geographical 
conditions were more favorable than they are at present 
Unless this can be shown to be the case, there is no necessity 
for referring to a difference in geographical conditions during 
that epoch as a cause of glaciation. This being so, it does not 
follow, because in my explanation of the cause of the Glacial 
epoch I may not, like Sir Charles Lyell and others, have spec- 
ulated on the effects which might have resulted had the dis- 
tribution of land and water been different from what it is now, 
that I ought on this account to be charged with undervaluing 
the importance of geographical conditions. 
r. Wallace refers to one case of a difference in geographi- 
cal conditions which he thinks might have aided glaciation. 
Professor Dana has expressed the opinion that, during the 
height of the Glacial epoch, Northeastern America was con- 
siderably elevated, bringing the wide area of the banks of 
Newfoundland far above water. This, Mr. Wallace thinks, 
would reduce the southward-flowing Arctic currents, causing 
the icebergs to hang about the American shores, chilling the 
air so as to produce constant fogs and clouds with almost per- 
petual snow-showers, even at midsummer. But Professor Dana 
has also shown that during the Glacial epoch Northeastern 
America was depressed as well as elevated. Now the point is: 
whether the elevation was contemporaneous with the cold, or 
. with the warm periods of the Glacial epoch? Mr. Wallace 
himself admits that depression, not elevation, of the land 
accompanied the increased cold; and he quotes Mr. Searles V. 
ood, Jun., approvingly as holding the same opinion (p. 115). 
It was quite natural for Professor Dana to suppose that the ele- 
vation to which he refers occurred at the time the country was 
buried under ice; for when he wrote he believed the Glacial 
epoch was chiefly dae to elevation of the land caused by the 
