xxxvi Journal of Proceedings.
fore, although he might advance in his mind, his bodily structure
would remain very constant. The fact that the earliest races of men
yet traced out present a type similar to man now existing is rather a
proof that the human species is immensely more ancient than we
hitherto have had any conception.
With reference to the Glacial Epoch in Geology, Mr. Wallace said it
was a subject which for upwards of fifteen years he had thought and
written upon. He was glad to say that he did not differ from their
good friend Sir Antonio Brady to the extent he believed. He quite
agreed that the period of the Mammoth and the earlier Mammalia was
a period close upon or within the Glacial Epoch. In point of fact he
considered that the time would come when they would find that changes
in climatal conditions have been the principal causes in producing the
changes of plants and animals on the earth. He believed that the
chief agent in inducing these changes of climate was the geographical
alterations in the contours of continents by submergence and upheaval
in different stages of the earth's history: He had lately been attempting
to show in some detail how it was that these changes in Geography
did afford us the means of explaining that hitherto insolvable problem
—the mild and luxurious vegetation of the Arctic regions during the
Miocene and many earlier Geological epochs. It was quite impos-
sible to accept in its entirety Mr. Croll's explanation; but Mr. Wallace
believed he had found the solution in Mr. Croll's own theory of Ocean
Currents. Mr. Croll maintained that there had been alternate mild
and glacial conditions in the northern hemisphere throughout the
Tertiary period; but the objection to this was that all the Geological
evidence showed that before the last Glacial Epoch mild climates alone
prevailed in the Arctic regions, whether in the Upper or Lower Mio-
cene, the Cretaceous, the Jurassic or the Carboniferous period;—in
fact, every Geological Formation in the Arctic Regions, anterior to the
Pliocene, furnished evidence of mild, and in no single instance of cold
climates. Now Mr. Croll had himself demonstrated the wonderful
power of the Gulf Stream in carrying the warmth of the Tropics into
North Temperate and Polar Regions. At present this was the only
important body of warm water that reached the Arctic Seas, but there
was good geological evidence that in earlier ages the great Northern
Continents—Europe, Asia, and North America—were not as now solid
masses of land, but were broken up and penetrated by arms of the sea
which carried other bodies of warm water northward. When this was
the case, the formation of ice in the polar seas would be entirely pre-
vented ; and when there was no ice the power of the sun during the
long day of the polar summer was amply sufficient to support the vege-
tation, the remains of which so astonish us in the Arctic Regions.
The last Glacial Epoch was undoubtedly produced by the astronomical
conditions which have been so well set forth and illustrated by Mr.