Physical Theory of Secular Changes of Climate. 93 
lateral pressure resulting from the shrinking of the earth's crust. 
It is now, however, pretty well established that the continental 
or elevated periods of the Glacial epoch, when our island was 
united to the mainland, were warm periods; for it was then 
that this country was invaded by tropical and subtropical 
mammals. Had the climate at that time been cold, and the 
Trusting that these preliminary considerations may tend to 
remove the partial confusion in which this somewhat complex 
subject has been involved, I shall now proceed to examine Mr. 
Wallace’s main argument. 
[To be continued] 
x 
ed by him as the Glacial period; that this era was followed both in 
America and Kurope, by a subsidence of the same land initiating the Champlain 
period, and that this was the era of meltin 
northward, an impossible occurrence in America during the Glacial era; that 
another era of i f much less extent occurred subsequently in Europe, if not 
also in North America, probably commencing with th he change in 
the land to its present level, and that this was the occasion of the destruction of 
© mammals of North Siberia, and other faunal changes. The evidences believed 
to favor these conclusions are stated in his various papers and his Manual of 
logy, and need not be here repeated. The latest discussion by him of the 
facts from Eastern North America as to the Champlain subsidence is contained in 
this Journal for 1882. 
a’ 
Mr. 8 opini 
Glacial era (that is, the era as he defines it) was a conclusion from facts that had 
: nd America, and not a supposition sugge , or 
thought to be sustained by, any theory as to the cause of the elevation, The e 
of maximum ice he always sup t of maximum or nearly maxi- 
mum cold; and the Cham i 
least) of milder climate, in which the Mammoth and the associated mammals and 
1€r Species of life, animal and vegetable, of the colder temperate and temperate 
latitudes, reached their farthest northern limit.—g. D. D.] 
