CHAP. IX.] 
GEOLOGICAL CLIMATES. 
197 
the testimony of Mr. J. S. Gardner, who has long worked at the 
fossil floras of the Tertiary deposits, and who states, that there 
is strong negative and some positive evidence of alternating 
warmer and colder conditions, not glacial, contained not only 
in English Eocene, but all Tertiary beds throughout the world . 1 
In the case of marine faunas it is more difficult to judge, but 
the numerous changes in the fossil remains from bed to bed only 
a few feet and sometimes a few inches apart, may be sometimes 
due to change of climate ; and when it is recognised that such 
changes have probably occurred at all geological epochs and 
their effects are systematically searched for, many peculiarities 
in the distribution of organisms through the different members 
of one deposit may be traced to this cause. 
General view of Geological Climates as dependent on the 
Physical Features of the Earth's Surface. — In the preceding 
chapters I have earnestly endeavoured to arrive at an explana- 
tion of geological climates in the temperate and Arctic zones, 
which should be in harmony with the great body of geological 
facts now available for their elucidation. If my conclusions as 
here set forth diverge considerably from those of Dr. Croll, it is 
not from any want of appreciation of his facts and arguments, 
since for many years I have upheld and enforced his views to the 
best of my ability. But a careful re-examination of the whole 
question has now convinced me that an error has been made in 
estimating the comparative effect of geographical and astro- 
nomical causes on changes of climate, and that, while the 
latter have undoubtedly played an important part in bringing 
about the glacial epoch, it is to the former that the mild climates 
of the Arctic regions are almost entirely due. If I have now 
succeeded in approaching to a true solution of this difficult 
problem, I owe it mainly to the study of Dr. drolls writings, 
since my theory is entirely based on the facts and principles so 
clearly set forth in his admirable papers on “ Ocean Currents in 
relation to the Distribution of Heat over the Globe.” The 
main features of this theory as distinct from that of Dr. Croll 
I will now endeavour to summarise. 
Looking at the subject broadly, we see that the climatic 
1 Geological Magazine, 1877, p. 137. 
