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. ^ 

 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 vieio of Geological Climates as dependent on the 

 Physiccd Features of the Eartlis 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. Croll's 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 tlie climatic 

 1 Geological Magazine, 1877, p. 137. 



