CHAP. IX GEOLOGICAL CLIMATES 203 



preserved ? Mollusca and many other forms of life are 

 abundant in the Arctic seas, and there is often a luxuriant 

 dwarf woody vegetation on the land, yet in no one case has 

 a single example of such a fauna or flora been discovered 

 of a date anterior to the last glacial epoch. And this 

 argument is very much strengthened when we remember 

 that an exactly analogous series of facts is found over all 

 the temperate zones. Everywhere we have abundant 

 floras and faunas indicating warmer conditions than such 

 as now prevail, but never in a single instance one which 

 as clearly indicates colder conditions. The fact that drift 

 with Arctic shells was deposited during the last glacial 

 epoch, as well as gravels and crag with the remains of 

 arctic animals and plants, shows us that there is nothing 

 to prevent such deposits being formed in cold as well as in 

 warm periods ; and it is quite impossible to believe that 

 in every place and at all epochs all records of the former 

 have been destroyed, while in a considerable number of 

 instances those of the latter have been preserved. When 

 to this uniform testimony of the pateontological evidence 

 we add the equally uniform absence of any indication of 

 those ice-borne rocks, boulders, and drift, which are the 

 constant and necessary accompaniment of every period of 

 glaciation, and which must inevitably pervade all the 

 marine deposits formed over a wide area so long as the 

 state of glaciation continues, we are driven to the conclu- 

 sion that the last glacial epoch of the northern hemisphere 

 was exceptional, and was not preceded by numerous 

 similar glacial epochs throughout Tertiary and Second- 

 ary time. 



But although glacial epochs (with the one or two excep- 

 tions already referred to) were certainly absent, consider- 

 able changes of climate may have frequently occurred, and 

 these would lead to important changes in the organic 

 world. We can hardly doubt that some such change 

 occurred between the Lower and Upper Cretaceous 

 periods, the floras of which exhibit such an extraordinary 

 contrast in general character. We have also the testi- 

 mony of Mr. J. S. Gardner, who has long worked at the 

 fossil floras of the Tertiary deposits, and who states, that 



