196 



ISLAND LIFE. 



[fart I. 



persistent cold epochs when the excentricity was as low as it 

 is now or lower, for that would imply that the duration of cold 

 conditions was greater than that of warm. Why then should 

 the fauna and flora of the cold epochs never be preserved ? 

 Mollusca and many other forms of life are abundant in the 

 Arctic seas, and there is often a luxuriant dwarf woody vegeta- 

 tion 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 strength- 

 ened 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 palgeon- 

 tological 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 glacia- 

 tion continues, we are driven to the conclusion that the last 

 glacial epoch of the northern hemisphere was exceptional, 

 and was not preceded by numerous similar glacial epochs 

 throughout Tertiary and Secondary time. 



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

 tions already referred to) were certainly absent, considerable 

 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. W^e have also 



