Date of the Glacial and the Upper Miocene Period. 38 1 



sun may have been greater during the earlier periods of the 

 earth's history. It must also be borne in mind that the simple 

 fact of the fauna and flora of that age indicating a warm and 

 equable condition of climate is not a sufficient proof that there 

 were no cold periods ; for a warm and equable condition of climate 

 is just as necessary a result of an increase of excentricity as a cold 

 condition; and the warm periods may be represented by organic 

 remains, and the cold periods not. 



Returning to the Postpliocene period. If this period afforded 

 no geological evidence of a warmer condition of climate in 

 Europe than now prevails, it would be so far a presumptive 

 evidence against the assumption that the glacial epoch resulted 

 from cosmical causes. But we have undoubted evidence that 

 the climate of Europe during a portion of that period was much 

 warmer and more equable than at present ; for we find evidence 

 of animals and shells existing in latitudes where they could not 

 now live in consequence of the cold. The Cyrena fluminalis is a 

 shell which does not live at present in any European river, but 

 inhabits the Nile and parts of Asia, and especially of Cashmere. 

 The U?iio littoralis, extinct in Britain, is still abundant in the 

 Loire. The Paludina marginata does not exist in this country, 

 but inhabits the more southern parts of Europe. These shells 

 have been found in Posttertiary deposits at Gray's Thurrock in 

 Essex, in the valley of the Ouse near Bedford, at Hoxne in Suf- 

 folk, in the fluviomarine beds of the Norfolk cliffs, in the fresh- 

 water formation at Mundesley, and other parts of England. 

 Along with these shells of a southern type have been found the 

 bones of the Hippopotamus, of a species closely allied to that now 

 inhabiting the Nile, and the Elephas antiquus, an animal re- 

 markable also for its southern range, and the Rhinoceros me- 

 garhinus. But what is most remarkable, along with these have 

 been found such animals of an arctic type as the Mammoth, the 

 woolly Rhinoceros, and the Reindeer. How these could all have 

 lived under the same conditions of climate has long been a puzzle 

 to geologists. But many geologists now, as Sir Charles Lyell* 

 and Mr. Boyd Dawkinsf, are inclined to believe that these did 

 not all live under the same conditions of climate, but imply os- 

 cillations of climate. During a cold condition of climate the 

 Mammoth and other arctic animals would move southwards ; and 

 when the climate assumed a warm and equable condition, the 

 animals and shells of a southern type would migrate northwards. 



This warm condition of climate was not confined to temperate 

 regions, but extended to high northern latitudes; for we find all 

 over the Arctic regions remains of ancient forests where now the 



* ' Principles/ vol. i. p. 193 (tenth edition), 

 t Quart. Journ. Geol. Soc. May 1867, p. 104. 



