308 LLOYD'S NATURAL HISTORY. 



many geologists is hostile to the new view, and it is probable 

 that the Mammoth saw both the incoming and the waning of 

 glacial conditions. 



The Rodents, or Gnawing animals, need not detain us long, 

 more especially since the burrowing habits of some of them 

 render the occurrence of their remains by no means trust- 

 worthy evidence that they are contemporaneous with the other 

 contents of the deposits where they are found. The Beaver, 

 although very rare in caves, occurs in the brick-earths of the 

 Thames Valley ; while the Siberian and South Russian Picas 

 (Lagomys pusillus) have been found in three caves and the 

 Ightham fissure. The northern Vole (Microfus ratticeps)> and 

 the Siberian Vole (Af. gregalis\ both of which have been 

 identified from the last-named deposit, are animals essentially 

 characteristic of desert or steppe regions ; and much the same 

 is true of the Susliks (Spermophilus\ several species of which 

 inhabited England during the Cavern Period. 



It will thus be seen that the problems presented by the later 

 Pleistocene Mammalian Fauna of Britain are so complex, and 

 apparently so contradictory, that at present it is quite hopeless 

 to arrive at any satisfactory conclusion. That so far as the 

 larger Mammals are concerned, we live in an impoverished age, 

 is perfectly true ; but whether, as Mr. Wallace supposes, this is 

 due to the effects of the Glacial Period seems more than doubt- 

 ful, if geologists are right (and we believe they are) in assigning 

 a Post-Glacial date to our brick-earths, river-gravels, and cavern- 

 deposits. 



II. THE FOREST-BED AND CRAG PERIODS. 



The fresh-water deposit on the eastern coast of England 

 known as the Forest-bed, of which the age is Pre-Glacial, occupies 

 a somewhat intermediate position in regard to its Mammalian 

 Fauna between the Cavern and Crag Periods; some of the 



