300 LLOYDS NATURAL HISTORV. 



destroyed by human agency, or because the climate became 

 unsuitable to them. Of such existing species we shall only 

 make mention when there is something of special interest 

 connected with them, and the reader will therefore under- 

 stand that we have no intention of attempting anything like a 

 complete list of the Mammalian fauna of this epoch. The most 

 remarkable feature connected with this fauna is the apparently 

 contradictory evidence which it affords as to the nature of the 

 climate then prevalent. The Glutton, Reindeer, Arctic Fox, 

 and Musk-Ox are strongly indicative of a more or less Arctic 

 climate ; many of the Voles (Microtus), Picas (Lagomys), and 

 Susliks {Spermophilui), together with the Saiga Antelope, 

 app:ar to point equally strongly to the prevalence of a steppe- 

 like condition ; while the Hippopotamus and Spotted Hyaena 

 seem as much in favour of a sub-tropical state of things. 

 Many attempts have been made to reconcile these apparently 

 contradictory circumstances ; one of the older views being 

 that while the tropical types of animals lived during a warm 

 interlude, they migrated southwards with the incoming of 

 colder conditions to the Arctic type of Fauna. Since, however, 

 it has now been ascertained that the remains of both Tropical 

 and Arctic forms have been found lying side-by-side in the 

 same bed, it is perfectly certain that such an explanation will 

 not meet the exigencies of the case. We have, however, yet 

 much to learn about the effects of climate on animals — our 

 experience being, unfortunately, confined to a single epoch j 

 and the fauna of the highlands of Tibet shows that many types 

 of animals formerly regarded as more or less essentially tropical 

 can withstand a winter climate of extreme severity. 



Among the forms that at first sight seem to indicate that 

 Britain enjoyed a mild climate during the deposition of the 

 brick-earths of the Thames Valley is a Monkey, more or less 

 closely alUed to the existing Macaques {Macacus), but, unfor- 



