_Cave and River Deposits._—Evidence of the existence of warm periods during the glacial epoch is derived from a class of facts which have long been regarded by geologists as very puzzling, namely, the occurrence of mollusca and mammalia of a southern type associated in England and on the continent with those of an extremely arctic character. For example, _Cyrena fluminalis_ is a shell which does not live at present in any European river, but inhabits the Nile and parts of Asia, especially Cashmere. _Unio littoralis_, extinct in Britain, is still abundant in the Loire; _Paludina marginata_ does not exist in this country. These shells of a southern type have been found in post-tertiary deposits at Gray’s Thurrock, in Essex; in the valley of the Ouse, near Bedford; and at Hoxne, in Suffolk, associated with a _Hippopotamus_ closely allied to that now inhabiting the Nile, and _Elephas antiquus_, an animal remarkable for its southern range. Amongst other forms of a southern type which have been met with in the cave and river deposits, are the spotted hyæna from Africa, an animal, says Mr. Dawkins, identical, except in size, with the cave hyæna, the African elephant (_E. Africanus_), and the _Elephas meridionalis_, the great beaver (_Trogontherium_), the cave hyæna (_Hyæna spelæa_), the cave lion (_Felis leo_, var. _spelæa_), the lynx (_Felis lynx_), the sabre-toothed tiger (_Machairodus latidens_), the rhinoceros (_Rhinoceros megarhinus_ and _R. leptorhinus_). But the most extraordinary thing is that along with these, associated in the same beds, have been found the remains of such animals of an arctic type as the glutton (_Gulo luscus_), the ermine (_Mustela erminea_), the reindeer (_Cervus tarandus_), the musk-ox or musk-sheep (_Ovibos moschatus_), the aurochs (_Bison priscus_), the woolly rhinoceros (_Rhinoceros tichorhinus_), the mammoth (_Elephas primigenius_), and others of a like character. According to Mr. Boyd Dawkins, these southern animals extended as far north as Yorkshire in England, and the northern animals as far south as the latitude of the Alps and Pyrenees.[122]