Ch. XIII] DEPOSITS IK VALLEY OP THAMES. 153 



Elephas primigenius, and the Rhinoceros tichorhinus, both of them quad- 

 rupeds of which the flesh and hair have been found preserved in the 

 frozen soil of Siberia, occur abundantly, with the bones of an hippopot- 

 amus, aurochs, short-horned ox, red deer, reindeer, and great cave-tiger 

 or lion.* A similar group has been found fossil at Maidstone, in Kent, 

 and other places, agreeing in general specifically with the fossil bones 

 detected in the caverns of England. When we see the existing reindeer 

 and an extinct hippopotamus in the same fluviatile loam, we are tempted 

 to indulge our imaginations in speculating on the climatal conditions 

 which could have enabled these genera to coexist in the same region. 

 Wherever there is a continuity of land from polar to temperate and equa- 

 torial regions, there will always be points where the southern limit of an 

 arctic species meets the northern range of a southern species ; and if one 

 or both have migratory habits, like the Bengal tiger, the American bison, 

 the musk ox, and others, they may each penetrate mutually far into the 

 respective provinces of the other. There may also have been several 

 oscillations of temperature during the periods which immediately pre- 

 ceded and followed the more intense cold of the glacial epoch. 



The strata bordering the left bank of the Thames at Grays Thurrock, 

 in Essex, are probably of older date than those of Brentford, although 

 the associated land and freshwater shells are nearly all, if not all, identi- 

 cal with species now living. Three of the shells, however, are no longer 

 inhabitants of Great Britain; namely, Paludina marginata (fig. 11 7, p. 

 133), now living in France; Unto littoralis (fig. 29, p. 28), now inhab- 

 iting the Loire; and Cyrena consobrina (fig. 26, p. 28). The last- 

 mentioned fossil (a recent Egyptian shell of the Nile) is very abundant 

 at Grays, and deserves notice, because the genus Cyrena is now no longer 

 European. 



The rhinoceros occurring in the same beds (R. leptorhinus, see fig. 

 136, p. 16*7), is of a different species from that of Brentford above men- 

 tioned, and the accompanying elephant belongs to the variety called 

 Elephas meridionalis, which, according to MM. Owen and H. von Meyer, 

 two high authorities, is the same species as the Siberian mammoth, 

 although some naturalists regard it as distinct. With the above mam- 

 malia is also found the Hippopotamus major, and what is most remark- 

 able in so modern and northern a deposit, a monkey, called by Owen 

 Macacus pliocenus. 



The submerged forest already alluded to (p. 13V) as underlying the 

 drift at the base of the cliffs of Norfolk is associated with a bed of lignite 

 and loam, in which a great number of fossil bones occur, apparently of 

 the same group as that of Grays, just mentioned. It has sometimes 

 been called " the Elephant bed." One portion of it, which stretches out 

 under the sea at Happisburgb, was overgrown in 1820 by a bank of 

 recent oysters, and there the fishermen dredged up, according to Wood- 

 ward, in the course of thirteen years, together with the oysters, above 



* Morris, Geol. Soc. Proceed. 1849. 



