454 GENERA INDEPENDENT OF CLIMATE. 



mammoth was found frozen in Arctic ice, the conclusion veered round ; 

 so that the animals, previously supposed to be sub-tropical, were 

 believed to have lived under colder conditions than the present 

 British climate. Such an example may warn us that, although the 

 Nipa fruit of the London clay of Sheppey is of the same genus as the 

 Kipa of the Ganges and Irrawaddy, and although associated in both 

 cases with crocodiles and fresh-water turtles, in a sediment which 

 includes many genera of shells found in eastern seas, we can no more 

 infer a sub-tropical climate for the plant life or reptiles or shells of the 

 London clay, than we can for the mammals of the gravel, which are 

 often inseparable as species, from the similar assemblage of mammals 

 now inhabiting the North of Africa. There has been a tendency to 

 hasty generalisation in the matter of climate, as inferred from palseonto- 

 logical evidence. 



It has often been pointed out that there is a correspondence 

 between the marsupial mammals of the Stonesfield slate and asso- 

 ciated cestraciont fishes, plants, and shells like Trigonia, with similar 

 forms now living in the Australian region ; and the conclusion has 

 been drawn that the British fossil fauna and flora of Stonesfield lived 

 under like conditions of climate. For such a view to be sustained, it 

 must be held, either that the Australian life is a survival of a creation 

 which was once universal, and of which a part was fossilised at 

 Stonesfield, or else that the life from Stonesfield migrated through 

 the equatorial region to the antipodes. Both views are equally unten- 

 able ; the former being disposed of by the occurrence of Cretaceous 

 and Tertiary strata in Australia, and the latter by the fact that, though 

 it is just possible that elevation of land might preserve equable con- 

 ditions between Britain and the antipodes, so that the equator should 

 be passed without the experience of an equatorial climate, yet this 

 hypothesis would require that the marine life should similarly and 

 simultaneously migrate along a sea-bed, depressed so deep in the 

 equatorial region that the climate was still temperate. 



It is difficult;, when dealing with living species in the newer geolo- 

 gical formations, to be sure that we do not attach too much importance 

 to the facies of the faunas of the Coralline Crag and the Middle Glacial 

 sands, as indicative of climate. For although the Pyrula, Cassidaria, 

 Valuta, Lingula, &c., of the Crag, suggest southern seas, and though 

 the same area came to be occupied subsequently by an assemblage of 

 shells which is now arctic, it is quite possible that climate may have 

 had nothing to do with the succession, but that it may have been a 

 continuous though slow migration of life southward, consequent upon 

 continued elevation of land to the north. 1 



Existing Distribution of Life. Since existing plants and animals 

 are the surviving descendants of fossilised forms which in bygone time 

 were distributed to different regions of the world from those which 

 their descendants occupy, it is only natural to find that the great 

 geographical groups of life on land do not coincide with present 

 arrangements of land and water. In fact, the present distribution 

 1 Cambridge Phil. Soc., March 3, 1862. 



