SUCCESSION OF SPECIES. 289 



naturalists to regard some of them as the direct ancestors of 

 species still existing in other parts of the world, so that the 

 Irish elk, the elephants, and the three species of rhinoceros 

 are perhaps the only ones which have left no descendants. 

 Most of the smaller species now inhabiting Europe already 

 existed in quaternary times, from which we may conclude 

 that the changes which have taken place were due to a 

 gradual change of circumstances, rather than to any sudden 

 cataclysm, or general destruction of life : it is also very im- 

 probable that the extinction of the different species was 

 simultaneous ; and, acting on this idea, M. Lartet has at- 

 tempted* to construct a palaeontological chronology. 



He considers that we may establish four divisions, namely, 

 the a^e of the cave-bear, of the mammoth and rhinoceros, of 



O ' 



the reindeer, and of the aurochs. It is evident, I think, that 

 the appearance of these mammalia in Europe was not simul- 

 taneous, and that their disappearance has been successive. 

 The evidence is very strong that in Central and Western 

 Europe the aurochs survived the reindeer, and that the rein- 

 deer, on the other hand, lived on to a later period than the 

 mammoth or the woolly-haired rhinoceros. But the chrono- 

 logical distinction between these two species and the cave- 

 bear does not appear to be so well established. Admitting 

 that the cave-bear has not yet been found in the river gravels 

 of the Somrne valley, we must remember that the animal was 

 essentially a cave-dweller, and that its absence is, perhaps, 

 to be attributed rather to the absence of caves than to the 

 extinction of the species. Moreover, the bones found in the 

 gravel are very much broken, and are seldom in such a condi- 

 tion as to enable the palaeontologist to distinguish the remains 

 of U. spelceus from those of other large bears. 



There is as yet no evidence that the cave-bear existed in 

 Europe before the commencement of the quaternary period, 



* Ann. des Sci. Nat, 1861, p. 217. 

 U 



