334 HISTORICAL PALiEOXTOLOGY. 



CHAPTER XXI. 



THE QUATERNARY PERIOD. 

 The Post-Pliocene Period. 



Later than any of the Tertiary formations are various de- 

 tached and more or less superficial accumulations, which are 

 generally spoken of as the Post- Tertiary fo?'matio7is, in accord- 

 ance with the nomenclature of Sir Charles Lyell — or as the 

 Quaternary forviatlons, in accordance with the general usage 

 of Continental geologists. In all these formations we meet 

 with no Mollusca except such as are now alive — with the 

 partial and very limited exception of some of the oldest de- 

 posits of this period, in which a few of the shells occasionally 

 belong to species not known to be in existence at the pre- 

 sent day. Whilst the Shell-fish of the Quaternary deposits are, 

 generally speaking, identical with existing forms, the Mammals 

 are sometimes referable to living, sometimes to extinct species. 

 In accordance with this, the Quaternary formations are divided 

 into two groups : (i) The Post-Pliocene, in which the shells are 

 almost invariably referable to existing species, but some of the 

 Mammals are extinct ; and (2) the Recent, in which the shells 

 a?id the Mamjnals alike belong to existing species. The Post- 

 Pliocene deposits are often spoken of as the Pleistocene forma- 

 tions (Gr. pleistos, most; kainos, new or recent), in allusion to 

 the fact that the great majority of the living beings of this 

 period belong to the species characteristic of the "new "or 

 Recent period. 



The Recent deposits, though of the highest possible interest, 

 do not properly concern the palaeontologist strictly so-called, 

 but the zoologist, since they contain the remains of none but 

 existing animals. They are " Pre-historic," but they belong 

 entirely to the existing terrestrial order. The Post - Pliocene 

 deposits, on the other hand, contain the remains of various 

 extinct Mammals ; and though jMan undoubtedly existed in, 

 at any rate, the later portion of this period, if not through- 

 out the whole of it, they properly form part of the domain of 

 the palaeontologist. 



The Post-Pliocene deposits are extremely varied, and very 

 widely distributed ; and owing to the mode of their occurrence, 

 the ordinary geological tests of age are in their case but very 

 partially available. The subject of the classification of these 



