34 6 HISTORICAL PALEONTOLOGY. 



(55) ' Palaeontologische Studien iiber die alteren Tertiar- 



schichten der Alpen.' Reuss. 



(56) 'Land- und Siiss-wasser Conchylien der Vorwelt.' 



Sandberger. 



(57) ' Flora Tertiaria Helvetica. ' Heer. 



(58) 'Flora Fossilis Arctica.' Heer. 



(59) 'Recherches sur le Climat et la Vegetation du Pays 



Tertiaire.' Heer. 



(60) ' Fossil Flora of Great Britain.' Lindley and Hutton. 



(61) 'Fossil Fruits and Seeds of the London Clay.' Bower- 



bank. 



(62) "Tertiary Leaf-beds of the Isle of Mull " ' Quart. 



Journ. Geol. Soc.,' vol vii. Edward Forbes. 



(63) 'The Geology of England and Wales.' Horace B. 



Woodward. 



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 formations, in accord- 

 ance with the nomenclature of Sir Charles Lyell or as the 

 Quaternary formations, 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 the species not known to be in existence at the pres- 

 ent 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 

 and the Mammals 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 



