306 THE AGE OF MAMMALS 



Flora and climate. — Owing to the expansion of the warm Mediterranean 

 Sea, the cHmate of the Lower Pliocene is mild. The very gradual cooling 

 or lowering of temperature continues. The entire Pliocene epoch was 

 marked by the slow southward advance of the northern forest types of 

 trees and by the corresponding recession to the south of the more delicate 

 types, the palms, for example, being driven 10° farther south. ^ The 

 European flora gradually loses its large palms and camphor trees; the 

 sabal (Sahal) flourishes for a while in Langucdoc, and the dwarf fan palm 

 (Chamcerops) maintains its existence near Marseilles up to the end of the 

 Pliocene period. After having retained for so long a time the sequoias 

 (Sequoia) and bamboos (Bambusa), Europe becomes populated with species 

 very similar to those o'f its present tree flora. 



A marked and most interesting peculiarity is that several very characteris- 

 tic Pliocene species of Europe are now found only in the great forests of North 

 America.^ Thus in the Pliocene of Europe there occur such trees as the 

 locust (Rohinia), the honey locust (Gleditschia) , the sumac (Rhus), the bald 

 cypress (Taxodium) , the tulip tree (Liriodendron) , the sweet gum (Liquid- 

 amhar), the sour gum (Nissa), which do not now occur in Europe, but are 

 at present very characteristic forms of the flora of temperate North Amer- 

 ica.'* The oak (Quercus), beech {Fagus), maple {Acer), poplar (Popidus), 

 walnut (Juglans), and the larch (Larix) predominate in central France, and 

 include forms which show affinities to existing types of North Africa (Al- 

 geria), southern Europe (Portugal), and even Japan. Toward the very 

 end of the Pliocene there is a marked lowering of temperature, and in the 

 higher mountainous areas there was perhaps a beginning of glacial stages. 



Other authorities "* believe that in the Pliocene there occurred a still 

 greater fall of temperature, that while we cannot speak of a uniform climate 

 over all Europe during the Miocene, this is even less the case during the 

 Pliocene. The flora undergoes a corresponding change, and there appear 

 many forms which seem to be identical with modern types, or at least are 

 varieties of recent species. 



Against the gradual cooling theory, however, may be cited the opinion 

 expressed by Deperet in 1893 '' that the Pliocene flora shows great uniformity 

 throughout, even in deposits of quite different ages; that from beginning 

 to end, the Pliocene flora of southern France and Italy shows none but the 

 slightest changes. This opinion is based upon the fact that the deposits 

 of the Val d'Arno, northern Italy, represent the entire range of the Pliocene, 



' Deperet, C, Note sur la Succession stratigraphique des Faunas de Mammifferes Pliocenes 

 de I'Europe et du Plateau Central en particulier. Bull. Soc. Geol. France, Ser. 3, Vol. XXI, 

 1893, p. 529. 



^ De Lapparent, A., Traite de Geologie, 1906, p. 1635. 



' Nicholson, H. A., A Manual of Palaeontology, Edinburgh and London, 1879, Vol. II, 

 p. 476. 



* Schimper und Schenk, Palseophytologie, 1890, p. 821. 



' Deperet, C, Note sur la Succession stratigraphique des Faunes de Mammifdres Pliocenes 

 de I'Europe, 1893, p. 528. 



