22 PLANT GEOGRAPHY 



Mimosece, and others, suggesting a sub-tropical flora in 

 Central Europe resembling that of Australia to-day. 

 There is some indication of latitudinal zones at this 

 period. 



The coal-seams of the Laramie series, towards the close 

 of the American Cretaceous, have yielded some 250 

 species, including palms, figs, oaks, poplars, planes, and 

 magnolias in considerable variety, three species each of 

 Aralia, Rhus, and Sequoia, besides Ginkgo and Eucalyp- 

 tus : a list which perhaps suggests that there was then 

 also a considerable divergence between the American 

 and the European floras. 



Passing to the lowest Eocene beds of Europe at 

 Gelinden, near Li^ge, and in various places in France, 

 we have oaks, chestnuts, laurels, Aralias, myrtles, 

 bamboos, and fan-palms, a flora comparable to that of 

 Southern Japan. In the Woolwich and Reading beds 

 of Southern England planes, laurels, figs, Robinia and 

 Taxodium suggest a sub-tropical climate and certainly 

 present an American " facies," though the now Aus- 

 tralian genus Grevillea also occurs. The drifted plant- 

 remains in the overlying London clay are more tropical 

 in character, including, with Sequoia, Ginkgo, and 

 Podocarpus, oaks, Liquidambar, Diospyros, Laurus, 

 Eucalyptus, fan-palms, and the fruits of Nipa, resembling 

 those now carried down by the waters of the Ganges. 

 Yet more tropical are the plants from the pipe-clays 

 of the Bagshot series at Alum Bay and Bournemouth, 

 comprising, as they do, Cassia, C&salpinia, Dryandra, 

 Eucalyptus, palms, custard-apples, and a cactus. 



The persistence of the American type of this flora in 

 America, as compared with its disappearance in Europe, 

 may be explained by the fact that, when unfavourable 

 colder conditions set in, there were in America no barriers 

 to a southward migration or to a northward return, the 

 great fold-mountains of Secondary rocks running north 

 and south ; whilst in Europe the east and west mountains, 

 Mediterranean Sea, both mainly of Tertiary origin, and, 

 perhaps, the Sahara, did offer such insuperable barriers. 

 Owing to the extermination of such genera as Diospyros 

 and Anona our existing European flora is poorer in 

 large fruits than that of America, or of our own area 

 in earlier Tertiary times. 



In Grinnell Land, in 81 N. lat., eleven conifers, an 



