156 ZOOLOGICAL GEOGRAPHY. [part hi. 



America corresponds generally with that of the European Miocene, 

 yet many of the tropical, and especially the Australian types, 

 such as Hakea and Dryandra, are absent. Owing to the recent 

 discovery of a rich Cretaceous flora in North America, pro- 

 bably of the same age as that of Aix-la-Chapelle in Europe, we 

 are able to continue the comparison; and it appears, that at 

 this early period the difference was still more marked. The 

 predominant feature of the European Cretaceous flora seems to 

 have been the abundance of Proteacese, of which seven genera 

 now living in Australia or the Cape of Good Hope have been 

 recognised, besides others which are extinct. There are also 

 several species of Pandanus, or screw -pine, now confined to the 

 tropics of the Eastern Hemisphere, and along with these, oaks, 

 pines, and other more temperate forms. The North American 

 Cretaceous flora, although far richer than that of Europe, contains 

 no Proteacese or Pandani, but immense numbers of forest trees 

 of living and extinct genera. Among the former we have oaks, 

 beeches, willows, planes, alders, dog-wood, and cypress ; together 

 with such American forms as magnolias, sassafras, and lirioden- 

 drons. There are also a few not now found in America, as 

 Arauca-ria and Cinnamomum, the latter still living in Japan. 

 This remarkable flora has been found over a wide extent of 

 country — New Jersey, Alabama, Kansas, and near the sources of 

 the Missouri in the latitude of Quebec — so that we can hardly 

 impute its peculiarly temperate character to the great elevation 

 of so large an area. The intervening Eocene flora approximates 

 closely, in North America, to that of the Miocene period ; while 

 in Europe it seems to have been fully as tropical in character as 

 that of the preceding Cretaceous period ; fruits of Nipa, Pandanus, 

 Anona, Acacia, and many Proteacese, occurring in the London 

 clay at the mouth of the Thames. 



These facts appear, at first sight, to be inconsistent, unless we 

 suppose the climates of Europe and North America to have been 

 widely different in these early times ; but they may perhaps be 

 harmonised, on the supposition of a more uniform and a some- 

 what milder climate then prevailing over the whole Northern 

 Hemisphere ; the contrast in the vegetation of these countries 



