CENO^OIC TIME — TERTIARY. 939 



arises whether these events are not in somp way a consequence of the con- 

 dition of the crust then for the first time reached. The conclusion has been 

 before stated} it is here announced in its place in geological history. 



CLIMATE. 



The climate of the United States, even the northern, during the early 

 Tertiary, was at least warm-temperate, as indicated by the fossil plants. 



There is evidence, as Asa Gray has remarked (1859, 1872), from the dis- 

 tribution of Tertiary plants in the Arctic, made known by Heer and others, 

 and their relation to similar kinds in the eastern United States and in Asia, 

 that the northern parts of the continents of America, Asia, and Europe were, 

 during that age, under a nearly common forest vegetation, with a compara- 

 tively moderate climate. The genus Sequoia, of California, has its species 

 (as Heer has shown) in the Eocene of Greenland, Arctic America, Iceland, 

 Spitzbergen, northern Europe ; and one Greenland species is very near the 

 great Calif ornian *S'. gigantea ; and these were successors to Arctic Cretaceous 

 species. There were two species of Libocedrus in the Spitzbergen Miocene 

 (Heer) ; and one {L. decurrens Heer) now lives with the Redwoods of Cali- 

 fornia, while the other occurs in the Andes of Chile. Gray adds that the 

 common Taxodium, or Cypress, of the Southern States, occurs fossil in the 

 Miocene of Spitzbergen, Greenland, and Alaska as well as Europe, and also, 

 according to Lesquereux, in the Rocky Mountain Miocene. The Arctic 

 Miocene-is now made by Dawson and others probably Eocene in age. 



Europe evidently passed through a series of changes in its climate, from 

 tropical to temperate. According to Von Ettingshausen, the Eocene flora of 

 the Tyrol indicates a mean temperature between 74° and 81° F. ; and the 

 species are largely Australian in character. The numerous Palms in England, 

 at the same period, indicate a climate but little cooler. 



The Miocene flora of the vicinity of Vienna the same author pronounces 

 to be subtrojyical, or to correspond to a temperature between 68° and 79° F. ; 

 it most resembles that of subtropical America. Farther north in Europe, 

 the flora indicates the ivarm-tem2')erate climate characterizing the North 

 American Tertiary ; and it is also prominently ISTorth American in its types. 

 In the Pliocene, the climate was cooler still, and approximated to that of 

 the existing world. 



The North American feature of the Miocene forests of Europe was proba- 

 bly owing to migration from America through the Arctic regions, and not 

 from Europe ; for a number of the European s|)ecies, as shown by Lesque- 

 reux existed already in the American Laramie and Eocene. The Australian 

 feature also may have been a result of migration, but from the opposite 

 direction. The Indian Ocean currents favor migration northward, along the 

 borders of Asia, and not that in the opposite direction. 



What was the temperature of North America and the other continents 

 at the close of the Tertiary, as a consequence of the addition of thousands of 

 feet, and in some regions, of tens of thousands, to the height of the land, is 

 to be learned from the events of the following era, the Quaternary. 



