162 TREE ANCESTORS 



humid climate and supported a rich fauna and flora, plane-tree 

 leaves nearly two feet in diameter have been collected. The most 

 southern Eocene record in the European area thus far discovered 

 is in deposits interbedded with the basaltic lava flows of this period 

 on the Isle of Mull from which staminate catkins, fruit and leaves 

 have been described as Platanus hehridicus. 



The Oligocene period which succeeds the Eocene was a period 

 of land emergence and dry hot climates. Consequently the locali- 

 ties where plane trees may be presumed to have flourished have 

 been regions where their . remains failed to become preserved. 

 North America is especially poor in Oligocene plant remains of all 

 kinds and no Oligocene species of Platanus have been discovered 

 although they must have been abundant since they again appear 

 in the North American fossil record after the close of the Oligocene. 

 Two or three species of Platanus of Oligocene age have, however, 

 been discovered in European plant beds. 



The Oligocene period was followed by the Miocene, a period 

 during the early part of which the Oligocene elevation culminated 

 and subsidence set in. Tliis was accompanied by a striking cli- 

 matic change, at least in the eastern United States. In our 

 Southern States the Oligocene faunas and floras were such as 

 flourish today under the equator. The succeeding Miocene de- 

 posits which overlie them in northern Florida and elsewhere con- 

 tain leaves of trees of the temperate zone and the remains of a 

 marine fauna which had advanced from the New Jersey-Maryland 

 region as the tropical fauna was driven southward. North America 

 does not contain very many Miocene plant beds but nevertheless 

 the remains of plane trees have been collected from Oregon and 

 CaHfomia on the Pacific coast, from the Yellowstone Park, and 

 from Virginia on the Atlantic Coast. In Europe where Miocene 

 plant beds are more frequent the leaves of Platanus are abundant 

 and widely distributed although they belong to but few species — 

 five have been described. One of these, Platanus aceroides, first 

 described by Goeppert in 1852, is the dominant Miocene form of 

 the whole Northern Hemisphere. Its European records include 

 Baden, Switzerland, Silesia, Italy and many localities in Austria 



