182 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



sheltered under its branches. In the wide plains liarren of trees, it is seen 

 looming far away as a fringe to a distant horizon, inviting the tired and thirsty 

 caravan of the western prairies to a place of rest, where it finds abundance 

 of fuel and water. 



All the species of Platanus are easily recognized by their leaves, gener- 

 ally of large size, somewhat thick, even coriaceous, especially in a fully ripe 

 state, palmately lobed and three- or five-nerved from above the base of the 

 lamina. These leaves have a strongly marked and a mixed nervation, the 

 primary nerves reaching the point of the lobes, while their divisions, as also 

 the secondary nerves, either end into the points of the teeth or curve along 

 the borders as camptodrome. 



Of the four living species, one, P. orientalis, Linn., is indigenous in Asia 

 Minor, whence it has passed to Europe, and has there become a favorite as 

 an ornamental tree. If more elegant in the distribution of its branches than 

 P. OCX iden talis, it is also generally of much smaller size. Two other species, 

 P. Imdeniana, Mart., and P. Mexicana, Moric, thrive in the valleys of Mexico; 

 the other, P. racemosa, Nutt., belongs to California. 



In the Cretaceous of the Dakota group, we find already four well char- 

 acterized species of this genus, one of which is by its leaves remarkably 

 similar to P. aceroides of tiie Miocene, the ancestor of P. occidentalis. Besides 

 these, three other forms have been ascribed to the same genus with less posi- 

 tive evidence. The Cretaceous formations of Europe have, to the present 

 time, no representatives of Platanus. Neither in the Cretaceous floras of 

 Greenland, of Quedlinburg, and of Moletin, by Heer, nor in that of Nie- 

 dershoena, by d'Ettingshausen, do we find any vegetable remains ascribed 

 to the genus. Nor is it mentioned, to my knowledge, in the manuscript 

 notes obtained from Devey and d'Ettin|shausen on the dicotyledonous plants 

 of the Cretaceous of Belgium. We find the same difference in passing up to 

 the Eocene formations. In the Lower Lignitic of the Rocky Mountains, 

 this disputed ground where Eocene evidence afforded by vegetable remains 

 is contested by animal paleontology, which points to the Cretaceous, four spe- 

 cies oi Platanus are recognized, one of which, P. Haydenii, Newby., is closely 

 allied to our living P. occidentals. The Eocene of Europe has none; at 

 least, no species of this kind is described from the Lower Eocene of Gelinden 

 and of Sdzanne, and I do not find any mentioned in the list of the species 

 recognized at Mount Bolca W(; have to go up to the Upper Miocene of 



