12 CRETACEOUS AND TERTIARY FLORA, 



Aralia, as Plaianns f/randifolia, P. dkjitata, P. Jatropcefolia, P. Hercules, Ung., 

 and P. latiloha, Newby. The leaf of Sassafras {Araliopsis) Platanoides 

 (pi. vii, fig. 1) has the fades and some of the characters of Platanus more 

 distinctly defined than any other of the group; the same characters are 

 even reproduced in Aspidiophi/Ilmn jylatanifolium (pi. ii, fig. 4). 



The geological distribution of the genus Platanus is truly remarkable. 

 No trace of it is recorded as yet in the Cretaceous of Europe, not even in 

 the Paleocene and Eocene of France, so rich in fossil vegetable remains. 

 Its first appearance in Europe is in the Upper Miocene of Oeningen. and 

 of Austria and Italy, where it is represented by two very similar forms, 

 Platanus GuiUelmce and P. aceroides, two species present in the same 

 formation from the northern parts of the arctic lands to Italy. It is fol- 

 lowed in the Upper Tertiary, or Pliocene, of this last country by Platanus 

 Academioe, Gaud., related as progenitor, perhaps, to the living P. orientalis. 

 I have remarked above that the relation of leaves of the Dakota Group to 

 Platanus has been considered as doubtful by some European paleon- 

 tologists. This doubt may have been induced by the understanding of the 

 total absence of Platanus leaves in the Cretaceous and Lower Tertiary of 

 Europe. If so, it is certainly removed by the presence in our lignitic 

 Eocene of some very beautiful and well characterized species of this genus : 

 Platanus Haydenii and P. Reynoldsii, Newby. These species, discovered 

 first in the Tertiary of the Upper Missouri River, near Fort Union, are pre- 

 dominant at Golden, Colorado, and are also found at Black Butte Station. 

 The third Tertiary Group, that of Carbon, has, for the more numerous 

 representatives of its Flora, leaves of Platanus aceroides and P. Guillelmce. 

 No species of this genus has been described from the Oligocene Green 

 River Group; but we have from the Upper Terliary {Pliocene) of Cal- 

 ifornia very fine specimens of leaves of two species, P. appendiculata and 

 P. dissecta, closely related by their characters to the living P. occidentaUs. 

 Therefore, and considering the geological records, we may trace the origin 

 of Platanus as far down as the North American Cretaceous, and follow its 

 development throiijh nearly all the stages of its Tertiary to our present 

 time, by a number of closely allied intermediate forms.^ 



' PUUanus Heerii, L. aud P. affinU L. are mentioned by Heer in the Cretaceous of Atane, Greenland. 



