442 LL. Lesquereux—Rocky Mountain Lignitic Formation. 
groups, perhaps over limited areas; for at other localities Dr, 
ayden found especially leaves of Lirioaendrons, Juglans, and 
of Platunus, genera scarcely represented at Salina and Fort 
Harker. The groups may still differ elsewhere. The present 
remarks, however, must be limited to what is known, and Sas- 
safras and Lvriodendron have to be considered yet as the genera 
the most profusely represented in the flora of the Dakota group, 
even more, perhaps, than they are in that of the present time. 
The American Eocene has not yet shown any remains posi- 
tively referable to these genera. I have described from speci- 
mens marked “ six mil-s above Spring Caiion” the lower part of 
two leaves as, perhaps, referable each to one species of Sassa- 
Jras and of Liriodendron; but such fragments cannot be taken 
into consideration for positive evidence in a comparison like 
this. They may represent leaves of different affinity. In the 
Miocene of Europe, per contra, the above genera are represented 
y a number of species. One of each, Lariodendron and Sassa- 
Jras, are described from the Miocene flora of Greenland, and 
more from that of Germany and Italy 
The genus Credneria, or Pterospermites, appears to represent 
forms of leaves of a lost type. We have no representatives of 
it at our time, nor have any been seen in the ene. It has 
left its remains, however, in the Miocene of Greenland in four 
different species. Seeds, too, of undecided affinity are referred 
to Pterospermites from the Miocene of Oeningen. The Hocene 
species of Platanus, at least the three splendid species described 
by Dr. Newberry—Platanus Haydenii, P. Raynoldsii, P. nobis 
—have no relation either to Miocene or Cretaceous types, which | 
are mostly analogous to Platanus aceroides. This last species, 
however, like its relative, P. Guillelme, are as common in the 
upper American Eocene as the former ones are in the lower.— 
Of the species of Salix I have remarked already that they are 
more numerous in the Cretaceous than in the Hocene of ours. 
They re-appear more abundant in the Upper Tertiary groups of 
Green River. | 
n the 
Cretaceous. It has been described from one leaf only, but I 
Fort Harker. Our Eocene has not ing like it, while ore 
Miocene forms of Europe. Massalongo in his Flora-del- 
galliese, has described and figured a Liguidambar scarabellianum 
with the divisions of the leaves entire, a form much like 
Pati em 
