344 GEOLOGICAL SURVEY OF THE TEERITORIES. 



Australian types, but from analogy I doubt if we may ascertain the 

 presence of any of these types even in our oldest floras. Now, we have 

 in our Cretaceous, as more easily recognized by their likeness to living 

 species, leaves of Sassafras and of Lirlodendron, the tulip-tree. If I 

 should judge by the profusion of leaves of Sassaft'as which I have seen 

 in the shale of the Dakota group, in the valley of the Saline liiver, and 

 around Fort Ilarker, in Kansas, I would assert that more than two-thirds 

 of the vegetation of this epoch did consist of species of this genus. 

 But then, as now, however, related species appear to have lived in 

 groups, perhaps over limited areas ; for at other localities Dr. Ilayden 

 found especially leaves of Liriodendron, Juglans, and of Flatamis, genera 

 scarcely represented at Salina and Fort Harker. The groups may still 

 differ elsewhere. The present remarks, however, must he limited to 

 what is known, and Sassafras and Liriodendron 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 positively referable to 

 these genera. I have described from specimens marked " six miles above 

 Spring Cafion^^ the lower part of two leaves as, perhaps, referable each 

 to one species of Sassafras and of Liriodendron ; but such fragments 

 cannot be taken into consideration for positive evidence in a compari- 

 son like this. They may represent leaves of different affinity. In the 

 Miocene of Europe, per contra, tlie above genera are represented by a 

 number of species. One of each, Liriodendron and Sassafras, are de- 

 scribed 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 Eocene. It has 

 left its remains, however, in the Miocene of Greenland in four dif- 

 ferent species. Seeds, too, of undecided affinity are referred to Ftcrosper- 

 mites from the Miocene of Oeuingen. The Eocene species of Platanus, 

 at least the three splendid species described by Dr. Newberry — Platanus 

 Haydcnii, P. Maynoldsii, P. nohilis — have no relation either to Miocene 

 or Cretaceous types, which are mostly analogous to Platanus aceroides. 

 This last sj)ecies, however, like its relative, P. GuiUelnue, areas common iil 

 the upper American Eocene as the former ones are in the lower. — Of 

 the si)ecies of Salix I have remarked already that they are more numer- 

 ous in the Cretaceous than in the Eocene of ours. They re-appear more 

 abundant in the Upper Tertiary groups of Green Eiver. — Liquidambar, 

 the sweet-gum, has one of its species in the Cretaceous. It has been 

 described from one leaf only, but I have found recently a number of 

 specimens of the same near Fort Harker. Our Eocene has nothing like 

 it, while remains of one species, Liquidamhar europeum, are found over 

 the whole Miocene of the old continent, together with a large number 

 of forms as yet doubtfully referable to this genus. Our Cretaceous leaf 

 is, perhaps, of this kind, on account of the entire divisions of its leaves ; 

 but this does not change its affinity to Miocene forms of Europe. Mas- 

 salon go, in his Flora-del-Senigalliese,has described and figured n Liquid- 

 ambar scarabellianum, with the divisions of the leaves entire, a form much 

 like that of our Cretaceous species, only smaller; and Unger, in Flora 

 of Sotska, has named Platanus sirii, a leaf still more similar to ours. 

 These leaves are considered by other authors as referable to the genus 

 Acer. This does not make any difference. They represent a type of 

 our Cretaceous and of the Miocene of Europe ; as yet not seen in our 

 Eocene. — It- is the same with Acer (maple) and Quercus, (oak.) They are 

 marked in our Cretaceous, the first by Acer obtusilobum,vfith chuTucterB 



