leaves certainly belong to a higher and more modern type of dicotyledonous 

 trees than has yet been found even in Jurassic rocks, and that therefore the 

 formation could not be of Triassic age. And though they recognized it in imme- 

 diate superposition to Upper Carboniferous or Permian rocks, they persisted in 

 the former opinion of Doctor Hayden, that the red sandstones of the Dakota 

 group were of Cretaceous age. Some sketches of these plants had been 

 sent to Prof. O. Heer, of Switzerland, and in the meanwhile the whole collec- 

 tion of the leaves had been subjected to the examination of Doctor Newberry, 

 who wrote, "that they did include so many highly organized plants, that 

 were there not among them several genera exclusively Cretaceous, he should 

 be disposed to refer them to a more recent era.'' After remarking that these 

 plants did not represent any vegetable type older than Cretaceous ones, he 

 says that the species, though probably all new, are closely allied to the Cre- 

 taceous species of the Old World. He refers them to the following genera : 

 Sphenopteris, Abietites, Acer, Fagns, Populus, Cornus, Liriodcndron, Pyrus, 

 Alnus, Salix, Magnolia, Credneria, and Ettingshausenia ; this last represented 

 by that peculiar trilobate leaf mentioned above, which from better and more 

 numerous specimens has been since admitted as referable to the genus 

 Sassafras. 



The discussion on the age of the Dakota group, which was then con- 

 sidered as Triassic by Messrs. Swallow and Hawn, and as Jurassic by 

 Professor Marcou, was then complicated by the opinion of Professor Heer, 

 who, answering Doctor Hayden's letter after the examination of the sketches 

 sent to him, stated : That although one of the outlines resembles a Cretaceous 

 genus, (Credneria,) the nervation being obscure, and the others more like 

 Tertiary forms than anything known in the Cretaceous of the Old World, he 

 was inclined to the opinion that they represent Tertiary species. From what 

 is now known of the characters of the flora of the Dakota group, it is clear 

 that, judging from mere sketches, the celebrated professor of Switzerland 

 could scarcely come to a different conclusion. But this has nothing to do 

 with the discovery of the fossil plants of the Dakota group, and with the 

 history of the Cretaceous flora as we know it now. The above remarks 

 merely tend to prove that the first discovery of the vegetable Cretaceous re- 

 mains of this western section is due to Dr. F. V. Hayden, who first by him- 

 self, and afterward in connection with Professor Meek, studied the formations 

 where these remains have been discovered, first in Nebraska and afterward in 



