GEOLOGICAL SUEVEY OP THE TERKITOEIES. Zl 



namomum and Fieus of the Tertiary, and the Credneria, with analogous 

 tyi^es, of the Cretaceous. Cinnamomum and Fi'cus, however, have not 

 left altogether our North American continent, but they have lost their 

 importance in the vegetation of ours, at least compared with the place 

 which they occupied in the Tertiary times. 



Each formation, of course, has lost some of its vegetable types in 

 acquiring new ones. The march of the increase and decrease of the 

 typical representatives, the search for appreciable causes which may 

 have fostered modifications of forms, is one of the most interesting parts 

 of the study of vegetable paleontology. 



On this subject, it is already evident, to my mind at least, that the 

 data presented in these notes, and in the former report of Dr. Hayden, 

 indicate a remarkable analogy of our present flora with that of the Ter- 

 ti'dry, and of this, too, with the flora, considered as of the IsTorth Ameri- 

 can Cretaceous, pointing out its ancient origin. But the indications are 

 not yet conclusive. The chain in the modifications of types from the 

 oldest formations (Upper Cretaceous) to the newer ones, (Upj^er Terti- 

 ary,) and from these to our flora, appears especially defective in its last 

 link, our knowledge with the Pliocene flora being as yet too limited. 

 The only locality, known to me, where strata of this age, with remains 

 of fossil plants, are xposed, is, as remarked in Report, p. 318, at Colum- 

 bus, Kentucky, on what is called the chalk-banks of the Mississippi. 

 The plants which I obtained there, in a too short tour of exploration, 

 are, to my opinion, scarcely, if at all, distinguishable from species now 

 living in the Southern States. I then identified, as far as identity can 

 be ascertained from fossil leaves, Quercus virens, Michx. ; Gastanea nana^ 

 Muhl.; Ulmus alata, Michx.; Planera Gmelini, Michx,; Prinos integri- 

 folia, Ell. ; Ceanothus Ainericamis, L. 5 Carya oUvaformis, Kutt; Gleditchia 

 triacanthos, L. ; and Acorns calamus, L. Professor Heer, to whom I sent 

 sketches of the leaves representing these species, objected to my deter- 

 minations, at least for some of them, and I have no doubt but that he is 

 right in some points. However, the identity of a number, at least, of 

 the species, is undeniable, indicating, therefore, an intimate relation of 

 our arborescent flora with that of the Pliocene. It would be important 

 to obtain a series of specimens numerous enough to give positive evi- 

 dence of the degree of that relation. The deposits of leaves above 

 Paducah belong to a more recent epoch, the Terrace epoch, apparently. 

 All the specimens of leaves obtained from this formation represent, with- 

 out doubt, even in the opinion of Heer, species of our time. In follow- 

 ing, then, the researches for the purj^ose of studying the march in the 

 flora from the Cretaceous times till ours, the strata of the West and 

 those of the Mississippi could furnish documents for such a clear record 

 as none other could be got elsewhere on the same subject. 



For conclusion it is right to recall in a few words the essential points 

 marked in this examination : 



1st. It adds to our list of fossil species of the Tertiary 20 new forms, 

 and describes 21 others, known already from the Miocene of Europe, 

 but not as yet observed in our Tertiary flora. The number of its spe- 

 cies is thus increased to 231. 



2d. It fixes the geological horizon of three localities in different 

 stages of the Tertiary, and marks the location of a group of specimens 

 of as yet unknown origin. 



3d. It more distinctly points out the relation of some important strata 

 for ascertaining contemporaneity or difference of age. 



4th. It indicates more i^ositively modifications in the characters of 

 ±he Tertiary flora of the North American continent according to climatic 



