2 ] 2 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



This distribution does not correspond with tliat of tliis order in tlie ancient 

 geological iloras of Europe. It may perhaps explain llie scarcity of the 

 species of the Lnurinece in North America. 



As far as it can be ascertained from fossil specimens, the origin of this 

 order is in the Cretaceous of both continents. Prof Heer has described a 

 species of Sassafras from the Upper Cretaceous of Greenland, and three 

 species of DaphnophyUum from that of Moletin; d'Ettingshausen has recog- 

 nized a Laurus and a Daphnogene in that of Niedershoena, Saxony. As 

 North America has afforded until now more materials for the study of dico- 

 tyledonous plants of the Cretaceous than Europe, it is a matter of course 

 that the number of leaves referable to Laurinea is proportionally large in this 

 formation. Thus we count in the plants of the Dakota group of Kansas and 

 Nebraska, as far as they are known to this time, ten species described under 

 the generic names of Laurus, Persea, Daphnogene, Oreodaphne, and Sassafras* 



On the contrary, when we consider the Tertiary floras of both continents, 

 we find an extraordinarily great difference in the distribution of the Laurincce 

 in favor of the European side, where fourteen species from the Eocene and 

 more than one hundred from the different stages of the Miocene have been 

 described. Among these, four species of Sassafras are recorded, while, 

 though a predominance of leaves referable, to this genus is remarked in the 

 Cretaceous of the Dakota group, no remains of plants positively referable to 

 Sassafras have as yet been found in the North American Tertiary. A mere 

 fragment of a leaf has been doubtfully referred to it, but its characters are 

 too obscure to be considered as evidence. It is a peculiarity of distribution, 

 which has a remarkable correlation with that of the genus Liriodendron, 

 which, although widely distributed in the Cretaceous of Nebraska, has only, 

 like Sassafras, one species predominant in the flora of our time, and has not 

 been observed until now in the North American Tertiary. These anomalies 

 in regard to the distribution of the species in the geological periods may be 

 merely illusive, or a consequence. of insufficient knowledge with the Tertiary 

 flora of this country; and possibly fossil leaves referable to these genera may 

 be found hereafter. They are, however, remarkable enough to merit a record 

 in the documents relating to the history of the present flora. 



All the species of haurima from the American Tertiary may be referred 



* I count only two species of Sassa/raa. Tbe question of reference of the numerous leaves of Saa- 

 aofiaa (Araliopaia) is as yet uneetlUd. (S<e Annual Report, 1H74, p. 34'.J. ) 



