ANALYSIS OF THE DAKOTA GROUP FLORA. 233 



were present in that of the Dakota Group, and that most of tliem liad loft 

 remains of allied specific or generic forms in the intermediate periods. In 

 support of the assertion I may be excnsinl for briefly reviewing- the distri- 

 bution of the more important types of the flora of the Dakota Group as far 

 as they are recognized in the succeeding formations. 



The Myricacea; have only the genus Myrica, which is i-epresented by 

 nineteen species in the flora of the Dakota Group, two of which arc* iden- 

 tifled in the schists of Atane, one of these passing also to the Upper Creta- 

 ceous stage of Patoot. Of the species of the Dakota, Group Mi/rica 

 emarginata Heer, recognized at Atane and Patoot, has its relation to M. 

 salicina of the Miocene; another, M. aspera Lesq., is the type of Jf. rcrifcra 

 Linn., the bayberry or wax myrtle now inhabiting the sea and lake shores 

 of the United States; AL Stcnihenjii has its affinity to a species foTUid at 

 Sezanne. Leaves of Myrica of coriaceous texture, having the nervation 

 more or less obscured by immersion in the thick parenchyma, are generally 

 of difficult determination, and their generic references therefore remain 

 doubtful in some cases for a long time. Mi/rica lo)i<ja Heer, for example, 

 was first placed in the Pi'oteaceje. Now, a large number of well preserved 

 leaves have been i-ecognized by their nervation as truly referable to this 

 genus, whose presence in the Cenomanian flora is confirmed by seeds and 

 scales of catkins abundantly found in the shale of the Dakota Group. 

 Myrica Torreifi Les(j., a species also rect)gnized in the Laramie Group, has 

 remarkably fine and distinctly characterized leaves. As yet its affiliation 

 with Ch-etaceous types is not known. Schimper mentions its relation to M. 

 huffifoUa Saji., of the Oligocene of France, and this, like 31. GrtcJ/ii Heer, 

 is closely allied to the living* M. califonika Cham. 



A large number of small leaves, very finely preserved in concretions, 

 have lately been collected in Kansas. Considering their essential charac- 

 ters, the form and nervation of the leaves, 1 regard them as related to 

 Betula, and have described them under the name of Betulites. Saixirta, 

 to whom a number of specimens have been sent, is disposed to i-efor them 

 to Viburnum. The leaves, as mentioned in the descriptions, ha\e the same 

 facies and the same chai-acters as those of our living Betula ni/jra, and I am 

 the more disposed to admit them as the original representatives of the genus, 

 since three species of Betula are recognized by Heer in the Senonian flora 

 of Patoot, in leaves that are all remarkably similar in form, size, nervation 

 and even in the peculiar dentation of their borders, to thos(» of the Dakota 

 Group. The same remarkable analogy of characters is observable, espe- 



