234 THE FLORA OF THE DAKOTA GROUP. 



cially in Betula coryloides Ward, of the Laramie flora, and henceforth in 

 numerous species of the Tertiary, which are more or less closely allied to 

 those of the present flora of North America. Besides the three species 

 described by Prof. Ward from the Laramie, one other lias been described 

 from Golden, two from the Green River Group, four from the Miocene of 

 Alaska and Oregon, and one from the auriferous gravel deposits (Upper 

 Miocene or Pliocene) of Califonua. In all these species the original type, 

 represented in the niunerous figui'es of leaves of Betulites, this volume (PI. 

 IV and PI. V), is more or less discernible, as well as in some of the eight 

 species, all of wide distribution, which are still living in North America. 

 The only living species exclusively pertaining to tlie flora of California, B. 

 occidentalis Hook., has its ancestor in B. ceqnuUs Lesq., of the auriferous 

 gravel deposits of the same State. 



With a less degree of evidence we may follow a gradual distribution 

 of the species of Alnus from the Cenomanian upward. A species of Alnites 

 is described by Dr. J. S. Newberry from specimens procured in the Dakota 

 Group of Nebraska, and another by Sir William Dawson from the ]\Iilk River 

 series of Canada. A species more cleary defined, Alnus profogrea Heer, is 

 from Patoot. Then we have another from the Laramie^ three from the 

 Green River Group, and four from the Miocene of Alaska and Oregon. 

 Among the last, A. Kcfersfeinii is the most common species of the Miocene 

 of Europe as well as of America. Of the six species of Alnus now living 

 in the United States the relation of A. incwna Willd., especially tlie variety 

 virescens, common along the mountain streams from Colorado westward, is 

 clearly marked with A. Kefersteinii, while that of A. maritima Nutt., of the 

 Atlantic States, is still more evident with A. coraUiiia Lesq., of the Miocene 

 of Oregon. 



In the Cupulifera3 a large number of vegetable remains of the Dakota 

 Group, especially leaves, are referred to Quercus or Dryophyllum. The 

 leaves are generally determined by distinct characters, which are easily 

 followed in their various modifications through geologic time. Of eighteen 

 species of Quercus, seven of the subdivision Dryophyllum are described 

 from the Dakota Group. Heer has six species from the schists of Atane 

 and eight from the Senonian of Patoot. Of these, Q. hkracifoUa Hos., of 

 the Senonian of Westphalia, is present in the schists of Atane, in the Dakota 

 Group, and in the flora of Patoot; Quercus hexagona Lesq. is reproduced in Q, 

 trniihnUU'S Heer, of the Senou of Atanekerdluk. In the specimens obtained 

 by the scioutific expedition of Princeton, which I consider as referable to the 



