38 



Salicinece ; groups represented, indeed, in a large proportion, but not larger 

 than in the vegetation of the present time. Of the Gamopetalous, it has the 

 Bicornes, Ebenacecc, &c. Of the Polvpetalous, the Magnolia, Menispermacece, 

 Sapindacece, &c, and therefore it has representatives of all the classes of plants 

 without disproportion in one degree or the other, as compared to what is con- 

 sidered the scale of the vegetable kingdom. This seems to prove a collateral 

 development of different primitive types, and therefore the appearance at 

 certain epochs of those original forms which, at each geological period, have 

 changed the character of the vegetable world, and which do not have any 

 connection with antecedent types. On this point of view, it is evident that 

 the flora of the Dakota group is as widely disconnected from that of the Ju- 

 rassic, even of the Lower Cretaceous, or as distincly original, as are the flora 

 of the Carboniferous compared to that of the Devonian, or the Permian types 

 compared to those of the Cretaceous. 



§8. — The flora or the Dakota group in relation to climate. 



The specimens from which this flora has been studied until now have 

 been obtained in different localities over the whole extent of the area covered 

 by the formation, from the 39° to the 47° of north latitude. In this space 

 of 18° the general facies of the vegetation has been apparently preserved 

 without marked changes in relation to latitude. At least the evidence 

 of a variation indicating atmospheric differences in the distribution of what 

 might be called northern and southern types, is not positive enough to be 

 considered as in correlation with the vegetable distribution of our present 

 time. The specimens obtained from Minnesota by Prof. Jas. Hall represent 

 a greater proportion of crushed fragments of conifers, stems, and cones espe- 

 cially, of which a few seeds only, doubtfully referable to the genus Cunning- 

 hamites, Presl., are recognizable. With these they have fragmentary leaves 

 of Laurus, of Lyriodendron, Sapotacites, Ficus, Andromeda, referable to the 

 species published from the specimens of the Blackbird Hills of Nebraska, by 

 Doctor Newberry and Professor Heer. These same paleontologists have 

 also described, from North Nebraska, species of Platanus, Populus, Diospiros, 

 Rhamnus, Quercus, Fagus, Sassafras, Proteoides, Magnolia, Lyriodendron, 

 and Acer or Acerites. All these genera are also represented in the specimens 

 of Doctor Hayden, from Decatur, and some of them also by the leaves which 

 the same geologist has collected in South Nebraska, Lancaster and Gage 



