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Counties. These represent more especially species of Populites, Platanus, 

 Quercus, and Belulu. The same genera are all recognized in the specimens 

 from Kansas, with the exception of Populus, Salic, Rhamnus, Betula, Fagus, 

 while Kansas has exclusively as yet representatives of the genera Liquidambar, 

 Credneria, Dombeyopsis, Pterospennites, and Aralia. The distribution, accord- 

 ing to species, is also somewhat different in Kansas and Nebraska. The 

 north has very few leaves of Sassafras, and these represent one species only ; 

 while in Kansas, especially near its southern limits, a large portion of the 

 fossil-leaves belong to five species of this genus. Per contra, the leaves re- 

 ferable to Laurus are more and more numerous toward the north in Nebraska 

 and Minnesota, where also are found in larger proportion the leaves referable 

 to Quercus, which there represents five species, while one only is described 

 from Kansas specimens. In considering these differences in the distribution 

 of typical forms, and the general facies imprimed to the flora by this distribu- 

 tion, one might suppose that the flora of the Dakota group indicates in Kan- 

 sas, by its character, a higher degree of temperature. This supposition re- 

 ceives some authority from the luxuriance of the vegetation, marked in Kansas 

 by Crednaria, Pterospennites, and Dombeyopsis, genera represented as yet in 

 this State only, and all with leaves of large size ; and by the diffex - ence in the 

 proportion of the leaves of species of some genera common to both States. 

 The species of Platanus, for example, P. netvberrii, P. obtusiloba, recognized 

 in Nebraska, have smaller leaves than Platanus heerii, of Kansas. The two 

 species of Liriodendron, of Nebraska, are of a very diminutive type compared 

 with that of L. giganteum, of Kansas. Sassafras mirabile, of Kansas, has 

 leaves measuring more than one foot in diameter, while S. creteceum, of Ne- 

 braska, is represented by small leaves. These differences may be ascribable 

 to local circumstances, to more or less favorable exposition, to a more fecund 

 composition of the ground, &c, rather than to a general atmospheric devia- 

 tion. This seems to be proved by observations of a more general character. 

 Considered as a whole, most of the types of the Dakota group, related 

 to those of our present flora, represent a moderate climate, like the one pre- 

 vailing now between the 30° and 45° of latitude north. The vegetable types 

 more distinctly characterized by their leaves, and which are recognized by 

 all the paleontologists, Salix, Fagus, Platanus, Sassafras, Aralia, Magnolia, 

 Liriodendron, Menispermum, Paliurus, Pints, &c, are all co-ordinate to iden- 

 tical climatic circumstances, or to the same average temperature which 



