MEDIAEVAL OR MESOZOIC TIMES. 185 



kota Cretaceous Group." I have also added these fossils to the cabi- 

 net of the State University, where they can be seen. 



Origin of the Flora of the Dakota Group. No geological ques- 

 tion is more involved in doubt than the source or origin of the 



O 



flora of the Dakota Group. So far as known it is entirely discon- 

 nected from all antecedent types. "The remarkable disproportion 

 between the number of genera compared to species in the Dakota 

 Group seems at first to corroborate the system so generally admitted 

 now of a successive development of vegetable forms, according to 

 a supposed rule of progression of more complex forms constantly 

 originating by the multiplication or subdivision of simple organs of 

 inferior types." (Lesquereux). According to this view, as we go 

 back in time there should be few species and more genera, and 

 what species there are should differ only slightly from the characters 

 assigned to the genera. There are, however, some genera in this 

 group represented by from six to eight species, and it is equally 

 probable that the others, if all the forms had been preserved, would 

 liave been fully as abundant. 



It is, however, not scientific to depend on suppositions on either 

 side. The facts, alone should be considered. And the facts, so far 

 as is now know^n, as already remarked, totally disconnect this flora 

 from all that went before it. 



We have already seen that the Dakota Group rests directly on 

 the Upper Carboniferous or Lower Permian. The Upper Per- 

 mian, the Triassic, Jurassic, and Lower Cretaceous are all wanting. 

 The uppermost vegetable remains in the Permian, a calamite in the 

 Rocky JMountains, is yet palaeozoic in type. Even if we look at the 

 vegetable remains in the Triassic of South Carolina and Virginia, 

 nothing is found but forms representing ferns, equisetacese, cycads 

 and conifers. Even in Europe the Triassic and Jurassic floras 

 belong to the same types. No dicotyledonous leaf has been found 

 anywhere before the Cretaceous. Now the slightest examination 

 of the flora of the Dakota Group shows the "prodigious difference 

 which separates this flora from that of any former epoch, even 

 considering the antecedent vegetation of the Jurassic, known as it 

 is from European specimens and publications." It differs equally 

 from anything yet found in the Jurassic in America. "The ferns, 

 conifers and cycads with a few equisetae, which constitute the 

 whole known flora of that epoch are all of peculiar types, without 

 relations to any of the species of the same families recognized as 

 yet in the flora of the American Cretaceous." (Lesquereux). 



