CRETACEOUS FLORA. 



Flora of the Dakota group.! 



are referable to the Urgoiiian or Lower Cretaceous, a group of plants has been dis- 

 covered composed of 1 algoid, 3 ferns, 12 Cycadece, 5 conifers and ;1 monocotyledon. 

 The characters of these plants are like those of the plants of the Wealden and of the 

 Jurassic. In Greenland, the Swedish expedition under the direction of Nordens- 

 kiold also found at Korne, in strata which by their fauna are referable to about 

 the same geological subdivision of the Lower Cretaceous as the Vernsdorf schists, 

 a group of 88 species of plants representing 48 ferns, 1 Marsilia, 1 Lycopod, 

 3 species of Equisetum, 14 Zamiece, 17 conifers, 5 monocotyledons with a few frag- 

 ments of a leaf of a dicotyledonous species, a Populus which Heer, who has examined 

 and determined the plants, has named Populus primceva. Here still we find precisely 

 the same elements of vegetation as in the Wealden and the Jurassic, except that 

 leaf of Populus. 



It is from this point or from above the lower Urgonian subdivision that 

 appear the earlier American Cretaceous strata, those of the Dakota group, imme- 

 diately superposed, in the western states to the Permian magnesian limestone. 

 Above this formation and up to the base of the Tertiary, one passes, in ascending 

 through the four geological subdivisions fixed by Hayden and Meek, the Benton, the 

 Niobrara, the Fort Pierre and the Fox Hill groups. The fauna of the Benton group 

 is that of the Cenomanian of d'Orbigny; by its position the Dakota group is referable 

 to the same subdivision, while its flora is that of the Middle Cretaceous of Greenland 

 and of the Quader sandstone of Germany. Its geological stage is thus positively 

 fixed as succeeding the Urgonian, where, as seen above, the types of the vegetation 

 are still mostly Jurassic and without any trace of dicotyledons, except that Populus 

 found by Heer among the 88 species of Korne. Now, the flora of the Dakota group 

 is of a totally different character. As known at the present it has in more that 200 

 species of plants which have been determined, 1 Equisetum, 6 ferns, 6 Cycadece, 10 

 conifers, 3 monocotyledons and 175 dicotyledons, these being in the proportion 

 of 81 per cent, while the other groups of plants, including the monocotyledons, 

 remain relatively the same. The flora of Atane which has been discovered in 

 Greenland in strata at a higher stage of the Cretaceous than that of Korne, and 

 which is also referable to the Cenomanian by its fauna, has about the same elements 

 in its composition. In 177 species described by Heer, it has 3 Fungi (ffypoxylece upon 

 leaves of dicotyledons), 31 ferns, 1 Marsilia, 1 Selaginella, 1 Equisetum, 1.1 Cycadece. 24 

 conifers, 8 monocotyledons and 97 dicotyledons, or a proportion of 55 per cent, of 

 dicotyledons. This group of plants has ;i greater number of ferns and conifers than 

 that of the Dakota group, a difference evidently due to the influence of local atmo- 



* 



spheric circumstances. In collections recently made of plants of the Dakota group, 



