438 FLORA OF THK LARAMIE GROUP. 



usually overlie these coal beds tell us that the rate of subsidence had 

 now exceeded that of the growth of tlie deposit and the shallow sea had 

 gained access, burying the last of the plants under its siliceous or argil- 

 laceous precipitations where they were preserved. Almost everywhere, 

 even when no leaves or twigs are i)reseut, we find the stout subter- 

 ranean rhizomas of the -cane and the scouring rush, which, not having to 

 be covered uj), stood a far better chance to be preserved. But in num- 

 berless i)laces the profusion of leaves is so great that there is too little 

 rock between them to render it easy or even possible to separate them 

 and obtain complete specimens. Above the plant beds, and occniiying 

 the intermediate strata between these more carbonaceous deposits of 

 coal, reeds, and leaves, we find thicker and often massive beds of sand- 

 stone or marl, which seem to denote the presence over the former de- 

 posits of dee]> water produced by continued subsidence and tlie reces- 

 sion of the shore lines to distances too great for the access of the falling 

 leaves, and the continuance of these conditions through prolonged pe- 

 riods of time. 



If now we compare the flora of the great Laramie group, as thus de- 

 scribed, with its invertebrate fauna, as elaborated by Dr. White, we 

 find that iu its ensemhle the former is much more variable than the lat- 

 ter. Tiie dicotyledonous species differ greatly at different parts of the 

 area covered by the rocks of this group, so greatly, indeed, that it is 

 not suri)rising that both Mr. Lesquereux and Dr. Newberry regard the 

 Fort Union plants as belonging to a difl'ereut age from those of the 

 Wyoming and Colorado Laramie. Still, as 1 shall endeavor to show, 

 this difference is not so great as it at first appears, aud not sufiflcieut 

 to warrant tiiis conclusion. In the first place, this difterence appears 

 chiefly in the dicotyledonous species, the only marked exception being 

 that palms occur much more abundantly in the southern than in the 

 northern districls. The same forms of reed-like plants are common at 

 all points, while the Conifera; do not difl'er more than might be ex- 

 pected on the theory of synchronism. The same is true of the abund- 

 ant Equisetums, while very few ferns are found within the group. 



Aside from the presence of palms the flora of the lower districts in- 

 dicates a difierence of climate greater than can be accounted for by the 

 small difierence of latitude. This is proved by the great prevalence of 

 the genus Ficus and the presence of Cinnamomum, both of which are 

 rare or wanting in the Fort Union group, while iu the latter occur a 

 great variety of Populus common to cold climates and the genus Corylus 

 in abundance, absent from the Wyoming and Colorado beds. There are 

 two way^ in wliich these differences may be explained, or at least an 

 explanation of them attempted, without denying the great diflereuce 

 of climate. In the first place, it is probable that the more southern 

 parts of the Laramie sea were also much nearer the ocean on both the 

 east and the west sides, and hence enjoyed a more equable climate, as 

 well as one more moist, such that few of the trees and shrubs would 



