MESOZOIC AND TERTIARY FLORAS 113 



is the increased number of forms that foreshadow the modern flora, a 

 few, indeed, being still living. As examples of the latter mention may 

 be made of the common sensitive fern (Onodea) and two species of 

 hazelnut (Corylus) all of which are now living in eastern North 

 America. In late Cretaceous time the sedges (Cyperus, Carex, etc.) 

 and grasses (Arundo, Phragmites) had but a poor representation, but 

 in the late Eocene these groups clearly became more numerously 

 developed both in types and species, and thus apparently made 

 possible the rise and development of the mammalia. 



Fort Union flora. — The largest and in many respects most impor- 

 tant Eocene flora is that of the Fort Union, which is found over a vast 

 area in the central Canadian provinces, north as far as the valley of 

 the Mackenzie River, and south over central and eastern Montana, 

 the western portions of both North and South Dakota, and at many 

 points in eastern and central Wyoming and northwestern Colorado. 

 It has recently been shown by the writer' that the Fort Union, exten- 

 sive as it was known to be, really embraces more than has commonly 

 been assigned to it. Conformably underlying the beds by some 

 geologists considered as the true Fort Union, occur beds which have 

 often been incorrectly referred to the Laramie, or its equivalents, but 

 which are now regarded as constituting the lower member of the Fort 

 Union formation. This lower member, which includes the so-called 

 "Hell Creek beds" and "somber beds" of Montana, and the 

 "Ceratops beds" of Wyoming, and their equivalents throughout 

 much of the area above outlined, contains a rich flora which is 

 inseparably bound to the flora of the upper member. 



The flora of the Fort Union considered as a whole embraces more 

 than five hundred species, and comprises ferns, sequoias, cedars, 

 yews, grasses, sedges, oaks, willows, poplars in great abundance and 

 variety, hazelnuts, walnuts, elms, sycamores, maples, a few figs, an 

 occasional palm, and other more modern types. Whatever the con- 

 ditions under which this flora grew and was entombed, it is beyond 

 question that the climatic conditions were very different from those 

 now prevailing in the region. But for the presence of palms and an 

 occasional fig it might be presumed that the conditions were not 

 greatly different from those now experienced in Atlantic North Amer- 



I Proc. Wash. Acad. Sci., Vol. XI, 1909, pp. 179-238. 



