MESOZOIC AND TERTIARY FLORAS 207 



number of known species probably does not exceed one hundred and 

 fifty. Nothing particularly new was established at this time, the 

 genera there being largely of older formations, though the specie;s are 

 mainly different. 



Laramie. — As the uppermost member of the conformable Cre- 

 taceous series above the marine Fox Hills, the Laramie has had 

 many vicissitudes of interpretation and was made to include beds 

 now known to belong to the Montana, Arapahoe, Denver, Fort 

 Union, etc. As logically restricted to the original definition of King, 

 the plant-bearing Laramie is confined largely to the Denver Basin of 

 Colorado and adjacent areas to the southward, with the probability 

 of its being demonstrated to exist west of the mountains in Colorado, 

 Wyoming, and New Mexico. As above restricted the Laramie flora 

 comprises about one hundred and twenty-five species, and proves to 

 be remarkably distinct from that of the Montana below as well as 

 from the Arapahoe, Denver, and Fort Union above. 



Tertiary. — The close of the Upper Cretaceous saw a considerable 

 percentage of the modern angiospermous types of vegetation fully 

 established, not only in North America but throughout the world, 

 and the ferns, cycads, and conifers relegated permanently to a sub- 

 ordinate position. Certain types of dicotyledons, such, for instance, 

 as magnolias, tulip-trees, sassafras trees, etc., had their maximum 

 development in the Cretaceous, and in the Eocene and subsequent 

 stages were greatly reduced until in the modern flora they are often 

 represented by a few or even a single species of very restricted habitat. 

 The most noticeable feature of the Eocene flora, broadly considered, 

 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 (Onoclea) 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 



