EARLIER TERTIARY (EOCENE AND OLIGOCENE). 763 



faunas. He does not consider that the floras furnish sufficient evidence for corre- 

 lation with the Tertiary, and he concludes : 



In the interior region of North America the formations between the uppermost marine 

 Cretaceous and the Wasatch together constitute a real transition from the Cretaceous to the 

 Tertiary. 



Notwithstanding the fact that there are several local unconformities at various horizons 

 and perhaps some of more general distribution, there is no conclusive evidence that any one 

 of these represents a very long period of erosion not represented by sediments elsewhere in the 

 region. 



The Fort Union formation, properly restricted, is of early Eocene age, the determination 

 resting chiefly on its stratigraphic position and its primitive mammalian fauna, which is related 

 to the earliest Eocene fauna of Europe. The very modern character of the flora tends to 

 confirm this correlation. 



The "Ceratops beds" are of Cretaceous age, as decided by stratigraphic relations, by the 

 pronounced Mesozoic character of the vertebrate fauna with absence of all Tertiary types, and 

 by the close relations of its invertebrate fauna with the Cretaceous. The relation of the flora 

 with Eocene floras is believed to be less important than this faunal and stratigraphic evidence. 

 Taken in their whole areal extent they probably include equivalents of the Laramie, Arapahoe, 

 and Denver formations of the Denver Basin. 



Knowlton,^"^ presenting the evidence from the point of view of the paleo- 

 botanist, also discusses the stratigraphy and regarding his conclusion states : 



The present paper deals with the extensive series of fresh-water deposits of the Northwest 

 (that is, broadly, the region east of the Rocky Mountains and between Wyoming and the valley 

 of the Mackenzie River), comprising what is here considered as the Fort Union formation. It 

 is shown that the Fort Union embraces more than has been commonly assigned to it. Con- 

 formably below the beds by some geologists considered as the true Fort Union occur dark- 

 colored sandstones, clays, and shales, which have often been incorrectly^ referred to the Laramie, 

 or its equivalent, but which are stratigraphically and paleontologically distinct from the Lara- 

 mie, and the contention is here made that these beds, which include the "HeU Creek beds" 

 and so-called "somber beds" of Montana, the "Ceratops beds" or "Lance Creek beds" of 

 Wyoming, and their stratigraphic and paleontologic equivalents elsewhere, are to be regarded 

 as constituting the lower member of the Fort Union formation and are Eocene in age. 



Knowlton ^°^^ sums up his argument as follows: 



1. The Fort Union formation is a fresh-water Tertiary formation of wide areal extent, 

 mainly east of the Rocky Mountains, ranging from Wyoming and western South Dakota over 

 western North Dakota, eastern and central Montana, the central Canadian provinces, and 

 reaching the valley of the j\Iackenzie River. 



2. It is shown that the Fort Union formation may be separated into two members on 

 lithologic grounds. The present paper deals only or largely with the stratigraphy and paleon- 

 tology of the lower member, which includes the "Hell Creek beds" and so-called "somber beds" 

 of Montana and the "Ceratops beds" of Wyoming. 



3. The areal distribution of the lower member is traced in Montana, North and South 

 Dakota, and Wyoming, and its probable extension in other areas is indicated. Complete lists 

 of the fossil plants are given by localities for each of the areas. 



4. It is shown that the lower member rests, in some cases unconformably, in others in 

 apparent conformity, on the Fox HiUs or Pierre, and the conclusion is reached that an erosional 

 interval is indicated during which the Laramie, if ever present, and other Cretaceous and early 

 Tertiary sediments were removed. 



