HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 237 



of the Rocky Mountains, the general elevation of the country, and 

 the permanent banishment of the sea, as well as the change in the 

 character of the sediments. Plants show distinctly the inauguration 

 of a new order of things, extremely few of the forms passing over 

 from the Laramie, while many new types are introduced, among 

 them a number of species which are living today, a condition not 

 known for the flora of any earlier American horizon. If, as has been 

 suggested, the line between the Cretaceous and Tertiary be drawn 

 at the point where the dinosaurs happened to disappear, we are 

 left without the support of contributory data. Diastrophism, oro- 

 genesis, continuity of sedimentation, floral similarity, as well as the 

 evidence of invertebrates and mammals, are nullified. 



Summary and Conclusions. 



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 prov- 

 inces and reaching the valley of the Mackenzie 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 paleontology 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 Mon- 

 tana, 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 uncon- 

 formably, in others in apparent conformity, on the Fox Hills 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. 



5. It is shown that the beds under consideration, being above 

 an unconformity, can no longer be considered as a part of the "con- 

 formable Cretaceous series" and hence are not Laramie. 



6. It is shown that the two members of the Fort Union, although 



