HISTORICAL REVIEW OE THE LAKAMIE PROBLEM. 



31 



here considered aa the Fort Union formation. It is shown 

 that the Fort Union embraces more than has been com- 

 monly assigned to it. Conformably below the beds by 

 some geologists considered as the true Fort Union occur 

 dark-colored sandstones, clays, and shades, which have 

 often been incorrectly referred to the Laramie or its equiva- 

 lent but which are stratigraphically and paleontologically 

 distinct from the Laramie, and the contention is here 

 made that these beds, which include the "Hell "Creek 

 beds" and so-called "somber beds" of Montana, the 

 "Ceratops beds" or "Lance Creek beds" of Wyoming, and 

 their stratigraphic and paleontologic equivalents else- 

 where, are to be regarded as constituting the lower member 

 of the Fort Union formation and are Eocene in age. 



In this paper a brief historical summary of 

 the Fort Union formation was followed by an 

 account of its areal distribution and Hthologic 

 character, in which I held that it may be 

 divided into two members. The areal distri- 

 bution and paleontologic contents of the lower 

 or dinosaur-bearing member were given as 

 completely as available facts then warranted. 

 The distribution included the following areas 

 in Montana: Hell Creek, Miles City and vicin- 

 ity, Forsyth, Custer, Bull Mountains, Mel- 

 ville, Red Iiodge, Glendive, and from Glendive 

 to Medora, N. Dak. Several areas in North 

 Dakota were discussed, as well as a probable 

 area Csince confirmed) in northwestern South 

 Dakota. Thence the formation was traced to 

 Weston County, Wyo., and thence northward 

 to connect with the area at Miles City, Mont. 

 Other areas in Wyoming were Converse County, 

 a great region east of the Big Horn Mountains, 

 and the Big Horn Basin. Thus it was shown 

 that the "Ceratops beds," originally supposed 

 to occur only in Converse County, Wyo., really 

 occupy a vast area distributed over four great 

 States. 



The essential results claimed in this paper 

 were sufficiently set forth in the "summary and 

 conclusions," 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 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 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 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 "conformable Cretaceous series" and hence 

 are not Laramie. 



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

 although usually distinct lithologically, can not be sepa- 

 rated structurally, sedimentation having been uninter- 

 rupted, except locally. 



7. The paleontological. elements of the lower members 

 are considered at length, beginning with the plants. It 

 is shown that of the 84 known species, 61 are common to 

 the upper member, and only 11 species to the Laramie of 

 Colorado, while 15 species are common to other American 

 Eocene, and 9 species to the Miocene. The Eocene age 

 of the Fort Union is fixed by tying its flora to thatjof vari- 

 ous Old World beds of known Eocene position. 



8. The invertebrate evidence is shown to be in sub- 

 stantial accord with that of the plants, there being only 4 

 of the 49 species common to the Colorado Laramie. All, 

 with a single possible exception, are fresh-water forms. 



9. It is shown that the vertebrates afford no positive e^\ i- 

 dence of Cretaceous age. That the dinosaurs exhibit 

 Cretaceous affinities is not denied, since, being without 

 known descendants, it is possible to compare them only 

 with their progenitors. It has been proved beyond 

 question that they survived the profound orogenic move- 

 ment and attendant physical break at the top of the 

 Laramie in the Denver Basin of Colorado and lived on in 

 Arapahoe and Denver time, and it is shown that in the 

 areas considered in this paper they passed over a similar 

 erosional interval and are found in association with the 

 Fort Union flora, which is of Eocene age. 



10. The mammals of the lower Fort Union show very 

 little relationship with Jurassic or Cretaceous forms but 

 find their closest affinities with those of the Puerco and 

 Torrejon, which are of acknowledged Eocene age. 



11. The chelonians are shown to be of little value in 

 their bearing on the age of the lower Fort Union, especially 

 when compared with the Judith River forms, which are 

 evidently in confusion. 



12. It is" held that the line between Cretaceous and 

 Tertiary should be drawn at the top of the true Laramie. 



13. The final conclusion is reached that the beds here 

 considered ("Hell Creek beds," "somber beds," "Ceratops 

 beds," "Laramie" of many writers) are stratigraphically, 

 structurally, and paleontologically inseparable from the 

 Fort Union and are Eocene in age. 



The above-mentioned paper was followed 

 almost immediately by a paper by T. W. 

 Stanton, 9 entitled "The age and stratigraphic 



9 Washington Acad. Sci. Proc, vol. 2, pp. 239-293, 1909. 



