HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS l8l 



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 con- 

 stituting the lower member of the Fort Union formation, and are 

 Eocene in age. 



Historical Summary. 



To all students of the late Cretaceous and early Tertiary forma- 

 tions of the northwest, the Fort Union formation is a familiar term. 

 The name was originally given by Dr. F. V. Hayden^ in 1861 to 

 his great lignite group which: "Occupies the whole country around 

 Fort Union, extending north into the British possessions, to unknown 

 distances; also southward to Fort Clark." At the same time it was 

 stated that the formation had also been observed under the White 

 River group on the North Platte River above Fort Laramie, and on 

 the west side of the Wind River Mountains. The beds were des- 

 cribed as consisting of clays and sands, with round ferruginous con- 

 cretions, and numerous beds, seams and local deposits of lignite. 

 The fossil contents were very abundant, consisting of great numbers 

 of dicotyledonous leaves, fresh-water shells of several genera, scales 

 of Lepisosteus, together with bones of Trionyx, Emys, Compsemys, 

 crocodiles, etc. The abundant fossil plants obtained by Doctor 

 Hayden were submitted to Dr. J. S. Newberry for study, and his 

 report on them was published in 1868.'' The plants were collected 

 at various points on the Missouri River, at Fort Clarke, at Red 

 Spring thirteen miles above, at Fort Berthold, at Crow Hills, one 

 hundred miles below Fort Union, at the mouth of the Yellowstone, 

 on O'Fallon's Creek one hundred miles above the mouth of the 

 Yellowstone, and in the valley of that stream. On account of their 

 association with invertebrates reported by Professor Meek to be of 

 Miocene age, as well as from their agreement with plants stated by 



^ In this paper the terms "Hell Creek beds," "Ceratops beds," "Lance 

 Creek beds," "Somber beds," "Upper Laramie" and "Black Buttes beds" 

 are placed within double quotation marks because these terms have not been 

 formally adopted by the U. S. Geological Survey. In other cases, e. g., 

 'Fox Hills,' 'Laramie' etc., single quotation marks are used only when the 

 beds are not regarded by the writer as properly identified. 



^ Proc. Acad. Sci. Phila., 1861, p. 433. 



* Ann. N. Y. Lye, vol. 9, April, 1868, pp. 27-76. 



