STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 71 



2. Clay containing few fossils, 80 feet. 

 I. Sandstone and clay, 90 feet. 



The thicknesses were purely tentative, as the party, owing to 

 unexpected complications, were compelled to make a remarkably 

 rapid reconnaissance. Several years later. Meek and Hayden pub- 

 lished an amplified section, based on examinations and collections 

 made by Hayden while associated with the Raynolds expedition.^^ 

 In this memoir, geographical names were applied to the several 

 formations. Fox Hills beds, No. 5 ; Fort Pierre group, No. 4 ; Nio- 

 brara division. No. 3 ; Fort Benton group. No. 2 ; Dakota group. 

 No. I. 



The Fort Union or Great Lignite Group, which overlies the Fox 

 Hills, was placed in the Tertiary. This grouping was based on the 

 fossil remains, not on the lithological features and it was applicable 

 apparently throughout the eastern part of the Cretaceous region. 

 In the early 70's discussion arose respecting the relations of some 

 coal deposits which had been referred to the Fort Union ; the term 

 "Laramie" was introduced for the deposits in dispute, to be em- 

 ployed without committing the writer to either Tertiar}^ or Cre- 

 taceous age. Studies in more recent years made necessary a change 

 at the base of the column. Barton's examination of the Black Hills 

 in northeastern W'yoming showed that the Dakota is complex, that 

 the middle and lower portions carry Lower Cretaceous forms, while 

 the upper portion belongs to the Upper Cretaceous. Some years 

 afterward, the same author, and later Lee and Stanton, discovered 

 fossils wath similar relation in the same beds within New Mexico. 

 These lower beds were correlated with the Kootenai of Canada. 



^^'hen, however, an attempt was made to apply the Missouri 

 River section to the country west from the io6th meridian, serious 

 difficulty was encountered. The character of the deposits was 

 wholly different. The matter was complicated by the fact that the 

 earlier explorers did not recognize that the great erosion was due to 

 post-Cretaceous elevation of the mountains and by the other fact 

 that they did not know that a grouping of fossils, resembling that 

 of the Fox Hills, occurs in that region low down in the column. In 



2" F. B. Meek and F. V. Hayden, Proc. Acad. Nat. Sci., Philadelphia, 1861, 

 citations from pp. 419, 432. 



