The field work, upon which this article is based, was done during the summer of 1911 by a party of United States Geological Survey, under the direct supervision of Mr. E. M. Parks assisted by the writer. The duty of this party was to map the coal for the purpose of land classification. The region examined is located in the extreme northwestern corner of South Dakota and township 21 north of latitude 44 degrees, range 5 east of the Black Hills meridian, which is the state line between South Dakota and Wyoming is taken as typical of the larger fields examined, and is described in detail in this article. This work is treated in three parts which fall under the following heads: Part I, a resume of the literature on the field abstracts of articles relating to descriptive geology but contains only mention of those articles dealing with age and origin of the formation; Part II, a detailed geologic description of Tp. 21 Rg. 5; Part III, a historical review of the opinion in regard to age and origin of the Lance, Fort Union and White River formations. / Master of Science