WAtti..] HISTORICAL REVIEW OF OPINION. 409 



Academy a rough geolojrical map of the country bordering on the 

 Missouri Eiver, from the mouth of the Platte to Fort Benton, with 

 explanations." According to this map the " Great Lignitic Tertiary 

 Basin " begins at the mouth of Heart Eiver and extends to uear the Mus- 

 cle Shell. It also stietches back on the Little Missouri to uear the base 

 of the Black Hills and on the Yellowstoue to the mouth of the Big 

 Horn. He also lays down an extensive " Tertiary " tract lying between 

 the South Fork of the Cheyenne and the Platte and extending east and 

 west from the 100th meridian to Fort Laramie. The Judith Eiver Bad 

 Lauds are also treated.as Tertiary, the too deep coloring of the map being 

 explained iu a foot uote on page 110. Of the Great Lignitic deposit he 

 remarks that " the collections of fossils now obtained show most con- 

 clusively ♦ * * that it cannot be older than the Miocene period." 

 Of the Judith Eiver basin he says that "the impurity of the lignite 

 forms the most essential lithological difference between this deposit and 

 the Great Lignite basin below Fort Union." 



Immediately following this communication iu the same volume is a 

 more extended one by Messrs. Meek and Haydeu, devoted primarily to 

 the description of new paleoutological mateiial from the same general 

 region, but containing an introductory discussion of the geological 

 problems involved. Besides sections of the beds above Fort Clarke, 

 and near the mouth of the Judith, this paper gives a general one for 

 the whole of this country, in which the "Tertiary system" is now classed 

 as Miocene. 



The first complete section of the "Tertiary " formations of the West 

 was drawn up by Messrs. Meek and Hayden, and also published in the 

 Proceedings of the Academy of Natural Sciences of Philadelphia, for 

 December, 18G1 (Vol. XIII, p. 433). The series is subdivided into the four 

 familiar groups: 1, Fort Union, or Great Lignitic; 2, Wind Eiver; 3, 

 White Eiver ; 4, Loup Eiver. We are concerned here only with the first, 

 or lowest member of this series, the so called Great Lignitic. This is 

 defined as " Beds of clay and sand, with round ferruginous concretions, 

 and numerous beds, seams, and local deposits of lignite ; great num- 

 bers of dicotyledonous leaves, stems, etc., of the genera Platanus, Acer, 

 Ulmus, Populus, etc., with very large leaves of true fan palms. Also, 

 Helix, Melania, Vivipara, Corbicula, Unio, Ostrea, Potamomya, and 

 scales of Lepidotus, with bones of Trionyx, Emys, Compsemys, Croco- 

 dilus, etc.; thickness: 2,000 feet or more; localities: occupies the whole 

 country around Fort Union, extending north into the British posses- 

 sions to unknown distances ; also southward to Fort Clarke. Seen un- 

 der the White Eiver group on North Platte Eiver above Fort Laramie. 

 Also on west side Wind Eiver Mountains." 



Although nothing is said either here or in the more general descrip- 

 tion which follows of the relation of the Judith Eiver beds to this 

 formation, we learn from a foot note appended to page 417 that the 



1 Sec Proceedings of the Acadeii;}- of Natural Sciences, Philadelpbia, Vol. IX, p. 109. 



