THE TERTIARY OF THE PLAINS. 187 



The divisions recognized by Messrs. Meek and Hayden are as follows, 

 beginning with the highest of the series : 



4. Loup Riverbeds, Pliocene Tertiary; consisting of loose sand with some limestone; 

 all of fresli- water origin, and containing the bones of JIastodon, Equus, Felis, 

 Castor, Canis, Tcstudo, etc. These are exposed only on the Niobrara and the 

 Loup fork of the Platte. 



3. White River group, Miocene Tertiary; consisting of light colored clays, often 

 arenaceous, and sometimes containing beds of limestone ; all of fresh-water 

 origin. They contain many fossil vertebrates, among which are Titanoiherium, 

 Oreodon, Rhinoceros, Testudo, and Equus. They occupy the bad-land country 

 of the White Eiver and extend over a large area south of the Black Hills and 

 Cheyenne Eiver. 



2. Fort Union group, Eocene Tertiary; consisting of clay, sand, and sandstones, with 

 much iron in ferruginous concretions and many beds of lignite. The basal 

 parts are of brackish-water origin ; the upper portions contain only fresh- 

 water remains. These beds contain in places large quantities of leaves of 

 dicotyledonous plants, Populus, Platamis, Sassafras, etc. The Fort Union 

 beds occupy a large area, extending from the South Cheyenne on the west 

 side of the Hills uorthward to the Missouri and far beyond. 



1. Judith Elver beds; consisting of sand and clay inclosing some beds of lignite. 

 They occur only over a small area near the mouth of the Judith Eiver and on 

 the upper Missouri. The best authorities are very nearly agreed in placing them 

 at the summit of the Cretaceous series, and they are only added here to com- 

 plete the joint section of the Cretaceous and Tertiary of the Plains. 



Of these divisions the only ones which occur in the immediate neigh- 

 borhood of the Black Hills are the Fort Union and White River; the former, 

 according to Dr. Hayden, overlies the Cretaceous at no great distance frond 

 the Hills, on the north, west, and southwest. The latter also overlies the 

 Cretaceous to the southward and eastward. In a northeastern direction a 

 belt of Cretaceous outcrop follows the valley of the Cheyenne and separates 

 the two Tertiary areas. On the opposite or southwest side of the Hills the 

 Tertiary areas conjoin, and the White River beds were there observed by 

 Dr. Hayden to overlie the Fort Union. 



The precise age of the Fort Union beds has been the subject of much 

 discussion, and by some investigators the propriety of referring them to 

 the Tertiary rather than the Cretaceous has even been questioned. There 

 is no need either to recite or to continue that discussion in this place, for 

 the reason that no relation has yet been determined between the deposition 



