RIVER BASIN SURVEYS — F. H. H. ROBERTS 381 



in Texas. Wliile not spectacular in the main, the results obtained 

 have been quite satisfactory. 



In the Missouri Basin the paleontological parties have devoted con- 

 siderable time to the Cretaceous and Tertiary deposits. In Lewis 

 and Clark and Broadwater Counties in Montana where the Tertiary 

 stratigraphy was imperfectly known from the time of its discovery 

 in 1904 by the late Dr. Earl Douglass, the River Basin Surveys' work 

 definitely established the presence of Lower and Middle Oligocene 

 and Lower and Middle Miocene in the area. In North Dakota it was 

 shown that the Cannonball Marine member of the Fort Union forma- 

 tion has a much greater areal distribution than previously supposed. 

 Investigations of the Eocene deposits in the Big Horn basin in Wy- 

 oming produced evidence that confirmed previous conclusions of mem- 

 bers of the United States Geological Survey who mapped the struc- 

 ture and stratigraphy of that area. Specimens collected there, al- 

 though for the most part rather fragmentary, were sufficiently well 

 preserved to establish the age of those beds as belonging to the Lost 

 Cabin faunal zone of the Lower Eocene, a fact that had not previously 

 been demonstrated. In the material obtained is the most nearly 

 complete skull yet found of the primitive insectivore Didelphodus. 

 Specimens collected from the Oligocene deposits in Montana consist 

 principally of marsupials, insectivores, rodents, and small artiodac- 

 tyls. One of the insectivores was found to belong to a problematical 

 family that previously was not known in deposits later than the 

 Upper Eocene. Furthermore, the specimen is the best preserved yet 

 collected and adds many details of the skull and dentition to the 

 knowledge of that group. The material obtained from the Miocene 

 deposits consists of large oreodonts, beavers, rabbits, and small ro- 

 dents. Collecting in the Upper Cretaceous Pierre shale provided 

 specimens of complete fish, Thrissofater; turtles, Archelon; and mosa- 

 saur skulls. 



Paleontological studies outside the Missouri Basin were confined 

 chiefly to the Garza-Littlo Elm and Lavon Reservoirs on the Trinity 

 River. The material from the Lavon area came mainly from the 

 Upper Cretaceous deposits and consisted of a small mosasaur (uni- 

 dent) skull and the skull of a large mosasaur ( Tylosaurus ? ) . At the 

 Garza-Little Elm project a small Pleistocene fauna was collected 

 from a borrow pit near the west end of the dam. Included in the 

 material are bison, horse, gopher, and aquatic turtle. 



The University of Nebraska State Museum carried on cooperative 

 paleontological work from the beginning of the interagency pro- 

 gram. Considerable collecting was done in the area of the Harlan 

 County Dam in southern Nebraska. Most of the attention of the 

 Museum field parties was directed to the Pliocene deposits and a 



