1002.] HATCHER — OLIGOCENE AND MIOCENE DEPOSITS. 115 



origin, there is in the South Dakota Bad Lands a series of pinkish- 

 colored nodular clays. These clays are faunally quite distinct, both 

 from the adjoining sandstones and the underlying clays of the lower 

 Oreodon beds. Unlike the Matamynodon and Protoceras sand- 

 stones, this upper series of clays is of wide distribution and has 

 been recognized in South Dakota, Nebraska, Wyoming and Colo- 

 rado. Dr. W. D. Matthew, in his most excellent memoir on the 

 Fossil Mammals of the Tertiary of Northeaster7i Colorado, has very 

 appropriately named these clays the Leptauchenia Beds, from a 

 genus of fossil mammals occurring abundantly in them. 



From the above remarks it will readily appear thai the White 

 River formation may be separated faunally into three sub-equal 

 primary divisions. These are, commencing with the lowermost, 

 as fellows : 



1. The Titanotherium Beds, consisting of 200 feet of fine, white 

 or greenish-colored clays with numerous intercalated lenses of 

 sandstones and conglomerates, the latter not faunally distinguishable 

 from the clays. 



2. The Oreodon Beds, consisting of 300 feet of pinkish-colored, 

 banded and frequently nodular but usually unlaminated clays, with 

 less frequent lenses of finer sandstones, faunally distinct and known 

 as the Metamynodon sandstones. 



3. The Leptauchenia Beds, consisting of 200 feet of pinkish- 

 colored, often nodular and banded, but unlaminated clays, includ- 

 ing the Proteceras sandstones above referred to. 



The Loup Fork was the name given by Cope to a series of sand- 

 stones and clays well represented in western Nebraska and Kansas. 

 This formation has since been found to have a very wide distribu- 

 tion, and to extend almost uninterruptedly all along the eastern base 

 of the Rockies from Mexico to the Missouri River. It attains its 

 greatest development in southeastern Wyoming and northwestern 

 Nebraska, where it has a thickness of more than 1500 feet. 



The sediments of the Loup Fork formation have not been so 

 thoroughly studied as those of the White River, and their faunal 

 and lithological characters are consequently less perfectly known. 

 The latest attempt at a differentiation of the various horizons within 

 the Loup Fork is that of Darton. Chiefly by lithological characters 

 he has divided the Loup Fork of northwestern Nebraska into three 

 divisions. Commencin.i{ below these are : 



