

398 N. H. DARTON STRATIGRAPHY OF THE BLACK HILLS, ETC. 



is presented an extensive series of red beds in the vicinity of Iron moun- 

 tain, Wyoming. 



SUNDANCE FORMATION 



Typical marine Jurassic deposits, with an abundant fauna, extend 

 continuously around the Bighorn uplift, and they are so similar to the 

 deposits in the Black hills that the same name is applicable. The thick- 

 ness averages about 300 feet and the succession comprises a sandy series 

 below and a considerable thickness of greenish, fossiliferous shales above. 

 At or near the base there usually is a hard, fossiliferous limestone layer 

 having a thickness of from 3 to 5 feet, increasing locally to 25 feet. Next 

 above are soft, sandy beds often containing large numbers of Gryphasa 

 calceola, variety nebrascensis. The greenish shales above contain thin 

 layers of highly fossiliferous limestones and a few thin, sandy layers. 



MORRISON FORMA TION 



This formation is easily recognized in the Bighorn uplift, presenting 

 the distinctive features which it has in the Black hills and in Colo- 

 rado. Shales preponderate, having the characteristic peculiar chalky 

 appearance and massive or joint clay structure. The colors are mostly 

 pale greenish or maroon, with darker clays at the summit. Several beds 

 of light gray to buff sandstone are included, varying in thickness from 2 

 to 20 feet. The thickness of the formation is about 150 feet to the north- 

 ward and 250 feet to the southward. The remains of Dinosaurs are 

 abundant, but no other fossils were observed. 



■CLOVERLY FORMATION 



Overlying the Morrison shales there is a thin bed of sandstone which, 

 from its stratigraphic relations and character, is believed to represent 

 the Lakota of the Black hills, overlain by and merging into clays resem- 

 bling the Fuson formation. Owing, however, to the lack of any definite 

 evidence as to the equivalency of these beds, and especially in the con- 

 sideration of the apparent absence of deposits representing the Dakota 

 sandstone above the clay, it has been thought best to give this series a 

 separate designation. Accordingly " Cloverly " is proposed, a name de- 

 rived from a postoffice oh the eastern side of the Bighorn basin. 



The sandstone member of the Cloverly formation usually gives rise to 

 a line of knobs or low ridges on the divide along the eastern slope of the 

 Bighorn uplift. Ordinarily it is a coarse grained, buff or dirty gray, 

 cross-bedded, massive sandstone, averaging 30 feet in thickness, but 

 varying from 10 to 60 feet. The overlying clay is rarely exposed, but 

 in a few outcrops it is seen to be a reddish to ash-colored clay, locally 



