182 T. W. Stanton— Fox Hills Sandstone. 



evidence of such a break has been found there. It is true that 

 at various levels throughout the Lance formation thel-e is evi- 

 dence of current action and irregular deposition shown in 

 cross-bedding, varying thickness and uneven surfaces of sand- 

 stones, and similar jihenomena. Such features are character- 

 istic of continental deposits, and have little weight as evidence 

 of important unconformities unless supported by other lines of 

 evidence. In this case all the irregularities observed seem to 

 be of purely local character. 



Valley of the Little Missouri from Marmarth to Yule, North 



Dakota. 



In the southwest corner of North Dakota, near the town of 

 Marmarth on the Chicago, Milwaukee & Puget Sound Rail- 

 way, the valley of the Little Missouri cuts down through the 

 Lance formation and the Fox Hills into the Pierre, and shows 

 a section comparable with those in the Indian reservations 

 which we have been discussing. The area has been described 

 by Prof. A. G. Leonard,* and my observations added little to 

 the facts lie has recorded. 



The Pierre shale is exposed on Little Beaver Creek, about 5 

 miles southwest of Marmarth, and yields a typical Pierre 

 fauna with less admixture of Fox Hills species than is found 

 in the top of the Pierre in the reservations. 



Immediately above the Pierre shale is banded shale with a 

 thickness of about 40 feet overlain by 40 feet of soft massive 

 sandstone, yellow with iron-stained bands and conci'etions 

 below, grading up into gray sandstone above. This sandstone 

 yielded a few marine fossils, including Leda ( Toldia) evansi, 

 Telllna scituLa, Entalis? paupercula and Jlalymeniles majo7', 

 which confirm Leonard's reference of the sandstone to the 

 Fox Hills. In several bluff exposures along the creek the top 

 of the gray sandstone shows an uneven ei'oded surface which 

 Professor Leonard has photographed and deseribedf as an 

 unconformity in the following words : "It is well shown at 

 two points on Little Beaver Creek in section 7, T. 132 N., R. 

 106 "W. Here the massive sandstone forming the top of the 

 Fox Hills is seen to have undergone erosion before the deposi- 

 tion of the brown and black highly carbonaceous and argilla- 

 ceous sandstone, which shows cross-limitation in places. Some 

 of the depressions of the former land surface have been eroded 

 to a depth of 6 feet below the adjoining elevations." Immedi- 

 ately above this eroded surface is the Lance formation, which 

 Professor Leonard has described as " somber beds " and " lower 

 Fort Union," with an estimated thickness of about 600 feet 

 extending northward down the river 15 or 20 miles to the 



*5thBieiin. Rept. N. Dak. Geol. Surv., 1908, pp. 29-114. 

 \ Op. cit., pi. V, p. 72. 



