T. W. Stanton — Fox Hills Sandstone. 183 



neighborhood of Yule P. O. There is a very slight northward 

 dip. Beds of carbonaceous shale and impure lignites are dis- 

 tributed throughout the formation beginning with the basal 

 stratum, and in the upjier half, according to Leonard, there are 

 5 or 6 workable coal beds. Dinosaur remains, including Tri- 

 ceratops and Trachodon, are not imcommon in the lower part, 

 especially in the badlands near the mouth of Bacon Creek, a 

 mile northeast of Marmarth. The formation is in evei"_y par- 

 ticular similar to the equivalent Lance formation in the Chey- 

 enne River and Standing Rock reservations. 



Irregular deposition and erosion with deep channeling are 

 strikingly exhibited at several localities and on different hori- 

 zons. One example of erosion which is worthy of description 

 in a separate article is clearly shown in a cut bank by the side 

 of the railroad yard at Marmarth, probably less than 100 feet 

 above the base of the Lance formation. A bed of carbonace- 

 ous shale with an average thickness of 20 feet is exposed to its 

 full length of 250 feet. Both the top and the bottom surfaces 

 are irregular as if eroded, and the underlying sandstone and 

 the argillaceous bands in the bed are filled with vertical roots 

 of plants. One end of the bed fingers out into cross-bedded 

 sand while the other end is abruptly truncated and abuts 

 against a friable, cross-bedded yellowish gi-ay sandstone similar 

 to and continuous with the sand that overlies the carbonaceous 

 bed. Here is evidence of erosion at the base of the carbonace- 

 ous bed apparently as great as that at the base of the whole 

 formation, and of still greater erosion at the top of the same 

 bed. 



It will be noticed that in this area there is no brackish-water 

 bed at the top of the Fox Hills. Instead the change is abrupt 

 fi'om marine to latid or fresh-watei- deposits, but there is evi- 

 dence that marine or at least brackish-water conditions con- 

 tinued in a neighboring area for some time after non-marine 

 deposition began. Professor Leonard reported the finding of 

 an oyster bed in the upper part of the " somber beds" about 

 five miles southwest of Yule in sect. 16, T. 135 N., R. 105 W., 

 which is only about 15 miles north of Marmarth. The locality 

 was visited last summer and the oysters were found associated 

 with a coal (apparently bed F of Leonard's section"^) about 175 

 feet above the river level and according to Leonard's estimates 

 approximately 500 feet above the base of the Lance formation 

 and certainly above all the dinosaurs that have been found in 

 the region. The abundant oysters referable to Ostrea sub- 

 trigonalis and Ostrea glabra lie a few feet above the coal in a 

 carbonaceous shale. In some places the shells form a nearly 

 solid band 6 inches thick, and they are distributed in thin 

 bands and scattered individuals through 7 feet of shale. Such 



*5th Bienn. Kept. N. Dat. Geol. Surv., 1908, p. 78. 



