94 THE GLACIAL LAKE AGASSIZ. 



bluff, removes the talus which elsewhere conceals its lower portion, and the 

 section rises with clift'-like steepness at an angle of 60"^ to 75°. Excepting 

 occasional thin beds, the whole thickness of tlie formation here exposed is 

 hard gray shale, more or less sandy, divided into layers from an eighth of 

 an inch to 2 or 3 inches thick, and much jointed, so that it crumljles into 

 small fragments on the weathered surface. Rarely a bed a few inches thick, 

 having the general dull-gray color, is harder and less jointed, owing to its 

 cementation bv carbonate of lime; and occasionally the ordinary shale is 

 blackened by the deposition of iron rust and of manganese oxide as tilms 

 in the jointage seams, the thickness of the i)ortion thus colored being usually 

 only a few inches, but in one place, half wa}' up the north bluff, 3 or 4 feet. 

 Gypsum was observed onlv in minute crystals in thin fissures coinciding 

 with the planes of stratification, and in the form of satin spar, filling the 

 mold from which some shell, connnouly Inocerauuis, has been dissolved 

 away. Fossils are very infrequent, but by careful search BaeuJites ovatns 

 Say and Scaphifes nodosns Owen were found, each represented by a single 

 specimen; also numerous Inoccramm casts, mostly I. sagensis Owen, besides 

 casts and fragments of other lamellibranchs, not yet identified; and the 

 teeth of fishes, apparently Prtf7///>7»'~~o(/»s JatiinentumQo])ea\\di Lamim miuhjei 

 Cope, or a smaller species.^ The teeth occur somewhat ])lentifully in a 

 remarkablv hard layer, 6 inches to a foot thick, about 50 feet above the 

 stream. With them this hard layer contains softer lumps, of somewhat 

 irregular form, from one-third to three-quarters of an inch in diameter, 

 of light-grav color inside, with a greenish exterior, which are probably 

 coprolites. The other fossils were found in the shale fragments forming 

 the talus, and their place in the section was not ascertained. Although 

 few, they supply decisive evidence that this is the Fort Pierre formation. 



The lowest exposure of this shale observed along the course of the 

 Pembina Mountain in North Dakota is 21' miles north of the preceding, on 

 the Pend)ina River, at the "fish trap," a rude weir of Ijrush and poles, in the 

 northeast corner of the northwest quarter of section 30, township 163, 

 range 57. Here the river falls 7^ feet in about 40 rods, its elevation being 



'For aid in the identification of tbese fossils, and of those collected on the Pembina River, I am 

 indebted to Dr. C. A. White, of this Survey. 



