332 Annals ok the Carnegie Museum. 



dantly evidenced by the frequent examjiles of cross-bedding and ripple- 

 .marked surfaces exhibited by the sandstones, by the want of continuity 

 in the different strata, by the character of the invertebrate fauna, the 

 character of the vertebrate fauna and by the manner in which the 

 complete or dismembered skeletons and isolated bones of the latter 

 have been entombed. 



At the close of the Dakota this entire region was subjected to a 

 greater subsidence and was uniformly covered by a great sea, save per- 

 haps for a few small islands. Evidence of this subsidence and the in- 

 gress of the sea consequent upon it, is seen in the uniform nature of 

 the several hundred feet of shales and limestones, with at this locality 

 a rather meager marine fauna, which overlie the Dakota sandstones 

 with apparent conformity and constitute the Benton shales or lower 

 member of the Colorado formation. Toward the top these limestones 

 and shales are replaced by a iew feet of brown sandstones closely re- 

 sembling in general appearances the Dakota sandstones, though sep- 

 arated from them by from 400 to 500 feet of marine shales and lime- 

 stones. This stratum of Benton sandstone may be seen on the north 

 side of a small bluff just below the mouth of Wilson Creek on the west 

 side of Oil Creek where the wagon road from Canyon City to Garden 

 Park passes around the end of a low hog-back about one-quarter of a 

 mile below the mouth of the canon. The softer shales and limestones 

 of the Benton are here obscured by the secondary deposits in the nar- 

 row valley of Wilson Creek which at this point ciischarges into Oil 

 Creek, or Four Mile, as the latter is locally more generally known. 

 The valley of Wilson Creek for some distance above its mouth follows 

 the strike of the inclined strata, and owing to the greater resistance 

 to erosion offered by the Dakota sandstones and the very similar layer 

 of brown sandstone just referred to as occurring at the top of the 

 Benton the breadth of the valley of this creek is here determined by 

 the total thickness of the more easily eroded Benton shales, along the 

 upturned edge of which the stream has cut its channel, following the 

 line of least resistance. 



Tlie Niobrara. — Immediately and conformably overlying the stratum 

 of brown sandstone just mentioned as occurring at the top of the Ben- 

 ton series there is a bed of shale about twelve feet thick followed by 

 about thirty feet of fine-grained (magnesian?) limestone. This lime- 

 stone is much jointed and is divided into a number of different strata 

 separated by thin seams of shale. This is one of the most continuous 



