90 W. N. LOGAN 



total thickness of the bed is fifty to sixty feet. When taken 

 from the quarry it is very soft and easily cut and carved into any 

 desired shape. It hardens somewhat on exposure. The lower 

 portion, except for the minute cocoliths and foraminiferae is 

 largely unfossiliferous. The upper portion contains many spe- 

 cies of invertebrates. 



In the Colorado area the lower fifty feet of the Timpas beds 

 is the equivalent of the Fort Hays. The zone is described as 

 being composed of layers of a compact, rather fine-grained lime- 

 stone of a light gray color which becomes creamy white on 

 weathered surfaces. The layers are from a few inches to three 

 feet in thickness, and are separated by thin beds of shale usually 

 one or two inches thick. 1 



In the Black Hills area the position of the Fort Hays is 

 occupied by a bed of shales containing a layer of limestone two 

 feet in thickness. In the Iowa-Nebraska area it seems probable 

 that the Fort Hays beds rest upon the Benton limestone, but the 

 line of separation may be difficult to establish. In the eastern 

 Dakota area the equivalent stratum reaches a thickness of 130 

 feet. 



The Ptera?iod<m beds. — The upper division of the Niobrara 

 comprises the true chalk of the Kansan area. The chalk varies 

 in color from a light blue through lavender, yellow, and buff, to 

 red and orange. Under fresh exposure it presents the appear- 

 ance of a blue shale, and has often been taken for such. The 

 freshly exposed beds, however, under the weathering influence 

 of air and water, soon change their shale-like appearance and 

 blue color. The change in color is probably due to a chemical 

 change in the iron compounds in the chalk. Chert beds occur 

 in some places interstratified with the chalk. These are only of 

 very local occurrence, however. The chalk is used to some 

 extent as a mineral pigment in the manufacture of paint. Fossil 

 wood is not of rare occurrence inthe chalk, and it is frequently 

 found pierced with the shells of Parapholce . Fragments of amber 2 



1 Gilbert, loc. cit. 



2 Williston, The Niobrara. Kan. Univ. Geol. Surv., Vol. II. 



