1 6 COLORADO COLLEGE STUDIES. 



tablished by Professor Prosser in the same article for 

 another quite different stratigraphic value, the Marion jihii 

 and concretionary limestone, a member of the Chase forma- 

 tion.* 



THE WELLINGTON SHALES. 



It has been established by numerous borings in the 

 region underlaid by rock-salt in Kansas that there is above 

 the salt-measures a body of clay-shales with a thickness 

 of 250 to nearly 450 feet, and having for the most part the 

 same and darker and lighter shades of the bluish-gray 

 color that prevails in the clays of the rock-salt deposits 

 themselves. This fact, though here stated from the 

 writer's early and independent observations, was recognized 

 by the late Prof. Robert Hay, who called this zone "the 

 gray shales" and "the gray beds,"f apparently in contrast 

 with the "red-beds" of the Cimarron series. It is for this 

 zone of gray beds, which must be distinguished strati- 

 graphically from the underlying and similar gray beds of 

 clay-shale in the Geuda salt-measures, and which is not 

 everywhere gray through its entire thickness, that the 

 formational name, Wellington shales, is here proposed. 



These shales are thicker in southern than in northern 

 Kansas, attaining their greatest known development be- 

 neath the town of Caldwell, where the drill has shown them 

 to have a thickness of 445 feet. They contain satin-spar 

 veins and infrequent and limited saHne impregnations, but 

 no rock-salt. Within the area of their outcrop and as 

 reached by borings near it, as respectively at Wellington 

 and Caldwell, the Wellington formation often includes beds 

 of impure limestone and calcareous shales and occasional 

 beds of gypsum and dolomite. 



Beneath Ellsworth, the WelHngton is 255 feet thick 



*Loc. cit., p. 772. 



tGeology of Kansas Salt. Seventh Biennial Report of the Kansas 

 State Board of Agricultui-e, Part II, pp. 83 to 9G. 1891. (See page 87.) 



