THE BARITE DEPOSITS OF MISSOURI 23 



The base of this series of rocks is not exposed in the area 

 studied. They are evidently not so thick as they are in the "Lead 

 Belt." The top of the formation is drawn where the pink, porous 

 dolomite ends, and the bluish-gray crystalline drusy dolomite of 

 the Potosi begins. This upper limit is easily and accurately de- 

 termined. 



Buckley^ subdivides the Elvins formation of Ulrich^ into 

 three parts, which he calls the Davis, the Derby, and the Doerun. 

 The Davis formation, at least, is the equivalent of the lower part 

 of the Elvins formation as described by Ulrich, and according to 

 Buckley is 170 feet thick. It includes the conglomerate beds 

 which are described above as being in the lower part of the El- 

 vins formation. This formation in the Flat River region con- 

 tains a so-called boulder bed near the central part. This bed is 

 entirely lacking in the Washington County area. Likewise, 

 there is very little shale in the upper part of what would be the 

 Davis formation, so that it is impossible to draw a line between 

 the Davis formation and the overlying Derby dolomite. 



The Derby formation, which is about 40 feet thick, is de- 

 scribed by Buckley as follows : 



"This horizon is characterized by massive beds of hackly 

 dolomite, which, upon weathering, break down into large poly- 

 gonal blocks often 20 feet in their greatest diameter. Weathering 

 proceeds rapidly along joint planes of which there are two espe- 

 cially prominent systems nearly at right angles to each other. 



"As a whole this formation is a fine-grained, crystalline, 

 slightly calcareous dolomite. Soft, porous beds alternate with 

 those that are hard, dense, and brittle. In color the dolomite 

 varies from a light gray through yellowish gray to reddish 

 brown. The pitted character of the weathered surface of some 

 of the beds appears to be due to the solution of the more calcar- 

 eous areas of the dolomite." 



Buckley describes the Doerun formation as a "horizon 

 which consists chiefly of argillaceous dolomite." There are "al- 

 ternating beds of argillaceous dolomite, finely crystalline dense 



''Buckley, E. R., Mo. Bur. of Geol. and Mines, vol. 9, Pt. 1, pp. 33-49. 

 1908. 



•Ulrich, E. O., Bull. 267, U. S. G. S., pp. 22-26. 



