THE BARITE DEPOSITS OF MISSOURI 73 



tion is at the surface of the rock to be removed. While there 

 are enlarged joints and fissures which extend downward into the 

 dolomite a considerable distance, the action of the ground water 

 is confined to the exposed surface of the dolomite. At a distance 

 of a few inches from this friable, granular dolomite, solid, per- 

 fectly fresh dolomite is found. This shows also the degree of 

 imperviousness of the dolomite. It was found that there was 

 1.94 per cent of insoluble material in the dolomites (exclusive of 

 the Elvins), the most of which enters into the residual clays. The 

 chert, quartz, barite, etc., in the dolomite remain behind and soon 

 become an essential part of the residual mantle rock. The deep 

 red color of the residual clay is due to the complete state of oxi- 

 dation of the iron in the dolomite. This color of the clay is in 

 part confirmatory of Steidtmann's^ recent statement that dolo- 

 mites contain isomorphous ferrous oxide. However, careful tests 

 showed that there was no ferrous iron in the Potosi dolomite. 



As these materials are brought nearer the surface by the 

 erosion of the overlying material they pass into the zone where 

 temperature changes are effective and there the larger fragments 

 are slowly disaggregated into the smaller pieces which are usually 

 found. Thruout the district the largest masses of barite are 

 found adjacent to, or still in the bed rock, while higher up small- 

 er fragments are the rule. The same is true of the chert. 



Source of the barite 



That the barite in the residual clay was derived from the un- 

 derlying dolomite is proven by many facts. The following are 

 the most important of these lines of evidence : 



(1) On the steeper slopes where the veins are exposed, or 

 partially exposed, the material which had accumulated on the 

 surface in the few pockets of clay was identical with the barite 

 in the vein. Absolute proof was shown in these instances. 



(2) Many pits have been sunk to the dolomite, following 

 the barite downward, and the barite in the dolomite is found to 

 be identical with that in the clay in every way, save size, that in 

 the dolomite being in larger masses. 



(3) The barite and quartz in the clay usually show casts 

 of dolomite crystals. This proves that they were deposited on 



"Steidtman, E., Science, vol. 44, p. 56. 1916. 



