72 UNIVERSITY OF MISSOURI STUDIES 



fairly rapid movement underground. Gentle slopes with a less 

 active run-off and a porous substratum greatly further chemical 

 action. This action is aided by the presence of a porous zone at 

 the contact of the dolomite and clay. There is much water in this 

 zone and most of the miners avoid going to bed rock unless they 

 find excellent barite there. Most of the mines are located on 

 these areas of gentle slope. 



Aside from conditions of slope the chemical character of 

 the material subjected to weathering is very important. While 

 all minerals are more or less resistant to weathering, certain ones 

 are especially resistant to the ordinary ground water solutions. 

 Some of these are kaolin, iron oxides, barite, and quartz. On 

 the other hand, the carbonate minerals are comparatively soluble, 

 especially in bicarbonate solutions. This is the dominant type of 

 solution in the region under discussion, and, as the rock associ- 

 ated with the barite is dolomite, it is readily attacked by such 

 solutions. 



If the surface of the dolomite were exposed, mechancial 

 forces in breaking up the rock would aid the egress of the solu- 

 tions. The solutions would also take advantage of the joints 

 which had been caused by deformative earth movements or 

 original changes in volume during the consolidation of the rocks. 

 Under such favorable conditions chemical weathering should 

 proceed rapidly, but as soon as sufficient mantle rock had accu- 

 mulated the entire process would be checked. As the water re- 

 moved more and more of the dolomite the accumulation of the 

 insoluble particles, kaolin, quartz, etc., would proceed until a 

 thick deposit of clay would result. Thru it would be scattered 

 any fragments of insoluble materials that were in the dolomite. 



In the Washington County area the solutions attacking the 

 dolomite first dissolve the smaller, more readily soluble grains. 

 The loose larger grains and the friable rock resulting from such 

 action are called "sand rock" by the miners. Its granularity is 

 suggestive of such a rock. 



As noted above, when water is present it is rather consist- 

 ently found at the contact of the clay with the dolomite. Some 

 occurs in the usual gravel layers in the clay, but the larger part 

 moves along the contact. Thus the zone of greatest solvent ac- 



