THE BARITE DEPOSITS OF MISSOURI 83 



tained from the surrounding rocks in sufficient quantities to 

 form such large deposits as are found. Its transportation by 

 chloride waters is a possibility, but its scarcity in such waters in- 

 dicates how small the amount available in the rocks usually is. 



Permeability of the rocks. — In order that such minute quan- 

 tities of barium as exist in the rocks could be concentrated it is 

 essential that the solutions be able to reach them. The porosity 

 of the rock must be taken into account. Unfortimately, there 

 are no determinations of the porosity of the Potosi or the Proc- 

 tor, but judging by the large openings scattered thruout the rocks 

 it is about 8 to 10 per cent. But this porosity does not represent 

 the ability of the water to move thru the rock, for the large 

 openings are disconnected and, therefore, the true permeability 

 of the rocks is that of the dense, crystalline dolomite. This must 

 be fully the equivalent of the permeability of granite, or about .5 

 per cent. This difference between permeability and porosity is 

 not generally recognized and porosities are taken that are com- 

 monly too high. 



Recent experiments made by a graduate student under the 

 writer's direction show that pressures of 1500 pounds per square 

 inch will not force Vi^ater thru a limestone with a porosity of .5 

 per cent. A pressure of 2800 pounds per square inch broke the 

 rock but failed to force any water thru it. 



Actually the movement of water thru rocks is mostly along 

 the divisional planes and not thru the body of the rock. The evi- 

 dence to support this contention is to be seen on every hand in 

 the field. The irregular erosion surface of all rocks is seen to be 

 related to the joints and fissures in the rock. The development 

 of solution cavities of all sizes begins along such openings, altho 

 by enlargement they may later come to be disregarded. It is 

 sometimes stated that the bedding planes are the principal pas- 

 sage for solutions, especially in carbonate rocks. This statement 

 should be modified, because the bedding planes in carbonate 

 rocks are marked by clay partings, and clay is relatively imper- 

 vious. If the formations have undergone a certain amount of 

 deformation the partings along the bedding planes probably be- 

 come more or less accentuated and are to be included in the 

 larger divisional planes along which the materials may be carried. 



