THE BARITE DEPOSITS OF MISSOURI 47 



of either the Potosi dolomite or the Proctor dolomite. It is un- 

 necessary to try to distinguish among them further. An uncon- 

 formity may exist between either the Potosi and the Eminence 

 formations, or between the Eminence and the Proctor forma- 

 tions. 



The Proctor dolomite was deposited in a quiet sea and at a 

 considerable distance from the shore. The presence of the mas- 

 sive beds tells the same story of undisturbed waters existing 

 when the Potosi dolomite was being deposited. The waters evi- 

 dently did not contain much silica, which was due either to the 

 fact that the land was far distant, or that the silica-bearing water 

 had been deflected into another part of the sea. The Eminence 

 formation of Shannon County with its abundance of chert may 

 be the time equivalent of the Proctor because of this deflection. 



The Proctor dolomite is overlain by the Gasconade forma- 

 tion. In Washington County the lower part of the latter is dolo- 

 mite and chert, with possibly a little sandstone, a sequence which 

 does not involve a very great change, altho one probably occur- 

 red. In central Missouri a sandstone member, the Gunter, is 

 known to occur at the base of the Gasconade formation. This 

 would suggest that the shore-line, for a time at least, was near 

 the area of deposition, altho a sandstone might be deposited at a 

 distance from the shore if the sea were shallow. Such a change 

 was probably due to deformation and favors the view that an 

 unconformity exists at this lower limit. 



It is, of course, possible that the sandstone was the first 

 member deposited upon an eroded surface by an advancing sea. 

 This also would mean an unconformity. Nearly all who have 

 studied these formations believe that there is an unconformity 

 between the Gasconade and the Proctor formations, and the 

 writer is in accord with this belief. 



The Gasconade formation represents an epoch during which 

 there were several changes, perhaps temporary, in the relation- 

 ship of the land to the sea. For the larger part of the time the 

 waters were shallow and far enough from land to receive little 

 in the way of terriginous sediments. When such sediments were 

 deposited they were sands, shales not appearing in this group of 

 rocks. This would seem to indicate a rapid shifting of the shore- 



