30 UNIVERSITY OF MISSOURI STUDIES 



ness and largely removed before the deposition of the Proctor, 

 but this has not been proved. The apparent erosion and faulting 

 in the Potosi formation, as explained above, is in favor of its 

 having been so. If the cherty horizon does represent the Emi- 

 nence chert, it is much thinner in this area than farther south. 

 Since the chert is so very different from the drusy quartz of the 

 Potosi formation, the cherty horizon was considered as the base 

 of the Proctor in the mapping. If it actually represents the Emi- 

 nence, as seems to be the case, its thickness should be taken from 

 that of the Proctor. It is, however, too thin to map on the maps 

 of the scale used. For the reasons given in discussing the thick- 

 ness of the Potosi formation and the presence of the Eminence 

 chert, it seems probable that an unconformity exists between the 

 Potosi formations and that during this erosion interval the 

 larger part of the Eminence formation was removed. 



Economic importance. — The Potosi formation is of greater 

 economic importance than any other formation in the area, as the 

 larger part of the barite is obtained from it. Nearly 200 years 

 ago lead was discovered in the mantle rock derived from the 

 Potosi dolomite and it has produced lead ever since, altho the 

 amount produced now is small. In the early days of the lead in- 

 dustry, the only areas prospected were those where drusy quartz 

 or "mineral blossom" was found. A connection between the 

 drusy quartz and occurrence of lead was recognized. 



Proctor formation 



The Proctor dolomite is found in more or less connected 

 areas over the western half of the district. Altho its outcrops 

 are scattered, it ranks next to the Potosi formation in areal im- 

 portance. It outcrops extensively farther up the valleys in which 

 the Potosi formation appears, is found on the slopes above the 

 Potosi formation where the latter appears in the valleys, and oc- 

 cupies the crests of those ridges not capped by the Gasconade 

 formation. 



Beginning four miles southeast of Potosi, the Proctor dolo- 

 mite forms a continuous outcrop to the northern part of the 

 county. About a mile southeast of Potosi the ridge is so low 

 that the Gasconade formation is wanting and the outcrop there 



