THE BARITE DEPOSITS OF MISSOURI 29 



the possible displacement. However, there is one feature which 

 is strong evidence of faulting, and that is the lack of continuity 

 of the heavy honey-combed masses of quartz. These appear to 

 belong near the top of the formation, but in many places are 

 missing at the horizon where they should be found. This might 

 be explained by faulting and erosion, as noted above. If there 

 was faulting it occurred before the deposition of the Proctor 

 dolomite, for this formation is very persistent in thickness over 

 the area. If faulting occurred, an unconformity exists between 

 the Proctor and the Potosi formations. 



Age and correlation. — No fossils were found in the Potosi 

 dolomite so its exact age is unknown, but its position in the series 

 suggests that it is Upper Cambrian. Ulrich^ places the Potosi 

 formation at the base of the Ozarkian in Missouri. In an eadier 

 paper^ he includes it in the Potosi group, as a part of the Gascon- 

 ade limestone. He called it the Lesuer limestone, a name pro- 

 posed by Keyes for this formation, but not until after Winslow 

 had given it the name of "Potosi", hence "Potosi" has priority. 

 Ulrich, in his revision of the Paleozoic systems, states that Buck- 

 ley's use of the term for this formation is best and he adopts it. 

 The formation is very easily recognized and is fairly easily de- 

 limited. 



The Eminence chert. — A question arises as to the possible 

 presence of the Eminence chert in this area. Ulrich recognizes 

 it as a formation of not less than 200 feet in thickness in Shan- 

 non County to the southwest. There it is a very cherty dolomite. 



In the Washington County district there is at the top of the 

 Potosi formation a band of very cherty dolomite, often several 

 feet thick. This member is rarely more than 25 feet thick, and 

 in most places only 5 to 10 feet. It was not mapped during the 

 field work, for lithologically it would be considered as the top of 

 the Potosi dolomite or as the base of the Proctor formation. The 

 color and texture of the dolomite associated with the chert are 

 the same as those of the formations above and below. It may 

 be that the formation was formerly present in considerable thick- 



•Ulrich, E. O, Bull. Geol. Soc. Am., vol. 22, p. 622; also. pp. 628-633. 

 1911. 



'Ulrich, E. O., Bull. U. S. G. S. 267. 



