THE BARITE DEPOSITS OF MISSOURI 33 



tary on the north side of Mineral Fork. At the former locality 

 they are apparently later than the barite. Joints are rather com- 

 mon. The major set strike N. 65° E., and locally are nearly east 

 and west, and the result of the two is the production of rhom- 

 boidal blocks, thus making mechanical erosion prominent. 



No fossils were found in the formation. 



The rock weathers to a rough, pitted surface (PI. VI, A), 

 usually of a color darker than that of the fresh rock. When it 

 contains enough pyrite it takes on a buff to yellow color, tho this 

 color is not common. The much pitted surface is due, in large 

 part, to the more rapid solution of the calcite spots in the dolo- 

 mite. The rough surface of the weathered rock is also due to 

 the abundant grains of dolomite that stud the surface. Here the 

 more rapid removal of the smaller grains has left the larger 

 grains on the surface. This type of weathering produces a 

 "sandy" surface, and when the products are not removed too 

 rapidly they produce what the miners call "sand rock." This 

 is merely the disaggregated product of the dolomite. 



Age and correlation. — The Proctor dolomite is regarded as 

 of Upper Cambrian age. Buckley® suggests that there is an un- 

 conformity at the top of the formation, and Ulrich also believes 

 there is one. Whether there is one or not cannot be determined 

 in this district, as not a single exposure was seen which showed 

 these formations in contact. As stated above (page 39), there is 

 evidence for thinking that an unconformity exists at the base of 

 this formation. The Proctor dolomite is one of the few forma- 

 tions in the Ozarks which has persistently held its formational 

 name. It corresponds to Swallow's^ Fourth Magnesian Lime- 

 stone. All others who have had occasion to give a section of the 

 stratigraphy in the Ozarks have called it the Proctor formation 



Economic importance. — The Proctor dolomite ranks next to 

 the Potosi formation in the production of barite. Doubtless some 

 barite from this formation is being mined 'from residual clay over 



'Buckley, E. R., Geol. of the Disseminated Lead Deposits of St. Fran- 

 cois and Washington Counties, Mo., Bur. of Geol. and Mines, vol. 9, pt 

 1, 1908. 



'Swallow, G. C., First and Second Ann. Repts. Mo. Geol. Sur., pp 

 114-131. 1855. 



