THE BARITE DEPOSITS OF MISSOURI 31 



is continuous with the outcrops along Mine a Breton and Bates 

 creek. It joins these outcrops again ten miles to the north along 

 Mineral Fork. It outcrops along the north side of Mineral Fork 

 from the western border of the district near Aptus to a point 

 near Kingston where it turns northwest towards Richwoods. 

 Here it divides, one outcrop following Little Indian Creek, and 

 the other running due north to the north side of the county. To 

 the east of Old Mines, the Proctor has been entirely cut away 

 along the road to Shibboleth, but to the northeast towards Fertile 

 there is an extensive outcrop. There is also a small area of 

 Proctor dolomite exposed along the North Fork of the Fourche 

 a Renault where it leaves the area in the southwestern part. 



The Proctor dolomite is from 80 to 125 feet thick, yet its 

 outcrops are rather broad over the entire area. This is due to 

 the lithological character of the formation. It is entirely free 

 from chert and hence is easily eroded. It forms the base of the 

 Potosi escarpment along its eastern outcrop, but to the west its 

 rather wide outcrops are due to the fact that it is largely the up- 

 per formation on the ridges. Around Fertile and Richwoods the 

 low relief explains the rather extensive outcrops. However, the 

 Proctor formation does not form a marked shelf on the slopes 

 where it outcrops, altho this would be expected. This shelf act- 

 ually is present in a few places. Its failure to appear widely is 

 probably due to the fact that the Proctor dolomite inherited a 

 rather heavy mantle of residual chert and sandstone from the 

 Gasconade formation. The presence of this material also made 

 the determination of its upper boundary difficult. 



Petrography. — The Proctor dolomite is a nearly pure dolo- 

 mite. As a rule, the color is some shade of gray, varying from 

 light to dark, and in places with a bluish cast, but buffs and 

 rarely pinks are also found. There is much variation in color 

 both vertically and locally. The rock is crystalline, altho there is 

 considerable variation in the size of the grains. Probably me- 

 dium-grained texture predomintes, but there are many fine- 

 grained phases. Ever5i'where the rock contains numerous small 

 cavities, rarely two inches long and usually not more than about 

 an inch. They are very irregular in shape and are lined with 

 crystals of dolomite, calcite, and, rarely, quartz. Many of the 



