34 UNIVERSITY OF MISSOURI STUDIES 



the Potosi dolomite. No lead occurs in the Proctor formation. 

 Gasconade formation 



The Gasconade formation includes dolomite, chert, sand- 

 stone, and a little shale. The exposures are so poor and few 

 that a detailed section could not be made. 



The Gasconade formation is chiefly in the southwestern and 

 middle western parts of the area, with various isolated exposures 

 in the central and northern parts. The southwestern area occu- 

 pies the upland country called the Salem Platform. One part ex- 

 tends to the north between Bates and Mine a Breton creek, and 

 another between the North Fork of Fourche a Renault and Bates 

 creeks. The other extension of the area is to the east along the 

 divide between the streams that flow south to Big River and 

 those that flow north to Mine a Breton. One spur extends to 

 within a mile of Summit on the Iron Mountain Railroad. The 

 long narrow ridge which the Old Mines road follows is capped 

 by the Gasconade formation. Just south of Old Mines, where 

 Old Mines Creek heads, the Gasconade outcrop divides, one part 

 extending about two miles northeast along the ridge, and the' 

 other part turning to the west along the high ridge that lies be- 

 tween Mine a Breton and the southern tributaries of Mineral 

 Fork. A branch of the latter follows the ridge between Mill 

 Branch and Old Mines Creek nearly to Mineral Fork. To the 

 east of Old Mines Creek, toward Fertile, there are isolated 

 patches of the Gasconade formation capping the higher hills and 

 ridges. From Aptus north to Richwoods there is a large area of 

 the formation, and a smaller area to the north of Little Indian 

 Creek. Most of the higher hills and ridges that are underlain by 

 the Proctor dolomite contain a considerable amount of residual 

 chert and sandstone from the Gasconade formation, which once 

 covered the region. 



The Gasconade formation is largely confined to the highest 

 hills and ridges. It remains here because of its great resistance 

 to erosion. This formation, with the Roubidoux, is the principal 

 surface rock thruout the central part of the Ozarks. 



Petrography. — The Gasconade formation includes dolomite, 

 chert, sandstone, and shale. Some of the dolomite is shaly, some 



