Art. IX.] j Watson, Manganese Ore-Deposits of Georgia. 173 



face the soft shales in long and narrow north-south strips, 

 forming narrow valleys among the dolomite hills. The fault- 

 blocks overlap each other, with rather steep dips toward the 

 east and southeast. 



Character of the Residual Decay. — The manganese ores of 

 the Cave Spring area are entirely limited to the residual clays 

 derived from the decay of the Knox dolomite. The decay 

 from this formation only will be considered. The ore-bearing 

 clay is usually of a deep-red, chocolate or brown color, with 

 lighter tints occurring. It is soft and plastic when wet, and is 

 generally associated with much siliceous material in the form of 

 chert, subject to wide variation from place to place. Its depth 

 is variable and, in places, the moderately fresh cherty limestone 

 is exposed as broken reefs on the ridge-tops. In other places 

 on the ridge-tops, excavations in mining expose the hard rock 

 at depths varying from 10 to 30 ft.; and, in still other places 

 on the same ridges, rock is not encountered at depths of 50 to 

 60 ft. 



Massive cherty layers or beds are of more frequent occur- 

 rence in the limestone of this area than for the same formation 

 at other points in northwest Georgia. Here the chert attains 

 considerable thickness, and, at times, almost entirely replaces 

 the limestone. Uusually the chert is a white or gray rock, 

 sometimes brown, rarely black, and is often encrusted with a 

 film or coating of the black oxide of manganese. The relation 

 of the chert and limestone is well illustrated along the ridges to 

 the southeast of the town of Cave Spring, where the rocks dip 

 to the southeast, with the limestone forming the lower part of 

 the hills and the chert the upper part. 



Manganifero2is Chert Breccia. — The very intimate associa- 

 tion of the chert and ore has resulted in the formation of much 

 breccia, composed of the angular chert-fragments cemented in a 

 manganese-oxide matrix. This seems to have originated in 

 most cases from the infiltration of surface-waters containing" 

 manganese in solution. The occurrence of the chert-breccia 

 beneath the clay covering is excellently illustrated in some of 

 the excavations on the ridge above the Cedar creek valley, and 



