I 88 Bulletin of Laboratories of Denison University. [Voi xii 



are secondary accumulations, resulting from chemical and 

 physical action during the decay of the rocks containing the 

 manganese. 



Abundant masses of breccia-ore are associated to some ex- 

 tent with other types of the ore in all deposits, but they 

 are especially characteristic of the lower zone of decay of the 

 quartzite, which consists of only partially decayed and broken 

 masses of the rock over the quartzite area. The formation of 

 the breccia-masses is due to the downward percolation of the 

 manganiferous solutions through the overlying mantle of decay 

 into the cracks and crevices separating the rock-fragments and 

 deposition of the manganese oxide. In the Cave Spring dis- 

 trict, where broken masses and beds of chert from the Knox 

 dolomite abound, a similar formation of chert-breccia is ob- 

 served. In some instances the percolation from above has 

 extended into the cracks of the moderately fresh rock below, 

 with deposition of manganese forming intersecting veins in the 

 rock. 



The frequent black color of the ore-bearing clays especially 

 noticeable near the ore-bodies, due to the presence of very 

 finely-disseminated particles of manganese oxide, finds explana- 

 tion in the precipitation of the manganese oxide from the per- 

 meating solutions. All of these associations and different types 

 of the ore are regarded as products of secondary chemical and 

 physical action. 



Finally, this process of local concentration of manganese 

 has its analogy in the present accumulation of manganese in the 

 residual decay of the crystalline rocks throughout the Southern 

 Appalachians. The writer has observed in his field-study of 

 rock-weathering, in parts of Virginia, the Carolinas and Geor- 

 gia, that, in the weathered materials of these rocks, some of 

 whose minerals were manganese-bearing, the decay was colored 

 black in spots from the oxide of manganese, and, frequently, 

 knife-edge stringers of the manganese were found filling the 

 cracks in the clays. 



The theory as outlined above is not new, but was pre- 

 viously elaborated in greater detail by Prof. Penrose in his ex- 



