Art. Tx.] Watson, Manganese Ore-Deposits of Georgia. 19 1 



of the manganese in the crystalHne rocks of the State is chiefly 

 from the various silicates containing manganese as one of the 

 base-forming elements. Upon decomposition of the complex 

 silicates, the manganese is either removed in solution in the 

 form of a soluble salt and deposited with the sediments formed 

 elsewhere, or it is retained in part or in whole in the form of 

 the insoluble oxide distributed through the residual decay of the 

 original rock, in situ. Numerous manganiferous silicates are 

 distributed through the rocks of the Georgia Crystalline area, 

 among the commonest of which are certain species belonging 

 to the amphibole, pyroxene, mica, garnet, epidote or olivine 

 groups. Besides the silicate form of manganese, the writer has 

 observed both the carbonate and oxide of manganese in several 

 localities in the crystalline rocks of Georgia. 



Rhodochrosite is found in Towns county, 2 miles west of 

 Hiavvassee, associated with the oxides of manganese and iron in 

 hornblendic rocks of the corundum belt. Manganese oxide, in 

 association with small grains and crystals of magnetite, occurs 

 in a magnetite-quartzite schist in Haralson and Paulding 

 counties. 



Residual Decay of the Crystalline Rocks. 



Atmospheric forces have been continuously operative on 

 the rocks of the Crystalline area of Georgia for an indefinite 

 period of time, resulting in the fresh rock being buried at pres- 

 ent under a considerable depth of residual decay. Conse- 

 quently, exposures of the fresh rock from which the decay was 

 derived are seldom seen except on the steeper slopes and 

 along the stream-courses. The mantle of decayed rock varies 

 greatly in thickness, from a few feet to several hundred feet. 

 Its character is equally variable, dependent mainly upon the 

 type of rock from which it was derived and the forces pro- 

 moting it. 



Mode of Occurrence of the Manganese- Ores. 



The lithological associations and modes of occurrence of 

 the manganese-ores are different from those of the Palezoic area. 



