of Oxides of Manganese. 177 



11th. Ferric sulphate solution reacts immediately upon cal- 

 cium carbonate, forming calcium sulphate, ferric hydrate and 

 carbonic acid. 



12th. Ferric sulphate solution digested cold or hot with 

 powdered manganese oxide was not altered. 



13th. Ferric sulphate solution was digested cold for nine 

 days with sawdust and powdered psilomelane ; considerable 

 manganese sulphate was formed. 



14th. Manganese sulphate solution is not altered by expos- 

 ure to air, but when so exposed, and also in contact with cal- 

 cium carbonate, manganese oxide is gradually formed. 



15th. Manganese sulphate solution, digested cold with cal- 

 cium carbonate in a sealed tube, is not altered ; when heated, 

 it is feebly affected, a little manganese carbonate being formed. 



In view of the foregoing observations and results, it appears 

 possible that many deposits of manganese in calciferous rocks 

 owe their formation to the action of solutions of sulphates, and 

 possibly an illustration of such action is presented in the man- 

 ganese deposits of Crimora, Augusta Co., Va., which occur 

 under the following conditions. 



In the Shenandoah Valley, the upper portion of formation 

 I (Rogers) is composed of shales which are well decomposed 

 to a great depth, interspersed with remaining calciferous 

 ledges, and as they pass westward these alternate with, and are 

 succeeded by, ledges of siliceous limestone. In these decom- 

 posed shales, we find pure neutral iron ores, free from manga- 

 nese, and associated with them there are manganiferous limon- 

 ites and also psilomelane of high grade, frequently appearing 

 to have grown in similar condition, and sometimes the same 

 mass is composed in part of manganese and in part of limonite. 

 South of the Potomac, no pyrites is visible in these shales, pos- 

 sibly owing to the great depth to which they have been de- 

 composed ; but at Harper's Ferry, the iron ore lying in the 

 same geological horizon has been worked down until compact 

 pyrites has been reached. The presence of the pyrites in the 

 latter renders it probable that it did exist extensively in the 

 shales above described. 



Assuming that pyrites did thus exist, generally distributed, 

 we might expect a deposition of ores to have occurred in some 

 such manner as the following. 



Where pyrites has been deposited and subsequently has been 

 exposed by reason of erosion, the outcrop is gradually con- 

 verted into limonite by weathering, and the acid solution of 

 ferrous sulphate which sinks into the underlying deposits, 

 must carry with it all manganese associated with the decom- 

 posing sulphide, also that in any disintegrating silicates and 



Am. Jour. Sci.— Third Series, Vol. XXXVI. No. 213.— Sept., 1888. 

 12 



