Decomposition of Iron Pyrites. 



399 



Locality. 



Kind of Pyrites. 



Rock-Matrix. 



Shoreham, Vt. 



Pyrite. 



Stafford, Corinth and Pyrrhotite, cbalcopyrite, 



Shrewsbury, Vt. and pyrite. 



Brookfield. Waterbury Arsenopyrite, pyrite, and 



and Stockbridge, Vt. 

 Nova Scotia. 



Albert, N. B. 



Notre Dame Bay, 

 Newfoundland. 



Elizabethtown, Ont., 



Can. 

 Lennox ville, Q., Can. 



Lachute, Q., Can. 



Limestone and black mar 

 ble. 



cbalcopyrite. 

 Pyrite, arsenopyrite, andjQuartz veins in slate. 



cbalcopyrite. 

 Pyrite nodules, inclined to Carboniferous sandstone. 



ready decay 



Pj-rite and cbalcopyrite. 



Pyrite, with a little pyrr 



hotite. 

 Pyrite. 



Pyrrhotite. 



Slate. 



Laurentian quartzyte and 

 gneiss. 



Laurentian crystalline 

 limestone. 



A consideration of the facts above presented renders it very 

 probable that in most of these instances the original condition 

 of the iron sulphide, along the Appalachian belt, has been that 

 of pyrrhotite, which now, as a rule, survives only in the belts of 

 less crystalline schists, especially mica-slates, and in the larger 

 beds and veins ; that its conversion into marcasite and pyrite, 

 ^ind other pyritous minerals, in the presence of Cu, Ni, As, etc.) 

 has generally attended the progress of the metamorphism of the 

 enclosing rocks ; that, as in Europe, the surplus of iron, separa- 

 ted in the transformation of Fe 7 S 8 into Fe S'", has been removed 

 by carbonated waters and re-deposited in the form of iron-car- 

 bonate within the interstices and larger cavities of limestone, ex- 

 cavated by the same solvent, through interchange for calcium 

 carbonate, and over the natural subterranean drainage-planes 

 afforded by beds of gneiss and mica-slate ; that some of these 

 ferruginous deposits may have been later converted into hematite 

 and magnetite, by local metamorphism, and that subsequent ox- 

 idation of all these deposits, partial or complete, still going on, 

 has been at least an important source of the limonite ores along 

 the Appalachians. 



Doubtless the origin of the limonite-deposits has been due to 

 several causes, and we can hardly question, for example, their 



