86 JOURNAL OF THE [June, 



carbonaceous matter. Nevertheless, it is everywhere diffused 

 in enormous quantities throughout the softer deposits at the 

 bottoms of the ocean, lakes, and running waters, quantities per- 

 haps equalling or exceeding those of the pyrites visible in the 

 rocks. Its constant and universal formation doubtless serves 

 the important purposes of rendering the iron oxides freely 

 soluble in water, of assisting their later distribution as a cement 

 through sandstones, and of causing their final accumulation as 

 bodies of iron ore. 



The substance to which I refer, is termed Iron protosulphide. 

 It has a very simple composition, a single molecule containing 

 one atom of iron to one atom of sulphur, indicated by the for- 

 mula Fe S. I have but repeated the ordinary view in stating 

 that it does not occur on the earth as a distinct, isolated miner- 

 al ; nevertheless, there are grounds, long ago advanced by the 

 chemist Frankenheim, for believing that this substance, iron 

 protosulphide, does exist as a well-known crystallized mineral; 

 and it is from this point of view that you are asked to-night to 

 examine in the first slide, the rare, hexagonal crystals of brown- 

 colored pyrrhotite from a vein at Elizabethtown, Canada. The 

 brilliant iridescent tarnish which these display, perhaps accounts 

 for the few occurrences of the unstable mineral in that form. 

 Under the name iron pyrites, with which all are familiar, there 

 are really comprised three distinct minerals ; namely, Pyrrho- 

 tite, Marcasite, and Pyrite, three comrades, clinging closely, 

 hard to be parted. Where one is, one or both of the others may 

 be found not far off. The one I have already mentioned, 

 pyrrhotite, is, I believe, the elder brother, almost always the 

 first one to be born — when metamorphism sets in and a rock 

 comes into being — out of the black mother-slime, rich in iron 

 sulphide, which permeates the silt and soil and mud-banks of 

 the earth's crust. But oxygen, all pervading, is the constant 

 foe of this simple compound, robbing it at its very birth of a 

 variable portion of its iron, so that the number of its atoms of 

 sulphur always exceeds those of iron; e. g., thus, Fe' S*, instead 

 of Fe" S^, which should comprise eight molecules of pure iron 

 protosulphide. 



In the further course of the subterranean conflict, in which 

 the oceanic sediments consolidate, the robbery to which I have 

 referred is consummated by the disappearance of half the 



