THE CHESTER EMEKY BED. 143 



ASSOCIATION AND I'ABAGENESIS OF THE MINERALS OF THE EMERY VEIN. 



The magnetite, which, when pure, is very fine-gi-ained, compact- 

 massive, with pecuhar purple tint, becomes mixed with emery in gradually 

 increasing proportions— the "emery-magnetite" of Professor Shepard's 

 classification. The emery increases until a harsh, rough-surfaced mass is 

 formed, in which the coppery-brown corundum crystals are abundantly 

 disseminated, like the feldspar in a porphyry. There is also a passage, 

 by the gradual increase of the corundophilite from the magnetite, into the 

 "corundophilite-schist" of Professor Shepard. The thin sections of the 

 latter rock show, however, no corundum, but abundant octahedra of mag- 

 netite, and I have been unable to convince myself of the existence of 

 anything con-esponding to the "stony emery" of Professor Shepard. Also 

 thin sections of the "fringe rock" show only magnetite. The pure mag- 

 netite is at times beautifully jointed. In one piece three systems ..f joints, 

 about 20"- apart, break up the mass into rhombohedra with about the 

 angles of calcite, and the parts are slightly slipped on each other and 

 recemented. Further, quite large irregular cavities in the chloritic mag- 

 netite have fine blades of the corundophilite prolonged freely into them 

 from the mass of the rock. 



In another mass the "compact emery" is brecciated; angular pieces 

 about 30-50"'- across are separated 20-30™"' from each other and the 

 interspace is filled with fine, scaly corundophilite. In other cases, as men- 

 tioned by Dr. Jackson, large rounded masses of the tough emery are 

 wrapped around on all sides by a schistose aggregate of comndophihte 



and raargarite. 



Again, as mentioned above, a great cross vein of the compact chlorite 

 rock, carrying much tourmaline and pyrite, cuts directly across the vem at 



the north mine. 



In one piece the light-pink and green schist is firml)' joined to a mass 

 of magnetite, with its laminae at right angles to the plane of juncti.m. 



In many cavities and open cross-joint fissures the surface is covered 

 by a thick layer-separated from the subjacent rock by a distinct suture, 

 and plainly of later formation under circumstances different from those 

 described above-of large, stout, six-sided crystals of corundoplnhte, all 

 placed with their vertical axes parallel to the surface, but taking any 

 direction in this plane, and terminated above by l)lack striated faces of the 



