THE CHESTER EMERY BED. 127 



jjarticles not exceeding in size those of certain varieties of steel or fine-grained cast 

 iron. The fracture is eft'ected witli the greatest difticailty, and takes ])lace as readily 

 in one direction as another. The surface, moreover, has an exceedingly hard feel. 

 Its color is a darker lirown than that of the preceding varieties. It also presents in 

 some specimens a faint violet-blue tarnish. It has often been mistaken for magnetite, 

 though its harshness of feel and very dilHcult frangibility easily distinguish its masses 

 from that ore. It has a tendency to occur throughout the vein in wedge-shaped, con- 

 torted masses, as well as in elliptical balls of all sizes, from a few ])ounds weight u]) 

 to a hundred pounds. 



{(1) Emery magnetite. — This is a massive magnetite containing a variable intermix- 

 ture of emery. It closely resembles magnetite, but it is distinguished by its superior 

 hardness, its purplish tarnish, and more difficult frangibility. It does not appear to 

 be abundant, though it is often liable to be met with throughout the course of the 

 vein. 



(e) Stony emery. — This in general is the chloritoidal rock or substance of the vein 

 in places where it is not replaced by one of the preceding varieties. It is a slaty, 

 tough, greenish-gray, rather heavy aggregate, containing everywhere fine-grained 

 emery in proportions varying between 10 and 20 per cent. Other minerals also are 

 present occasionally, such as tourmaline, epidote, margarite, ottrelite, magnetite, etc. 

 A variety of stony emery in thin, highly contorted, schistose layers enveloping the 

 compact emery frequently presents itself. Its color is a delicate greenish white, and 

 it is often interlaminated by seams of pinkish margarite — the entire aggregate being, 

 nevertheless, rich in emery. 



2. Magnetite. 



Next in abundance among the constituents of the vein stands the present species, 

 that richest and most precious of all the ores of iron. Its composition being so strictly 

 accordant with that of emery, their joint occurrence would, on chemical grounds, be 

 looked for almost as a matter of course. Like the emery itself, it here occurs massive, 

 thin-veined, granular, and disseminated. The massive variety is found perfectly 

 pure and unmixed. Laving a structure between the coarse-grained (shot oi-e) of the 

 Lake Champlain region and the fine-grained, compact ore of Franconia and Danne- 

 mora, Sweden. It sometimes exhibits in the fracture a slightly purplish tint not 

 observable in any other magnetite with which I am acquainted. It is also a shade 

 blacker than most magnetites. It is wholly free from pyrites and all traces of rust, 

 and consequently is bright and fresh in luster throughout. It is magnetic with polar- 

 ity, but does not give rise to examples of the native magnet. It presents itself in 

 considerable quantity at several places on the course of the vein. For example, at 

 the top of the North Mountain it constitutes a continuous seam from 10 to 15 inches 

 thick in a chloritoidal vien, itself 4 or 5 feet wide, and made up of the disseminated 

 variety, presently to be mentioned. This vein of magnetite forks ofl" from the great 

 emery vein on its eastern side at an angle of about 30° and then pursues its course 

 between the talcose slate strata, within which it has already been opened for 



