strata.

"The immediate vicinity of the mine presents a succession of lengthened rocky swells with rather precipitous sides, having summits between 750 and 1000 feet above the level of the principal streams by which the hills are traversed. The longer axis of the elevations generally coincides with the directions of the แ The emery vein traverses in an unbroken line the crests of two of these adjoining mountains, and scarcely deviates as a whole from the magnetic meridian. Each mountain is estimated to have a length of two miles, thus giving four miles extent to the metalliferous stratum, for such it may be truly called, consisting as it does so largely of the metals iron and aluminum. The Westfield river, here a small stream about four rods in width, flows directly across the northern end of the vein, dividing it into two equal portions. The height of each mountain is estimated at 750 feet.

"The emery vein, whose average width may be taken at four feet, is situated near the junction of the great gneiss formation constituting the western flank of the mountains with the micaslate forming the eastern slope. To speak more exactly, however, it lies just within the gneiss, having throughout a layer of this rock of from four to ten feet in thickness for its eastern wall. Nor does the mica slate advance quite up to this outside layer of the gneiss; but in place thereof, an extensive intrusion of talcose slate occurs, having an average thickness of twenty feet on the south mountain, and widening out at the north mountain to a breadth of nearly 200 feet as it reaches the terminus of the vein, in the bed of the Westfield river.

"The gneiss, more especially in the vicinity of the vein, is a very peculiar rock. It abounds in thick seams of a coarsegrained, very black and shining hornblende; and where this is not found, it is much veined and penetrated by epidote. The stratification is much contorted also; and when the surface of the formation happens to be weathered or water-worn, its basseting edges strikingly resemble in color some of the serpentine marbles. It is also noticeable that in it quartz is everywhere singularly deficient. Traces of a white calcareous spar (calcite) are now and then visible upon the joints of the gneiss, with occasional specks of yellow copper, together with malachite stains; but no corundum, emery, or magnetite particles have thus far been detected as constituents of the gneiss. It is quite otherwise, however, with the talcy rock exterior to the wall of gneiss; for that formation in all its different varieties of talcose slate, soapstone, chloritic aggregates (with included seam of indianite), talcy dolomite, &c., which together constitute the stratum separating the gneiss from the mica slate, contain here and there disseminated grains of either emery, corundum, or magnetite; but,

like the gneiss again, are strikingly free from quartz or uncombined silica in any of its forms. Indeed this generally abundant substance is altogether wanting, not only in the emery-vein but in the talcose formations constituting its eastern boundary.

"It makes its appearance, however, in abundance in the mica slate as soon as the talcose rocks are passed-showing itself not only as the usual constituent of the slate, but in more or less continuous seams, from a few inches thick up to above six inches, and sometimes a foot, in width. Where the seams are thin and discontinuous, the included masses thin out at each end before disappearing, the sharp edges being curved in opposite directions, so as to form frequent white patches upon the surface of the rocks in the shape of the letter S."

Mineralogical Character and Composition of the Chester Emery.

It resembles more nearly that from Gumuchdagh (near Ephesus,) than any other that I know of. It is of a fine grain, and dark blue bordering on black, not unlike certain varieties of magnetic iron ore; with it there are frequently found pieces of corundum of some size. The interior of the mass is free from micaceous specks, such as are found in the emery of Naxos. Its powder examined under the microscope shows the distinct existence of more than one mineral, which are often so inseparably connected that the smallest fragments contain them together. The two predominating are corundum and magnetic oxyd of iron. Several specimens were submitted to chemical examination from those most largely impregnated with magnetic oxyd of iron to those that appeared to contain least. They all consisted essentially of alumina and oxyd of iron; but I invariably found a little titanio acid and silica, and most commonly a minute quantity of magnesia. No. 1 was an inferior specimen; No. 2, the better quality of rock; No. 3, the emery rock crushed and prepared for market in the form of emery; No. 4, the same, and called emery crystals.

1.

2.

3.

4.

I examined a specimen of No. 2: grain fine, and treated repeatedly with hydrochloric acid and water over a water-bath: a great deal of oxyd of iron and a little alumina were dissolved; the residue on analysis proved to be nearly pure corundum, giving,

All the chemical and physical examinations made go to show that the emery of Chester is, like all other emeries, a mixture of corundum and oxyd of iron; a fact that will be reverted to again a little farther on.

Prof. Jackson analyzed two specimens, after digesting them with nitro-muriatic acid, and has given as the composition,

and then goes on to state, "from which it would appear that protoxyd of iron is an essential chemical ingredient in emery, and not an accidental admixture. Dr. J. Lawrence Smith's experiments lead to the same result, but he considers the oxyd of iron to be an irregular mixture with the alumina and not a regular chemical constituent. In either case, I think emery ought to rank as a separate species, and not as a granular variety of corundum, from which it differs so in physical characters."

I would here remark that Dr. Jackson's conclusion would be correct in the first state of the case, were the iron an essential chemical ingredient; but in the latter, it would be erroneous, and introduce inextricable confusion into the science of mineralogy by admitting mere mechanical mixture as a specific distinction.

Prof. C. U. Shepard writing on the same point says, “His conclusions (Dr. Jackson's) would obviously be acquiesced in were it not for the strong resemblance in striæ and cleavage between the emery and common corundum, making it impossible for us to separate the substances crystallographically from one another. Nothing like a perfect crystal of emery has yet been found at the mine; but it is quite remarkable that the mineral is here generally coarsely massive, or in large separate individuals often of the size of kernels of Indian corn, whose cleavages are perfect, and which present on their planes the delicate striæ so characteristic of corundum from the Carnatic." Yet Prof. Shepard is for making emery a new mineral species and calling it Emerite, with the formula FeAl.

If the views of Profs. Jackson and Shepard are to be taken as correct, the question as to the mineralogical position of emery is easily settled without resorting to any new mineral species. It is simply a massive iron-spinel (hercynite) with the anomaly of having a hardness equal to corundum.

I would say, at this point, that if the mineral of Chester is to be regarded as an aluminate of iron, the rock called emery

2 An examination of my analyses in 1850, which it is supposed are the ones referred to here, most certainly do not sustain the conclusion.-J. L. s.

coming from Naxos and other well known localities is not that compound, and that if one is emery the other is not. But as I do not take their view of the matter, I consider the Chester mineral as true an emery as that of Naxos.

As there seems to be some mistake and incorrect quotation in regard to my analyses of emery and corundum, I reproduce the tabular statement of the analyses, and effective hardness, referring the reader to the original paper for a correct view of what is understood by the effective hardness.

By the above it will be seen that the magnetic oxyd of iron in the emery of Naxos, Ephesus, &c., varies from 13 to 33 per cent, the water from 19 to 50 per cent, the silica from 16 to 9.6 per cent. All of these ingredients form minerals apart from the corundum, which is represented by the principal portion of alumina. Some of the alumina found in the analysis is associated with the above ingredients to form associate minerals which have been fully studied. This last will serve to explain why it is that emeries having the same amount of alumina may have different degrees of effective hardness. Thus: Nos. 9 and 4, both Kula emeries, containing about the same amount of alumina, have effective hardness in the proportion of 40 to 53; but it will be seen that No. 9 contains 9.6 per cent of silica, which doubtAM. JOUR. SCI.-SECOND SERIES, VOL. XLII, No. 124.—JULY, 1866.

less appropriates a portion of the alumina, thus reducing the alumina attributable to corundum; so that, were it possible to ascertain the exact amount of corundum present in 9 and 4, it would doubtless be in proportion to their effective hardness. So again, if we compare Nos. 8 and 1, the effective hardness will be found in the proportion of 42 to 57, while their amounts of alumina vary only as 60 to 63; but if we regard the amount of water in the two it is as 56 to 19, much of this water coming from diaspore that is intimately mixed with the corundum; and in several specimens I possess, the two minerals shade into each other so completely, that it is impossible to tell where one begins and the other ends. The above facts were all well examined when my first memoirs appeared on this subject, which accounts for the following remark then made:

"Those emeries which contain the least water, everything else alike, are the hardest, as instanced by that from Kulah, notwithstanding the quantity of iron it contains. The silica existing in emery is most often in combination with alumina, or the oxyd of iron, or both; for this reason we must not always regard the quantity of alumina as an indication of the quantity of corundum in emery."

In concluding this part of the subject I would state that while I do not consider my opinions infallible in this matter, still all my experience and research, gathered from such varied sources, point to the conclusion that emery is a mixture of several minerals, principally corundum and magnetic oxyd of iron, the former being the effective agent in the mechanical abrasion to which it is applied; the oxyd of iron is not to be considered as an unimportant ingredient, it serving by its presence to destroy to some extent the harsh cutting action of the corundum.

Minerals associated with the emery of Chester.

Corundum.-This mineral, as might naturally be expected, is found with the emery, sufficiently distinct and separate to be at once recognized, sometimes in thin seams, massive in its character, but more commonly in flattened crystals of small dimensions.

Diaspore.-Very excellent and beautiful specimens of this hydrate of alumina have been found at this emery locality; it is often in distinct and separate prismatic or bladed crystals, quite colorless and transparent.

Emerylite or Margarite.-Some of the finest specimens of this mineral that are known have been found at this locality. It will be seen by referring to my former papers on emery, that I first discovered this mineral associated with emery; its composition showed it to differ from any other then known mineral. I compared it subsequently with margarite, which had been discovered before, and suspected the identity of the two minerals;