ON THE MINERALOGICAL LOCALITIES IN AND AROUND NEW YORK CITY.
PART IV.
By NELSON H. DARTON.
Montville, Morris County, New Jersey.--This locality is an old one, and well known to mineralogists. It is outside of the limits prescribed in introducing this series of paper, but by only a few miles, and being such an interesting locality, I have included it in the granular limestone, which occurs in a small isolated ridge in the gneiss within a space of ten acres, about two miles north of the railroad station of Montville, on the Boonton Branch of the Delaware, Lackawanna, and Western Railroad, and is reached by a road running north from about a mile east of the railroad station. This road branches into two at the limestone kilns, about a mile from the railroad track, and the left hand branch is taken, which leads more directly to the quarry, which is on the right hand, about a mile further on, and quite conspicuous by the loose rock lying in front of the quarry. It is on the property of a Mr. John J. Gordon, and produces a very fine limestone for use in the furnaces and forges in the vicinity, as well as lime for agricultural purposes, it being the only limestone in the vicinity for fifteen miles. Between it and its walk of gneiss occur veins of the minerals so characteristic of the locality, and for which it has become famous--serpentine, asbestos, phlozopite, gurhofite pyrites, biotite, aragonite, dolomite, tremolite, and possibly others in lesser quantity.
Serpentine.--All the varieties of this species, and of every color from nearly white to black, is profusely distributed through the limestone in the lower or main quarry in veins and pockets. It is generally soft, translucent, and to be found in masses from a pea to a cubic foot in size. Much of it is of a pure oil green color, rich and translucent, making a very fine and attractive looking mineral specimen. No difficulty need be experienced in producing all the varieties of this mineral, as much has been removed and may be found in the vicinity of the quarry, as it is always carefully separated from the limestone as being useless, and thrown aside, or in some instances, when of peculiar beauty, sold as specimens. The variety of serpentine known as marmolite, which is made up of numberless plates of the mineral packed together similar to mica, but of the green color of the serpentine picolite, or fibrous serpentine, also frequently occurs of a light grass green color, and is a very interesting variety.
In selecting specimens of serpentine, care should be taken to procure that which is the most translucent, and that holding miniature veins of asbestos. These are not so plentiful as those of the pure serpentine alone, but occur in the southern end of the main quarry. The width of these veins of asbestos is seldom over an inch, but those of even much less are highly prized as specimens. These veins of asbestos are, in places, several inches in length, but are generally much broken in removing them, as their fibrous structure, at right angles to their length, makes them very fragile, and pure specimens of asbestos can seldom be found. However, they make much finer specimens when with the serpentine. Frequently these specimens may be obtained with a layer of gurhofite above them, and separated by the serpentine; this assortment is very interesting, revealing to us the manner in which they were formed, which was by a process termed segregation.
This gurhofite, called bone by the quarrymen, occurs in white, dense looking masses, intermingled with the serpentine, especially in the upper end of the quarry, where veins six and eight inches in thickness are abundant, and from which specimens may be readily obtained showing the fibrous structure of the gurhofite and the association with the serpentine, to which it is found attached; it is quite different from the limestone in appearance, and need not be mistaken for it.
Phlozopite.--In a vein near the lower end of the quarry, near the asbestos locality, occurs large plates of this mineral, which is a variety of mica, and has all of the characteristics of a pure silvery white color, and from one by three inches in area to less. It is easily separable in folia, and cannot be confounded with any of the other minerals. A huge mass of the veinstone holding abundance of this mineral is exposed, whence it may be plentifully obtained in excellent crystals.
Pyrites.--White and yellow iron pyrites are abundant in the gneissic rock adjoining the limestone, and frequently very fine, perfect crystals may be found handsomely dressed upon the rock. There is no particular portion of the quarries in which they abound.
Biotite.--This is a variety of mica in small crystals, of a dark brown color, and quite plentiful in the gneiss inclosing the veins of limestone. Up in the older quarries it is more abundant; on the north wall of the vein it is often in very fine specimens, and there even in large number, in a locality, generally a pocket in the gneiss.
Tremolite is quite abundant on a large mass of limestone in the extreme upper quarry, which is a short distance east of the main one, over a small hill. The tremolite occurs in white crystals, about a quarter inch in width and from a half to three inches in length. The crystals are opaque, but very smooth and glistening, lining cavities in this mass of limestone. It is a variety of hornblende, composed of silica, lime, and magnesia, with a little alumina. It probably occurs in places in the vicinity of this block, and in finer specimens, as these are frequently, when near the surface, much weathered and worn. This is a characteristic granular limestone mineral, and a very interesting one. We will again meet it when examining the New York city localities.
Aragonite occurs in very small masses, of a light yellow color and fibrous structure, between layers of serpentine. When they are separated by a small interspace, as it frequently is, the fibers are very large, coarse, and brittle, and thus do not resemble asbestos, although in some instances they might be mistaken for picolite, but, distinguished from it by effervescing on contact with a drop of acid, as it is a carbonate of lime, and also containing a trace of iron. I have never seen any fine specimens of it from this locality, but deeper down in the rock it may occur in greater profusion.
Dolomite occurs to a limited extent as such; most of it, being in the form of gurhofite crystals, may be occasionally found with aragonite of a light pearly gray color and rhombohedral crystals. As before noticed, Staten Island is the best locality for this species.
Calcite.--In places the limestone is perfectly crystallized, and of a pure white or other color, when it forms an attractive mineral, and often worth removing. The limestone of the main quarry, carefully averaged, was found to have the following chemical composition.
Lime. 11.09
Magnesia. 37.94
Carbonic acid. 30.61
Silica. 10.22
Water and loss. 4.90
Iron and alumina. 5.24
------
100.00
In places it is spotted with the serpentine, and judging from its rough state resembles "verde antique," and at that of a beautiful color; samples of this should be obtained.
Feldspar.--This mineral occurs very plentfully in the space between the limestones and gneiss. It is generally of a flesh red color and often in very perfect crystals, in some instances an inch and a half in length; as its hardness is 6, it can be readily distinguished from calcite, which it much resembles, but which has only a hardness of 3, and dissolves with effervescence in acids.
A visit to this locality is a delightful manner in which to spend a holiday or other time of leisure; and as it affords so many interesting and valuable minerals, it forms a very profitable trip as well. In reaching it many interesting localities are passed, and if one has an early start these may all be visited. I will describe a few of these, which are alike possessors of beautiful scenery and instructing geological features and not far from the main line of travel.
Starting from the Erie depot, on the Greenwood Lake road, the first stop may be at Arlington, about seven miles west of Jersey City. Here a visit to the Schuyler copper mine may be profitably taken; and as I have written a full account of this locality in a previous portion of these articles,[1] I will not reiterate it here, but refer to that paper. The mine, I might add, is only a mile north of the railroad station, and on Schuyler Avenue, a short distance north from its junction with the Jersey City and Paterson turnpike. Coming back to Arlington depot, and walking on the track for about a quarter of a mile west through the deep cut, the manner in which the sandstones and shales which constitute so large a portion of New Jersey are laid and arranged can be seen to great advantage, this being one of the finest exposures in the formation. At a point about equidistant from either end is a fault in the layers of shales and sandstone; this fault is noticeable as a slight irregularity in the otherwise continuous sides of the cut, and is a point at which the layers of rock on the east have fallen vertically, the western side remaining in its original position. This fault has a thrust of only three feet, but is an instructive example of faults which occur on a tremendous scale in some of the other formations. It will be noticed that between the two edges of the separated layers there is a deposit of a talcky substance, which has been derived from infiltrating waters. Fissure veins are generally in positions of this kind, formed and filled in a similar manner, but with the various metallic ores. Passing further west a short distance we reach the Passaic River, and walk along its banks for a mile north to the Belleville bridge; at this point is the intake of the Jersey City water works, with their huge Worthington pumps and other accessories, which may be conveniently visited. The Passaic River is then crossed, and the train on the Newark and Paterson road may be taken for three miles to Avondale, from whence it is two miles east to the Belleville sandstone quarries, or the bank of the Passaic may be followed and the quarries reached in an hour from Belleville. Here again are met the sandstones and shales, besides another and larger fault, and many interesting features of the sandstone and its quarrying may be examined. The railroad station having been regained, Paterson is the next point of interest. The first thing noticeable in approaching the city are the quarries in the side of the hills to the south, and these may be visited the first; they are but a short distance southeast of the station. Here the sandstone will be found in contact with the trap above and the layers of basalt, trap, tufa, sandstone, shales and conglomerates are exposed. Regaining the nearest railroad track (the Boonton branch of the D., L. & W.R.R.), this is followed for some distance west, when the various strata can be examined in the cut of the railroad and a fault of nearly sixty feet in the trap; this is noticed as a depression in the face of the cliff, and it may be seen by the superposition of the layers of trap and basalt. Where the fault occurs a short distance further west, there is another smaller fault. A visit to the Great Falls of the Passaic is a very pleasurable diversion at this point, and these are about a half mile north of this locality. Here the arrangement of the trap and sandstones can be again profitably studied, and the mineralogical localities which I have described in a former one of these articles[2] examined, not omitting the one at West Paterson, wherein so much phrenite may be found. Taking the train from West Paterson to Little Falls, a walk of a few miles south brings us to the Little Falls, and here is another interesting locality wherein the contact of the sandstone and trap may be examined and the numerous additional phenomena studied. A quarry near the Falls is the best point in which to find these exposures, and from the viaduct crossing the river an excellent view of the surrounding country may be obtained. Regaining the train, Montville is soon reached and visited, and after this, if time sufficient Boonville, two miles west, may be taken in, or it may be necessary to go there to catch a return train, as but few stop at Montville. At Boonton there are many interesting features--iron works furnaces, localities in which fossil remains are found, footprints, conglomeritic beds, and many other things, of which I will endeavor to give a detailed account in some other of this series of articles.
[Footnote 1: See SCIENTIFIC AMERICAN SUPPLEMENT, No. 363.]
[Footnote 2: See SCIENTIFIC AMERICAN SUPPLEMENT, No. 363.]