Art. IX. Discovery of Native Crystallized Carbonate of Magnesia on Staten-Island.
Art. IX. Discovery of Native Crystallized Carbonate of Magnesia on Staten-Island, with a Notice of the Geology and Mineralogy of that Island, by James Pierce, Esq. of New-York, in a Letter to the Editor.
New-York, October 19, 1818.
Dear Sir,
I forward you a few mineral specimens characteristic of Staten-Island, including native carbonate of magnesia, in acicular crystals. I discovered this new form and locality of magnesia in examining the strata exhibited in an excavation now making, under the delusive expectation of finding gold, about three miles from the Quarantine. In descending the shaft, sunk perpendicularly in steatite, magnesite, veins of talc, and green translucent asbestus were observed at depths from six to thirty-five feet. The magnesite was found to embrace veins and cavities containing native carbonate of magnesia, in very white acicular crystals, grouped in minute fibres radiating from the sides, but not always filling the veins and cavities. The crystals were, in some instances, suspended, assuming a stalactical form. This carbonate of magnesia dissolves entirely in diluted sulphuric acid, with considerable effervescence and chemical action, producing a bitter compound, from which salts of easy solution are formed by evaporation. The magnesite in which these crystals are found, appears to be composed of carbonate of magnesia, steatite, and talc, disintegrating readily upon exposure to air and moisture: it effervesces considerably in sulphuric acid, forming a very bitter fluid that soon exhibits crystals, indicating that magnesia enters in large proportion into its constitution. Magnesite may perhaps be found at this place in quantity sufficient for a successful manufacture of Epsom salts. Small regular hexaedral crystals of mica, were noticed in steatite. Chromate of iron was sparingly diffused through the different minerals raised from various depths.
A few remarks and facts respecting the geology and mineralogy of Staten-Island, may, perhaps, give some additional interest to the specimens presented.
Staten-Island (which constitutes Richmond county) is situated about seven miles southwest of the city of New-York, extends from northeast to southwest about fifteen miles, in a straight line, with an average width of six. It exhibits a considerable diversity of surface. The eastern part is composed principally of elevated ground: a mountain chain is observed to take its rise in the vicinity of a narrow sound called the Kills, and sweep, in a semicircular form, near the eastern shore; it then ranges southwest, parallel with, and distant from Amboy Bay, about two miles, terminating near the centre of the island, and forming, with the exception of some passages, a continued chain, which, on the eastern and southern sides, is very steep, but not precipitous; it gradually declines to the west and north, and, in some places, it presents on its summit table land of considerable extent. A prominent ridge crosses the island, connecting the elevated ground of the south, with the hills of the northern part. A species of steatite, containing veins of common, indurated, and scaly talc, amianthus, and most of the varieties of asbestus, and some chromate of iron, constitutes the nucleus of the whole mountain range and elevated ground of the eastern division, stamping it as primitive. This steatite approaches, in most places, within a foot and a half of the surface, and appears in small angular loose blocks, wherever the soil has been removed. Its colour is a greenish yellow; it is brittle, very adhesive to the tongue, but little unctuous, and probably contains more alumine and less magnesia than steatites in general. Much of it decomposes when exposed to air and moisture, and forms a good mould, whenever the descent of ground permits an accumulation of earth. It is not improbable, that in most places of the Staten-Island hills, when magnesia constitutes a considerable ingredient of the rock, it will be found saturated with carbonic acid, obviating the objection to common magnesian minerals in agriculture.
The minerals observed on the surface of the northeast part of this chain of hills are, secondary greenstone, asbestoid, sandstone, granite, and gneiss, sparingly scattered in rolled masses. In addition to these rocks, in the middle and western part of the chain, a mineral of uncommon appearance is observed. It is composed principally of quartz, rough, with numerous cells of various forms, in which small siliceous crystals are generally found: the veins or plates of quartz that intersect each other, often embrace talc and oxide of iron, which, decomposing, gives some specimens the appearance of volcanic origin. Associated with this cellular ferruginous quartz, brown hæmatite is often observed; this valuable ore often yields eighty per cent. of iron of best quality; its fibres assume a variety of shapes; they were observed at Staten-Island, straight and curved, radiating from a centre, and exhibiting the stalactical, cylindrical, and botryoidal forms, often displaying a black polished surface and glistening lustre. Ferruginous minerals are abundant on the mountain for several miles. A granular oxide, called by miners shot-ore,[21] from its being principally composed of spherical grains of various sizes, was often noticed, and appears in some places in extensive beds: it is easily fused, and affords a large per centage of good iron for castings. A heavy ore, with a smooth surface and some lustre, bearing a considerable resemblance to native iron, is sometimes seen. Banks of white sand, resembling the siliceous particles of the seashore, are noticed on the mountain tops, containing masses of compact, heavy ferruginous sandstone, similar to the rocks of our alluvial seaboard. Large beds of water-worn siliceous pebbles, in no way differing from those washed by the ocean, are seen on the height of the ridge, in which excavations have been made several feet, leaving the depth of the mass uncertain. On some of the eminences, for a considerable extent, vegetation is entirely excluded by an iron-bound soil. Iron ore, imbedded in an earth coloured by, and partly composed of, oxide of iron, occupies the surface; and chalcedony and radiated quartz are sometimes observed on the primitive ridge. Prospects from many of these eminences are extensive and diversified. On one side, the ocean and a great extent of coast are in view; on the other, a rich landscape of hills and plains, the eye resting on the highland-chain and the mountains bordering Pennsylvania; the harbour, at your feet, presents a busy, ever-varying scene, and the city of New-York appears to great advantage from this point of observation.
The district between the mountain and the narrows, the thickly settled and well-cultivated plain bordering Amboy bay, and much of the western division of the island, are decidedly alluvial. Adjacent to Fort Tompkins, detached pieces of copper ore have been found. I have observed petrifactions of marine shells in rocks excavated in that neighbourhood, twenty feet from the surface, and sixty above the ocean.
The western part of the island presents moderate elevations; the soil, a good medium of sand and clay, is in general fertile; but a tract near the termination is sandy and barren. Some creeks penetrate to near the centre of the island, and are bordered by extensive salt meadows. Except at the primitive range, I have observed in no part of the island large beds of rock that can be called in place; but rolled masses of greenstone, sandstone, gneiss, granite, red jasper, and indurated clay, appear in general sparingly, but sometimes in abundance, on the surface. Lignite has been found in small quantities in the western part of the island. A chalybeate spring, of no great strength, is the only mineral water met with in Richmond county. The ponds, wells, and streams, contain a soft water, holding no lime in solution.
REMARKS.
We have already published ([p. 54].) Mr. Pierce's discovery of the pulverulent carbonate of magnesia, and have pointed out its connexion with Dr. Bruce's previous discovery of the hydrate of magnesia, or pure magnesia combined with water only. Mr. Pierce has now added another important link to this chain, and future mineralogists may quote the vicinity of New-York as affording,
1. Pure magnesia, crystallized and combined with water only.
2. Carbonate of magnesia, pulverulent and white.
3. Carbonate of magnesia, in very delicate and perfectly white acicular crystals.
We possess specimens of them all.