Art. V. New localities of Agate, Chalcedony, Chabasie, Stilbite, Analcime, Titanium, Prehnite, &c.
Art. V. New localities of Agate, Chalcedony, Chabasie, Stilbite, Analcime, Titanium, Prehnite, &c.
Deerfield, &c. In the account of the Mineralogy and Geology of Deerfield, by Mr. Hitchcock, in the present Number, it will be seen, that these interesting minerals (with the exception of titanium) exist in the secondary greenstone of that place. We have specimens, (through the kindness of Mr. Hitchcock,) and observe that the agates, chalcedony, analcime, and prehnite, are imbedded in the trap; the agates are in some instances very delicate in the disposition of their bands, and need nothing but polishing to make them beautiful; the same is true of the chalcedony. The chabasie and stilbite occupy cavities, and the chabasie is often distinctly crystalized in a rhomboid, so nearly approaching a cube, in the quantity of its angles, that the mistake is easily committed of supposing them to be cubes; the crystals are sometimes transparent, and the largest a quarter of an inch in diameter. Titanium is found in Leyden; it is the red oxide—very well characterized—in reddish brown crystals as large as a common goose quill,[18] and, in some instances, perfectly geniculated. It is rare to see finer specimens.
East-Haven. It will be observed, that the great ranges of secondary greenstone, which cut Connecticut and Massachusetts in two, terminate at New-Haven, on the one hand, and some way above Deerfield on the other. By comparing the account of the termination at New-Haven (Bruce's Journal, v. i. p. 139.) with that now published, of the termination at or near Deerfield, it will be seen that the geology and imbedded minerals are very similar. At East-Haven, (one of the branches of the greenstone of New-Haven, and within from three to four miles of the latter town,) chalcedony is often found, sometimes imbedded in the trap, (but perhaps more frequently loose among the fallen stones,) which, although in small pieces, is as perfect in its characters as the chalcedony of the Feroe Islands. It is of a delicate gray, translucent, mamillary, botryoidal, stalactitical, or impressed by crystals of quartz, which have usually fallen out; sometimes these crystals incrust the chalcedony.
Agates also are found in considerable numbers, both imbedded and loose. They usually consist of bands of chalcedony and quartz, and sometimes of the latter only, variously striped or spotted, or interlaced with jasper, carnelian, and cacholong.
The form of the imbedded agates at East-Haven is commonly ovoidal, or egg-shaped, and frequently it is conical. Some portions of pure chalcedony occur, which are shaped like a long, slender carrot or parsnip, and the situation of the latter in the ground would exactly represent that of the chalcedony or agate in the rock.
The imbedded masses are frequently altogether quartz, and then they are most commonly geodes or hollow balls lined with crystals, commonly very perfect and brilliant, although rarely large. These crystals are commonly transparent and colourless—but they exhibit also most of the varieties of colour which quartz assumes—the amethyst—the smoky—yellow, &c., and occasionally they are tipped and spotted with red jasper.
The spontaneous decay of these trap rocks causes many specimens to be found among their ruins, and many more are imbedded in the solid rock; but the industry of successive classes from the neighbouring college, issuing from Col. Gibbs's cabinet, has now made specimens more scarce.
Woodbury. Twenty-four miles from New-Haven, N.W.
In a geological sketch of parts of the counties of New-Haven and Litchfield, which may appear in a future Number, it will be seen that prehnite, stilbite, and agate are found at Woodbury, in the little basin of secondary greenstone which exists there; the prehnite is abundant—it is not known whether the agates are so, although it is asserted to be the fact; the stilbite was not observed to be abundant, although it was well characterized.