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Updated: October 6, 2025
FIRST, a white syenite, streaked and mottled with red; it consists of well- crystallised feldspar, numerous grains of quartz, and brilliant, though small, crystals of hornblende. The feldspar and hornblende in this and the succeeding cases have been determined by the reflecting goniometer, and the quartz by its action under the blowpipe.
Guadaloupe, an active volcano, the height of which, according to Leboucher, is 799 toises; according to Amie, 850 toises. Montserrat, a solfatara; fine porphyritic lavas with large crystals of feldspar and hornblende near Galloway, according to Mr. Nugent. Nevis, a solfatara. St. Christopher's, a solfatara at Mount Misery. St.
It is situated among rocks of syenitic porphyry in broad dikes, and gneiss tilted on edge, and having a strike to the N.E. There are many specimens of half-formed pumice, with greenstone and lava. Some of the sandstone strata are dislocated by a hornblende rock and by basalt, the sandstone nearest to the basalt being converted into quartz.
In the case of the mines now working on this lode, the basin of hornblende is more than two miles in width, and is possibly many thousands of feet in depth, so there seems to be a reasonable prospect of there being a long future before the workers on the Champion lode. The Kolar gold field is about seven miles in length, and averages about two to three miles in width.
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.
Among the cataracts, and wherever the Orinoco, between the Missions of Carichana and of Santa Barbara, periodically washes the granitic rocks, they become smooth, black, and as if coated with plumbago. The colouring matter does not penetrate the stone, which is coarse-grained granite, containing a few solitary crystals of hornblende.
But in many places a variety occurs which is composed simply of feldspar and hornblende; and in examining more minutely this duplicate compound, it is observed in some places to assume a fine grain, and at length to become undistinguishable from the greenstones of the trap family.
The trachyte is generally of a pale brown colour, stained with small darker patches; it contains broken and bent crystals of glassy feldspar, grains of specular iron, and black microscopical points, which latter, from being easily fused, and then becoming magnetic, I presume are hornblende.
Those geologists who have doubted whether granite could have been formed by igneous liquefaction, because minerals of different degrees of fusibility impress each other with their forms, could not have been aware of the fact of crystallised hornblende penetrating phonolite, a rock undoubtedly of igneous origin.
Other conical hills or short ranges, with irregular rugged crests, were composed of granite of many varieties, red and white, fine grained without hornblende, or containing the latter substance, and changing into sienite; and, at one place, it seemed as if it had broken through Psammite. I observed quartzite in several localities, and a hard pudding-stone extending for a considerable distance.
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