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These extensive sheets of water are surrounded by banks of tuff and volcanic sand, in which fragments of augite, leucite, and crystals of titanite are distributed.
The gneiss of the littoral Cordillera, in the province of Caracas, contains almost exclusively garnets, rutile titanite and graphite, disseminated in the whole mass of the rock, shelves of granular limestone, and some metalliferous veins.
Plagioclase, microcline and quartz are the predominating minerals, while biotite, titanite, epidote, apatite, zircon and garnet are present in smaller quantities. There is also a small amount of hematite, pyroxene and sericite. The rock, which is of a granitic composition, contains numerous crystallites and has been subjected to considerable strain and crushing, which has resulted in foliation.
We found some from one to two toises broad, full of small fasciculated crystals of rutile titanite. We sought in vain for cyanite, which we had discovered in some blocks near Maniquarez. Farther on the mica-state presents not veins, but little beds of graphite or carburetted iron. They are from two to three inches thick and have precisely the same direction and inclination as the rock.
The direction and inclination of the stratum remain the same, and the thonschiefer, which takes the look of a transition-rock, is but a modification of the primitive mica-slate of Maniquarez, containing garnets, cyanite, and rutile titanite.
The quartz predominates in the mass; and is generally of a milky white. I observed neither hornblende, black schorl, nor rutile titanite, in this granite. In some ledges we recognised round masses, of a blackish gray, very quartzose, and almost destitute of mica. They are from one to two inches diameter; and are found in every zone, in all granite mountains.
It is traversed by veins of quartz, containing cannulated and often articulated prisms of rutile titanite two or three lines in diameter. In the fissures of the quartz we find, on breaking it, very thin crystals, which crossing each other form a kind of network.
True, in the august presence of rhombohedral crystals, retinasphaltic resins, gehlenites, Fassaites, molybdenites, tungstates of manganese, and titanite of zirconium, why, the most facile of tongues may make a slip now and then.
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