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Updated: June 25, 2025
The banks of the river were sandy and sterile, and the soil contained much small quartz. The bed rock was a talcose schist near to Ocotal, but higher up the river it changed to gneissoid and quartz rocks, the latter in hard and massive beds. As we ascended the valley, the ranges bounding it got higher and steeper, the soil more sandy and barren, with scattered pine trees growing amongst the rocks.
Decomposing into Spherical Masses. Rude columnar Structure. Graphic Granite. Mutual Penetration of Crystals of Quartz and Feldspar. Glass Cavities in Quartz of Granite. Porphyritic, talcose, and syenitic Granite. Schorlrock and Eurite. Syenite. Connection of the Granites and Syenites with the Volcanic Rocks. Analogy in Composition of Trachyte and Granite.
That they exist below at no great depth we can not doubt, for at some points, as in the Valorsine, near Mont Blanc, granite and granitic veins are observable, piercing through talcose gneiss, which passes insensibly upward into secondary strata.
Tertiary deposits also appear in a less elevated position on the flanks of the Eastern Alps; but in the Central or Swiss Alps, the Palaeozoic and older Mesozoic formations disappear, and the Cretaceous, Oolitic, Liassic, and at some points even the Eocene strata, graduate insensibly into metamorphic rocks, consisting of granular limestone, talc-schist, talcose- gneiss, micaceous schist, and other varieties.
The formation is upper Silurian or lower Devonian, a transition to gneiss, but not highly metamorphic. No fossils have yet been found: if any exist they would be microscopic. Where talcose it is bluish, and shows streaks of 'black sand, titaniferous iron. The grey sand washes to white. There are pot-holes which have been filled with either a pudding or a breccia of quartz.
The granite still remaining unstratified, becomes charged with green particles; and the talcose gneiss assumes a granitiform structure without losing its stratification."
The mountain heights which bound it, being composed for the most part of schist, mica slate, and talcose slate, large masses become detached in winter split off by the freezing of the water behind them when they descend, on the coming of thaw, in terrible avalanches of stone and mud.
This road is cut out of a talcose gneiss* in a state of decomposition. Travellers suffer from the dust in winter, while in the rainy season the place is changed into a slough. On descending the table-land of Buenavista, about fifty toises to the south-east, an abundant spring, gushing from the gneiss, forms several cascades surrounded with thick vegetation.
Talcose Granite, or Protogine of the French, is a mixture of feldspar, quartz, and talc. It abounds in the Alps, and in some parts of Cornwall, producing by its decomposition the kaolin or china clay, more than 12,000 tons of which are annually exported from that country for the potteries. The former of these is an aggregate of schorl, or tourmaline, and quartz.
With inadequate material and appliances to hand, the following will be found easier to construct and more lasting when constructed. Only a single piece of iron is required, and, at a pinch, one could even dispense with that by using a slab of talcose material, roughly shaping a hearth therein and making a hole for the blast. First, construct a framing about the height of an ordinary smith's forge.
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