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Updated: June 5, 2025
So, if a man is going to build a boat, you might show him a collection of fossils, and discourse to him of the gneiss system, the mica-schist system, or talk of the atomic theory and protoplasms. Such knowledge would help to enlarge his views, extend his range of vision, and strengthen his memory, but would not help the man to build his boat.
These Scotch metamorphic strata are of gneiss, mica-schist, and clay-slate of vast thickness, and having a strike from north-east to south-west almost at right angles to that of the older Laurentian gneiss before mentioned.
On its east and north, however, the country is of a different character. There the geological formation is what is termed primitive. The rocks consist of granite, sienite, gneiss, etcetera; and, as is always the case where such rocks are found, the country is hilly and rugged. On the western shores a secondary formation exists.
It must have been a dreary spectacle at that time, low, bare hills of gneiss, granite, etc.; low valleys half-filled with broken rock and over everything a sprinkling of erratic boulders; no living thing in sight, nothing green, nothing growing, nothing but evidence of mighty power used only to destroy.
Some hot-springs burst from the bank of the Lachen a mile or so below the village: they are used as baths, the patient remaining three days at a time in them, only retiring to eat in a little shed close by. A conferva grows in the hot water, and the garnets are worn out of the gneiss rock exposed to its action.
There are, however, several other varieties of gneiss regularly foliated, and alternating with each other in so-called strata. The lines of mountains, but not always each separate hill, range nearly in the same direction with the foliation and so-called stratification, but rather more easterly.
The fourth and last great division of rocks are the crystalline strata and slates, or schists, called gneiss, mica-schist, clay-slate, chlorite-schist, marble, and the like, the origin of which is more doubtful than that of the other three classes.
The different rocks to the westward of Kaonka's, talcose gneiss and white mica schist, generally dip toward the west, but at Kaonka's, large rounded masses of granite, containing black mica, began to appear. The outer rind of it inclines to peel off, and large crystals project on the exposed surface.
Mica-slate is the most frequent rock in the peninsula of Araya and the group of Macanao, which forms the western part of the island of Marguerita. Beds of granular limestone are most common in the primitive northern chain; and it is somewhat remarkable that they are found in gneiss, and not in mica-slate.
From this example we may learn how impossible it is to conjecture whether certain granites in Scotland, and other countries, which send veins into gneiss and other metamorphic rocks, are primary, or whether they may not belong to some secondary or tertiary period.
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