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Such facts may induce us to consider whether many granites and other rocks of that class may not sometimes represent merely the extreme of a similar slow metamorphism.
Berzelius, who, at my request, examined these crusts, recognized in them, as in those of the granites of the Orinoco and River Congo, the union of iron and manganese.
The ferruginous sandstones, granites, and marbles, that become cinereous and sometimes brown in damp air, have an aspect altogether different. In reflecting upon the lustre and equal thickness of the crusts, we are rather inclined to think that this matter is deposited by the Orinoco, and that the water has penetrated even into the clefts of the rocks.
Points of unconformableness in the overlying aqueous rocks, connected with protrusions of granites, and other similar presentments of the internal igneous mass, such as trap and basalt, mark the conclusions of subsequent sections in this grand tale.
The material of the houses and defences are rough stones, the granites and sandstones of the hills, cemented, like the ancient Galla cities, with clay. The only large building is the Jami or Cathedral, a long barn of poverty-stricken appearance, with broken-down gates, and two white-washed minarets of truncated conoid shape.
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.
And suddenly, in the mist of the deep nocturnal calm of this temple, isolated here in the lake, comes again the sound of a kind of mournful booming, of things that topple, precious stones that become detached and fall and then, on the surface of the lake, a thousand concentric circles form, close one another and disappear, ruffling indefinitely this mirror embanked between the terrible granites, in which Isis regards herself sorrowfully.
To a somewhat less depth it has been leached of its lime and other soluble ingredients. In the weathered zone its pebbles, especially where the till is loose in texture, are sometimes so rotted that granites may be crumbled with the fingers. The Kansan drift is therefore old. THE WISCONSIN FORMATION. The Wisconsin drift sheet is but little weathered and eroded, and therefore is extremely young.
It may perhaps be suggested that some metamorphic strata, and some granites, may be anterior in date to the oldest of the primary fossiliferous rocks.
The brunt of the controversy settled about the unstratified rocks granites and their allies which the Plutonists claimed as of igneous origin. This contention had the theoretical support of the nebular hypothesis, then gaining ground, which supposed the earth to be a cooling globe.
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