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Updated: June 5, 2025
Yet one other possible solution may be mentioned, a solution which is becoming more and more generally accepted, namely that the granite was not after all really melted, but that the vitrification should either be attributed to the fusion of the argillaceous mass, which has been subjected to an igneous transformation, such as that which often takes place in furnaces for baking bricks and in lime-kilns.
Through the unintermitting labors of geologists, so immense a mass has been accumulated, that many volumes would be required to contain the details. It is drawn from the phenomena presented by all kinds of rocks, aqueous, igneous, metamorphic.
This igneous matter, so active, so subtle, dissipates itself with great facility, then requires to be reinstated in his system by means of aliments that contain it, which thereby become proper to restore his machine, to lend new warmth to the brain, to furnish it with the elasticity requisite to the performance of those functions which are called intellectual.
I have shown specimens of this incrustation to several geologists, and they all thought that they were of volcanic or igneous origin! In its hardness and translucency in its polish, equal to that of the finest oliva-shell in the bad smell given out, and loss of colour under the blowpipe it shows a close similarity with living sea-shells.
I had observed that the old schistose rocks on the sides dipped in toward the centre of the country, and their strike nearly corresponded with the major axis of the continent; and also that where the later erupted trap rocks had been spread out in tabular masses over the central plateau, they had borne angular fragments of the older rocks in their substance; but the partial generalization which the observations led to was, that great volcanic action had taken place in ancient times, somewhat in the same way it does now, at distances of not more than three hundred miles from the sea, and that this igneous action, extending along both sides of the continent, had tilted up the lateral rocks in the manner they are now seen to lie.
At the present time the pre-Cambrian region about Lake Superior leads the world in the production of iron ore, its output for 1903 being more than five sevenths of the entire output of the whole United States, and exceeding that of any foreign country. A theory held by many refers the ultimate source of the iron to the igneous rocks of the Archean.
Few scientists can now be found to advance the purely igneous theory of lode formation, though it must be admitted that volcanic action has probably had much influence not only in the formation of mineral veins, but also on the occurrence of the minerals therein.
MacCulloch, after examining with great attention these and the other igneous rocks of Scotland, observes, "that it is a mere dispute about terms, to refuse to the ancient eruptions of trap the name of submarine volcanoes; for they are such in every essential point, although they no longer eject fire and smoke."
From daily experience, we acquired a sort of instinctive feeling as to the course we should adopt, and were seldom wrong in our decisions. The ridges, near the water-holes on which we were encamped, are composed of an igneous rock containing much iron, with which the water was impregnated to such a degree, that our tea turned quite black and inky.
The greater energy and more extended range of igneous action in those very remote periods when Africa was formed, embracing all the flanks, imparted to it its present very simple literal outline. This was the length to which I had come.
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