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Page:Popular Science Monthly Volume 21.djvu/630

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THE POPULAR SCIENCE MONTHLY.

cupy—for most of them have been worked—the beds of all the watercourses, but they were also placed in beds on the table-lands and in the gorges of the mountains, at levels which the waters never reach in our day, even in times of freshet. They have a peculiar appearance, that never deceives the eye of the experienced miner. At first sight, they resemble the gravels of our rivers. They are formed of rounded pebbles of various colors, and are composed of numerous species of minerals, of which I, still only at the beginning of my studies of the subject, have already recognized more than thirty. Of these, quartz, the oxides of titanium, titanic iron, tourmalines, phosphates, fibrolite, octahedric oligist iron, and magnetite, which are well known to the miners and distinguished by them under various fanciful names, are the true satellites of the diamond, its veritable train, and are with rare exceptions sure to be found with it at Diamantina. They have so intimate a connection with it, in fact, that we are justified in believing that the same formations include the primitive beds both of these minerals and of the diamond. The form of the specimens leaves no doubt as to the causes to which they owe it. They have been brought down by the waters and worn round by friction. They can not, however, have been turned into spherical balls by a simple transport of a few hundred yards. The diamond itself, the hardest of all bodies, has not escaped this action; and fragments of it are found from which every trace of crystallization has disappeared, and which are as round as marbles. Not the sands of the large streams alone, but also those of the smallest brooks, even those near their sources, present the same characteristics. The stones must, then, owe their shapes to the polishings which they have suffered by being held in the windings of the rocks and rolled around them by the eddies of the waters. While they have been thus polished off, they have produced an analogous phenomenon on the bottoms of the rivers, where they have caused the wearing out of those circular holes—the "giants' pots," the caldeiroes of the diamond-hunters, with which the beds of the streams of Diamantina are pock-marked. The sands in these holes are naturally richer than the other sands; for the lighter elements are carried away by the water, and more fragile substances than the diamond are ground to powder in them. For a hundred and fifty years the miners have considered it a piece of great good fortune to discover one of these caldeiroes; but new ones are now very seldom found. A few hundred yards above the bridge of the Diamantina road over the Jequitinhonha, the course of the water is barred by enormous blocks of diorite, between which the current has excavated subterranean passages. The river having been partly turned from its course, one may now go into one of these grottoes, which is occupied by a cascalho of extraordinary richness. The sides of the rock are as polished as the best-worked marble; the light of the torches is reflected as from a glass; and the visitor perceives at every instant cylindrical holes as regularly formed as if some skillful potter had shaped