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Page:Popular Science Monthly Volume 32.djvu/839

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ores of copper and tin which the miner's operations had taken from her, and from which the furnaces of the metallurgists had laboriously extracted the two metals of bronze.

Lead pipes, of which there were a great number in connection with a white marble piscina, had suffered a no less energetic alteration. They were deeply corroded and perforated, and had by solution formed minerals with bases of lead—the sulphuret, or galena, and the chlorocarbonate, or phosgenite.

Among the iron compounds the bisulphuret, or pyrites, is of special interest, on account of its abundance in the crust of the earth. At Bourbonne, and in the basins of other thermal springs at Aix-la-Chapelle, Bourbon-Lancy, Bourbon-l'Archambault, and Saint-Nectaire, pyrites has been detected in course of formation, but only in the deeper parts of the basin remote from atmospheric oxygen.

In view of these changes, wrought by thermal water on inorganic bodies, it is not surprising that the same agent should also act upon organic bodies. The wood of the piles supporting a masonry-work, while it has perfectly preserved its texture, has become hard and heavy with the mineral matter which it has absorbed. The original substance has almost disappeared, and given place to carbonate of lime, which has penetrated, as the miscroscope shows, to the most minute interstices of the vegetable cells.

These springs of Bourbonne have given rise, within a very limited space, to not less than twenty-four species of crystalline minerals, in combinations which, accumulated and grouped as they are, closely resemble the ancient metalliferous beds—in detail as well as in generaL

Other evidences of the mineralizing power of thermal waters have been exhibited in their operation for considerable distances below the surface of the ground. Penetrating the subsoil at Plombières, they have since the Roman period engendered a series of species no less remarkable than the preceding series, although they did not attract attention by a metallic luster; they are silicates of the zeolite group, opal, and chalcedony. When we try to apply the experimental method to the reproduction of geological phenomena, we are met, among other difficulties, by the brevity of human life, which is very short in comparison with the immense periods which have presided over the formation of the crust of the earth. Such facts as these, fortunately, make up for this inability, and put us in the presence of experiments that are forbidden to our laboratories, from which we learn what can be effected by very weak actions prolonged through ages. By these synthetic demonstrations, carried on during twenty times the duration of human life. Nature teaches us that she is still employing processes similar to those which she used in the most remote epochs.

We come now to see how subterranean waters obtain a heat which makes them thermal springs, and which connects them by intermediate