escape, to flow on to the fish-ponds, through a vertical chimney of cut stone. Carefully examining the bricks which had been immersed for centuries in the mineral water, I discovered that they had undergone a transformation of the most interesting character. New combinations, silicates of the family of the zeolites, had been developed in the cavities with which the bricks were riddled; chabesite in striated crystals, grouped exactly like those in Nature, and with the same angles; and christianite, the crystals of which, intersecting one another in the form of a cross, are identical with those of the volcanic rocks. There was, besides, a product of opal, translucent and colored like drops of dew. The tissue of the bricks contained little fibrous and radiated globules, which optical characteristics showed to be chalcedony. The same species had been formed even in the minutest pores of the brick. These minerals, of contemporaneous production, were found later in the Roman masonry-works of Luxeuil and Bourbonne-les-Bains. With the aid of time, thermal water had there acted chemically on the bricks and on the limestone, and had engendered gradually and by a curious collaboration the substances we have named, without calling in the high temperature that we were ready to suppose was necessary, nor water very strongly mineralized. A very slow but incessant action was sufficient. Does not this demonstration, even to the minutest particulars, account for the formation in ancient epochs of zeolite, agate, and the substances that usually accompany them? In view of their complete similarity with those of which Plombières has revealed the history, can we not say that all these minerals were reproduced in rocks still incompletely cooled, by the chemical action of hot or lukewarm waters which infiltrated themselves into their easily permeable texture, and of which the parasitic zeolites accurately trace the ancient history?
On account of the multiplicity and extent of the works of exploitation that traverse the metalliferous beds in numerous countries, and the mathematical exactness with which all the details of their forms and composition are revealed every day, these beds bring to bear very precious data on the functions as mineralizers of the ancient springs. The veins of the most usual type have the form of plaques rarely exceeding a few metres in thickness. Horizontally, they are prolonged to considerable superficies, sometimes to ten or fifteen kilometres. This measurement is given by the extent to which workings have been promoted, and can be visibly exemplified on the surface of the ground, when the quartzose parts of the veins, persistent against denuding agencies, appear as steep ridges, of imposing height, which the eye can follow in the distance. Sometimes they stretch out like a gigantic wall irregularly notched, sometimes they rise in needles. In
