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Page:Popular Science Monthly Volume 21.djvu/846

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THE POPULAR SCIENCE MONTHLY.

depths of the globe, has absorbed oxygen from the air, has become sulphuric acid, and, acting upon the already formed limestone, has produced gypsum, as in the previous theory. 3. Salts already formed in the interior of the globe have been brought up to the surface partly in solution, partly sublimed. These hypotheses are all wholly gratuitous; and, with regard to the first, it is impossible to admit that sulphuric acid, already formed, coming up from the depths of the globe, should have traversed, without saturating them, the enormous thickness of the underlying calcareous beds to make gypsum in the tertiary formation. The second hypothesis is more admissible, especially since M. Dumas has found gypsum that was evidently formed in that way; but while we may easily suppose a mass of limestone, of which one part has been transformed into gypsum by the action of free sulphuric acid, while the other part remains limestone, we can not admit such an intervention of the acid in a case where the gypsum is interpenetrated in all its parts with carbonate of lime. The third hypothesis, that the saline deposits have been brought up from the depths of the globe, is only a continued appeal to those mysterious actions which figure so prominently in the infancy of all the sciences; but, besides that it explains nothing, I believe that it is a real error. My studies of chemical geology have led me to the conclusion that the salts now held in solution in the waters of the seas, the salts existing in solid masses in the strata of our globe, and those which furnish the mineral constituents to saline waters, have a common origin, and that that origin is exterior to the first strata that were formed in the consolidation of the earth.

According to the conditions assumed in the nebular hypothesis of the origin of the earth, the rocks forming the first solid envelope of our globe solidified at a temperature of between 2,000° and 2,500° Cent. (3,600° and 4,500° Fahr.). Now, according to the law of dissociation, as discovered by Sainte-Claire Deville, chlorine, sulphur, and their constant compounds, with oxygen and hydrogen, were present in the atmosphere at the former temperature, and even below it, in a state of complete dissociation; and only at a much later stage than this was it possible for chlorine and sulphur to effect combinations so as to react upon the exterior crust and form sulphates and chlorides. The sulphates and chlorides, in their turn, could have been produced only at successive and extremely distant epochs. Thus, to mention only the two chlorides which constitute the largest part of the saline substances contained in marine waters, the chloride of sodium and the chloride of magnesium; the former has been formed at a high temperature, for it can support a high temperature without suffering decomposition. But the chloride of magnesium can not have been composed until a prodigiously more advanced epoch—that is, one nearer to our own time, when the temperature of the earth had descended to about the boiling-point of water; for the chloride of magnesium can not sup-