We speak of the beds of gypsum as _deposits_, in common with those of the sandstone matrix in which they are imbedded. It appears, however, on inquiring into the theory of their origin, that they are not strictly such in the true sense of deposits—originally as gypseous deposits—but altered limestones, metamorphosed by the action of gases which have escaped from beneath, and permeated the calcareous mass. The carbonates of lime have been converted into the sulphates of lime, by means of gaseous emanations produced in unknown volcanic depths. Even the dolomitic member of the group is supposed to have a like metamorphic origin; the needful elementary agencies having entered into the parent limestone, and converted it into the magnesian type. Why nature should not have done these things directly, at the first off-throw, science could not, perhaps, very satisfactorily answer the skeptically inquiring mind; but, as the ingredients are all chemically well known, and more especially as there is a vast laboratory ever at work, filled with all kinds of elements, in her subterranean regions, any hypothesis of formation is as rapidly established as it is conceived, and the interest of the subject humanly speaking augmented. The celebrated Berzelius, when questioned on the point, had his ready solution of the problem, easily derived from his unparalleled stores of chemical knowledge:—“Give me a substance containing sulphur—admit the presence of the vapors of sulphur, or sulphurous or sulph-hydrous vapors,—let limestone be also present, and water on the surface or in the atmosphere, AND WE SHALL READILY HAVE GYPSUM.” The origin of the saltness of the ocean is still a mystery in science; equally involved in doubt and conjecture is that of the other member of the series, the rock-salt formation. The generally adopted theory, however, is, that it was dependent on volcanic agency for development, as it both contains, and is uniformly associated with, the acids, and other materials found in connection with volcanoes. The chlorides of sodium and gypsum, for example, are at present sublimed from volcanic vents; vapors charged with sulphuric acid are constantly issuing from the same sources; and these passing through or associated with the saline waters of the period, must have aided in the formation of rock-salt and gypsum, which occur more frequently in irregular masses than in true stratified deposits. An additional corroboration of the theory is inferred from the circumstance, that the gypsum accompanying the rock-salt is anhydrous, that is, free from water before exposure to the action of the atmosphere. Hence the conclusion, that the consolidation of both the rock-salt and the gypsum must have been effected by the agency of heat, as, by means of aqueous deposition, a hydrometric influence would have been sensibly perceived.