Both MM. St. Claire Deville and Fouqué have succeeded in demonstrating the perfect accordance of the chemical composition of the products of volcanic eruptions, both gaseous and solid, with the doctrine that salt water has been largely present in volcanic foci. If so, why are there no salts of magnesia in volcanic fumeroles? These salts are readily decomposable by hot steam, and when water and heat are present they produce hydrochloric acid and magnesia. M. Fouqué affirmed that he witnessed an eruption of Mount Etna in 1865; the gaseous emanations agreed in kind with those which we might have looked for if large volumes of sea-water had gained access to reservoirs of subterranean lava, and if they had been decomposed and expelled with the lava.[48] We have obtained three facts, viz., that communications probably exist between volcanic foci and sea-water; that fumes of hydrochloric acid which accompany the lava deposit common salt; and that the salts of magnesia are decomposed by heat; and what more probable than that all living organisms which pass with the sea-water are utterly obliterated?
By the preceding observations, the reader will see that salt is not subject to geological laws, by reason of its being confined to no particular strata, and by the absence of organic remains; and that it is not derived from sea-water, because there are no marine organisms to be found in it.
That though it may have a pristine source, it has (though it may appear paradoxical) a dual inchoation—by its being found as rock-salt, and by its being present in sea-water, and, as I have stated, in a condition of immaturity.
Rock-salt appears to be the result of volcanic agency, from its being almost invariably (with but few exceptions) in juxtaposition with gypsum, which is known to be of volcanic origin; by its being found forced up independently of other formations, even through the crust of the earth; by the presence of fumes of hydrochloric acid with lava during volcanic eruptions.
It has undoubtedly an igneous origin, and the entire absence of organic remains may be accounted for by the fact that while in a state of fusion it may have disintegrated, absorbed into itself, or altogether obliterated all remains of living organisms with which it may have come into immediate contact. All other formations have preserved the impress and structure of vegetable and animal life; salt is the sole exception to the rule; and if while in a state of fusion it possessed the property of destroying and obliterating all marks of animal and vegetable remains, we can easily account for their absence.[49]
We have also seen that sea-water has access to volcanic foci, by reason of fumes of hydrochloric acid, which deposit common salt, and by the proximity of the volcanoes to the sea.
One question is naturally evolved out of this: does the sea obtain its saline constituents from vast reservoirs, or beds of salt, through the medium of communication with volcanic foci?
This question I leave unsolved, for were we to discuss it, we should probably have to enter into other matters which would be somewhat foreign to my subject. My opinion is that sea-water (if my hypothesis that it is nothing else than salt in a state of immaturity is correct) obtains its chloride of sodium in this way; and, if so, it accounts at once for the absence of marine organisms, upon which phenomenon geologists have always laid so much stress. Besides, if salt is derived from evaporation of sea-water, and subsequent deposition of salt, we should be able to obtain remains of marine organisms, if not those of land animals. This one fact alone would tend to prove that sea-water is the result of some subterranean communication with reservoirs of salt, through the media of volcanic foci.
We have thus before us certain geological facts relative to salt, which show that though it has not been discovered in the old stratified rocks, it is nevertheless met with in nearly all the later formations, and also that it is in process of formation, and notably so in the Crimea. This undoubtedly is the case; but still we cannot apply any of the laws of geology so as to make our conjectures confirmative by certain facts which support one hypothesis and overthrow another.