The history of salt

by Evan Marlett Boddy

The salt which we obtain from brine-springs contains the same constituents as that which we extract from the sea, though in their course upwards they collect on their way soluble salts, and therefore the water goes through certain modifications, which the reader doubtless recollects. For instance, the brine-springs of Lancashire and Worcestershire rise up through strata of sandstone and red marl, which contain large beds of rock-salt. The origin of the brine, therefore, may be derived from beds of fossil-salt; but as the muriate of soda is one of the products in volcanic regions, the original source of salt may be as deep as that of lava.[46]

We have also seen that the base of all mineral waters is the chloride of sodium, and that their ingredients are collected and dissolved as they ascend to the surface; therefore they may probably both have the same origin as the sea, as regards the chloride of sodium, which they both hold in solution. We can account for their other characteristics by the wide expansiveness of the sea, which is perpetually absorbing and emitting vapours, and by the several strata through which the mineral waters pass. There may be, though there is nothing that we can advance as corroborative, a subterranean communication existing between them, which would imply a common origin, the differences arising from the physical surroundings, atmospheric influences, and the absorption of soluble salts from the several strata.

What is the origin of salt lakes and salt marshes? This is, to a certain extent, more easily explained. One theory as to the origin of salt lakes (we naturally include inland seas, such as the Caspian and the Aral) is the overflow and subsequent retirement of the sea-water, their sites having been originally the bed of the ocean when it receded to its present limits, leaving in its course depressions of land, volumes of water of various depths, elevations, and extent of surface, according to their deepness, altitude, or angles of declivity.[47] Other ingenious hypotheses have been broached, which, I need hardly say, are not worth considering, as they are entirely visionary. In the case of isolated salt lakes, the above theory is not applicable; and geologists tell us that they are doubtless the result of volcanic agency, but at what period of time it is impossible to estimate, for the density of the water found in them is not equable, and neither is their specific gravity the same as that of sea-water, nor are there any remains of marine organisms; and as their depth is variable, they are not confined to any particular strata.

I have hinted previously that these isolated salt lakes are (if I may venture to designate them as such) geological abortions. Had the power which forced them into their present situation been accompanied by that agency which has raised such huge masses as those near Cordova, in Spain, and by the Dead Sea, and which probably brought about their present crystalline form, others by reason of some unexplainable and gradual transition, by chemical means, or decrease of temperature, which naturally would occur the nearer it approached the earth’s surface, these lakes might have developed into beds or mountains of salt.

The salt which is dug out of the earth, and that which is excavated out of isolated salt-mountains, are alike in every respect, and are much more probably the result of volcanic explosion than of the deposition of salt from sea-water, accruing from evaporation while pent up in confined spaces. It may have been, though incalculable ages ago, deposited from the sea, and then in course of time forced up while in a state of fusion by some internal disruption.

We thus see that the six conditions under which we find the chloride of sodium more or less indicate a common origin from sea-water, notwithstanding the absence of marine organisms.

If we take salt as a whole, leaving out of the question altogether the different conditions in which it is found, and with no reference at all to its existing either in the earth, above the earth, in lakes, or in the sea, but looking at it simply as it is, a mass of rock, or a volume of water holding it in solution, it inclines one to the belief that it possesses a dual inchoation, though the original source of both may have been connate; but owing to extraneous causes which were brought to bear, one branch became crystallised rock-salt, while the other, through immaturity, remains in a state of solution. One is rock-salt, which has been heaved up by volcanic power, and the other is what is known as sea-water; the former has produced the mines, and the solitary mountains, and the Indian Salt Range, and that salt which generates mineral waters, and, it may be, those saline lakes like that which exists between Bombay and Nagpur.

According to Sir Charles Lyell, sea-water has access to volcanic foci. He says: “Although the theory which assumes that water plays a principal part in volcanic operations does not necessarily imply the proximity of volcanic vents to the ocean, it seems still to follow naturally that the superficial outbursts of steam and lava will be most prevalent where there is an incumbent body of salt water, or any regions rather than in the interior of a continent, where the quantity of rain-water is reduced to a minimum. The experiments of the most eminent chemists have gradually removed, one after another, the objections which were first offered to the doctrine that the salt water of the sea plays a leading part in most volcanic eruptions. Sir Humphry Davy observed that the fumes which escaped from Vesuvian lava deposited common salt.”

All the principal volcanoes are situated close to the sea, and therefore the hypothesis that a communication exists between them is practically certain; their proximity to the sea, and the deposition of salt from the fumes of lava, as Sir Humphry Davy noticed, are two strong facts. But for all that, it does not prove satisfactorily that salt is solely the result of volcanic agency, and indirectly from the sea, because there is not the slightest trace of the remains of marine organisms, unless they are totally destroyed and obliterated when it is in a state of fusion; if so, it is more conclusive that salt such as we find it is solely due to volcanic force. Salt may have been in times past, as the observations of Sir Humphry Davy seem to corroborate, and as confirmed by more recent chemists, deposited by volcanic agency in the same way that salt is deposited by fumes of hydrochloric acid, which are emitted with the lava during eruptions of such volcanoes as Vesuvius and Etna, by reason of some communication with the sea.

As hydrochloric acid is found in the vapours which are disengaged from red-hot lava, and as magnesia, which is not volatile, is left in the lava itself, constituting one of its most important elements, it would certainly lead one to surmise that there is a communication which, though not always in existence, may be periodically caused by the action of the volcano.