The history of salt

by Evan Marlett Boddy

Salt or brine springs occur in various parts of the United States in the old transition slate rocks. Sir Charles Lyell tells us that, “in the middle of the horizontal Silurian rocks, in the State of New York, there is a formation of red, green, and blueish-grey marls, with beds of gypsum, and occasional salt-springs, the whole being from 800 to 1000 feet, and indistinguishable in mineral character from parts of the Trias of Europe.” Salt-springs also occur in England in the coal measures. The rock-salt of Cheshire and the brine-springs of Worcestershire occur in what is called the old red sandstone group. The salt of Ischl, in the Austrian Alps, belongs to the oolitic, as does also that found in the Lias of Switzerland. The immense mass or bed of salt near Cordova occurs in the cretaceous group; while the salt deposit of Wieliczka belongs to the supracretaceous group.[45]

The reader doubtless remembers, as I stated in the first chapter, that the origin of salt is one of those enigmas of nature which, as yet, has completely frustrated the most accomplished and scientific geologists, and no suggestion has yet been made which will satisfactorily and conclusively account for its formation; for whatever hypothesis has been stated, there is sure to be an objection so difficult to overcome, that the author has been fain to admit that it is thoroughly impracticable, and therefore inadmissible. That it is decidedly not amenable to the received laws of geology, is apparent, which all must admit; therefore one cannot possibly apply them so as to determine the place it occupies in relation to other strata, or practically fix that period of time in which it was deposited; for it is erratic, and its position is anomalous—erratic in the variety of appearances it assumes in creation, and anomalous because it belongs to no particular strata, and therefore no exact period of time can be assigned to it as to other formations.

That salt is either due to volcanic agency, marine explosion, or to overflow of sea-water and subsequent evaporation, or resilience, and ultimate deposition, are the only three hypotheses which can with any credibility be advanced to account for its formation.

That we have it presented to us in six different conformations are facts which when considered separately seem to point to one common origin, but when taken as a whole indicate a separate inception.

Is it due to volcanic agency? In some respects it undoubtedly is, otherwise how can we reasonably account for those gigantic mountains of fossil or rock salt, which rise up isolated in the midst of a country perfectly free for miles round of saline deposits, which present not even the slightest trace of it? How can we account for it by any other means when we find it in intimate relation with gypsum, which we know is solely the production of subterranean activity? What reason can we possibly assign for those salt lakes which are above or below the sea-level and are perfectly solitary, and which have no communication with the sea or with rivers, if they are not phenomena resulting from volcanic agency? And how can we account for those masses of salt below the earth’s surface which in some countries is of such adamantine hardness that it requires to be blasted with gunpowder, if it is not the production of volcanic force? If so, why is it that no remains of organic matter are found imbedded in it? How comes it, if it is the result of subterranean agency, that organic remains are found in the gypsum and none in the salt, when both are caused by volcanic explosion? Thus we see the theory of volcanic explosion is met with a most formidable objection.

If marine explosion is the sole cause of the formation of salt, and if the sea has through rents and crevices of the earth forced up its superabundant saline constituents wherever there has been a vent for their egress, and which has in the course of time become condensed owing to the evaporation of the water or through its percolating into the lower strata, another difficulty crops up quite as unanswerable seemingly as that which stands in the way of the volcanic hypothesis: there are no remains of marine organisms to be found, nor are there any traces of vegetable matter.

The overflow and evaporation of sea-water and the subsequent deposition of salt holds good in certain respects as regards salt lakes and salt marshes when they are in close proximity or in the same locality; but then those other inorganic constituents which are found as a general rule in sea-water are not present in those open reservoirs, which is a difficulty as formidable as the others, and admits of no evasion.

These are the three hypotheses with their obstacles; the hypotheses feasible, the obstacles apparently unanswerable.

We have salt, or the chloride of sodium, presented to us in six different conditions, viz.: sea or salt water, salt or brine springs, salt lakes, salt mines, mountain or fossil or rock salt, and salt marshes. The characteristics of salt are just the same fundamentally, whether we extract it by evaporation from sea-water or salt lakes; whether we obtain it from salt-springs; whether we dig it out of the earth or by the excavation of salt mountains; or whether we acquire it from salt marshes: there is no alteration in its ingredients, though it may be impure from the admixture of arsenic or the sulphates of soda and magnesia, or other impurities, or it may be discoloured red by the oxide of iron derived from decomposed trap-rocks; still, for all that, the chloride of sodium remains intact. The properties of salt are not subject to the slightest change or modification: the acid is the hydrochloric or muriatic, the base sodium, and the combination, the chloride of sodium.

We find salt, or the chloride of sodium, in sea-water, the amount averaging from 4 to 5·7 per cent., so that we see it is present in no inconsiderable quantity; it is more or less impure from other salts being held in solution in conjunction: where it comes from no suggestion has yet been broached. We know that it is present, and we also know that it can be obtained by adopting certain measures for extracting it; and we are aware, from recent investigations, that the colour and density of the sea is dependent on the quantity held in solution. This is all we really know regarding the presence of the chloride of sodium in the ocean.