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. 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]