This gypsiferous layer is of various colours; it is crystallised, striated, and mixed with sea-shells: this admixture would decidedly lead us to conclude that the salt was originally deposited in bygone ages from the sea. On the contrary, the salt in Cheshire is not accompanied by a bed of gypsum, there are no vestiges of marine exuviæ, nor indeed any organic remains to be detected in any of the strata. If the formation of salt (I am referring to mountains of rock-salt such as we see near Cordova, in Spain,[42] and salt-mines as we see in Galicia, and Cheshire, and also isolated salt lakes, like that which exists in Western Thibet) is solely due to volcanic action, or marine explosion, we may easily account for its irregular and unequal distribution; also for its elevation into mountains, and as beds beneath the surface of the earth, by reason of the greater or less force which was employed for its upheaval; and also the thickness or solidity of those strata of rocks through which it was propelled in its upward course. If this were so, it is strange that it should be entirely free from organic remains, whose absence therefore is a formidable objection to this theory. Being accompanied by gypsum in some districts and not in others, would decidedly point to the presumed fact that salt has been the result of some volcanic agency; for were it not so we should find, on the contrary, owing to gradual formation, that gypsum would invariably be present with it, in the same way as we find one stratum of rock either above or below the stratum of another rock. From the fact that deposits of salt are not confined to any particular group of strata—for while the salt-mines of Galicia belong to the tertiary formations, those in the State of New York are found in the middle of the Silurian system—we may say that salt is not subject to geological laws by reason of its somewhat erratic appearances in different strata. As the chlorides of sodium and gypsum are frequently sublimed from volcanic vents, an igneous origin has been ascribed to many of the beds of salt and gypsum; and Mr. Bakewell threw out the suggestion that the consolidation of both salt and gypsum must have been effected by heat, because the great deposit of gypsum that occurs with rock-salt at Bex, in Switzerland, was found by M. Carpentier to be anhydrous when exposed to the atmosphere. If this hypothesis is correct, and if salt and gypsum[43] were at some period in a state of fusion, it is difficult to believe that when consolidated they are so perfectly distinct and in two different strata, so that one contains organic remains, whilst the other is altogether free from the slightest vestige. It may have been possible that one was in a state of fusion when the other was consolidated, and different degrees of heat might have been necessary for the purpose.