For the third and last reason we will say that salt is in all
created things; and this we learn from water passed over the ashes
and cinders of burnt things; and the urine of every animal, and the
superfluities issuing from their bodies, and the earth into which
all things are converted by corruption.

But,--to put it better,--given that the world is everlasting, it
must be admitted that its population will also be eternal; hence the
human species has eternally been and would be consumers of salt; and
if all the mass of the earth were to be turned into salt, it would
not suffice for all human food [Footnote 27: That is, on the
supposition that salt, once consumed, disappears for ever.]; whence
we are forced to admit, either that the species of salt must be
everlasting like the world, or that it dies and is born again like
the men who devour it. But as experience teaches us that it does not
die, as is evident by fire, which does not consume it, and by water
which becomes salt in proportion to the quantity dissolved in
it,--and when it is evaporated the salt always remains in the
original quantity--it must pass through the bodies of men either in
the urine or the sweat or other excretions where it is found again;
and as much salt is thus got rid of as is carried every year into
towns; therefore salt is dug in places where there is urine.-- Sea
hogs and sea winds are salt.

We will say that the rains which penetrate the earth are what is
under the foundations of cities with their inhabitants, and are what
restore through the internal passages of the earth the saltness
taken from the sea; and that the change in the place of the sea,
which has been over all the mountains, caused it to be left there in
the mines found in those mountains, &c.

The characteristics of sea water (948. 949).