elsewhere. But the actual mining of
rock-salt as such in England dates back only as far as the reign of King
Charles II. of blessed memory, or more definitely to the very year in
which the 'Pilgrim's Progress' was conceived and written by John Bunyan.
During that particular summer, an enterprising person at Nantwich had
sunk a shaft for coal, which he failed to find; but on his way down he
came unexpectedly across the bed of rock-salt, then for the first time
discovered as a native mineral. Since that fortunate accident the beds
have been so energetically worked and the springs so energetically
pumped that some of the towns built on top of them have got undermined,
and now threaten from year to year, in the most literal sense, to cave
in. In fact, one or two subsidences of considerable extent have already
taken place, due in part no doubt to the dissolving action of rain
water, but in part also to the mode of working. The mines are approached
by a shaft; and, when you get down to the level of the old sea bottom,
you find yourself in a sort of artificial gallery, whose roof, with all
the world on top of it, is supported every here and there by massive
pillars about fifteen feet thick. Considering that the salt lies often a
hundred and fifty yards deep, and that these pillars have to bear the
weight of all that depth of solid rock, it is not surprising that
subsidences should sometimes occur in abandoned shafts, where the water
is allowed to collect, and slowly dissolve away the supporting columns.

Salt is a necessary article of food for animals, but in a far less
degree than is commonly supposed. Each of us eats on an average about
ten times as much salt as we actually require. In this respect popular
notions are as inexact as in the very similar case of the supply of
phosphorus. Because phosphorus is needful for brain action, people jump
forthwith to the absurd conclusion that fish and other foods rich in
phosphates ought to be specially good for students preparing for
examination, great thinkers, and literary men. Mark Twain indeed once
advised a poetical aspirant, who sent him a few verses for his critical
opinion, that fish was very feeding for the brains; he would recommend a
couple of young whales to begin upon. As a matter of fact, there is more
phosphorus in our daily bread than would have sufficed Shakespeare to
write 'Hamlet,' or Newton to discover the law of gravitation. It isn't
phosphorus that most of us nee