“It is strange that in a thin bed of fine clay, occurring between two masses of sandstone, we should thus have convincing evidence preserved concerning some of the earth’s inhabitants at this early period. The ripple mark, the worm track, the scratching of the small crab on the sand, and even the impression of rain drops, so _distinct as to indicate the direction of the wind_ at the time of the shower,—these and the footprints of the bird and the reptile are all stereotyped, and offer an evidence which no argument can gainsay, no prejudice resist, concerning the natural history of a very ancient period of the earth’s history. But the waves that made that ripple mark have long since ceased to wash those shores; for ages has the surface then exposed been concealed under great thicknesses of strata; the worm and the crab have left no solid fragment to speak to their form or structure; the bird has left no bone that has yet been discovered; and the fragments of the reptile are small, imperfect, and extremely rare. Still, enough is known to determine the fact, and that fact is the more interesting and valuable from the very circumstances under which it is presented.”[75] But reminding ourselves of one part of the title of our book, which professes not only to describe the crust of the earth, but also to point out its uses, we must add a few words on the economic value of this small but interesting formation. In this same new red sandstone are found the salt mines of Cheshire, and the brine pits of Worcestershire, which supply all the rock and table salt consumed in England, besides vast quantities for exportation. The rock salt of Cheshire was first discovered near Northwich, while searching for coal; but the largest mine, called the Wilton Mine, is at Nantwich, and still yields about 60,000 tons of salt annually. The salt is generally found from twenty-eight to forty-eight yards beneath the surface, in thick strata varying from fifteen to thirty-five yards in thickness. Besides these beds of salt, there are brine springs from twenty to forty yards in depth. Our common table salt is almost exclusively derived from these springs, which is produced by evaporating the water, and allowing the salt to settle at the bottom of the pans, where, after being washed, it is placed in moulds like the China clay, and comes to our grocers’ shops in the blocks we frequently see. “So far as observation has yet gone, the English supply is practically inexhaustible; no limit is known to the extent of the beds or the springs; and it ought to be regarded as one of the blessings which we owe to the mineral wealth of our country, that the beautiful table salt of England may be obtained at such an extremely low price as that now charged for it.”[76]