The Story of Rock Salt, Salt under ground

by Unknown

Salt under ground! It seems a strange thing, at first, to find salt amongst the rocks, deep down in the earth. What does rock-salt tell us? It reveals to us a place where once a sea existed; the water has since flowed away, leaving some salt behind. We know that ordinary salt exposed to the air soon gets damp, and then becomes quite fluid, but rock-salt away from air and sun keeps firm for ages. Rock-salt is found in various layers of the earth's crust. Some of the spaces of underground water are called 'seas,' but in fact, large as they were, they often did not resemble the 'seas' we have now, because they were much shallower. A few were fairly deep, however. Then, again, these ancient seas were sometimes so salt that no animal could live in them, and only a few plants. Such seas, in fact, were mostly 'dead,' and this accounts for the masses of salt deposited along their bottoms. But we find also signs of rough water in the numerous pebbles of the layer where the salt is found amongst hard red gravel and brown quartz.

Germany once had a tolerably deep sea, not very salt, and the bottom surface of it shows coral reefs. There are signs in it of great fishes armed with strong teeth, enabling them to crush the shell-fish upon which they fed. These swarmed below the sea in thousands. North England and the Midlands have the Kemper beds, where the 'seas' were always shallow, and where we can trace the marks of rain-drop filterings and sun-cracks. The rock-salt is often in a layer one hundred feet thick. It is supposed that one part of these seas was separated from another part by a bar of sand, over which the waves toppled only now and then. In the cut-off sea, evaporation went on through the ages, and of course a deposit of salt was formed, while the occasional overflow from outside replaced the water which had evaporated. But really this is not known for certain. It is only clear rock-salt contains the minerals we find in our present sea-water, bromine, iodine, and magnesia.

Generally, this salt is not mixed with fragments of a different substance, but is in columns of rough crystals. Now and then there is found a layer of rock-salt, with one of marl and shells under it, succeeded by rock-salt again, showing that for a time a change had taken place.

Rock-salt sometimes melts a little under the earth, and if that happens, the rocks above it sink, and in that way hollows have been formed.

Upon the land near these shallow salt seas lived some singular animals, unlike those of our earth in the later centuries of its history. There were remarkable reptiles belonging to the frog or Batrachian family. One of the species was the size of a small ox, with peculiar complicated teeth, and feet which left prints on the earth so exactly like the impressions of the human hand, that geologists gave it a Latin name meaning 'the beast with the hand.' Another strange creature was a sort of lizard, with a horny bill, and feet resembling those of the duck; it had somewhat the appearance of a turtle, it is supposed. Then there were some warm-blooded animals about the size of a rat, which had pouches in their cheeks, and preyed upon small insects.