THE MARBLE ROCKS AT JABALPUR
The gorge of the "Marble Rocks," near Jabalpur, India, is a mile long and of an unearthly beauty of which even this little picture will give you some idea. The walls gleam white and golden in the sun. They are not really marble but limestone, which, as you will learn in this chapter, is the stone that becomes marble in "the fairyland of change." It looks as if nature had begun the making of marble columns in those cliffs, doesn't it? This is because the cliff is cut up by joints. You can also make out in one of the "pillars" the strata, or horizontal divisions of the rock, as it was laid down in the sea.
Among other things, the scientists search the pockets of the rocks, so to speak, for further evidence as to whether one kind changes into another. Chemistry is a great help in doing this, and, of course, the microscope. They find in this way that rocks that are full of crystals, such as granite and marble, and that look so different from the rocks that are not crystallized—such as limestone and sandstone—have in them the very same substances—silica, lime, potash, iron, and so on.
And again they put the oysters on the witness stand. (You remember how, long ago, oysters helped tell that mountains were once a part of the sea bottom.) They put a piece of limestone in a certain acid, and it bubbles and gives off a certain kind of gas. Then they do the same thing to an oyster-shell, and it gives out the same kind of gas. Then they try it on a piece of marble and out comes that very gas again! So all three—the limestone, the oyster-shell, and the marble—must be pretty close relations. Marble is just oyster and other shells warmed up and then allowed to cool.
But they don't stop here—these students of the rocks. It isn't enough that all these facts point to one conclusion. They want to actually try it out. So what do they do but change chalk—which is a kind of very soft limestone—into marble in the laboratory? This they do by heating the chalk and then cooling it under immense pressure.
III. The Fairies of the Fairyland of Change
If there really are fairies in this deep-down fairyland of change—and surely there must be—I should say they were the very same fairies we find in a lump of sugar—the crystals. For it is when these crystals take different shapes—the very thing fairies are always doing, you know—that things change into something else, so different you can hardly believe it. One could easily believe that charcoal and coal are related, they look so much alike in the face; but who would say that a piece of charcoal and a diamond were made of the very same stuff? They are. But diamonds are made of crystals and charcoal is not; and that must be it. The carbon of the charcoal was never touched by the wand of the Crystal Fairy.
SIX MEMBERS OF THE CRYSTAL FAMILY
Introducing six interesting members of the crystal family. The crystals of common salt and of gold, among others, take the form shown at A. Alum and diamonds crystallize as shown at C; while B and F belong to a system of crystals which we find built up into ice and arsenic. D and E are building-blocks for green vitriol, borax, and sulphate of soda.