If you will think a little for yourselves about these wonderful discoveries made with the magic-glass, you will see how many questions they suggest to us about the minerals which we find buried in the earth and running through it in veins, and you will want to know something about the more precious crystals, such as rubies, diamonds, sapphires, and garnets, and many others which Nature forms far away out of our sight. All these depend, though indirectly, upon the strange effects of underground heat, and if you have once formed a picture in your minds of what must have been going on before that magnificent lava stream crept down the mountain-side and added its small contribution to the surface of the earth, you will study eagerly all that comes in your way about crystals and minerals, and while you ask questions with the spectroscope about what is going on in the sun and stars millions of miles away, you will also ask the microscope what it has to tell of the work going on at depths many miles under your feet.
[1] For the cindery nature of the surface of such a stream see the initial letter of this chapter.
[2] This arrangement in lines is called fluidal structure in lava.
[3] Micros, little; lithos, stone.
[4] Leucos, white; tephra, ashes.
CHAPTER VI
AN HOUR WITH THE SUN
