I have the extremely difficult task of representing emotions by words—­glories of color and form seen by the eye by symbols meant to be addressed to the ear.  Before seeking to describe the diverse colors made largely by one substance, let us remember that while silica, the principal part of these water-built mounds, is one of the three parts of granite, namely, the white crystal quartz, it is also the substance of the beautifully variegated jasper, the lapis lazuli, the green malachite, and the opal, with its cloudy milk-whiteness through which flashes its heart of fire.  Silica and alumina combine to make common clay, but alumina forms itself into the red ruby, the golden-tinted topaz, the violet oriental amethyst, the red, white, yellow, and violet sapphire, and the beautiful green emerald.  With substances of such rare capabilities we may expect rich results in color and form.

We turn now to deposits from water of these two substances, especially the first.  About the Old Faithful geyser is a mound about one hundred and forty-five feet broad at the base, twelve feet high, jeweled over with pools of beauty of every shape, beaded and fretted with glories of color never seen before except in the sky.  How were they made?

Water is a general solvent.  It can take into its substance several similar bulks of other substances without greatly increasing its own, some actually diminishing it.  Hot alkaline water will dissolve even silica rock.  When water is saturated with sugar, salt, or other substance, if a little or much water is evaporated some of the saturating substance must be deposited as a solid.  All crystals, as quartz or diamonds, have been made by deposits from water.  Hot water can hold in solution much more of a solid than cold water.  Therefore, when hot water comes out of the earth and is cooled, some of the saturating substance must be deposited as a solid.  It is done in various ways, especially two.

Suppose a little pool with perpendicular sides, say twenty feet across.  It leaps and boils two feet high.  It deposits nothing till the water comes to the cooling edge.  Then it builds up a wall where it overflows, and wherever it flows it builds.  The result is that you walk up the gentle slopes of a broad flat cone, and find the little lakelet in a gorgeous setting, perfectly full at every point of the circumference.  If there is but little overflow, the result may be to deposit all the matter where it first cools, and make a perpendicular wall around the cup two or ten feet high.  If the overflow is too much to be cooled at once, the deposit may still be made fifty or one hundred feet from the point of issue.  If the overflow is sufficient, it may be building up every inch of a vast cone at once, every foot being wet.

[Illustration:  The Punch Bowl, Yellowstone Geysers.]