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 t