Many minerals are held in solution and are deposited at various stages of evaporation.  Let us suppose the lake to have the bottom sloping toward the abysmal center; the different minerals will be assorted as if with a sieve.  At the Sunlight Basin the edge is as flaming red as one ever sees in the sunlit sky.  And every color ever seen in a sunset flames almost as brilliantly in the varying depths.  Suppose a low cone to be flooded only occasionally, as in the case of the Old Faithful geyser.  The cooled water falling from the upper air builds up, under the terrible drench of the cataract, walls three or four inches high, making pools of every conceivable shape, a few inches deep, in which are the most exquisite and varied colors ever seen by mortal eye.  You walk about on these dividing walls and gaze into the beaded and impearled pools of a hundred shades of different colors, never equaled except by that perpetual glory of the sunset.

Consider the case of a pool that does not overflow.  Just as lakes that have no outlet must grow more and more salt till some have become solid salt beds, so must this pool, tossing its hot waves two or three feet high, evaporate its water and deposit its solids.  Where?  First, against the cooler sides of the rock under the water, tending to reduce the opening to a mere throat.  Second, each wavelet tossed in air is cooled, and deposits on the edge, solid as quartz, a crust that overhangs the pool and tends to close it over as with hot ice.  It may build thus a mound fifteen feet high with an open throat in the middle.  Thus the pool has constructed an intermittent geyser.  If the water supply continues, it also destroys itself.  The throat closes up by its own deposits.  It is a case of geyseral membranous croup.

I exceedingly longed to try vivisection on a geyser, or at least take one of half a hundred, drain it off, and make a post-mortem examination.  On my very last day I found opportunity.  I found a dead geyser, though not by any means yet cold.  It was still so hot that people had given it an infernal name.  I squeezed myself down through its hot throat, which seemed a veritable open sepulcher, and found a cave about twenty-five feet deep, twelve feet wide, and about sixty feet long.  It was elliptical in form, the sides coming together at a sharp angle at the ends, bottom, and top.  The way down to the fiery heart of the earth had simply grown up by deposits of silex on the sides and at the bottom.  The water had evaporated by the intense heat, and I was in the hot hollow that had once held an earthquake and volcano.  When I squeezed up to the blessed upper air I was glad there was no help from below.

I could tell of mounds that grew so fast as to inclose the limbs of a tree, making the firmest kind of a ladder by which I climbed to the top; of floods that overflowed acres of forest, leaving every tree firmly planted in solid rock; of mounds hundreds of feet high, covering twenty acres with forms of indescribable beauty—­but I despair.  The half has not been told.  It cannot be.  Great and marvelous are all Thy works, Lord God Almighty!  In wisdom hast Thou made them all.