else was absolutely natural.  No knife had sculptured it.  No hand had given a support to its uplifted arm.  Even the dog which followed us appeared deceived, for he barked furiously at the strange intruder.  There was to me a singular fascination in this solitary freak of nature; and, surrounded though I was by immeasurably greater wonders, I turned again and again to take a farewell look at this dark, slender figure, raising its hand, as if in threatening gesture to some unseen foe.

[Illustration:  A FALSE ALARM.]

Leaving the lake, we presently entered the loveliest portion of the Park,—­a level, sheltered area of some fifty square miles, to which has been given the appropriate name of Hayden Valley, in commemoration of the distinguished geologist, Doctor Ferdinand V. Hayden, who did so much to explore this region and to impress upon the Government the necessity of preserving its incomparable natural features.  Even this tranquil portion of the Park is undermined by just such fiery forces as are elsewhere visible, but which here manifest themselves in different ways.  Thus, in the midst of this natural beauty is a horrible object, known as the Mud Geyser.  We crawled up a steep bank, and shudderingly gazed over it into the crater.  Forty feet below us, the earth yawned open like a cavernous mouth, from which a long black throat, some six feet in diameter, extended to an unknown depth.  This throat was filled with boiling mud, which rose and fell in nauseating gulps, as if some monster were strangling from a slimy paste which all its efforts could not possibly dislodge.  Occasionally the sickening mixture would sink from view, as if the tortured wretch had swallowed it.  Then we could hear, hundreds of feet below, unearthly retching; and, in a moment, it would all come up again, belched out with an explosive force that hurled a boiling spray of mud so high that we rushed down the slope.  A single drop of it would have burned like molten lead.  Five minutes of this was enough; and even now, when I reflect that every moment, day and night, the same regurgitation of black slime is going on, I feel as I have often felt, when, on a stormy night at sea, I have tried to sit through a course-dinner on an ocean steamer.

[Illustration:  HAYDEN VALLEY.]

[Illustration:  APPROACHING THE MUD GEYSER.]

[Illustration:  A STRANGER IN THE YELLOWSTONE.]

Not far from this perpetually active object is one that has been motionless for ages,—­a granite boulder enclosed by trees as by the bars of a gigantic cage.  It is a proof that glaciers once plowed through this region, and it was, no doubt, brought hither in the glacial period on a flood of ice, which, melting in this heated basin, left its burden, a grim reminder of how worlds are made.  Think what a combination of terrific forces must have been at work here, when the volcanoes were in full activity, and when the mass of ice which then encased our northern world strove to enclose this prison-house of fire within its glacial arms!  One of our party remarked that the covering of this seething, boiling area with ice must have been the nearest approach to “hell’s freezing over” that our earth has ever seen.