ve its moorings. We follow
in the direction from which the sound proceeds and at length discover
the cause.

On approaching the source of the sound we see a large volume of steam
rushing with immense velocity from an opening in the ground, while the
rock around the orifice is black as jet. The guide tells us that this
huge steam vent is called the Black Growler, and that it continues
vigorously active summer and winter, year in and year out. Its roar can
be heard four miles away.

[Illustration: The Yellowstone National Park, Wyoming Beehive Geyser]

The chief wonder of Lower Firehole Basin is the Great Fountain Geyser.
Its formation is unique. At first sight one is led to believe that the
broad circular structure which he sees is artificial. On close
inspection numerous pools, moulded and nicely ornamented, are seen sunk
in this stone table, while in the centre there is a large and deep pool
filled with hot water, but looking like a beautiful spring. At the time
of eruption this central pool of water is shot up to the height of one
hundred feet or more. Near the Great Fountain Geyser is a small valley
in the upper part of which is a large hot spring called the Firehole.

When this spring is visited on a windless day, a light-colored flame
seems to be constantly issuing from the bottom, flickering back and
forth like a torch, and the visitor feels sure he is gazing at the
hidden fires beneath that heat the water. It is the illusion caused by
superheated steam escaping through a fissure in the rock and dividing
the water. The reflection from the surface thus formed and a black
background formed by the sides and bottom of the pool account for the
phenomenon.

Surprise Pool is found near the Great Fountain; it will make good its
name should you throw into it a handful of dirt. Excelsior Geyser, not
far away, is really a winter volcano, its crater being a seething
caldron near the Firehole River, into which it sends six million gallons
of water each day, even when not in eruption.

At times it sends up a column of water, fifty feet in diameter, to the
height of two hundred and fifty feet. The eruptions take place at long
intervals--seven to ten years. On account of the great depth and extent
of this geyser it has sometimes been denominated "Hell's Half-Acre."

Following along Firehole River we pass into the Upper Basin, a section
the most popular with the majority of tourists. Among the geysers in
this basin we shal