volcanic glass. This mineral was used by the Indians for
making arrow-heads and spear-heads.

In constructing a road around the base of the cliff, great difficulty
was encountered on account of the hardness of the obsidian. The
superintendent in charge of the work hit upon a happy device by which to
quarry it. Log fires were built along the base, and when the volcanic
glass was hot cold water was thrown upon it. This method cracked the
material into fragments which were easily removed.

[Illustration: The Yellowstone National Park, Wyoming Mammoth Hot
Springs. Summit Pools]

Opposite the base of Obsidian Cliff is Beaver Lake, the home of numerous
beavers and a great resort for waterfowl during a part of the year.
After passing Obsidian Cliff, hot springs become more numerous until we
reach Norris Geyser Basin. In this locality the odor of sulphur is
strong and unpleasant. A little farther on a loud roar startles us, and
a few moments later we see the cause of the explosion; it is a powerful
steam jet issuing from the summit of Roaring Mountain. When Dame Nature
"turns on steam" there is no nonsense about it.

Norris Basin seems to be of more recent volcanic development, since some
of the steam vents in other basins have ceased action during the past
few years; moreover, several new ones have opened, one of which rivals
Roaring Mountain. Constant and Minute-Man Geysers, though small, are
frequent and vigorous in action. In passing through this section the
road-bed is hot for some distance, showing that the subterranean rocks
which heat the water cannot be very deep down in the earth.

In going to the Firehole Basins we follow Gibbon River to within four
miles of its mouth, then, crossing a point of land to the Firehole, we
ascend the right bank of the stream to Lower Basin. On the road we pass
many springs; the most conspicuous of which, Beryl Spring, lies close to
the road. It discharges a large volume of boiling water and the rising
steam frequently obscures the road.

In one locality outside the beaten track of tourists there is a
veritable Hades on earth. Here, as we walk over ground that is very hot,
we are nearly suffocated by the fumes of sulphur. All around us are
hundreds of seething, boiling vats of water, and the whole area is
cracked and filled with holes from which noxious vapors rise.

Soon after we leave this infernal region we hear a constant roar like
that coming from a large steamer about to lea