vacated, and saw with considerable chagrin that the next step was down a
perpendicular wall more than ten feet in height, facing a high, narrow
fissure, the floor of which was merely two shelves sloping to an open
space along the middle, almost two feet wide, with the darkness of
continuing crevice below. Further progress seemed absolutely impossible.
All things are, however, possible to those who will, and it had been
willed to pay a visit to the grandest portion of Wind Cave. In order to
do so the descent must be made and was. Then some little distance must
be traveled along the crevice, but the angle of elevation taken by both
sides of the bisected floor served as a sort of prohibitory tax together
with the calcite paving, since to maintain an upright position on such a
surface would require long training of a certain professional character.
That difficulty, too, was overcome by placing a foot on either side of
the open crevice; the first consideration, of course, being safety and
not grace.

We now came to the enjoyment of the reward of merit. Flooded with the
brilliant white light of magnesium ribbon, the crevice walls could be
seen drawing together at a height of sixty-five feet, and both composed
entirely of larger box work than any seen before and very heavily
covered with calcite crystal, colored a bright electric blue and glowing
with a pearly lustre. This is the Centennial Gallery, and leaving it
with reluctance we passed on into the Blue Grotto to find it finer
still. It is somewhat wider and higher, while even the extremely rough,
uneven floor shows no spot bare of heavy box work of a yet deeper blue.

The wonderful beauty of this Blue Grotto necessarily stands beyond
comparison because in all the known world there is nothing like it. The
forms of crystal are chiefly aragonite.