tour.

"By George, I believe it _is_ silver," exclaimed Frank, when they were
within a few feet of the dome. "No other metal has that precise color.
And look! There is a wheelbarrow and some mining tools. Leland has
been cutting away some of the material."

Sure enough, there was indisputable evidence of the truth of his
statement. And the material was undoubtedly silver!

"Silver Dome," breathed Tommy, holding a lump of the metal in his
hand. "A solid dome of pure silver--fifty feet high and a hundred in
diameter. How much does that figure in dollars and cents, Frank?"

"Maybe it isn't solid," said Frank dryly, "though it's worth a
sizeable fortune even if it is hollow. And we haven't found Leland."

* * * * *

They circled the dome twice and looked into every corner of the great
cavern, but there was no sign of the man for whom they searched. The
wheelbarrow was half filled with lumps of the heavy metal, and maul
and drill lay where they had been dropped by the lone miner. A cavity
three feet across, and as many deep, appeared in the side of the dome
to show that considerably more than one wheelbarrow load had been
removed.

"Funny," grunted Tommy. "Seems almost like the old dome had swallowed
him up."

At his words there came the terrific vibration. The light of the dome
died out, leaving them in utter darkness, and from its interior there
rose the mounting scream that had frightened old Thomas away. From so
close by it was hideous, devastating; and the two men clung to each
other in fright, expecting momentarily that the earth would give way
beneath their feet and precipitate them into some terrible depth from
which there could be no return.

Then the sound abruptly ceased and a gleam of light came from under
the dome of silver. A crack appeared between its lower edge and the
rocky floor of the cavern, and through this crack there shone a light
of dazzling brilliancy--a warm light of rosy hue. Wider grew the
opening until there was a full three feet between the floor and the
bottom of the dome. Impelled by some irresistible force from within,
the two men stumbled blindly to the opening, fell to the floor and
rolled inside.

There was a heavy thud and the dome had returned to its normal
position, with Frank and Tommy prisoners within its spacious hollow.
The warm light bathed them with fearful intensity for a moment, then
faded to a rosy glow that dulled their senses and qu