d toward
the western side of the cave.

"Oh, ho!" he cried, and on his knees he went to work, soon forcing up one
of these stones, and under it was the metal rod, lying in a groove
considerably larger than itself. Burke now followed the line of stones to
the western side of the cave, where the roof was so low he could scarcely
stand up under it. To make sure, he took up another stone, and still
found the rod.

"I see what this means," said he. "That bolt is worked from clean
outside, and I've got to find the handle of it. If I can't do that, I'll
go back and cut through that bolt, if my chisel will do it."

He now went back to a point on the line of stones about midway between
the side of the cave and the mound, and then, walking forward as nearly
as possible in a straight line, which would be at right angles with the
metal rod, he proceeded until he had reached the entrance to the
passageway which led to the outer caves, carefully counting his steps as
he went. Then he turned squarely about, entered the passage, and walked
along it until he came to the door of the room which had once been
occupied by Captain Horn.

"I'll try it inside first," said Burke to himself, "and then I'll
go outside."

He walked through the rooms, turning to the right about ten feet when he
came to the middle apartment,--for the door here was not opposite to the
others,--but coming back again to his line of march as soon as he was on
the other side. He proceeded until he reached the large cave, open at the
top, which was the last of these compartments. This was an extensive
cavern, the back part being, however, so much impeded by rocks that had
fallen from the roof that it was difficult for him to make any progress,
and the numbering of his steps depended very much upon calculation. But
when he reached the farthest wall, Burke believed that he had gone about
as great a distance as he had stepped off in the cave of the lake.

"But how in the mischief," thought he, "am I to find anything here?" He
held up his lantern and looked about. "I can't move these rocks to see
what is under them."

As he gazed around, he noticed that the southeast corner seemed to be
more regular than the rest of the wall of the cave. In fact, it was
almost a right-angled corner, and seemed to have been roughly cut into
that shape. Instantly Burke was in the corner. He found the eastern wall
quite smooth for a space about a foot wide and extending about two yards