And then they built that valve apparatus, which was also submerged, so that they could let out the water when they wanted to get at this stone thing, whatever it is.

What a scheme to hide anything! Even if anybody discovered the lake, which would not be likely until some part of the cave fell in, they would not know it was anything but a lake when they did see it.

And as for letting off the water, nobody but the people who knew about it could possibly do that, unless somebody was fool enough to take the cold bath I was obliged to take, and even then it would have been one chance in a hundred that he found the lever, and would know how to turn it when he did find it.

This whole thing is the work of the ancient South Americans, and I imagine that this stone mound is the tomb of one of their kings." At this moment the captain heard something, and turned to listen.

It was a voice--the voice of a boy.