The _Lightning Loose_ gave a shudder and a bound and hung for what seemed a long moment on the edge of the precipice down which the underground river was pouring itself in a smooth sleek stream, rather like poured treacle, over what felt like the edge of everything solid.
[Illustration: Plunged headlong over the edge.] The moment ended, and the little yacht, with Philip and Lucy and the parrot and the two dogs, plunged headlong over the edge into the dark unknown abyss below.
'It's all right, Lu,' said Philip in that moment.

'I'll take care of you.' And then there was silence in the cavern--only the rushing sound of the great waterfall echoed in the rocky arch..