For these people had built their castle down on the very edge of the sea, and the Pebbly Waste rose and rose to a mountain that hid their castle from the eyes of the camel-riders who were now drawing near to the scene of their next deed.
The Pebbly Waste was all made of small slippery stones, and the children understood how horrid a horse would have found it.

Even the camel went very slowly, and the dogs no longer frisked and bounded, but went at a foot's pace with drooping ears and tails.
'I should call a halt, if I were you,' said Polly.

'We shall all be the better for a cup of cocoa.

And besides----' Polly refused to explain this dark hint and only added, 'Look out for surprises.' 'I thought,' said Philip, draining the last of his second mug of cocoa, 'I thought there were no birds in the desert except you, and you're more a person than a bird.

But look there.' Far away across the desert a moving speck showed, high up in the blue air.