Instead, steep and rugged cliffs rose on
each side, and overhead, instead of a starry sky, was a great arched
roof of a cavern glistening with moisture and dark as a raven's
feathers.

'We must turn back,' said Philip. 'I don't like this at all.'

'Unfortunately,' said the parrot, 'there is no room to turn back, and
the _Lightning Loose_ is not constructed for going backwards.'

'Oh, dear,' whispered Brenda, 'I wish we hadn't come. Dear little dogs
ought to be taken comfortable care of and not be sent out on nasty ships
that can't turn back when it's dangerous.'

'My dear,' said Max with slow firmness, 'dear little dogs can't help
themselves now. So they had better look out for chances of helping their
masters.'

'But what can we _do_, then?' said Philip impatiently.

'I fear,' said the parrot, 'that we can do nothing but go straight on.
If this river is in a book it will come out somewhere. No river in a
book ever runs underground and stays there.'

'I shan't wake Lucy,' said Philip; 'she might be frightened.'

'You needn't,' said Lucy, 'she's awake, and she's no more frightened
than you are.'

('You hear that,' said Max to Brenda; 'you take example by her, my
dear!')

'But if we are going the wrong way, we shan't reach the Great Sloth,'
Lucy went on.

'Sooner or later, one way or another, we shall come to him,' said the
parrot; 'and time is of no importance to a Great Sloth.'

It was now very cold, and our travellers were glad to wrap themselves in
the flags of all nations with which the yacht was handsomely provided.
Philip made a sort of tabard of the Union Jack and the old Royal Arms of
England, with the lilies and leopards; and Lucy wore the Japanese flag
as a shawl. She said the picture of the sun on it made her feel warm.
But Philip shivered under his complicated crosses and lions, as the
_Lightning Loose_ swept on over the dark tide between the dark walls and
under the dark roof of the cavern.

'Cheer up,' said the parrot. 'Think what a lot of adventures you're
having that no one else has ever had: think what a lot of things you'll
have to tell the other boys when you go to school.'

'The other boys wouldn't believe a word of it,' said Philip in gloom. 'I
wouldn't unless I knew it was true.'

'What I think is,' said Lucy, watching the yellow light from the lamps
rushing ahead along the roof, 'that we shan't want to tell people. It'll
be just enough to know it ourselves and talk about it, just