“Why, I kicked it,” said Jim. “A good thing it’s so big: I always thought Norah gave it to you with the idea that you might club a few Germans with it, if you got the chance—and scalp ’em afterwards. Get out!—” as Wally tipped his cap off. “Remember that you’re in a subterranean locality, and behave as such. Hark at that echo!”

He had raised his voice, unwittingly, and the echo had sent it shrieking round the cave. It was quite a relief when the sound died away to a low murmur.

“I’m not at all sure that it isn’t the Bunyip, an’ he livin’ here at his aise, as Con would say,” Wally muttered. “Come on; we’ll see how far this place goes.”

The light grew dimmer as they moved on, away from the crack overhead. Fortunately, Jim was never to be found without a tiny electric torch in his pocket, and its little beam of light was sufficiently to guide them. But for the torch their explorations would certainly have come to an end immediately, for it was not half a minute before they found themselves against a wall that apparently ended the cave.

“Well, it isn’t much of a cavern, after all,” Jim remarked. “Not bad as a dressing-room for Norah, if she wants to bathe from this beach—there’s clear sand right down to the water from the entrance in one place. She will have to come at low tide, though.”

He flashed his torch into the comers as they turned to retrace their steps. One was plainly nothing but solid wall: but in the other something caught his eye; a darker patch of shadow that was not quite like the rock.

“Why, I believe there’s an opening in that corner,” he said. “It must be another cave, communicating with this one. Come and see.”

The opening was only wide enough to admit one at a time, and so screened by a jutting boulder that it was almost invisible. Within was a cave very like the first one, though much larger; differing from it, too, in that the sand ended, and the floor was of fairly smooth rock, which, in the middle, held a great pool of water. This time there was no doubt that they were at the end of their subterranean journey; Jim flashed the light right round the wall, but there was no break in the solid rock, glistening with wet.

“Well, that’s the finish,” Wally said. “It isn’t a wildly exciting place, except for that demoniacal echo. We’ll bring Norah and the others here and make it talk. I’d like to hear what its little efforts would be like if one gave a football yell!”

“Something would break,” said Jim, suppressing a laugh. He strolled across to the pool, and turned the light on its black surface.