We were too excited to return to the camp, but must make our first exploration at once. Lord John had an electric torch in his knapsack, and this had to serve us as light. He advanced, throwing his little clear circlet of yellow radiance before him, while in single file we followed at his heels.

The cave had evidently been water-worn, the sides being smooth and the floor covered with rounded stones. It was of such a size that a single man could just fit through by stooping. For fifty yards it ran almost straight into the rock, and then it ascended at an angle of forty-five. Presently this incline became even steeper, and we found ourselves climbing upon hands and knees among loose rubble which slid from beneath us. Suddenly an exclamation broke from Lord Roxton.

“It’s blocked!” said he.

Clustering behind him we saw in the yellow field of light a wall of broken basalt which extended to the ceiling.

“The roof has fallen in!”