We had proceeded some five more miles when again we saw a white arrow upon the rocks.  It was at a point where the face of the cliff was for the first time split into a narrow cleft.  Inside the cleft was a second guidance mark, which pointed right up it with the tip somewhat elevated, as if the spot indicated were above the level of the ground.

It was a solemn place, for the walls were so gigantic and the slit of blue sky so narrow and so obscured by a double fringe of verdure, that only a dim and shadowy light penetrated to the bottom.  We had had no food for many hours, and were very weary with the stony and irregular journey, but our nerves were too strung to allow us to halt.  We ordered the camp to be pitched, however, and, leaving the Indians to arrange it, we four, with the two half-breeds, proceeded up the narrow gorge.

It was not more than forty feet across at the mouth, but it rapidly closed until it ended in an acute angle, too straight and smooth for an ascent.  Certainly it was not this which our pioneer had attempted to indicate.  We made our way back—­the whole gorge was not more than a quarter of a mile deep—­and then suddenly the quick eyes of Lord John fell upon what we were seeking.  High up above our heads, amid the dark shadows, there was one circle of deeper gloom.  Surely it could only be the opening of a cave.

The base of the cliff was heaped with loose stones at the spot, and it was not difficult to clamber up.  When we reached it, all doubt was removed.  Not only was it an opening into the rock, but on the side of it there was marked once again the sign of the arrow.  Here was the point, and this the means by which Maple White and his ill-fated comrade had made their ascent.

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!”

In vain we dragged out some of the pieces.  The only effect was that the larger ones became detached and threatened to roll down the gradient and crush us.  It was evident that the obstacle was far beyond any efforts which we could make to remove it.  The road by which Maple White had ascended was no longer available.