There was nothing to do but retreat as he had come. This he presently did, reluctantly turning from the half-uncovered cavern and wading into the pool.
Without his torch, and swimming towards the light, he was now enabled, to some extent, to discern the limits of the cave. He could see a portion of the ceiling and a bit of the wall on his left. Both were featureless, to all appearances. The water's surface presented a more extensive aspect with the light thus spread before him, but its farther limits could not be descried, where its inkiness blended with the gloom.
When he came at length to the ledge that formed a natural dam across the entrance, thereby impounding the water, he looked it over with greater care than when he had first trod upon it, to determine where would be the likeliest spot for a blast to break it down.
There could be no debate upon this subject. Over against the upright wall, on the left-hand side looking out, the ledge not only narrowed down, where a pot-hole pitted it deeply, but a tiny crevice extended so nearly through the remaining substance that a trickle of water already oozed downward towards the sea. The perpendicular wall here also was broken, a number of fragments of exceptional size appearing so loose as to threaten toppling over.
Grenville was leisurely in all this examination. He was either obliged to permit his body to dry in the air or dress while dripping wet. Yet at length he was once more clothed and ready to depart. He remained for a moment, taking a final survey of the place and planning the details of his blasting operations, then stooped and made his exit from the place.
The brilliant light of outer day bewildered him momentarily. He stared below, however, as if he felt he might be blind. The raft was not where he had left it.
Hastily scrambling down the incline of the ledge, he promptly arrived at its base. His view was limited, even then, to a segment of the open, purple sea. But the worst of his fears was confirmed. The raft had floated away. It was nowhere to be seen!
The tide had run out with amazing swiftness. Its level was such that the ceaseless swells ran under his ledge, instead of up about it. The creeper-cord, which he had utilized to moor his craft to the bowlders, hung uselessly over the edge. It had parted at once when the ponderous raft had been caught in the swirl of an eddy.
This eddy was running intermittently, as Grenville soon discovered. Disgust with himself for his carelessness, and a vague disquiet concerning his helpless situation, addressed his comprehension together. He was bounded by huge overhanging walls and a water abounding in sharks. If only by boat could the cavern be reached, then only by boat——
He thought of his ladder, dangling in air where he had left it, and believed for a second he could hook it in with his pole, still lying on the rocks. But no sooner had he climbed a little up the ledge, to a point from which the ladder could be seen, than he realized the folly of his hope. It was twenty feet off at the least, and fully eight above the water.