"By Heavens!—it can't be human," Grenville muttered, as the programme recommenced with only a slight variation.
To Elaine's dismay he started for the cliff.
"Mr. Grenville!" she cried, and helplessly followed where he went.
The wail was dying, in a horrid series of feebler repetitions, when Grenville came to the edge of the wall and peered down below at the water.
There was absolutely nothing to be seen in any direction. The direful sounds, fast progressing once more to that nerve-destroying climax, appeared to issue from a natural cove, a little along to the left.
Grenville continued around the edge, to a point directly above them. But here, as before, there was nothing in all the sea suggestive of boats or beings. The tide, Grenville thought, ran in and out with particular force, reversing at a certain point, and performing singular movements in a basin of hollowed stone.
Elaine had paused behind him, a rod or more from the brink. He waited deliberately for all the cycle of sounds to be repeated, then turned away with a smile.
"I think we have come upon the explanation of the island's uninhabited condition," he informed the girl, as he came once more to her side. "Those noises are made by the sea, forcing air to some cavern in the cliffs. It is doubtless repeated twice a day at a certain stage of the tide."
"It's horrible!" Elaine replied in dread, as a feebler rehearsal of the chorus filled all that tropic breeze, "simply horrible!"
"It may be our greatest bit of good fortune," Grenville informed her, sagely. "I much prefer those sirens to a colony of Dyaks who might otherwise live on the place."