“I’ve heard of singing-fish,” said Brace. “There’s not likely to be anything of that kind in the river, is there?”
“No,” replied Lynton decidedly. “I’ve heard them out at sea sometimes, when we’ve been in a calm among the islands.”
“More like to be a kind of frog,” put in Briscoe. “There are some which whistle and pipe in chorus very softly; but—”
The sound came swelling down the canon more loudly, and the speaker stopped short to listen, till the tones once more died away.
“That’s not frogs in chorus,” said Briscoe decisively. “Anyone would think there was an abbey somewhere near, and the nuns were singing hymns; only it’s impossible, of course.”
“Impossible, of course,” said Brace softly. “There: it is gone again.”
The three men stood listening and straining their ears in the direction from which the sounds had come, but there was a faint whispering as of running water down below, a trickling gurgle, and then startlingly loud came the nasal quant of some night-heron at the water’s side.
This was answered twice at a distance, while again and again overhead there was the flutter and swish of wings, probably those of the oil-birds circling about the mouth of the cavern.
“It’s all over,” said Briscoe at last, “and it’s night-birds of some kind, I believe. Here, I’ve been listening so intently that I’ve forgotten my cigar. I’ll go in and light it again with one of the bits of smouldering wood.”
He left his two companions, and they heard his footsteps as he went softly into the cavern to reach the fire.