it isn't. Because--"

He broke off, in his ruminative talk. The collie, bored
perhaps, by standing still so long, had at first turned
seaward. But, as a wavelet washed against his white forefeet,
he drew back, annoyed, and began aimlessly to skirt the swamp,
to landward. Before he had traveled twenty yards, he
vanished.

For a second or so, Gavin Brice stared stupidly at the
phenomenon of the jungle-like wall of mangroves that had
swallowed a seventy-pound dog. Then his brow cleared, and a
glint of eagerness came into his eye. Almost running, he
hurried to the spot where the dog had vanished. Then he
halted, and called softly:

"Come, puppy! Here!"

In immediate obedience to his call, the dog reappeared, at the
swamp's edge, wagging his plumy tail, glad to be summoned.
Before the collie could stir, Brice was at his side, taking
sharp note of the direction from which the dog had just
stepped out of the mangroves.

In front, the wall of leaves and branches still hung,
seemingly impenetrable. The chief difference between this
spot and any on either side, was that the mangrove boughs had
apparently been trained to hang so low that the roots were
invisible.