There they sat late in the night, until midnight came, and so on into the morning.  At last the scene before them changed from a sheet of water to a broad expanse of mud.  The water had all retired, leaving the bed of the river exposed.

Of all the rivers that flow into the Bay of Fundy none is more remarkable than the Petitcodiac.  At high tide it is full—­a mighty stream; at low tide it is empty—­a channel of mud forty miles long; and the intervening periods are marked by the furious flow of ascending or descending waters.

And now, as the boys sat there looking out upon the expanse of mud before them, they became aware of a dull, low, booming sound, that came up from a far distant point, and seemed like the voice of many waters sounding from the storm-vexed bay outside.  There was no moon, but the light was sufficient to enable them to see the exposed riverbed, far over to the shadowy outline of the opposite shore.  Here, where in the morning a mighty ship had floated, nothing could now float; but the noise that broke upon their ears told them of the return of the waters that now were about to pour onward with resistless might into the empty channel, and send successive waves far along into the heart of the land.

“What is that noise?” asked Bruce.  “It grows louder and louder.”

“That,” said bart, “is the Bore of the Petitcodiac.”

“Have you ever seen it?”

“Never.  I’ve heard of it often, but have never seen it.”

But their words were interrupted now by the deepening thunder of the approaching waters.  Towards the quarter whence the sound arose they turned their heads involuntarily.  At first they could see nothing through the gloom of night; but at length, as they strained their eyes looking down the river, they saw in the distance a faint, white, phosphorescent gleam, and as it appeared the roar grew louder, and rounder, and more all-pervading.  On it came, carrying with it the hoarse cadence of some vast surf flung ashore from the workings of a distant storm, or the thunder of some mighty cataract tumbling over a rocky precipice.

And now, as they looked, the white, phosphorescent glow grew brighter, and then whiter, like snow; every minute it approached nearer, until at last, full before them and beneath them, there rolled a giant wave, extending across the bed of the river, crescent-shaped, with its convex side advancing forwards, and its ends following after within short distance from the shore.  The great wave rolled on, one mass of snow-white foam, behind which gleamed a broad line of phosphorescent lustre from the agitated waters, which, in the gloom of night, had a certain baleful radiance.  As it passed on its path, the roar came up more majestically from the foremost wave; and behind that came the roar of other billows that followed in its wake.  By daylight the scene would have been grand and impressive; but now, amid the gloom, the grandeur became indescribable.  The force of those mighty waters seemed indeed resistless, and it was with a feeling of relief that the boys reflected that the schooner was out of the reach of its sweep.  Its passage was swift, and soon it had passed beyond them; and afar up the river, long after it had passed from sight, they heard the distant thunder of its mighty march.