If, by chance, the sea should break through, the peril to life and property would be great.

He therefore caused to be constructed and fitted inside each tunnel, at the point where it branched from its main gallery, a stout iron door, roughly hinged at the top and falling, in case of need, into the flange of a thick wooden frame.  The framework was fitted to the opening on the seaward side, in a groove cut deep into the rock round each side and top and bottom.  The heavy iron door, when open, lay up against the roof of the tunnel and was supported by two wooden legs.  If the sea should break through, the first rush of the water would sweep away the supporting legs, the iron door would fall with a crash into the flange of the wooden frame, and the greater the pressure the tighter it would fit.

So the weight of the sea would seal the iron door against the wooden casement, which would swell and press always tighter against the rock, and that boring would be closed for ever.  And if any man should be inside the tunnel when the sea broke through, there he must stop, drowned like a rat in its hole, unless by a miracle he could make his way along the tunnel before the trap-door fell.

Gard never ceased to enjoin the utmost caution on the men who undertook these outermost experimental borings.

His strict injunctions were to cease work at the first sign of water in these undersea tunnels, make for the gallery, close the trap, and await events.

Believing absolutely in the existence of one or more great central deposits whence all these thin veins of silver had come, and hoping to strike them at every blow of his pick, old Tom Hamon was the keenest explorer and opener of new leads in the mine.

“The silver’s there all right,” he said, time and again, “it only wants finding,” and he pushed ahead, here and there, wherever he thought the chances most favourable.

He took his rightful pay along with the rest for the work he did, but it was not for wages he wrought.  Ever just beyond the point of his energetic pick lay fortune, and he was after it with all his heart and soul and bodily powers.

For months he had been following up a vein which ran out under the sea, and grew richer and richer as he laid it bare.  He believed it would lead him to the mother vein, and that to the heart of all the Sark silver.  And so he toiled, early and late, and knew no weariness.

His tunnel, in places not more than three and four feet high and between two and three feet wide, extended now several hundred feet under the sea, and was fitted at the gallery end with the usual raised iron door.

It was hot work in there, in the dim-lighted darkness, in spite of the fact that the sea was close above his head.  Fortunately, here and there, he had come upon curious little chambers like empty bubbles in one-time molten rock, ten feet across and as much in height, some of them, and curiously whorled and wrought, and these allowed him breathing spaces and welcome relief from the crampings of the passage.