HOW OLD TOM FOUND THE SILVER HEART One of the first things Stephen Gard had seen to, when he got matters into his own hands, was the safeguarding of the mines from ever-possible irruption of the sea.

The great steam pumps kept the workings reasonably clear of drainage water, but no earthly power could drain the sea if it once got in.
The central shafts had sunk far below sea-level.

The lateral galleries had, in some cases, run out seawards and were now extending far under the sea itself.
From the whirling coils of the tides and races round the coast, he judged that the sea-bed was as seamed and broken and full of faults as the visible cliffs ashore.
In bad weather, the men in those submarine galleries and the outbranching tunnels could hear the crash of the waves above their heads, and the rolling and grinding of the mighty boulders with which they disported.
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.