Around the Black Rock the cliffs do not stand very high. They reach to little more than a hundred feet above the solid shelf below. In colour they are of a deep liver hue. They lean outward and take the form of huge broad broken pilasters, set against an irregular wall. These cliffs, like the Rock, are always damp, but, unlike the Rock, never clammy. They are smooth and flat, with sharp angles and rectangular fractures. They are cold and hard, and seem built by nature to define for ever the frontier of the ocean.
At the point of the Rock furthest inland the cliff is of a softer nature, and hence the water has eaten deeper in here. The cliff is part clay, part gravel, and part boulder. Here is a temporary break in the continuity of the regular formation. There is no depression on the downs above to correspond with this fault. Thus at the back of what has been called the bay, there are about two hundred yards long of cliff, which the sea would soon tear away if it could get at it. But the Black Rock stood between the greedy ocean and the vulnerable point of the cliff. It formed a sufficient outpost. This part of the bay slants inwards, not outwards, as the two arms. In this part a little copper ore was once found, and a shaft sunk. But the mine proved of no practical value, and, after absorbing much money, was abandoned fifty years ago. The shaft was sunk two hundred feet; but here, even if the mine had proved rich, the water would have presented serious difficulties, for after getting down a hundred and twenty feet it began to appear, and at a hundred and fifty it occasioned delay and inconvenience. Forty years ago the top of the shaft had been covered with planks and clay to prevent accident. Long ago the machinery and wooden engine-house and tool-house had been carried away, and now the site of the head of the shaft was indistinguishable from the other bramble-grown parts of the sloping cliff over the Black Rock. This head of the mine was always carefully avoided by the inhabitants, for every one said some day or other the planks were sure to give way and fall to the bottom. It was of no interest whatever to visitors, for nothing was to be seen, and a landslip had destroyed the rude road long ago made to it. It was on the right-hand side of one looking seaward.
On this inside of the bay of stone ran downwards the path leading to the great table below. It was a natural path almost the whole way. Art of the simplest kind had cut a little here and filled up a little there, and levelled a little in another place, but the lion's share of the work had been found ready to man's hand. There was no attempt at road-making, or attaining to a surface. Those were luxuries of civilisation: this was a work of rough art and benignant nature.
As one faced the sea, the path crossed over from left to right, then from right to left, and finally from left to right. Standing on the cliff at the middle point of the bay, and looking down at the broad expanse of slanting rock, only two things caught the eye, when the dimensions, the colour, and conformation had been taken in. Directly in front, and almost in the middle of the Rock, rose the apex of what has been likened to the shell of a barnacle. It was not more than ten feet above the level of the Rock, twenty feet from its centre, and was part of the Rock itself.
In a direct line with the apex, and about half-way between it and the outer rim of the Rock, there is a black spot which, upon closer inspection, proves to be a hole of some kind. At the distance it is impossible to perceive any more.
Towards this hole O'Hanlon pointed his arm, and said to O'Brien:
"There's the Hole. You know it well enough."
"Of course. But you could not recognise him so far off," said O'Brien, shading his eyes to look.
"No; but I told you I saw him in here quite close;" and he pointed. "He or it went on without hesitation, and then jumped in. He or it, whichever you prefer, O'Brien, went in as sure as I have a head on me. Either that or I am going mad."
O'Brien thought awhile in silence, with his hand on his chin and his eyes turned on the bleak, dreary waste of stone and water before him.