We struck a light, and, worming ourselves through the narrow entrance, gained the interior,--a true rock gallery, vastly more roomy and lofty than one could have anticipated from the mean vestibule placed in front of it. Its extreme length we found to be two hundred and sixty feet; its extreme breadth twenty-seven feet; its height, where the roof rises highest, from eighteen to twenty feet. The cave seems to have owed its origin to two distinct causes. The trap-rocks on each side of the vertical fault-like crevice which separates them are greatly decomposed, as if by the moisture percolating from above; and directly in the line of the crevice must the surf have charged, wave after wave, for ages ere the last upheaval of the land. When the Dog-stone at Dunolly existed as a sea-stack, skirted with algae, the breakers on this shore must have dashed every tide through the narrow opening of the cavern, and scooped out by handfuls the decomposing trap within. The process of decomposition, and consequent enlargement, is still going on inside, but there is no longer an agent to sweep away the disintegrated fragments. Where the roof rises highest, the floor is blocked up with accumulations of bulky decaying masses, that have dropped from above; and it is covered over its entire area by a stratum of earthy rubbish, which has fallen from the sides and ceiling in such abundance, that it covers up the straw beds of the perished islanders, which still exist beneath as a brown mouldering felt, to the depth of from five to eight inches. Never yet was tragedy enacted on a gloomier theatre. An uncertain twilight glimmers gray at the entrance, from the narrow vestibule; but all within, for full two hundred feet, is black as with Egyptian darkness. As we passed onward with our one feeble light, along the dark mouldering walls and roof, which absorbed every straggling ray that reached them, and over the dingy floor, ropy and damp, the place called to recollection that hall in Roman story, hung and carpeted with black, into which Domitian once thrust his senate, in a frolic, to read their own names on the coffin-lids placed against the wall. The darkness seemed to press upon us from every side, as if it were a dense jetty fluid, out of which our light had scooped a pailful or two, and that was rushing in to supply the vacuum; and the only objects we saw distinctly visible were each other's heads and faces, and the lighter parts of our dress.