Whilst engaged in this excursion, we had heard the sound of hammering somewhere away in the heart of the rock. It was our three friends attempting to break into a promising gallery, which ought to cross the vestibule of the main cavern and connect the two groups of upper caves. We were not long in joining them; and now with pick, hammer, and crowbar we attacked the barrier in force. The chief obstacle was a great flat rock standing on end across the unexplored opening, and propped up by a heap of boulders, which we gradually smashed up or removed to one side. Still the big fellow would not budge, and we had to sap his foundations by degrees. Yet this huge rock was but a fragment that had fallen from the edge of a vast and threatening leaf of rock, which now hung over our heads like a monstrous guillotine. The upper caves are waterless, and it soon became desirable to send one of our number to fetch us a drink. Presently we heard a plaintive cry from the distance: his candle had gone out, and he had forgotten the matches. Going to the rescue, I found him groping about on a shelf of rock, 30 feet from the floor, hard by the Spur and Wedge; he had lost his bearings altogether. On his return, we made another onslaught upon our rocky adversary, the five of us sitting on his shoulder and pushing against the wall, whilst our leader waxed grimly facetious as to what would happen to us if the shock brought down the guillotine. Slowly and painfully we tilted the mass of rock over, but only a few inches, leaving just room enough for a thin man to crawl behind. Squirming eagerly into the opening, I looked under, and was disappointed to see that, if wide, it was still heaped right to the crown of the arch by the rubbish flung there long ago by the river. Nevertheless, Mr. Balch was not dissatisfied. Though parts of these ancient waterways are choked with débris, it is unlikely, nay impossible, that the main channels should not remain open. Our day's work had taken us on another stage in our slow journey. The labour of removing the new obstacle will be considerable, but the result is sure.