took an old spade and industriously cleared the rubbish away. Presently he revealed a large cracked flagstone. He went down on his knees and busily endeavoured to dislodge one of the broken fragments. He scraped and tore and pulled at it to no purpose. Then he stood up and stamped upon it. The rattling of loose earth underneath encouraged him to continue.
"Can you find such a thing as a pickaxe?" questioned Colonel Ossington.
Colin shook his head, but ran, nevertheless, in search of some such instrument, returning some minutes afterwards with a heavy sledge-hammer. With this he opened an assault upon the flagstone, and soon succeeded in loosening one small fragment. A small brown rat darted out from the excavation and scampered across the uneven floor.
"Wait!" cried the colonel; "lend me the hammer. Let us try first to remove this smaller stone, then we can better get at the larger one."
He took the sledge-hammer, raised it over his shoulder, and brought it down with a well-directed blow upon the smaller stone, splitting it. A second blow broke it into splinters. These he removed. Beneath them he discovered the end of a rusty bar of iron that was shot like a bolt through an iron ring. The bar seemed to extend under the larger flagstone, supporting it through its centre of gravity. For many minutes he hammered at the rusty iron, and with each blow the flagstone trembled on its axle and a shower of loosened stones and gravel fell into the depths below. With each development the old soldier's energy increased, while Colin looked on absorbed in boyish expectation.
At last the corroded bar broke. The flagstone collapsed and slipped a few inches into the void, where it was arrested by some obstacle. Its removal revealed an irregular opening, some two feet in diameter.