When I came to myself I explained to them the danger of approaching any cavern or other place where the air has for a long time been stagnant. "Unless air is incessantly renewed it becomes vitiated," I said, "and fatal to those who breathe it. The safest way of restoring it to its original state is to subject it to the action of fire; a few handfuls of blazing hay thrown into this hole may, if the place be small, sufficiently purify the air within to allow us to enter without danger." We tried the experiment. The flame was extinguished the instant it entered. Though bundles of blazing grass were thrown in, no difference was made. I saw that we must apply some more efficacious remedy, and sent the boys for a chest of signal rockets we had brought from the wreck. We let fly some dozens of these fiery serpents, which went whizzing in, and disappeared at apparently a vast distance from us. Some flew like radiant meteors round, lighted up the mighty circumference and displayed, as by a magician's wand, a sparkling, glittering roof. They looked like avenging dragons driving a foul, malignant fiend out of a beauteous palace. We waited for a little while after these experiments, and I then again threw in lighted hay. It burned clearly; the air was purified. Fritz and I enlarged the opening, while Jack, springing on his buffalo, thundered away to Falconhurst to bear the great and astonishing news to his mother. Great must have been the effect of Jack's eloquence on those at home, for the timbers of the bridge were soon again resounding under the swift but heavy tramp of his steed; and he was quickly followed by the rest of our party in the cart. All were in the highest state of excitement. Jack had stowed in the cart all the candles he could find, and we now, lighting these, shouldered our arms and entered. I led the way, sounding the ground as I advanced with a long pole, that we might not fall unexpectedly into any great hole or chasm, Silently we marched---the mother, the boys, and even the dogs seeming overawed with the grandeur and beauty of the scene. We were in a grotto of diamonds--a vast cave of glittering crystal; the candles reflected on the wall a golden light, bright as the stars of heaven, while great crystal pillars rose from the floor like mighty trees, mingling their branches high above us and drooping in hundreds of stalactites, which sparkled and glittered with all the colors of the rainbow. [Illustration: I ADVANCED WITH A LONG POLE] The floor of this magnificent palace was formed of hard, dry sand, so dry that I saw at once that we might safely take up our abode therein, without the slightest fear of danger from damp. From the appearance of the brilliant crystals round about us I suspected their nature.