ground rumble beneath his horse's hoofs. Mouths of Avernus yawn on every side. Some caverns have sunken in, leaving serpentine ravines. One cave has been traced three miles without finding the end. Some of these caves are partially filled with ice. There is one in particular, fifteen miles south-west of the mountain, which is known as Ice Cave. This is very small, not over four hundred feet long, but it is a marvel of unique beauty. Its external appearance is that of a huge well, at whose edge are bunches of nodding flowers, and from whose dark depths issue sudden chilly gusts. Descending by means of a knotty young tree which previous visitors have let down, we find ourselves on a floor of ice. The glare of pitch-pine torches reveals a weird and beautiful scene. A perfect forest of icicles of both the stalactite and stalagmite forms fills the cave. They are from ten to fifteen feet in length and from one to three in diameter. From some points of view they look like silvered organ-pipes.
These caves have been formed in some cases by chambers of steam or bubbles in the yet pasty rock which hardened enough to maintain their form upon the condensation of the vapour. Others were doubtless produced by a tongue of lava as it collected slag and hardened rock upon its moving edge, rising up and curling over like a breaker on the sand. Only the “cave of flint” instead of turning into a “retreating cloud” had enough solid matter to sustain the arch and so became permanent. Others were no doubt formed by products. A tongue of flowing lava hardens on the surface. The interior remains fluid. It may continue running until the tongue is all
