“In a sharp, deep valley of Albemarle we had broken in the roof of a bubble; and as we looked in we saw we had opened the way into a tunnel about fifteen feet in width, and extending either way as far as we could see from our position. By the lights which entered from above, we made out the floor as about twenty feet beneath us, and that the walls were curiously marked with columnar forms. My companion, who had dabbled in the sciences, proposed that we should take an underground view of volcanic action and appearances.

“So, on the following day, provided with a couple of lamps, a coil of knotted line, and a couple of waist-lines and iron poles for staves, we proceeded on our exploration. We descended with the knotted rope around our bodies, and stuck our feet into the rough side, lighted in our way by a single lamp. We carefully watched for any side openings which might confuse us or lead us astray in returning, but we saw none and felt safe. It soon became evident that the tunnel had not been formed by a rent of the mass after cooling, but rather by the molten lava’s having drained away after a crust had formed upon it. This may account for the singular and beautiful formations by which we found ourselves surrounded. After proceeding some distance through a passage with a pretty uniform width of fifteen to twenty feet, and of about equal height, we paused to examine the formation of the cavern. The dim light of our lamps illuminated the pilastered walls, and a roof raftered and groined with straight and curved beams of crystalline structure many feet in length. Some of these were of a reddish appearance, and others had a vitreous lustre, resembling immense crystals, in places broken into the semblance of foliage, which reflected an olive green light. The gloomy splendor of this solemn architecture was relieved by the gold or amber reflections of crystals of sulphur, which, like marigold or sunflower, gleamed in the passage.

“The broad bases of the pilasters were enriched with counterfeits of fern, palms, and growths intricate and delicate as the penciling of the frost spirit’s pictures. But these metallic pictures, under the limning of the fire-fiend had been inlaid with the brilliant facets of igneous minerals, green and brown in tint. Tempted onward by the increasing beauty of the scene, our lamp revealed new objects of interest in the increasing lustre of the arched ceiling, and the carved and painted walls. Our lamp was multiplied by the sparkle from the faces of unknown minerals. In places the passage was divided by central columns of basalt crystals, which terminated in curves, and were in form and tracery varied beyond man’s power. The rude Goth for his cathedral, the Moslem for his mosque, the Celestial for his pagoda, might have drawn inspiration from this solemn portal to Nature’s vast workshop.

“As we advanced further into the recesses of the mountain, the character of the cave changed. The angular crystalline forms which indicated the sudden withdrawal of the molten matter, or the deposit of elements sublimed by intense heat, yielded to smooth and rounded structures, like the worn rocks of the river side, giving the impression that the walls had served as a sluice to fiery torrents pouring from the volcano. A few steps farther showed us the singular curtain-like foldings of a substance resembling lampblack. Absolutely without lustre, and absorbent of every ray of light, it was present, as it were, only to the touch. With certain misgivings under this curtain of gloom, we entered a cavern the form or extent of which could only be known by touch of hands, for no possible brilliancy of light would command an answering reflection from the absorbent surface. Broken as was the surface to the touch, to the eye it was without form. The floor was invisible, and we were guided in our steps by our staves alone. It was like stepping into primal chaos, before light and form had birth. A profound chasm seemed to yawn at our feet; yet the rocky floor rang to the blow of the staff, and with cautious tread we proceeded. The flame of the lamp met no responsive glow; save from the two intruders who stood awe stricken in this strange emptiness; it stood in the still blackness unflickering, like a solid. Feeling the broken walls, the hand was met by an oily softness; the eye was useless, and even the touch now failed to guide us. Solid walls were not to the eye; rocky barriers seemed simply impenetrable darkness to the hand.

“From repeated contact with sooty walls, we also became covered with this strange, light-absorbing powder, until we were enveloped in an invisible mantle, and also passed from each other’s sight. Eye alone answered to eye in their reflections of light. Too deeply impressed for conversation, we stood still with outstretched hands. My comrade asked at length, ‘May it not be even so in the valley of the Shadow of Death?’ And we looked for strength into each other’s eyes and linked our arms that we might have the companionship of touch. We were now thoroughly frightened, and turned to retrace our steps; but which way? We stood in a sea of nothingness—locked in the foundations of the mountain. The walls were lost to the sight, and were nothing to the touch. We stooped to the deep dust of the floor and held the flame to read our foot-prints; but the soil absorbed the light, as the sand of the desert does the raindrop. We reached forward, and the hand failed to meet the wall; we reached downward; there, too, was empty space. The light showed no defining edge between the solid rock and the void. We swung the lamp from the brink on which we lay; it revealed nothing. We dropped a heavy stone into the chasm and listened for the rebound. No sound was returned as it sank into the profound. We cast another stone across to test the width, but this, too, was lost to the senses. Silently they passed away, as the mist wreath on the hill side. And then we knew we had been preserved from death. A careless step and we had found a grave in the depths of the world’s foundations. We realized that we were lying in trembling safety on the threshold of the extinct volcano, and lifting our useless eyes from the impenetrable blackness, the awful whisper ‘Lost!’ passed between us. We were afraid to move; but the wasting oil of our lamp warned us that time must not be lost. Presently our ears caught the heat of surf on the rock as the tide came in, and following this direction, we finally reached the entrance, almost fainting from joy when we stood beyond this chamber of gloom. Once more we stood under the wondrous tracery and reflections of the outer gates of the inter-world of mysterious.”

A most thrilling experience, and one giving a fine picture of what may be found in the mysterious depths of a lava bubble. In some cases the bubbles are very thin; and an unwary passer might be suddenly plunged into unfathomable depths should he tread on one. Usually, however, they are formed over horizontal currents or passages.

We have endeavored to give the well-established facts concerning the principles of volcanic action. It only remains, ere we leave this phase of the subject, that we notice the one point on which as yet our knowledge is not clear. That point is, the source of the heat which produces the remarkable effects.

Several theories are advanced. One class of scientists believes that the earth is a mass of molten matter, with only a thin outer shell of cooled material. That a very