North of Maui, the tumbled rise went up a regular, ascending slope, terminating at the peak which was the island. We lay, at twenty-one degrees, thirty-three minutes, ten seconds N., one hundred and fifty-six degrees, eight minutes W., in two thousand fathoms. The slope was another thousand beneath us; but we could see its higher crags down there, and as we moved slowly south, toward Maui, holding the two thousand depth, the crags came up to meet us. We went cautiously, with only one light preceding us. Winding now, down in the ravines and furrows of the steady upward grade. Silent, mysterious passages! Sometimes they seemed about to close over us; or opened into valleys, with cliff-walls and jagged rims. Darkly, sinister depths! Our half-dimmed light showed us very little. Like a silent, cautious monster, surprising this other marine life which sometimes we saw fleeing before us, we slowly felt our way along. We came to a sharp, winding gully, barely a hundred feet wide, with sides twice as high. Its jagged, uneven floor wound upward. Once, perhaps, lava had come down here. But now its side-walls were eroded with many cavelike openings larger than the Dolphin. Still more slowly, with our little light struggling ahead of us, we followed the gully. We were all in the forward instrument room. I was at the controls, with the others around me. Nereid and Arturo stood together at my elbow with the port forward bull’s-eye before us. Occasionally he would whisper to her. With the tenseness of it, we all spoke instinctively in undertones. We were in no more than three hundred and thirty fathoms now; the Dolphin handled steadily. Some two thousand feet over us was the surface of the sea. The gully was narrowing; rising steeply ahead to what seemed a crest. Nereid whispered something. Arturo said suddenly: “Turn off the light, Jeff.” I cut off the Franklin. Through the bull’s-eye a grim, sullen darkness leaped to enfold us. But in a moment, what Nereid had seen, we began to see. A dim, pale-green effulgence far ahead, a glow, a radiance. It seemed very distant, as though the source of it might be down behind this gully-crest--a radiance in the upper water which was our sky. I heard Dr. Plantet’s sharp intake of breath; and Arturo’s murmur: “Keep our light off, Jeff. Can you see to get us up there? Stop at the crest.” We crept on up, holding close to the gully floor. The green radiance faintly painted the gully walls. At the crest we paused. * * * * * There lay before us a sharp declivity--a drop of perhaps five hundred feet to a broad oval caldron. It must have been ten miles or more in width. Beyond it, in a great steep rise the main slope ascended toward Maui.