Having reached the widest portion, which is near the end, Herbert directed me to turn, so as to come down the jump-off feet first, where there was a little difficulty in landing, as the perpendicular wall, which proved to be almost five feet high, offered only one projecting help, and that within a few inches of the base; but in obedience to his advice to "reach one foot a little farther down and then drop," I advanced the right one, to be told not that, but the other, and was soon down where it was possible to observe with interest that the right foot had been swinging above an open fissure. We stood in a wide crevice running at right angles to the obnoxious passage we had just quit, and immediately found a guide's mark on a large rock, and others followed at intervals of a few feet over extremely "rough country" as the guides say. Everywhere the work of water was apparent, not in the crystal deposits of still water as in other portions of the cave, but the erosion due to its rushing through. Carefully following the marks, they led into a cross-crevice that took us under Rainy Chamber, and ends there by widening into a circular chamber of about fifty feet width in either direction, and rising to a height of nearly fifty feet in a fine dome. Down the wall from near the top of the dome there appears to flow a beautiful waterfall showing a variety of colors in the straight lines, as if from refraction. The fall is, of course, dripstone, and I knew we had found Niagara, although we had gone beyond the reach of the guide's voice almost at the start. A huge rock directly under the dome has received the falling drip until it represents a mountain cataract. These deposits testify to the great age of the chamber they adorn, as they were necessarily not commenced until all heavy flow ceased, and in Crystal Cave the accumulation of dripstone is so slow that it is said six years' observation can detect no increase whatever. Several small passages at the floor level gave exit to the great volume of water that evidently at one time entered this crevice, from Rainy Chamber, by the route we followed, and being checked in its course the lower end of the crevice became filled, under pressure; and the low position of the outlets gave this water a whirling motion that in time excavated the dome-shaped room. No part of Crystal Cave has ever been occupied by a river, but its fissures, opened by the violence of earth movements accompanying nearby volcanic disturbances, have been filled more than once by the inrush of waters which repeatedly submerged the whole Black Hills region.