A study of the Caves in connection with the active Geysers indicates that the theory he suggests and then rejects, is probably the true explanation of the difference between the two kinds of geysers.  It seems that the length of the tube must necessarily have more effect on the height of the jet than on the generation of steam; as after an eruption the tube is hotter than at any other time and therefore the generation of steam in it should be less than usual, unless the fresh inflow of water was cold.  Then if the storage cavities are broad but low, the steam cannot accumulate above the water; but when the pressure becomes sufficient to force a passage through the tube, the water and steam are expelled together until the pressure is exhausted.  But if the storage chambers are vertical fissures, as Wind Cave illustrates, vast quantities of steam must accumulate above the water level in the main reservoirs before the pressure can become sufficient to expel the water in the tube, after which steam alone continues to rush out until the pressure is so relieved that it can no longer force a passage through the water remaining in the trap, when quiet is restored.  By the constant addition of fresh water from the surface, by percolation or other usual ways of sinking, the necessary conditions for the generation of steam are maintained with surprising regularity.

The differences in the shape and general arrangement of the cavities and tubes of the two caves, indicate that their action as geysers was very unlike.  Wind Cave evidently sent a rather slender column to a great height, nearly perpendicular, and the water eruption was followed by a long steam period.  Crystal Cave ejected a much larger jet more frequently, at a low angle of inclination, the eruption was sooner over, and was not followed by a steam period of any consequence.

Thus it can be seen that the caves of the Black Hills prove the theories in regard to geyser action in Yellowstone Park, and those theories, in turn, prove the past history of the caves.  The study of geyser action also shows that the conical or dome shape of some of the cave chambers is not due to the whirl of incoming floods, as in other regions, but to jets of water forced up from lower levels.

Perhaps the finest geyser basin, and possible cave, ever in existence was destroyed when the Grand Canon of the Yellowstone became a canon.  Evidences of the former conditions in control of this gorgeously brilliant scene are neither wanting nor doubtful.  Steam constantly issues from numerous small vents in the canon walls, and a field glass reveals miniature geysers in action down in the depth of the canon, nearly half a mile below the top of the wall; while the entire canon shows, in both the color and character of its rocks, that chemical agencies have wrought changes here that have not been effected in other exposures of similar nature.  It seems not improbable that the relation of Yellowstone River to the Grand