the close of the Cretaceous Age, is sufficiently evident in the fact that portions of the Red Beds show similar fractures with the cracks filled with gypsum, and gypsum, as we have already seen, is a salt water deposit. After the crushing was done the cracks in the Carboniferous Limestone were filled with water heavily charged with calcium carbonate, taken in solution from the rock, first from pulverized particles, and afterwards by percolation and contact with exposed surfaces. This calcium carbonate was slowly deposited in crystalline form, so that in time the cracks were filled and the crushed rock firmly cemented with calcite seams. But in the meantime the removal of the calcium carbonate had started disintegration of the more exposed portions of the rock, which steadily continuing, finally reduced the porous body between the crystal seams to a soft clay which was gradually dissolved and carried out through small imperfections in the thin crystal sheets, leaving the empty box work as we find it. But where blasting has exposed fresh surfaces, much of the solid limestone carries the box-like sheets of crystal. The thinnest box work is seen in the upper levels, from which the waters retired soonest, and the heaviest and most beautiful is in the Blue Grotto, on the eighth level where the water remained longest and its diminished volume became most heavily charged. In many places, however, there is another heavy variety known as pop-corn box work, which seems to be an impure lime carbonate not so finely crystallized as the other, but at the time of my visit no explanation had been given of the manner of its deposit; and my own theory that it was not formed under water had nothing to sustain it until, a few weeks later, while visiting Crystal Cave, the work was found in active progress on surfaces occupying every position, and the agent was dripping water. In all cases the original box work has been in thin sheets of calcite, and the heavy varieties are due to later deposits of calcite and aragonite crystals or, pop corn. The colors are white, yellow, blue and chocolate brown; the last named predominating to a great extent in that portion of the cave most easily traveled by visitors, and forming the ceiling and a part of one wall in the Post Office, where, as has been said before, it first appears. The effect is not dreary as might be imagined, and parties are generally photographed here because one side of the room is white and greatly assists the flash. This is a smooth, perpendicular wall marking the line of the fissure and showing the strata of the rock in horizontal position whitened with a thin coating of carbonate of lime. All visitors are cordially invited to please themselves in leaving cards, letters or papers in this chamber, which is reserved for that purpose, and to refrain from leaving them in other portions of the cave or defacing the walls with names.