Advancing through Audubon Avenue, we soon find the roof and floor approaching to form what is called Bunker Hill, around which we pass by a narrow defile. The Mushroom Beds attract our attention, to which we have already referred as having cost far more than they ever returned by way of profit, although the idea itself is feasible. Above a floor encumbered by debris hang formations needing an explanation. Limpid drops trickle through the roof, saturated with bicarbonate of lime. The supply of water is constant, but so meager as to drip instead of flow; and as the dripping goes on each drop lays down its load as a ring slight enough for a fairy’s finger. Ring follows ring till a pendant is formed like a pipestem. The pipestems thicken to the size of candles, and often grow as large as tree-trunks. Occasionally they broaden into elegant drapery, or are twisted into fantastic shapes. All these stone icicles are called “stalactites.” Such lime-laden drops as fall splash about and on evaporation deposit, not rings, but films thin as tissue-paper, building up stalagmites that are solid from their base upwards. Often these downward and upward growths meet as stately shafts, like the pillar named the Sentinel, which guards Olive’s Bower a few steps beyond it. The general term “dripstone” is conveniently applied to all these deposits, and their finer varieties are known to the mineralogist as “oriental alabaster.” A central stalactite in Olive’s Bower is very large and cone-shaped, amid many smaller ones. Below is a rampart, looking over which we see, some twenty feet below, a limpid pool that reflects the overhanging formations. Before leaving the subject of dripstone it should be remarked that, chemically regarded, it is simply the hard carbonate, not the bicarbonate, as is often alleged; the latter being an unstable compound, readily changing on any change of its conditions. The pit which arrests our progress beyond Olive’s Bower might, if explored, prove this locality to be connected with White’s Cave, whose features it resembles. On returning to the Rotunda we again inspect the historic relics of the War of 1812, and mark the grooves cut in the limestone walls by the hubs of the primitive cart-wheels that were slowly drawn along by oxen to collect the nitrous earth for the saltpeter vats. We notice that the bottoms of these vats were made of small logs halved and grooved and laid in layers on supports; the lower layer with its grooved surface up, to receive the second layer in reversed position, making a method for conveying the lye into reservoirs, whence it was pumped out to the crystallization troughs. Dr. Call was the first to direct attention to this ingenious device.