“Farther on is another vaulted chamber, which is one hundred feet long, thirty-six wide, and twenty-six high. Its walls are filled with grotesque concretions. The effect of the lights placed by the guides at various elevations, and leaving hidden more than they reveal, is extremely fine. At the extremity of another range of apartments, a magnificent hall, two hundred and fifty feet long, and thirty-three feet high, suddenly appears. Here is a splendid sheet of rock-work running up the centre of the room, and giving it the aspect of two separate and noble galleries. This partition rises twenty feet above the floor, and leaves the fine span of the arched roof untouched. There is here a beautiful concretion, which has the form and drapery of a gigantic statue; and the whole place is filled with stalagmitical masses of the most varied and grotesque character. The fine perspective of this room, four times the length of an ordinary church, and the amazing vaulted roof spreading overhead, without any support of pillar or column, produce a most striking effect. In another apartment, which has an altitude of fifty feet, there is at one end an elevated recess ornamented with a group of pendant Stalactites of unusual size and singular beauty. They are as large as the pipes of a full-sized organ, and ranged with great regularity: when struck they emit mellow sounds of various keys, not unlike the tones of musical glasses. The length of this extraordinary group of caverns is not less than one thousand six hundred feet.” In the case of Stalactites and Stalagmites the actual formation of limestone by the influence of Chemical action is brought home forcibly to the mind, and, in a manner, made palpable to the senses. We shall now pass to other examples in which the process is scarcely less open to observation, and in which the limestone assumes a somewhat more massive and rock-like form. Every one who has been in Italy is familiar with the limestone rock called Travertine. It is seen in the ancient walls and the venerable temples of Pæstum, which have withstood unharmed the wasting hand of time for upward of twenty centuries. In Rome, too, this stone is associated in our minds as well with the enduring monuments of antiquity, as with the imposing splendor of Christian art. The Coliseum, the most stupendous of ruins, and St. Peter’s, the most sublime of temples, are built of Travertine. In fact it seems to have been, in every age, the chief building stone employed in the architecture of the Eternal City; and the quarries from which it was taken in ancient times may still be seen at Ponte Lucano, near Tivoli. Now it is an interesting fact, that close to this very spot, at the Solfatara lake on the one side, and at Tivoli itself on the other, the formation of Travertine is going on in our own time, by the precipitation of lime from a state of solution.