The rock of Isola is most interesting to the geologist, consisting of large fragments of black pumice cemented together by volcanic ashes deposited under water. It is literally a huge heap of cinders thrown out by the rapidly intermittent action of some neighbouring volcano, probably the crater of Baccano, or that which is now filled with the blue waters of Lake Bracciano. The whole mass is very friable, and in every direction the soft rock is hollowed out into sepulchral caves. By many this isolated rock is considered the arx or citadel of Veii; but the existence of so many sepulchral caves in it is, as Mr. Dennis says, conclusive of the fact that it was the Necropolis of the ancient city, which must therefore, according to Etruscan and Roman usage regarding the interment of the dead, have been outside the walls. The tombs have all been rifled and destroyed, and many of the sepulchral caves have been turned to the basest uses for stalling goats and cattle. An air of profound melancholy breathes around the whole spot. It seems to be more connected with the dead than with the living world. And the hamlet which now occupies the commanding site is of the most wretched description. All its houses, which date from the fifteenth century, are ruinous, and are among the worst in Italy; and the baronial castle which crowns the highest point,--built nearly a thousand years ago, the scene of many a conflict between the Colonnas and the Orsinis, and captured on one occasion after a twelve days' siege by Caesar Borgia,--has been converted into a barn. The inhabitants of the village do not exceed a hundred in number, and present a haggard and sallow appearance--the effect of the dreadful malaria which haunts the spot. It is strange to contrast this blighted and fever-stricken aspect of the place with the description of Dionysius, who praised its air as in his time exceedingly pure and healthy, and its territory as smiling and fruitful. In the little square of the village are several fragments of marble and other relics of Roman domination; and the church, about four or five hundred years old, dedicated to St. Pancrazio, is in a state of great decay. The walls are damp and mouldy, and all the pictures and ornaments are of the rudest description, with the exception of a faded fresco of the coronation of the Virgin, which is a fair specimen of the art of the fifteenth century. The service of the church is supplied by some distant priest or friar in orders.