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194 elevated and developed form, it appears to have been occasioned by the ancient topographical conditions of the place having been changed, a great part of the rocks having been carried elsewhere, while they continued with those that remained. The sub-Apennine limestone is usually tufaceous in appearance, very friable, and almost entirely formed of minute fragments of zoophytes and marine shells, many specimens of which are found enclosed in a complete state of preservation in the rock. This rock, which is most abundant in the province of Bari, we have never found in the heart of the Apennines. Sometimes it is not so tenacious, and not so rich in fossils. The sandstones (arenarie), are generally friable, and one might rather say were deposits of sand; thus they are easily distinguished from the compact sandstone of the preceding formation, called Macigno. They often enclose small pebbles of different kinds, which, gradually increasing in size and number, at last form a conglomerate of large pebbles, of which there are amazing deposits. The greater number of these pebbles are formed of limestone, often marly, of Piromaco which sometimes changes into Diaspore, and of very compact sandstone. There are some pebbles of granite and other crystalline rocks, which we can easily understand came from the Macigno of the preceding formation, which, as we have seen, sometimes contains them in great abundance. From the other rocks of the same formation, or from the Apennine limestone, they have undoubtedly obtained other kinds of pebbles. We may mention those of quartz and Piromaco, which often still preserve between two opposite surfaces the limestone in which the Piromaco had been imbedded in the form of little strata, precisely as we find it in rocks of the first series. Deposits of pure sand with small pebbles are met with everywhere; but the large pebbly conglomerate is only found in mountainous regions, or near them, whilst the Calcareous Tufa exclusively covers the plains. The argil then, which is always more or less marly, is habitually of a sky-coloured grey, and, owing to its plastic qualities, is much better adapted for pottery than the fucoidal argil. In Calabria, where there are extensive mountains of rock crystal, the sub-Apennine deposits occasionally manifest particular characteristics, owing to the mineralogical elements of the neighbouring mountains which