The same circumstance which prevents Italy from abounding in deep bays and bold headlands also prevents its coasts from being studded with islands, which are but relics of projecting mountain chains. If we omit Sicily, which is in fact a continuation of the peninsula separated by a channel of two or three miles broad, and the Lipari islands, which are due to the volcanic action still at work beneath Etna and Vesuvius, the islands of Italy are insignificant. Capreæ (Capri) on the one hand, Prochyta (Procida) and Ischia on the other, are but fragments of the two headlands that form the Bay of Naples. Igilium (Giglio) and Ilva (Elba) stand in a similar relation to the headlands of Argentaro and Piombino. Besides these may be named Pontiæ (Ponza), Pandataria, with a few more barren rocks off the Bay of Gaeta, and a few even less important on the coast of Tuscany. Except in northern Italy, which abounds in noble rivers, the narrowness of the peninsula forbids the existence of really large streams. Yet, the Apennine range, which forms on its southern side long parallel valleys, enables numerous torrents and rills which descend towards the south to swell into rivers of not inconsiderable size. Such especially are the Arno and the Tiber. Their waters are separated by the hills which terminate in the headlands of Argentaro and Piombino, so that the Arno flows northward, and enters the sea on the northern frontier of Tuscany, after a course of about 120 miles; while the Tiber runs in a southerly direction receiving the waters of the Clanis from the west, and those of the Nar (Nera) and Velinus from the east, till its course is abruptly turned by the Sabine hills. The entire length of its channel is about 180 miles. These two well-known rivers, with their affluents, drain the whole of Etruria, the Sabine country, and the Campagna of Rome. Similar in their course, but on a smaller scale, are the Anio (Teverone) and the Liris. They both rise in the Æquian hills, the Anio flowing northward to swell the stream of the Tiber a little above Rome; the Liris, joined by the Trerus (Sacco) from the west, running southward so as to drain southern Latium and northern Campania, till it turns abruptly towards the sea, and enters it about the middle of the Bay of Gaeta, after a course of about eighty miles. The Vulturnus and the Calor run down opposite valleys from the north and south of the Samnite territory, till they join their streams on the frontier of Campania, and fall into the Bay of Gaeta only a short distance below the Liris. Both of these streams measure from their sources to their united mouth not less than one hundred miles.