The disorder and ruin of these several points of the original system, and the almost total destruction of its northern part, were undoubtedly caused by the _third_ and last upheaval which gave the island the form it presents at the present day. Its direction was from north to south, and so long as the mass then raised did not come in contact with the land created by former upheavals, it preserved its regular line, as we find in the mountain-chain of Capo Corso. But when, on emerging above the surface of the sea, this mass had to overcome at its southern extremity the resistance of the primary rocks upheaved long before, and now become hard and consolidated,—in that terrible shock, on the one hand, it changed, crushed, or ruined all that obstructed its progress, while, on the other, it varied its own direction and was itself broken up in many places, as appears from the openings of the valleys communicating from the interior with the plains of the eastern littoral and giving a passage to the torrents which fall into the sea on this coast,—the Bevinco, the Golo, the Tavignano, the Fiumorbo.
The fundamental rocks brought up by this third and last upheaval are ophiolitic, and metamorphic, or primary, limestone, overlaid in some places by secondary formations. “The granites on the west, as well as the south, of the island include some beds of _gneiss_ and _schistes_ at their extremities.”—(_Gueymard_). Almost everywhere the granite is covered—an evident proof that the epoch of its eruption preceded that when the deposits were formed in the depths of the sea, and deposited in horizontal strata on the crystalline masses of the granite.
Masses of euritic and porphyritic rocks intersect the granites, and a distinct formation of porphyries crowns Monte Cinto, Vagliorba, and Pertusato, the highest summits of the _Niolo_, covering the granite. These porphyries are pierced by greenstone two or three feet thick, and the granites are intersected by numerous veins of amphibolite (hornblende) and greenstone, generally running from east to west.
Transition rocks, as they are called, occupy the whole of Capo Corso and the east of the island. They consist of talcose-schiste, bluish-grey limestone, talc in beds, serpentine, black marble similar to the oldest in the Alps, quartz, feldspar, and porphyries.