The mountains of Capo Corso, extending in a chain nearly north and south, at a short distance from the east coast, form the third orographic division of the island; this chain, as observed in a former chapter, being cut by deep valleys of short extent, the channels of torrents discharging themselves into the Tuscan Sea.
Between this long chain, extending from Monte Antonio to Monte Incudine, and the tortuous ranges detached obliquely from it, lies a central area equal in surface to a fifth part of the whole island of which it forms the heart—the interior. The general inclination of this area, with the openings of the valleys, tends to the east. It does not form one single bason, but, intersected as it is in various directions by secondary ranges, and by mountains linking the principal chain, its contour is composed of a series of deep and generally narrow valleys, rising one above the other. The grandest as well as the most elevated of these basons is that of the Niolo, the citadel of Corsica.
These lofty mountain chains, with the numerous ramifications detached from them, and extending in all directions, render the communications between one place and another, between the coasts on opposite sides of the island, extremely difficult. The passage from the western to the eastern shore can only be effected by climbing to great elevations, through long and narrow gorges, through deep ravines of savage aspect, and covered with dense forests. The Corsicans give a lively idea of some of these toilsome paths by calling them scale,—ladders, staircases;—and such, indeed, they are, the steps, often prolonged for miles, being partly the work of Nature, partly cut in the rock by the hand of man.
GEOLOGY OF CORSICA.
In the present state of science there can be no difficulty in ascribing the origin of the three great lines of the Corsican mountains, to which all the others are subordinate, to three vast upheavings of the soil in the direction they take. The order of these elevations above the surface of the ancient sea thrice repeated in the long series of past ages, giving the first existence to the island, and by successive conglomerations shaping its present bold and irregular profile, may be also distinctly traced.
The masses first raised to the surface of the sea, supposed to be of igneous origin, lifted by the intense action of fire or subterranean heat from vast depths, and called by English geologists “Plutonic rocks,” as differing from “Volcanic,”—these masses constitute nearly the whole south-western coast of Corsica, one half of the whole island.
If an ideal line be drawn diagonally from a point so far north-west as Cape Revellata, near Calvi, to the point of Araso, far down the south-east coast near Porto Vecchio, this primary eruption may be traced in the several ranges, perpendicular to the ideal line and parallel with each other, which descending to the sea in the direction of from north-east to south-west, terminate in the principal promontories on the western coast, and form the numerous valleys which appear in succession from the Straits of Bonifacio to the Gulf of Porto.
Thus at the earliest epoch the principal axis of the island had its direction from the north-west to the south-east. The Capo Corso of those times lifted its head above the Sea of Calvi, and who can say how far the island extended at the opposite extremity? All we know is, that the group of rocky islets called the Isole Cerbicale, south-west of Porto Vecchio, with the Isola du Cavallo, and that Di Lavazzi off the coast at Bonifacio; and again, the islets Die Razzoli and Budelli on the opposite side of the Straits, with the larger islands of La Madaléna and Caprera, all of a similar formation with the primary Corsican range,—like detached fragments of some vast ruined structure,—appear to form the links of a chain which united Corsica with the mountain system of the north-eastern portion of the island of Sardinia.
These primitive masses are almost entirely granitic; and thus, at the epoch of its first emergence from the waters of the Mediterranean, no spark of animal or vegetable life existed in the new island.
So also one half of the masses raised by the second upheaval, having the same general direction, are granitic. But, as we advance towards the north-east, the granites insensibly resolve themselves into ophiolitic rocks,—a name given by French geologists to certain volcanic eruptions of the cretaceous era,—which are also found in the Morea.[21] There are but few traces remaining of this second upheaval, which evidently laid in ruins great part of the northern extremity of the former one, cutting it at right angles to the east of the Gulf of Porto. This line, ranging from the south-west to the north-east into the heart of the Nebbio, is broken up and destroyed through nearly its whole length.