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Fig. 126.—THE STRAIT OF BONIFACIO.

Scale 1 : 300,000.

The highest summits of the island are found in the central portion of this crystalline chain, where the Gennargentu, or “silver mountain,” rises to a height of 6,116 feet. A little snow remains in the crevices of this mountain throughout the summer. The inhabitants of Northern Sardinia formerly imagined that their own Gigantinu, or “giant,” in the mountains of Limbarra, constituted the culminating point of the island, but careful measurements have shown that that superb peak only attains an elevation of 4,297 feet.

The secondary mountain groups in the western portion of the island are separated from the main chain by recent geological formations. The granitic {341} region of La Nurra, to the west of Sassari, almost uninhabited in spite of its fertile valleys, and the island of Asinara adjoining it, which abounds in turtles, are amongst these insulated mountain regions. Another, intersected by the beautiful valley of Domus Novas, occupies the south-western extremity of the island. Geologists look upon it as the most ancient portion of the island, and the plain of Campidano, which now occupies the site of an ancient arm of the sea, is of quaternary formation. The transversal range of Marghine occupies the centre of the island, and there, too, we meet with vast limestone plateaux pierced by volcanic rocks. The ancient craters, however, no longer emit lava, nor even gases, and the villagers have tranquilly built their huts within them. Thermal springs alone indicate the existence of subterranean forces. Volcanic cones of recent age are met with in the north-western portion of the island, as well as in the valley of the Orosei, on the east coast. The trachytic rocks of the islands of San Pietro and Sant’ Antioco are of greater age. They sometimes present the appearance of architectural piles, especially at the Cape of Columns, which is, however, rapidly disappearing, as the stone is being quarried to be converted into pavement. On Sant’ Antioco, which a bridge joins to the mainland, there are deep caverns, the haunts of thousands of pigeons, which are caught by spreading a net before their entrance.

In addition to the changes wrought by volcanic agencies, Sardinia exhibits traces of a slow upheaval or subsidence due to the expansion or contraction of the upper strata of the earth. Raised beaches have been discovered by La Marmora near Cagliari, at an elevation of 243 and 322 feet above the sea-level, where shells of living species are found together with potsherds and other articles, proving that when this upheaval took place the island was already inhabited. Elsewhere there exist traces of a subsidence, and the old Phœnician cities of Nora, to the south-west of Cagliari, and Tharros, on the northern peninsula of the Gulf of Oristano, have become partly submerged.

Amongst the rivers of the island there is only one which deserves that name. This is the Tirso, or Fiume d’Oristano, which is fed by the snows of the Gennargentu and the rains which descend on the western mountain slopes. Other rivers of equal length are hardly more than torrents, which at one time invade the fields adjoining them, and at another shrink to a thin thread of water meandering between thickets of laurel-trees. Most of the river beds are dry during eight months of the year, and even after rain the water does not find its way into the sea, but is absorbed by the littoral swamps.

All these swamps have brackish water. The largest amongst them communicate freely with the sea, at least during the rainy season, but others are separated from it by a strip of sand. But these, too, are brackish, for the sea-water percolates through the soil, and keeps them at the same level. The water of the inland swamps is likewise saturated with saline substances derived from the surrounding soil. They generally dry up in summer, but the coating of salt which then appears is hardly dry enough to repay the labour of collection and refinement. The only salt marshes actually exploited are those of Cagliari and of Carlo-Forte, on San {342} Pietro. They have been leased to a French company, and yield annually nearly 120,000 tons of salt.

Swamps and marshes envelop nearly the whole of the island in a zone of miasmata, which are carried by the wind into the interior, producing fever even in the more elevated mountain districts. There are localities on the island the air of which no stranger can breathe with impunity. The coast districts of Sardinia, with their stagnant waters, are, in truth, the most unhealthy in Italy, and quite one-fourth of the area of the island is exposed to the scourge of malaria, which sufficiently accounts for the small population of the island and the little progress made.