Page:Africa by Élisée Reclus, Volume 2.djvu/254

 204 NORTH-WEST AFRICA. masses, while in the neighbourhood of the coast granitic peaks crop out above the surrounding Miocene layers. Gneiss prevails on the northern slopes of the Jurjura, and the headlands projecting seaward consist largely of trachytes and basalts. Minerals, marbles, gypsum, salt, and thermal springs occur in many places, constituting for Algeria a considerable reserve of future wealth. According to M. Bourdon the coast near the mouth of the Shelif shows signs of upheaval. Thus the cliffs near Karuba and at other points are disposed in distinct terraces or beaches, strewn with shells of the same species as those of the surrounding waters. The coastlands are also subject to frequent earthquakes, the offects of which have been felt in Oran, Tenes, Algiers, and other towns. Many of the headlands consist of eruptive rocks, and it seems probable that the whole seaboard, like that of Tuscany and Naples, follows a line of fault in the terrestrial crust. In few regions are the traces of former erosion more evident than in Algeria ; but it is difficult to say whether they are to be attributed to the action of running waters or of snows and glaciers ; for there can be no doubt that Algeria also had its glacial period, of which clear indications are still visible on the northern slope of the Jurjura range. The work of erosion is still going on incessantly, especially in the Dahre district, where the hills are formed of a compact mass of very argil- laceous white clay, without any appearance of stratification. Similar phenomena are also very active south of the Shelif Valley, in the argillaceous and marly hills skirting the plateau. But the crests are here crowned with sandstone laj'ers from 30 to 130 feet thick, which resist atmospheric influences much longer than the underlying strata. North of the Sahara the great Algerian quadrilateral, consisting almost exclusively of plateaux and highlands, nowhere presents any conspicuous heights dominating the surrounding masses. The four chief groups of the Warsenis and Jurjura in the north, and the Amur and Aures in the south, are grouped in a sort of symmetrical order, none of them constituting a central nucleus distributing the running waters in well-defined basins. Thus no river valley is found which, by its exceptional fertility or favourable position for intercourse, might have become a natural centre of attraction for the whole country. Hence Algeria is divided into as many distinct territories as there are isolated upland regions and river basins, and it is this disposition of the land that has at all times rendered its conquest so difficult. At present a centre of attraction denied it by nature is being gradually created by artificial means at the city of Algiers, with its new harbour, routes, and railways radiating in all directions. The Coast Range.s. In the extreme north-west the Trara coast range, whose gorges afford an outlet to the Tafna river, has a mean altitude of less than 1,650 feet, culminating in the limestone peak of Mount Filhausen (3,860 feet), to the south-east of Nemours. From this, as well as from several other summits between Oran and the jyjarocco