rocks of the interior, as well as the plains of Tertiary formation, are for the most part unproductive, while vast tracts are entirely destitute of trees, and even of scrub, Boundless spaces occur in, which nothing grows except coarse herbaceous plants.
Bat in the central regions of the plateau there are also some rich and fertile valleys, where the vegetable
soil washed down by the running waters has been deposited in thick layers, and where the peasant receives a tenfold return for his labour. The geological constitution of Madagascar is revealed, so to say, by the distribution of its woodlands, which are disposed in a continuous belt round the periphery of the island, either on the low-lying coastlands or in the zone of the outer escarpments. On the east side the belt of forests is twofold, divided by an intermediate depression. On the west side there occurs a broad gap on the uninhabited plains which stretch to the west of the Ikopa River. Some wooded tracts of varying size are also scattered over the surface within the outer forest zone.
The Madagascar flora, which is better known than that of the opposite regions on the African mainland, presents several features of an original character. There are probably altogether about four thousand five hundred species, of which two thousand five hundred have already been studied and classified. Of these some have their analogies in the African and others in the South American vegetable world; but in their general physiognomy they approach nearest to the Asiatic kingdom. The vegetation is also most varied and exuberant on the eastern seaboard, that is,on the side facing the Asiatic continent. The southern and
