Page:Africa by Élisée Reclus, Volume 4.djvu/524

428 • SOUTH AND EAST AFRICA. On the west side the uplands are also skirted by similar terraced formations and e:icarpmenU disposed in the direction from north to south in a line with the main axis of the island. As many as three of these parallel ramparts follow in succession between the plateau.x and the sea, themselves merging in secondary plateaux, wherever they are not separated one from the other by intervening fluvial valleys, plains denuded by erosion, or lacustrine tracts that have been gradually filled up by uUuviul deposits. Unlike the central mountain masses, the outer ridges are not of granitic formation, but consist mostly of secondary rocks. Here Grandidier, Richardson, iind Ilildobrandt have found fossil remains ranging between the oolitic and the chalk periods, as well as the fossil bones of large animals now extinct. Some scattered boulders occurring at the foot of the mountains in various parts of the country are believed by Sibree to be erratic, so that Madagascar would also appear to have had its glacial epoch. , Volcanic Agenxies. . But however this be, the island has certainly had its period of volcanic activity, dating from times long antecedent to all historic records. Xear the edge of the eastern escarpments explorers have discovered hundreds of cones whence were formerly discharged copious lava streams. Several craters also occur near the granite formations in the central mass of Ankaratra, and the higher summits them- selves, culminating points of the island, are also igneous cones, the centres of former volcanic activity. From them lavas have been discharged in all directions, but especially towards the south. One of the streams on this side is no less than 24 miles long, the lavas ramifying far into the plains, where their dark colour presents a sharp contrast with the bright red tint of the surrounding argillaceous formations. Around the shores of Lake Ilasy, towards the north-west, Mullens reckoned as many as forty cones of all sizes, some still perfect, others with breached craters, some isolated, others clustered in separate groups. To their overflow was due the creation of the lake itself, whose waters were gradually collected in a single reser- voir behind this obstruction to tlie natural outflow. Farther south a whole plain, resimbling that of the " Plilegra^an Fields " in Italy, is thickly studded with mounds and hillocks, the flues of a vast but now extinct furnace. According to a vague local tradition, tho-se underground fires were still smouldering since the occupation of the country by the ancestors of the present inhabitants. Since the time of Mullens, the volcanic region grouped round Lake Itasy was again vi.%itedin I880 by Mr. U. Baron, who gives a detailed account of the typical volcano of Amboditaimamo, on the north side of the lake, and towards the northern verge of this igneous district. " It possesses a breached crater turned towards the east ; from this has issued a stream of lava which, following the direction of the lowest level of the ground, has swept through a small valley round the northern end of the mountain, and spread out at its west foot. This sheet of lava, which is hor- ribly rough on the surface, occupies but a small area of two or three square miles.