Page:Africa by Élisée Reclus, Volume 4.djvu/570

 458 SOUTH AND EAST AFEICA. tures in the Indian Ocean. Occasionally a column of smoke shoots up from tlie crater, a yawning chasm 500 feet deep and over a mile in circumference. In 1858 copious lava streams flowed down the western slopes of Kartal, encircling like an island a village perched on an older eruptive rock. Several other cones, some perfect, some breached, also produce a striking effect with their headlands terminating in columnar basalt cliffs. But besides the igneaus rocks, there are also some granitic and sedimentary formations. In many places the beach, strewn with sandy or shingly lavas min<^kd with ferruginous ores, is of a bright black and reddish colour, forming a striking contrast with the dazzling white of the neighbouring coral reefs. These coralline masses present great differences of form in the different islands, in Great Comoro and Moheli lying close in shore, while at I^Iayotte they are disposed in an oval ring round the coast, with openings here and there giving access to shipping. At a certain height above the present sea-level, are seen layers of sand and of shells absolutely identical with those still inhabiting the surrounding waters, and consequently attesting upheaval in relatively recent times. The seasons are bettor regulated in the Comoros than in Madagascar, the islands not being large enough greatly to modify the system of atmospheric currents. The dry seasjn, lasting uniformly from May to October, is not very unhealthy for Europeans, thanks to the. comparatively low temperature, which oscillates between 68^ and 84° F. During this period the south-eastern trade- winds prevail ; daily, however, veering round with the sun to the south and south- west. In October begins the wet and hot season, when the glass ranges from 77° to 95° F. and when the north-west trades bring copious rains, causing a discharge of 1 20 inches and upwards on the slopes of the mountains. At times the currents from opposite quarters neutralise each other, producing either calms or cyclones, which, however, are never so violent as in the Mascarenhas waters. Despite the excessive rainfall caused by the north-western monsoon, Great Comoro has not a single perennial stream, all the precipitated water disappearing rapidly in the thick deposits of volcanic ashes and scoriae covering the surface. In the other islands a few rivulets wind through the verdant valleys. Such is the fertility of the volcanic soil that, before they were inhabited, the islands were completely covered with a dense forest vegetation ; but at present not more than one-sixth of the surface is clothed with large timber. A few forms appear to be indigenous, but the greater part have been introduced either directly by man (European vegetables), or by the marine currents and other natural agencies. During the southern monsoon a local counter-current occasionally causes the upper waters to flow back, generally towards the south, and in this way the seeds of many Malagasy plants have been brought to the archipelago. From Madagascar also comes the greater part of the insular fauna. Most of the species in the two regions are identical, or at least belong to the same genera. Besides one species of lemur, the group possesses a bat {ptcropus comorensis) which ranges thence eastwards to Australia, but is absent from Africa. There is also a species of black parrot allied to a form occurring in Malasia.