In one of the valleys to the west of the Ankàratra massif there is a river called Antsèsika, which is quite lost to sight and sound for about a mile and a quarter. It disappears under a mass of enormous gneiss boulders, which have filled up the valley of the river, so that the stream runs for a considerable distance at an immense depth below the general level. In the upper part of its course, this river passes over a series of grand falls before diving deep into the earth, as just described. Its name of Antsèsika is very appropriate, as it means “that which is thrust in.”
EXTINCT LEMUROID ANIMALS
Some members of the extinct fauna of Madagascar (Æpyornis, hippopotamus and crocodile) have been already noticed, but we must here mention other discoveries made within the last few years. About twenty years ago a skull, in a sub-fossil condition, was discovered on the south-west of the island, and proved to be that of a gigantic form of lemuroid animal. This skull is very much larger and longer than those of any existing lemurs (which are fairly globular in shape), and belonged to a creature more like a gorilla in size and strength. More recently, at a place called Ampàsambazìmba, which is five miles north of Itàsy, the remains of a number of species (fourteen or fifteen) of extinct lemuroid animals have been discovered; in fact this spot seems like the burial-ground of a whole fauna now entirely passed away, and probably quite recently; for Dr Standing, who conducted the excavations, thinks that not more than five centuries have elapsed since some at least of these animals were living. Several new species of apparently quite distinct genera have been disinterred; they are mostly larger than any existing lemuroid; and some of them form links between the true monkeys and the lemurs—families of primates now very distinct from each other. Some of these newly discovered creatures seem, from the position of the nostrils, eyes and ears (like those of the hippopotamus), to have been adapted to a partially aquatic life. There is abundant evidence of the former existence of extensive lakes in the surrounding country, where now there is only marsh or dry land. Others of these extinct animals were arboreal; and from the remains of leaves and branches, together with bones, not to mention other evidence, there is no doubt that much of what is now open down and bare hill was formerly covered with forest. There was therefore appropriate habitat for them all; and their needs, whether in water or on the trees, would be met by the former conditions of the country. It seems highly probable that the physical changes of the interior have been the chief cause of the extinction of so many living creatures, although the advent of man upon the scene may have hastened the process.[23]
PHYSICAL CHANGES
As this chapter necessarily touches less on popular and more on scientific matters than the rest of this book, a few more words may be added on the palæontology and geology of Madagascar. Besides those extinct creatures already spoken of, remains of gigantic tortoises have been discovered; also species of swine and river-hog; an ox differing from the existing cattle of the country, and a large rail and a goose exceeding in size any living species. All these belonged to the Quaternary and Recent geological epochs. But far back in the period of the Secondary rocks a species of sloth lived in the forests, old forms of crocodile lived in the rivers; and there were three at least of those gigantic lizards which were the largest of all known land animals, and were the master existences of the Jurassic period.
To sum up in a sentence or two the salient features of Madagascar geology, it may be said that the whole eastern part of the island from north to south, comprising probably about three-fifths of the entire area, is composed of crystalline rocks—gneiss, granite, mica-schist, etc. But the western two-fifths of its surface consists chiefly of Secondary strata, including chalk and sandstones and limestones of the Jurassic and Cretaceous, periods, as well as a smaller area of rocks of the Eocene and Oligocene eras. A fringe of Quaternary deposits is also found along a great part of the west coast. It is evident, therefore, that the western side of the island has been repeatedly under the sea during the geological periods just mentioned, leaving the upper highland of ancient rocks as an island not half the extent of the present Madagascar. It has quite recently been found that a narrow edging of chalk rock extends for about one hundred and twenty miles on the central part of the east coast.[24] Plutonic rocks are found in several places in both the great geological divisions of the island, and also many outflows of volcanic rocks, of a much more recent date.
We have already spoken of the two principal groups of extinct craters which exist in the central portion of Madagascar. In the more southerly of these groups, Dr Mullens speaks of an ascent of Ivòko, one of the finest old volcanoes, which is eleven hundred and thirty feet high. This, he says, “was a vast crater, a quarter of a mile across; the encircling wall was complete except at the south, where the opening was fifty feet wide. Beneath us, half-a-mile to the east, was another crater, Iatsìfitra, second only to Ivòko, with its opening to the north. On the north-west shoulder of Ivòko were two other large craters, overhanging the village of Bétàfo, two more were close by to the north-east, and others were conspicuous ten miles to the north. On the south again were several others, the horseshoe shape being very marked in them all. Descending to the crater of Iatsìfitra, we observed that the lava rocks which had issued from it were black, sharp and fresh, as if they had been broken yesterday. On the plain I counted thirty greater piles of lava, like ruined fortresses, and numberless smaller ones. It was clear that like the Phlegræan fields in Italy, the entire plain had at some time been on fire; and that a hundred jets of flame and molten lava had spurted from its surface, hurling their blazing rockets into the sky. Altogether, in our journey to the west and south-west of the capital, we counted a hundred extinct craters, extending over an arc of ninety miles.”
A VOLCANIC BELT
Madagascar appears, therefore, to be the extinct central portion of a volcanic belt which extends from Great Comoro to the north-west, through the other islands of the group, Nòsibé and northern and central Madagascar, to Réunion to the east, a distance of thirteen hundred and sixty miles. And it is noteworthy that at each extremity of this belt there is a still active volcano—viz. Piton de Fournaise, in Réunion, and one eighty-five hundred feet high in Great Comoro.
EARTHQUAKES