Madagascar Geology 2

Madagascar Geology Part II

The climate of this region, hot (average annual temperature, almost constant, of 24 °) and humid (3 m. of rain per year in Tamatava, 4 m. in the region of Maroantsetra, which are distributed throughout the year), is in fact favorable to a luxuriant vegetation and colonial crops that are exercised by Europeans. The rivers that flow into the east coast of Madagascar have a relatively short course, because the mountains from which they originate rise near the coast, but because their bed opens in the ancient impermeable soils, and has a steep slope, and because they are fed by abundant rainfall, they flow wild, especially in the hot season, the rainiest, and have great erosive power; the most important are: the Antanambalana which flows into the bay of Antongil, the Maningory, the Rianila, the Mangoro, the Mananjari and the Mananara. Alongside these, many other watercourses descend from the sides of the mountain, but rarely reach the sea, not being able to overcome the barrier of sand that the sea currents continually deposit along the coast. Thus a ring of small lakes was formed between this strip of sand and the foot of the hills, which, connected to each other by man-made canals, constitute a safe and peaceful navigable way, sheltered from storms and sea ​​winds, still used by the natives with their pirogues; these lakes also supply abundant fish, which together with cassava, rice and corn constitutes the main nourishment of the natives. The east coast of Madagascar, rectilinear especially in the central and southern section, becomes a little less monotonous and higher at N. wide bay of Antongil; at the northern end of the island there is the beautiful bay of Diego Suarez, one of the safest in the world.

According to PICKTRUE, the western region of Madagascar differs completely from the eastern and central regions: instead of an intricate system of mountains where the soil, red and compact, is covered in the east by thick vegetation and in the center by thin and stunted grasses, plains are generally found slightly bumpy, which date back to the Secondary and Tertiary, limestone or arenaceous, with a vegetation of tall grasses and palm forests, dominant here, while they are rare on the other side or tufts of woods. The rainfall is less than in the central plateau: it does not reach 400 mm. nodded. The average annual temperature ranges from 25 °, 2 to 26 °, 6, with maximums of 34-35 ° and minimums of 13 °.

Great rivers, coming from the central and eastern mountains, cross these plains: among the major ones, the first one encountered proceeding from S. to N. is the Onilahy, which flows not far from Tuléar, and which in its lower course leads the name of S. Agostino; further to N. flow the Mangoky and the Tsiribihina, which also drain large basins; less important are Manambolo and Manambao. On the north-western coast, the Betsiboka, the largest river on the island, flows into the bay where Maiunga arose; in this stretch of coast we should also remember the Mahavavy, the Sofia, the Maevarano, etc. The largest of these rivers originate in the central and eastern area of ​​ancient soils and then cross the permeable western planes, losing part of the water: poor in the dry season, however, they are very rich in water in the rainy season, from May to September. The western coast of Madagascar is low and sandy, and it is lined with paletuvieri sea branches; but in S. del Capo S. Vincenzo is protected by a coral reef. The north-western coast has a different aspect, indented by many bays, some very wide, and fronted by islets and coral reefs. The western plains are suitable for farming and numerous herds of oxen graze there.

The extreme southern region is similar to the previous one, consisting of a limestone plateau, 120-150 m high, which ends in a cliff on each side; in the eastern part rise quite high mountains. It is characterized by a great drought: in addition to the three rivers that cross it (the Manambovo, the Menarandra and the Inlinta), rivers which remain dry for a large part of the year, there are only a few ponds. In the triangle formed by the Manambovo, the southern coast and the Menarandra, only the rain, which falls at intervals of several months, supplies the relatively numerous residents with the necessary water. All living beings in southern Madagascar have adapted to such drought. Especially the plants have undergone this adaptation to the highest degree, as it seems it is not found in other parts of the world, except perhaps in certain desert areas of southern Africa and Mexico; by way of natural selection almost all the plants that have been able to resist a climate so unfavorable to life belong either to the group of succulents or to that of the euphorbiaceae; almost all are full of thorns, which are vegetative organs atrophied due to lack of nutritional elements in the soil. When the rain suffices to make them mature, the natives grow beans and millet; they also have oxen, which roam in search of the scarce grasses on the limestone plains bristling with anthills. Large land turtles are found in this region.

Capo S. Maria forms the extreme southern tip of the island, and there the great current, after having crossed the entire Indian Ocean, breaks, as at the Cape of Good Hope, and at any moment causes strong slopes on the cliff. G. Gran.

Madagascar Geology 2

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