SOILS OF THE ARID AND HUMID REGIONS. 



407 



the southeast trade winds is first condensed, the precipitation 

 reaching ten to twelve feet (120 to 144 inches) annually. 

 The western portion is relatively dry, but rains fall more or less 

 throughout the year; while in the eastern and central moun- 

 tainous part there is a distinct subdivision into a wet and a dry 

 season. Here, while the rivers are largely torrential, many 

 large fertile valleys have been created by the heavy denudation 

 of the mountain slopes. This is especially the case in the 

 Imerina province (in which the capital, Tananarive, is sit- 

 uated), and here the valley soils are deep, and rich in humus. 

 The western portion is but thinly forested. The soils of most 

 of the island are " red '" with ferric hydrate, resembling the 

 laterite soils elsewhere ; yet the iron percentages are not usually 

 very heavy, ranging mostly from 4 to 6, more rarely to 10% 

 and more, of ferric oxid. Most of the red soils are clayey, 

 crack open in summer and become very hard in drying. 



Of the 4/6 soils analyzed by Miintz and Rousseaux, 156 are 

 from the province of Imerina, 56 from the adjacent province 

 of Betsileo, therefore 212 from the central, mountainous part 

 of the island. The remainder are scattered around the coasts ; 

 the most productive being apparently those of the northern 

 end, Diego Suarez, which is mostly underlaid by the eruptive 

 rocks forming the mountain mass of Mount Amber, from 

 which numerous fertile valleys radiate. The valleys of the 

 west coast also, in the provinces of Bara, Tulear and Betsiriry, 

 have some very productive soils. 



The subjoined table, giving fourteen analyses selected as rep- 

 resentative from the mass of material presented by Miintz and 

 Rousseaux, gives a fair general idea of the character of the 

 soils of the great island. It is at once apparent that lime and 

 potash are extremely deficient in the soils of the mountain 

 slopes of central and southern Madagascar, these substances 

 having, as elsewhere in the humid region, been leached down 

 into the valleys; and the materials being mostly quite clayey, 

 these valley soils have not, as in the case of the sandy alluvium 

 of the Brahmaputra, themselves been again leached of their 

 mineral ingredients. Practically these valleys seem to form 

 the only profitably cultivable area of the central portion; while 

 along the larger river courses, such as the Mangoky, Ikopa, 

 Mahajamba and others, good alluvial " bottoms " and deltas 



