406 SOILS. 



analyses should give a very full understanding of the agricul- 

 tural capacity and adaptation of so comparatively limited an 

 area; unfortunately, we are here again confronted by more or 

 less imperfect data accompanying the samples collected by 

 government agents, and by the use of an analytical method 

 different from those of all other nations, and hence incom- 

 mensurable except, as in the case of Wohltmann's method, in 

 regard to certain ingredients. 



The French chemists use nitric instead of chlorhydric acid; 

 cold for phosphoric acid and lime, boiling-hot for five hours 

 for potash ; considering the remainder as of no practical import- 

 ance. Since nitric acid is in general much less incisive than 

 chlorhydric in its solvent power, comparison with the analyses 

 made by other nations becomes difficult. As in the case of 

 Wohltmann, magnesia, lime, and phosphoric acid may be con- 

 sidered to be quite thoroughly extracted by the treatment, 

 while extraction of possibly available potash is doubtless very 

 incomplete. On the whole, however, the estimates of soil- 

 fertility based on percentages is very nearly the same as those 

 assigned by \Yohltmann in the table given above. Like 

 Wohltmann. they emphasize the axiom that the same percent- 

 age-gauge of fertility cannot be applied in the tropics as in the 

 temperate zones. 



General Cliaractcr of tli c Island. The island of Madagascar, 

 lying between the iith and 25th degrees of south latitude, is 

 quite mountainous in its central and eastern portion, where 

 the coast falls < if pretty steeply into the sea, leaving only 

 a narrow coast belt of properly agricultural land in the 

 lower valleys and at the mouth of the torrential streams. 

 The mountains rise at one point to the height of nearly 10,000 

 feet. The western portion of the Island is much less broken, 

 has much plateau land with low intersecting ranges and 

 streams of moderate fall, with considerable alluvial lands near 

 the coast. The rocks are almost throughout gneisses and 

 mica-schists, which, as heretofore stated (chapter 4, p. 51), 

 form mostly poor soils. There are a few areas of eruptive 

 rocks and tertiary calcareous deposits, and on these the lands 

 are much more thrifty. The rocks and red soils of the central 

 mass, however, extend seaward almost everywhere. 



The rainfall is high on the east side, where the moisture of 



