SOILS OF THE ARID AND HUMID REGIONS. 



409 



form available lands. It seems to the writer that, in view of 

 their own expressed opinion that tropical soils are not to be 

 gauged on the same percentage-basis of soil-ingredients as 

 those of temperate regions, Miintz and Rousseaux rather un- 

 derestimate the productive value of many of these lands; re- 

 garding which the field notes report good production, and 

 the crops of which are certainly not the first that they have 

 borne in the course of Malagassy history. It is as though their 

 anxiety to forestall overestimates of agricultural prospects by 

 intending settlers, had led them to somewhat overshoot the 

 mark. 



Be that as it may, the influence of the tropical climate and 

 rainfall upon the composition of these soils is certainly very 

 marked. While gneiss is not credited with producing first- 

 class soils, its usual content of orthoclase feldspar should at 

 least insure a respectable average content of potash ; but this, 

 it will be seen, is mostly not the case; and that of lime seems 

 even worse, aside from the case where, as in some regions near 

 the coast (especially in the west and south), calcareous forma- 

 tions, probably of tertiary age, have contributed to soil-for- 

 mation. At some points there seem to exist phosphate deposits, 

 well known elsewhere to occur in such rocks, which impart to 

 the soils exceptionally high percentages of phosphoric acid, 

 even exceeding one per cent. The phosphates of course remain 

 practically untouched by the leaching processes, and appear to 

 be somewhat widely diffused ; so that the soils of Madagascar 

 may be said to be, on the whole, well supplied with this import- 

 ant plant-food. 



In the central province of Imerina the valleys and lower 

 slopes show a fair content of both lime and potash ; but in the 

 province of Betsileo, adjoining it on the south, nearly every 

 one of the soils analyzed is reported as containing only 

 " traces " of lime, together with very small amounts of potash 

 in most cases. The ultimate analyses of ignited red earths, 

 of which an average is here given, are of interest in this con- 

 nection. 



ULTIMATE ANALYSIS OF IMERINA RED SOILS, IGNITED ; AVERAGE OF THREE. 



Silica 55.2 



Potash 3 



Lime trace 



Magnesia i.i 



Ferric oxid 10.6 



