Volume VII SEPTEMBER, 1915 Part II 



THE EFFECT OF CLIMATE ON SOIL FORMATION. .jukaky 



By J. WALTER LEATHER, V.D., F.LC. soTanical 



Imperial Agricultural Chemist, Agricultural Research Institute, 

 Piisa, Bengal. 



In a recent volume^ of the Journal of the Royal Agricultural 

 Society of England, Russell deals with some of the effects of climate 

 and weather on soils. 



In the opening paragraphs the effect of climate on the formation 

 of "the mineral framework of the soil" is alluded to and the laterite 

 of the Tropics is mentioned as an example of a soil produced "under 

 wholly different conditions" of cUmate, i.e. different from the chmate 

 of Europe. 



There are two soils in India whose mode of formation is still unex- 

 plained. The laterite is one and the other is the Regur or Black Cotton 

 Soil, the latter occupying very much the larger area. These two soils 

 are very distinct in their several chief characteristics. 



The Regur is black or dark brown in colour ; when wetted it expands 

 to an unusual degree and on drying large fissures form in it ; it retains 

 unusually large amounts of water; it is practically devoid of stones 

 except where near rock formations ; in chemical composition it frequently 

 contains 5 to 10 per cent, of calcium carbonate, though also the pro- 

 portion of this constituent sometimes falls to less than 1 per cent. 

 It rests on various rock formations; a large part of the area rests on 

 the Deccan trap, but it is also found on metamorphic rocks in Southern 

 India and on the Cuddapah quartzites. 



When laterite rock is first exposed it is soft and light coloured, but 

 it rapidly hardens on exposure and after breaking down to soil is red ; 

 it frequently or generally contains gravel, including limonite, but the 

 soil has otherwise no very special physical features. Like the Regur 



1 Vol. Lxxiv. p. 1, 1913. 

 Joum. of Agric. Sci. vu 10 



