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that it i<5 a common mistake to suppose that the black cotton 

 soil of Southern India is very rich and it is only richer than 

 the surrounding gravelly red and brown soils. If regur be 

 boiled with concentrated sulphuric acid for several hours, the 

 insoluble residue (i. e., the silicates) is very dark brown. 

 Other soils similarly treated usually give a white residue. 

 The black colouring matter of the silicates digested with 

 strong sulphuric acid if due to organic matter would dis- 

 appear under this treatment, and it must be concluded that 

 the blackness of the silicates in regur is due to some dark 

 coloured mineral and not to organic matter. 



74. We next come to the brown alluvial soils of Madras 

 The loamy ones contain high proportions of iron and alumina. 

 The amount of lime is small and the amount of magnesia high. 

 They areas a rule rich in potash but not in P 2 O 5 and N. These 

 are believed to be very fertile soils, but the analyses do not show 

 them to be any more fertile than the Indo Gangetic alluvium. 



75. The Red Soils of Madras. The amount of lime 

 in these is small or only moderate, that of magnesia 

 also is not high, while that of phosphoric acid is uni- 

 formly low. The proportion of potash is indifferently 

 high or low, that of ferric oxide and alumina rather high. 

 The proportion of Nitrogen and of organic matter is low. 

 They resemble laterite soils in composition, the main differ- 

 ence being in the proportion of P 2 O 5 . Some laterite soils 

 have a high proportion of this constituent, and others very 

 low, whilst the Madras red soils of Coimbatore, Madura, 

 Karnool, Trichinapoly and Kistna are all uniformly poor in 

 P 2 O 5 , the extreme variation in the samples analysed by Dr. 

 Leather being between '04 and 'ii per cent. 



76. Laterite Soils With these and with alluvium soils 

 we have chiefly to do in Bengal, and we might learn the 

 actual figures given by Dr. Leather in connection with the 

 analyses of some of the laterite soils of Hazaribagh, Lohar- 

 daga, Singhbhum and Manbhum. 



