SOILS OF THE ARID AND HUMID REGIONS. 411 



be dealt with, and which certainly occupy by far the larger of 

 the Indian cultivated area," are : The Indo-Gangetic alluvium, 

 covering the chief cultivable areas of the Indo-Gangetic plain ; 

 the black cotton soils or regur, occupying the main body of the 

 plateau of the Central provinces (the Deccan) from the 

 Vindhya range south ; the red soils lying on the metamorphic 

 rocks of Madras; and the " latcrite" soils which are met with 

 in many parts of India. To these should be added the alluvial 

 soils of the Brahmaputra valley, in Assam. It is hardly to 

 be expected that so large an area as that of India, with its 

 diversified topography, and a climate ranging from about four 

 inches of rainfall in the northern Pandjab to the world's 

 maximum in Assam, and southward to typical tropical condi- 

 tions, could be even thus briefly characterized. The observers 

 have rarely given for the several soils analyzed, special local 

 and climatic data, which cannot always be obtained from the 

 official publications; so that it is not easy to discuss them from 

 the points of view of aridity and humidity. 



The Indo-Gangetic Plain. The general rain-map of India 

 shows the Pandjab and Rajputana to be arid throughout; 

 thence eastward the rainfall increases to 25 and 30 inches on 

 the Ganges; notwithstanding which, alkali ( reh ) is abundant 

 about Aligarh, Meerut and Agra. Thence toward Calcutta 

 there is a steady increase of rainfall until, at the head of the 

 Bay of Bengal, 70 inches is reached. 



If under these conditions the Indo-Gangetic plain admits of 

 any generalizations as regards soil composition, it must be at- 

 tributed in the main to its predominantly alluvial character. 

 It should therefore be relatively rich in lime, magnesia and 

 potash. So far as the first is concerned. Leather remarks that 

 the only rocky particles larger than sand to be found in all 

 this large belt of land is the nodular limestone called kankar, 

 formed by the deposition of calcium carbonate within the soil, 

 at the depth of a few feet. It occurs very generally in India, 

 and as stated above (chapters 9 and 19). this occurrence of 

 calcareous hardpan, of varying hardness, is almost universal in 

 the arid regions. The analysis given in the table, selected 

 as representative from those given by Leather, show that 

 the general forecast is realized in them, as soils of an arid 

 region. 



