SOILS OF THE ARID AND HUMID REGIONS. 415 



cribes, in part, the long duration of fertility in the regur lands. 

 The regur also contains fragments of calcareous hardpan (here 

 called guvarayi), just as in the Great Valley of California, 

 The eighteen analyses of regur given by Leather agree so 

 nearly in their essential points that it is admissible to average 

 them ; two other examples are however also given in the table. 



It will be noted that while the contents of lime, magnesia and 

 alumina are uniformly high, the content of potash has a wide 

 range; it rises very high (1.14%) in the maximum, while the 

 average is fair. 



One conspicuous defect of these soils is their extremely low 

 content of nitrogen, in view of which their lasting productive- 

 ness is difficult to understand ; unless it be that, as in California, 

 their high lime-content causes a copious crop of leguminous 

 weeds, constantly replacing the nitrogen supply. 1 Unfor- 

 tunately we have no determinations of humus or of its nitrogen- 

 content. Leather attributes the black color of the regur to 

 some mineral substance rather than to humus ; but his argu- 

 ments are not quite convincing, so long as the Grandeau test 

 has not been made. In view of the low rainfall and the close- 

 ness of the texture of regur, it is probable that little if any 

 nitrates are currently washed out of the black cotton lands. 



The regur soil-sheet seems to be underlaid over the greater 

 part of its area by a basaltic eruptive sheet (not by meta- 

 morphic rocks, as stated by Leather), and it is not easy to con- 

 ceive how such a soil stratum can have been formed from such 

 rocks as a sedentary formation. Elsewhere such soils are 

 usually rather light and porous, as is the case in the Hawaiian 

 and Samoan islands ; and very high in iron-content. The 

 regur has the character of an alluvial backwater or lake de- 

 posit; but how such a formation can have occurred on the 

 Deccan plateau, is a question not easily answered. 



Red Soils of the Madras Region. Interspersed with and to 

 seaward of the regur lands there are in the Madras presidency 

 considerable bodies of " red ' lands, which appear to be 

 sedentary soils formed from underlying dark-colored, mostly 

 eruptive rocks. Some of these are very rich in lime and pot- 

 ash, others very poor, and it seems impossible to classify them 



1 See Voelcker, Report on the Improvement of Indian Agriculture, 1892, p. 46, 

 par. 60. 



