98 FOOTE : GEOLOGICAL STEUCTURE OF THE EASTERN COAST. 



and eastern parts of our areas ; the red soil, or lal, prevails over the 

 southern and western parts, but is also to be seen almost everywhere 

 around the bases of hills, or where the ground is very broken. It is the 

 direct product of decomposition of ferruginous rocks. Cotton soil, on the 

 contrary, is an indirect product, as it contains a much larger admixture of 

 organic matter. Its great development over such large areas may in all 

 probability be attributed to the former existence of large and thick forests, 

 and to the former prevalence of a moister climate than now exists. 

 Cotton soil an old ^ ne cotton soil was the humus formed in such 

 numus - forests. It overlies all the formations of these 



regions indiscriminately, but yet shows no signs of aqueous deposition 

 except in the manifestly washed up beds in the alluvial basins. Much 

 of the regur, however, which lies on the surface of the river and coast- 

 alluvia was formed in situ as a humus ; at least this appears to be the 

 only explanation of its occurrence over such extensive surfaces in the 

 absence of all traces of any transportation by water and deposition as a 

 true sediment. 



The sub-aerial deposits met with can all be referred to two classes, the 

 results of chemical and of mechanical action, — the 

 former including all the tufas (kankar, &c), the 

 latter represented by the blown sands. 



The tufas, including all the numerous forms of kankar, are met with 

 pretty well everywhere and in every formation as 

 foreign bodies introduced as products of decompo- 

 sition or by infiltration. The commonest form of kankar is the gravelly 

 or nodular, which forms so large an ingredient at 



Varieties of kankar. 



the base ot nearly every cotton soil throughout 

 the country, and which plays so large a part in so many of the less ferru- 

 ginous gravels of lateritic ages as already pointed out. It is needless to 

 specify any examples of a formation of such exceedingly wide distribu- 

 tion and common occurrence. 



Infiltration kankar which fills the joint clefts, and all possible cracks 

 and crannies in the older rocks, and which in innumerable cases cements 

 ( 98 ) 



