ALLUVIAL FORMATIONS. 75 



CHAPTER VIII. 



THE ALLUVIAL FORMATIONS. 



A large area of the region described in this memoir is occupied by 

 Effects (5f lono- conti- ^^® marine and fluviatile alluvia, but there is little 

 nued wet cultivation. ^^ g^y about them relatively to the superficial 



extent, as very few sections were met with, and as nearly the whole surface 

 has been greatly altered by the vast scale on which wet cultivation has 

 been carried on for many centuries. Practically the greater part of the 

 alluvial surface is " made ground/^ the long continued operations of irri- 

 gation having in many parts, both of the great and small irrigated val- 

 leys, extensively raised the general surface of the country by a process 

 technically known as " warping.^^ 



Of deep sections furnishing any real idea of the beds composing the 



alluvial deposits in depth, not a single one was 

 No deep sections. r« i • 



met with, nor do any oi the rivers attord sections 



more than a few feet in depth. Over very large tracts of country the 



surface is completely hidden by paddy-fields or by the waters of the very 



numerous irrigation tanks, many of which are of very lar<^e size. 



The soil thrown out of the bottoms of these tanks and piled up to 

 form the " bunds " sometimes affords some clue as to the local character 

 of the superficial alluvium, but even this is very often hidden by the 

 piles of humus and silt that have during the course of ages been thrown 

 out when the tanks have been cleared. 



In some of the smaller rivers, however, the character of the alluvia 

 Unaltered aUuvlum of IS not SO utterly disguised by cultivation, as for 

 "^^^^^'^ example in the case of the Palar (the upper part 



of the Tirupatur river in Madura district). Here the unusually high 

 banks generally reveal a reddish loam derived from the red soil of the 

 gneissic tracts in which it rises to the north-east of the Siru Malai. 

 Prevailino- type of -^^ far as the great spreads of irrigated cultivation 

 river aUuvium. ^i|^^ ^f recognition of the true character of the 



surface beds of the alluvium, there is a very great similarity in composi- 



( 75 ) 



