30 GEOLoriV OF TRicjiixoroLV; &■(■. [Chap. IT, 



receiving affluents from the Kolymullays and Patchaniullaya:. From 

 this spot to beyond iVndtoray^ in South Arcot^ the alhivium forms but a 

 narrow band on either side of the river^ which here widens out g-reatly^ 

 but narrows again eastward of Yerdachellum to a width of al>out 5 

 miles. Eastward of the great Veeranum tank^ it widens out greatly^ 

 the southern boundary trending rapidly to the south-east^ till about 

 3 miles east of Lallpett^ the alluvium of the Vellaur unites with that 

 of the Cauvery delta. 



The northern boundary trends away rapidly to the north-east by 

 northj till at Cuddalore the alluvium of the Vel- 

 laur joins that of the Guddalam (Guddelom) and 

 Pooniar rivers. Like the Cauvery alluvium^ that of the Vellaur is 

 bounded successively by the gneiss^ cretaceous^ and grit formations, in a 

 direction from west to east. 



Of the great expanse of the alluvium west and south of Verda- 



,„ , ., c ^T 11 chellum, much is uncultivated and covered by scrub- 



Black soil of Vellaur •' J 



alluvium. jungle j and it is here that perhaps the largest 



extent of black humic soil of all the alluvial deposits of the different 

 river systems in this part of Southern India occurs. In this instance, 

 the black soil approaches very closely to what is commonly called '' cotton 

 soil" ; in fact, it may be said to shade, as far as appearances and consti- 

 tution go, very gradually into the " Regur," which covers the country so 

 extensively to the westward. That this wide spread of cotton-soil-like 

 earth in the alluvial deposits of the Vellaur^' is the result of an inland 

 swamp or lake, which was backed up by the low plateau of Cuddalore 

 sand-stones to the eastward before it was breached at the present passage 

 of the river, can scarcely be doubted, looking at the physical structure of 



* It is not impossible tliat luncli of tliis black alluvium is true Rcgur denuded away from 

 the great spreads occurring on the higher grounds west of the Madras and Trichinopoly 

 road, and washed up at this lower level during gre.it Hoods, such as tliis river hi somclimes 

 subject to. 



(25:3) 



