30 CRETACEOUS ROCKS OF S. INDIA. [PaRT II. § 1. 



A strip about 2 miles broad along the outer or Northern edge consists of 

 a dark argillaceous soil, differing much from the pale sandy loam of the 

 river-banks, and identical with the superficial deposit which, known 

 as regur or cotton soil, extends up to the higher ground and covers a 

 great part of the district. This soil is apparently of distinct and prior 

 origin to the river alluvium, (See Fig. 1, which shows the regur underly- 

 FiG. 1. Sketch showing relations of Regur and Alluvium near Paroovalapoor. 



ing the alluvium, near Paroovalapoor, where the latter is very thin) ; but 

 as this fact was not clearly ascertained until the survey of a great part 

 of the country had been finished, and as, moreover, the scale of the 

 map is such as to preclude the distinct representation of the soils together 

 with the varied features of the older formations, the alluvial boundaries 

 as originally laid down, are shown. The tract, which on the map is colored 

 as alluvium, includes therefore, together with the fluviatile alluvium, so 

 much of the cotton soil as occupies a part of the river valleys, and is of 

 such thickness that the nature of the underlying rock cannot be certainly 

 ascertained. In the case of the Cauvery and its tributaries, the practical 

 discrepancy thus arising is of no great amount ; but the great plain 

 which spreads out on the upper course of the Vellaur consists entirely of 

 regur with the exception of narrow strips bordering the principal streams. 

 Granite. — To the North of Trichinopoly, at a distance of 2 to 3 miles 

 from the North bank of the Coleroon, the Crys- 

 talline rocks rise from beneath the alluvial plain 

 with a well marked declivity. A broad band of barren stony ground 



