138 GEOLOGY OF TRICHINOPOLY, &C. [ChAP. VI. 



First. — Soils of organic origin^ in which animal life was more pre- 

 valent than vegetable life^ as proved by the cxces- 

 Mixed regur soil. 



sive quantity of kunkur formed by decomposition 



of shells, &c., and subsequent precipitation of the carbonate of lime 

 derived from them. 



This class is one which undergoes many changes in its composition 

 and texture, according to the greater or lesser amount of kunkur parti- 

 cles which may be distributed through it, becoming of a light grey or 

 even whitish colour. 



Seconciy. — We find soils of an origin only in part organic, which 

 assume a dark brown or reddish tinge, owing to the admixture of ferrugi- 

 nous matter derived from the rock in the immediate neighbourhood.* 



Some of the transition soils are of great fertility, especially the dark 

 chocolate-coloured loams met with at the junction of rich red soils with 

 black soils. 



The most barren of all the soils is the white or salt soil, generally a 

 mixture of clay and sand in variable proportions, containing considerable 

 quantities of both soda and potash, together with some common salt. 

 These salts are derived from the decomposition of the highly felspathic 

 rocks in the neighboiurhood. 



This white soil is generally met with in hollows or swampy plains, 

 and often contains small but troublesome quicksands. 



On the south bank of the Cauvery, there are several spreads of this 

 white soil, where large nullahs which have had a rapid course over the 



* In the valley of the Cauvery, south of the PatehamuUays and Kolymullays, there 

 appears to be some connection between the dark coloured soils (not Cotton-soil) and the rocks 

 they overlie ; for here I observe that these soils are spread over so much of the low 

 country of this valley as is formed of frequently alternating beds of gneiss, schist, and 

 hornblende rock. Ihese rocks lie along the noAh side of the Cauvery valley, in which are 

 -wide spreads of dark soils, which are rather like Cotton-soil, and the same rocks occur on 

 the south side of the valley, just at the edge of our area, where the very same kind of soils 

 again appears. 



(360) 



