126 GEOLOGY OF TEICHINOPOLY, &C. [ChAP. VI. 



shows this most strikingly. SiDreading- away to the east and west and up 

 to the Cauvery, which is indicated by a dark green belt of palm-trees 

 lining its banks, is an irregular waving country, covered with cultivated 

 tracts, and lines and topes of fine trees, among which are scattered 

 numerous villages, while massive granitic bosses and large tanks remove 

 the sameness of what would otherwise look like a great wooded plain. 



The same character of country, as far as regards the surface soil, 

 distinguishes the greater part of the district in which the granite is deve- 

 loped on the north bank of the Cauvery ; but hornblende rock and schist 

 come in here, and are in this case covered by cotton soil and its varieties. 



With regard to the connection of the red soil with the underlying 

 rocks, we may observe that where granite and quartz abound, a coarse dry 

 soil of reddish or brown colour prevails, as is the case over the greater part 

 of the Trichinopoly district south of the Cauvery. Where hornbleudic 

 rocks prevail, the soil shows rapid alternations of red of all shades, some 

 very bright, others toned by an admixture of brown. This is generally 

 the case over the whole of Salem district, so far as it has come under 

 survey. The presence of magnetic iron beds renders the soil generally 

 of a very dark red or reddish-brown. Talcose-schist, such as occurs largely 

 in the southern part of the Baramahal, near Huroor, is covered ordinarily 

 by a rather pale red soil. The coarse quartzo-felspathic granitoid gneiss 

 of South Arcot yields nearly pure sand of very pale reddish colour. 



A formation of some interest, which may be observed in many of 



the mountain valleys of our area, may be here very 



Torrent mounds. • , i • ^ -, mi n 



appropriately consiclerecl. ine lormation in ques- 

 tion consists of an assemblage of numerous large and irregularly- shaped 

 mounds of red sandy loam, with here and there small particles of kunkur ; 

 the mounds often occupy both sides, and in other places one side or the 

 middle of the valleys in which they occur ; occasionally they alternate 

 from side to side down the course of the valley. Such mounds may be 

 seen to the greatest perfection, perhaps, in the pass which divides the 

 { 34.8 ) 



