Chap. XII.] soils and superficial deposits. 



189 



On studying the distribution of the soils, it will be seen that 

 the sandy soil covers a number of isolated areas surrounded by regur, 

 and a narrow band of the former also runs round the base of the hills. 

 I have already mentioned that the sandy soils affect elevated ground, 

 and that this distribution is determined by local relative elevation 

 irrespective of absolute height above the sea. There is another import- 

 ant point to be noticed in connection with elevation, viz. : that with 

 reference to the general fall of the country, as indicated by the drain- 

 age system, the red soil descends to a lower elevation on the outer or 

 lower slope than on the inner or upland slope, or in the particular case 

 of those areas which are nearest the coast, the red soil descends lowest 

 on the sea-ward slope. The accompanying diagram section of the 

 Shillagoody ridge will serve to illustrate this. (Fig. 19.) The part of 

 the ridge, across which the section is made, has its Southern slope 

 towards the Cauvery valley and the Murdayaur tributary which runs at 



Fig. 19. Diagram! Section of Shillagoody Hill, in Trichinopoly, showing relation 



OF Eegue and Sandy Soil. 



Soil boundary. Soil boundary. 



Shillagoody Station. 



r., r., regur : I., I., red sandy soil. 



The dotted horizontal line indicates the sea level. 



The an-ow the general fall of the adjoining country. 

 no great distance parallel with the line of section, runs in the direction 

 indicated by the arrow. Now, on the Northern slope of this ridge, the 

 regur ascends very nearly to the summit level, while the Southern slope 

 is covered with the red soil down to the foot of the ridge, that is to a 

 level of probably not less than 20 feet below its limit on the Northern 

 slope. The difference is^ I believe, even more than this, but its exact 



