J 33 GEOLOGY OF THICIIINOPOLY, &C'. [ClIAP. VI. 



Eastward of the Mookanoor peak. Cotton -soil is again found, at a 



very high level,* and spreads, without any impor- 

 east of Mookanoor ; 



tant break, as tar south as the bend of the Toopoor 



river. A long strip occupies the northern part of the Munjawaddy valley, 



and extends northwards along the foot of the Tainandamullays, for 3 



or 4 miles. 



Several small but typical spreads of Regur occur in the eastern 

 part of the Salem-Ahtoor valley, and also in the great Cottaputty 

 valley which divides the Kalroyenmullay from the Tainandamullay. 



A considerable area of the Kullakurichi TaMq northward of the 

 town is covered with Regur. 



Detached spreads extend a few miles northward from the Munni- 

 mootaur, along the eastern boundary of the metamorphic rocks. 



Lastly do we meet with a very extensive and typical Cotton-soil area 

 north of the Ariankoopum river, which Mr. 

 Blanford considers to be continuous with the Mer- 

 canum black soil swamp. 



The very black soil lies, as far as we have seen, on the higher un- 

 dulations of the comparatively flat country. It 



Varieties of Regur. . n n j i v • -i. i.i i i 



IS generally oi a very dark brownisn- black colour, 



with occasionally greyish or blueish shades. The mineral composition of 

 Cotton-soil varies considerably, some varieties being so sandy as to con- 

 stitute a clayey loam, while others are marly, or still more rarely form a 

 very stiff clay, all agreeing, as a rule, in the absence of coarse mineral 

 particles. 



In dry weather the surface is seamed with gaping cracks, which 

 break it up into irregular polygonal figures, and the soil is then very 

 friable, but in wet weather it becomes a highly tenacious mud. 



Many of the larger cracks extend 3 or 4 feet in depth, and where 

 numerous, render the ground unsafe for rapid riding. 



* Mullapooram Eailway Station stands 1,413 feet above sea level. 



(35i) 



