76 FOOTE : GEOLOGY OP MADURA AND TINNEVELLY DISTRICTS. 



tion in the alluvia generally, as indeed might he reasonahly expected from 

 the fact that nearly all the rivers rise on the gneissic tracts in or at the 

 foot of the Southern Ghats. The prevailing type is a pale red or red- 

 dish white or pale brownish sandy loam passing into clay or nearly pure 

 sand in some places. 



An exception to the I'ule is the alluvium of the Virudupatti (Virdu- 



Exceptional character putty) river (the main northern tributary of the 

 of the alluvium of A''iru- _ n i • i n 



dupatti river. Vaippar) m North Tinnevelly, which flows through 



great tracts of typical black soil or regur, and which has covered the 

 low level of its valley with a thick bed of washed-up regur. The allu- 

 vium near the mouth of the Vaippar shows the effect of the dark 

 particles of the regur it has carried down, in the dark grey or grey- 

 brown fine silt it has there deposited. Intermediately the sandy and 

 locally somewhat gravelly character of the alluvium prevails as may 

 be well seen to the north-west of Velati Kulam ( Vullauticolum) . 



The alluvium of the Vaigai like that of the rivers to the north of 



Alluvium of the i* ^^ generally a very sandy loam. Near to 



^^^S'^^- Madura it is here and there gravelly, and near 



Ramnad extremely sandy. Here and there the beds vary to coarse grit 



or even fine gravel or quartz and rolled kankar. 



Owing to the great offtake of water from the Vaigai by irrigation 

 channels it rapidly dwindles in size below Permagudi and evidently 

 flows only during heavy freshes. 



The alluvium of the Tambraparni which chiefly drains tracts covered 



with light red gritty soil is of a pale reddish 

 Of the Tamhraparni. „ 



colour and very sandy. Large quantities or calcar- 

 eous tufa (pipe kankar and nodular kankar) show in the sandy banks 

 of the river to the south and south-east of Tinnevelly town, and have 

 solidified the otherwise highly sandy beds into a hard and almost 

 rocky consistency. At and above the bridge between Tinnevelly and 

 Palamcotta is a considerable spread of coarse tufaceous conglomerate 

 forming a low platform in the bed of the river on which some small 

 temples have been built ; the conglomerate includes much gneiss debris. 

 ( 76 ) 



