122 GEOLOGY OP TUICIIINOPOLY, &C. [ChAP. VI. 



careous matter held in solution iuto sandy soil. vSucli may be seen in 

 several places on the banks of the upper reaches of the Vellaur and some 

 of its tributaries. Where the infiltration process has been active, a rude 

 branching", and faintly coral-like mass of kunkur concretions becomes 

 solid a yard or two higher up in the section_, while in a downward direc- 

 tion the branches become disconnected, and further down still the kun- 

 kur occurs only in pellets imbedded in the red sand. The horizontal 

 extension of such aggregations of kunkur are generally limited to a few 

 score yards, where the infiltration has been but trifling ; only a few rudely 

 cylindrical concretions may be seen in a vertical position. 



The form of kunkur resulting from the decomposition of gneiss in 

 Kunkur from decom- '^^^^^ ^^^ ^^^7 ^^*^^^ observed to any extent in sections 

 position in situ. exposed by the digging of weUs, and these are 



mostly in the neighbourhood of alluvial deposits, such as the cultivated 

 flats below tank bunds, and spreads of cotton soil, the difficulty in these 

 cases being to find a fresh section. At Runganadapooram, 3^ miles 

 north of Toriore, the following section was found in a recently dug tank : 

 at the surface, cotton soil containing grains of kunkur ; this, after a foot 

 or so in depth, gradually changes into a white semi-compact kunkury 

 marl, having small grains of gneiss and quartz in it. There is about 2 

 feet of this, when another gradual change into time gneiss in siht ap- 

 pears. In this space of change from kunkury marl to gneiss, there are 

 remains of folia with fragments of undecomposed gneiss in position, 

 having their laminae parallel to the true direction of foliation. A like 

 change is also often observable on the banks of streams, where the gneiss 

 is decomposed into a white calcareous rock of marly appearance, for 

 some inches from the surface, which still retains foliation marks and un- 

 decomposed laminse of quartz and mica, and occasionally sporadic garnets."'^ 



* Since the above was written, I have seen numerous instances of kunkur resulting 

 from decomposition of gneiss in situ especially among horhblendic schists. Such instances 

 are very frequent in the schistose gneiss of the soutli-eastern portion of the Nellore 

 district.— W. K. 



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