Plate X. 



Concentric weathering with formation of kankar in an ultra-basic band. 



The ultra-basic bands which have been injected along the foliation planes 

 (see plate IX) often show concentric weathering like basic dykes. In the 

 Coimbatore district, where the climate is moist during the monsoon without 

 great precipitation of rain, the rocks are decomposed, and, on account of the 

 limited circulation of subaerial water, the lime is only partially carried away 

 from the decomposition products. Instead therefore of obtaining a ferruginous 

 product like the laterite which is formed on the Western Ghats, where the rain- 

 fall is heavy, a calcareous and argillaceous kankar is formed by weathering. 



