iEOLIAN FORMATIONS. 87 



CHAPTER X. 



^OLIAN FORMATIONS. 



Blown sands, tens and coast dunes. 



There is no part of the south of India in which blown sands play 

 Red sands or teris; white ^o large and important a part as in Tinnevelly 

 s.inds or coast duues. district and along the south coast of Madura. 



They are of two kinds, differing both in colour and origin — the red sands 

 or teris^ and the white which are ordinary coast dunes. Of these the 

 former are the more interesting as well as the more important^ — the more 

 interesting as some obscurity has hitherto attached to their origin^ the 

 more important as occupying a considerably larger area than do the 

 coast dunes. 



I have already in the foregoing chapter mentioned my belief that 

 the teris owe their orign to the action of the heavy and continuous gales 

 prevailing during the south-west monsoon on the broad belt of deep red 

 loam which skirts the eastern base of the ghats. By these fierce winds 

 the dry surface of the loam is swept clean, and vast clouds of red dust 

 carried away to the eastward and dropped near the coast. These gales 

 blow in some years for nearly four months without ceasing, so their efEeet 

 is far greater than that of the north-east monsoon, which is much less _ 

 violent and often fixes the loose sands by heavy showers. The teri sand 

 is mainly composed of grains of quartz with an admixture of fine red 

 clay dust in very variable quantity. A small and varying percentage. 

 of minute grains of magnetic iron is also of general occurrence in the 

 teri sand. From the red colour of the sand one might not unreasonably 

 expect to find a large quantity of garnet sand in it, especially as small 

 garnets are of such extreme commonness in the gneiss of Tinnevelly 

 district. In reality, however, garnet sand does not occur in pure teri 

 sand, at least I have examined scores of specimens from many teris with a 

 pocket lens and never noticed a speck of garnet among the quartz grains. 



The red colouring of the quartz grains is entirely superficial, a 

 coating of ferric oxide probably derived from the deep red loam in which 



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