ALLUVIAL FOBMATIONS. 79 



for at least 2 miles southward down the valley. A large show occurs 

 too just above the estuary. The valley of the small stream above the 

 saltpans at Kuthankuli, 3 miles east-north-east of Yiziapatti, is also 

 occupied by a large show of massive tufa. 



9. The valley of the Hannamnadi (Annam aur) is not wanting in 

 In the valley of the tufaceous deposits, but the massive variety is less 

 Aunam-ar. strikingly developed here. 



Curiously enough all this great development of tufa did not yield 

 a single fossil organism, though it was closely searched in many 

 places by myself and a very smart collector. Nor does Bishop Cald- 

 well, who is intimately acquainted with the formation as seen near 

 Iddayaugudi and Sathankulam, appear to have been a whit more 

 successful. 



There can be no doubt as to the origin of these extensive and inter- 

 esting tufa beds ; they were formed by the deposi- 



Oiigin of the tufa. p t i - p ^ 



tion of lime by evaporation oi the waters which 



brought the calcareous matter in solution from more distant sources. 



What those sources were I am not prepared to say 

 Sources whence the • f» i i 



calcareous matter has de- as yet. The gneiss of the low country contains, 



as far as my observations went, no conspicuous 



beds of crystalline limestone, nor do many hornblendic beds occur which 



could have yielded a large supply of lime. It is very probable, however, 



that such beds do occur on the tops and flanks of the Southern Ghats, 



which remain as yet unsurveyed. 



Of the marine and estuarine alluvia it is impossible to say much, for 



Marine alluvia much they are almost entirely covered up along the Tin- 



"^"^ ^ ' nevelly and Madura coasts by the blown sands, 



whether red or white, which are so largely developed in these regions. 



Moreover, these formations require much longer study than could be 



devoted to them during a rapid general survey. The rate at which they 



increase, the direction in which such increase takes place, or the converse, 



the rate at which, and the direction from which, they are destroyed by 



encroachment of the sea, are all questions of considerable interest, but 



( 79 ) 



