236 NILGHIRI HILLS. 



« 



have accumulated and become cemented together, forming a rock un- 

 distinguishable from many varieties of the laterite of the plains. 

 The probable origin of There are no absolute beds of laterite on the 

 *'^"'^' hills, but observations made in numerous localities 



on the plains, where this rock occurs in true beds sometimes even con- 

 glomeratic, seem to show that the materials may have been derived 

 from a similar source to the above, and escept that they have been 

 probably distributed by water over the surface of the country instead of 

 accumulating by simple gravitation, the mode of consolidation into 

 laterite may have been also very similar.* 



The manner in which the gneiss of Makurty weathers, leaving hard 



bands projecting from the surface of the ground. 

 Weathering in bands. 



has been already adverted to, and the phenome- 

 non admits of easy explanation, viz., that the hard bands are more 

 quartzose than the gneiss on either side, and hence they disintegrate 

 far less readily. 



It is unnecessary to do more than mention the occurrence of kaolin, 



which has been noticed in two or three places on 

 Kaolin. . 



the hills, VIS., on the road between Pykara and 



Neddiwuttam ; in the vicinity of Fairlawns, on the road from Oota- 



kamund to Avalanche, and in a valley about two miles South of Oota- 



kamund (See Map). The origin of kaolin, and the chemical theory 



of its formation are too well known to require comment. That of the 



hills only differs from the kaolin of other countries in being formed 



by the decomposition in situ, of a very felspathic variety of gneiss, 



instead of being the result of decomposed granite. The masses of 



this mineral at the localities mentioned do not 



Kot valuable. . , , . , 



appear to be very extensive, and the mineral 



itself contains too much iron to be of much economic value. 



* Subsequent observations on the Laterite of Tanjore confirm this view of the origin of 

 that roek. 



