94 



MANUAL OP THE NILAGIRI DISTRICT. 



CHAP. V. lakes Mr. Blandford says : "It is evident that any obstacle closing a 



Gkolog7 and valley excavated by running water must be of subsequent date to 



MiNEJtALoGY. the formation of the valley, and, therefore, if the Neelgherry 



valleys now occupied by alluvium be really of fresh water origin, 



as seems most probable, there must have been subsequent to 



their formation some changes in the levels of the country, which, 



by stopping the drainage, converted the pre-existing valleys into 



lakes.^^ Again : ^' The form of the valleys which they (the 



alluvial flats) occupy precludes the idea that the former were 



excavated by any other agent than the hill-streams, and such 



being the case, it is, as already stated, only by subsequent 



, disturbance that they could be converted into lakes. ^' 



2|^^j#«*{if3 



I'Hi. Vllr ALLUVIAL PLAIN ON A fLFOE-B 0F7HE PVKARA RIUhR NEAR TUKULHULLYHETTA- 



Economic 



Limestone. 



The rocks of the hills yield but few substances of any econo- 

 mic value. Limestone, which, as already stated, exists in the 

 subjacent plain of Coimbatore, has not been found on the hills 

 either in the crystalline or gravel form. Some of the gneissose 

 rocks are fairly adapted for building purposes, but the localities 

 where such varieties occur are generally inaccessible. In most 

 cases the stone is either very loosely foliated or extremely bad ^ 

 and deficient in joints. Where the structure is loose the stone 

 seems to have a great tendency to decompose. This is doubt-, 

 less a great objection to the use of such stone for road metal, j 

 but in case of building the evil might probably be greatly j 

 neutralised by placing the blocks so that the cross section of the 

 foliation only shall be exposed. The gneiss of the Kundas in 

 the neighbourhood of Sisapara, from its finely jointed character, 

 is stated to promise well for quarrying purposes ; but the 

 distance precludes its use. The iron ore of the plateau would 

 probably yield well, but the dearness of fuel militates against 



