244 NILGHIRI HILLS. 



to the formation of the valleys, and therefore, if the Neelgherry 

 valleys now occupied by aUuviutn be really of fresh-water origin, as 

 seems most probable, there must have been, subsequent to their forma- 

 tion, some changes in the levels of the country, which by stopping the 

 drainage converted the pre-existing valleys into lakes. In such cases, 

 the drainage would seek an outlet either by cutting still deeper its old 

 channel, or in another direction by cutting away a low ridge, or through 

 some open fissure, and in course of time, if the rock at its new point 

 of exit be hard, the stream would cut a narrow gorge-like channel 

 such as has been described, and through this the lake would be 

 finally drained. There are indications that something of this kind 

 has taken place in one or two instances. Thus the stream which 

 has been mentioned as flowing down the gorge through which the 

 Mailur road is carried (See Map) may originally have followed the 

 course of the Avalanche road to the South. A slight elevation of 

 the country to the West of the Mailur road, and the simultaneous 

 formation of a small fissure along the line of the present gorge, would 

 convert the valleys now occupied by alluvium into a large lake, until 

 the stream had sufficiently enlarged the present gorge to carry off' 

 the water. 



The above appears to be the most probable explanation of the 

 origin of these alluvial plains. The form of the valleys which they 

 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. 



Economic Geology. — Almost the only article of any economic value 



furnished by the crystalline rocks of the Neelgherries is stone, whether 



for the purposes of building or road making. The 

 Building stone. \. j 



various forms of the Gneissose rocks are abund- 

 antly obtainable for either of these purposes, but for the former they 



