222 NILGHIPJ HILLS. 



The most common varieCy of the Gneiss over the central part of the 



hills, where, however, its mineral composition is 



Quaternary Gneiss. , . • i i - /■ i • i i 



extremely variable, is a rinely grained rock com- 

 posed of qnartz, garnet, and hornblende, with a variable proportion of 

 felspar. It usually exhibits an indistinct foliation, and almost invar 

 riably on the weathered surfaces ; it is very decomposable, except on the 

 large precipitous faces, which occasionally present 

 Spheroidal deeompo- themselves on the slopes of the spurs of the 



sition. '■ 



Dodabetta range, and when so decomposed 

 breaks up into spheroids which scale off as the decomposition pro- 

 ceeds and remain embedded in a mass of quartzose ferruginous clay 

 arising from their decomposition. The cause of this decomposition 

 •will be treated of in another place. When large undecomposed faces 

 of the rock are exposed it sometimes shows a tendency to split off 



in enormous slabs slightly curved to the form of 



Scales off in slabs. 



the hill side. The cause of this is not very 



apparent, but it may possibly be due to the heat of the sun causing 



the exposed surface to expand rapidly, and thus separate from the 



underlying cooler portion of the rock. After heavy rains, the earthy 



decomposed mass becoming saturated with water, frequently rushes 



down as a great landslip, scattering the em- 

 Cause of Landslips. , , . 



bedded boulders, often oi enormous size, over 



the valleys and low grounds. A large landslip of this kind which 



took place some years since on the side of 



Landslip at Avalanche i • i , i. i 



the iiundahs at a spot near which the road 

 to the Sispara Ghat passes, has given the name of Avalanche, usually 

 pronounced Avalanchy, to the locality. Such landslips are not unfrequent 

 On Kaitee Escaro- '^^ ^^^^ great escarpment overlooking the Eaitee 

 ^''^'" valley to the S. E. of Ootakamund, and cause great 



injury to the Goonoor Road, which is carried along the face of this 

 escarpment. The gaps formed by similar landslips are frequently notice- 



