Dec. 1861.] 



Geology of the Neilgherries* 



251 



for a considerable time the result is acted on by the magnet. 

 Tinges borax the color indicative of iron. This mineral occurs 

 with the variety of reddle, in a rock consisting of green felspar, 

 and blue quartz. 



In the course of a ride to Coonoor I had an opportunity of add- 

 ing another to the list of geological causes that, degrading moun- 

 tains and filling up valleys, have contributed so largely to alter 

 the conformation of tthe face of our planet. The discovery like- 

 wise enabled me to account for the singularly polished and smooth- 

 ed surfaces of some of the hills, and eminences I have seen in 

 different parts of India, which had hitherto baffled my penetration. 

 On the side of one of the branches of Dodabett I observed a bluff 

 scarp of rock which projected out of the side of a hill presenting 

 a smooth dark coloured surface suggesting the idea of a shce hav- 

 ing been recently cut off it perpendicularly. Proceeding to dis- 

 cover if possible the cause of this phenomenon, I found the whole 

 upright facade or face of the rock, some feet in thickness, and 

 many yards high, had actually separated itself from the mass, and 

 in sliding downwards left a bare smooth surface behind it. This 

 facade preserving its original contour now rested at an angle 

 against the base of the mass from which it had slid. It was this 

 circumstance that enabled me to arrive at a proper conclusion. 



I consider myself fortunate in having made the discovery, ap- 

 prehending that in most cases the facade from its high fall is dash- 

 ed to pieces on reaching the base of the rock where it lies in a 

 heap of stoney ruins. Water percolating through the pores of the 

 rock, destroying the adherence of the facade to the mass, has pro- 

 bably been the agent which achieved the dilapidation. 



I can conceive the water to have percolated through upright 

 fissures seated horizontally beside each other— fissures the element 

 may have worn for itself, or it may have disintegrated a stratum of 

 some inconsiderably adhesive mineral connecting the facade with 

 the parent mass. 



Very few rocks or minerals of interest are met with between 

 Coonoor and Ootacamund, green syenite being the prevailing for- 

 mation. About a mile however from the bungalow of the former 

 place I found the subjoined minerals. 



