420 Geological Sketch of the Neilgherries. [Aug. 



may be found in many other places, which I have had no opportunity 

 of visiting. 



What I have said of the quartz veins is also applicable to the more 

 numerous felspathic veins, which traverse the rock ; with this differ- 

 ence, that they are decomposed, and converted into porcelain earth, 

 while those of quartz are entire and unchanged. But the continuity 

 of the vein is evident, although one-half of it has changed nature. 



An additional, although negative, proof regarding the transforma- 

 tion of the granitic rock into lithomargic earth, is, that on those 

 hills where no rocks containing hornblende are found, this earth is 

 wanting. This is the case on the summits of Dodabetta, Elk Hill, 

 Kaiti pass, &c, in which places the protruding rock being either 

 granite, or pegmatite, it exfoliates in laminae like granite, instead of 

 decomposing into red lithomargic earth. 



It would be worth ascertaining, whether the crimson -coloured dots 

 and streaks in the lithomargic earth be owing to the decomposition 

 of the numerous garnets contained in the original rock. I have had 

 opportunities, more than once, to remark, that in those localities where 

 the sienitic granite abounds with garnets, the lithomargic earth, 

 resulting from its decomposition, has the crimson coloured dots similar 

 to those in the undecomposed rock (No. 14). I have made the same 

 observation in the decomposed gneiss in the Northern Circars, where 

 it abounds with this mineral. 



A question naturally presents itself after the above remarks, regard- 

 ing the decomposition of the granite, and hornblende rock of the 

 Neilgherries. The same identical rocks are found in many parts of 

 the Peninsula, particularly along the chain of the eastern ghats ; and 

 yet their decomposition does not give rise to the same results. As I 

 have visited but very few localities in India where these rocks prevail, 

 I cannot positively say whether or not the result of their decompo- 

 sition in both localities be the same*. But, this is certain, that 

 the causes, which may have contributed to decomposition in one place, 

 do not exist in the other : of that class are cold, damp, frost, eleva- 

 vation, &c, which are not found in the low lands. Besides, is this 

 decomposition the effect of existing causes, or the consequence of 

 time and revolutions gone by ? 



Here I must remark, that in some localities, such as near the bund 

 of the lake, on the road below the church, above the bazar, &c. the 

 red earth assumes the composition, texture, and appearance of real 

 lithomarge. 



* Doctor Heyne says, " a red soil prevails where sienite forms the apparent 

 ground rock." — Tracts Historical and Statistical on India, page 349. 



