218 NILGHIEI HILLS. 



foliated class, which have received from Sir Charles Lyeil the appellation 

 of Metamorphic rocks. The use of this term is perhaps premature, until 

 the really metamorphic nature of these rocks in all cases be clearly 

 established. The evidence of the actual metamorphism of the vast spread 

 of similar masses, forming the bottom rock over the whole surface of 

 the Indian Peninsula, and probably extending far into Central Asia, as 

 well as of the enormous tracts of Gneiss and Mica Schist occurring in 

 other countries* is yet very deficient, and although, as will be fully 

 explained hereafter, certain observations made during the course of the 

 present survey seem to indicate that the schistose rocks around Coimba- 

 toor, and possibly those of the Neelgherries also, are rocks of sedimentary 

 origin, altered and rendered crystalline by heat, it is perhaps better for 

 the present to restrict ourselves to the term Gneissose rocks, Gneissf 

 being the best known and most typical of the series. 



The other rocks of the district consist of alluvial deposits, a few small 

 basaltic dykes, and some quartz veins on the hills ; 



Other rockfs of Neel- g^^^j jjj ^j^g plains, of numerous small granite veins, 



glierries, -^ o ; 



which are especially abundant in the neighbour- 

 hood of Sunkerry Droog to the East of the Cauvery. No trace of Granite 

 or of any rock of that class has been discovered on the Neelgherries. 

 Gneissose Rocks. — The rocks of this class occurring in the Neelgher- 



„ . ries and the surrounding country are extrenielv 



Granitoid Gneiss. •' 



varied in mineral character, and frequently assume 



an appearance, which would lead a casual observer, or indeed most persons 



who have not made these rocks a matter of especial study, to regard 



them in many cases as rocks of Plutonic origin. A careful and extended 



examination, however, will show that, however indistinct their foliated 



Distinct from true Structure may be in places, they mvariably pass 



^''^'^"'^' by insensible degrees into those of a more typical 



* Darwin on South America ; Strzelecki on Australia, &c. 



t The term Gneiss is frequently used throughout thisBcport as a generic, implying the 

 Gneissose rocks in general 



