GEOLOGICAL FEATURES, II 



often decomposed, the resulting minerals being as a rule chlorite and 

 iron ores. The chlorite is formed at first in thin bands along the 

 cracks (PI. 2, fig. 2), whence it gradually extends till nothing remains 

 but a few minute grains of garnet in a confused mass of chlorite 

 (PI. 2, fig. 3). Where the garnet has been more than usually ferru- 

 ginous, it is decomposed into a mass of limonite containing some 

 chlorite and a few still unaltered fragments of garnet. The alter- 

 ation is always most strongly marked in the neighbourhood of the 

 charnockite intrusions. 



The remaining minerals found in the gneiss may be regarded 

 merely as accessory constituents, though a few, 



Accessory constituents. 



such as chlorite, zoisite, epidote, — all probably 

 of secondary origin— are rarely absent. Calcite occurs in the biotite 

 gneiss of Hadiabetta, in the neighbourhood of the quartz reefs. 



As already stated, intrusions of charnockite are found at several 



Intrusive* in the gneiss: P oints in south and south-east Wainad : where 

 charnockite. these occur, the biotite gneiss has undergone 



considerable alteration (PI. 3, fig. 1) ; the felspars are de- 

 composed and contain much epidote, rutile and kyanite (PI. 3, fig. 

 2) ; the quartz is full of microscopic granules and rods — possibly 

 rutile — and actinolite is common but is usually altered into chlorite. 

 An exactly similar rock has been described by Mr. Holland from the 

 neighbourhood of Salem, 1 as the result probably of alteration of the 

 biotite gneiss by charnockite : throughout south-east Wain£d it has 

 invariably been found between these two rock-series where they 

 approach one another closely, nor has it been found except when 

 those conditions prevail, and it would, therefore, seem safe to assume 

 that it is a product of contact action between the two series. 



Other phenomena, similar to those already noticed in Salem by 

 Mr. Holland (loc. eit.) } and pointing to an intrusive origin for the 

 charnockite, occur also in Wainad : these are — 



{a) the presence of irregular masses and bands of charnockite 



1 Geology of the neighbourhood of Salem. Mem. Geol. Surv. Ind., 

 Vol. XXX, Pt. 2, p. 1 22. 



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