On the Red Marl Formation of Mysore. 37 



This granite is the hornblendic kind which is so universal 

 in South India, and the surface of the larger masses appears 

 generally to have a cleavage into layers, which yields to 

 the heat of a wood fire upon it, and it is in consequence 

 generally used as building material. From this tabular 

 cleavage, and its being generally striped with veins darker 

 than the rest containing more hornblende, it has been called 

 gneiss by some writers. But both gneiss and other schists 

 are almost unknown in this formation, and the only part in 

 which I have seen any gneiss is near Nundydroog. Gneiss 

 and striped granite are often confounded by Indian penolo- 

 gists, but I think there could be no mistake if attention was 

 given to the way in which they cleave with regard to their 

 structure. 



Hornblendic granite is often seen in mammillar masses, 

 crossed by a regular striped structure, exactly resembling 

 the lamination of gneiss ; but it has no cleavage at all in the 

 direction of the appai'ent lamination, and on the contrary Dr. 

 Benza has pointed out that the tabular cleavage is almost 

 universally horizontal, while the apparent lamination is ver- 

 tical ; while in both hornblendic and micacious gneiss the 

 cleavage corresponds with the apparent lamination, both of 

 which are generally vertical when in situ. 



The red marl in some very few instances may be seen 

 lying immediately upon the granite, but almost always a 

 stratum of coarse kaolin is interposed between the granite 

 and the red marl. This kaolin is generally of a pure white 

 colour, and of a soft friable structure, and it is in conse- 

 quence often mined for the purpose of being fraudulently 

 mixed with chunam, which I have above remarked is very 

 scarce in this tract. 



Near the granite the kaolin has a coarse granular and cellu- 

 lar structure containing grains of quartz, and it shews a very 

 apparent graduation within the space of about three or four 

 feet into a fine white pulverulent earth meagre to the touch ; 



