Geology of Southern India. 189 



influence of atmospheric agents. These are neither trivial 

 nor uninteresting, since to this source there seems now but 

 little doubt that the formation of the laterite, so long an 

 apple of discord among the observers of Southern India, is 

 to be traced. A mass of observations gleaned from many 

 well developed lateritic localities both on the coast and 

 inland have recently been made public in an interesting 

 paper on this formation by Dr. Clark, H. M. 13th Dra- 

 goons; and by the careful examination and discussion of 

 these, the question of its origin seems to me to be satis- 

 factorily answered. Before this paper came to my know- 

 ledge, a conviction that the laterite was the result of the 

 aggregation of the decomposed constituents of the rocks 

 which it usually overlies, was forced on my mind by obser- 

 vations in several of those identical localities whence I 

 find Dr. Clark has gathered a considerable portion of his 

 information ; and it was with pleasure that I found a con- 

 clusion based on limited data, supported by an examina- 

 tion so extensive and so ably conducted as that of Dr. 

 Clark. In the vicinity of Bangalore where both the la- 

 teritic and lithomargic formations are largely developed, 

 an opportunity was afforded me of studying them in de- 

 tail. Many of the protruding masses of sienitic granite 

 and gneiss which are the prevailing rocks, exhibit nature 

 as it were in the simultaneous acts of decomposition and 

 aggregation. Their surfaces are usually covered with a 

 coating of dark coloured and weathered matter resulting 

 from the felspar or hornblende, studded with small 

 undecomposed and ferruginous pebbles of quartz, while 

 round their bases the laterite forms a regular talus of 

 variable size. It is usually of the compact quartzose and 

 distinctly marked variety: sometimes however it assumes 

 the cavernous or vesicular structure, the dark red matrix 

 exhibiting a series of small cavities. One example was 

 of peculiar interest, for in consequence of the existence of 

 a basin-shaped hollow in the side of the rock, the materials 



