103 



On the Geological characters of the 



[Jul* 



have some idea of the causes which have formerly been in operation, 

 from the effects we now see."* 



The latest notice of the laterite is by Dr. Benza, a writer who has 

 already contributed more towards a knowledge of the geology of Pe- 

 ninsular India, than any of his precursors, and from whom we may, 

 happily, expect much more. 



To his able Geological Sketch of the Neilgherries, and to the memoir 

 which adorns the pages of the present number of this Journal, I must 

 refer for his opinions on the origin of the laterite; only stating here, 

 that they will be found confirmatory of the views 1 have taken of the 

 subject. 



Dr. Benza, in a letter to my address, written in May 1834, states his 

 Opinion that the laterite, in places where he had met with it, had re- 

 sulted from the decomposition of granitic, or other crystallized, rocks. 

 And I cannot resist the temptation of transcribing a passage from a 

 letter by Mr. Malcolmson (whose name will carry great weight with 

 it on any scientific subject), written to me in allusion to Dr. Benza's 

 opinions, expressed in the above mentioned letter, which I sent to 

 him for perusal. 



" I was much interested by Dr. Benza's remarks on the laterite ; 

 without a distinction between different kinds, we cannot expect to 

 arrive at a correct theory. Thus the specimen I have got, with Toy- 

 seys label, is not a conglomerate rock, at least as seen by the naked 

 eye. The red cellular stone used here (Madras) is characteristic, 

 and I have little doubt formed as Dr. Benza supposes, by the de- 

 composition of sienite. The same abounds towards Nellore, and not 

 far from that place I found a bed of hornblende slate. At Chicacole 

 there is a black sienitic rock, and, a little up the river, the red stone. 

 At Malacca a strong yellow or white clay is covered with a stone ex- 

 ceedingly like the Madias laterite, and, you know, granite is in the 

 mountains seen from the town. At Rangoon, a little below the sur- 

 face, a similar stone, but much mixed with sand, is found over the 

 plains ; on this lies a very soft sand-stone, apparently formed, and form- 

 ing, from the annual deposits, and in the puddles much ochre is found. 

 In the Hyderabad country the granite containing iron rapidly decom- 

 poses, becomes red and forms a hard mass. The Indoor and Nir- 

 mul magnetic iron, also, rapidly becomes red on exposure, and the 

 rock, on being broken and the ore separated by washing, leaves a red- 

 dish clay. Veins of quartz pass through the granite and sometimes 

 contain magnetic iron, by which the colour seems to be given to the 

 amethystine quartz. I traced a vein of this kind, in which, while 



* Gleaning' s in Science, May 1831, p. 130, et seq. 



