552 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 13, 



possible modification of the views I endeavoured to maintain, or the 

 correction of an error into which I may have unintentionally led 

 them.— [W. J. H.] 



9. On the Origin and Formation of the Red Soil of Southern 

 India. By Dr. W. Gilchrist, Surgeon H.E.I.C. Madras Pre- 

 sidency. 



(Communicated by Sir R. I. Murchison, V.P.G.S.) 



Various opinions have been entertained regarding the nature and 

 origin of the " Red Soil," which constitutes the surface-formation of 

 several extensive tracts of India* ; and believing the subject to be 

 one on which geologists wish for further and more exact information, 

 I steadily kept it before my mind during the prosecution of a public 

 duty entrusted to me, of opening up a line of road through one of 

 these Red-Soil tracts ; and the opportunities thus offered, by sec- 

 tions, &c., have afforded me some interesting facts respecting the 

 character of the Red Soil, its origin, and the probable mode of its 

 deposition. 



The characters of the Red Soil. — The Red Soil of Southern India 

 is very variable as to thickness. It varies, according to my observa- 

 tions, from 25 feet to a few inches. Of the thickness of about a foot, 

 I have traced it constituting the surface-soil over a tract of several 

 square miles, the bed-rock below the water-worn stones which occur 

 in its lowest portion being granitic gneiss (of which also these stones 

 consist), generally in a friable state, from disintegration. 



In regard to mineral composition, the Red Soil in its purest state 

 consists mainly of quartz with peroxide of iron, and a small quantity 

 of carbonate of lime (in consequence of the presence of which, it gene- 

 rally effervesces more or less when a mineral acid is thrown on it) ; 

 more or less alumina also is contained in it generally. Quartz and 

 peroxide of iron are invariably found as ingredients, and frequently 

 these only are found to constitute the deposit ; but hornblende, 

 granite, &c., rounded into gravel, and of various degrees of size, are 

 frequently found as part of the formation. Different localities pre- 

 sent different mixtures, as might be expected in a deposit which, 

 previously to final deposition, had been moved to and fro by water. 



It may be added, that, agriculturally speaking, the Red Soil is 

 fertile : it is also much used by the natives of India for constructing 

 the walls of their huts, and even in the better sort of native houses 

 it is used instead of mortar (of lime and sand) for plastering the 

 interior. The oxide of iron and quartzose sand exert a mutually 

 binding or hardening power, so that, when completely dry, the 

 mixture is as hard as the native-made bricks, perhaps more so. 



I am not prepared to speak as to the relative geological age of the 



* [For a notice of the Red Soil of the Nagpur District, see Quart. Journ. Geol. 

 Soc, No. 43. p. 354.— Ed.] 



