ICO On the Geological characters of the [Jul*/ 



VIII. — 0?i the Geological position and association of the Laterite, or 

 Iron Clay, formation of India; with a description of that Rock as 

 it is found at the Red Hills near Madras. — By Robert Cole, Esq. 

 of the Madras Medical Establishment ; Secretary to the Asiatic 

 Department of the Madras Literary Society, and Auxiliary Royal 

 Asiatic Scciely. 



In the volume of Reports of the British Association for the Advance- 

 ment of Science for 1831-32, occurs the following passage, in the Report 

 on Geology, l>y the Reverend W. P. Cony heare : " We learn that pri- 

 mitive formations, in which granitic rocks hear the principal proportion, 

 occupy not only the great Himalayan northern chain, hut also three- 

 fourths of the entire Peninsula, from the vale of the Ganges- below 

 Patna to Cape Comorin ; although these rocks are frequently overlaid 

 by a thin crust of laterite — (a ferruginous clay considered as associat- 

 ed with the trap formation.)"* 



Now that so little should be known concerning the laterite, a mineral 

 so extensively distributed, and offering so peculiar a feature in Indian 

 geology, constitutes an opprobrium to the science whichitis desirable to 

 efface ; and I, therefore, propose to offer my imperfect observations on 

 the position and character of the laterite found in the neighbourhood 

 of Madras, prefaced by an account of what has been written hitherto 

 on this remarkable rock, by way of inciting geological observers, in 

 various parts of India, to note down similar particulars, that so, by the 

 accumulation of observations from various localities, some precise 

 data may be arrived at, by which we may be enabled to assign its true 

 geological position and history, to this singular mineral product. 



The name laterite was bestowed by Buchanan, who first described it 

 in the following passage. " In all the hills of the country the iron ore 

 U found forming beds, veins, or detached masses, in the stratum of in- 

 durated clay that is to be afterwards described, and of which the greater 

 part of the hills of Malabar consists. ****** « What I have 

 called indurated clay is not the mineral so called by Mr. Kirwan, who 

 has not described this of which I am now writing. It seems to be the 

 Argilla lapidea of Wallerius I. 395, and is one of the most valuable 

 materials for building. It is diffused in immense masses, without any 

 appearance of stratification, and is placed over the granite that forms 

 £he basis of Malayala. It is full of cavities and pores, and contains a 

 very large quantity of iron, in the form of red and yellow ochres. In 

 the mass, while excluded from the air, it is so soft, that any iron instru- 

 ment readily cuts it, and is dug up in square masses with a pick axe, 

 and immediately cut into the shape wanted with a trowel, or large 



* Reports. 1832, p, 395. 



