1836.] 



Laterite, or Iron Clay, 



111 



difficulty, when it evidently appears that they are water-worn pebbles, 

 presenting considerable angularity of surface, yet still sufficiently 

 rounded to indicate their having undergone attrition, most likely by 

 the turbulence of an inundation, which bore them away from their 

 original position as parts of a solid rock, and deposited them, in their 

 present conglomerate form, with the mud which now agglutinates 

 them. 



The nodules are observed of all dimensions, from the size of a fil- 

 bert, to masses a foot or more in diameter. Their fracture exhibits the 

 structure of a coarse grained sand stone, or grit, of a deep chocolate, or 

 claret hue (No. 1).* This nodular sand-stone is made up of frag- 

 ments of quartz (some rounded, but for the most part angular), from a 

 minute sand up to the size of a pea. Added to the quartz, there are 

 occasionally found small masses of a white earth, like lithomarge, 

 appearing to be felspar in a state of decomposition (No. 2). This is 

 found in small nests, here and there ; but I have no doubt that a good 

 deal, minutely subdivided, went to form the paste which united the 

 parts of this conglomerate together. Thirdly, mica is found a consti- 

 tuent of these sand-stone nodules, in very minute scattered leaves. 



This sand-stone precisely resembles the specimen from Puddayaram, 

 near Samulcottah, in the Northern Circars, deposited in the Minera- 

 logical Cabinet of the Madras Literary Society, by Dr. Benza, who has 

 thus described its structure and relations in the above locality — " The 

 ferruginous sand-stone is the lowermost, and has a great degree of 

 compactness, so as to fit it for architectural purposes, in which it seems 

 to be largely employed. It is evidently stratified, the strata being 

 nearly horizontal ; the quartz particles are agglutinated by a ferrugi- 

 nous cement. 



" The sandstone, nearly in the whole extent of the hillock, supports a 

 lithomarge of a whitish or flesh colour, sometimes having a bluish 

 tint. The stratum of this earth is not very thick, and in many places, it 

 is overlaid by a purple red, compact, slaty heematitic iron ore, which 

 passes insensibly in the upper part into a cellular rock, full of tubular 

 sinuosities, very much similar to the laterite. In some places this ore 

 lies immediately over the sand-stone, without the intermediate litho- 

 marge." f 



These three minerals, then, are plainly discoverable in these imbed- 

 ded masses of conglomerate sandstone, but there is an argillo-ferrugi- 

 nous cement uniting the whole together. This cement gives the 

 colour to the entire mass, which is of a purple-red hue, as mentioned 



* The Numbers refer to specimens presented to the Society, in illustration of the 

 Paper. 



* Journal of the Asiatic Society of Bengal, August IS33, p. 437. 



