1836.] 



Laterite, or Iron Clay* 



the finer crystals were amethysts, there were various masses of a red 

 colour, and cavities and some crystals of a fine red. These appear- 

 ances seemed to be connected with a large vein of red pisiform iron ore, 

 which led me to entertain a kind of fancy — more I would not yet ven- 

 ture to call it — that the volcanic action, so evident throughout these 

 tracts, had exerted a great influence in the formation of the so-call- 

 ed laterite. In the veins in question, this is often decided, and in 

 others, trap dykes are near, and exactly similar pisiform ore is found 

 in the volcanic insulated hills through the granitic tracts. This 

 pisiform structure is frequently visible in the porous or nodular masses. 

 The laierite of Beder is found on granite, but hot springs, and hills 

 capped with trap, are found not far off. I believe no organic remains 

 have been found in the laterite." 



I have thus stated all the evidence that 1 have been able to collect 

 on the geological position and association of this peculiar Indian for- 

 mation — all the evidence extant, as far as I am aware of, but some ac- 

 counts may have escaped my research, or be contained in books to which 

 I do not enjoy access. I submit that the foregoing account of what 

 others have written is neither uninteresting nor unimportant, tending, 

 as it does, to point out an error, proceeding from so high a quarter as 

 the individual selected by the British Association for the Advancement 

 of Science to deliver the address,before that august assembly of savans„ 

 on the present state of geological science : an error, which, propound- 

 ed ex cathedra on such an important occasion, might have led to the 

 establishment of a false view of an important scientific question. The 

 accomplished geologist who was chosen for the highly honorable post 

 of orator before such a brilliant re-union of philosophers, will pardon 

 an obscure admirer of the science, for presuming to controvert his opi- 

 nions i but, in truth, I cannot be said to combat his views, but the theo- 

 ries of those from whom, in the absence of other information, be con- 

 fessedly derived his notions on the subject. 



We have seen, then, that there is very little reason to doubt that the 

 laterite is a mechanical deposit, composed of the debris of older rocks ; 

 and I shall now proceed to narrate what I have observed of this mine- 

 ral in the vicinity of Madras. 



And here it may be proper to mention, that my attention was first di- 

 rected thus particularly to the subject, and I was induced to investi- 

 gate the opinions of others concerning it, after witnessing in one loca- 

 lity, the Red Hills, the palpable character of this rock. Until thus in- 

 cidentally led, by the opposite evidence there found, to form an opinion 

 of my own on the subject, I had always bowed to the dictum of Voysey, 

 and considered laterite as allied to trap. 



