NOTE ON THE LATERITE OF OEISSA. 287 



passage, all which have come under my notice, and thej^ are very 

 numerous, have occurred in old sections, which are utterly untrust- 

 worthy for the purpose of investigating the phenomena of these ferru- 

 ginous deposits, for water impregnated witli iron runs from the upper 

 formation down the sides, and the whole surface becomes, by weather- 

 ing, hard, irregular, and homogeneous, with the well known appearance 

 of blocks of Laterite, which have long been exposed to the air. Few 

 good sections moreover are seen in Orissa, except in wells, which 

 are difficult of access for the purpose of cai-eful inspection, while exca- 

 vations for building material are generally confined to the detrital 

 form. 



It remains to ascertain the source of the large quantity of iron in 



What is the source of '^^^"*® ^"^ *^^^ underlying clay, and the method 

 the iron? I^y. ■^yl;ji(.h these rocks have become impregnated. 



It is evident that if we can determine the manner in which the iron 



By what course did it Penetrated the rocks, we shall Lave advanced a 

 penetrate the rocks? gjgp towards ascertaining its source. Now there 



seem to be three possible ways of accounting for its presence in the two 

 formations. We may suppose : — 



I. That the Laterite was originally an ordinary detrital deposit, and 



that it and the underlying rock were together 



Possible hypothesis. . , . , . 



impregnated with iron, in other words, that the 

 source of the iron was extraneous : 



II. That the Lithomarge is the source of the iron, and that Laterite 

 is merely the result of its denudation and re-consolidation : 



III. That Laterite is an original ferruginous deposit, and that all, or 

 nearly all the iron, contained in the Lithomarge, is merely obtained 

 from the former rock by the percolation of surface waters. 



Of these three hypothesis, the first is the least probable. From what 



imaginable extraneous source could iron be sup- 

 Pro, et con. 



plied, which should, over hundreds of square mile 



