292 NOTE ON THE LATERITE OF ORISSA. 



This sudden decrease at the water level points strongly to infiltra- 

 tion from above. Below the water level, the amount of iron contained 

 is veiy nearly uniform, averaging 5 '13 per cent. 



These results coincide exactly with the theory above proposed. They 



also agree nearly with what- might have been 

 Therefore the laterite 

 was the source of the expected were the first hypothesis correct, but 



reasons for dissenting from its conclusions have 



already been given. 



To recapitulate, I have endeavoured to shew that, in Orissa, two 

 formations have been confounded under the name of laterite ; — that of 

 these the lower is produced by the decomposition of felspathic rocks 

 near the surface, and the infiltration of iron into them ; — that the Upper 

 is a detrital deposit, and that it is the source of the iron, with which the 

 lower one is impregnated. 



It only remains to ascertain the source of the iron in laterite, and 



What is the source of *^^ '"°*^® °^ formation of this extraordinary de- 

 the iron in laterite itself, p^gj^.^ Unfortunately I am obliged to confess that, 



on tliis point, the most interesting in the whole history of the formation, 

 I can add little or nothing to what is already known. The only sugges- 

 tion I can offer towards its elucidation is the following. . 

 Over many districts of gneiss rocks in Eastern India, and probably 



Possible sourc'e of the '° °*^^ P^^^^^' ^^^'^^ ^'''^ f°""'^' ^"^ variable 

 ferruginous nodules. quantities, scattered through the soil, some of 



the small ferruginous nodules which form a considerable proportion 



of the mass of laterite. These, when broken, are mostly black inside, 



they almost always contain magnetic or some other form of iron ore, 



and quartz sand. They are generally rough outside, on account of 



grains of sand adhering to them, but when they have been rolled in 



streams, and even when shaken together slightly, the sand comes ofi", 



and they are then seen to be covered with a crust of brown peroxide o/ 



iron. 



In sandstone districts, small pieces of highly ferruginous sandstone 



