286 NOTE ON THE LATEUITE OF ORISSA. 



The undei'lying form varies so much in constitution according to the 



rock from which it is derived, that scarcely any 

 Litliomarge. . .,,... 



petrological term will include all its varieties. 



As a rule however, it is, when derived from gneiss or other felspathic 

 rock, a more or less ferruginous clay varying in purity. To such sub- 

 stances the name Lithomarge has frequently been applied, and it seems 

 the most applicable in the present instance, it being understood that 

 all the impure varieties derived from quartzose raetamorphic rocks or 

 sandstone are here included in the term. 



Many instances occur in which the Lithomarge appears to pass into 

 , ^ „ laterite, and therefore, despite the clear evidence 



Apparent passage oi '. ' '^ 



Lithomargeinto Laterite. ^f tj^g;;, distinct origin, it has been supposed that 



the latter is merely the result of a further alteration of the former. The 



small nodules so abundant in Laterite, and so characteristic of it, are 



sometimes found, though only in small quantities, in the upper part of 



the decomposed rock beneath, especially where it has been exposed. 



There is nothing unnatural in the formation of small nodular concretions 



of iron in a highly ferruginous rock, consequently their presence in both 



is no proof of the two kinds of rock being iden- 

 Its explanation. 



tical. And, with regard to the cases of apparent 



Geology of the Southern Conoan, Edin. New Phil. Jour., vol. iv. p. 67. Their relations to 

 each other have however hitherto, so far as I am aware, not been explained and a critical 

 re-capitulation of their differences appears the only method by which to appreciate the 

 connexion between them. Manj- of the points mentioned above have been noted bj' other 

 observers, as by Mr. Stirling (Asiat. Eesear. Bengal, vol. xv, p. 163,) in the locality 

 described in the present paper. It will be seen that I differ from all previous observers 

 (at least with all with whose writings I am acquainted) in accounting for the iron in the 

 altered clay or underlying form of laterite. This iron has always, I believe, been con- 

 sidered as derived from the decomposing rock beneath. 



It is only right to add that this paper was written before reading Lieut. Aytoun's 

 valuable description of the laterite of the Western Coast. It will be seen on comparing 

 the two descriptions that the rock of the Concan is precisely similar to that of Orissa. 



