183S.] 



On the Laieritic Formathn. 



345 



large nullah, where they remain agglutinated together through the mediuta 

 of clay. At the bottom of such nullahs there is generally a quantity 

 of -lay, rising from the decomposition of felspar, and the quartz 

 pebbles transported thither fix themselves in this clay, and the bottoms of 

 suci; liulirths are one mass of a species of laterite, which, according to 

 circurn-^anices, may either be the quartzose or the detrital — the water 

 conlinuaHy passing along, although unable to remove them from their 

 position, percolates through the mass and assists in oxydising it, and 

 establishing that tubular and cavernous structure so peculiar. Water, 

 therefore, as a decomposing, oxydising and transporting agent has much 

 to do in the formation of laterite, and if these deposits of pebbles form- 

 ing into laterite, were by any convulsion of nature, or by the falling 

 in of the banks of the nulLihs, to be hidden beneath the earth, and 

 no relict of a water-course visible, it would be difficult hereafter to ac- 

 count for their position and formation. Such are my views respecting 

 laterite, a formation, the result of oxydatlon and decomposition — ^the na- 

 tural decay incident to primitive rocks in countries like India, where cir- 

 cumstances favour such decomposition, and where, perhaps, since the 

 flood, disturbing forces have very slightly operated. How different from 

 the new world, where, even in a very limited extent of country, primi- 

 tive, transition, secondary and tertiary formations, meet — where dis- 

 turbing forces have been at work — a portion of the globe which has 

 been made, modified, and again, as it were, broken to pieces. But 

 India has remained in its primitive simplicity, almost as unchanged as its 

 great Creator ; and in a geological, as well as historical, sense, truly 

 deserves the very appropriate cognomen of the Old World. 



The circumstances which favour decomposition are both external and 

 internal. The external are heat, and, as on the western coast of India 

 great heat and moisture combined. The internal, or what would be 

 called in medicine the immediate cause of the laterite formation, 

 seems to be the ferruginous nature of the constituents of the rock, or 

 the existence of iron ores. Iron, we know, exists more or less in most 

 rocks in the state of oxide, and when therefore speaking of oxydation 

 throughout this paper, I beg it may be borne in mind that I mean hyper- 

 oxidation. A species of laterite not mentioned by me is found beyond 

 and near Nundidroog, forming slight elevations. The specimens are of 

 the colour and appearance of burnt brick, only much harder ; on those 

 pieces exposed to the in^uence of the atmosphere, there are a few small 

 cavities from the decomposed felspar having been washed away, but the 

 specimens can scarcely be called cavernous. The basis has, as just ob- 

 served, the appearance of burnt brick, in which are nests, streaks and 



