078 On the Local and Relative Geology of Singapore, [July, 



this letter I made the following remarks with reference to laterite : — 

 " Many of the clayey hills here [in Singapore] appear to me to be de- 

 composed sienite, sometimes unaltered by supervening volcanic action, 

 but generally partaking in the metamorphism which the matter of most 

 of the elevated land has suffered from that cause." 



May I venture to suggest that the hypothesis which is developed in 

 this paper for Singapore, might, if applied to the laterite of India, 

 perhaps explain its origin, and, in doing so, to a certain extent also 

 reconcile the conflicting opinions that have been maintained regarding 

 it. All that I have read of the great laterite formations of the south of 

 India, and which extend to the heart of Bengal, where they are describ- 

 ed by Dr. Buchanan Hamilton, leads to the conclusion that they are 

 not purely volcanic, sedimentary, or decomposed matter, but what I 

 have termed semi-volcanic. The same formation is found at Malacca, 

 and analogous deposits occur at Singapore, and both are inseparably 

 associated, and evidently contemporaneous, with altered rocks of the 

 kind previously noticed. If we conceive an area with trap, granite, 

 sandstone, shale, &c. exposed at the surface, (in the atmosphere or in 

 the sea,) and partly decomposed or disintegrated, to be subjected to a 

 peculiar species of minor volcanic action like that which is described in 

 this paper* (the distinctive phenomenon, probably, of one and the same 

 geological epoch), the results would be, that with the occasional excep- 

 tion of matter ejected from nq great depth, and some dykes and veins, 

 the previous soft surface rocks would be merely altered and metamor- 

 phosed by heat and impregnated with iron, derived perhaps from the 

 basaltic and other ferriferous rocks through which the discharged steam, 

 gases and water had passed in their ascent. Whether the action took 

 place under or above the sea would be determined by the presence or 

 absence of the ordinary marks of oceanic denudation. When clays 

 strongly ferruginous and soft from saturation with water, are dried, the 

 iron previously held in solution by the water is deposited between the 

 particles and cements them into a hard compact rock. Hence the 



* Whether the upper plutonic rocks were the direct sources of the igneous action, or 

 were themselves, together with the sedimentary rocks acted on by a lower plutonic sea, 

 does not affect my explanation of the formation of laterites ; for whether I adopt the one 

 or the other view of the source of the injections and impregnations which produced the 

 laterites, or remain in doubt on the subject, the fact, deduced from the actual examination 

 of these rocks, that they have been so produced, is not at all rendered doubtful. 



