Dr. L. Leigh Fermor — What is Laterite ? 461 



the rock is evidently a qurirtzose laterite, which would graduate with 

 increase in the amount of quartz into a lateritic sand or sandstone. 

 Such a quartzose laterite might result from the action of lateritizing 

 processes on a rock containing free quartz, such as granite or gneiss, 

 the original quartz being then one of the insoluble constituents. 

 If, however, the quartz is of secondary origin, as in some of the 

 so-called laterites of Professor Harrison, then it is obvious that the 

 lateritizing processes have not acted normally, for this quartz should 

 have been removed in solution on the breaking up of the silicate 

 containing it. In fact, its presence indicates that the process by 

 which the original rock has been altered cannot be accurately described 

 as a lateritic one and the resultant rock as laterite, in the sense 

 of p. 460. In any case, such a rock should be regarded as but 

 imperfectly-formed laterite, requiring a qualifying adjective, such as 

 siliceous, before the word laterite. 



Litliomargic Laterite. — If the silica is present in the combined form, 

 it indicates the presence of kaolin or lithomarge, and consequently 

 that the process of lateritization of the rock has, again, not been 

 pushed to a finish, and that this rock also is an imperfectly-formed 

 laterite, requiring a descriptive adjective, such as litliomargic. With 

 any large quantity of combined silica present, calculation would show 

 that there was a larger amount of lithomarge than of free oxides and 

 hydroxides, and the rock would then be correctly designated a lateritic 

 lithomarge} 



Pisolitic and Oolitic Rocks. — Amongst laterites and the related rocks 

 pisolitic and oolitic forms are moderately common. The pisolitic and 

 oolitic bauxites are true laterites, as also are some of the pisolitic iron- 

 ores. But the pisolitic and oolitic manganese-ores at present known 

 are later ito ids,- and they are, it is interesting to note, also the most 

 aluminous of the aluminous lateritoid ores (see analyses Nos. 9, 10, 14, 

 on p. 1188, loc. cit., of ores from Kumsi manganese mine in Mysore, 

 showing 12 to 18 per cent of Al 3 3 ). Whilst many of the concretionary 

 iron-ores are true laterites, certain deposits of pisolitic limonite, such 

 as those forming part of the laterite formation 3 near Katni in the 

 Jabalpur district, 4 or such as the pisolitic limonite cementing the 

 bauxite conglomerate of Yeruli in the Satara district, 5 ma) 7 have been 

 deposited chemically from bodies of water, on the analogy of the 

 Swedish lake ores. Such lateritic deposits, in cases where there is 

 a considerable degree of probability, might suitably be termed lake 

 laterite. Under this term would also be included any laterites formed 

 by chemical deposition in bogs after the manner of bog iron-ores. 

 By admixture of the iron Irydroxides, at the time of deposition, with 

 mechanically deposited sand and cla)', siliceous lake laterites would be 

 formed, and if the amount of siliceous material were excessive the 



1 An analogous expression is bauxitic clay used by T. L. Watson in his 

 account of the "Bauxite Deposits in Georgia", Bull. No. 11, Geol. Surv. 

 Georgia, p. 52, 1904. 



3 Mem. G.S.I., xxxvii, p. 381, 1909; and infra. 



,! See infra for the use of the term laterite in a stratigraphical sense. 



4 Mallet, Eec. G.S.I. , xvi, p. 103, 1883. 



5 Mem. G.S.I. , xxxvii, p. 375. 



