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



rock, it seems to roe desirable to develop what I think are the 

 general ideas of Indian geologists on this question. 



I propose to deal in this communication only with the nomenclature 

 of laterite and to avoid as far as possible any discussion on its origin, 

 and consequently I will first summarize the discussion that has taken 

 place in the pages of tin's Magazine. 



II. The Pkkvious Discussion. 



On pp. 100-3 of his work The Geology of the Goldfields of British 

 Guiana (1908) Professor J. B. Harrison describes under the name of 

 laterite certain residuary earths of which analyses are given, and 

 which are obviously not true laterites in the sense outlined above. 

 This work is reviewed in vol. vii of the Bulletin of the Imperial 

 Institute, 1909, pp. 133, 134, a protest, in my opinion both justifiable 

 and necessary, being raised by the reviewer against Professor Harrison's 

 use of the word laterite. The reviewer says — 



" The exact sense in which it is used is not defined, but the weathering 

 products included under it appear to be in all cases ferruginous and siliceous 

 clays. . . . These can scarcely be laterites in the modern sense of the word, 

 which should be restricted to that product of weathering in hot moist climates 

 which contains free aluminium hydroxide. The analyses of laterites proper 

 usually show excess of alumina with silica as a subordinate constituent, though 

 a considerable amount of iron and titanium oxides may be present." 



Mr. J. B. Scrivenor 1 objects to the reviewer's attempt to restrict 

 the meaning of the word laterite, regarding it as impracticable, and 

 putting forward the interests of engineers as follows : — 



" The reason of this is that the term ' laterite ' has been used, in the Malay 

 Peninsula at least, for many years by a large body of engineers for what are 

 essentially masses of iron oxide replacing portions of weathered rock and filling 

 fissures in such rock near the surface. This (Malayan) laterite is most 

 abundant in weathered schists, and is largely used for public works. Small 

 quantities of aluminium hydroxide may or may not be present in these masses 

 of ironstone, but that question is of no immediate importance to the engineer, 

 who values the stone for its hardness." 



The material referred to in this passage is probably identical with the 

 rock I have designated lateritoid 2 amongst the Indian lateritic rocks 

 in order to indicate its resemblance to, and yet difference from, the 

 more typical laterites (infra). 



Mr. Scrivenor' s letter leads to a reply from Mr. T. Crook, 3 of the 

 Imperial Institute, who quotes Buchanan's original definition, and, 

 remarking that the author of the term clearly distinguished iron-ore 

 from the laterite in which it occurred, objects to the application of the 

 term to iron-ores and ferruginous clays. Incidentally Mr Crook 

 remarks — 



"It is a complex product, essentially characterized by the presence of free 

 hydrated alumina, but usually containing also notable amounts of titanium and 

 iron oxides, whilst free silica is generally present, and hydrated silicate of 

 aluminium is not necessarily absent. The amount of iron oxide is very variable, 

 but when it becomes excessive it usually separates out in the form of con- 

 cretionary iron ore." 



1 Geol. Mag., 1909, p. 431. 



2 Mem. Geol. Surv. India, xxxvii, p. 381, 1909, and infra. 



3 Op. cit., p. 524. 



