562 Dr. L. Leigh Fermor — What is Later ite ? 



of British Guiana commonly termed 'Laterite' ", in the Geological 

 Magazine, 1910, pp. 439, 488, and 553. 



On p. 441 is given a table of analyses of "laterite soils". Only 

 one of those soils contains less than 50 per cent of " gravel + quartz 

 sand + clay, silica, and insoluble silicates", namely, the soil derived 

 from hornblende-schist at M aburima. This might be termed argillaceous 

 laterite, the adjective applicable depending on the exact nature of the 

 29 - 16 per cent representing the third item above. Some of the other 

 soils, namely, those containing considerable amounts of oxides of iron 

 and aluminium, such as Eos. 1, 4, 9, 12, and 13, might be termed 

 lateritic clag, soil, or sand, whilst the majority of the others would be 

 best designated clay, gravel, sand, or soil, without the dignity of the 

 adjective 'lateritic'. 



In Table II, on p. 444, showing decomposition products from Issorora 

 Hill, the red lateritic earth is correctly named. The concretionary 

 ironstones and ironstone pisolites are also correctly named, but might be 

 regarded as varieties of laterite, being the results, in fact, of the 

 segregation of the lateritic constituents of the lateritic earth. 



In Table Y, on p. 447, three rocks are boldly classed as laterites. 

 To none of them is the name, in my opinion, applicable. The earths 

 from Tumatumari, Omai Falls, and Mazaruni contain 47"3, 458, and 

 39 9 per cent of lateritic constituents respectively, and should, by 

 preference, be termed lateritic earths. 



The sericitic earth represented by Table VII on p. 449 contains 

 37'6 per cent of lateritic constituents and might also be termed 

 lateritic. The three samples of bauxite or laterite shown in Table IX 

 on p. 451 are correctly so named, and are in fact the only "residual 

 earths " noticed in Harrison's paper to which the term can be 

 correctly applied, with the exception, perhaps, of the segregations of 

 concretionary ironstone or lateritic iron-ore in the red lateritic earth 

 of Issorora Hill. 



But these three samples which I regard as the only true laterites 

 described by Harrison, represent, according to this author (p. 488), 



" the extreme of the formation of laterite, where tlie igneous rock, in place of 

 weathering to a mixture of quartz, of kaolinite, of bauxite, and of the oxides 

 and hydrates of iron, changes almost completely to quartz and to hydrates of 

 alumina and the oxides and hydrates of iron." 



Further, he says (p. 489) that the foregoing examples, that is to say, 

 all the various soils, earths, and laterites noticed above, 



" represent the types of the residual deposits in situ in British Guiana, which 

 I have regarded as and termed laterite." 



And in Table X he gives the mean proximate composition of the 

 British Guiana lateritic earths examined by him as follows : — 



Quartz 24 



Iron-ores (including pisolites) ..... 32 



Kaolin, Sericite, and other felspathic debris, etc. . 24 



Bauxite 20 



100 

 This corresponds to 52 per cent of lateritic material and 48 per cent 



