Dr. L. Leigh Fermor — What is Laterite ? 561 



The term bauxite was, as is seen above, extended by Deville to 

 rocks very high in Fe 2 O s , and it has often been used in France 

 to correspond with rocks ranging from the most aluminous to the most 

 ferruginous laterites of India. Mr. Scrivenor's contention, then, 

 would seem to be upheld, namely, that we can replace the term 

 laterite by the word bauxite. But it should be remembered that the 

 term laterite dates from 1807, and the term bauxite only from 1847. 

 The French mineralogists have, therefore, used the word bauxite for 

 a substance for which a name already existed, and therefore if any 

 change were necessary we should call upon our French colleagues to 

 drop the term bauxite and to substitute for it the term laterite. 

 Such a course would be absurd, and I think the most desirable 

 procedure is to restrict the term bauxite to those varieties of laterite 

 sufficiently rich in alumina to be used as aluminium-ores. If the 

 rock contains more Fe 2 3 than Al 2 O s , it is not likely to be used as an 

 aluminium-ore, and therefore I think the term bauxite might be 

 restricted to those laterites that contain at least as much Al 2 O s 

 as Fe 2 O s . 



Lacroix follows a somewhat similar course. He says (p. 346) that 

 he reserves the name bauxite (sensu stricto) for rocks of the type of 

 those of Provence, and to the very aluminous and often pisolitic 

 patches (accidents) in laterite, whilst he uses the word laterite in 

 its customary sense — defined earlier (p. 345) as the red rock that 

 is formed in tropical climes by the decomposition in situ of the most 

 diverse rocks, e.g. granites, diorites, basalts, gneiss, etc. — and applied 

 it in addition to rocks of the same composition, such as the bauxites 

 of the Puy-de-D6me (alteration of gneiss) and of Hesse (alteration of 

 basalts), of which one can prove the formation in situ at the expense 

 of silicate rocks {roches silicatees). 



In closing this section it is interesting to notice that Mr. Scrivenor, 

 whilst quoting Professor Lacroix to the effect that bauxite is a rock 

 and not a mineral, has apparently overlooked the same author's 

 distinction between the terms bauxite and laterite, which conflicts 

 with his (Scrivenor's) suggestion that the term laterite should be 

 replaced by the term bauxite. 



V. The Lateeitic Earths of British Guiana. 



I will conclude this paper with a brief consideration of the surface 

 decomposition rocks of British Guiana, as discussed in this Magazine 

 (already summarized), and which have given rise to this communication. 

 I will take Professor Harrison's paper entitled "The Residual Earths 



two notes, on pp. 936-8 and 1115-18 respectively, by M. H. Arsandaux, " Sur 

 la composition de la bauxite." In the earber note it is shown by treating 

 certain French bauxites with concentrated H CI, and then attacking the insoluble 

 residue with concentrated H2 S Oi, that nearly all the alumina is present as 

 AI2 3 . H2 0, thus corresponding, although the rocks were found in thin sections 

 to be completely isotropic, to the composition of diaspore. The iron is shown to 

 be present as anhydrous Fe 2 O3 . The titania is believed to be present as meta- 

 titanic acid, Ti02.H 2 0, and the small quantities of silica as 2H 2 0. Al2 03.2Si0 2 

 (the kaolin or lithomarge formula). The second note deals with the more 

 siliceous bauxites (also completely isotropic) , and indicates the existence of every 

 gradation between clay and AI2 O3 . H 2 0. 



DECADE V. — VOL. VIII. — NO. XH. 36 



