526 Correqjondence — F. J. Bennett. 



scientific usage ; and the loose application of the term to ordinary 

 ferruginous clays, iron ores, etc., is wholly unwarranted. 



From a scientific standpoint, Mr. Scrivenor's suggestion that the 

 term bauxite should be applied to laterite in the sense here defined 

 is not justifiable. Bauxite is a mineral name, signifying a hydrated 

 alumina of fairly definite composition. Laterite is properly a rock 

 name, signifying the product of a special kind of weathering; 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 concretionary iron ore. In 

 defining the word laterite, however, Buchanan, as we have already 

 seen, clearly distinguished such iron ore from the laterite in which 

 it occurred ; and in no case did he apply the term to material 

 resembling that referred to by Mr. Scrivenor as " masses of iron ore ". 



The term laterite is used in a loose way not merely for material 

 which is essentially iron ore and which should be described as such ; 

 it is also used by some people as a name for any ferruginous clay, 

 sand, or gravel which may occur at or near the surface in tropical and 

 subtropical countries. Such uses of the term are unscientific, and 

 cannot properly be adopted by geologists, any more than they can 

 adopt the engineers' use of the term granite to cover all holo crystalline 

 igneous rocks, including syenite, diorite, and gabbro. 



T. Crook. 



Imperial Institute, 

 London, S."W. 



"AN EGYPTIAX OASIS." 



Sir, — In your review of this work (p. 477) you call special attention 

 to Mr. Beadnell's suggestion, that a lake in the Kharga district may 

 have been due to the letting loose of artesian waters through denu- 

 dation of the once overlying impervious beds. This interested me 

 much, as I had attributed to the same cause the formation of swallow- 

 holes and valleys. (See "Ightham", Homeland Association, 1907, 

 pp. 127-30, and also more fully in Geographical Jotirnal, September, 

 1908.) It is, therefore, gratifying to have my views independently 

 confirmed by one who has had such intimate experience of flowing 

 artesian wells as Mr. BeadnelL' 



I may say that before my views were published I put them forth 

 in correspondence with some leading geologists, and they were 

 strongly contested by some and not really accepted by any. Those 

 who attended the Loose Valley Excursion this year of the Geologists' 

 Association in July saw an area near Maidstone where, as I consider, 

 this suggested method of valley formation is particularly well shown. 



F. J. Bennett. 



"West Malling. 



October 7, 1909. 



^ See also Capt. H. G. Lyons, Quart. Journ. Gaol. Soc, 1894, vol. 1, p. 541. 



