Correspondence — T. Crooh. 525 



composition". The word has, however, been consistently used as 

 a scientific term, and its meaning, at least so far as geologists are 

 concerned, should be decided not by the loose usages of engineers, but 

 by the way in which it was first defined and subsequently used by the 

 best authorities. 



The term laterite was introduced in 1807 by F. Buchanan in his 

 Journey from Madras, through Mysore, Canara, and Malabar. He 

 describes the occurrence of iron ore at Angadapuram in the hills west 

 of Calicut on the Malabar coast, and in vol. ii, p. 436, remarks as 

 follows : — " In all the hills of the country the ore is found forming 

 beds, veins, or detached masses in the stratum of indurated clay, that 

 is to be afterwards described, and of which the greater part of the 

 hills of Malabar consists." 



It will be seen that Buchanan clearly regarded the indurated clay 

 as distinct from the iron ores. On p. 440 he continues: "What 

 I have called indurated clay ... is one of the most valuable 

 materials for building. It is diffused in immense masses, without 

 any appearance of stratification, and is placed over the granite which 

 forms the basis of Malayala. It is full of cavities and pores and 

 contains a very large quantity of iron in the form of red and yellow 

 ochres. In the mass, while excluded from the air, it is so soft, that 

 any iron instrument readily cuts it, and is dug up in square masses 

 with a pickaxe, and immediately cut into the shape wanted with 

 a trowel, or large knife. It very soon after becomes as hard as 

 a brick, and resists the air and water much better than any bricks 

 I have seen in India. ... As it is usually cut into the form of 

 bricks for building, in several of the native dialects it is called the 

 brick stone [Itica cullu). . . . The most proper English name would 

 be Laterite, from Lateritis, the appellation that may be given to it iu 

 science." 



The laterite thus described by Buchanan is the clay-like material 

 which occurs extensively in India as the product of one type of 

 tropical or subtropical weathering of crystalline rocks, containing 

 aluminous silicates, and which is essentially characterized by the 

 presence of hydrated alumina. It has, as Buchanan says, the power 

 of hardening on exposure, and for that reason it has been extensively 

 used as road metal. It is to this material that the word laterite has 

 been for many years mainly applied in India, not only by geologists, 

 but also by engineers. 



The recognition of the fact that laterite is essentially characterized 

 by the presence of free hydrated alumina is due to Professor Max 

 Bauer, who worked on the laterite of the Seychelles {Jahrbuch filr 

 Mm., etc., 1898, vol. ii, pp. 192-219). 



The conclusions arrived at by Max Bauer were confirmed and 

 amplified by Sir Thomas Holland, late Director of the Geological 

 Survey of India, in a paper " On the Constitution and Dehydration 

 of Laterite", published in this Magazine (Decade IV, Vol. X, 1903, 

 p. 59), and have been almost universally adopted among Continental 

 geologists. 



We find, therefore, that Buchanan, who introduced the term laterite, 

 attached to it a significance which is in strict agreement with modern 



