H. Sf F. J. Warth — On Indian Laterite. 159 



proportion of combined silica which is present, and which we may 

 fairly assume to be a constituent of clay. In the table the amount of 

 clay is calculated according to the composition of pure kaolin 

 (kaolin equals Si O2 46*4 per cent., Al, O3 39-7 per cent., HgO 

 13"9 per cent.). The balance which is left after deducting both free 

 quartz and clay consists of free alumina and ferric oxide with water. 

 This is really the substance of bauxite, with gradually decreasing 

 proportion of alumina. The results of the analysis agree thus 

 remarkably well with the theory according to which the low-level 

 laterite is derived from the high-level laterite, and has during its 

 transport to a new site taken up sand and clay as impurities. 

 Further, the results show that the term laterite has a distinct meaning 

 throughout the many varieties of this rock. Laterite is bauxite 

 in various degrees of purity, from the richest wocheinite down to 

 such specimens in which the free alumina has entirely disappeared. 

 In this sense the specimen from Burmah which has been analysed 

 by Captain James, aud recorded in the Manual of the Geological 

 Survey of India, is also still a true laterite. Its composition is 

 similar to that of our two last specimens, No. 22 and No. 23. The 

 sample contained 30-7 per cent, quartz and 14'8 per cent, clay, and 

 the balance was made up almost completely of ferric oxide 

 (47'4 per cent.) with 4-7 per cent, water and only 1-3 per cent, free 

 alumina. 



It cannot be said with certainty what the state of hydration of the 

 alumina is in these detrital laterites. They vary so much in 

 composition, and the colours indicate that the ferric oxide may in 

 some cases be anhydrous and in other cases be present as limonite. 

 Taking all the specimens together, the average composition is such 

 that there is about as much diaspore as there is gibbsite and about as 

 much hematite as there is limonite. 



As regards the method of analysis, we found fusion with hydrogen 

 sodium-sulphate the best, if not the only method for all cases. By 

 it the free silica is readily determined as distinct from the combined 

 silica, the ii-on is obtained in solution, and so is the titanium. With 

 larger proportions of titanium (1 per cent. Ti Oj and upwards) we 

 resorted to the method of separation by long-continued boiling, and 

 small proportions of Ti Og were determined colorimetrically by means 

 of hydrogen peroxide. 



To carry out this work at a distance from India would have been 

 impossible, had we not received very liberal help in procuring 

 specimens from a deposit which extends over an area of thousands 

 of square miles. We desire to express our thanks to H.M. Secretary 

 of State for India, through whose kind intervention the bulk of 

 the very richest and most important specimens came into our 

 hands; also to Mr. Edgar Thurston of Madras and to Dr. D. 

 Hooper of Calcutta, who obtained for us the specimens by which 

 the true nature of the high-level laterite was proved for the 

 first time. 



