H. 8f F. J. Warth — On Indian Laterite. 157 



The above specimens of Indian laterite are arranged in order of 

 their contents of free alumina, with the exception of the first, the 

 pure gibbsite, which, however, is the richest in alumina if the water 

 is eliminated. The specimens range from 68 per cent, of free 

 alumina down to nothing. There is thus every gradation in alumina 

 from nearly theoretically strongest downwards, with no gap to Speak 

 of. If, however, we take into consideration the other constituents 

 we find the specimens to fall into four distinct groups. 



I. By itself stands the gibbsite from Kodikanal, which is so much 

 free of foreign matter that in the ignited state it contains nearly 

 95 per cent, of aluminium oxide. As stated in the notice in the 

 Mineralogical Magazine, this mineral was found to form a deposit 

 of one foot in thickness, consisting of loose crusts or plates which 

 gave the impression of having been extracted from the underlying 

 charnockite. The sp. gr. of this gibbsite was 2'42. 



We next come to specimens of the far more extensive and thick- 

 bedded surface deposits, which have hitherto all been classed under 

 the name ' laterite.' 



II. Of these laterites the first four specimens belong to our second 

 group. They agree, as already stated, very well with those richest 

 bauxites which have been given the separate name ' wocheinite.' 

 They are characterized by their small amount of iron, and have even 

 less silica than the recorded analysis of the celebrated original 

 wocheinite, on an average 1"77 per cent, compared with 6'29 per 

 cent, at Wochein. On the other band they contain much more 

 titanium - dioxide. This large proportion of titanium - dioxide 

 (maximum 6'61 per cent.) is very characteristic of the rich bauxites, 

 and. a reference to the whole of the tables will show that the 

 titanium-dioxide gradually decreases with the free alumina until 

 there is only -01 per cent. left. It remains a subject for further 

 enquiry in what form the titanium exists when there is such a large 

 proportion. From the fact of its dissolving when the entire mineral 

 is treated with hot hydrochloric acid, and because there is always 

 enough iron present, we are inclined to believe that it exists chiefly 

 as ilmenite. As already mentioned, the specimens of this group are 

 mixtures of about three-fourths gibbsite and one-fourth diaspore (by 

 weight). The mean specific gravity of two specimens was 2'49, 

 which is more than that of the Kodikanal gibbsite. Our specimens 

 have also the characteristic pisolitic structure, the globules varying 

 from two to four millimetres in diameter. 



III. The third group includes specimens such as geologists have 

 hitherto called high-level laterites. They are bauxites which have 

 formed from highly ferruginous igneous rocks. They belong mostly 

 to the area of the Deccan trap, and we find that the proportion of 

 ferric oxide in these bauxites is in close relation to the proportion of 

 iron in the trap. In the same way the small proportion of iron 

 in the preceding group of wocheinites indicates their origin from 

 less ferruginous, probably gneissic rocks. A glance at the table, 

 group III, also shows the regularity with which the water decreases 



