SEDENTAEY MATEEIALS: EESIBUAEY DEPOSITS 299 



mistaken. The more massive forms show usually a horizontal 

 banding. Some forms of laterite show a breceiated structure, 

 due to its detrital fragments becoming recemented into masses 

 closely resembling the original rock. The high level form, that 

 which occurs capping the hills and plateaux on the highlands 

 of central and western India, is fine grained and compact and 

 of a fairly homogeneous structure, although the iron oxide may 

 be somewhat irregularly distributed and sometimes segregated 

 in pisolitic nodules sufficiently abundant to form an ore. The 

 lower level form, that which covers large areas of both east and 

 west coasts, frequently contains grains of sand and pebbles 

 embedded in a ferruginous matrix. It is, as a rule, less homo- 

 geneous than the high level form, but nevertheless passes into it 

 by insensible gradations. 



The origin of both high and low level forms of the laterite 

 has been the subject of much speculation. It is probable that 

 all of it is of a residual nature, i. e.^ represents the less soluble 

 portions of pre-existing rock masses. That which is found on 

 the high levels occurs overlying the Deccan trap sheets, into 

 which it can in many instances be traced, proving conclusively 

 its origin from this rock by the ordinary processes of weather- 

 ing. The low-lying variety can, in many instances, in like man- 

 ner be traced back to its origin from more siliceous, gneissic, and 

 granitic rocks. A part of the material, however, has the ap- 

 pearance and structure of a clastic rock of sedimentary origin, 

 and so it is considered, by the best authorities, to be. 



The chemical composition of a very ferruginous laterite is as 



below: 



Chemical Analyses of Latebite, Eagoon, India 



Constituents 



Silica (Si02) .... 

 Alumina (AI2O3) . . . 

 Iron sesquioxide (Fe203) 

 Lime (CaO) .... 

 Magnesia (MgO) . . . 



Alkalies 



Water and loss . . . 



Insoluble 



30.728% 

 2.728 ■ 



6.802 



40.258 



Soluble 



6.848% 

 6.783 

 46.279 

 0.742 

 0.090 



59.742 



100.00 % 



Bulk 



37.576% 

 532 



j 55. 



6.892 



97.270 



