Chap. XIX.] 
HIGH LEVEL LATERITE. 
371 
disintegration and transportation of laterite from higher levels by 
the agency of water, to be deposited at lower levels as low-level laterite. 
As a consequence of its mode of formation, materials derived from the 
mechanical disintegration of other rocks than laterite get mixed with the 
detrital lateritic materials in the formation of low-level laterite. Hence, 
low-level laterite may contain many other substances besides those men- 
tioned above as characteristic of laterite, and of these extraneous substances 
fragments of quartz are perhaps the commonest ; in any case the low- 
level laterite on analysis would usually be found to contain a considerable 
amount of silica, whilst the true high-level laterites are usually compara- 
tively free from silica, either free or combined. The whole is cemented 
together by segregative and chemical changes taking place in the 
ferruginous materials of the deposit, probably with the addition of a 
certain amount of ferric oxide deposited by percolating waters. The 
best account of low-level laterite that has been published is contained in 
P. Lake's paper on the geology of South Malabar^ Prom this it 
appears that there is a considerable amount of low-level laterite of non- 
detrital origin, formed, according to Lake, by the decomposition in situ of 
Mangiiiipse-cre m the underlying gneiss with a certain amount of re- 
low-levol laterite. arrangement by rain, etc. No account of the laterite 
of Goa seems to have been published ; but I have recently been able to 
examine it in several places, and think that practically all that I saw 
was of non-detrital origin and formed at least in part by the replacement 
of the underlying rocks. In some places it is free from visible manga- 
nese-ore, in others it contains spots and patches o f m anganese-oxide 
of no value, whilst at quite a number of localities it is highly manga- 
niferous and worked as a source of manganese-ore. The laterite seemed 
very similar to the high-level laterite of Talevadi in Belgaura. 
Hig^h-level Laterite. 
The high-level laterite is found best developed on the plateau known 
as the Deccan, and further north in the Central Provinces and Central 
India. It seldom occurs at levels lower than 2,000 feet and never at 
'I'levations greater than about 7,000 feet^. A small portion of it is 
1 Mem. Qeol. Surv. /wZTxXIV, pp. 217-233, (1891). ~ 
2 This figure is given on the assumption that true laterite exists in the Nilgiri Hills 
and Palni Hills. If, however, Medlicott and Blanford are correct in their statement that 
no true laterite occurs in these places, then the upper limit must be given as about 5,000 
feet. Since this was written I have been able to visit the Nilgiris. I found the surface 
rocks to be — where not the gneisses of the charnockite series — li thorn arges and 
clays of various colours, sometime? with associated ochres. Where I happened to go 
laterite was rare ; but in one or two places 1 found rocks to which it seemed to me this 
term could fairly be applied. 
II K 2 
