118 
Kex T. Pbider. 
Table II. 
CHEMICAL CHANGES IN THE FORMATION OF THE LOW-LEVEL LATERITE. 
1. 
2. 
3. 
4. 
!Ferriiginoiis 
sandstone 
(Weight %) 
LoAv-level 
laterite 
(Weight %) 
2. recalculated 
to quartz 58-51 
Gains and losses 
during laterit- 
isation. 
(Gnis/lOO gms. 
of original rock) 
58-ol 
36-69 
58-51 
\Combinecl 
5*42 
8-18 
13-05 
r- 7-63 
AhOs 
3*17 
24-63 
39-27 
-1- 36-10 

27-63 
14-82 
23-63 
~ 4-00 
TiOo 
0-99 
1-25 
1-99 
4- l-OU 
JVInO 
0-02 
0-01 
0-02 
• « . 
H^O 
4-40 
14-61 
23-30 
18-90 
100-14 
100-19 
159-77 
Gain 63-63 
Loss ' 4-00 
Net Gam 
... 
... 
... 
59 ■ 63gm.s. 
per. 100 gms. 
original rock. 
There lias been a slight loss in Pe.O.„ slight gain in titania and eoni- 
bined silica Imt vei'}' marked gains in alumina and Avater. The signiticant 
changes are those in the alumina and water content and these are in the 
molecular proportions alumina ; water =- 3dT : 1050 i.e., 1 : 3 so that 
the material added to the original rock during the lateritisation process 
is essentially aluminium hydroxide (Al(OH).d. The source of this 
aluminium hydroxide is unknown — the ferruginous sandstones are poor 
in alumina but the alumina may have come from the underlying gi’anitie 
rocks as there is only a thin veneer of sandstone, but on the other hand 
it may have been dei’ived from an overlying shale or mudstone which has 
noAV been entirely removed by erosion. 
The low-Ievol laterite is therefore a true laterite, and not a lateritite, 
■due to the accumulation of alumina in the near-surface layer, formed in 
situ over the f(*rruginous sandstone. This laterite formation iDvobably 
took place shortly after the sand-covered marine bench (the Ridge Hill 
Shelf) was elevated a few feet above sea-level. This Avas later than the 
tormation of the high-level laterite. 
(;J) The I elloiv Sands . — The VelloAv Sands constitute tlie youngest 
formation and are exposed in the Avesternmost part of the mapped area 
Avhere they foi-m an even gentle slope doAvn to the level 'of the coastal 
plain to the Avest. The boundary betAveen the yelloAV sands and the earlier 
rocks is irregular (see Plate 1) thus precluding the possibility of a faulted 
contact or fault scai'p against AAdiich the sands have accumulated. There 
is an abi'upt change from the ferruginous sandstone and low-level laterite 
to the yelloAv sands and this has been Avell exposed by rainAvash in a 
di’ain on the south side of the railway line at seven chains soulh-Ave 5 ^t 
from the 14-mile peg. 0\*er the laterite this drain is tAvo feet deep but on 
-reaching the boundary Avith the incoherent yelloAv sand it deepens abruptly 
