1.8.C. 18  Procs. of the Asiatic Soc. of Bengal. [N.S., XVIII. 
is equally peculiar and interesting. In the area in which the 
deposits are found, the infranummulitic rocks include, at a 
depth of about 60 ft. below the coal of these parts, a pisolitic 
and sometimes ferruginous clay, which in turn lies super- 
positionally on a ferruginous breccia or brecciated quartzitic 
grit, and this again covers unconformably the ‘ great lime- 
stone’ of unknown age. Besides lying below the coal, it is 
very probable that the pisolite is contemporaneous with it, 
inasmuch as at one place it passes laterally into coal for a 
short distance. 
The folding of the rocks in conjunction with the hill 
ntours, in certain places such as Chakar, Sangar Marg and 
Salal Fort hill, has resulted in large spreads of this pisolitic and 
clayey rock being left as a skin lying on dip slopes of varying 
steepness and uncovered by any of the overlying formations. 
This is of course a mere physiographic coincidence, but one 
cannot help seeing a certain superficial resemblance between 
these spreads and the lateritic bauxite plateaux of other parts of 
ndia, a resemblance that is carried out as well in the average 
thickness (about ten or twelve feet) and in the cliff-like way in 
which the outcrops end. The particular feature that gives 
them value as a source of alumina is that, wherever this skin 
or spread of clayey rock is sufficiently isolated from its 
overburden, and left clinging to rather steep slopes, its upper 
layers have been converted into a residual white pisolitic or 
compact bauxite, having a composition akin to that o 
diaspore (Al,O, . H,O). Its lower layers, by gradual increase 
of silica pass into white or creamy white kaolin as also do 
the layers that are not isolated on dip slopes but pass under- 
ground beneath the overlying strata. 
Detailed surveys and a large number of chemical analyses 
of systematically collected samples have been made of the 
bauxite layers, which show that considerable amounts have 
a composition as follows :— 
Alumina 70 to 80 per cent. 
Silica 1 to 10 2 
Titanic acid 2 to 4 Pe 
Ferrie oxide 2to 4 » 
Water 13 to 15 Pr 



