Chap. XL. ] 
VIZAGAPATAM : KODUR. 
1061 
This indicates kaolin containing only 6 ,33 per cent, of free quartz, 
the presence of which is rendered evident by a gritty feeling on powder- 
ing up the rock. The coloured lithomarges owe their colouration to 
oxides of iron, and often contain a small quantity of quartz, not usually 
visible to the eye, but easily separable by powdering and washing. 
^ The yellow ochre found in some places consists 
partly of limonite rendered impure by litho- 
marge and quartz, which are left behind on treating the powdered ochre 
^ with hydrochloric acid. The wads, also, often 
consist of lithomarge impregnated with oxides 
of iron and manganese, so as to impart a brownish black to black 
colour ; when treated with hydrochloric acid they leave a residue of 
white lithomarge and quartz. One specimen of black wad was subjected 
to complete analysis by Messrs. J. & H. S. Pattinson with the result 
given on page 119. As there shown, the analysis indicates the wad to be 
an admixture" of oxides of manganese and iron with over 6% of kaolin. 
The constituents of commercial significance are shown below : — 
S-pecimen No. A. 338. 
Manganese ........ 41-59 
Iron 410 
Silica 3-40 
Phosphoius . 0-114 
Moisture ........ 4-35 
These lithomarges, wads, ochres, etc., were no doubt formed during 
the chemical changes by which the manganese-ores were produced 
from the manganese silicates, such as spandite and manganese-pyroxene. 
The rocks from which they were derived were no doubt mainly felspar- 
and quartz-felspar rocks ; but any or all of the other rocks noticed 
below may have contributed to their formation. Such extensive chemi- 
cal changes naturally led to great changes in volume, and many small 
slips must have taken place in the lithomarges before equilibrium was 
set up. In many cases the wad has been formed by the impregnation 
of lithomarge with manganese oxide, and this impregnation has often 
taken place up to some crack and stopped abruptly at it, so that there 
are often very sharp changes from black oi yellow, to white, red, or 
2 G 2 
