376 
MANGANESE DEPOSITS OF INDIA i GEOLOGY. 
[ Pakt ii : 
cement was formed under water in a lake (or perhaps in a marsh orbog, 
why should not the remainder of the lateritic layers at Yeruh, which are 
usually non-pisolitic, have been formed in the same way ? They may 
have been ; but that they were more probably not is indicated by the fact 
that there is apparently a gradual passage downwards from the laterite 
into the underlying rock, as will now be noticed. It so happens that 
a large number of pits were sunk on this plateau in former times by the 
natives of these parts, it is said in search of copper ; but much more 
probably for the extraction of the iron, although for this purpose they 
seem to have chosen a particiilarly aluminous mass of laterite. One of 
these shafts had been cleaned up just before my visit and deepened a 
little. It went through 38 feet of laterite, both aluminous and ferru- 
ginous, and then passed into a soft lavender-grey rock. On accoimt of 
the presence in this rock of soft white spots, resembhng in size and 
Composition. abundance those frequently seen in the amygdaloidal 
earthy traps of the region, we can suppose that it was 
derived from such an amygdaloidal earthy trap by some method of 
chemical alteration. The composition of this altered rock is shown by 
the following partial analysis carried out by S. Sethu Rama Rau, 
Sub-Assistant in the Geological Survey :— 
Mahabaleshwar. 
Yeruli. 
Si02 
35-60 
38-98 :m 
35-51 
35-05 
Fe203 + Ti02 
16-91 
15-81 
Undetermined 
11-98 
10-16 ' 
100-00 
100-00 
The analysis shown in the first column was also made by Sethu Rama 
Rau, on a sample of very similar material obtained near the lake at 
Mahabaleshwar at its eastern end. The similarity of these two analyses 
is very ftriking. 
