Chap. XXXVI.] 
NAGPTJR : PALI. 
959 
by Plate 42. A considerable part of the limestone was once black and 
has since been largely converted into black chert, but some of the black 
limestone still remains. The most interesting feature of this quarry 
is, however, the occurrence in the limestone of pockety masses of most 
p J beautiful pyrolusite (Plate .3). These masses have 
apparently been formed by the solution of the non- 
manganiferous and consequently light-coloured limestones with forma- 
tion of cavities in which manganese dioxide was deposited by waters 
carrying manganese-salts derived from the neighbouring manganiferous 
limestones. But whether the cavities were first formed and then the 
pyrolusite subsequently deposited in them, or whether it was a case of 
simultaneous solution of the limestone and deposition of manganese 
oxide, cannot of course be definitely determined. In the former case, 
however, we might have expected some of the cavities to be filled only 
partly with pyrolusite. I was unable to find any such cavities and am 
inclined to think that the second theory is the true one and that the action 
was similar to the reaction by which manganese dioxide is precipitated 
in the Pattinson process for estimating manganese. The equation would 
then be somewhat as follows : — 
Mn H2(C03)2 + CaCOg + O2 ' • " ' 
= Mn02 + CaH2(C03)2 + CO2 
The masses of pyrolusite seem never to be very large and are probably 
nearly all connected to each other by thin veins and bands. When 
amass of pyrolusite is broad, it is apparently never more than 1 to 3 feet 
deep and when it fills a cleft in the limestone it is never more than 2 feet 
wide. A large proportion of the pyrolusite is found in beautiful radiate 
masses with concentric, more or less spherical, surfaces of parting, which 
are roughly at right angles to the radiations. These spherical surfaces 
are 1 to 2 inches in diameter. They have a beautif al dark steel-grey 
colour something like that of a black-leaded stove, and the effect is 
improved by the fact that the spherical surfaces are not quite smooth, but 
are made up of little circular scales of ore. These masses are often of 
great purity. As pure a piece as could be picked out was analysed 
at the Imperial Institute with the following result : — 
Spccirneti No. 932. 
Per cent. 
Manganese peroxide (irn02) . ...... 9.5 •.'57 
Manganese protoxide (MnO) . . . . . . 0'4I 
Ferric oxide (Fe203) . ... . . . . .0-06 
Alumina (AI2O3) ........ 0-4.3 
Baryta (RaO) 1-34 
Lime(CaO) 0-00 
Magnesia (MgO) 0-09 
Combined silica (Si02) . . . . . . . 0'33 
Free silica (Si02) . . . . . . . . O'OO 
