Chap. XV.] 
GONDITE SERIES IN NARUKOT. 
321 
granite contains inclusions of various of the rocks of the gneisses series 
(see Plate 17). Amongst the rocks so included are some of the mangani- 
ferous varieties, both manganese-silicate-rocks and crystalline manganese- 
ores. In some cases these ores seem to have been formed by the 
alteration of the manganese silicates ; but in the majority of cases they 
were formed at the time of the metamorphism of the manganiferous 
sediments, by the compression of the manganese oxides, with absorption 
of the small amount of silica required for the formation of braunite in 
accordance with the equation given on page 290. In so far as any portions 
of the ore found in these masses of rock included in granite can be 
Alteration of man" clearly distinguished as having been formed by the 
ganese silicate to alteration of the manganese silicates, they may be 
manganese-ores took , , .j ^i. ^ .1, x ^- e 
place in ArcliaJan regarded as evidence that the formation of the 
tinies. manganese-ores from manganese-bearing silicates 
took place before the intrusion of this granite, that is in all probability in 
Archaean times. And as the manganese-bearing rocks of this hill are suffi- 
ciently like those of the Central Provinces to justify the supposition that 
they were formed at the same time and imder similar circumstances, it 
seems justifiable to extend this piece of information to the rocks of the 
Central Provinces and suppose that there also at least a portion of the 
alteration of manganese silicates into manganese-ore took place in 
Archaean times. 
Although the rocks of this hill are many of them very similar to those 
occurring in the gondite series in the Central Provinces, yet they are some- 
what different owing to the frequent presence of apatite in considerable 
abimdance. A reference to the description of this occurrence of manga- 
nese-bearing rocks on page 330 will show the great variety of these 
rocks, containing as they do the following manganiferous minerals : — 
spessartite, rhodonite (?), piedmontite, manganese-mica, manganiferous 
pyroxene showing the blanfordite type of pleochroism, and another 
pyroxene also probably containing manganese. Since some of these 
manganiferous rocks contain felspars, a rather unusual mineral in the 
gondite series, it is evident that, if the rocks were formed from sediments, 
these sediments must have been, in at least some cases, felspathic. 
Also, from the fact that some of the manganese-bearing rocks contain 
calcite, it is evident that the sediments were often calcareous. The other 
constituents point to the presence of quartz and clay in the original sedi- 
ments. The various banded rocks associated with the manganese-bearing 
rocks are also of somewhat unusual character, and if they were formed by 
