Chap. XLL] 
SHIMOGA DISTRICT. 
1129 
proportion of the manganese- ore deposits lie in reserved forest, and to 
work them it is necessary to clear the jungle first. 
For our knowledge of the geology of this district we are indebted main- 
, , ■ . ly to Mr. Slater, who has produced unusually 
Geology and origin. _ ' f J 
detailed maps for Archaean areas. In Vol. 4 of 
the Records of the Mysore Geological Department there is a map (Plate 
III), on the scale of 1" = 4 miles, of portions of the district north and N. 
W. of Shimoga. In Vol. 5 there is a map (Plate II), on the same scale, of 
the portions of the district to the west and S. W. of Shimoga town, and in 
Vol. VI there is a map (Plate II), on the scale of V' = l mile, of parts of 
the district east andN. E. of Benkipur station. On these maps are to 
be found all the manganese-ore localities yet known. From them it wiil 
be seen that the whole of the district is covered by two divisions of the 
Archaean series — the Dharwdr Schists and the Granites and Gneisses. 
The Dharwars are probably older than the granites ; but there are 
some portions of the gneisses that are said to be of pre-Dharwar age. 
As might be expected the manganese-ores occur only in association with 
the Dharwars. The Dharwars of this district form, of course,^ a por- 
tion of the Dharwar-Shimoga band of Dharwars of Foote. They 
comprise a great variety of rocks, as described by Mr. Slater. The 
most prominent of these to one visiting the manganese areas are the 
phyllites, slates, and resultant clays ; the dolomites and limesI:ones ; 
the quartzites and ferruginous quartzites. The manganese-ores occur 
in cappings — often on the tops of hills — resting on these rocks, and 
chiefly on the phyllites — or rather their decomposed equivalents — and 
quartzites. They almost invariably crop out in the form of irregular 
lateritoid — i.e., resembling laterite — masses of more or less horizontal 
upper surface. When they are quarried into they nearly all show a 
downward passage from the mixed manganese- and-iron-ores into 
decomposed wads, lithomarges, and friable saccharoidal quartzites. Thus, 
although many geologists would probably not be disposed to regard 
these rocks as true laterite, like the laterite that forms horizontal sheets 
of some considerable extension, there seems to me little doubt that they 
are closely related to laterite, and are really one variety of it. 
According to the evidence of the many deposits I examined, they are 
formed by the superficial replacement of the phyllites and quartzites. 
