254 
MANGANESE DEPOSITS OF INDIA : GEOLOGY. [ PaRT II : 
abundant than the felspar. The garnets were both isolated and in Uttle 
aggregates, and spatkled from the reflections from tiny faces, though on 
the whole they were rounded. The proportions of the constituents are, 
however, very variable so that it is not possible to give any definite 
chemical composition for the rock. Judging merely from appearances, 
the proportions by volume would be somewhat as follows in typical 
kodurites : — 
Spandite . . . . ! Spanditfi . . . | 
Apatite * to Apatite . . . . i 
Orthoclasc . . . . h Oithoclaso . . . | 
there being every gradation from these to rocks composed entirely of 
spandite and apatite, or entirely of orthoclase. 
On examining such mines as Kodur it is found that the more basic 
Magmatie differentia- rocks, such as spandite-TOck, occur as large patches 
tion of the kodurite and streaks, surrounded by zones of less basic com- 
position such as kodurite, in a general matrix of 
quartz -felspar -rock or felspar-rock, the most acid members of the series. 
Assuming for the moment that the mineral composition of the rocks is 
sufficient to show that the kodurite series is of igneous origin, then it is 
found that the relations of its various members are easiest explained as 
being the result of magmatie difierentiation, by which patches and streaks 
of the more basic rocks have separated out from the general magma, 
leaving the latter of a somewhat more acid composition than it otherwise 
would have been. It seems probable that this differentiation took place 
before the eruption of the magma and that the basic segregation patches 
thus formed were drawn out into streaks when the magma was intruded 
into its present position. Had the differentiation taken place after erup. 
tion we should have expected to find the more basic rocks located on the 
margins of the intrusions and the more acid rocks in the centre. The 
very opposite is, however, the case. Thus at Garbham the ore-band, 
which corresponds to the original manganese-silicate-rocks, occupies a 
roughly central position with regard to the masses of Hthomarge, corres- 
ponding to the original felspathic rocks, which form the north and 
oouth walls of the quarry (see figures 87, 88, pages 1087, 1088). 
Occurrences of the various rocks of this series will be found mentioned 
LocaUties for rocks in Part IV Under the localities shown in the follow- 
of the kodurite series, ing list. This list will also give some idea of the 
relative abundance of the various rocks. 
