SYNOPSIS OF PART 11. 
Ixxxv 
2. A portion of the ores has been formed directly by the compres- 
sion of the purest of the original manganese-oxide sedi- 
ments. 
3. Another portion of the ores has been formed by the subsequent 
alteration of the manganese silicates produced by the above- 
mentioned metamorphism. 
Points that are more doubtf ul :— 
4. The ores formed by the alteration of the rocks of the gondite 
series were formed by a combined decomposition and 
replacement of the gondite, spessartite-rock, or rhodonite- 
rock, as the case may be. 
5. The alteration of manganese-silicates to manganese-ores took 
place at the close of the Dharwar period of folding, and 
hence in Archaean times. 
6. The alteration took place at considerable depths, so that, taken 
in conjunction with the supposition that a portion of the 
ores are merely compressed manganese-oxide sediments, 
workable ores may be expected to extend in some places 
to as great a depth as the rocks of the gondite series, 
7. The alteration was due to the attack on the manganese-silicate - 
rocks by waters containing either carbon dioxide or 
sulphuric acid, more probably the former ; and also oxygen. 
8. The carbon dioxide may have been a portion of that liberated 
in the conversion of original impure calcareous sediments 
into the quartz-pyroxene-gneisses of this area ; and the 
oxygen a portion of that liberated in the conversion of 
original impure manganiferous sediments into the manga- 
nese -silicate- rocks . 
9. A small proportion of softish and more or less porous ore has 
been formed since the rocks of the gondite series were 
exposed at the surface, and is probably still bemg formed. 
[CHAPTER XIX.] 
Manganese in La' erite. 
Laterite consists essentially of a mixture of hydiated oxides of iroil 
and alumina, with often a considerable percentage ef titania, and 
