« 
Chap. XL. ] izagapat.\m : mamidipilli. 1109 
hand -specimen of this shows at one end that the felspar is being con- 
verted into manganese- ore by replacement, with the production of 
pseudomorphs in manganese oxide after felspar showing the original 
cleavage of the felspar. In this part the garnet remains unaltered. In 
another part of the same specimen the felspar is fresh (giving a potas- 
sium reaction), while the garnets are represented by ochreous spots, the 
manganese having been removed in solution. By the completion of 
these two processes, accompanied by kaolinization, tliis piece of rock 
would at one end become psilomelane studded with garnets, and at the 
other end kaolin or lithomarge with ochreous spots. 
Another section showed psilomelane in large patches joining together 
in the kodurite, the ore forming the major portion of the rock. The 
kodurite was here largely kaolinized with a great abundance of apatite 
weathering out. The apatites were mostly rounded stumpy prisms, 
sometimes showing hexagonal faces, and up to J inch long. 
In one place in this section the surface of the manganese-ore formed 
by replacement and altera^^ion of the kodurite was coarsely botryoidal, 
the spherules being nearly 2 inches in diameter. The outer layer of the 
spherules, about ^ to -I inch thick, was composed of limonite. 
In another pit I found an unique rock, namely an altered form of a 
biotite-kodurite. This is practically the cnlv 
Biotite-kodnrite. . . . " 
example I have found of mica m the Vizaga 
patam manganese-intrusives (see also page 252). The other example was 
at Perapi, where in one pit was a coarse quartz-felspar-rock, the felspar 
being predominant, with a fair amount of small scattered scales of an 
altered biotite-mica The Perapi rock is not, however, certainly a part 
of the kodurite series of intrusives. The Mamidipilli rock is largely 
converted into chalcedony and ochre (often forming together a brown 
chert), but still shows biotite scales (now no longer elastic) averaging 
about ^ inch across, spandite, and apatite. There is no longer any fel- 
spar left, but, judging from numercus examples I have found of chalce- 
donized or opalized kodurite, in which the garnet remains fresh while the 
felspar is changed to chalcedony or opal, it can fairly be deduced that at 
least a portion of the chalcedonic ground-mass of this rock corresponds 
to original felspar and that the original rock was a biotite-apatite-span- 
dite-felepar-rock ; i.e., a biotite-kodurite. 
IV 2 K a 
