60 
J. R. H. McWhae. 
iron and silica-rieli rocks. Probably the original rocks were finely bedded 
quartz sands and magnetite sands, similar to those of Yampi Sound (5^ 
p].:). 67-75), with some bands of impure iron-rich sediments containing 
greenalite or siderite (17, p. 369). 
As ])anded hematite-quartz rocks with little or no amphibole (ii) occur, 
it a 2 )pea]'s that pure iron ores and (juartz do not react to any extent, so 
it is considered that group (ii) is derived from finely laminated quartz- 
magnetite sediments, AvJiile group (i), in which iron-rich ampliiboles and 
garnet are jii’esent, is the result of intense metamorphism of banded quartz 
and impure iron-rich sediments (greenalite or ferrous carbonate). 
(Iroiip (iii) is considered to be the result of lateritisation of the 
metajaspilile.s especially the very iron-rich forms. This is a ease of 
extreme retrograde metamorphism (katamorphism ) as a result of weather- 
ing of higli grade mctamorphic rocks. The original bedded structure is 
in most cases clearly visible, the iron-rich minerals a^^parently have been 
metasomatically replaced by limonite so the rock may be considered to 
he a lateritoid (a term proposed by Fermor (11, pp. 381-3) fo-r rocks similar 
to latcrite but formed by metasomatism). 
2. Meta-igneous Rocks. 
(a) Iloruhlende schist and its variants. 
These are fine to medium-gTained, uniform-textured, schistose rocks 
dark greenish gi'ey in colour and identical with those of the Toodyay 
Area (23, p. 104-107). A granohlastic microstrueture and the absence of 
any distinct crystallohlastie order is characteristic of the group. 
(i) Quartzq)lagioc!iise umpliibolite (22733) is the most common type 
as it is in the Toodyay Area (23, p. 104-105). The optical properties of 
the hornblende at kawnswood are X = yelloAV, h ^ Y olive green, 
Z — hlm^-green, absorption X > Z > Y, (-) 2Y large, -c a Z = 20°, 
P = 1.670. Its approximnte composition is hornblende 65 per cent., oligo- 
clase (Alg Aiiu) 25 i)e]’ cent., fpiartz five per cent., accessories (microcline, 
radio-active titanife and green diopside) five per cent. 
(ii) Qnartz-])l;)gioclase-pyroxene granulite (22732) is a variant of 
the idagioclase amphibolite. Tt is a granular type in Avhich green diopside 
is greatly developed wliile hornblende is rare or absent. The diopside 
is a bi’iglit green very feebly pleochroic variety, Z and X appearing to 
be gi’een and b — Y = yellow green, optically ])ositive, q /\ Z := 40° 
with simple twinning developed. The approximate composition of this 
is diopside 50 per cent., oligoclase 45 per cent., quartz four per cent., 
titanite one per cent. 
(iii) Quartz-zoisite-liornblendc schist (22583) — The hornblende schist 
layer intercalated in the Avestern metasediments differs from those 
described above in the prtHlominance of quartz and the absence of felspar. 
The presence of an aggregate of zoisite and sericite is probably the result 
of retrograde metamorphism (felspar ^ sericite + zoisite). Accessories 
are apatite, iron ores, ]mT])le zircon, and rutile. Titanite is absent. The 
approximate composition is (jiiartz 55 per cent., hornblende 30 per cent., 
zoisite and sericite 15 per cent. 
