Geology and Petrology of Part of Toodyay District, W.A. 97 
Grossularite is present in small amount only, in irregular shaped, isotropic, 
yellow granules, always closely associated with the diopside. There is no 
epidote in 15405, but it occurs in similar rocks and possesses similar characters 
o that in specimen 1249 above. 
15405 is the only rock in which any carbonate has been noted. It occurs 
in small xenoblastic forms, always with concave boundaries towards the 
other constituents. It is most abundantly developed in the vicinity of diopside 
and hornblende (figure 6B). The complete absence of twinning suggests that 
it is dolomite rather than calcite. 
There can be no doubt that 15405 and related rocks are meta-dolomitic 
sandstones. Failure of the carbonate to react completely with the silica 
appears to indicate lack of sufficient aluminous and ferruginous impurities in 
the original sediment. The co-existence of quartz, grossularite, and calcite 
(or dolomite) indicates that these rocks have been developed by regional 
metamorphism under high pressure, for, if thermal metamorphism were 
responsible, then it would be expected that the remaining carbonate would 
liave reacted with silica to give wollastonite. 
The rocks described above are representative of the sparsely distributed 
calcareous seams in the original sandstones. They undoubtedly represent 
T'('gionally metamorphosed impure dolomitic sandstones with a varying car- 
bonate content. Kaolinic and ferruginous impurities have led to the forma- 
tion of epidote and grossularite and a certain amount of iron has entered 
into the dolomite-quartz reaction producing diopside. In rare instances an 
insufficiency of impurities has inhibited the dolomite-quartz reaction. The 
grossularite in these rocks appears to have developed under conditions of 
regional metamorjDhism in the sillimanite zone. Tilley (1937, p. 372) has 
<lescribed the development of grossularite under stress conditions in the Loch 
Tay limestone of Perthshire. Here the grossularite, together with vesuvianite 
and diopside, first makes its appearance in the Almandine Zone. The Tood- 
yay grossularite rocks show^ remnants of epidote, which in the Loch Tay 
limestones appears earlier than grossularite and disappears in the deeper 
})arts of the Almandine Zone. The presence of epidote in the sillimanite 
zone at Toodyay, along with grossularite, indicates that epidote may, under 
<-ertain conditions persist through the Almandine Zone. 
(3) The Mica ScTists. 
These politic members of the Jimperding Series occur at two horizons. 
In the upper part of the series, a band of mica schist, approximately 250 feet 
thick, forms the upper limit of the series. This band is characterised by 
al>undant andalusite. Another thinner band near the bottom of the series 
is characterised by sillimanite. Throughout the whole area the mica schists 
m-(' considerably weathered, making examination o fthem somewliat difficult. 
The lower jnica schist can be ti’aced from the south-east corner of the 
ai-ea alniost to the western side. It is interbedded witli (piartzites and is 
<‘\'erywhere c.ontorted by small dragfolds consequent upon its having been 
t()ld(^l between the two more competent quartzite beds. In the central 
part of tlie area and in the immediate vicinity of the townsite of Toodyay, 
it is considerably thickened by folding and it has l)oen impossible in this 
<'rumpled portion to map all the minor folds. 
