88 
Kex T. Prider. 
inverted), then the order of succession, with approximate thickness of the 
individual beds 
is as follows : — 
Upper .... 
Andalusite-muscovite schist .... 
> 250' 
Quartzite 
Upper Granite gneiss (with rare basic igneous 
and 
500' 
meta-sedimentary xenoliths) 
1900' 
Quartzite 
110' 
Hornblende schist 
40' 
Quartzite 
570' 
Sillimanite schist 
100' 
Quartzite 
375' 
Lowei’ Granite gneiss (characterised by the j)resence 
of basic igneous and sedimentary xenoliths) 
5,400' 
Quartzite 
050' 
Hornblende schist 
35' 
Lower .... 
Quartzite 
Unknown 
These rocks form the Jimperding series and are intruded in succession 
by the following - 
1. Coarse non-foliated microcline granite. 
2. Pegmatites, garnet aplites, and garnet muscovite granites. 
3. Quartz dolerites. 
4. Serpentinised ultrabasic sills and dykes. 
The age relation of the quartz dolerite series and ultrabasics is not at 
present known. 
Large scale faulting in the metamorphic rocks has been noted in several 
places, the most notable being in the part of the area situated about one and 
a-half miles east from Nardi Trig Station where a faulted block of the meta- 
morphics is found. This block has suffered a displacement of approximately 
one and a-half miles along the fault plane (see E.~W. section through datum 
on Plate I.). 
The lithology and structure of the area are reflected in the topography. 
The metasedimentary areas are all rough country, whereas the granite gneiss 
and granite areas are comparatively smooth. The main stream, the Avon 
River, as will be seen from the geological map (Plate T.) follows the structure 
very closely, and its main tributary (the Jimperding Brook) behaves in a 
similai’ fashion in the upper part of the series. 
The distribution of the later quartz dolerite dykes is interesting in con- 
nection with the structure of the area. A glance at the geological map shows 
that they trend generally in a N.N.W.-S.S.E. direction. There are some 
exceptions to this, but the greater number of dykes have this trend. They 
have apparently come up along lines of weakness approximately parallel to 
the tectonic ‘‘ strike " (or tectonic axis). 
III. PETROLOGY. 
A . — The Jimperdinq Series. 
Tlie metasedimentary members of this series, \dz., the (juartzites and 
mica schists will be described first and the igneous members (plagioclase 
amphibolites and granite gneisses) later. 
(1) The Quartzit-s. 
These are mostly coarse grained alnmst pure ([uartz rocks occurring in 
well defined bands. In the field they have a well bedded, flaggy appearance 
and are much iointed. 
