84 
Rex T. Prider. 
I. INTRODUCTION. 
The area which measures about 12 miles in an East-West direction, by 
three to four miles in a North-South direction, lies several miles to the south 
of the town of Toodyay, which is situated about 50 miles north-east from 
Perth, It is occupied almost entirely by a series of crystalline schists to which 
the name “ Jimperding Series” has been given (Clarke, 1930, p. 167) and 
which is believed to be of an early Pre-Cambrian age. This series comj^rises 
politic and psammitic metasediments with intercalated basic and acid igneous 
bands. A study of the politic members shows that over the wliole area mapped 
the rocks lie within the sillimanite zone. 
This series has been intruded by granite (and its associated aplitic and jjeg- 
matitic dykes) and afterwards by a series of quartz dolerite and rare ultrabasic 
dykes — none of these igneous intrusions has metamorphosed tlie older rocks. 
The only rocks of later age than the quartz dolerite series are of supei-- 
ficial character — laterites (duricrust, Woolnough, 1930) and recent alluvial 
deposits. The duricrust occurs at an elevation of about 900 feet above sea- 
level, and has been developed over all the older rocks, even the extremely sili- 
ceous quartzites. Neither it nor the alluvial dejDosits will be considered in this 
paper, which deals with the Pre-Cambrian rocks. 
A brief accoimt of the rocks from the western part of this area has betai 
published (Prider, 1934, pp. 1-16) but, ’other than this, there is no account of 
the petrology of any of these Pre-Cambrian rocks. Simpson has described a 
number of the minerals occurring in the metamorphic rocks of the Darling 
Range, several from the area at present under consideration, viz., andalusite 
from Jimperding (Simpson, 1928, p. 50), sillimanite, also from Jimperdinir 
(Simpson, 1936, p. 10), and grossularite from Key Farm (Simpson, 1937, p. 32 j. 
Clarke (1930, p. 167) shows that the Jimperding Series forms the greater 
part of the northerly extension of the Darling Range. From the vicinity of 
Toodyay, the rocks extend in a belt which has been traced as far north as the 
Irwin River District (about 200 miles north from Toodyay) and Ninghanboun 
Hills (Simpson, 1931, p. 138). I have examined the rocks in the Irwin River 
District and they appear to be essentially the same as those developed at 
Toodyay. 
To the south of Toodyay the Jimperding Series has been traced through 
Clackline (the series exposed here is the upper portion of the Jimperding 
Series) to York, a distance of 30 miles. 
Previous to the publication of a paper by Forman (1937, pp. xvii.-xxvii.), 
the Jimperding Series had been regarded as the oldest formation in the Western 
Australian Pre-Cambrian shield, Forman (1937, p. xxv.) regards the green- 
stones ” of the Kalgoorlie Series as being older than the Jimperding (= Yil- 
garn) Series. Feldtmann (1919) describes a greenstone series at Bolgart (situ- 
ated approximately 20 miles north from Toodyay) and correlates it with the 
Kalgoorlie Greenstone Series and Forman considers that these rocks probably 
underlie the Jimperding Series (1937, p. xxvi.). I have examined slices of some 
of the Bolgart rocks collected by Mr. R. W. Fletcher and find, in them, the 
counterpart of rocks occurring as xenoliths in the granitic gneisses in the 
Toodyay District — this would be confirmatory evidence that the Jimperding 
Series is younger than the Bolgart “ greenstones,” were it not that similar 
rocks are interbedded with the metasediments of the Jimperding Series. 
