172 
Clakkk and Williams. — Geology of Darling Hange. 
Thoir mode of lield'OcouiTeiico is mentioned in the physiography 
section. Tlieie is little difficulty in mapping them fairly accu- 
rately in tlie steeper jiarts of the an^as; they can in many places 
be seen outcrop])ing for majiy chains, and in the intervals tlieir 
('(uirses are indicated by tlie almndance of c])idiorite boulders, hy 
Die dark red soil, and by the predominance of a ’white barke<l 
eucaly])t wliicli contrasts strongly with the dark trunks of the 
Man-i and Jarrali which jiiedominate on granite. However, on 
some of Die high-level terraces, boulders of granite and epidiorite 
are promiscuously distributed, jirobably by the river corrading late- 
rally during jiauses in the u}dift along the Darling Fault. On these 
areas, tliough mucli time was spent in trying to decipher the courses 
of tlie dykes, the mapping may be inaccurate. 
Potrologically, average sjiecimens of ejiidiorites from the t’wo 
areas are identical, and there apjiears to be little variety except 
111 coarsimess of giain. Hand-specimens are of a uniform dark 
green colour, the feldspars only showing clearly in weathered 
sj'ecimens. In a few specimens small grains of pyrite are visible. 
The grain size varies with the width of the dyke. The margins 
are in every instance fine grained and more or less slieared, differ- 
ing markedly in this respect from the acid and ultra-acid intrusions. 
Veins of e])idoto are common, lioth in the epidiorite itself and 
in the enclosing granite. It may b«‘ noted that irregular quartz 
\‘<dns of small size are not uncommon in the epidiorites. 
In thin section the rock is seen to consist of lath shaped 
crystals of plagioclase, set in a ground-mass of uralite. ^fuch of 
tlie ])lagioclase is zoned; in average composition it is a labradorite. 
The uralite forms a fibrous mat between the feldspars. It is 
])artly chloritised. There are traces of ophitic structure, plates 
of uralite enclosing the plagioclase ci’ystals. 
The three analyses A, B, and C below of epidiorites from the 
Darlington Area were made liy Mr. F. F. Allsop as part of his 
course in Geology in 1924. 
The analyses D, hi, and F of epidiorites from the Darling 
Itange near the areas under diseussion have been made available 
to us through the kindness of Dr. E. Simpson, Government 
Analyst and Alinernlogist, in whose laboratory they wei’e made. 
