Clarke and Williams. — Geolofiy of Darling Range. 
175 
The eejitral zone, a]>out 4 feet wide, eoiisists of massive iine- 
ji’vaiiied salary (|uavtz eoiitninin^' scattered g'raiiis of cdear quartz 
of larji'ei' siz(‘ than tiie ground-mass. Cnder the mici'oscope tiie 
ground-mass is seen to he a hne-grained a^'^rejiate of ([uartz show- 
iup' no undnlose extinction. The scattered frai>'ments of clear (|Uartz 
exhil)it ]tronoum-ed undulose extinction, and ai’e similar in size, 
sliape, and strain structure to the quartz trains in the unreplaeod 
scricite scliist. The lar^'est (piartz g'rains ai)])ear to have been 
orisi'inal constitiumts of a schist the other minerals of wliicli are 
now almost entirely replaced by secondary (piartz. 
The central (piartz reef merj^es on either side into quartz rock 
with a well defined cleava^'e parallel to the schistosity of the 
vhole bi'lt, and containinji' lenses of much, weathered sericite schist, 
some only a fraction (tf an inch wide, also parallel to the schistosity. 
! ’roc('edinji' farther t(>wards tlu‘ ed^'O of the belt, tlu' amount of 
secondary (juartz is seen to become less and less, the rock ])assing‘ 
into a normal sericite schist. A network of (juartz veins cuts 
both the replaced and uiiret)laced rock. 
There are many similar (piartz reefs in the district, several 
of which are clearly continuous across epidiorite dykes, but few 
of the exposures are g'ood. The sheared ^ii'ranite g'eiierally weathers 
more rajiidly than the more massive enclosing' country, but tlie 
presence of the reefs is indicated liy the abundance of cpiartz 
floaters, often associated with frag'immts of schistose rock. I he 
larger jiegmatite veins give rise to soriieudiat similar (piartz blows, 
but the presence of fragments ot kaobnised fiddsjiar indicates that 
the underlying rock is pegmatite, whereas, if pieces of schistose 
rock are found, the underlying rock is a (piartz reef. 
After in\’estiga.ting the (piartz ri'efs of the Darlington Area, 
a visit was made to iiart of the Darling Fault Scarp east of 
Gosnells, Avhere there is a \'ory consjiicuous outci'op of ipiartz lock, 
This formation Avas found to be, in its essential features, iden- 
tical with the Darlington Area type, but develoi*ed on a much 
Inroer scale. The belt of slnniring varies in width from a fewv 
chains up to about a (piarter of a mile and trends ai>pi'oximateIy 
north and south, i.e., pai'allel to the Darling fault. The (piaitz 
reefs are several chains Avide, but vary in Avidth along the strike, 
lake the Darlington Area type, they are comimsed of massive 
angary quartz in the middle, and grade through schistose quartz 
into sheared granite on either side. The Avhole belt is tiaAiused 
by numerous quartz A'cins, disjiosed Imtli parallel to and across' 
tlie planes of schistosity. Beveral basii- dykes were oliserved to 
end abruptly at the edge of the shear zone. 
