228 
Maitland. — \Vcstcn> A ustraliau (ieoio<jy. 
TIu' geiiei'al instability of th<' Wosteni Australian avoa about 
this time is evideneed })y the fvai-turing of some of the eoastal 
areas by extensive faults, having apparently eoiisidevablc down- 
throws westward towards the Tudia]i Ocean. The Darling .Range 
fault Scar]', wiiich extends from the south coast northward over 
6 degrees of latitude, in all prol)ability forms tlie eastern boundary 
ot a series of sunken strijis of tlu‘ crust, of which the western 
wall is to be found 'ii that narrow ridge of ancient crystalline 
1 ‘ocks from Flinders to Geogra])he Hay. The fiiudaineiital rocks 
of tlu' islands of Rottnest ami Routman’s AbroHios possibly mark 
its northward extension. The shar]) ti-eml northwards of the IMur- 
chison River close to its mouth and the remarkable coastal indents 
near Shark’s Bay are suggestive of its prolongation in that direction. 
Shortly after the deposition of the Tertiary strata there came 
a period of temporary elevati(m, erosion and igneous activity. 
Extensive basaltic eruptions, probably through long conduits rather 
than great volcanoes, together with eruptions belonging to the 
iiitrusive ])hase took place in the western portion of the South- 
West Divirtiou and probably reached its climax during the early 
stages of the late Tertiary ])criod and became subdued if not 
surpressed at the end of this tinn^ j)vior to the Pli'istocene epoch, 
together wdth the formation of the Ooastal ('ave Limestone. 
The grim-lilack terraces of basaltic lava llows are to be seen 
on th(> sea coast at Pmiibury and elsewhere on the south coast. 
They may also bo seen in the (*a]>el River, at several places in the 
’.alley of the Bbu-kwood, and jiear Silver Mount betAveen the Warren 
and the Donnelly Rivers; they were also cut in tAvo of the bores 
put doAvn in the search for ipetroleum in the Wbu-ren River. The 
!)asaltic lavas, coA’ering an area of about 3000 square miles, remain 
as a fragment of tlie enormous flows Avhidi ])robably spread oaxu’ 
tln^ extreme south-Avestern ))ortion <.if Western Australia, and prol»- 
ably ov(‘r a much larger ])ortion mnv buried under the Indian 
Ocean aiul the sea along the south coast. 
In the inland area of the (Viitr.-tl Division there are many 
scattered veins and dykes of remarkaldy fi'esh dolerite, Avhich, as 
at Norseman, can l)c folloAved across country for seA’oral miles. At 
times they may be seen intersecting the gold-bearing deposits. 
These, may possibly Ixdong to the same period of Tertiary igneous 
activity as the Ijasaltic lavas. 
The only direct evidence of the geological age of the oliviue- 
dolerites at present known is met Avitli in the neighbourhood of 
Albany, Avhere a basic dyke is seen to intersect a member of the 
Plaiitaganet Beds, the organic remains in Avhicli proA'e them to 
be Miocene Tertiary. The dolerite dykes and basic lavas seem to 
