IVTaitland . — IVesirrn A nstraUan G('olo(/y. 
22 ) 
from tlivoe to six wi^U', wiiit-h av(‘ra}<,'p aixmt 82 pov cent of 
cinomito. Tli<' siM-pentine appears to liav'c been dei-ive<l from eitliei’ 
a pvt'oxc.nil(‘ or a pi'ridoiite in whicli the clironiite is ]jres(‘iit as 
a ])rimary constituent. Whether these lenses of chromite were 
segregations from the direct cooling of an igneous rock, or owe 
their presence to replacement since consolidation, yet remains to 
be investigated. 
The occurrence of the mimn-al alnnite (a sulphide of aluminium 
and potassinin ) at Kanowna, in the Kast Coolgardii' (ioldfield, in 
an aureola of alteration surrounding a mass of acid j)or])hyiT at 
Ked Hill intruding the metamoi'])liic stMlinumls, is of considtu'able 
scientific importance. The alnnite lua-urs in veins varying from a 
mere tliread u]) to two feet in thi(d^iu‘ss, which may r<'i)reseiit 
off-shoots from tlie poiphyry. Tin* miinn-al may owe its origin to 
[K'rcola ting Avater charged \vith siiiphuric a.oid, resulting from the 
decom])osition of pvriU's, or by sulphnrous exhalations from an 
extinct volcano acting on fc‘ls]>a1liic rocks. The lied Hill poi'])hyry 
.and the satellitic <lykes foiin tlu' denuded relics of an ancient 
eruptive vent. 
An nmisual and uni(|m‘ type* of an alnnite deposit, and one 
not recorded from any oilier country, has been nu‘t with at Lake 
l^roAvn, near lbirraco[)]'in. Thi‘ deposit occurs in one of the chij 
pans Avliich form part of an ancient watercourse draining into 
tlie Avon Iliver. Tlie matenal of wliicli the deposit is made up 
is in till' form of a juiwilei' consisting of ([iiart/., kaolin, mica, 
fels])ar, salt and gypsum with sonu‘ organic' inattei', and has been 
foumi to contain ~>0 pi,*r cent <n‘ more of alnnite. 
The niiiieial ]>yrites, reported liy Ibiwley as occurring in 
some of the adjacent rocks, is jirobably tlie original source of 
the siiljihuric acid rc‘(|uired for tlu' foi'inatioii of the alnnite. 
It Avill have been ai>parent from, the earlier ])orti(ni of tlie 
address that Western Australia presents many gc'ological proldems 
{‘f alisorbing interest upon wliich research is recpiired, but there 
is one connected Avilh that gi-eat climatic revolution in tin' history 
(f its Middle Ages (alnmt dO or 100 million years ago), resulting 
in a Avides]>read refrigeration of a very large' ]>ortion of the 
b’tate, whiidi pnA’idos almost as strong atti'actimis as tlie ]iages 
of roina n "e, viz, , the Pornn i-( ki rboo 1 1 eroiis ( fiaeia t i on . 
No pc'riol pei-liaj'S in the geological history (tf the State is 
(T such imporlainm and appeals S(* pOAverfiilly to our senses or 
comes into sm-h dose and intimate contact with our material 
wants and enjoyment as that; of tlm Ik'rmo-Carboniferoiis, to AvhicU 
Ih.e Collie and Irwin IHver coalfields lielong. 
