^rAiTLAXD. — -Trcsfri'/i A ustraUan Geology. 
213 
(It'oeiuleiit iniiU'val pvodiu'ts than n]K)ii tlio c'Oinnio(Uties of 
aiiv otlu'v uatuval 
Tu tlie l'n)a<] area of tho Stato ])U‘tty nearly all geologieal 
systems have tli(‘ir re])reseiitativ(‘s in the ]-ocks vhich huihl up tlio 
territo ry. 
One of tlie most fiindameiita.l featui'es in tlu‘ ^'eulogy of 
Western Australia is the similarity in structure of its I'oc'ks 
to those of tlie couutri(‘s bordering the Indian Ocean, vi/., 8mith 
Africa, ^Madagascar, Tudia and the Xetherlauds Indies, This notc- 
■\voi'thy r(‘seml)laiice is paralhded in the vliole of the geological 
formations develoji'Ml in the State; a close association ’whicli being 
n fleeted in the similarity of tyju's of Western Australian mineral 
deposits is of considerable economic as well as scientific interest. 
Tlie Pre-(kunl)riau Kocks occupy nearly 400,000 stpiare miles 
out of the 07b, 020 which constitutes the area of tlie State, and 
contain witiiin the boundaries ]uaciically the whole of the metallic 
wealth of the State, of which about £100,000,000 havi' been raised. 
These Tfl'e-Oambrian rocks, from the staud])oint of their charactm-, 
the complexity of their structural relationships, their develo}unent, 
their origin and the idianges they have nndm-gone, contain the 
matmials for probably onedialf of the geological history of tiie 
earth. There are prolialdy few parts of the Australian Continent 
which can Imast of a finer develoimumt of these rre-Cambrian 
rocks than Wi'steim Australia, and tlic variety of lithological ty]ies 
bids fair to make the State a classic fiidd for petrological research. 
It is to these Pre-( 'ambrian Formations that geological attention 
has naturally lieen princi]>ally devotial on account of the economic 
possibilities which such rock associations offer. Investigations have 
shown that esiiecially iiotewortliy nmoiigst them is the piesence of 
huge coupiosite liatholiths of granite and gneiss with some crys- 
talliiie schists resulting from the ti'ansmutation and imvtial assimi- 
lation of the granite, together -with a grouj) of schists, mostly 
altered sediments, and rocks of an allied uaTure, as well as their 
more or less coiitemjioraneous igneous associates. These igneous 
rocks, principally of basic comiiositiou and of somewhat different 
g'eological types, have undergone extensive and widesjiread meta 
morjiliism, itroduciug rocks of the epidiorite ty]ie on the one hand 
and the caiiionated greenstone on the other. Cltradtasic io(ks, 
represented by seri'cntine, jicrididite, pymxeiiite, and their tramw 
uuited derivatives, are also of frepnent occurrence. 
The distribution of the Pre-(iunbriaii Kocks resembles some 
what, as may be seen by an inspection of the geological map of 
the State, a sea of granite, stmhhul with great islands of green- 
stone and their associatiul sedimentarics- -an arrangement stated 
to have resulted from crustal foundering. 
