^Iaitland. — IVesfcni Australian Gcolof/y. 
219 
Witli regard to tiu' Natiual History of the Ore and Gem- 
bearing I’eginatites, tlu' late Mi'. H. I*. Woodward made the ini- 
]>oi'tnnt olfservation that th.e acid <lykes of tlu‘ (tr(‘eii])uslies Tinfudd 
gave evidence of metasonialic action aftc]’ solidification. 
A Ciiinpleto si'vies of rocks ^ Mllustrat iv(> of the gradual transition 
from a ];eginatil(' composed niostly of albite, through greisen, into 
a pure (piartz sjiecinieii, whieli when examined microscopically still 
exhibits the granitic structure, whilst toniunaline and cassiterite are 
the only associated minerals, which have so far been found to 
exist throughout the entire series” was obtained. Since the date 
of these observations in 1908, geologists have come to much th.o 
same conclusion frmn investigations carried out on the pegmatites 
of other mining districts in Africa, America and elsewhere. 
The general geological stviictnre of the State’s ])rincipal gold 
IM'odncing mining ciuitre, the Hast Ooolgardie Ooldtield, which has 
yi(‘l<led about one lialf of the total gold ont]mt of the State, has 
now l)een definitely establislied. The gold deposits of the pro- 
ductiv(' area, a))t>i'*’]'i'ijMely designated the '‘Golden Alile, ” are 
virtually confined to a groii]) of genetically related rocks, originating 
by the transmutation of a (jiiartz-doli'rite (diabase) which is tra- 
versed by a miinlier of acid dykes of variabh' \vi<lth a.nd of con- 
sidevalile length. Tlie gold d(‘i)Oslts are chiefly masses of crushed 
and fi'uctured country rock of grc'at horizontal extent and lenticiilai 
in shape, which, have bi'eu metasomatically replaced and impreg- 
nated With (|imrtz, iiyrites, and other sididiides, so as to form 
ex])loitable ore liodies without any well defined Avails. The gold 
occurs in the Honlder lodt's both in the native state and, as has 
been previously pointed out, in coniltinatlon Avitli tellurium. 
The most plentiful of all the tellurides of Boulder is the 
mineral (hlaverite, the telluride of gold, occurring in largt' len- 
ticular masses. One of the finest specimens, from the Golden 
Horseshoe Aline, consisted of a solid mass of Galaverite 6 inches 
long, 5 inches Avido, and a quarter of an inch thick. The telluride 
of mercury, Coloradoitc, is, with tlie exce])tion of Galaverite, the 
most widely distributed of all the tellurides. Alagiiifieent specimens 
have been 'met with during mining oiierations and masses several 
pounds in Aveight have been recovered. One of the finest siiecnnens 
from tlie ceiel.rate.l “Oroya Slioot,” which alone has produc-d 
mairly A8, 000, 000 worth of g(dd, consisted <.f a lens of (Mloradmt'' 
ubont 5 inches long, ^ inches wid<‘. and an inch thick, embedded 
ill a green sevicite schist, is now in the Geological Survey ( o-- 
lection. 
It is a remarkable c 
it Avere the home of the 
ircnmstance that though Boulder is as 
telluride minerals, fcAV if any crystals 
