170 
('i.AKKE AXD WfLT.iAAis . — GeoJofiy of Darling liange. 
(d) Kx]insui-('s of imisco^-ite aro rare, exco])t ‘witliln 
;■ small ari'a oast of the crook shown on tho v/ostorn sido of the 
Koloystono maj). Tho inlnorals are tnicvocliiK', oli^’oclaso, (juart/ 
and iniiscovito. 
(o) Quartz voins aro found cutting all tho ahovo inti-usiv('s. 
Tlioy const ituto tho oxtronio acid nioinbor of tho scries. 
All thoso rocks a])])oar to ropi'osont tho rosidual acid portions 
of tho granitic magma, and to have Ik'Oii intruded before tlio 
com])leto consolidation and cooling of the main mass of granite. 
A num])or of (piartz veins associated with regions of sluniring 
and fi'acture in tlio granite, and ]u-(‘S(‘nting well dofinoil conta<ds 
with tlu‘ latt(‘i' aro consiilori'd, for reasons to bo gi\'on in the 
section ‘‘(juartz roofs in shear-zones. ' ’ to b(> later than the ({iiar»z 
voins just montionod. 
4. Magmaiic Ilintory. -The fmituros notcul abov(‘ may In' to]i- 
tativoly ascrilnMl to tho following series of events: — 
-Magma of granitic com|)ositiou welled u]> into tho zone of 
crystallisation. Tho earliest ininonils to form wore biotito, plagio- 
claso and quartz. Tho cimtros of ci'ystallisation of tho biotito, 
])lagioclaso, ajid (piartz ci-ystals ajiiioar to have boim closely simced, 
giving ris(‘ to a large* numln'r of small crystals. Alicrocline began 
to crystallise at more- widely separated points, and grew to 
conijiai'atively lai'ge crystals, whi.h often included a number of 
small oligoclase, (piartz ami biotito individuals. This microedine 
is reiu'esented l)y the phenocrysts in the rock now exjiosed. The 
])!'oc(‘ss continued until the crystallisation of ])ortions of the magma 
was a])])roaching completion. 
Kenewal of the activity of intrat('lluric forces then caused the 
furth(‘r movemi*nt of this paidly crystallised magma, and its in- 
fection into tlu' position the granite now occu])ies. During this 
movenu'nt mixing of magma fractions in various stages of crystal- 
lisation took ])lace. Those portions in the more advanced stages 
of crystallisation develojied a gneissic sti'ucture, l)ut those portions 
in which but little crystallisation liad taken jdace could not retain 
th(‘ inpiress of tlu* renewed mo\'('inent, and solidified as massi\'e 
r(;cks. The ])rogressive stages of crystallisation are rejiresented 
by tin* gradations from gneissic and jmrjih vritic to even-grained 
massive granites as exjmsed to-day. Under these conditions no 
(b'finite boundaries \vould exist between the diffen'iit types of 
granit(\ The more rajiid cooling of the magma in the second 
magma chamber — its present position — was responsible for tlie 
