SoitE KvAX ITE-liEAHl X(i KOOKS EK0-\[ TELE EasTERX ( lUEDFiEEDS, 
W ESTEliX A CSTKALl A. -i 
for 1>, and in tlu' Quinn's rocks for K and ai)proxiinaIcly 5.(H)Oc ior 
F. In th<* Alt. Ivcnncth rocks this tiiiui'c lies ladwt'cn lOy; juid tor (\ 
while for rock 1) the' aniounl of alumina availai)l(‘ after satisfyino- the soda 
and potash is too small to pennit of the production of any aiidalusite. Tiie 
percentage of alkalies in most of the rot'ks is very low^ — in all but one specimen 
(D) beino- h‘ss tlian and of these the Nad) content is generally sliyhily 
in excess of the Kd)- The All. Kcmiieth ami Quinn's rocks all sliow an o\’e;'- 
wheliuinj^ (hnninance of AI^’() o\'er C'aO — and the total lime conhmt in all 
the rocks ('.\cept A is extreiiH^ly loAW 
Th(» hit’ll silica pmaamtaye, the predominance of alumina o^'('r linu' and 
the a]kali(*s, tlu> dominance of maj^'uesia over lime and the iow alkali content 
are criteria I'avoui'inu the sedimentai'v oriiiin ot a nietamorphit' rock. (20). 
The pi'csence of tai‘,u'(" i|uantities of andalusite or the allied kyanite or silli 
maiiiti* in i|Uart/ose crystallint* schists retlects tile existtaice ot an abundant 
alumina content and is usually a reliabh' indication ot‘ conla(d or thermal 
metamorphism ol' original sedimentary material in the case ol' andalusite, 
and of a hi^'her yradi* moi'c I'eyional type of metaniorphism wheri' kyanite 
or sillimaniti* predmninates. 
The (Utwei <ui<l Mf. Jjeouora Rods. 
As has already been sliown by tlu' microscopic descri[)tions, the (lamel 
Humps and Alt. Leonora rocks are similar in composition, tin* essential 
minerals ol' the fonma* bein^- puart/. and kyanite' with, minor (juantities o! 
rutile, and of the latter ijuartz, andalusilt‘ (and kyanite or sillinianite) and 
1 ‘utile. The ace-essories in each e-ase are. confined to a little mica, iron ore and 
deti'ital /ircon, with possibly a slightly increased (luantity of "rapliitic 
mateiial in tlu‘ Leomu'a rock. The ])ercenta^’i‘ of aluminium silicate minerals 
in both is ap| i'oximat(dy the same, ran^'in^' fT’om about 20^?^, to 20%. 
The microscopic^ texture and the miueralo^'ica I and chemical <-om])ositions 
of both the ('auud llump-^ ami tlu' Leonora rocks, then, an* (’sseiitially 
typical of metamorphosed .sedimentary rather than igneous rocks. They 
Avere ])robably both originally fairly puie, fiiu* grained argillaceous sand- 
stones (slightly ('arbonaceous in the case* of th(‘ lattcu*) deriv(*d from the 
mechanical denudation of an original granitic or acid sedimentary t(*rrain. 
AVithout <‘onsid(‘rably more* detailed field obs<u*\'ations little c-an be said re- 
garding the conditions of sedimentation but the material oi’iginally deposited 
evidently consisted of an admixtuiH* of tim* sand and clay, whicdi suggc'sts a 
comiiaratively rapid deposition with little mechanical sorting under such 
conditions as may be exp<'c((‘d to c^xist, say, in d(*ep water near the mouth of 
a stream channel. Tht* aj^parently locali.sed occuri-ences of the clay-])earing 
sands within what appear to la* (‘xtensive ferruginous sandy Inals may also 
suggest oi'iginal delta deposits. 
The pronoumaal titanium (mntent indicated by tlu; ahundaiua; of rutile 
in both tla^ t'amel Humps and the Leonora I'tx'ks, and i-etlected in the analyses 
of the laltc'r, was ])r()l)ably d(*rived in part from detrital rulii<‘ but also 
from tin* break-down of the original huieoxeiie and biotile in the sediments 
befoi'e and during dejxisition. Tbider increasing temperature (amdilions t'l'C'sh 
rutile has crystallised out contemporaneously with the d(‘\('lopment of the 
aluminium silieatc* minerals. 
The metaniorphism in both the Lamel Humps and the L(*onora areas 
apj)ears to he* essentially of the regional type due probaiiiy to deprcvssioji of 
these* [lortions of tin* earth’s erust into a zone of liiglier t<*mperatnre and 
