210 
IJOROTHY Carroll 
Vcitioii ot the r-)oiinyl)i‘ook saiul.stojies troni older beds or from a tori'aiu which 
was almost entirely granitic. 
(^arnet is angnlar to si>mewliat ronnd<'d, colourless grains is one of the 
ininor constitinmts, tor it occurs as odd grains only in four of the residues. 
Carnetiferous giieiss('s weiv oA'idtuilIy not present to any appreciable extent 
in tlu‘ ei’od<‘d tei'raiu, and (lie scant\’ gaiJU'l. in these I'esidues could have been 
jjassed on from a pre-existing sediment. 
Kyainte, siMiniaiiUej and sfau/rojite : Tlu‘s(! metamor])hic mi]H*rals oc('ur 
in the majority of tin- specimens, kyauil(‘ Ixung the. most [)vomiuent. The 
kyanite grains are usually well-worn, some b(*ing almost I'ouiul, but others 
are merely binkeii fragments with “sb'ps^’ due to Innaking along cleavages. 
8tauroliU‘ occurs in nunn than halt the residues as bright, brownish-yellow, 
strongly pleochroic grains, most of wliich are either angulai- or sub-angular. 
The pinsence of kyanil<‘, sillimanite, and staurolite indicates that at some time 
Pre, -Cambrian meta-sediments contrilmted materia! to the Donnybrook sand- 
stones, but in vicAV of the scarcity of these minerals, Avith the ('xet'jdion of 
kyanite, it is unlikely that llu'y wf're derived direiTly, i.e, thes(* minerals iiave 
come to lh(' Donnyhi'ook sandstones via soim* ('arliei' sediment. Xo sources for 
thes(' minerals are known in the Donnybrook district, but, as mentioiu'd iire- 
vioiisly, there is little detailed knowledge of th(‘ Pre-Cambrian complex in 
the vicinity. 
Xpmc/: Odd grains of gr<-en spinel w(*r(> found in four of tlie residues. 
Spinel is commonly present in residues derived from the Ib’o-Chnubrian in 
the soutli-A\cstei‘u pai‘t of \A estcrn Australia. These s])in{‘] gi'ains are W(!ll- 
worn, but otiun’wise arc typical. 
Mnscovifc: With ty])i(‘a] i>Iaty habit is only present in one residiun 
SIGNIFICANCE 
OF DETKITAL HEAVY MIXERAI.S 
DONNYBROOK SANDSTONES. 
IN THE 
It lias be(m staled {Saint-Smith, D)]L>, p. ^21) that the Donnybrook 
sandstone has hvau derived more or less directly, witli little transpoif, from 
tile weathering ef tin; PrivCanibrian rocks upon whifdi it rests. The liea\'y 
lesidues show that this is ratlier unlikely, foi' tlie nuiun'ais wliicli are kuoAVu 
to ha present in the underlying and suri'ounding Prc'-t kniibrhm rocks are 
pooi-ly re])resented in the r(*sidnes separated from tlu* sandstones. Moreover, 
a feature wliich was not known when Saiut-Smitli’s statement was made, is 
that most of the heavy miiU'ral grains lun'(‘ been lonmled by alu'asion during 
transport. Again, altlumgh there is a considerable numlier of minerals in 
the residues, xircon is the only one of flu’ non-opa(fue minerals Avhich is 
pres(‘nt in large quantities, and this suggests that part at least, of the forma- 
tion Avas (lt'ri\a*d from a pr(*-existiug s(Hlinu'ntary series. 
The assemblages ari* dominantly granitic as shoAvn by zircon, tourmaline, 
si)hene, and monazite. IMinei'als derived fi’om greenstones occur very 
sparingly, as do the metamorjihie minerals (tf Avhich the most conspicuous 
is kyanite, the most resistant of these to Aveathrring and alirasion. Andahr 
site, Avhich generally aeeompainh's these motamorphic minerals, is absent. 
Ihis suggests some transi>ort of the material, from the place of origin, for 
andahisite does not seem to he able to survive much abrasion. The almost 
complete absence of garnet and the scarcity of tourmaline in most of the 
residues is conclusive evidence that the source Avas not in the Donnybrook 
district, for garnetiferous and tourmaliue-bc'aring rocks are plentiful in the 
Preston Valley^ but these ro<'ks Aven* (wideiilly not uncovered Avhen the a/md.. 
