J. R. H. McWhae. 
58 
the variety tibrolite oceiirring in very tine ])rism 3 associated with elongated 
magnetite grains. It appears to be developing at the expense of biotite 
(23, p. 98). Muscovite, iron ores, zircon, sillimanite, and felspars, the latter 
occurring only in specimens from near the intrusive granite, are accessory 
minerals. 
The avei-age composition is cpiartz 40 per cent., biotite 15 per cent., 
eordierite and pinite 15 ])er cent., sericite 15 to 20 per cent., fibrolite is 
sometimes as high as 10 per cent. 
(iii) Garnet schist.^ — A highly weathered whitish to brownish schist 
witli numerous efiuidimcnsional, dark brown limonitic grains pseudomorphic 
after garnet (the original crystalline form being retained) has been noted 
only in th(» lire-clay (juai'ry at Clackline. The rock has a maculose tex- 
ture with about 40 per cent, of limonite pseudomorphs after garnet three 
to five mm. in diameter, the remainder of the rock being fine-grained 
quartz and mica. 
Origin of thr wivn sc-hh (^. — These mica schists are thought to be. the 
result of extreme regional nudamorphism of sandy argillaceous sediments or 
possibly glauconitic shales (20, p. 13). 
Silliinanile-(|uartz-cordicrito-hiotito schists were probably formed at 
this stage of high regional metamorphism, with a tendency of the biotite 
to change to fibrolite and magnetite. Proliably the original composition 
of the sediment deteianined whether the schist formed therefrom Avas 
high in sillimanite, mica, or garnet. 
The sillimanite clay (juarried at (Tackline is thought to be a highly 
kaolinised Auiriety of sillimanite-rich mica schist from the kaolinised zone 
below tlie laterite, i.e., the result of weathering, and not the result of 
hydrothei'iiial metasomatism at the time of the intrusion of the Younger 
Granite, as are the sillimanitic clay deposits at WilliamstoAvn, South Aus- 
tralia, (1, p. 10). 
Considerable retrograde metamorphism probably took place as a result 
of the intrusion of the Youngei' Granite. '‘Hot alkaline potash solutions ’’ 
(26, j). 13) metasomatised the sillimanite and cordierite producing sericite 
after sillimaniU; and pinite after cordierite and some of the biotite Avas 
altered to muscovite. 
{ c ) Metajaspilites. 
(i) Banded <iuartz-magnetite-garnet-amphibole rocks have been des- 
cribed by Miles (17, p]>. 325-328). Megascopically they are heavy, dark 
green, medium to coarse-grained, gTanular, coarsely banded rocks. The band- 
ing is considered to be a relict structure of the original bedding. In (19956) 
there are tliree ly])e.s of bands: (1) (Quartz-rich with subordinate pale green 
amphibole (gi'ain size of both t wo to three mm.) ; (2) a layer in which pale 
green amphibole predominates and wliicli has subordinate dark amphibole and 
garnet and rare magnetite; (3) a layer of red garnet (1 mm. diam.), dark 
amj)hiboIe ( two to three mm. diam.) and magnetite ( half to one mm. 
(diam.) with subordinate ])ale green amphibole. 
The rock has a coarse granoblastic striTctnre. The quartz forms a coai*se 
mosaic and has gas-liquid inclusions and sometimes slight undnlose extinc- 
tion. Xenohlastic inclusions of amphibole sometimes occur in the quartz. 
