208 
structure. The whole rock has been much jointed, the joint 
planes cutting sharply vhrough groundmass and boulders in- 
diseriminately. At Williamstown the metamorphism has 
been much more severe, so that in many places the rock be- 
comes a somewhat friable mica gneiss. All the pebbles are 
much elongated, and in certain places it is diffieult or im- 
possible to distinguish where the pebble ends and the ground- 
mass begins. 
The rock under consideration is that which forms the boul- 
ders in the Inman Valley occurrence. 
M a:cir.o0ss oopvadsdk åra tems. Dense; hard; 
greyish quartzite of rather fine grain. Тһе individual con- 
stituents cannot be satisfactorily made out, but a black mine- 
ral is present. 
Microscopoc character sA < completely 
granulated mass, consisting essentially of quartz, felspar, 
muscovite, and ilmenite. More than 50 per cent. of quartz, 
forming a perfect mosaic. Well-marked foliation. Strain 
has been relieved by perfect shattering, so that undulose ex- 
tinction is not marked. Feispar is slightly decomposed and 
is all untwinned orthoclase, with no triclinie felspar at all. 
Muscovite about as abundant as felspar in granular aggre- 
gates and largeish plates. Fair amount of ilmenite in scat- 
tered, irregular grains. Numerous small crystals and grains 
of zircon and rutile, the latter exceptionally dark in colour. 
There is also a very little dark blue-brown tourmaline. 
(Plate xxxiv., fig. 3. 
xxxvi. Ln man Var Т ену, Groundmass of the 
above conglomerate. 
Macroscopic characters —As noted above, 
this groundmass is coarse in texture and gneissic in structure, 
with well-marked “auge” of quartz. It is very strongly 
micaceous, and a very conspicuous feature in it is the great 
abundance of ilmenite in large plates and grains. In some 
places the groundmass of the conglomerate contains nearly 50 
per cent. of this mineral. 
Microscoprtc characters.—Consist mainly 
of quartz and muscovite. The former occurs in large grains, 
showing evidence of crush in shadowy extinction and the 
presence of a “halo” of finely granulated material. “Augen” 
structure is even more marked than it is macroscopically. 
Much of the quartz is opalescent by reflected light. Some of 
the muscovite is in large plates, but most of it occurs in the 
form of minutely granular aggregates, in the most thorough- 
ly comminuted parts of the rock. There is a good deal of 
ilmenite in irregular granular aggregates. Its lustre by re- 
flected light is rather bright, and suggests magnetite, but 
the alteration around the edges into very typical “sagenite” 
> c smt 
