259 
Chum Railway and Victoria Reef mines; andl six from the Big Hill railway 
tunnel, near Ravenswood, at distances of from 1,400 feet to 1,600 feet 
rom the grano-diorite contact. 
All these are lower Ordovician sedimentary rocks, and belong to the 
Bendigo series, founded by Mr. T. S. Hall, M.A., on the Graptolite 
fauna.* 
The primary object of the examination was to determine whether 
there is any indication of the deep workings of the above mines approach¬ 
ing the underlying granitic rocks. 
New Chum Railway Mine. 
A. Specimens from the 2^6-feet level. 
One of these is a dark grey, well cleaved slate, with a silky lustre. 
With the pocket lens some minute flakes of a micaceous mineral can be 
seen on the cleavage faces. It is very easily scratched with a knife. Under 
the microscope it is seen to be a typical fine-grained slate, composed for 
the most part of fine white flakes of a hydrous mica, which may here 
be called sericite, formed by the alteration of the original constituents, t 
Parts of the flakes form bands, in which they are parallel to one 
another, but between these bands the mica lies in all directions. The 
mica is intimately, associated with green chloritic material, which is typical 
of the slates, and' is not found in shales and clays. In addition, there are 
numerous minute clay-slate needles (rutile) and small black dots and 
patches, which are probably carbonaceous. There is a distinct cleavage 
developed. The slide as a whole presents a finely laminated appearance, 
due to the somewhat deeper colour of some of the bands. 
The other specimen from this level is a fine-grained grey sandstone. 
The quartz grains are large enough to be seen with the naked eye. There 
are a few cubes of pyrites scattered through the rock, which is fairly 
hard, but can be scratched with a knife. Microscopically, it is seen to 
consist for the most part of quartz grains, generally rounded, though some 
are quite angular. The quartz encloses little zircons, &c., and many 
fluid'cavities, and has all the appearance of having been derived from a 
granitic rock. Amongst the quartz grains are a few scattered fragments 
of a plagioelase felspar, which appear quite undecomposed—a remarkable 
fact, considering the great age of the rock, and that the felspar is one 
of the original constituents. It is polysynthetically twinned, the 
twinning being moderatelv fine. The only section from the 001-100 zone 
in the slice gave an extinction angle of 15 deg. This agrees with the 
measurements made by Dr. A. W. Howitt, who examined a large number 
of these rocks in 1893^, and indicates andesine. It is particularly interest¬ 
ing, as, being found together with granitic quartz, it suggests the existence 
of a pre-Ordovician rock similar to our Devonian grano-diorites. The 
remaining original minerals are a few flakes of muscovite, now much 
bent and distorted, some grains of zircon, a few broken crystals of brown 
tourmaline, and some flakes of chlorite that may represent biotite. 
These minerals are set in a “ paste” of sericite and chlorite, with 
numerous clay-slate needles and secondary quartz. In places there are 
patches of calcite. 
* T. S. Hall, M.A. The Graptolite-bearing Focks of Victoria, Australia.— Geol. Mag. Vol. VI., 1899. 
t Hotelling's, W. M. On the Origin of Some Slates.—Geol. May 1900. . 
t Notes on Samples of Kock collected in the 180 Mine at Bendigo.—Spec. Kept., Dept, of Mines, 
1893. 
