THE GEOLOGY OE WINEGLASS 
BAY AND NEIGHBOURHOOD. 
(By A. D. Mackay.) 
Wineglass, or Thouin, Bay is situat¬ 
ed on the east coast ot Freycmet Penin¬ 
sula, in the midst of a strip of granite 
that stretches in a broken line from the 
tin districts of the north-east to the 
Hippolyte Rocks ofl Tasman Peninsula. 
It is probably one of the most pictur¬ 
esque spots m all Tasmania. A deep 
bay worn out of a granite mass, and 
surrounded by mountains from 1,500 
to 2,000 feet high, forms an ideal spot 
for both the artist and the scientist. 
It would appear that the flat between 
Wineglass and Hazard Bays was once 
covered with water. South Freycinet 
was then in much the same state as 
Schouten Island is now. Later, when 
the land had risen, sand was carried 
there and bound together by vegeta¬ 
tion. There is little doubt that the la¬ 
goon was formed by the sand dunes 
blocking the escape of rainwater from 
the hills and flat itself. 
The sand forming the beach at Wine¬ 
glass Bay is very white, and is compos¬ 
ed almost wholly of rounded particles 
of quartz, together with a little round¬ 
ed felspar, and scales of mica. Shell 
fragments are conspicuous by their ab¬ 
sence. Essentially it is a disintegrated 
granite. The sand at Hazard Bay is 
more yellow in colour, and contains 
more felspar, as well as numerous shell 
fragments. 
Our granite is considered to be of 
Lower Devonian age, that is, soon after 
the close of the Silurian. It occurs ex¬ 
tensively in the north and east, and 
underlies the whole of the West Coast. 
At Wineglass Bay the granite varies 
considerably. The typical rock is a 
fairly dark red rook, containing biotite, 
quartz, and orthoclase, both red, 
light yellow, and white. It is fairly 
coarse* in structure, the orthoclase cry¬ 
stals being generally about one-third of 
an inch in length. Crystals were ob¬ 
tained up to an inch and a half in 
length. One of these was almost cer¬ 
tainly a plagioelase, either albite or oli- 
goclase. Reversions of the normal or¬ 
der of crystallisation were noticed, hut 
may be due to decomposition of the 
felspar. The rock may contain tin, but 
in the absence of a rock analysis it is 
impossible to say. Also very little can 
he said about its structure without a 
microscope slide. 
The ton of one of the hills presented 
an interesting example of temperature 
erosion. Owing to the different heat 
expansions of the minerals quartz, fel¬ 
spar, and mica, the daily variation of 
temperature reduces the whole surface 
of the rock to a granular condition, 
when it is easily removed. 
The rock near the north end of the 
beach is not a red granite, however, but 
a grey. The typical rock is rich in bio¬ 
tite, while the* felspar is white or light 
brown to yellow. Reversions of the 
normal order are frequent. It also 
contains numerous veins of quartz two 
inches wide or le.ss. and of pink felspar 
in width up to a foot, and containing 
flat crystals of biotite an inch long. 
These veins preserve sharp boundaries 
and are frequently faulted. Besides 
these veins, numerous secretions were 
observed of an oval shape, and some 
tour inches across. They are of a line 
texture and dark colour, and consist 
largely of biotite. They are possibly 
the first products of solidification of the 
granitic magma. 
Between the grey granite and the 
pink normal granite is a red granite, 
which, like the rest, varied somewhat. 
It is very rich in felspar, and contains 
muscovite, as well as a little biotite. It 
is thus a ‘two mica granite. It con¬ 
tains green chlorite, which shows that 
decomposition has begun. It is coarser 
than the normal granite, and the ortho¬ 
clase is frequently twinned. In places 
it had a rounded structure, all the min¬ 
erals forming roughly equidnnensional 
grains. This is a grannlitic structure, 
,-md probably results from motion dur¬ 
ing solidification. 
At the southern end of the beach, 
near the camp, the rock is fairly fin®* 
It contains pink orthoclase, dark 
quartz, and bright yellow muscovite; 
also a brown decomposition product, 
and chlorite. Smhll patches, about six 
inches long, wore observed, in which the 
minerals had crystallised on a larger 
scale than the rest. Some of these con¬ 
tained vughs in which a drusy 
tnre was apparent. Reversions of the 
normal order were met with, but may 
only ho due to decomposition of the 
felsnar. . . ... 
The Coles Bay granite is very like 
the normal granite, but contains more 
red felsnar. It also contains light yel¬ 
low and white felspar, biotite, quartz, 
