274 PROCEEDINGS OF SECTION C. 
At St. Marys the granite, at its contact with the Silurian 
slates just E. of the bridge on the road to the Pass, forms 
granite porphyry, and the dark granite of the Pass itself 
is essentially the same rock, viz., a microgranitic ground- 
mass of alkali felspar and quartz containing phenocrysts of 
alkali and soda-lime felspars, quartz, and hypersthene. This 
is the granite-porphyry modification of granite, occurring 
sometimes towards the margin of large masses. As differen- 
tiation has taken place, it belongs properly to the dyke and 
complementary rocks. 
The George’s Bay rock is quartzose-biotite granite, with 
more quartz than felspar. At Moorina the biotite-granite 
is composed of orthoclase + plagioclase + quartz + apatite. 
At the Arba Tin Mine it is a muscovite-granite = ortho- 
clase + plagioclase + quartz + muscovite (with very vivid 
interference colours, probably lithia mica) ; the quartz con- 
tains a few tourmaline prisms. At Weldborough we have 
a coarse biotitegranite containing much quartz and 
dominant orthoclase. There is a good deal of radiating tale 
in this rock. At Gould’s Country the granite contains 
biotite and muscovite, and orthoclase poikilitic with quartz 
is the dommant felspar. 
The granite at Mt. Heemskirk on the western shore of 
Tasmania is also a biotite-granite, with the addition of mus- 
covite locally, and often contains similar porphyritic felspars 
to those in the granite on the east side of the Island. On 
the Lucy River biotite-granite also occurs, containing some- 
times alittle muscovite, and consisting of orthoclase + plagio- 
clase + biotite, with accessory apatite. The structure is 
often graphic. 
At Wombat Hill, 5 miles from Waratah, biotite-granite 
occurs with dominant orthoclase and a little hornblende. 
At the Heazlewood, too, is a large-grained biotite-granite, 
with a little yellowish-greenhornblende. At the Hampshire, 
2 miles from the railway, the biotite-granite is coarse; the 
dominant felspar is orthoclase, and the structure is highly 
graphic and perthitic. At Golden Hill, Middlesex, the 
granite is the biotite variety, and its felspars are greatly 
pinitised. 
Augite-granite, so far, is not recorded, but some of the 
augite-syenites of the Heazlewood District tend in that 
direction by an increase of quartz, and pass over into 
granite. 
Hornblende-granite is rare in the Island. It has been 
found so far, in sitd%, in only one district, the Heazlewood, 
where, by insensible gradations with diminishing qvartz, it 
passes over into syenite. At Bell’s Reward, south of Jupp’s. 
