276 PROCEEDINGS OF SECTION C. 
fypical elvanor muscovite-bearing granite-porphyry occurs 
in the Silurian slates at Alberton, Mt. Victoria, where it has 
been cut through in the level of the Ringarooma Mine. A 
strong muscovite elvan with phenocrysts of quartz, alkali, 
felspar and lime-soda felspar strikes through biotite-granite 
on Schouten Main. Elvans are not uncommon on the Blue 
Tier. 
At the Silver Echo Mine near St. Helens is a wide dyke 
of aplite, part.of which passes over into pyrrhotite, and ulti- 
mately into pure quartz. Similar instances are recorded 
in petrographical literature. The transition appears to be 
characteristic of aplite and pegmatite dykes. The dyke-rock 
consists of quartz grains and small crystals of felspar sur 
rounding larger lumpsof quartzand orthoclase and oligoclase 
crystals giving isometric sections. Large crystals of biotite 
and irregular shreds of muscovite are present, the latter 
rather abundant. The dyke is in Silurian strata, and the 
lode portion of it has been prospected for gold and silver. 
It apparently has its source in the tin-granite. 
The granite at St. Mary’s Pass at its contact with Silurian 
slates, and for a width of two or three miles, has acquired a 
granite-porphyry facies. Specifically, it is hypersthene- 
granite porphyry, for phenocrysts of hypersthene are abun- 
dantly developed in it. The other porphyritic constituents 
are orthoclase, oligoclase-andesine, biotite, and quartz. 
These are cemented together by a ground-mass of allotrio- 
morphic quartz and idiomorphic felspar. This rock is unique 
in the Island. The specific gravity, 2-68-2-69, is low, con- 
sidering the quantity of hypersthene present. We have 
here an instance of a rock of the dyke division occuring as 
a marginal differentiation of a plutonic mass, and not in the 
form of a dyke. 
A normal granite-porphyry occurs on the road to Corinna, 
4 miles from Waratah. Large phenocrysts of ortho 
clase, oligoclase, and biotite exist in a coarse ground-mass 
of granular quartz, idiomorphic felspar, and biotite. 
Acip EFFUSIVES. 
The effusive forms of the granite magma in Tasmania 
consolidated prior to Permo-Carboniferous times, and are 
known under the names of quartz-porphyry, felsite-porphyry, 
felsite, and granophyre. It is not settled whether any of 
them were poured out at the surface as sheets of rhyolite 
lava; hence the American term “ aporhyolite ” is inapplic- 
able here. The trend of the evidence is so far rather in 
the direction of their occurrence as dykes, apophyses of 
