304 . PROCEEDINGS OF SECTION C." 
the bulk of the felspar is orthoclastic. But the applica- 
tion of the term to our tin granite, which is not porphyritic 
but. hypidiomorphic in structure, appears to me a mistake.. 
Our biotite granites are often porphyntic, with large ortho- 
clase felspars, but the rest of the stone is not a ground-mass, 
nor is there any porphyritic quartz. We cannot, therefore, 
call them granite-porphyries, only porphyritic granites. On 
the other hand, the hypersthene rock in St. Mary’s Pass is a 
true granite- porphyry, and the dykes at Mt. Bischoff may be 
cailed topazised quartz-porphyry, though more strictly the 
rock is the quartz-porphyry facies of granite-porphyry dykes 
(elvans). 
(c.) Diabase or Dolerite.—-If petrologists would only agree 
~ to call the fresh rock dolerite, and the chloritised rock dia- 
base, most of the Tasmanian occurrences would be dolerite. 
Here and there are patches which are chloritised ; the dykes 
in the East Coast granite are invariably so. The older dia- 
base rocks in the Magnet district carry large quantities of 
chlorite. Dolerite is a very convenient term for those holo- 
crystalline plagioclase-augite rocks which have never reached 
the surface as lavas; but so long as American and Conti 
nental authors adhere to the name diabase, the latter will 
have to be retained. Continental petrographers keep the 
term dolerite for the holocrystalline parts of thick lava- 
flows. At present diabase has it on the voices, but a wait- 
ing attitude is the correct one, and during the next decade 
we shall see how petrographical opinion shapes itself. The 
Tasmanian diabase occasionally varies into gabbrolike 
forms, e.g., summit of Mt. Faulkner, and then there is barely 
any difference between it and gabbro, for diallage is no’ 
longer considered an, essential of the latter. The structure 
here is that of a plutonic rock. 
(d.) Gabbro-amphibolite and Gabbro-diorite-—Our gab- 
bros have now and then suffered dynamometamorphism 
along a line of contact with granite, sometimes becoming 
amphibolitic and laminated. When they have become 
schistose in character, and a secondary hornblende is de- 
veloped in them, I propose to use the term gabbro-ampht 
bolite. When the development of amphibole is unaccom- 
panied by any cendency to a schistose habit, the rock may 
be called gabbro-diorite. | For example, the hornblende 
schist of the Rocky River would be gabbro-amphibolite; the 
massive hornblendic gabbro near Mt. Agnew would be 
gabbro-diorite. 
(e.) Limurite——This contact-rock is omitted by Rosen- 
‘busch from his text-books, probably as lacking the char- 
