IGNEOUS ROCKS OF TASMANIA. 27) 
should prefer to see the term granitite dropped altogether, 
and muscovite-granite, biotite-granite, hornblende-granite, 
pyroxene-granite used as sub-divisions of granite. 
Mr. Hogg restricts the term granite to plutonic felspar- 
quartz-biotite rocks in which the dominant felspar is mono- 
clinic; and when this felspar becomes the subsidiary one, 
he uses the term granitite. But seeing that there is a very 
general agreement among petrologists to classify and name 
normal granites according to the coloured constituents, I 
thing it is a pity to break loose from this arrangement and 
begin to base the nomenclature upon the crystallisation of 
the felspars. Moreover, if such rocks are to receive a name, 
it is undesirable to adopt “ granitite,’ which has already 
been widely used in a different sense. The rocks referred 
to resemble the passage-rocks between granite and quartz 
diorite, called granodiorite by some American petrologists, 
namely, diorites, which vary into granite by the addition of 
orthoclase. G. F. Becker* described a quartz-diorite or 
granodiorite as containing plagioclase as an essential felspar, 
and considerable orthoclase——next to plagioclase the most 
abundant constituent is quartz—hornblende and biotite 
occur sparingly. Mr. Hogg’s notice of the increase of 
plagioclase felspar in certain granites receives expression 
where it is most pronounced, in the classification by coloured 
constituents, for the addition is most marked in the horn- 
blendic granites. Mt. Roland is one of the localities in Tas- 
mania where these passage-rocks occur. Plagioclase is in 
excess, and hornblende and biotite are in nearly equal pro- 
portions. 
In Tasmania there are everywhere signs of underlying 
granite. Its age is generally regarded as Devonian. We 
have an instance of it being intrusive in Upper Silurian 
rocks at Middlesex, and on the East Coast we have proof 
of its denudation in Lower Permo-Carboniferous times. The 
granite on South Mt. Darwin and at Mt. Farrell has a some- 
what more ancient look, but it, too, was apparently sub- 
sequent to the Silurian. 
At Mt. Cameron, the Blue Tier, Ben Lomond, and all 
down the East Coast wa St. Marys, Seymour, Bicheno, 
Freycinet’s Peninsula, Schouten Island, Maria Island, to as 
far south as the Hippolyte Rocks there are exposures which 
must be assumed to be connected underground. Over this 
area nearly all the manifold types characteristic of large 
granite massifs may be met with. I do not know that we 
have the granite proper of Europe, namely, quartz + 
* Geology of the Yukon Gold District, 1898, p. 229. 
