296 PROCEEDINGS OF SECTION C. 
The rocks are developed in surprising variety, and have 
an unusual facies compared with elzolite syenites and pho 
nolites in other parts of the world. Beyond a preliminary 
study* nothing much has been done in the direction of their 
definite nomenclature, which is a subject inviting attention. 
They have been broadly assigned to three physical groups— ~ 
soda-syenite, soda-aplite, soda-trachyte. Further examina- 
tion has resulted in a tentative division, as follows:— 
Alkali Syenite group— 
Phonolitic trachyte. 
Alkali Syenite. 
Elaeolite Syenite growp— 
Trachytoid Phonolite. 
Haiiyne Phonolite. 
Sdlvsbergite. 
Tinguaite. 
Tinguaite-porphyry. 
Klaeolite-Syenite. 
Theralite growp— 
Nephelinite. 
N.B.—It is very doubtful whether volcanics oie occur ; 
hence, the terms trachyte and phonolite are provisional. 
At the Regatta Ground a grey medium-grained plutonic 
rock is exposed on the beach, varying a good deal in places, 
but all the varieties evidently belong to one plexus. The 
coarse variety is an elaeolite syenite, rich in biotite; 
pyroxene is apparently absent; idiomorphic natrolitic 
pseudomorphs after nepheline are abundant. A fine variety 
carries quartz, garnet, and egirine-augite; this is an alkal+ 
syenite, and must be allied to nordmarkite, but no horn- 
blende is present. This rock has its effusive, or probably 
dyke, equivalent, a (soda) hornblende-quartz holocrystalline 
trachyte on the back road from Lymington (near Marten’s). 
This is a striking rock, light grey, resembling a fine-grained 
granite, and carrying porphyritic glassy felspars, often with 
rhomb-shaped sections (anorthoclase). A specimen of one 
of the elaeolite syenites south of the Regatta Ground was 
sent to Professor Rosenbusch, who communicated the results 
of his examination, as follows:—‘‘ No. 87 is a medium to 
fine-grained elaeolite syenite. It is not. at all poor in elaeo- 
lite, or nepheline, in idiomorphic, somewhat dusty crystals. 
In hexagonal cross-sections, I observe the interference figure 
a: On Haiiyne-trachyte and allied rocks in the districts of Port 
Cygnet and Oyster Cove. W.H.T. and W. F. Petterd. Proc. 
Roy. Soc. Tas., 1898-9. 
