IGNEOUS ROCKS OF TASMANIA. 29% 
with — sign. Besides orthoclase felspar and elaeolite, or 
nepheline, egirine augite is abundant, also a peculiar biotite, 
and melanite garnet, in beautiful crystals (110), often with 
splendid zonary structure, and in grains as well. The biotite 
has a plainly oblique extinction, as occurs mostly in the 
alkali rocks. In addition to the fresh elaeolite, or nepheline, 
there are natrolitic pseudomorphs after sodalite. You 
would lay me under an obligation if you could send me a 
few larger specimens. Compared with the numerous elaeo- 
lite syenites known to me, this Port Cygnet rock has decided 
characteristics of its own.’’* 
On the same beach, near the Regatta ground, holocrystal- 
line tinguaites are common, carrying nepheline, egirine- 
augite, hornblende, and abundant biotite. Some distance 
south a remarkable tinguaitic dyke-rock is met with, greenish 
in colour, and containing glistening layers of tabular crystals 
ef sanidine. Under the microscope the green tint was 
found -to be due to a fluidal mass of needles of aegirine, and 
the rock was referred to aegirine-trachyte. This was also 
transmitted to Professor Rosenbusch, who has replied, as 
follows :—‘ No. 83 I would call a tinguaite-porphyry, or, 
perhaps better, sdlvsbergite-porphyry ; but I have no objec- 
tion to your name, although I can scarcely believe the rock 
was effusive. There are phenocrysts of sanidine, and a 
strikingly light-coloured aegirine (and aegirine augite), with 
a:c up to 20° in 010, in a ground-mass of felspar and 
aegirine needles. Staining in the colour-bath shows the 
ground-mass to contain very small quantities of nepheline. 
The aegirines often contain a kernel of amphibole, with a:c 
equal to 17°. It is noteworthy that the sanidine pheno- 
crysts often contain aegirine as an inclusion. TI also saw 
melanite twice in the same relation. The rarer elaeolite 
minerals are more plentiful than in No. 84, but I could not 
determine them with certainty. There is also some titanite 
present.” 
The presence of melanite garnet is a strong characteristic 
of rocks of the whole series, and different varieties of it 
appear to exist. 
In 1889, Mr. O. E. White and Mr. W. A. M‘Leod de- 
scribed a new variety of garnet, to which they gave the name 
of Johnstonotite, occurring in a trachytic dyke-rock south 
of the Regatta Ground. This rock, too, has been submitted 
te Professor Rosenbusch, who writes:—‘‘No. 84, with 
the. beautiful crystals of garnet (211), I would call a 
garnetiferous mica-sdlvsbergite. Apart from the garnet 
* Petrographical Report. W.H.T., 1900. 
