Microscopical Society of Victoria. 
87 
soda-lime varieties, the mica would, in all probability, were it 
possible to examine it chemically, prove to have soda or lime as 
its mineral base. 
(b). Hornblende .—The hornblende seen in the thin slices bears 
out the inference to be drawn from the fragments standing out in 
relief on the weathered rock surfaces. It usually, occurs in ill- 
defined prisms or lamellae* but in some few cases perfectly formed 
in crystalline outline. Its colour in the slice varies from dark 
blackish green to greenish yellow. The section is generally 
strongly dicliroic. The crystals are frequently twinned according 
to the usual hornblende law. (-Fig* 7.) 
In samples taken from a large dyke near the Bulgoback Post 
Office I found the hornblende in more or less well-formed crystals 
of the ordinary form ; the sections became translucent in shades 
of yellowish brown, and the crystals had a somewhat glassy 
appearance. In other slices from this dyke I found the hornblende 
in long and rather bladed crystals of a greenish or yellowish 
colour. All this hornblende is strongly polycliroic, the angles formed 
by the plane of vibration, with the prismatic cleavage in sections, 
approximately parallel to the axis c, I found to be 12° 30' in two 
of the most satisfactory measurements, and 14° 30' in a third. 
In some instances, when the hornblende occurred as greenish 
rather fibrous lam el to the angle was unusually high, two 
instances giving 28° 30' and 32° 30 respectively. Such angles 
are suggestive of pyroxene, were it not that the slices of this 
minerial are strongly dicliroic. The many observations which I 
have now made as to the analogous groups, pyroxene and amphibole, 
lead me to see that there are apparently varieties in the latter, 
which represent diallage in the former, and that their occunence, 
together with triclinic felspar (anorthite or labradorite), produces 
a rock which may be well termed amphibole gabbro. 
Where the hornblende has a crystalline form the characteristic 
prismatic cleavage is well-marked in sections perpendicular to the 
prism. 
The amount of included substance (ground-mass), is large. It is 
either in rounded grains, or where central, often has the form of 
the hornblende crystal. It would seem that the central neucleus 
of the hornblende crystal has been a portion of the ground-mass 
round which the crystal has formed, and it must have been plastic 
