Microscopical Society of Victoria. 
89 
well as the colourless acicular crystals, which are plentiful in the 
ground-mass, and also occur in all the porphyritic crystals are 
probably all apatite. 
(/). Pyrite . — Ordinary iron pyrites occurs in grains and masses 
of grains throughout the dykes, but is nowhere plentiful. 
( g ). Chlorite . — I have mentioned a variety of chlorite as 
occurring constantly, associated with the triclinic felspars. Some 
variety of this group also occurs throughout the samples, often as 
no more than a green pigment, and is an alterative product of the 
hornblende. 
I may, in conclusion, say a few words on the granitic rocks in 
which these dykes occur. I prepared slices from samples collected 
near where the large dyke crosses Granite Creek, and others from the 
adit of the Mt. Budgee Gold Mining Co. The rock is a crystalline 
granular compound of : — 
(a). Felspar . — Of this mineral there are two varieties; one 
monoclinic, and the other triclinic. Usually the former is larger 
in dimensions than the latter. It in fact fills in large spaces, and 
thus conforms to the outlines of other minerals. These felspars 
are not twinned, and intergrowth with other felspar is rare, and 
confined to isolated lamella?. I have observed, however, that 
where the crystals had suffered from alteration there often 
remained margins of perfectly clear and perfect substance, while 
the interior was extensively kaolinised. The margin, in one instance, 
was partially banded, and I regard this as a case of envelopment 
of orthoclase, by some triclinic form. In addition, there are 
always more or less of smaller and well-crystallised tri clinic felspars, 
which from the angles formed in them by the planes of vibration, 
I judge to be probably of the group albite and oligoclase. I 
observed in a slice from a sample from the Mt. Budgee adit that 
the felspar was entirely triclinic, and of the above character. 
The alterations of these felspars are all more micaceous than 
kaolinic. Many of the crystals and crystalline masses are almost 
wholly converted into micaceous substances, composed of very 
minute flakes ; in fact, mere scales, but locally larger, and these 
are either arranged side by side or divergently. Their clear and 
colourless condition, and their bright chromatic polarization and 
optical characters, are those of muscovite. As, however, they 
arise from the alteration of triclinic felspar, they should be 
