IGNEOUS ROCKS. 3 
labradorite ever occur in the granitic compound, the species of triclinic 
felspar, often observed in it and generally supposed to be albite, having 
been found to be “oligoclase.” The ingredients commonly considered 
as essential for granite are, nevertheless, sometimes replaced by others ; 
and we consequently find many transitions from granite into other rocks, 
such as granitic porphyry, quartz porphyry, protogine (talcose granite), 
schorl rock, felstone, felspar porphyry, syenite, and greenstone: these 
latter rocks passing into the porphyritic, syenite, and greenstone groups, 
or the basic igneous rocks of the Plutonic division. Some of the speci- 
mens illustrate these transitions. EADE T 
SYENITE is a granular compound of orthoclase and hornblende. 
Porpnynrite consists of a felsitic matrix, with individual crystals 
of felspar (oligoclase or orthoclase), mica, or hornblende. 
GREENSTONE is a compound of some species of felspar (not ortho- 
clase) with hornblende, hypersthene, or augite. This class of rock is 
never found in the form of genuine lava, but always, more or less, shows 
its Plutonic origin, in which probably consists the whole difference (not 
very great) between it and the basalts, or the basic igneous rocks of the 
Volcanic division. It is highly probable that the same basic compound 
which, ‘consolidating near the surface, produced the basaltic rock, when 
it attained the solid state at a greater depth, formed the greenstone. 
The basalts and greenstones, consequently, in general very much re- 
semble each other, both in chemical composition and mineral character. 
The chlorite, by which some of the greenstones are alone distinguishable 
from the basalts, is usually a product of transmutation. 
The following are some of the minerals occasionally found as 
accessories in granitic rocks :—Garnet, topaz, beryl, fluor spar, calcite, 
corundum, zircon, titanite, gold, oxide of tin, magnetic iron-ore, 
molybdenite, mispickel, &e. i i 
Tin-ore, gold, titanite, magnetic iron, and corundum, occur in con- 
siderable quantity in the detrital matter in many of the granite districts 
in Victoria. No specimens showing these minerals embedded in granite 
have yet been found,* and their occurrence in the drifts can only 
be explained, either by supposing them to have been originally dis- 
tributed as grains through the mass of the rock in the detritus of 
which they are now found, or that veins containing these minerals 
traversed the strata which doubtless once covered the granite, and 
have since been entirely broken up and removed by denuding forces, 
which were not able to transport the heavier minerals. No veins 
or lodes have been found containing tin-ore, nor are there any authen- 
ticated instances in Victoria of auriferous quartz veins in the ‘granite, 
though fragments of vein quartz, as well as of gneiss, mica, schist, and 
other metamorphic strata are not uncommon in the detritus that rests 
on the granite, and often contains rich deposits of tin-ore, fine gold with 
titanite, corundum, black tourmaline, zircon, sapphire, diamond, and 
other precious stones. 

* Gold, and a new mineral compound, supposed to be gold and bismuth, occurs | 
in granite veins associated with the Nuggetty Reef, Maldon. 3 
