(i 
cracks. The plagioclase is in lath-shaped crystals in the base. 
The olivene crystals are corroded by the magma. The felspar 
microliths in the base show the flow-structure well. The augite 
encloses some dark grains, undetermined. The whole mass is 
rather scoriaceous in character, so the specific gravity was not 
determined. It is quite a typical olivene basalt. 
II. Oxnivenrt Basatt, Mount Gambier, S.A. 
The minerals composing this rock are—Olivene in rounded 
grains, cracked and a good deal corroded by the magma ; they 
are fresh and clear. Augite of a brownish-green color, fresh and 
giving good polarisation colors ; it is allotriomorphic. Plagioclase 
Jelspar in lath-shaped clear crystals in the ground mass. Mag- 
netite is plentiful in the usual black grains scattered throughout 
the mass. The sp. gr. of the rock =2:°73, which is rather low 
due perhaps to the presence of cavities and gas-holes. It isa fine 
grained typical rock, and shows flow-structure. 
III. Oxrivene Basatt, Kangaroo Island. 
This exceedingly interesting rock consists of plagioclase felspar, 
both as porphyritic crystals and as the usual laths in the base. 
The former at times show most beautiful zoning and inclusions, 
with the usual lamellar twinning of plagioclase. 
Augite is plentiful. It is, curiously enough for a basalt, quite 
clear and colorless, and well-twinned in some crystals, while 
others exhibit good “ hour-glass” structure. Owing to its being 
colorless and having such a high refractive index, it is not always 
easily to be distinguished from some of the olivene present. 
Olivene occurs as fresh and clear grains corroded by the magma, 
while magnetite is abundant in the usual black grains. 
Felspar and augite are the most abundant constituents, then 
olivene, and lastly magnetite. The rock is typically ophitic in 
structure, and there is a good deal of glass of a dirty brown-green 
color in the base, which is quite isotropic. The rock is a very 
basic one in character, as may be guessed from the mineral com- 
ponents, and it has a sp. gr. of 2°88. The rock is not holocrys- 
talline, but it has otherwise rather the character of a dolerite 
(ophitic), but I have called it a basalt since I have no informa- 
tion as to its field occurrence, but since the specimen was 
labelled ‘‘Columnar Diorite,” I presume it must exist as a lava 
flow. If, however, it occurs as a dyke-rock, dolerite might per- 
haps be applied to it as a name rather than basalt. This seems 
to have been the rock noted by Dr. Chas. Chewings.* The most 
important and perhaps also the most valuable feature of this 
*“ Beitrage zur Kenntnis der Geologie Siid und Central Australiens” 
(Petrographischer Anhang.), Heidelberg, 1894. 
