324 
there would be discovered a wide range in composition. This is the more 
probable from the fact that the black basalt grades into obsidian in different 
samples of that rock. It is now proved that acidic volcanic glass, similar 
in composition to that of australites, exists in Victoria associated with the 
newer volcanic rocks. 
In Victoria volcanic activity prevailed over a wide area from Miocene 
times to the beginning of the Recent period, and extensive areas of the 
surface were Govered by material poured out of volcanoes as lava or hurled 
out of their throats as agglomerate or lapilli. 
Although the volcanic fires may have burned intermittently at any 
particular site, they may have burned continuously in one place or another 
over the affected area throughout the great lapse of time that separated 
the Miocene from the Recent outbreaks. 
The volcanic rocks of Victoria range from basic to highly acidic, and the 
glassy forms of these rocks, as might be expected, range widely in their 
silica contents. 
In Selwyn’s catalogue, 1868, page 80. the following analyses are given, 
made by J. Cosmo Newberv :— 
Specimen 21 — 
Australite. 
Specimen 24 — 
Obsidian, Geelong District. 
Specimen 24a — 
Blue Obsidian, Geelong. 
Silicia ... ... 73*70 per cent. 
Sesquioxide of Iron ... 6"08 ,, ,, 
Alumina ... . 4'99 ,, ,, 
Lime ... .. 4'20 ,, ,, 
Magnesia ... ... 0*10 ,, ,, 
Peroxide of Manganese 
Titanic Acid ... ... 
Soda ... ... 5"20) 
Potash .. ... 4-83J ” 
Loss by ignition ... 0"55 ,, ,, 
7 2 *23 per cent. 
2-28 „ ., 
16*43 „ „ 
3-17 „ ,, 
2-12 „ „ 
4 65 ,, ,, 
013 „ ,, 
68*45 per cent. 
7-21 „ „ 
5 '38 ,, ,, 
8*11 „ „ 
F03 ,, ,, 
0-50 „ ,, 
0-30 ,, „ 
7‘36 ,, ,, 
99-65 
101-01 
98-34 
Sp. gr. . .. 2-47 
2-41 
2-36 
At Meredith (Victoria), Mr. Ferguson, of the Geological Survey staff, 
discovered a tachylite of bluish colour on the outside and bluish black on 
the fracture. Part consists of glass, and portions are spherulitic. An 
analysis of the glassy portion was mad$ by Mr. A. G. Hall, of the 
Geological wSurvey Laboratory, and is given below :— 
SiO* 
Al 2 b 3 ••• 
Fe 2 0 ;i ... 
FeO ... 
MgO ... 
CaO ... 
Na.,0 ... 
K 2 0 ... 
H- 2 0-f- ... 
ICO- ... 
Tit) 2 ... 
P 2 05 
Cl 
MnO ... 
NiO and CoO 
CoO ... 
50 "87 per 
cent. 
14-33 „ 
5 > 
5-37 „ 
5 5 
7-25 ,, 
y y 
451 ,, 
y y 
8*22 ,, 
y y 
3 39 ,, 
yy 
1-35 ,, 
y y 
0-17 „ 
y y 
0-33 ,, 
y y 
3*38 ,, 
y y 
0-07 ,, 
Strong trace 
y y 
0-58 ,, 
y y 
0-06 ,, 
trace 
y > 
Sp. gr. 2-831. 
99-88 
