278 PROCEEDINGS OF SECTION C. 
Renison Bell Mine and South Renison Bell, Dundas, similar 
tourmaline-quartz porphyry dykes occur; also at the Upper 
Emu River, above the Hampshire Mine; but these belong 
rather to the class of veins than to rock-masses. 
There are a few occurrences of spherulitic felsite in the 
Island. One of these has been found 2m situ in the swamp 
between the Montana and Western mines at Zeehan. At 
first the stone was believed to be a loose boulder, but last 
year it was ascertained to be a reef which traverses the 
Silurian strata. It has a certain degree of interest when 
considered in connection with the neighbouring stannite- 
lode at the Oonah Mine. The rock is charged with closely- 
packed spherules, showing a dark cross between crossed 
nicols. The little ground-mass which there is between the 
spherules presents the speckled aspect of felsitic substance in 
polarised light, but contains no distinct crystals of felspar. 
Loose pieces of essentially similar rock have been found at 
Trial Harbour, at Strahan, and in the bed of the Castray 
River, Heazlewood. Thesespherulesare identical with those 
familiar to petrologists as occurring in rhyolite-glass, but in 
this case they probably belong to the selvages of dykes pro- 
ceeding from the granite. 
Obsidian bombs in the form of bolts, buttons, and other 
sub-spheroidal lumps of natural glass are found in the Ter- 
tiary tin and gold-bearing drifts in different parts of the 
Island. So long as they were considered as derived from 
the volcanic centres which overwhelmed the country with 
basaltic lava in Tertiary times, these objects attracted little 
attention beyond that which they excited as curiosities. 
In 1897, in conjunction with Mr. W. F. Petterd, I pointed 
out that their ascription to any basaltic source is inadmis- 
sible, for the glass is not basic, but acidic. Their specific 
gravity ranges from 2 45 to 2:47, while that of different 
specimens of Tasmanian tachylyte was found to be 2:72 to 
2°77. The specific gravity of rhyolite obsidian from Mexico 
and United Statesisgiven by Rosenbusch as2-360 and 2-344 
respectively.(*) F. Zirkel cites that of obsidian from Lipari, 
Iceland, and the Yellowstone National Park, U.S., as 2-37, 
2°42, 2-441.() No analyses of the Tasmanian bombs have 
been made yet. It is highly desirable to sacrifice a speci- 
men, and obtain a complete analysis. Similar bombs in 
Australia have been analysed, and their SiO , percentages 
are 64:68, 71°22, 71°38, 73-40, 73-70, wich specific gravity 
varying from 2:44 to 2°47.(‘) 
(*) Elemente der Gesteinslehre, H. Rosenbusch, 1898, p. 255. 
») Lehrbuch der Petrographie, 1894, vol. ii., p. 280. 
‘) Die Herkunft der Moldavite, F. E. Suess, 1900, p. 238. 
