114. PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
orthoclase varying from 0-5 to 0-75 mm. in length set in a 
groundmass of a trachytie nature and composed of quartz, 
felspar, and smal! dark rods and granules of a mineral 
which may be dark-brown hornblende. The rock has been 
analysed and the results are shown on Table I. (Micro. 
359.)? 
Rhyolite from The Hump, Rhyolite Range, Portion 8v, 
Parish of Wildash. This rock, which is typical of much of 
the material of Rhyolite Range and of the Tunnel Block 
areas, is pale-pink on the fresh surface and white on the 
weathered surface. It shows fluxion structure very freely, 
and here and there through the very fine groundmass there 
is an occasional erystal of felspar. Under the microscope a 
few crystals of cloudy orthoclase are seen, set in erypto- 
crystalline groundmass through which there are frequent 
streaks of secondary silica corresponding to the lines of 
flurion. Density 2-561. (Micro. 452.) 
Spherulitic Rhyolite from The Hump, Rhyohte Range. 
In the hand specimen there are isolated rounded spherulites 
of cloudy felspathic material set in a greenish-grey ground- 
mass, giving much evidence of secondary silicification. The 
spherulites average approximately 5 mm. in diameter, and 
occur frequently enough to be separated from one another 
by a few millimetres only. Under the microscope the 
ercundmass shows as a eryptocrystalline mass through 
which there is much secondary silica. The spherulites 
appear to be masses of kaolin stained brown by limonite. 
Density 2-526. (Micro. 453.) 
DACITEs. 
The dacites are difficult to distinguish from some of the 
rhyolites, but have a more melanocratic appearance. They 
are markedly porphyritie and are of two types, one showing 
quartz and felspar phenocrysts, and the other felspar 
phenocrysts only. 
The descriptions of the two following rocks will serve 
to illustrate very well the main characteristics of the dacites. 
Dacite from Portion 1663, Parish of Wildash, Eight 
Mile Creek. In the hand specimen it is a dark-grey colour 
with abuudant clear rounded erystals of quartz and stout 
erystals of a pink plagioclase. Under the microscope the 
2 These numbers refer to the petrological collections in Dept. of 
Geology, Univ. of Qld. 
