\ i 
' P 
332 T. G. TAYLOR AND D. MAWSON. | 
Bear Paw Mountain (Montana) described by W. Weed and 
L. Pirsson, (Am. Jour. Sc., May 1896) but is of finer texture. 
Perhaps ARFVEDSONITE QUARTZ TRACHYTE isaSuitable name. 
Other trachytes of the district.—A hard bluish trachyte 
can be obtained from a quarry on the east side of the 
Berrima road, about one and a half miles from Mittagong. 
The felspars are decomposed somewhat and of two gener- 
ations. Large corroded augites are sparsely scattered 
through the mass. 
No. 4. Locality Southern End of Cone near 
Gib. Tunnel. 
Light brown glassy matrix containing subangular grains 
of quartz, and fragments of trachyte. The latter consists 
of small felspar laths showing flow structure. Magnetite 
is present chiefly in the trachyte fragments but also in the 
matrix. Patches of secondary calcite are fairly abundant. 
None of the rocks of the. neighbourhood resemble the 
included trachyte very closely, except the trachyte exposed 
in the quarry on the Berrima Road, about two miles from 
Mittagong, which,also contains grains of magnetite. 
Name.—The rock is evidently a tuff, composed largely of 
fragments of trachyte, and may therefore be termed a 
TRACHYTE TUFF. 
No. 5. Locality # miles H.N.E. of Mittagong 
Station, in private ground. 
Texture—Pilotaxitic. Large plagioclase phenocrysts. 
Fabric—Hypidiomorphic groundmass of felspar, augite 
and magnetite, which are confusedly mixed together. 
The felspar appears to be last formed, since in several 
instances it has developed round the other two minerals. 
Minerals present (approximate areas)— 
Felspar ... i’. a th ae an OOe 
Augite ... af ve he fs A ae 
