PROCEEDINGS OF SECTION C. 467 



still further. For this distance they maintain their Uthological charac- 

 teristics, and at intervals expose their characteristic ore deposits. 

 Large lenses of magnetite and hematite occur, with which are associated 

 a variety of minerals — copper, silver, gold, pyrrhotite, baryta, arsenide, 

 and antimonial sulpharsenide of nickel, cobalt molybdate, asbestos, 

 siderite, dolomite, calcite, arsenopyrite, quartz, &c. On each side of 

 the ore bodies, and separated from them only by bands of more siliceous 

 schist, is the hornblende rock, which is sometimes gneissoid and fissile, 

 resembling a compact diorite, or is coarsely granular, with irregular 

 fracture. Talc-Uke schists accompany this rock. 



With this variability of aspect the rock might easily be called 

 gneiss, schist, gabbro, or diorite, according to the particular specimen 

 under examination. Still the mineral constituents are the same, 

 whatever the variety of structure. 



A rather fresh-looking acid plagioclase felspar (albite ?), in large 

 plates ; a green hornblende, often decidedly bluish green in this section 

 but with the extinction angles of common hornblende ; apatite, in 

 large formless crystals ; quartz and much epidote, are the elements 

 which form the rock. 



It obviously belongs to the amphibohtic crystalline schists, but 

 it is not easy to say what it was originally. A possible hypothesis is 

 that it was once gabbro, the pyroxene of which has been replaced by 

 hornblende, and its basic felspar transformed into more acid felspar 

 and quartz. The presence of the nickel ore and the common develop- 

 ment of serpentine on joint faces of the rock are consonant with this 

 theory. It would appear to belong to Grubenmann's order of epi- 

 amphibohtes and to his family of albite amphibolites. 



Further north, at the junction of the Whyte River with the Nine 

 Mile Creek, on the latter of which some copper mining has been carried 

 on, this zone contains actinolite schists, distinguishable from the Rocky 

 River schists by the amphibole being actinolite and by the absence of 

 felspar. The entire belt, however, forms a geological unit. 



These are lithographically so different from any of the members 

 of the Silurian and Ordovician and Cambrian, as known in Tasmania, 

 that we refer them to a more ancient date. What their definite age is 

 cannot be stated. It may be surmised that they are Pre-Cambrian ; 

 but whether they are Pre-Algonkian or not must remain an open ques- 

 tion for the present. 



HORNBLENDIC SCHISTS ON THE FORTH RIVER. 



At Hamilton-on- Forth a picturesque river gorge exposes the ancient 

 Tocks beneath a thin covering of Tertiary basalt, occasionally limbur- 

 gitic or felsparless. To the north-west of the township crags of sac- 

 charoidal white quartzite overlook the river. The bearing of this is 

 west of north. The strata to the east of the quartzite are micaceous 

 schist, with similar strike and dipping west. About half a mile from 

 the township along the road an exposure of the rock on the west side 

 of the quartzite is seen. This is serpentine. All our serpentine rocks 



