468 PROCEEDINGS OF SECTION C. 



in Tasmania are believed to belong to the Devonian, or close of the 

 Silurian, and there is no reason to believe that the Forth occurrence 

 forms an exception. The width of the serpentine intrusion is obscured 

 by the basaltic capping and its talus, but to the west of it is a wide 

 belt of garnetiferous zoisite-amphibolite with the general strike and 

 dip of the quartzite and schists. Hornblendic schist, more or less 

 garnetiferous, continues for a good distance up the road to the south 

 over a mile, and is succeeded by quartz, micaceous and graphitic 

 schists extending to the waterworks building six miles from Hamilton, 

 where an intrusive mass of quartz porphyry (Devonian) occurs, bounded 

 on the west by slate. 



The aspect and hthological characters of the quartzites and schists 

 suggest that their age is Pre-Silurian, and I have long regarded them as 

 Pre-Cambrian. The amphibolite, or hornblende schist, if we prefer that 

 name, may represent the metamorphism of a basic rock, the original 

 pyroxene having contributed to the formation of amphibole, and the 

 plagioclase and ohvine being represented by the garnet and zoisite. 



Garnet is found occasionally in purely eruptive rocks, but in schists 

 such as these it must be a metamorphic mineral. 



Zoisite is a mineral which is characteristic of the middle zone 

 (Katamorphic zone, zone of cementation [v. Hise]), in which both the 

 dynamic and chemical efiects of pressure are the chief factors in rock 

 reconstruction. 



Although this rock may be a metamorphic eruptive, it is, as said 

 before, associated with quartzite, and it is consequently difficult to 

 relegate the series to the Archsean complex. Rather may the Forth 

 group be referred provisionally to the great Algonkian formations 

 (Proterozoic, of Chamberlin and Salisbury), which fill the interval 

 between the lowest Cambrian and uppermost Archaean. The charac- 

 teristics of the Algonkian do not give the stratigraphist any very firm 

 foothold ; but as a rule gneiss is met with only occasionally, and rocks 

 of sedimentary origin are dominant. On the other hand, in the under- 

 lying Archaean, orthogneiss and other eruptives are abundant, and 

 the tectonic structure of the complex is variable and involved. 



COX'S BIGHT. 



This district borders on a broad bay on the south coast of Tas- 

 mania, about 12 miles east of the south-west extremity of the island, 

 and seven or eight miles from the head waters of Bathurst Harbor, 

 Port Davey. Mr. T. B. Moore, in a report to the Surveyor-General, 

 1901-2, mentions it as follows : — " At Cox's Bight a granite boss, 

 about a quarter of a mile in diameter, rises through the Silurian strata 

 at the southern end of the Bathurst Range. The creeks on the east and 

 west side of this intrusive mass have been worked in a very primitive 

 way for alluvial tin." 



The country between here and Recherche Bay, at the southern 

 end of D'Entrecasteaux Channel, is wholly uninhabited by man. At 

 the bight at present a few miners arc pursuing their calling, but the 



