ON HAUYNE-TRACHYTE AND ALLIED ROCKS 

 IN THE DISTRICTS OF PORT CYGNET AND 

 OYSTER COVE. 



By W. H. Tvv^elvetrbes, F.G.S., ais^d W. F. Petterd, 



C.M.Z.S. 



The igneous rock at Port Cygnet, in Southern Tasmania, 

 lias been known for a long time by the name of felspar- 

 porphyry. As the porphj'ritic crystals of felspar are 

 rather strikingly displaj'ed in the rock, specimens have 

 now and again, through collectors, found their way to 

 different parts of the Colony. Microscopical study of 

 some of these samples made us aware that the handsome 

 porphyries were soda-trachytes, and we classed them as 

 such in our last year's sketch of the igneous petrology of 

 Tasmania.* Since then we have found the felspathoid 

 mineral haiiyne or nosean in them, which confirms our 

 previous determination, and a recent excursion to the 

 locality has enabled us to recognise quite a group of these 

 rocks, as well as to fix their geological age. 



The country round Lovett and Lymington furnishes 

 several sections which may be used by the geologist, but 

 -one of the most valuable of these is, perhaps, that which 

 is afforded by the Livingstone mine. The mine shaft and 

 buildings are on the crest of a hill, GOO feet al)Ove sea- 

 level, about two miles N.E. of the township of Lovett. 

 .Just before reaching the crest the trachyte may be seen in 

 the road-cutting underlying the sandstones and slaty 

 arenaceous beds which form a large portion of the hill. 

 On the saddle there are some fossiliferous beds of the 

 Permo-Carboniferous System, charged with spirifera and 

 fenestellidae, and a little higher the trachyte appears 

 again. In one form here it has a slabby habit, due to its 

 being largely composed of parallel layers of large tabular 

 crystals of orthoclase felspar, some of which measure as 

 much as two inches in length. The Livingstone mine 

 shaft is close by, and appears to be sunk in banded 

 trachyte and quartz. One hundred and fifty feet below 

 this a tunnel has been driven for 360 feet, passing through 



* Trans. Aust. Inst. Mining Engineers, 1898. Vol. V., p 108. 



