r»o 



Seal, or Hummock Island of the Chart, and on Kent's Group^ 

 neither of which was I able to visit. 



3. Arfvcdsouite. — "A higlily ferruginous variety of am pinhole or 

 black hornblende," containing one per cent, of copper. " The copper 

 which it contains exists in part or all as oxychloride coating the 

 crystals of Arfvedsonite" (G. Foord), locality 8 wan Island. 



4. 7'in. — The oxide of tin occurs in various parts of Cape Barren 

 Island, and of Flinders Island as stream tin, in rolled fragments. 

 This is the most valuable form in which the ore is obtained ; it 

 contains about 75 per cent, of tin, and the value varies from £80 

 to £100 per ton, according to recent fluctuations of the market. 



5. Bournonite. — An ore of antimony and lead, occurring in 

 patches near the junction of the slates and granite on the south- 

 east shores of King's Island. 



6. Iron I 'y rites. — Marcasite, often mistaken for gold by the 

 islanders, is a variety of iron pyrites, and occurs in veins in the 

 slate formation 



7. Topaz. — This mineral occurs in crystals and washed pebbles in- 

 great variety of form, colour, and size, and in many localities 

 associated with oxide of tin, zircons, tourmaline, etc., etc. It is 

 derived from the granite, and crystals may, though rarely, be 

 obtained in situ from rugs in the granite, together with rock 

 crystal and with crystallized feldspar. I have the pleasure of 

 introducing one very beautiful example of this to the notice of the 

 Society. They are abundant on the north-east side of Killicrankie 

 Bay in a creek descending from the ranges, and upon the beach, 

 and are equally so in a gulchway about two miles south of the 

 first-mentioned spot, and across the bay from it. I also found 

 them inland in the creek descending westward from the Quoin, and 

 in the Sanfra River on the south side of Flinders. 1 am also 

 informed of their discovery in other creeks on the south end of 

 Flinders, diverging from the peaks, and in a variety of spots 

 upon Cape Barren Island ; such as in Deep Bay and vicinity of 

 Dover River upon the north, and Battery Bay and Kent's Bay upon 

 the south side of Cape Barren. They are also occasionally found upon 

 the outlying islands. 



In regard to their occurrence, I may note that a remarkable 

 feature in the granite is usually the index of their presence. 



This rock which is in general throughout the islands an ordinary 

 ternary granite moderately close-grained, or occasionally some- 

 what porpliyrytic, appears to have been subjected to some 

 abnormal condition of cooling, which has resulted in certain 

 localities in the aggregation of its constituent minerals into masses 

 of exceptional siz^. Thus it is not unusual to see vein-like streaks 

 traversing the granite, varying from one to several feet in width, 

 and composed of a material which can only be illustratively des- 

 cribed as granite highly magnified. The materials are identical 

 with those of the surrounding granite, but the size of the individual 

 minerals is enormously increased, so that blocks of feldspar quartz 

 and even mica occur, up to several feet in dimensions. These ajDpear 

 to be the scene of the most abundant sources of the topazes which 

 have crystallised out into natural cavities, from whence they have 

 been delivered by erosion. 



