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NOTiilS ON THE GEOLOGY OF WINEGLASS BAY. 



By W. H. Clemes, B.A., B.Sc. 



[Received 20tli Ma-rcli, 1919. Read 14th April, 1919.] 



During a recent visit to Wineglass Bay I was enabled 

 to make a cursory examination of the neighbourhood, aiid, 

 as the locality has not been described in any detail, a few 

 notes may be useful as a guide to future workers. 



Wineglass or Thouin Bay is situated on the eastern 

 side of the isthmus joining Freycinet Peninsula to Schou- 

 ten Main, which, together with Schouten Island, form the 

 eastern boundary of 05'ster or Fleurieu Bay. The whole 

 consists of a magnificent series of granite peaks, extending 

 for 12 miles in a north and south direction, the highest. 

 Mount Freycinet, rising to the height of 2,014ft. above 

 the sea. This granite occurs in a. meridional line, extend- 

 ing fronr Flinders Island to the Hippolyte Rocks, off Tas- 

 man Peninsula, and is contemporaiieous with the granite 

 massifs of the West Coast. It is to be found penetrating 

 all rocks earlier than the Permo-Carboniferous, but has 

 not been seen intrusive in strata of a later age. It is usual- 

 ly distinguished from the earlier granites and syenites by 

 its uncrushed character, tho^lgll in places it has been sub- 

 jected to a certain amount of dynamic stress. 



The granite at Wineglass Bay varies considerabi}''. 

 The noi-mal rock is a, coarse-grained granite, pink with 

 flesh-coloured orthoclase. The chief constituents are ortho- 

 clase, quartz and biotite. The latter appears in green- 

 chloritised crystals, and is quite subordinate in quantity. 

 In large boulders at the northern end of the beach ap- 

 pears a medium-grained biotite-granite, the composition 

 of which is quartz, biotite and felspar. Much of the lat- 

 ter will probably be found to be plagioclastic. This is the 

 more typical East Coast granite. Running through this 

 are veins of granite porphyry, in which the ground mass 

 lookg quartzosie, with scattered crystals of quartz, biotite 

 and muscovite throughont. In other veins there is a concen- 

 tration of the biotite. A wide vein of this biotite-granite 

 was reported as running up the hill from the water's edge 

 on the northern side of the bay, but I did not come across 

 it. A broad vein about 20ft. wide is found on the south 

 side of the bay. This is also a granite poi'phyry of mag- 

 nificent appearance. It consists of pink orthoclase and 

 quartz in a qiiartzose ground mass. The ferro-magnesian 



