20 NOTES ON THE GEOLOGY OF WINEGLASS BAY. 



east coast great cliffs have been formed, seamed with 

 cracks and joints, and showing traces in parts of columnar 

 structure on the outer • and upper faces. The structures 

 seen in many of the cliffs indicate that there has been in- 

 tense dynamic stress taking place in part during consoli- 

 dation, but mostly subsequently. The sinking of the land 

 to the East, approximately along this line of granite, may 

 have tended to weaken the structure. The deformation 

 •of the granite on Maria Island appears to have been of a 

 more intensive nature, though not nearly so severe as in 

 the earlier granites. 



Very few traces of the older or subsiequent strata are 

 to be found. The i"ate of denudation and sea erosion is 

 and has been very great. Silurian slates appear at Blue 

 istone Bay. Cretaceous diabase is found at Buckley's, on 

 the south side of Hazard Bay, and on Schouten Island, 

 tne two latter deposits being fringed with Mesozoic sand- 

 stones. In speaking of Oyster Bay. Mr. Twelvetrees re- 

 ports : — "The form of Oyster Bay illustrates the eroding 

 force of the waves on a large scale. We must believe that 

 the surviving fringe of diabase on the E. side of the bay 

 at Hepbui'n's Point, on the S.W. of the Peninsula, and on 

 Schouten Island, was once continuous witn the sea-front 

 of tne same rock on tne Swansea side of the bay. The 

 fragmentary deposits of Mesozoic sandstone (freestone) as- 

 sociated with the diabase indicate that it, too, extended 

 across the bay to Kelvedon. It follows, accordingly, that 

 the present Oyster Bay has been scooped out of the coal 

 measures, sandstones and diabase, the eroding process 

 being, perhaps, assisted in its initial stages by the weak- 

 ness of the strata along the contact line of the diabase 

 with granite on the eastern shore of the bay. The ex- 

 cavating process has extended to a depth of 12 fathoms, on 

 the average. The present depth of the bay does not repre- 

 sent the sum total of erosion since the coal period, for it 

 has probably been reduced by deposition in Tertiary times 

 of sediments, which have since been denuded as the land 

 has i-isen again. The Tertiary deposits in tne lower part 

 of the valleys of the Swan and the Apsley illustrate the 

 depression and subsequent elevation of the land during 

 that period, observed frequently elsewhere in Tasmania." 



The sand forming the beach at Wineglass Bay is very 

 white, being composed almost entirely of quartz and small 

 rounded pai-ticles of felspar. In Hazard Bay, however, it 

 is more yellow in colour, and contains much felspar and 

 many shell fragments. The isthmus itself is composed of 

 a broad flat, fringed with high sandhills, and somewhat 



