'^ JAM ] S 192Jb ^' 



II. Coastline PnYSioHii^^.^^^ ^\\^^^%^ 



A glance at the map (fig. 1) will showtH^*idi?tfiGution of 

 the igneous rocks, and at the same time serve to indicate how 

 the coast owes its configuration to the presence of the resistant 

 masses of granite. The coastline has a general N.E.-S.W. 

 trend, with two prominent projections at Port Elliot and 

 Rosetta Head respectively. Not quite midway between these 

 Granite Island lies, just off Port Victor, separated from the 

 blunted point of land by a very shallow expanse of water, and 

 evidently but recently severed from the mainland. On the 

 other side of Rosetta Head the coastline curves round to 

 another minor projection. King Point, off which lies West 

 Island, which, like Granite Island, was at no distant geological 

 date connected with the mainland. ^5) 



The two main projections, as well as the two islands 

 referred to, are composed of granitic rocks which have offered 

 a stubborn resistance to the attacks of the sea, which has 

 eroded those portions of the coast not so protect-ed. This has 

 resulted in the production of the long unbroken cuspate 

 stretches of sandy beach with nodes at Port Elliot, Port 

 Victor, and Rosetta Head, as well as the concave stretch of 

 coastline between Rosetta Head and King Point. 



Prof. Howchin has inferred from the glacial evidences in 

 the vicinity that a great granitic mountain mass formerly 

 extended to the east and south of the present coastline in 

 Permo-Carboniferous times, which has since foundered, and 

 of which Granite Island, West Island, and a number of 

 smaller islets oft" the coast, form a remnant. 



Tlie original boundary of the granite outcrop was evi- 

 dently not far inland from the present coastline. 



III. Genral Field Relations of the Igneous Rocks. 



The igneous rocks are intrusive into mica-schists, which 

 Prof. Howchin considers to be ''probably Lower Cambrian," <^^ 

 and the contact can be studied at the north side of Rosetta 

 Head, where a fine section is exposed. Lying unconformably 

 on the schists are the practically level-bedded glacial deposits 

 of the Permo-Carboniferous : these outcrop prominently just 

 close to the granite on the south-west side of Port Elliot, 

 at various points near sea level between Port Elliot and Port 

 Victor, and along the coast with little interruption round to 

 Rosetta Head. On top of these there is in places a covering 

 of nodular "travertine" or kunkar, which is extensively 



(5) Howchin : Trans. Roy. Soc. S. Austr., vol. xxxiv., 1910, 

 p. 7. 



(6) Geology of South Australia, p. 363. 



