72 



West, again, level, seemingly barren country, support- 

 ing sheaoak, yacca, and heath, forms a peneplain, elevated 

 several hundred feet, and extending far towards Coffin Bay. 

 In that direction, the Marble Ranges stand out in the dis- 

 tance as solitary imposing ridges; only minor undulations 

 modify the intervening expanse. 



On the Gulf side, commencing some two miles north of 

 Port Lincoln, a narrov»? aggraded peneplain extends north- 

 wards at an elevation of some 20 feet above the sea. As it 

 proceeds up the coast, it broadens out considerably to a 

 maximum width of 10 miles at Red Cliff, above Louth Bay. 

 It also varies considerably in elevation. In part, especially 

 where it is broadest, this surface owes its planation to degra- 

 dation. Some of the clilf exposures in the aggraded areas 

 show mottled clay-beds, quite similar to those classed as 

 freshwater Miocene in the vicinity of Adelaide. This stage 

 of peneplanation is therefore to be correlated vvdth the mid- 

 level plane so strongly marked in the hills near Adelaide. 



The uniformly level surfaces of Tumby Island and the 

 islands of the Banks Group in Spencer Gulf appear to be 

 topographically continuous with this peneplain, and indicate 

 a former continuity in that direction. Inland from Tumby 

 Bay, where the hills commence, traces of a peneplain can be 

 noted standing at higher elevations, abruptly terminated on 

 the eastern side by the lower coast plains. West, for about 

 15 miles, this high-level planation extends, though much 

 warped and dislocated. 



III. Geological Features. 



(a) Recent. — A soft recent limestone, a few inches to 

 many feet in thickness, occurs as a covering on the older rocks 

 over a wide area in the Port Lincoln district; especially is 

 this formation more abundant towards the south. It is found 

 thickest on lower ground, but patches occur high up on the 

 flanks of Winter's Hill, elevated at least 600 feet. In its 

 unaltered state it is composed of foraminiferal tests and 

 comminuted shell fragments ; at other times it is formed of an 

 exceedingly fine calcareous powder, resembling chalk, though 

 sufficiently hard to be of some use as a building stone. Tra- 

 vertinization has developed an upper harder crust, as much as 

 several inches in thickness, and in places downward percolat- 

 ing waters have formed travertine tubes, with a general 

 megascopic appearance, not unlike some species of Litho- 

 thamnion. 



A similar limestone formation has been described by 

 various authors from Southern Yorke Peninsula and other 

 parts of the State. According to Mr. Howchin, who is 



