34 



notes on Recurrent Transgressions of the Sea 

 at Dry Creek. 



By Walter Howchin, F.G.S., Lecturer in Geology and 

 Palaeontology, University of Adelaide. 



[Read July 11, 1912.] 



By the courtesy of Mr. T. G. Ellery, Town Clerk of Ade- 

 laide, my attention was called to an interesting section exposed 

 by the sinking of a drainage tank connected with the City 

 Abattoirs. The tank is situated in the south-east corner 

 of Section 920 (Grand Junction), Hundred of Port Adelaide, 

 at the five cross-roads, about a mile to the south of the Dry 

 Creek Railway Station. I visited the spot in company with 

 Mr. Filmore, an officer of the City Council, and was enabled 

 to make a careful examination of the section, which proved 

 to be as follows : — 



ft. in. 



1. Surface soil — loamy clay 5 6 



2. Reddish sharp sand, slightly argillaceous ... 2 



3. Very compact red clay 7 6 



4. Bluish, grey, to whitish clay, thickly beset with 



fragmental shelly matter ... ... ... 2 6 



5. Bed of Ostrea, Area, etc., in great numbers... 2 



6. Blue clay of unknown depth ... ... ... 6 



20 



The flats between Port Adelaide and Dry Creek Railway 

 Station have been but recently elevated above sea-level. The 

 railway at Dry Creek is, according to the official figures, 

 16 ft. above low-water mark, and as the average height of 

 the tidal wave is estimated at 8 J ft., it follows that the rail- 

 way is only 7 J ft. above high-water level. Indeed, the eleva- 

 tion of the maritime plains is still incomplete, as is evidenced 

 by the extensive estuarine area of the North Arm, with 

 numerous reticulating creeks and swamps which occupy most 

 of the area. The intervening land surfaces are mostly saline 

 and covered with samphire growths. These flats have been 

 built of estuarine mud containing shells characteristic of such 

 a habitat. The shells can be found abundantly strewn over 

 the surface of the ground and along the sides of the creeks, 

 but especially on the artificial embankments that have been 

 constructed by heaping up the adjoining mud. Among the 

 commonest forms thus found are Chione corrugata, Ampul- 

 larina quoyana, species of Risella, and Bittium estuarium. 



