35 



Several small creeks in the neighbourhood of Dry Creek arise 

 from seepings from the higher ground, are moderately fresh, 

 and flow north-westerly into the North Arm inlet — the tidal 

 waters of the latter come up to within about a mile of 

 Dry Creek. 



On the eastern side of Dry Creek Railway Station there 

 is a gradual rise of the land, which is at once made evident 

 by a change of herbage, but in some directions the marine 

 shells can be traced on the eastern side of the railway. as well 

 as on the western. It is, however, difficult to draw the limits of 

 the old estuarine area as, since the retreat of the sea, a cer- 

 tain amount of land-wash and the accumulation of a humus 

 soil have made a covering that obscures the estuarine silts. 

 In constructing the new portion of the line to the Abattoirs, 

 on the north-east side of the railway station, and at about a 

 quarter of a mile from the latter, it was found necessary, 

 in making an embankment, to excavate to a shallow depth the 

 soil on either side of the permanent way, and in doing this 

 the shelly marine clays that underlie the top soil became 

 exposed. In this situation Ampullarina quoyana is very 

 common, Risella is less so, and Chione is rare — at least so 

 far as surface indications go. The elevation of this bed 

 above present sea-level (tested by aneroid) appears to be about 

 the same as that of the Dry Creek Railway Station. The 

 slightly drier conditions at this point have permitted the 

 growth of a travertine crust overlying the shelly bed, varying 

 in thickness from \ in. to 3 in. It is not a pure limestone, 

 but the partial decomposition of the shells has yielded a 

 cementing agent by which the immediately overlying soil has 

 become consolidated into a crust. The material thrown out 

 from recently dug post-holes, adjacent to the shelly bed, sup- 

 plies evidence that much of the underlying red sands have 

 also been hardened, probably from a like cause, into a sand- 

 rock. Marine shells were rarely found thrown out from these 

 post-holes, which suggests that the shelly bed is superficial 

 and, in this position, of no great thickness. 



The occurrence of this raised sea-bed was recognized by 

 the late Professor Ralph Tate soon after his arrival in South 

 Australia, and in his Presidential Address before this Society 

 (then known as the Adelaide Philosophical Society) in 1879, 

 stated, "The estuarine limestone, which fringes the Dry Creek 

 salt marsh, and which is of about 6 to 12 in. thick, and 

 crowded with Amphibola [Ampullarina] quoyana, Risella 

 melanostoma, and other littoral shells, is not more than 12 ft. 

 above ordinary high-water mark. The limestone overlies the 

 drift, but graduates into the estuarine muds and sands which 

 occupy the salt marsh. The marsh is at rare intervals over- 



