38 



tions near Port Adelaide. In 1886 I submitted to the Society 

 a short paper (2 ^ on one such an exposure, and therein stated 

 that "there are strong presumptive evidences, based on several 

 collateral lines of proof, that the Post-Tertiary beds of the 

 seaboard do not represent a regular succession of marine beds, 

 but that there was a break in the continuity of their deposi- 

 tion. In the view we have taken, there is an older and a 

 newer bed of recent marine, with an intercalated formation 

 of fresh-water origin dividing the same, and connected with 

 the fresh-water bed two horizons representing dry-land con- 

 ditions." ( 3 ) 



The above conclusion, reached twenty-six years ago, has 

 received its confirmation in the Dry Creek section. When 

 allowance is made for the different situations and the natural 

 thinning of the beds to landward, the two sections may be 

 regarded, in their main geological features, as practically 

 identical. In the Glanville section the upper marine bed 

 was laid down on an open sea beach, consisting of white sand, 

 littoral waste, and layers of sea- weed deposited by wave action ; 

 while at Dry Creek the corresponding bed is an estuarine clay, 

 laid down in a land-locked back-water, of which the present 

 North Arm inlet is the shrunken remnant. The lower marine 

 bed at Glanville is highly calcareous, in places almost a lime- 

 stone, and was laid down probably under some depth of 

 water, while the corresponding bed at Dry Creek is a silt that 

 accumulated under shallower conditions. The range of life 

 was much more restricted in the Dry Creek area than it was 

 in the open sea conditions represented at Glanville. The large 

 warm-sea foraminifer, Orbitolites complanta, which occurs 

 plentifully in the Glanville section, is entirely absent from 

 the Dry Creek bed, probably excluded by the shallowness of 

 the waters and their more muddy condition, but the important 

 time-indicator shell, Area trapezia, is abundant in both 

 localities. 



By the courtesy of the officers of the Engineer-in-Chief s 

 Department I am informed that the level-crossing at the 

 railway, situated a short distance to the west of the excavation 

 at Dry Creek, is 19 84 ft. above low- water mark. The 

 difference of level between this crossing and the excavation is 

 inappreciable, so that it may be said that the upper limits 

 of the Ostrea-Arca bed is about 2 ft. above present low-water 

 mark, and that, were it not for the land-wash that has 

 dammed back the sea, the bed in question at Dry Creek would 



(2) ''Remarks on a Geological Section at the new Graving Dock, 

 Glanville, with Special Reference to a supposed Old Land Surface 

 now Below Sea-level," Trans Roy. Soc, S.A., vol. x., pp. 31-35. 



(3)Xoc. cit., p. 36. 



