31 



Remarks on a Geological Section at the 

 Ne^w Graving Dock, Glanville, ^with 



SPECIAL REFERENCE TO A SUPPOSED OlD 



Land Surface no^w below Sea Level. 



By Walter Howchik-, F.G.S. 



TEead December 7th, 1886.] 



The excavations in connection with the new G-raving Dock at 

 Glanville have exposed what is probably the best section of the 

 local Post-Tertiary beds hitherto known. By a comparison of 

 the strata at the Glanville excavation with those penetrated 

 in the making of the " New Dock," as shown by samples of the 

 latter exhibited in the Port Adelaide Museum, there appears 

 to be a general correspondence between the two sections, but 

 the beds thicken slightly as they pass westward, the limestone 

 crust in the " New Dock " being at a depth of 25 ft., whilst in 

 the Glanville excavation it is about 27 ft. below the natural 

 surface. The section now under review is a particularly 

 interesting one, as it supplies on what, I think, indisputable 

 evidence that these recent marine beds which occupy our sea- 

 board were not deposited in one uninterrupted succession, but 

 that they occur as an older and a newer marine bed, with an old 

 land surface intercalated and separating them. The section 

 may be given as follows : — 



No. 1. Made ground 



2. Surface clay 



3. Whitish sea-sand with shells 



4. Do. with bands of decomposed veget- 



able matter ... 

 J, Blue clay ) 

 Brown clay j 



6. Limestone crust 



7. Calcareo as sand and shells, about 



8. Brown argillaceous sand (not exposed) 

 No. 2 is the ordinary surface clay of the marshy flats border- 

 ing the river, lying at or about high water level, and which has 

 accumulated by deposition of material from the tidal waters in 

 their periodical overflow. This clay contains the usual 

 estuarine mollusca of the flats, as well as a few species of 

 foraminifera generally found in such a habitat, the occurrence 

 of the latter proving that within recent times considerable 

 areas of these flats bordering the river were permanently under 

 water. 



Nos. 3 and 4. Underlying the thin covering of surface clay is 



