On a Geological Section from the Head of 

 St. Vincent Gulf East^ward across the 

 Wakefield and Light River Basins. 



By J. J. East. 



Plate I. 



[Read November 4, 1884.] 



INTEODUCTOEY. 



The sectional line here spoken of extends from Port IVake- 

 field across the Wakefield Plains, and through the Adelaide 

 chain of the Plinders Ranges to their eastern slopes overlooking 

 the valley of the Murray Eiver. 



The form of the ground's surface naturally suggests its 

 division into two portions, viz., a level or gently undulating 

 plain reaching back from the waters of the gulf for 22 miles, 

 when it gives place to a tract of hilly country. This hill 

 region is formed by a succession of parallel ranges having a 

 nearly meridional strike, and separated from each other by 

 valley-plains often of considerable extent. The ranges as a 

 rule appear about the same average height above the plains, 

 but on a line from west to east they really, with the valleys 

 between, form a series of terraces, each valley and range on 

 the east having a greater absolute elevation than that on the 

 west. The eastern range is the highest of all, the summits of 

 several points being over 2,000 feet above the sea. It forms a 

 wide-topped swell many miles long, and is known as the table- 

 land. From the eastern slope of the tableland the surface of 

 the country falls rapidly towards the Murray Eiver, but no 

 long creeks nor permanent waters exist in the 35 miles of 

 scrub and plain which intervene between that channel and the 

 hills. 



In consequence of the terraced formation of the hill country 

 the whole of the surface drainage is towards the gulf, the 

 western ranges being drained by the Eiver "Wakefield, and the 

 central and eastern ones by the Light and its tributary the 

 Gilbert. 



THE WAKEriELD PLAINS. 



In describing the series of beds or strata met with along the 

 line of section it will be advantageous to begin with the wes- 

 tern or "plains" portion. 



On the edge of the gulf at Port Wakefield a deep borehole 



