16 



contain only a few small stagnant pools at distant intervals. 

 The river fails to reach the sea, becoming lost in the absorbent 

 soil near the township of Lower Light. 



The Red Banks, where the outlier of Lower Cainozoic 

 rocks occurs, take their name from a series of large washouts 

 on the left bank of the River Light (Section 5, Hundred of 

 Grace), near the bridge on the main road to Mallala. At 

 this point the river makes a remarkable bend to the south 

 and then returns north by a course almost parallel with 

 itself. The inside of the loop consists of alluvial deposits, 

 somewhat lower than the normal banks, built up largely by 

 flood waters. On the east side of the bend a few small 

 and local streams (which only run when heavy rain occurs) 

 have cut deeply into the banks by falling over the cliffs, 

 and the latter have retreated, irregularly, from the river for 

 nearly a quarter of a mile. The banks consist of red clay 

 (which is sometimes white or mottled), loamy clay, sand, 

 coarse grit to file gravel. The walls are steep — in places 

 perpendicular — and are undergoing rapid waste. 



Between the river level and the top of the retreating clay 

 banks there is an extensive platform, or middle terrace, rising 

 slightly in level towards the head of the washout and, opening 

 out inwards, the banks are arranged around this middle plat- 

 form in amphitheatre form. 



This middle platform, or terrace, owes its existence to a 

 hard floor of Cainozoic limestone which underlies the alluvial 

 cover, and has presented a greater resistance to the erosive 

 action of the streams than the soft sediments. The following 

 measurements were determined by aneroid : — From river level 

 to limestone platform, 40 ft. ; from top of limestone to highest 

 point of adjacent cliffs, 40 ft. 



A complete section of the beds is as follows : — 



(a) Marly soil with nodules of surface travertine, 6 ft. 



(b) Light-reddish-coloured clay loam, 14 ft. 



(c) Dark-red and mottled clays and loam, 20 ft. 



(d) Fossiliferous Cainozoic limestone (thickness not 

 proved), 20 ft. 



Near the head of the washout, the stratum (b ) is replaced 

 by light-coloured to reddish sand and fine gravel which occupy 

 a gutter of erosion about 40 ft. in width. This gutter does 

 not seem to pass down into stratum (c) and is covered un- 

 conformably by the superficial bed (a). It has no accordance 

 with the present lines of drainage. 



