820 GEOGRAPHY OF BLUK MTS. AND SYDXICY DISTRICT, 



allowed the lieav}- waves coming in through the Botany Heads 

 to form a great sand bar about 1,000 yards inland of the present 

 Lady Robinson's Beach. On this sand-bar formed by the heavy 

 waves and about six miles in length the wind piled up sand to 

 form a beach seaward of the original shore-line, and separated 

 thence by a lagoon from 300 to 600 yards in width. The flat 

 drained by the present Muddy Creek indicates the site of this 

 old lagoon. As more material was swept into the ba}', the bar 

 grew ofF-shore, and another beach was piled up by the winds. 

 Thus two great curving parallel bars were formed, separated by 

 a long shallow trough. Many times this action was repeated 

 until a whole series of sympathetically curving bars (beaches) 

 with rounded tops and long rolling troughs were formed, and 

 totalling about 1,000 j^ards in width (Plate xliv.). The crests 

 are several miles in length, and the intervening troughs are from 

 6 to 15 feet lower. Doubtless peaty growths will l)e found in 

 various places under the surface, representing marshy conditions 

 of the inter-beach areas. The shape of the beaches indicates 

 bottom action, the horns giving it a symmetrical concave aspect 

 to the heavier seas, along-shore transportation being negligible. 



Subsequently to this formation came the very late elevation of 

 some 10 feet, and the series of sand bars and associated trough 

 areas became dry land. 



Another bar is now forming at a short distance off-shore. As 

 time advances Muddy Creek will become dry land — in fact it has 

 advanced partly to that stage from the lagoon marsh meadow by 

 draining. 



3. Sheets Creek. — This, as has been shown in detail b}' Prof. 

 T. W. E. David and R. Etheridge, Junr.,* evidences the action 

 of the recent oscillation of subsidence. Botaii}^ ^^y^ as shown 

 by their map, formerly extended to Redfern, but shoaling ensued, 

 and the recent elevation converted the shoals to dry land and 

 mud flats. These flats represent the shoaling of quieter waters, 



*Journ. Proc. Roy. Soc. X.S. Wales, xxx., 1S96, pp. 158-185. 



