CHAPTER VI 

 SAND-WAVES IN TIDAL CURRENTS 



The Mawdach Estuary, Barmouth, N. Wales, its drying sand- 

 banks and their waved surface — Measurements of length 

 and height — D shape of estuaries, influence on course of 

 tidal currents and effect in producing unsymmetrical sand- 

 waves upon the drying sandbanks — Measurements showing 

 how far these sand-waves depart from uniformity — Ratio 

 of length to height — Sand-waves in the estuaries of the 

 Findhorn and South Esk — The estuary of the Severn : 

 smooth sandbanks at Severn Bridge, waved sandbank 

 near Severn Tunnel ; explanation of the difference — Sand- 

 waves in estuary of the Dovey, North Wales — Stakes fixed 

 in sandbank and measurements of size and movement of 

 sand-waves during seventeen days — Effect of velocity of 

 current and depth of water upon the sand-waves — Sand- 

 waves upon the North Goodwin Sand — Pools left after 

 partial obliteration of sand-waves, similarity of their form 

 to that of the pits called fuljes which occur in sandy 

 deserts. 



Sand-reefs in the Mississippi. 



Their size and movement — Not true transverse waves — 

 Their formation in freshly deposited sediment — How the 

 size of the sand-grains limits the size of the sand-wave — 



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