20 CONTENTS 



Current-mark. 



In vei-y slow streams with a smooth surface — Effect of 

 making the course of the stream straight — Action of 

 current upon a body projecting above the bed of the 

 stream — Current-mark in shallow streams with a waved 

 surface and a velocity of i'5 feet per second — Moving 

 down-stream — The same in a stream with a velocity of 

 22 feet per second move up-stream — Dr. Owens' 

 experiments on the diminished rate of settlement of 

 sand in sandy water — Explanation of the up-stream 

 movement of the current-mark or sand-ripples in a 

 shallow stream with a rapid motion — Effect of pro- 

 gressive water-waves upon the current-mark of streams 

 — Ratio of length to height of current-mark compared 

 with that of ripple-mark. 



CHAPTER VI 



SAND-WAVES IN TIDAL CURRENTS .... 29I 



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

 sandbanks and their waved surface — Measurements of 

 length and height — D shape of estuaries — Influence on 

 course of tidal currents and effect in producing un- 

 symmetrical sand-waves upon the drying sandbanks — 

 Measurements showing how far these sand-waves de- 

 part 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 



