CHAPTER V ; 



RIPPLE-MARK AND CURRENT-MARK 



Ripple-mark. 



Sir G. H. Darwin's experimental reproduction of ripple- 

 marks — My measurements of natural ripple-mark — Osborne 

 Reynolds' experiments. 



Current-mark. 



In very 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 1*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 progressive water-waves upon the 

 current-mark of streams — Ratio of length to height of 

 current-mark compared with that of ripple-mark. 



Rip pie -mark. 



The best knov^^n example of a sub -aqueous sand- 

 wave is the ripple-mark of the sea-shore, produced 



257 



