RIPPLE-MARK AND CURRENT-MARK 273 



make and move the ripples foir a time, both pro- 

 cesses coming to an end owing to a redistribution 

 of material. I have not yet been able to test 

 the above explanation by further observations. 



Returning now to the Branksome brook, I will 

 describe the ripples in the lower part of its course 

 across the sandy beach, where it flows more swiftly. 

 Where the velocity attained 15 feet per second 

 the surface of the water was in waves 3 inches 

 in length and of no great breadth of front, and 

 under each was a sand-wave with a rounded crest 

 and nearly the same profile as the water-wave. 

 The sand-waves had a height of ^ inch. They 

 travelled down-stream at the rate of i inch in 

 3I seconds, or "024 foot per second, the sand con- 

 tinually pouring over from the weather to the lee 

 side of the crest. This progression was, I thought, 

 due to that of the superincumbent water-waves, 

 although these were of the form called stationary, 

 or standing, waves. The circumstance that the 

 water-waves themselves travelled down-stream was 

 apparently due to erosion at the place of their 

 origin, where the sandy bank or bed was eaten 

 away by the action of the undeflected current. 

 Accordingly, when I produced a train of water- 

 waves by placing in the stream a stone too heavy 

 for the current to move, the sand -waves whjich 



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