278 WAVES OF SAND AND SNOW 



stand in a ridge against the horizontal thrust of 

 the current, as is the case with the sand of the 

 Branksome brook, ripples or waves will imme- 

 diately form. If the sand be too light, the level 

 of the surface of stationary sand will be uniformly 

 lowered, and above it there will be a stratum of 

 water heavily charged with sand in suspension. 



The most remarkable property of the sand-waves 

 produced in very shallow water when the velocity 

 attains about 2' 2 feet per second is that they travel 

 up-stream. This I have observed in the Brank- 

 some brook ; at Mundesley, in Norfolk ; at Grange, 

 in Lancashire ; at Torquay, at Cannes, and in other 

 places. These sand-ripples which travel up-stream 

 are indeed formed wherever tidal waters make 

 their way swiftly through sand in a shallow current. 

 The rate of up-stream motion in the case of the 

 sand-ripples of the Branksome brook, of which 

 the dimensions have been given, was 0*4 inch 

 per second, or 2 feet per minute. It is very curious 

 to see a group of these sand-ripples moving in 

 procession up-stream against the current which pro- 

 duces them. The sand can be seen to be accu- 

 mulating on the up-stream face of each, whilst 

 the down-stream face is scoured away. If a stone 

 be placed in the trough between two ridges, it is 

 soon covered by the advances of the ridge below 



