RIPPLE-MARK AND CURRENT-MARK 269 



pointed out elsewhere ^ that a winding course is 

 inimical to the formation of river waves of fixed 

 position and size, because the lower layers of water 

 do not flow in the same vertical plane ^ as the 

 upper, so that there is always a tendency to set up 

 whirlpool motion instead of wave motion. 



The presence of bottom currents crossing the 

 direction of those of the surface is likewise inimical 

 to the formation of transverse sand-ridges. 



I was at first much puzzled by the fact that 

 although the sand ripples in the Bourne were so 

 numerous, regular, and well -developed, they 

 appeared to be scarcely stirred by the water. I 

 put sticks into the sand at the edge of the little 

 cliffs, and after a quarter of an hour I found that 

 the cliffs had not moved. Now, the sand ripples in 

 the Branksome brook had moved half an inch per 

 minute under the action of a somewhat slower 

 current. I came to the conclusion that the current 

 of the Bourne had had time and opportunity to do 

 all it could to the sand. The troughs were covered 

 with coarse-grained material. The broad, nearly 



^ See " The Travels of Ellen Cornish " (published by W. J. 

 Ham-Smith, 1913), p. 134, on the waves of the whirlpool rapids 

 of Niagara. 



2 See James Thomson " On the Winding of Rivers in Alluvial 

 Plains." 



