RIPPLES OF THE BEDFORD AND BEREA IN OHIO 263 



type, that is, formed by the slight forward-and-back motion of 

 the water which is caused by the passage of a wave. Not a single 

 occurrence has been noticed which suggests typical "ripple-drift," 

 the type of ripple which is produced by strong currents of water 

 moving in one direction. The ripple crests are usually from three 

 to five inches apart and rarely reach six inches. This interval 

 varies within a few feet on any surface. 



Considerable experimental work has been done on the ripple- 

 marks produced in sand by such waves. Notable is the work by 

 Forel, 1 A. R. Hunt, 2 and G. H. Darwin. 3 The work of these men 

 shows that, when a wave passes over a body of water, the slight 

 oscillation of the water beneath it can be detected to a considerable 

 depth below the surface. To what limit it may extend is unknown. 

 This oscillation sets up small vortices in the water next the bottom, 

 and in the course of time sand ripples are produced by the action 

 of these vortices. These sand ripples are produced at right angles 

 or nearly at right angles to the direction of movement of the wave : 

 that is, they are approximately parallel in direction to the lateral 

 extent of the wave. If the waves on a body of water extend in a 

 northwest-southeast direction (at right angles to the direction of 

 their movement) the ripples generated by them in the sands of 

 the bottom would trend, in general, in the same direction. If we 

 are seeking the factor which controlled the sand ripple directions 

 in the Waverly, we find it directly in the waves which have pro- 

 duced them. It then remains to ask how the direction of water- 

 waves is controlled, and what kept them practically parallel over 

 a wide area throughout a considerable interval of geological time. 



Hunt 4 has recorded his observations on ripple direction on the 

 north shore of Torbay which faces the English channel toward 

 the southeast. A portion of the beach examined was so protected 



1 "Les rides de fond," Archives des Sciences Physiques et Naturelles Geneve (1863). 

 This paper has not been seen by the writer but his results are stated, apparently quite 

 fully, in the paper by Darwin. 



2 "On the Formation of Ripple-Marks," Proc. Royal Soc. London, XXXIV 

 (1882), 1-1S. 



3 "On the Formation of Ripple-Mark in Sand," Proc. Royal Soc. London, XXXVI 

 (1883), 18-43. 



4 Ibid., 6 and 7. 



