816 STUDIES FOR STUDENTS 



one to the effect that no ripple-forming vortex occurs in the lee 

 of an obstacle over which a steady current is passing, and that 

 hence "a steady current is unable either to generate or to maintain 

 ripple mark." 



The British Association Reports for the years 1889, 1890, and 

 1 891 contain three papers by Reynolds on the action of waves and 

 currents in model estuaries, in which are some valuable observa- 

 tions regarding what may well be termed giant tidal ripples. 1 

 While experimenting with artificial tidal currents, Reynolds dis- 

 covered that current ripples were formed in the model estuaries. 

 By making due allowance for the difference in size between the 

 model estuaries and those in nature, he concluded that real tidal 

 currents ought to produce very large current ripples, possibly 

 7 or 8 feet in height and 80 to 100 feet apart. 2 Some years later 

 Vaughan Cornish discovered natural tidal ripples of the same type 

 as those produced artificially by Reynolds, having a height of 

 2 feet and an average distance of more than 37 feet from crest to 

 crest. 3 In two later papers Cornish described giant tidal ripples 

 more fully, and illustrated their essential features with a large series 

 of beautiful photographs. 4 Some of these ripples have a height 

 of nearly 3 feet above the intervening troughs, and a distance 

 between crests of from 66 to 88 feet in extreme cases. The giant 

 ripples are often covered with ordinary ripple mark, and while 

 Cornish recognized that the larger forms were produced by the 

 continuous steady flow of tidal currents, he was at first inclined to 

 invoke pulsatory currents in order to explain the smaller ripple mark. 5 



1 Osborne Reynolds, " Report of the Committee Appointed to Investigate the 

 Action of Waves and Currents on the Beds and Foreshores of Estuaries by Means of 

 Working Models," Rept. British Assoc. (1889), pp. 327-43; ibid. (1890), pp. 512-34; 

 ibid. (1891), pp. 386-404. 



2 Ibid. (1889), p. 343- 



3 Vaughan Cornish, "On Tidal Sand Ripples above Low-Water Mark," Rept. 

 British Assoc. (1900), pp. 733-34- 



* Vaughan Cornish, "Sand Waves in Tidal Currents," Geogr. Jour., XVIII (1901), 

 170-202; "On the Formation of Wave Surfaces in Sand," Scottish Geogr. Mag., XVII 

 (1901), 1-11. 



5 Vaughan Cornish, " On Tidal Sand-Ripples above Low-water Mark," Rept. British 

 Assoc. (1900), p. 733; "Sand Waves in Tidal Currents," Geogr. Jour., XVIII (1901), 

 197-98; "On the Formation of Wave Surfaces in Sand," Scottish Geogr. Mag., XVII 

 (1901), 8. 



