STUDIES FOR STUDENTS 811 



force. The crests are sharp and narrow as compared with the more 

 broadly rounded intervening troughs. De la Beche, in his Geo- 

 logical Observer describes another type of ripple mark, produced 

 by the action of a current flowing steadily in one direction over 

 a bed of sand. 1 These "current ripples" have a long, gentle slope 

 toward the direction from which the current comes, and a shorter, 

 steeper slope on the lee side. Sand grains removed from the gentle 

 slope are carried to the crest and dropped down the steeper slope, 

 causing the ripples to migrate slowly with the current, much as 

 sand dunes migrate with the wind. 



Sorby gave a very good description of current ripples in The 

 Geologist for 1859, but failed to recognize the existence of wave- 

 formed oscillation ripples, although he noted, and even pressed too 

 closely, the analogy between true waves and ripples. 2 For many 

 years current-formed ripples were the only type recognized in most 

 textbooks. In 1882, in opposition to the general view, Hunt 

 claimed that as a rule ripple marks are the product of oscillatory 

 wave action, and supported his claim with observations based on 

 the artificial production of ripple marks, as well as with numerous 

 observations of naturally formed ripples. 3 He was evidently 

 unaware of the fact that Siau had supported the same theory some 

 forty years earlier, and in a later paper he erroneously credited 

 Forel with priority in the recognition of oscillation ripples. 4 Hunt 

 incidentally describes oscillation ripples in his paper "On the 

 Action of Waves on Sea-Beaches and Sea-Bottoms." 5 He also dis- 

 cusses the nomenclature of ripple marks at much length in a paper 

 published in 1904, 6 and elsewhere quotes Lieutenant Damant, R.N., 



1 H. T. De la Beche, The Geological Observer (Philadelphia, 185 1), p. 506. 



2 H. C. Sorby, "On the Structures Produced by the Currents Present during 

 the Deposition of Stratified Rocks, " Geologist, April, 1859, p. 141. 



3 A. R. Hunt, "On the Formation of Ripple-Mark," Proc. Roy. Soc. London, 

 XXXIV (1882), 2, 18. 



•>A. R. Hunt, "The Descriptive Nomenclature of Ripple-Mark," Geol. Mag., 

 N.S., I (1904), 411. 



s A. R. Hunt, "On the Action of Waves on Sea-Beaches and Sea-Bottoms," 

 Proc. Roy. Dublin Soc, N.S., IV (1884), 261-62. 



6 A. R. Hunt, "The Descriptive Nomenclature of Ripple-Mark," Geol. Mag. 

 N.S., I (1904), 410-18. 



