818 STUDIES FOR STUDENTS 



suggested that they might represent fossil beach cusps seen in 

 cross-section. 1 



In 191 1 A. P. Brown published a paper entitled "The Formation 

 of Ripple-Marks, Tracks, and Trails," in which he endeavored to 

 show that asymmetrical ripples (current ripples) are formed by 

 deposition, whereas symmetrical ripples (oscillation ripples) 

 result from the erosion of a formerly smooth botton, consequent 

 upon the rippling of overlying water by wind action. 2 His con- 

 clusions do not appear to be supported by a sufficient body of con- 

 vincing evidence, and are opposed by theoretical considerations 

 and by the great body of experimental data already referred to. 

 In presenting his theory this author makes no reference to the 

 many previous investigations of ripple marks of all kinds, the 

 important results of which have been summarized above. 



Ripple marks have repeatedly been discussed in connection with 

 the interpretation of fossil ripples found in sedimentary rocks. 

 We need mention but a few of these discussions in the present con- 

 nection. As early as 1831 Scrope described fossil ripple marks 

 found on slabs of marble, and explained them as due to the oscil- 

 latory movements of shallow water. 3 Darwin, starting from the 

 very questionable assumption that a great ebb and flow of the tide 

 is essential to the formation of numerous ripples, concluded that 

 the presence of a large number of ripple marks in a geological 

 formation indicates with a considerable degree of probability that 

 the tides of early times rose higher than those of today. 4 Van Hise 

 figured and described one type of oscillation ripples, and empha- 

 sized their value as criteria for determining the original altitude 

 of steeply inclined strata. 5 



1 J. C. Branner, editorial note, Jour. Geol., IX (1901), 535-36. 

 3 A. P. Brown, "The Formation of Ripple-Marks, Tracks, and Trails," Proc. 

 Assoc. Nat. Sci. Philadelphia, LXIII (191 1), 536-47. 



3 G. P. Scrope, "On the Rippled Markings of Many of the Forest Marble Beds 

 North of Bath, and the Foot-Tracks of Certain Animals Occurring in Great Abun- 

 dance on Their Surfaces," Proc. Geol. Soc. London, I (1831), 317-18. 



4 G. H. Darwin, "On the Geological Importance of the Tides," Nature, XXV 

 (1882), 214. 



5 C. R. Van Hise, "Principles of North American Pre-Cambrian Geology," 

 Sixteenth Ann. Rept. U.S. G. S., Part I (1896), 719-21. 



