STUDIES FOR STUDENTS 819 



Spurr showed that where continuous deposition takes place from 

 a current which constantly maintains asymmetrical ripples on the 

 surface over which it flows, the forward movement of the ripples 

 combines with the deposition of heavier and larger fragments in the 

 troughs and lighter particles on the crests to give a peculiar type of 

 false bedding in the resulting formation. 1 Jaggar criticized Spurr's 

 conclusions on the ground that his own experiments and observa- 

 tions indicated that ripple marks could not be produced in hetero- 

 geneous material; 2 but Spurr met the criticism with a fuller 

 discussion of the matter in which his original contention is well sus- 

 tained. 3 A short time previously Sorby had described a somewhat 

 similar phenomenon in a paper 4 printed almost exactly half a 

 century after the publication of his first account of ripple marks, 

 already cited. From an examination of the " ripple-drift " type of 

 false bedding in rocks, Sorby believed that one could "ascertain 

 with approximate accuracy, not only the direction of the current 

 and its velocity in feet per second, but also the rate of deposition 

 in fractions of an inch per minute." 5 Additional discussions of 

 fossil ripple marks are cited by Kindle in his paper referred to at 

 the beginning of this article, but need not be repeated here. 



1 J. E. Spurr, "False Bedding in Stratified Drift Deposits," Amer. Geologist, XIII 

 (1894), 43-47- 



2 T. A. Jaggar, Jr., "Some Conditions of Ripple-Mark," Amer. Geologist, XIII 

 (1894), 199-201. 



* J. E. Spurr, "Oscillation and Single-Current Ripple Marks," Amer. Geologist, 

 XIII (1894), 201-6. 



* H. C. Sorby, "On the Application of Quantitative Methods to the Study of the 

 Structure and History of Rocks," Quart. Jour. Geol. Soc. London, LXIV (1908) , 180-85. 



'Ibid., pp. 181, 197-99. 



