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XXVII. 



FORMATION OF SAND-RIPPLES. 



By J. JOLY, B.A.L, D.So., F.R.S., F.G.S., 

 Professor of Geology and Mineralogy in the University of Dublin. 



[Eeceived for Publication, August 15 ; Published, September 23, 1904.] 



Observations made on the sandy shore of Ballinskelligs Bay, 

 Co. Kerry, appeared to show that sand-ripples were formed on 

 the sand by the wind in the following manner. 



The particles of sand rolled by the wind up to the crest d 

 [see figure] were projected from it by the force of the wind ; 

 described a trajectory under wind -impulse and gravitational 

 force, reaching the next slope at some point near a second 

 crest C 2 . Up this they were again transported until projected 

 from the crest C 2 . In addition to these movements, grains were 

 rolled over the crests (apparently the larger and heavier grains, 

 on the whole), and so gave rise to a gradual forward travel of 

 the ripples. 



It is evident, if this be the mode of formation of the ripples, 

 that the spacing of the ripples (wave-length) and their height are 

 inter- dependent. 



To test this theory, I raised a temporary ripple of almost three 

 times the normal height. It rapidly blew away at the crest, and 

 at the same time an elevation, several normal wave-lengths 

 removed from it, began to form in its lee ; while the hollow 

 between, being insufficiently fed from the raised crest, began to 

 deepen by wind-scour till the damp and firm sand beneath was 

 exposed to view. 



