Notices of Memoirs — V. Cornish — Rippling of Sand. 521 



(corals), Mr. J. W. Kirkby (entomostraca), Dr. H. Woodward 

 (other Crustacea), Mr. F. A. Bather (echinoderras and brachiopods), 

 Dr. Wheelton Hind and Mr. E. J. Garwood (lamellibranchs and 

 gasteropods), Messrs. G. C. Crick and A. H. Foord (cephalopods), 

 and Mr. R. Kidston (plants). 



The Committee recommends that a grant be applied for, in order 

 to pay for the services of collectors, who are to be under the 

 direction of the Secretary of the Committee. 



X. — The Rippling of Sand by Water and by Wind. By 

 Vaughan Cornish. 



~T)EGULAR ripple-mark is produced in various ways in rolling 

 JLL sand. The billows formed by deposition of flying or floating 

 sand are considered in another paper (Section E — Geography). The 

 author distinguishes three principal kinds of rippled sand, viz. : 



1. The Ripple-mark of Sea. 



2. The Ripple-mark of Streams. 



3. The Ripple-mark of Dunes. 



In (1) symmetrical, knife-edged ridges are built up, owing, as 

 is well known, to the complete reversal of the current at short 

 intervals, which results in an effective co-operation of the direct 

 current with the vortex formed in the lee of projections on the 

 rough surface of the sand. This mechanism in the vertical plans 

 raises the ridges, and, in plan, extends them laterally, so that the 

 mottled surface of the initial stage is changed into long lines of 

 parallel ridge and furrow. 



If the direction of the waves changes, another set of ridges is 

 formed, and this produces polygonal figures. These have an even 

 number of sides, and the sides are arranged in opposing pairs. 

 This serves to discriminate polygonal forms due to fossil ripple- 

 mark from Hitchcock's supposed fossil tadpole-nests. 



2. The symmetrical, rounded, ripple-mark of the sandy bottom 

 of a stream is formed by the alternate acceleration and retardation 

 of current which occurs wherever the surface of the water is 

 corrugated by a train of standing waves. This form has been 

 called Ripple Drift. The ridges only travel when the whole train 

 of water-waves travels ; when the train of waves arises from a fixed 

 obstacle the sand ridges are stationary. 



3. The ripple-mark of dunes is produced when sand-grains 

 roll before the wind. These ripples are not symmetrical, but they 

 preserve their sectional shape during their growth, the height and 

 length increasing in the same proportion. They grow laterally in the 

 same way as (1). They are produced by the steadiest natural wind, 

 and even by a steady artificial blast, the resistance offered by the 

 sand-grains being sufficient to produce in yielding air a periodic 

 motion such as must be independently produced in water for the 

 formation of the ripple-mark of sea or stream. 



Flying-sand falling upon the surface of a sand-dune blurs the 

 pattern of the ripples, hut if the shower be not too thick the graius 

 aie soon sorted into position as they roll. 



