414 A. R. Hunt — Nomenclature of Ripple-mark. 



water-oscillation which forms the ripple-mark. What to an English^ 

 observer is the crest to crest length of ripples, is to Professor Forel 

 their ' largeur ' or ' breadth.' 



Professor Darwin speaks of a " rotational oscillation with a jerking 

 motion of small amplitude " ; ^ of the height of ripples, and of the 

 'wave-length' of ripples. With him also 'amplitude' expresses 

 the idea of motion. 



Ripple-marks so closely imitate in form motionless water-ripples 

 (such as may be seen in a sharp current) that it is most natural to 

 describe them by the phraseology used for true waves, such as 

 ' height ' and ' wave-length.' But even here we do well to remember 

 that the height of a sand-ripple can never be synonymous with the 

 height of a water-ripple, since the latter is referred to the level 

 of repose of the water. The sand-ripple reposes corrugated as 

 comfortably as it does flat. In fact, the height of ripple-mark is 

 from trough to crest, and therefore does not even correspond with 

 the ' height ' of water-ripple, which is from crest to mean level. 



In 1900 I was nominated by Section C a member of a joint 

 committee with Section E to investigate ' Terrestrial Surface Waves.' 

 I was reluctant to accept the nomination, which had been made in> 

 my absence, because, as I at once pointed out, I could see no geological 

 bearing in the subject, which related in the first place to snow 

 phenomena,' and I knew nothing about it. On receipt of the first 

 report I found that I was quite uncertain as to the meaning attached 

 by the committee to the technical terms used in describing the 

 dimensions of snowdrifts. In fact, I might go further, as I do not 

 understand the terms used to describe the object of the committee's 

 researches, viz. ' terrestrial surface waves.' I found that both 

 snowdrifts and snow-ripples were described exactly as though they 

 were real waves, and not merely wave-like forms. The following 

 quotation will indicate my difficulty : — 



"The height of these waves [of snow] was generally not more 

 than six inches. They are flatter than the homologous asolian sand 

 ripples, the wave-lengths being often forty or fifty times the 

 amplitude. . . . There are also regularly undulating surfaces 

 carved by the wind in more coherent snow . . . it is pro- 

 posed to call them tmdtilates " (Rep. Brit. Assoc, 1901, p. 398). 



It will be observed that the geographers have captured the 

 entire wave-nomenclature, e.g., ripples, wave-length, height, ampli- 

 tude, and undulating. If we refer to Murray's Dictionary we shall 

 find that the primary meaning of amplitude is width or breadth ; 

 that its astronomical meaning is angular distance ; and that its 

 physical meaning is the vibration of a particle. With regard to the 

 word ' undulating,' we have Pope's line " Through undulating air 

 the sounds are sent." The geographical and geological use of 

 'amplitude' to express height forces the word into a meaning in 

 direct conflict with both its ordinary use and its derivation. 

 Professor Lapworth, in his address to Section C, points out that the 

 form of the " wave or fold of the geologist resembles that of the 



1 rroc. Roy. Soc, 1883, p. 2. 



