412 A. R. Hxint — Nomenclature of Rijjple-mark. 



In the present article I propose to call attention to the extreme 

 ambiguity of the phraseology in common use in the discussion of 

 sand-ripples and cognate phenomena. 



With reference to the meaning of ' breadth ' and ' amplitude ' 

 a distinguished mathematician writes, " I cannot regard these 

 questions of phraseology of much importance." It no doubt matters 

 nothing when the ideas are clear, but I feel sure that inaccurate or 

 inadequate terras, and especially when they are avowedly descriptive 

 terms, must end in confusion of thought. 



In the case of ' ripple-mark,' Sir Archibald Geikie summarily 

 disposes of the difficulty by rejecting all such expressions as ' current- 

 mark ' and ' ripple-drift,' which, though accurate as far as they go, 

 are calculated to mislead. Both expressions might lead the reader 

 to suppose that ripple-mark can only be produced by the drifting 

 action of a continuous current of air or water, whereas current-mark 

 and ripple-drift might well be regarded as specific forms of the 

 genus ripple-mark. 



The foregoing three terms, together with ' wave-marks ' as used 

 by Dana, are a truly misleading quartette. ' Ripple-marks ' are 

 collections of sand in the form of water-ripples. There is no 

 pretence that they are made by water-ripples. But current-mark, 

 a completely parallel expression, professes to describe collections 

 of sand in the form of ripples made by a current. The ' current ' 

 here is avowedly the agent, whereas the ' ripple ' is merely the 

 illustration of the effect. In Dana's 'wave-marks,' an expression 

 even more closely allied to ' ripple-marks,' the 'wave' is the agent 

 and not merely the illustration. In ' ripple-drift ' we have a still 

 further element of confusion, as here ' ripple ' is not the illustration, 

 but has come to mean the actual sand, which has been collected in 

 ripple-like forms by drifting. 



' Wave-mark ' would be an excellent term descriptive of ordinary 

 marine ripple-mark were it not that ' wave ' would indicate the agent, 

 whereas ' ripple,' which is no more than a small wave, would be 

 used in an entirely different sense. Moreover, Dana has used ' wave- 

 mai'ks ' for a very unimportant marine phenomenon, viz., the faint 

 mark which is very occasionally left by a wave on a sandy beach. 



If ripple-marks and waves are to be subjects of discussion, 

 it is absolutely necessary that some definite meaning should be 

 attached to descriptive terms such as height, length, breadth, and 

 amplitude. 



We will now inquire how these terms are actually used in the 

 case of real waves. 



What do we understand by the height of a sea- wave? A sailor 

 undoubtedly measures height from ti'ough to crest. For instance, 

 in October, 1887, the Admiralty communicated to the Press a letter 

 from Captain Fisher descriptive of a voyage of the battleship 

 " Inflexible." He mentioned that " the waves were occasionally 

 twenty-four feet high and three hundred feet in length." This 

 height is obviously from trough to crest, and even so, very high 

 for the wave-length. 



