334 WAVES OF THE SEA 



much as the appearance that the poetical student 

 of Nature has relied for conveying his impressions 

 of these scenes. Tennyson's phrase to " babble 

 on the pebbles " is a familiar example. When he 

 speaks of the " drumming thunder " of a great 

 waterfall, he records by ear the partial intermittence 

 superimposed upon a steady motion, which will 

 be dealt with in the next section of this paper. 



On Gushing Motion in Cataracts and on the 

 Conical Structures produced by the Break- 

 up of a Waterfall 



We have seen how in a swift shallow stream the 

 frictional retardation of the layers next to the 

 bed imparts a gushing motion to the water, which, 

 when the channel is straight and of uniform cross - 

 section, produces a train of long waves of the 

 bore form with foaming fronts transverse to 

 the current, following one another in regular suc- 

 cession down the stream. In cataracts and water- 

 falls there is also a gushing motion, but it is 

 irregular. In hilly or mountainous districts the 

 noisy cataract of white water replaces the clear 

 babbling brook with standing waves which is 

 characteristic of undulating country, or the silent 

 stream of the plain with its curling currents and 



