242 WAVES OF THE SEA 



solitary. I obtained two photographs showing the 

 level of the water when the bore was passing, and, 

 a few seconds afterwards, during this subsidence. 



On the Want of Concordance between Height of 

 Tide and Height of Bore, and on the Con- 

 ditions which Determine the Starting-point 

 of the Bore 



The capricious character of the tidal bore is 

 one of the most interesting characteristics of this 

 phenomenon in the Severn, and I suspect that it 

 is capricious in other rivers also. 



The disturbing cause lies in the sand-banks 

 below Hock Cliff, and we will therefore now 

 describe the character of the river or estuary 

 below that point. The change which there com- 

 mences is not only that which has been mentioned 

 the straight, diverging banks of the high -water 

 channel, in place of winding, nearly parallel banks 

 but also a change of gradient. The low-water 

 slope, which from Gloucester to Framilode is slight, 

 becomes very steep below Hock Cliff, and con- 

 tinues of unusual steepness to the Sheperdine 

 Sands. Below the Severn Bridge, which prac- 

 tically bounds the view down-stream from Hock 

 Cliff, the steepness is slightly increased. Below 

 the Sheperdine Sands to Aust the low-water 

 gradient is again slight. 



