226 WAVES OF THE SEA 



that uniformity of depth across the stream is im- 

 portant for the preservation of a roll -wave. In 

 a channel with deep longitudinal grooves and 

 shallow shores such waves would change their 

 direction and discharge laterally upon the shelving 

 banks . 



I have received the following account of the roll- 

 wave at Aysgarth from a resident at that place : 



" The Aysgarth local name for a flood was 

 ' spate ' or * freshet.' I was one evening in the 

 middle of the river, about 100 yards below the 

 lower Force, fishing, when I heard a roar above, 

 and presently a wall of water some 2, feet or 3 feet 

 high came dashing over the fall. I, fortunately, 

 gained the bank in time to see it rush past me, 

 filling the bed, rushing madly over the boulder 

 rocks, and spoiling my fishing. The rocks here 

 are limestone, with great fissures and pot-holes. 

 Below the Force is the great salmon-hole, the limit 

 of the up -rushing fish. 



" Above the lower Force the stream runs in 

 reaches over shelving limestones from the second 

 Force. At the foot of this there is a very deep 

 hole. . . . Succeeding this Force the water comes 

 beneath the picturesque bridge from the beautiful 

 upper Force, a succession of ledges, forming holes 

 beneath. " 



