Waves 9 
altered, however, whenever they meet obstructions and they 
slow down when reaching shallow water. As everyone knows, 
one of the outward evidences of a shoal is the change in form 
and speed of the swells that encounter it. 
STURBANCE 
“=~ 
DI 
DIRECTION 
OF SWELL 
The change in shape of swells is observed in other ways as 
well. For example, when waves strike a vertical cliff, they are 
turned back upon themselves. Far offshore an experienced 
eye will detect these reflected swells riding back over the 
