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HYDROGRAPHY 



362 



a. From eddies.- — Eddies are produced by a current being disturbed in its progress 

 by a shoal. It should be noted that the mark of the eddy is always downstream from 

 an isolated shoal, the distance depending on the depth of the water and the velocity of 

 the current. Likewise, eddies are more marked the stronger the current and the greater 

 the difference in depth between the shoal and the surrounding bottom. Dangers and 

 shoals are best detected from their eddies during tlie last of the ebb or the first of the 

 flood tide. 



6. From kelp.— Where k -Ip grows it is one of the best indications of dangers because 

 it is generally associated with rocky bottom. The value of kelp in this respect is 

 described on page 2, Alaska Coast Pilot, Part II. Each isolated growth of kelp, even a 



Figure 61. ^Taking sextant angles from an elevated station. 



