The amount of iron in the beach sands have no relationship to magnetic north 
as to origin,  but rather are a function of the iron content of the igneous, 
sedimentary, or metamorphic rocks that outcrop or subcrop in the general  
vicinity of the beach.  When the rocks are decomposed, iron and other heavy 
minerals originally contained in the rock are found along with the silica 
sands.   Rip tides and current action might move the heavy minerals away from 
the area of origination, but they should not move too far away, relatively 
speaking, because of their high specific gravity relative to that of water.
Al Hrubetz

_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)