It appears for all the world to be a natural formation.
http://www.freerepublic.com/focus/chat/2757720/posts?page=27#27
http://www.freerepublic.com/focus/chat/2757720/posts?page=40#40
http://www.freerepublic.com/focus/chat/2757720/posts?page=52#52
Nothing to see here, move along - move along...! < /humor >
What I would like to see is a scale that could determine the approximate size of this object, it may be just the shell of a long gone crab or other sea creature..