In reply to pebbles:
never been there, but from what you describe it could be dessication cracks. a layer of mudstone which litterally dried out a cracked into polygon shapes. these cracks then get filled in by sand or a coarser mud when the surface is re-submerged, effectively beccoming fossilised.
but if you are talking about something close to the previous posters photo then its nothing particularly interesting, just an artefact of how that area of rock has weathered as it apears to be near the high water mark.