Collision course?

One coming and one going from Sheerness Docks - actually passing well apart.  This was taken from Minster beach on the Isle of Sheppey - looking north across the Thames Estuary towards Southend-on-Sea, Essex,  in the distance. The beach had many of these birds on the shoreline but what intrigued me was that it was covered in  large pebbles that looked like they were chunks of fossils.  Any ideas anyone?