Bridge is old so the sea level rose , sedimentation etc.Besides even a dredging ship could not dredge the Ram Sethu and was helpless which they had call another ship called the Hanuman to resuce the dredger. So it is not made of sand or coral, but something alot harder like stone. Besides the coincidence of it being located in very place stated in the Ramayana that Lord Ram built Ram Sethu. These facts cannot be deny.
