The mystery continues over what caused one of the worst dolphin strandings ever on the Treasure Coast in Onslow County Monday. Fifteen dolphins were found stranded on North Topsail Beach early Monday morning. A dozen of the striped dolphins, normally deep-water animals, died. And Tuesday, marine mammal experts spent the day in a lab at North Carolina State's School of Veterinary Medicine, examining those dolphins. Preliminary results have found no cause for the mass stranding. Three dolphins were saved when volunteers pushed them back into deeper water.