Cities and towns in coastal York County were cleaning up and assessing damage Monday as remnants of a relentless nor’easter pounded the Maine coast for a fourth day. Through the weekend, surging high tides and wind-driven waves tore through rock sea walls, washed away dunes and roads, and damaged dozens of homes and businesses. In York, the angry Atlantic revealed a nearly 200-year-old shipwreck that had been concealed beneath Short Sands Beach. The destructive storm rode the upper edge of a nor’easter that knocked out power to 1.8 million homes and businesses in states south of Maine.