Chesil Beach, beach, county of Dorset, England, that stretches 18 miles (29 km) from Bridport to the Isle of Portland. One of the best-known natural features in Britain, it consists of shingle (pebbles), 98.5 percent of which is hard flint or chert rock. From Abbotsbury to Portland (12 miles [19 km]) the beach is separated from the mainland by a lagoon. The most remarkable feature of the beach is the lateral sorting of the shingle: at the northwestern end it is pea-sized, and at Portland the average diameter of the stones is 2 inches (5 cm).