and east Devon coast that is important for its geology and landforms. The South West Coast Path runs around the coast; it is the United Kingdom's longest national trail at . Portland is unusual as it is connected to the mainland at Abbotsbury by Chesil Beach, a tombolo which runs north-west to West Bay. Portland is sometimes defined incorrectly as a tombolo—in fact Portland is a tied island, and Chesil Beach is the tombolo (a spit joined to land at both ends). There are eight settlements on Portland, the largest being Fortuneswell in Underhill and Easton on Tophill. Castletown and Chiswell are the other villages in Underhill, and Weston, Southwell, Wakeham and the Grove are on the Tophill plateau. Many old buildings are built out of Portland Stone; several parts have been designated Conservation Areas to preserve the unique character the older settlements which date back hundreds of years. The Isle of Portland has been designated by Natural England as National Character Area 137. It is adjoined by the Weymouth Lowlands to the north. Geology Geologically, Portland is separated into two areas; the steeply sloping land at its north end called Underhill, and the larger, gently sloping land to the south, called Tophill. Portland stone lies under Tophill; the strata decline at a shallow angle of around 1.5 degrees, from a height of near the Verne in the north, to just above sea level at Portland Bill. The geology of Underhill is different to Tophill; Underhill lies on a steep escarpment composed of Portland Sand, lying above a thicker layer of Kimmeridge Clay, which extends to Chesil Beach and Portland Harbour. This Kimmeridge Clay has resulted in a series of landslides, forming West Weares and East Weares. underneath south Dorset lies a layer of Triassic rock salt, and Portland is one of four locations in the United Kingdom where the salt is thick enough to create stable cavities. Portland Gas applied to excavate 14 caverns to store of natural gas, which is one percent of the UK's total annual demand. It was proposed that the caverns should be connected to the National gas grid at Mappowder via a pipeline. Plans had it that the surface facilities should be complete to store the first gas in 2011, and the entire cavern space available for storage in winter 2013. As part of the £350 million scheme, the Grade II listed former Old