well at Kimmeridge which has been producing oil since the early 1960s. Dorset's diverse geography ensures it has an assortment of rivers, although a moderate annual rainfall coupled with rolling hills, means most are typically lowland in nature. Much of the county drains into three rivers, the Frome, Piddle and Stour which all flow to the sea in a south-easterly direction. The Frome and Piddle are chalk streams but the Stour, which rises in Wiltshire to the north, has its origins in clay soil. The River Avon, which flows mainly through Wiltshire and Hampshire, enters Dorset towards the end of its journey at Christchurch Harbour. The rivers Axe and Yeo, which principally drain the counties of Devon and Somerset respectively, have their sources in the north-west of the county. In the south-west, a number of small rivers run into the sea along the Dorset coastline; most notable of these are the Char, Brit, Bride and Wey. Most of Dorset's coastline is part of the Jurassic Coast, a World Heritage Site, which stretches for between Studland and Exmouth in Devon. This coast documents the entire Mesozoic era, from Triassic to Cretaceous, and is noted for its geological landforms. The Dorset section has yielded important fossils, including Jurassic trees and the first complete Ichthyosaur, discovered near Lyme Regis in 1811 by Mary Anning. The county features some notable coastal landforms, including examples of a cove (Lulworth Cove), a natural arch (Durdle Door) and chalk stacks (Old Harry Rocks). Jutting out into the English Channel at roughly the midpoint of the Dorset coastline is the Isle of Portland, a limestone island that is connected to the mainland by Chesil Beach, a long shingle barrier beach protecting Britain's largest tidal lagoon. The county has one of the highest proportions of conservation areas in England—and two Areas of Outstanding Natural Beauty (AONB) covering 53% of the administrative county. It has two Heritage Coasts totalling and Sites of Special Scientific Interest covering . The South West Coast Path, National Trail, begins at South Haven Point at the entrance to Poole Harbour. There are also substantial areas of green belt surrounding the South East Dorset conurbation, filling in the area between this and the Cranborne Chase and the West Wiltshire Downs AONB. Climate Dorset's climate of warm summers and mild winters is partly due to its position on Britain's south coast. The third most southerly county in