The Dorset Downs are an area of chalk downland in the centre of the county Dorset in south west England. The downs are the most western part of a larger chalk formation which also includes Cranborne Chase, Salisbury Plain, Hampshire Downs, Chiltern Hills, North Downs and South Downs.
The Dorset Downs are bounded on the north, along the steep scarp face, by the Blackmore Vale, a large clay and limestone valley. On the east, the Downs were once, thousands of years ago, continuous with Cranborne Chase, but the River Stour now cuts a valley between them, which is the location of Blandford Forum and the eastern boundary of the downs. From the northern scarp face, the hills dip gently southwards before the chalk disappears beneath the Bagshot Beds which form the heathlands of the county, between Dorchester and Wareham. South of the River Frome, the chalk reappears in a narrower strip, forming coastal cliffs east of Weymouth and, further east, the steep ridge of the Purbeck Hills. This southerly strip of the visible chalk continues westwards behind Weymouth, and rejoins the main body of the downs at their western extremity at Eggardon Hill. In the west the chalk dips down under marl.
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