It was one of the islands of chalk left when the sea broke through to form the English Channel in 6500 BC: the others are now beneath the sea. It was left separated from the mainland by what became known as the Wantsum Channel, until the deposition of silt from the River Stour along the coast joined the Isle to the mainland. Today Thanet consists of 26 miles of golden sandy beaches and grade A1 farmland, set on quick-draining chalk sub-soil.