The Hilsea Lines are a series of defunct fortifications on the island's north coast, bordering Portsbridge Creek and the mainland. Portsdown Hill dominates the skyline in the north, and contains several large Palmerston Forts such as Fort Fareham, Fort Wallington, Fort Nelson, Fort Southwick, Fort Widley, and Fort Purbrook. Portsdown Hill is a large band of chalk; the rest of Portsea Island is composed of layers of London Clay and sand (part of the Bagshot Formation), formed principally during the Eocene.
The Hilsea Lines are a series of defunct fortifications on the island's north co.ast, bordering Portsbridge Creek and the mainland. Portsdown Hill dominates the skyline in the north, and contains several large Palmerston Forts such as Fort Fareham, Fort Wallington, Fort Nelson, Fort Southwick, Fort Widley, and Fort Purbrook Portsdown Hill is a large band of chalk; the rest of Portsea Island is composed of layers of London Clay and sand (part of the Bagshot Formation), formed principally during the Eocene.