Benue Trough the Central African Shear Zone and for the volcanic island of St. Helena in the Atlantic ocean. Three periods of magmatic activity (volcanic action) have been identified, 147–106 Ma, 97–81 Ma and 68–49 Ma. The first is prominent in the north of the trough, and contemporary with magmatism in Brazil, probably occurring during a period of crustal extension before the Atlantic started to open. The second is found only in the south of the trough, and may belong to a period when the extension of the Atlantic had slowed down, ending with a period of compression. The third and last
Rockall "Two Royal Marines and a civilian naturalist, led by Royal Navy officer Lieutenant Commander Desmond Scott, raised a Union flag on the island and cemented a plaque into the rock". Prior to this the island was legally "terra nullius". In 1972, the British Island of Rockall Act formally annexed Rockall to the United Kingdom. The UK considers the island administratively part of the Isle of Harris and, under the Scottish Adjacent Waters Boundaries Order 1999 a large sea area around it was declared to be under the jurisdiction of Scots law. A navigational beacon was installed on the island in