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 sovereignty for itself. The consistent position of successive Irish Governments has been that Rockall and similar rocks and skerries have no significance for establishing legal claims to mineral rights in the adjacent seabed or to fishing rights in the surrounding seas." The origin and meaning of the islet's name "Rockall" is uncertain; the Old Norse name for the islet, "Ròcal", may contain the element "fjall", meaning "mountain". It has also been suggested that the name is from the Norse "*rok", meaning "foaming sea", and "kollr", meaning "bald head"—a word which appears in other placenames in Scandinavian-speaking areas. Another idea is