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 base. The nearest permanently inhabited settlement is 366.8 km, or 198.1 nmi, west of the headland of Aird an Rùnair, near the crofting township of Hogha Gearraidh on the island of North Uist at . North Uist is part of the "Na h-Eileanan Siar" council area of Scotland. The exact position of Rockall and the size and shape of the Rockall Bank was first charted in 1831 by Captain A. T. E. Vidal, a Royal Navy surveyor. The first scientific expedition to Rockall was led by Miller Christie in 1896 when the Royal Irish Academy sponsored a study of the