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 expedition made a brief attempt to return to the ship, but could not find the frigate in the haze, and soon gave up and returned to Rockall. After the haze became a fog, the lookout sent to the top of Rockall spotted the ship again, but it turned away from Rockall before the expedition in their boats reached it. Finally, just before sunset, the frigate was again spotted from the top of Rockall, and the expedition was able to get back on board. The crew of the "Endymion" reported that they had been searching for five or six hours, firing