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 flora and fauna. They chartered the "Granuaile". A detailed underwater mapping of the area around Rockall undertaken in 2011–2012 by Marine Scotland showed that Rockall itself is a minor pinnacle, whilst Helen's Reef extends in a sweeping arc of fissures and ridges to the north-west of the islet. Between the islet and Helen's Reef is a deeper trench much used by squid fishermen. The area where Rockall is in, is located in the pathway of the warming and moderating Gulf Stream. Although the rock does not sustain any weather station, the isolated nature of the setting dictates an extremely maritime