Place : Adrar of Mauritania.
Description : The mystery of the formation of Guelb Richat still called '' the eye of Africa '' by the astronomers, remains whole and is worth for many other scientific forwardings.
Several assumptions were considered: impact of a large meteorite, tectonic structure or convexity caused by the installation in the Precambrian rocks sediments of major origin. This last assumption is favoured today. The whole eye extends on 180 mile (350 km) and its pupil on 20 mile (40 km).