the lava outpourings that ended the karoo deposition of rocks, not only covered the african surface, and other parts of gondwana with a 1.6 km thick layer basaltic lava, but it also forced its way, under high pressure, between the horizontal layers of sedimentary rocks belonging to the ecca and beaufort groups, to solidify into dolerite sills. the long vertical fissures through which the lava welled up solidified into dikes which resemble the great wall of china from the air.