During an investigation of the upper part of the Sabi Valley made just before the war in company with my son, the late C. F. Mennell, two well-marked ring structures and indications of others were met with. Reference to these was made in a communication to the Rhodesia Scientific Association in 1938 before the investigation had been concluded or any of the rocks collected had been sliced. The suggestion was then made that they owed their remarkable features to the action of the enclosing granite on the limestone still forming their cores.