Faunistics and Ages of the East African Islands

Abstract

ON an ordinary map the three low tropical islands of Pemba, Zanzibar and Mafia appear to bear a similar relationship to the African continent, from which they are all distant less than thirty miles. In fact, however, while the last two islands are on the continental shelf, Pemba is surrounded by water 2,500 ft. deep. Geological opinion is unanimous that Zanzibar and Mafia have been separated from the mainland only since Pleistocene times, but the geological history of Pemba is more uncertain. It has been maintained by Stockley^1,2 that this island has not been connected with Africa at least since Miocene times and his views have obtained wide currency. Actually the geological evidence on which this view is based is not very conclusive; for it is limited to the apparent non-existence of an unconformity between the (non-fossiliferous) Wete beds and the Chakechake beds which are dated as early Miocene.