Dr P. M. Allen writes: I appreciated Culver & Williams' up-to-date interpretation of the geology of Sierra Leone, but I take issue with their reinterpretation of the stratigraphic position of the Taban Formation. Whereas I consider it to be younger than the Rokel River Group, they contend that it should be divided into the Taban and Tibai members and designated part of the Tabe Formation, which is at the base of the Rokel River Group. Their justification is that the member 'exhibits greenschist metamorphism and folding consistent with other pre-orogenic Rokel River Group strata.
The main difficulty in determining the stratigraphic position of the Taban Formation, as I defined it, is that there is no physical continuity between it and the Rokel River Group. However, I did a careful survey of the different lithologies among pebbles and cobbles in the formation and found rock types throughout it identical to those from within the Rokel River Group. In parts, nearly all the pebbles and cobbles were attributable to this source. Among the rock types are distinctive volcanic and sedimentary rocks, some of the latter displaying cleavage. On this evidence I interpreted the Taban Formation as being post-orogenic molasse younger than the Rokel River Group. I am unaware of any other volcano-sedimentary succession in that part of West Africa which serves better as a source for the detritus in the Taban Formation than the Rokel River Group, and I cannot accept that the evidence presented by Culver & Williams invalidates my conclusion.