About 80 surface and subsurface samples from the Ewekoro limestone quarry and the Akinsinde borehole, approximately 10 mi south of the quarry, were examined for foraminiferal evidence bearing on the nature and vertical extent of the Ewekoro Limestone and the ages of the suprajacent and subjacent beds. A detailed bed-by-bed sampling of the section exposed at Ewekoro was carried out. Altogether, about 78 species of benthonic and planktonic Foraminifera were identified. Although some ostracods and Foraminifera have been studied previously in this area, the present investigation revealed the presence of additional Foraminifera species which either have not been recorded previously or else were misidentified.

The undoubtedly early Eocene age of the shelly limestone commonly referred to as the "Ewekoro Formation" is substantiated by the presence of important index Foraminifera species including Bolivina ottaensis Reyment, Globorotalia bollii El-Naggar, and Pseudohastigerina wilcoxensis (Cushman & Ponton).

The biostratigraphic units established in the area have been correlated with equivalent units elsewhere in the western state. Detailed lithostratigraphic data in the form of charts and cross sections reveal the variability within the different units.

Data have led to the unmistakable conclusion that the deposition of the entire sequence referred to as "IMO Formation" occurred in a shallow-marine environment that succeeded the deposition of the Abeokuta Formation. The shelly limestone hitherto assigned a formational status is a member of the IMO Formation.

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