Until the entire collection of fossils has been examined and determined, it is somewhat premature to attempt to fix the age of the series on palaeontological grounds. Up to the present the foregoing lists show the species which have been provisionally or finally determined. Some of these appear to be identical with species which have been recorded from Upper Eocene deposits of Europe, such as _Potamides scalaroides_, _P. tiarella_, while others, such as _Melania_ cf. _Nysti_, _Natica crassatina_ (found below the basalt in the so-called Sandberger Hills north-east of the Fayûm escarpment), are typically Lower Oligocene. Other forms, such as _Turritella angulata_, are common to both Eocene and Oligocene elsewhere. If Blanckenhorn’s determinations of these forms are confirmed, we may regard the upper beds, i.e., those immediately above the basalt, as undoubtedly of Lower Oligocene age. The beds below the basalt mark the transition from the Eocene to Oligocene, while the base of the series, so far unfossiliferous as far as molluscan remains are concerned, must be regarded as of Upper Eocene (Bartonian) age. We may hope that when the important vertebrate fauna occurring chiefly in the basal part of the series has been thoroughly exploited, and the remains systematically determined, confirmatory evidence will be obtained. At present the only forms described and determined, beyond pointing to a pre-Miocene age, do not indicate any definite horizon. Probably most of the animals will prove to be new, and although on that account more interesting from one point of view, will probably not assist us greatly in the exact determination of the age of the beds in question. _G._—=The Position of the Land-mass from which the Mammal Remains were Derived.=