[Footnote 61: Details of a section of the lower beds of this group near the end of the lake have already been given on p. 44.] [Footnote 62: As might be expected, vertebrate remains occur chiefly in the sandy and clayey beds. Skeletons of marine animals such as _Zeuglodon_ and _Eosiren_ may, however, be frequently observed embedded in the hard intercalated limestones. Limestone cranial-casts of these animals are thus sometimes found, and one of these has already been figured and described (Elliot Smith, _The Brain of the Archæoceti_, Proceedings Royal Society, Vol. 71, pp. 322-331. Some most beautifully formed casts from one of the limestone beds were eventually determined by Andrews to be casts of the air passages of crocodile skulls.] [Footnote 63: Schweinfurth appears to have been the first to examine these beds.] [Footnote 64: One would imagine that there must have been a considerable amount of ferruginous matter in the water at the time of deposition of the Fluvio-marine series, the prevailing colours of the deposits being red and yellow.] [Footnote 65: Mayer-Eymar appears to believe the depression of the Fayûm is the result of the volcanic activity which produced these basalt flows. He says (op. cit. _Nouvelles recherches, etc._, p. 218.) “Or, de cette extension extraordinaire du phénomène volcanique dans l’ouest du grand désert, il est, en premier lieu, permis de conclure que c’est par suite de son action excavante qu’a eu lieu l’effondrement rempli de nos jours, en partie par le lac de Fayum.” Personally, we cannot see the slightest evidence in support of this. Where the basalt occurs as a hard band it usually causes steep cliffs as at Widan el Faras, owing to its protecting the underlying beds from denudation. To the west, in Jebel el Qatrani, its thickness and hardness determine the character and steepness of the escarpment below.] [Footnote 66: Pebble bands are occasionally met with in the coarser sandstones of the Fluvio-marine series, and it would seem that from them are derived the pebbles of quartz and flint which so invariably strew the desert-surface to the north to beyond the latitude of Cairo. Those flints on the surface are largely broken up and flaked by changes of temperature, but show comparatively little shaping by blown sand; the white quartz pebbles on the other hand, while seldom or never broken or flaked, are invariably more or less facetted, frequently into typical “dreikanter” or pyramid-pebbles; below the surface both varieties are perfectly water-rounded.] [Footnote 67: Many of the fossils mentioned in this profile were only discovered after long search, and had to be inserted in the measured section afterwards. Their position therefore is only approximate, as individual beds could not always be correlated at the different points where fossils were collected.]