yptiaca_ and _Araucarioxylon
Aegypticum_). They are conformably overlain by clays and limestones
with _Exogyra Overwegi_ belonging to the Lower Danian, and these by
clays and white chalk with _Ananchytes ovata_ of the Upper Danian. In
many instances the Tertiary formation, which occurs between Esna and
Cairo, unconformably overlies the Cretaceous, the Lower Eocene being
absent. The fluvio-marine deposits of the Upper Eocene and Oligocene
formations contain an interesting mammalian fauna, proving that the
African continent formed a centre of radiation for the mammalia in
early Tertiary times. _Arsinoitherium_ is the precursor of the horned
Ungulata; while _Moeritherium_ and _Palaeomastodon_ undoubtedly
include the oldest known elephants. Miocene strata are absent in the
southern Tertiary areas, but are present at Moghara and in the north.
Marine Pliocene strata occur to the south of the pyramids of Giza and
in the Fayum province, where, in addition, some gravel terraces, at a
height of 500 ft. above sea-level, are attributed to the Pliocene
period. The Lake of Moeris, as a large body of fresh water, appears to
have come into existence in Pleistocene times. It is represented now
by the brackish-water lake of the Birket-el-Kerun. The superficial
sands of the deserts and the Nile mud form the chief recent
formations. The Nile deposits its mud over the valley before reaching
the sea, and consequently the Delta receives little additional
material. At Memphis the alluvial deposits are over 50 ft. thick. The
superficial sands of the desert region, derived in large part from the
disintegration of the Nubian Sandstone, occupy the most extensive
areas in the Libyan Desert. The other desert regions of Egypt are
elevated stony plateaus, which are diversified by extensively
excavated valleys and oases, and in which sand frequently plays quite
a subordinate part. These regions present magnificent examples of dry
erosion by wind-borne sand, which acts as a powerful sand blast
etching away the rocks and producing most beautiful sculpturing. The
rate of denudation in exposed positions is exceedingly rapid; while
spots sheltered from the sand blast suffer a minimum of erosion, as
shown by the preservation of ancient inscriptions. Many of the
Egyptian rocks in the desert areas and at the cataracts are coated
with a highly polished film, of almost microscopic thinness,
c