1863..
ADAMS NILE VALLEY.
D
the soil has been undisturbed and exposed to the action of the atmo-
sphere for a length of time. The formation is going on at present,
and is caused, no doubt, by some affinity between the air and the
chemical components of the river- alluvium. When met with on
the sands of the desert, it indicates an alluvial deposit underneath.
Among the ancient river- deposits on the plain eastward of Wadi
Halfeh, at the foot of the Second Cataract, this substance abounds,
either in the shape of nodular fragments

on the surface, or in masses
mingled with the soil. It has a great resemblance to the Kunkar of
India, with which it appears to me almost, if not absolutely, iden-
tical f .
3. Terraces of the Valley

their Cliffs and Caves. — Taking a gene-
ral view of the Nile Valley between the First and Second Cataracts,
one is struck with the regularity with which terrace-cliffs and flats
continue

indeed, except at broken intervals, these appearances are
pretty clearly denned even as far down as Selsileh, about 36 miles
below the First Cataract. At first there may be some difficulty in
tracing these levels, but after a little experience their presence be-
comes evident

and, except where the soil has been removed by the
action of rain, .fcc, I had no difficulty in finding abundance of river-
shells at altitudes of at least 120 feet above the highest Nile of the
present time.
The junction between the sandstone and granitic rocks is not
always observed to be even or regular, as we find the latter often,
as it were, dovetailing into the sandstone above, as here represented
(%. I)-
Fig. 1. — Diagram showing the Line of Junction of the Granite and
Sandstone in Nubia.
Sandstone.
"•• » o o
Granite.
In this way Ave can suppose the insular prominences of the Cata-
racts to have been caused by the softer sandstone being washed
away.
The point of junction between the two rocks is often marked by
layers of rounded water-worn pebbles, or coarse gravelly sand,
which, however, may be frequently seen running in veins throughout

See Specimen No. 6.
t Veins of oxide of iron are common between Thebes and Gofu, and are best
seen on the face of the recent alluvial banks, where they run horizontally for
several miles in the form of reddish