GEOLOGICAL HISTORY OF EGYPT AND THE NILE VALLEY. dol 
more recent channels due to occasional storms. The wide 
and ramifying valleys, such as the Wadies Queneh, Tarfeh, 
and Sonoor, by which the Arabian Mountains east of the 
Nile are traversed; those of the Sinaitic peninsula,* and of 
the Arabah, the deep-cut channels of the Edomite, Moabite, 
and Palestine table-lands, all testify to the existence of rivers 
in former times which have either altogether disappeared, or 
are represented only by occasional and evanescent floods. 
The same observation applies to very large regions of Central 
Africa.f Hence, we are obliged to have recourse to cosmical, 
and not merely to local, agencies for an explanation of this 
remarkable diminution of rainfall, and consequent drying up 
of the springs and rivers. 
In casting about for such agencies, we are brought face 
to face with the fact that, about the period at which we have 
now arrived in the history of Egypt, physical conditions very 
different from those of the present prevailed over the 
Northern Hemisphere. I refer to the conditions of climate 
during the Glacial period already referred to. These are now 
so generally recognised that it is unnecessary to insist upon 
them, so that [ need only observe that during their prevalence 
a climate resembling that of the Arctic Regions prevailed 
over the northern and central portions of Europe and Asia: 
the higher mountainous regions besides much of the plains 
and valleys were filled with perennial snow and ice, where 
these are only to be found now during winter. The Lebanon 
was the seat of glaciers; aud where these now exist, as in 
the Alps, Pyrenees, and Caucasus, they descended at the 
time referred to far below their present limits. Under such 
conditions of Northern and Central Europe, it is evident that 
the regions lying immediately to the south of the snowy tract 
must have experienced a climate very different from that of 
the present day. Their climate would necessarily be of a 
humid and temperate character, with abundant rainfall and 
vegetation. Large streams would flow down the valleys of 
Egypt, Libya, Sinai, and Southern Palestine, where now 
there are none; it is thus that the erosion of these great 
valleys may be accounted for. To the same period may in 
all probability be referred the erosion of those remarkable 
* Maps of the Ordnance Survey of Sinai, under Col. Sir Charles 
Wilson, R.E. 
t As noticed by Livingstone in his Last Journals, vol. ii, p. 217. Prof 
Henry Drummond states that Lake Nyassa is slowly drying up, Tropica 
Africa, p. 196. ; 
VOL. XXIV. 2A 
