Dr. W. F. Hume—Origin of the Nile Valley. 389 
For the Gulf of Suez, it seems difficult to explain the present 
conditions of its cutting through a gigantic dome, taken together 
with the inequilateral structure of the parallel ranges bordering the 
gulf, without invoking the aid of very serious fractures, whose 
activities are marked in most pronounced fashion on the peninsula 
of Sinai. ‘Thus we have an earth wave-system gathering strength as 
it passes from east. to west, the great trough being Egypt itself with 
its river in part marking the basin centre, while the wave-crest 
reveals itself in the serrated peaks and barren hills of the Eastern 
Desert and the wilderness of Sinai. Necessarily, as with the waves 
of the sea, this great system is broken into minor crests and hollows, 
domes rather than anticlines will be the rule, while curved fault- 
systems will surround them. All these features will no doubt become 
more and more marked as the detailed geological structure demands 
attention from economic or other reasons. In Sinai the north-west 
trend of the waves is replaced by a dominant north-eastward direction, 
but we know far too little of Northern Arabia to dogmatize as to its 
meaning and significance. A second, or transverse system of folds, 
is no doubt of great importance, and its true meaning will become 
more obyious as study proceeds, but as this involves work in regions 
difficult of access, or complicated in outline, progress will necessarily 
be slow, nor do these earth-movements bear prominently on the 
question. 
Briefly summarizing the point of view I at present hold— 
1. The main structure of Egypt is determined by two major fold- 
systems, one having dominant north or north-west trend, the other 
more or less transverse to this system. 
2. In the north-trending fold-system the wave-crests and troughs 
become more pronounced from west to east, finally resulting in 
fractures of the greatest geographical importance. 
3. In the depression containing the oases, comparatively gentle 
folding has resulted in the denudation of those portions where the 
anticlinal structure is most pronounced, fracture being unimportant 
as regards surface-features, though in Kharga of great moment for 
water-supply. 
4. The Nile Valley is regarded as due in the main to the com- 
bination of the north-trending fold, erosion of the softer Cretaceous 
strata in the southof Egypt, and the less resistant members of the 
Middle Eocene in Northern Egypt, the connecting Nile ravine 
following the axial line of the centre of the synclinal trough. 
5. The Gulf of Suez, though in direction determined by the 
dominant fold-trend, has required fracture for its full formation, 
there being possibly a minor fold region due to such fracturing 
between the Red Sea Hills and the main range of Sinai. 
6. In Sinai itself the fold-trend swings from north-west to north- 
eastward, and fracture-lines almost completely mask the original 
folds, which are only indicated by the trends of the gulfs and their 
parallel valleys. 
