16 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
and the Chart of Suakim Harbour gives the features of a typical specimen. 
The characteristics more or less prominently developed in all are :— 
(1) Canal-like outline. 
(2) Crossed branches running N. & 8. and H. & W. 
(3) A nearly uniform depth gently shoaling as one passes landwards. 
(4) A flat bottom of coral-mud. 
(5) Precipitous sides of growing reef below sea-level and cliffs above. 
The latter are of course the height of the neighbouring plain, 
generally 2 feet or so in Suakim Harbour, or up to 12 feet in Khor 
Shinab. 
The late Mr. Barron, who was Geologist to the Sudan Government, 
explains these formations as resulting from two systems of faults at right 
angles to one another. The almost rainless climate, the absence of very 
strong tidal currents, and the protection afforded by growing coral, have 
allowed the above-mentioned characteristic and almost bizarre features to 
remain, whereas in the corresponding structures on the equatorial coasts of 
East Africa the erosion of powerful tidal currents and of freshwater streams 
has, in most cases, widened creeks into bays and broken down their vertical 
sides into shelving shores. 
The Red Sea has an evil reputation with navigators on account of the 
number and complexity of its coral-reefs and the presence, in certain areas, 
of that especial horror, the coral pinnacle which rises out of deep blue water 
toijust under the surface. The reefs may be divided into :— 
(a) Fringing reefs along the coast and round islands. 
(6) A Barrier system, oiitdh 3 is especially typically develoned between 
19° N. and 24° N. 
(c) Scattered reefs, including some of Atoll form. 
The climate is noted for an extreme aridity, which is however not so 
complete in the southern part of the coast asin the northern. Among the 
hills furious rain-storms are frequent in. August and winter, which flood 
the valleys for a few hours at a time in the way described by travellers in the 
Sinai Peninsula, and by Egyptian Survey Department officials for the desert 
bordering the Gulf of Suez*. These conditions are of course the best 
possible for the conveyance of the large quantities of detritus which have 
formed the great alluvial maritime plain. 
The tides have been referred to in the Narrative (p. 3), where it is stated fae 
the middle part of the Red Sea is practically tideless. There are, however, 
variations of level of two feet or thereabouts which occur almost daily, but 
their occurrence is subject to no fixed rule. The rise or fall may be fairly 
regular for several days, high water being at nearly the same time each 
day, then it may remain continuously low or continuously high for a short 
period. Occasionally the water may sink to a foot below its lowest normal 
* Barron & Hume: “ Topography and Geology of the Eastern Desert of Egypt, Central 
portion,” issued by the Survey Department, Public Works Ministry, p- 282. 
