Cc. CROSSLAND—PHYSICAL PESCRIPTION OF KHOR DONGONAB. 265 
Reports on the Marine Bronoey of the SupANEsE Rep Sea.—XVIII. A 
PuysicaL Description of KHor Dongonas, RED SEA. By Cyrin Cross- 
LAND, M.A., B.Se., F.L.S., F.Z.S., Marine Biologist, Sudan Government. 
(PLaTES 28-34 and 3 Text-figures.) 
A SuPpLEMENT to the Author’s “ Recent History of the Coral Reefs of the Red Sea,” in 
Journ. Linn. Soc., Zool. vol. xxxi. (1907) p. 14. 
[Read 19th January, 1911.] 
{Dongonab is the correct pronunciation of the place-name spelt Dongola on those few 
maps which insert it, and so spelt by me in my paper of 1907. Khor Dongonab is marked 
Dongonab Bay on the last Admiralty Chart published. 
The Arabic word Khor is very loosely applied to almost any depression of the ground, 
ereat or small. Khor Dongonab is a bay 15 miles long by from 3 to 8 wide. Other 
Khors are inlets like Suakin harbour, a mile or more long by a few yards wide, or shallow 
watercourses on land which contain rushing torrents once or twice in a year, or deep 
ravines among the hills. The word has even been applied to an artificial trench 10 feet 
wide by 4 deep. | 
In the paper to which parts of this may be regarded as a supplement 
I showed that the very peculiar structure of the Red Sea coasts * is due to 
certain earth-movements which were consequent upon the opening of the 
Great Rift Valley t of which the Red Sea is a portion. Briefly this structure 
is as follows :— 
The Rift Valley.—The sides of the trough are represented by a chain of 
hills of Archean rocks, the summits of which are from four to eight thousand 
feet above sea-level. From their bases, where it is at a level of several 
hundred feet, there slopes down a plain of alluvium, which joins the band 
of coral-rock forming the coastline. At its highest this is an undercut cliff 
up to ten feet high, below which are fringing reefs, two miles to one-tenth 
of a mile in breadth, and seawards a deep channel two to five miles wide, 
and finally the barrier reefs (see Map 1, Pl. 28). 1t was shown that this 
barrier system is founded upon a range of submerged hills similar to those 
low sandstone hills which now break the maritime plain, and which, like all 
the features enumerated, run more or less parallel with the Archean hills, 
the real sides of the Red Sea trough. These sandstone hills are, so far as 
* My papers refer particularly to the coast between Rawaya and Suakin, but a slight 
acquaintance with the east coast about Jedda and the west side north of Rawaya to the 
Gulf of Suez, shows that the remarkable uniformity of the portion particularly examined is 
found generally in the northern part of the Red Sea. 
+ J. W. Gregory, ‘The Great Rift Valley.’ 
