18 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
remains much the same, except that the modern stones are but a fraction of 
the size of the monoliths of the old days. 
Some particularly conspicuous cases of raised erosion-lines on cliffs are to 
be seen at Tella Tella Suraya Island in the south, and on Haysoit Island in 
Khor Dongonab in the north. These are treble lines, the modern one at sea- 
level, and two others at points 3 and 5 feet above this. <A single raised line 
may be seen in the harbours of Port Sudan and Suakim. The larger of the 
islets of the landlocked North Bay of Khor Dongonab is of limestone, and hasa 
line of undermined cliffs along its northern, or exposed, side, the base of which 
is now some feet above sea-level and separated from the shore by a stretch of 
sand about a hundred yards wide, and covered with the xerophytic plants 
usually found on these dry sandy islets. One should note that the higher cliffs, 
seen from a distance, appear to show lines of undermining in some cases, but 
that these, on a nearer view, turn out to be the results of subaerial denudation. 
The hills are formed of horizontal strata which are in some cases alternately 
hard and soft, and the latter, standing out from the general level, simulate 
the overhanging part of a marine cliff. But in these selected cases, as in 
that described below, the smaller details of wave-action are preserved so that 
the former, lower, position of the cliff is evident beyond doubt. 
The horizontal position of the strata shows that the elevation of the lime- 
stone from the sea has been effected in a regular manner ; but evidence of the 
steadiness of this movement is given by the occurrence everywhere of elevated 
coral colonies, which are in the same position exactly, relatively to the 
surrounding rock, as that in which they once grew in the sea. Such colonies 
may be of quite delicate branched species, and good examples of such are 
exposed in the trench which surrounds one of the blockhouses which once 
protected Suakim from the Dervishes, but generally the fact is more easily 
made out in the case of massive species. Very conspicuous examples were 
seen on Tella Tella Suraya, an island of which the Admiralty ‘ Pilot Book ’ 
notes that it is distinguished by the presence of many cairns of stones 
upon its highest parts. The island is about 40 feet high and surrounded by 
cliffs, mostly of rather loose coral-fragments and abundant shells &e. of 
present-day species. The “cairns” on the level summit of these cliffs are 
simply large hemispherical coral colonies which survive the weathering 
that has removed the surrounding softer material. Corals similarly 
situated are exposed in many places on these coasts, the summit of Jebel 
Tétawib in Khor Dongonab bearing a_ particularly fine series. There 
would be no difficulty in identifying them as species at present living 
in the adjacent sea. The island is a miniature elevated atoll, the present 
bottom of the lagoon being just above the sea-level, and consisting of 
a flat sheet of mud, which was drying and slightly crusted with salt at the 
time of our visit, at the beginning of March. This depression is surrounded 
by high ground, its present communication with the sea being probably 
subterranean. The lagoon is bordered by bushes, of the species which live in 
