C. CROSSLAND—PHYSICAL DESCRIPTION OF KHOR DONGONAB. 267 
three folds have remained the same throughout these changes, the second and 
third folds were below the depths at which reef corals flourish, and were 
merely submerged banks. 
Successive uplifts of Coast-lands——The formation of the maritime plain 
began at once, detritus from the hills tending to fill in the channel between 
the mountains and the barrier reefs. Elevation being in progress the 
barrier reefs began to emerge from the sea, and finally by the extension of 
the alluvial plain became islands of sandstone in a sea of gravel and sand. 
At the same time the depth was decreased over the submerged bank, which 
is the second fold, coral growths arose upon it, and this, with further 
uplifting, brought it to the surface and levelled it up as a nearly continuous 
second barrier system. The maritime plain, the formation of which was 
renewed by this uplift, still extended rapidly into the quiet water within this 
barrier, reached now its maximum modern seaward extension, generally 
nearly up to the barrier, sometimes throwing deposits of gravel over the 
growing reefs. Finally, another elevation converted the barrier into dry 
land, the present coastline, and the spaces left between it and the gravel 
plain were filled in with fine alluvium, making the present continuous 
maritime plain, a few spaces of water being left as the inner arms of 
harbours. 
During this last uplift the third fold came within the range of coral life, 
and the northern portions of the submarine hill range emerged as the hills 
of Shadwan, Ras Benas, Rawaya, and the outer coral ridge of Ras Salak. 
Also the whole fold shifted seawards, so that portions which, like Rawaya, 
were once continuous with the maritime plain and received from it fragments 
of Archean rock from the high hills, are now separated from the mainland 
by four miles of sea. 
The Harbours.—At this time also were formed those very remarkable 
features of this coast *, the landlocked harbours (fig. 2), referred to in my 
former paper. It is shown later that these harbours are the most recently 
made of all these structures, and their position on the summits of the present 
fringing and barrier reefs indicates that these are synclinal folds and 
that their uplifting was accompanied by increase of folding which was 
relieved by cracking along the summit of the syncline. The long deep pools, 
which may be miles long and several fathoms deep, on the flats of the fringing 
reefs have the same origin. 
* The equally striking harbours of the raised coral coast of Equatorial East Africa— 
é. g., Mombasa, Wasin, Tanga—were formed in the same way. 
