C. CROSSLAND—PHYSICAL DESCRIPTION OF KHOR DONGONAB. Zee 
consolidated, but is sticky like clay, and full of the delicate shells of sand-loving 
lamellibranchs, being in all respects like the sand at the bottom of the harbour. 
Hxamination shows at once that the great bulk of this sand is inorganic like 
the sand-drifts, the difference in colour being due to admixture of organic 
matter, e. g. calcareous sand from the shells which have inhabited it, traces 
of carbonaceous remains of the bodies of lamellibranchs and worms or of the 
two marine phanerogams which abound in all these lagoons. It must be con- 
siderably affected by its passage through the intestines of holothurians, a large 
burrowing form of which is so abundant that its great conical casts cover the 
whole bottom. The clayey consistence is easily accounted for by the fact 
that the wind carries sand of all degrees of fineness, and that in these lagoons, 
which are almost tideless and perfectly sheltered, the very finest dust remains 
near shore instead of being cleaned out from the coarser sand and carried out 
to deeper water. In a shallow excavation this impalpable dust colours the 
water which collects to just that shade of red-brown which is so characteristic 
of the Nile flood, and it is probably nearly of the same composition as that 
valued fertiliser *. With great difficulty we carried our excavation toa depth 
of 12 feet, the character of the clayey sand remaining the same throughout. 
We made one interesting find, viz., the bones of a dugong. These, though 
well preserved and hard, were found in small pieces only an inch or two long, 
and could only be identified by the presence among them of the tusks. The 
fact of so many fragments being found close together suggests that the bones 
had been carefully broken up for cooking, and human agency is corroborated 
by the presence with them of fragments of pottery. It is very probable that 
they were thrown overboard from a sambuk of the olden days anchored at 
this spot, now a hundred yards inland. Other evidence of the presence of 
man in times centuries past is afforded by the heaps of pearl-shells found by 
digging almost anywhere in the plain up to 100 yards inland at least (I have 
not excavated further), and the larger heaps on some of the islands. These, 
now brittle and of an opaque dull yellow colour with age, are obviously relics 
of the time when mother-of-pearl was of no value, and the fishery was 
followed for the sake of the pearls alone ft. Their presence indicates that the 
beach was very near at hand at the time they were opened and thrown away, 
there being no inducement to carry them inland. 
Climate-—The climate is at times the most disagreeable in the world, at 
times most delightful, but the formation of the plain is only due to the former 
conditions. 
During the summer are intervals lasting three to ten days each, and 
* Floods from the hills have the same colour, and so fine is the mud that after a flood 
Port Sudan Harbour remains red for days. 
+ Nowadays the fishery is for the shell, or mother-of-pear], the pearls found adding only 
a percentage to the profits. 
