624 
had died off and by a thick cover of manganese revealed their 
long stay in the sea-water after their dying off. The nearest point 
in these regions where living reef-building corals occur near the surface 
lies at 42 kilometres from the point where the dredging took place, 
so that those deep-sea corals could not originate there. In order to 
explain the result of this dredging I should rather suppose that on 
that spot in the Ceram Sea from the sea-bottom which lies at a 
depth of about 1600 m. a drowned coral island rises to about 
1300 m. below sea-level. Such a supposition seems justified if it is 
borne in mind that the Ceram Sea is one of the most remarkable 
trough-shaped deep basins in the eastern part of the Indian Archi- 
pelago, the origin of which is probably connected with crust-move- 
ments in pleistocene and post-pleistocene times. They were formed 
by downward movements, simultaneous with and more or less com- 
pensated by elevations of about equal amount of other parts — 
nowadays highly elevated islands — in that region. Now a fairly 
large number of cases has already become known which render it 
probable that subsidence caused by diastrophism '), such as took 
place in the Ceram Sea, can proceed relatively quickly, which is 
very likely not the case where islands subside through yielding to 
the influence of gravity — isostatic subsidence — which is to be 
assumed in the central Pacific. Thus the chance that coral islands 
may be drowned must be esteemed larger in the former case which 
is present in the Ceram Sea than in the latter. 
Perhaps the remarkable dredging N°. 177 of the Siboga expedition 
may become the starting point for an explanation of the interesting 
fact that although the deep sea-basins in the eastern part of the East 
Indian Archipelago, have been formed by depressions of large amount 
in pleistocene and post-pleistocene times, reef-structures of the type 
of the barrier reefs and atolls, certainly within those basins occupy 
a very modest place.*) 
A second consequence of the outlined hypothesis is that it must 
not only hold good for the true oceanic volcanic islands in the 
Pacific but also for those in the Indian Ocean and the Atlantic. 
Now it is certainly remarkable that for the only true oceanic island 
which in the Atlantic is found within the area of the reef-building 
1) Very interesting are the examples of important differential movements by 
diastrophism since post-pliocene times which Lawson mentions of the coast and 
coastal islands of Southern California. A. C. Lawson, The post-pliocene diastrophism 
of the coast of Southern-California. Bull. of the Dep. of Geology. Univ. of California 
Ip. 415, 1893: 
2) Compare J. i. Niermever, Barrière-riffen en atollen in de Oost-Indische 
archipel. Tijdschr. Kon. Ned. Aardr. Gen. 2. Vol. XXVIII, p. 877, 1911. 
