418 
are marked on the map (Fig. 1) by the 40-fathom line in the China 
Sea, in the Strait Sunda and towards the east between the coast of 
Borneo and the southern part of Strait Macassar. 
From the deeper isobaths e.g. those of 100 and 200 m., it appears 
that from the coast of the former Sunda Land in pleistocene time a 
large shelf extended into the southern portion of the China Sea. On 
this shelf the depth of the sea increased very slowly and the sea-water 
was probably muddy, large rivers from the Sunda Land carrying 
their sediments into it, as may still be inferred from the character 
of the present bottom-deposits. The conditions for the development of 
shore-reefs, therefore, were unfavourable here. Hence one cannot be 
surprised to find now-a-days reefs rising from the ancient coast-line 
only here and there from a depth of 40 fathoms nearly up to the 
level of the sea. Nevertheless, it is a striking fact, that the only coral 
islands, now found in the South-China Sea, fairly follow the course 
of the 40-fathoms contour line drawn on our map, i.e. the probable 
coast-line of the submerged Sunda Land. 
It is difficult to say whether or no along such a peculiar coast 
as the upper part of Sunda Bay must have been, the conditions for 
the forming of coral-reefs were favourable. As observed above, as 
early as in the pleistocene period the Sunda Bay cut deep into Sunda 
Land and was formed right to the south of the present Hoorn-islands and 
Pajung-island into adeep gully, which passed into a wide estuary of 
a stream coming from the north-east. 
It is decidedly remarkable, though, that the area to the north-east 
of Sunda Strait, formerly the upper part of the Sunda Bay, contrary 
to all other parts of the Java Sea, abounds in true coral-reefs, which 
rise clear of the land from a depth of 20 fathoms or more, up to 
or near the level of the sea. Many of them, especially those rising 
up from a low depth, are most likely young and were generated 
by the union of small patches of corals, developed independently 
on loose rocks, as has been shown by Sruirrr*). In shallow water, 
e.g. of a depth of 12 fathoms new coral islands even now continue 
to grow up from the bottom. However, with regard to those islands 
of the group of ‘“Duizend-eilanden”, which rise from a depth of 40 
fathoms and more, as e.g. Pajung-island and others, I ascribe their 
origin to upward growth of reefs that had already been developed 
“in the ancient Sunda Bay at the shore of the pleistocene Sunda Land 
before its submersion. 
1) C. Pu. Sturrer. Einiges über die Entstehung der Korallenriffe in der Javasee 
und Branntweinsbai, und über neue Korallenbildung bei Krakatau. Nat. Tijdschr. 
voor Ned. Indié XLIX p. 365 et seq. 1889. 
