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synelinal troughs of Sumatra partly, and of Java entirely have derived 
the non-voleanie material now found deposited in them? 
Where, in other words, is to be found the continental area L, to 
whose shores these geosynclines were marginal ? 
This continental area L lay to the north-eastward; it is the 
neogene Sunda Land, the greater part of which had been overflowed 
by the sea after the close of the ice-age. The part of Sunda Land 
which is now submerged is indicated by the dotted area in 
the sketch map Fig. 2, the contours of which have been derived from 
the present isobath of 40 fathoms. The dotted portion, however, 
does not represent its extent in Neogene time, but the largest extent 
which it reached only in Pleistocene time. 
It appears, thus, that the geosynclines in which the three large 
oil-fields of the Duteh East-Indies, to wit those of Java, of Sumatra 
and of Borneo, have originated, during their development were 
marginal to one and the same continental area of denudation, the Sunda 
Land. This marginal position is now only noticeable in the Kutei- 
oilfield, of East-Borneo, because Borneo is the only portion of the 
former neogene Sunda-continent which still emerges from the sea as 
a small continental area. In order to understand the original relations 
between the area of denudation and its marginal geosynclinal belts, 
we must imagine the now overflowed portion of the neogene Sunda 
Land, viz. the JavaSea and the South China Sea, to be united again 
with Borneo, thus forming one continuous land. The assumption is 
admissible that originally the geosynclinal deposits constituted an 
entirely or almost entirely uninterrupted belt round the neogene 
Sunda Land. This is not the case now in the oil-fields hitherto known. 
The four oilbearing terranes, that of North-Sumatra, that of Djambi- 
Palembang, that of East-Java and that of East-Borneo are separated by 
large intervals. In Central-Sumatra, in the gap between the first- 
mentioned two territories, the geosynclinal deposits are present and 
petroleum may also occur in them, but, if so, presumably only ata 
great depth and overlaid by younger, posttertiary mostly volcanic 
deposits of considerable thickness. The same probability holds for 
the Lampong districts in the extreme south-east of Sumatra. 
There is good reason to expect the occurrence of petroleum in 
deposits of the neogene geosyncline along the north coast of Java 
to the west of the peninsula of Japara, i.e. in the gap between 
the East-Sumatra- and the KEast-Java-oilfields. Here, however, the 
petroliferous strata will be overlaid, besides by more recent sediments 
of unknown thickness, also by the sea to a depth of 50 metres at 
the utmost. 
