447 
The rapid improvements in the methods of boring will in the 
near future probably enable to prove conclusively which portions 
are still in existence of the deposits of petroleum and lignite which 
have originated in the far-extending geosynclinal trough marginal to 
the neogene Sunda-land. 
CONCLUSIONS, 
1. The three large petroleum-fields of Sumatra, Java and East- 
Borneo have originated in a similar way in neogene time in geo- 
synclinal belts, marginal to the former Sunda Land, which after the 
close of the Pleistocene age for the greater part has been overflowed 
by the sea. | 
2. It may reasonably be accepted that, along the north-coast of 
West-Java, oilfields may occur below the surface of the sea over- 
laid by younger deposits down to a depth not established as yet. 
These oil-fields are closely connected to and fill the gap between 
those of East-Sumatra and East-Java. 
3. It is improbable that in the eastern part of the East-Indian 
Archipelago '), more especially in the volcanic Lesser Sunda-islands, 
however much their geological structure may resemble that of Java, 
neogene lignite- or petroleam-deposits will be found, because one of 
the conditions for their genesis has not been fulfilled there, namely 
the presence of a geosynclinal belt of sedimentation, marginal to a 
continental area of denudation. 
4. The opinion, enunciated by VerBrek ®) and Rurren*), that 
the Strait of Macassar had already been formed as a deep depression 
in Old-Miocene time, is supported by the way in which the oil- 
fields occur. 
5. The fact that in Neogene time a continuous, or nearly con- 
tinuous, geosynclinal area (which was folded afterwards) extended 
in a semicircle along the coast of the continental Sunda Land, makes 
it doubtful whether Have and P. Sarasin are right in considering 
the Hast-Indian Archipelago as the area where the Alpine and the 
circum-Pacific orogenetic systems meet or are interlaced. 
This fact rather points to the conclusion, that it would be prefe- 
rable to distinguish between a circum-Asiatic and an Australo-Pacific 
orogenetic system as those, which may be surmised to meet or to 
be interlaced in the East-Indian Archipelago. 
1) With the exception of New Guinea and the adjacent islands. 
9) R. D. M. Verpeex, Rapport sur les Moluques. Jaarboek van het Mijnwezen 
XXXVII, p. 823. Batavia 1908. 
5) L. Rurren, Modifications of the facies of the Tertiary formations of East Kutei. 
These proceedings. Vol. XIX, p. 728, 1917. 
