427 
I have not been able to collect sufficient data to unravel the 
geological history of this shelf. Suffice it to say that the rivers of 
Northwest Australia now emptying themselves into the Sahul Shelf-sea 
show the characteristics of drowned rivers. The fjordlike lower 
course of the Prince Regent River presents a typical example of a 
submerged or drowned valley. 
Conclusions. 
The conditions for shelf-building in pleistocene time were very 
favourable and reached an optimum in tropical regions at the close 
of the Pleistocene. 
In tropical regions the sea-level stood in pleistocene time during 
the maxima of glaciation, at least 40 fathoms (72 m.) lower than 
at this day. 
Malacca, Sumatra, Java, and Borneo were united into one continuous 
land, the Sunda Land. 
In that Sunda Land the vast Sunda-peneplain has been developed 
into great perfection in the pleistocene age during the periods of 
low sea-level. 
After the close of the pleistocene glacial period submersion of the 
Sunda-peneplain gave origin to the Sunda Sea and the Sunda Shelf, 
during optimal conditions for shelf-building. 
The Great Sunda-barrier-reef originated by upward growth of the 
coast-reefs of the pleistocene Sunda Land during the period of general 
rise of the sea-level, which succeeded the ice-age. 
The atolls and the atolliform coral-islands in the southernmost 
part of Strait Macassar have originated chiefly in the way which 
Darry in his glacial control theory puts forth as the typical mode of 
origin of coral-islands. 
POs: Tf SC Relea: 
After the above communication had been concluded an article by 
L. J. C. van Es*) reached me which treats of a subject, in many 
respects related to my own. I am not in a position to discuss 
here fully the conclusions arrived at by van Es, and to compare 
them with my own. I only wish to refer to some points treated 
in the summary of this article, which, for the rest, contains many 
interesting details. Van Es imagines the island of Borneo to be 
united with Sumatra, and Sumatra also with Java and Malacca, 
1) L. J. C. van Es. De voorhistorische verhoudingen van land en zee in den 
Oost-Indischen archipel en de invloed daarvan op de verspreiding der diersoorten, 
Jaarb. van het Mijnwezen XLV p. 255. 1918. 
28 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
