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Sunda Shelf, then also Borneo, probably with the exception of the 
northern part, Malacca and the eastern coastal region of Sumatra, 
and perhaps here and there a strip of the northern coast of Java 
and Madura. All the land bordering on the Indian Ocean, which 
belongs to the Malay geosyncline, does not belong to this Sunda 
Land in the strict sense of the term. Evidently this region of tectonic 
activity is the prolongation of the folds of the western portion of 
the Birma-are, still one of the regions of the earth where the oro- 
genetic activity is very great. It is not possible to fix the precise 
boundary between the stable and the unstable portion of the former 
Sunda Land; very likely there is no firm line of demarcation, | am 
inclined to class the volcanic regions, which are characterized by 
rocks of the Atlantic type, such as the Muriah, the Lurus and the 
Ringgit, under the stable region, because the Bawean-Islands with 
their Atlantic rocks certainly belong to it and because the voleanoes 
of the Malay geosyncline, like those of nearly all other geosyn- 
clines on the earth, have yielded exclusively rocks of the Pacific 
type. Doing so, however, the boundary-line between the stable and 
the unstable region must inevitably be drawn in such a way that 
the two regions encroach upon each other in Eastern Java. Perhaps 
the two relations are represented accurately in this way. The Sibbalds 
Bank, the Kalukalukuang Bank, the Laars Banks, the Bril, the Pater- 
noster Islands and the Postiljon-Islands, now all coral-islands, and 
perhaps also the Spermonde Shelf and part of South Celebes formed, 
as I believe, in pleistocene time islands that belonged to the stable 
Sunda Land. 
Now, what peculiarities are known of the present Sunda Sea, its 
islands and its shores? 
The Present Sunda Sea. 
a. General topoyraphy of the floor of the Sunda Sea and of the 
adjacent shores. 
The Sunda Sea has a strikingly uniform depth, averaging 40—45 
in., seldom exceeding 50 m. The shallowest part is that where the 
islands of Bangka and Billiton are situated. A depth of more than 20 
fathoms is the exception there. 
Excepting some gullies, larger depths than 28 fathoms (50 m.) 
are found only in the farthest eastern part, where the depth gradu- 
ally increases towards the much deeper Macassar Strait, and also in 
the northern part towards the deeper basin of the China Sea and 
finally in the neighbourhood of Sunda Strait. The most striking 
characteristic of the Sunda Shelf-sea, therefore, is its equal depth, 
