568 H. A. BROUWER 
the gently sloping northwestern part of this asymmetrical geanti- 
cline and found drowned river valleys which were observed far 
inland from the coast. Thus the upheaved island Jamdena is 
separated from the row of upheaved islands to the northwest by a 
zone which is covered by the sea, and in which during the youngest 
evolution of the geanticline positive movements have prevailed. 
These facts can be explained in much the same way as has been 
done by Escher’ for the group of islands southeast of Celebes which 
are known as the Tukang Besi Islands and which consist of four 
rows. ‘Two of these rows consist of islands with elevated reefs 
which mark the anticlinal axes, whereas the two remaining show 
barrier reefs and atolls which mark the synclinal axes (Fig. 3). 
=== FF 
Fic. 4. One of the possible evolutions of two parallel rows of islands, of which 
different phases are represented in the southeastern Malay Archipelago (schematic 
representation). IV, Stage with elevated central basin. 
We suppose that the geanticline at the Tenimber Islands is 
developing as two secondary geanticlines with an intermediate 
secondary geosyncline. The greater breadth of the islands in the 
southeastern secondary geanticline (although the reefs are not 
elevated to higher altitudes) may be the result of the prevalence 
of horizontal movements which caused the development of the 
asymmetrical reef cap (Fig. 4). 
1B. G. Escher, “Atollen in den Nederlandsch Oost-Indischen Archipel: De 
Riffen in de Groep der Toekang Besi Eilanden,” Meded. Encyclop Bureau, Afl. XXII 
(1920). 
