822 



upheaved to about 1300 m., with those of the islands of Rotti and 

 Jamdena elevated respectively to =t: 470 and ± J 50 m, which may 

 be of the same geological age. 



Downward moving longitudinal coasts sometimes occur with rising 

 islands. Let us take e. g. one of the possible cases in the develop- 

 ment of an asymmetrical reefcap, as is shown in Fig. 1. The 

 points P, A and Q will, in a later stage of development have 

 reached Px, Ai and Q^. The sealevel is indicated by the line JS'Z. 

 The portion AB of the geanticline rose above the sea in the initial 

 stage as an island, and may possibly have been covered by a 

 continuous reefcap. 



During the development into the second stage, discussed by us, 

 the island will increase in circumference and rise higher above the 

 sea. On the north coast, however, downward movements are observed, 

 while the South coast is moving upwards. 



What was originally the oldest reefcap, AB, will ha\e been 

 transformed and partly disappeared under the sea, while the highest 

 reefs in the second stage are l)y no means the oldest, so that older 

 reefs will occur on a lower level than the younger ones. 



In connection with the abo\e-mentioned downward movement 

 along the gently sFoping part of the asymmetrical geanticline, we 

 refer to the drowned river valleys, observed by us far inland along 

 the northwest coast of the island of Jamdena of the Tenimber 

 group. The downward slope can be onlj apparent also here, rel- 

 ative to a postglacial rise of the sealevel ^) '). 



In contradistinction to Timor, Rotti and Jamdetia are now also in 

 their central parts covered for the most part with a continuous 

 reefcap. We attribute this to the intluence of erosion in connection 

 with the predominating horizontal movements at right angles with 

 the geanticlinal axis. Along the longitudinal coasts of the last-men- 

 tioned islands these movements caused more resistant reefcaps to 

 be formed, which moreover were not upraised so high, so that for 

 two reasons the reefcap was attacked less while it disappeared 

 completely (or for the greater part) along the rapidly raised longi- 

 tudinal coasts of central Timor also for two reasons. 



Of the aspect of asymmetrical reefshields it is often said that one 

 coast is lifted more than the one opposite. This assertion, however, 

 does not assign significance enough to the horizontal component of 



1) R. A. Daly. The glacial-contral theory of coral reets. Proc. Amer. Acad, of 

 Arts and Sciences. Vol. 51. N^. 4, p. 3 57. 1915 



*) G. A. F. MoLENGRAAFF. The coral reef problem and Isostacy. Proc. Kon. Ak. 

 V. Wet. XIX, NO. 4. 



