SUBMARINE MOUNTAINS 89 



troughs roughly paralleling the respective axes of the chains; 

 while inside the arc there may be a "back-deep," namely, a 

 basin occupied by a "mediterranean" sea. 



Seventh: The dry-land cordilleras show signs of having 

 been vertically upwarped after the paroxysms of folding and 

 crushing were ended. 



Now for comparison with the structure indicated by the East 

 Indian "strip of negative anomalies of gravity." The map of 

 Figure 52 bears a thick curved line indicating the axis of the 

 "strip," whose tremendous scale may be appreciated by the 

 width of the area covered by the map, namely 3500 miles. 

 Clearly any direct evidence of intense deformation within the 

 "strip" is to be sought only in the accessible parts, the islands 

 located within the belt. In total length these represent no 

 more than a small fraction of the "strip," but they do give 

 affirmative testimony. Beginning with Siberoet and Sipoera 

 islands off Sumatra, we have, in succession, Timor, Saumlaki, 

 Tanimbar, Kei, Ceram, and Banggai islands, and the eastern 

 part of sprawling Celebes. The rocks of all those visible parts 

 of the "strip" are strongly deformed. On the other hand, the 

 larger islands, Sumatra, Java, Soembawa, and Flores, though 

 also elongated and aligned, were not seriously deformed by the 

 pressure that crushed the "strip" islands. 



Geologists can date the epoch of intense folding and crush- 

 ing; it falls in the latter part of the Tertiary Era. They have 

 also proved that in the deformed belt the more superficial 

 rocks, of sialic composition, were thrust, one over another, so 

 as to increase greatly the original thickness of the sial under 

 the belt. It became clear, too, that the composite mass, so 

 thickened, sank under its own weight and therewith displaced, 

 pushed away, more plastic material below the earth's crust. 



From the map we see that the Vening Meinesz theory satis- 

 fies also the fifth criterion: the "negative strip" is like the dry- 



