94 THE FLOOR OF THE OCEAN 



of the range geologists have found big tongues of once-molten, 

 now solidified granite, which rose from depth and penetrated 

 the upper rock formations of the range. The intrusion of the 

 molten granite took place while, and immediately after, the 

 mountain rocks were crushed, and it is probable that the 

 deeper part of the bulky granitic mass is still expanded by heat. 



The bearing of these different considerations on our im- 

 mediate problem appears when we remember: first, that the 

 strong folding and crushing along the East Indian strip oc- 

 curred a good many millions of years after the main Alpine 

 and Himalayan paroxyms; and, secondly, that on account of 

 the slowness with which heat is conducted through rock, it 

 takes millions of years for the wave of heat from the earth's 

 deep interior to cause much expansion of the root rocks. For 

 this reason the amount of uplift should have been much less 

 along the East Indian strip than in the Himalayan belt. 



However, there is reason to doubt that the strip rocks will 

 ever be pushed up to heights comparable with Alps or Hima- 

 laya. Each of these latter structures, now so lofty, was made 

 inside the limits of the old Eurasia-Africa continent. Before 

 the epoch of mountain-making, the sial there had normal 

 continental thickness and therefore floated relatively high on 

 the earth's body. There also, the mountain-making meant 

 piling of sialic slices and overturned folds on sial of normal 

 thickness. In two respects the conditions in the East Indies 

 may have been different. It is possible that here the sial was 

 originally thinner than the sial under undisturbed Eurasia. 

 And the second condition: from the topographic map and 

 known rock structures it seems clear that along the East Indian 

 strip the sial was thrust over, and thickened on top of, the 

 sub-oceanic simatic crust, which has density about 10 per cent 

 greater than the density of the sial. See Figure 30. When, 

 therefore, the crust shall here have come to equilibrium in both 



