00 THE FLOOR OF THE OCEAN 



A second generalization: Each structure forms a long, com- 

 paratively narrow belt. 



Third: The more conspicuous chains were developed dur- 

 ing the Cenozoic or Tertiary Era, the latest principal division 

 of geological time. 



Fourth: The folding and piling of slice on slice thickened 

 the sial in the belt of deformation. 



Fifth: The deformed belts are characteristically curved, 

 arcuate, in ground-plan, and the arcs in coastal regions are 

 convex toward the ocean. Figure 51, showing with curved 

 lines the axes of the Asiatic chains, supplies examples. 



Sixth: In many instances the mountain-built belts are 

 fronted by so-called "fore-deeps," that is, long, water-filled 



FIGURE 51. MAP OF AXES OF THE ASIATIC MOUNTAIN CHAINS, WITH ILLUS- 

 TRATION OF THE EARTH'S NECESSARY PLASTICITY. AFTER C. P. BERKEY AND 



F. K. MORRIS. 



