252 W. H. HOBBS THE ASIATIC ARCS 



Within its middle and most mature portion it shows on its outer side 

 elevated reef terraces with the islands as a wdiole sloping toward the 

 interior of the arc. On the western margin of this zone are found extinct^ 

 though recent, volcanoes. Toward the north the arc is continued by a 

 line of active volcanoes, but these are aligned on a curve which is interior 

 to that of the main line of islands (figure 2). Thus differentiated, the 

 perfection of curvature which characterizes the Marianne arc appears 

 quite remarkable, as can be seen from the large scale hydrographic map 

 of the region. Tlie contrasted characters of the southern, medial, and 

 northern sections of this arc are set forth in figure 3. 



