Tectonic Geography of Eastern Asia. — Hobbs. 373 
series and in like manner the innermost projecting points of the 
larger islands, the two nearly ])arallcl lines of arcs are obtained, 
which are distant from each other about 60 k. m. — the breadth 
of the island zone. (See Fig. 2.) To the southward this dis- 
tance is, however, contracted to less than 34 k. m. The inter- 
ior of the two arcs consists of older, presumably Palaeozoic 
sediments, which are intruded by granite. The outer arc, on 
the contrary, is occupied by rocks of Tertiary age. The zonal 
structure of the double arc and the conformity of the strike 
of the rocks to the direction of the arc, as well as the constant 
dip of the beds toward the inner side, render it probable that 
fold structores, perhaps accompanied by overtlirusts, may be 
largely responsible for these areal peculiarities. Landward from 
the double belt of islands and closely following its inner mar- 
gin, runs the zone of new volcanic islands which are strung like 
pearls upon a string. To the southward the outer Riukiu arc 
