ART. l.-S. YOSHIWAEA: 



TJie Okinawa Group. 



This group is composed of the main island, Okinawa, (together 

 with more than 1 7 dejDendent islands), and of the two subgroups of 

 Iheya (with 5 islands) and Kerama (with more than 12 islands), and 

 also four other islands named Kume, Tonaki, Aguni, and Tori. 



Okinawa-jima has a coast line of about 200 miles, and is divided 

 administratively into three districts or gun, called Kunchan, Nakagami 

 and Shimajivi. In geological time, the Palœozoic mountain-range of 

 which the first two districts are mainly composed, formed a long 

 island, while the district of Shimajiri was entirely under water. 

 During that time the reefs were built chiefly along the southern part, 

 coverin cr an extensive area of Tertiary rocks which now form the whole 

 surface of Shimajiri, and also a part of the surface of the Paleozoic 

 formation. The thickness of the reefs in Okinawa is small in com- 

 parison with their great extent, being considerably smaller than in the 

 other islands, for instance, in the Miyako subgroup. The following 

 table shows the elevations of raised coral reefs above the sea-level : 



Ömine-san (in Shimajiri) 121 ft. 



Sunaga-jima (in Shimajiri) 142 ft. 



Sôjun-yama (near Tomori in Shimajiri) 151 ft. 



Shuri 496 ft. 



Yoza-jima (in Nakagami) 557 ft. 



Benga-dake (near Naha) 598 ft. 



That the reefs do not attain a great thickness is shown by the 

 fact, that when a boring is made from the surface, the underlying 

 Tertiary (Pliocene) rocks are met with at the depth of about 30 ft. In 

 a geological .age not far removed from the recent epoch the district of 

 Shimajiri was in all probability entirely covered with the coral reefs, 

 and the scattered patches now seen here and there are to loe looked 



