10 



AKT. l.-S. YOSHIWAKA: 



The recent com] reefs of southern Japan, scarcely exix>sed above 

 tlie sea-water, are all fringing reefs; there iDcing found neither atolls 

 nor barrier reefs among them. The coral shows luxuriant growth 

 alon"- a line running parallel to the sea coast and at a few hundred 

 feet from it. Between the fringing reefs and the sea-beach, there is, 

 sometimes, a flat sandy bottom Avith a few groups of living corals. It 

 is frequently so shallow, that Ave can wade across it at low tide. On 

 the north-east of ]Miyako-jima, are the vast and dangerous rocks of 

 Yaebise, consisting entirely of recent reefs, wliich are scarcely above 

 the level of the sea at low tide. The islands known as Kikai-ga-shima, 

 Miyako-jima and others must have been of this type in past time. 

 The coral islands of recent formation are nothing but heaps of coral 

 fragments; as Yuni lying between Hatoma-jima and Iriomote-jima, 

 and the Ivei islands on the west of Naha. 



Although the strata of older sediments in the Riukiu Curve are 

 all inclined, which is a result of the upheaval of the islands above the 

 sea, the reefs lying upon them have as a rule remained horizontal, the 

 exceptions being the locally disturbed ones found at Tarama-jima, 

 Tokuno-shima, and other places. This shows that a gradual depres- 

 sion and elevation took place after the formation of the Riukiu Curve. 



The raised reefs are mostly a true coral formation and homoge- 

 neous in structure. But in some places as at Tarama-jima there is, 

 besides, a thick Foraminiferal deposit which attains a thickness of 10 

 ft. and is inter bedded between tw(3 successive coral reefs. The species 

 found in such a zone at Kamezu (in Tokuno-shima), Unten (in Oki- 

 nawa-jima) Jind Yoda (in Okinœrabu-jima) is gigantic Operculma 

 (PI. I). In the south of Okinoerabu-jima the raised reefs consist 

 essentially of corals, there being no layer of sand. Towards the 

 north the coral layers are found interstratified with sand layers. At 

 Kametoku in Tokuno-shima there are found thick beds of loose sand 



