Corals from the China Sea. 355 



to be (lead ; but the tlretlge witli swabs attached brought up 

 from tliis bank an abundance ot" living forms. 



Of tlie tliree islets on the Tizard Bank (see PL XII.), that 

 named Sand-Kay is the smallest and the most recent ; though 

 it has increased in size within the last twenty years, it is still 

 only a quarter of a mile in lengtli. The surface is somewhat 

 depressed in the centre ; it is entirely conijiosed of sand and 

 small coral debris. Surrounding the island is a platform of 

 coral-rock half a mile broad, covered generally with sand, but 

 licre and there with patclies of growing coral which increase 

 in number as the water becomes deeper, and they grow very 

 luxuriantly amongst the breakers on the outer edge of the 

 platform both next the sea and next the lagoon. Just below 

 high-water mark there are parallel lines of hard solid rock 

 formed by coral debris and sand cemented together, and a 

 reef at a depth of 5 fathoms extends uninterruptedly to the 

 "westward for a distance of 4 miles. 



Tiie islet of Nam-Yit is rather larger than Sand-Kay; its 

 highest part is not more than 12 feet above high water, and 

 in bad weather the waves, according to the natives, break all 

 over it. It is well covered with small trees, and the surface- 

 soil is therefore of a brown and earthy character ; beneath 

 this is a conglomerate of sand and small coral debris. A well, 

 6 feet deep, passed through loose sandy rock. 



The striking parallel lines of cement-rock are well marked 

 on both sides of this island, more particularly on the south or 

 weather side ; they have an apparent dip of about 60° from 

 the centre, one layer superimposed on the other. This islet 

 is likewise surrounded by an extensive shore-platform with 

 isolated rocks at its edge, and at its northern end there are 

 sand-banks forming horn-shaped prolongations, which partially 

 inclose a small lagoon ; on the open side of this, facing the 

 lagoon, there are many rocks just below the surface. 



Itu-Aha, the largest islet, is three quarters of a mile in 

 length and covered with large trees of considerable age ; it is 

 similarly surrounded by a shallow-water platform. Outside 

 this, in 6 fathoms water, the number of living corals was 

 found by the diver to be much fewer than elsewhere ; but 

 from the reef, in 21 fathoms water, several massive specimens 

 were obtained, and a rich variety of species was found on the 

 lagoon side of the reef. 



A comparison of the sections (PI, XIII.) taken across diffe- 

 rent portions of the Tizard Bank shows very great similarity in 

 the form and slope of the bank throughout. Thus in all, 

 with the exception of section C near Nam-Yit, there is a broad 

 plateau sloping very gradually to a depth of 10-12 fathoms, 



