ENCIRCLING CORAL REEF 29 



30 feet, etcetera; hence it would appear that the Diamond Head and 

 Punchbowl tufas were ejected through this modern limestone. 



Coral Reef 



Oahu is mostly encircled by a fringing coral reef, whose limits are 

 exhibited on plate 1. At low tide one can walk a long distance on this 

 reef in various directions, off the city of Honolulu, near Koko head, and 

 in Kaneohe bay. The polyps living on and enlarging the reef are of the 

 genera Porites, Pocillopora, Astrea, M eandria and Fungia, together with 

 Millepora, echinoderms, mollusks, serpulae, gorgonise, nullipores, with 

 seaweeds, etcetera. The life is much better developed at Kaneohe bay 

 than at Honolulu, because the trade winds impinge directhy against the 

 shore, bringing food in great abundance to the animals, while the har- 

 bor is on the lee side of the islands and subsistence is less easily obtained. 

 Where the fresh- water streams of Nuuanu and Kalehi valleys and Pearl 

 river enter the sea, channels are produced, because the animals can not 

 nourish in fresh water. The Nuuanu channel is utilized for shipping, 

 and the Pearl River outlet bids fair to form the entrance to the finest 

 harbor in the Pacific ocean when the bar at the mouth has been removed. 



The loose character of the ordinary reef rock is shown in the large 

 blocks used for stone walls and buildings. A better quality is exhibited 

 in the walls of the Kawaihao church, and the very best is a compact 

 variety made by the washing of limestone fragments into fissures and cav- 

 ities, which have been cemented by its own substance in solution. The 

 sea water has worn the reef into very irregular shapes, not easy to walk on. 



The plain of Honolulu rests on coral limestone, beginning easterly 

 near Moiliilii church and Paakea, and it has been covered b3 7 the basaltic 

 flow of Kaimoki. It crops out in many places within the settled dis- 

 tricts, as on the banks of the Nuuanu river near Palama chapel and sea- 

 ward from the terminus of the tram railroad at Kapalama. A very 

 large excavation in it shows an abundance of corals and shells. Boulders 

 of basalt strew the surface of the unexcavated portion, and it ma} 7 ex- 

 tend beneath the Kamehamaha schools and Bishop museum, being fully 

 20 feet above the sea. The original floor of the crater of Aliapakai con- 

 sists of coral, and it both overlies and is intercalated in the tufa that 

 flowed from Makalapa, exposed along the railway in the southeast locks 

 and the islands opposite. Most of the islands and points about Pearl 

 river consist of this material, as at Fords island, Pearl City peninsula, 

 Laulaunui, etcetera. About Ewa plantation the limestone area is 9 

 miles long and 1} miles wide. It skirts the shore and railroad the whole 

 length of the southwest shore of Oahu. At an abandoned quarry 3 miles 



