156 BULLETIN OF THE 



compared with tb.it on the weather side on the reefs of Kaneohe Bay. 

 This difference is due to the fact that much of the pelagic life brought 

 by the trade winds against the weather side of Oahu is swept past the 

 lee side without bringing any great quantity of food to the coral reef. 

 This is plainly shown by the comparative scarcity of pelagic life, even on 

 the most favorable days, on the lee side along the sea face of the Hon- 

 olulu reef, as contrasted with that of Kaneohe Bay. On such days little 

 could be seen off Honolulu beyond a few Salpa?, a huge species of 

 Appendicularia in its house, a few Diphyes and Praya, and a few pelagic 

 Crustacea, even when the wind had been blowing from the south, and 

 was driving the pelagic fauna towards the lee shores agaiu. The Hon- 

 olulu reef contrasts also with the Florida Reef in the scarcity of Sponges. 

 The very gradual sea slope of the Honolulu reef is one of its marked 

 characteristics. 



The in-shore flat of the reef, left bare at low tide, as well as all the 

 low land extending to the base of the hill slopes to a height of nearly 

 twenty feet above the level of the sea, is made up of coral reef sand. 

 This is the character of the whole reef, whether west of Honolulu or 

 east, all the way from the outskirts of the city to Waikiki, and to the 

 base of Diamond Head. At Diamond Head the coral reef sand is mixed 

 with the volcanic material washed down from its slopes, and where 

 it is washed directly into the sea we find the lava sand as well as the 

 coral sand remodelled by the action of the water, forming either layers 

 of clear lava sand overlaid by coral sand, or all possible gradations be- 

 tween a mixture of fine sands of the two and a modern conglomerate 

 or breccia of the larger fragments cemented together by the lime car- 

 bonate held in suspension, or by the finer or coarser sands. Pot-holes, 

 gullies, and corrugations, due to the wearing action of the sea-worn lava 

 gravel rolling up and down the lava beds, characterized them wherever 

 exposed to the action of the breakers or of the sea ; while, if subsequently 

 protected, these or similar holes and corrugated surfaces are gradually 

 tilled by a deposit of finer or coarser washed material, which, becoming 

 cemented, produces very striking effects. Some of the larger pot-holes 

 in the lava beds in the adjoining elevated portions of the reef often con- 

 tain masses of Porites and of Maeandria of considerable size, more or 

 less washed, as well as numerous fragments of mollusks, the whole 

 cemented together in a solid calcareous mass, as we find it on the exposed 

 part of the shore edge of the reef. Towards Diamond Head the outer 

 slope of the reef approaches the shore. (Plate IV.) The reef there is 

 narrow, and, owing to the greater depth off shore and the narrowness of 



