MUSEUM OF COMPAEATIVE ZOOLOGY. 145 



a species of Porites on the inner channels opening to the sea on the 

 frinofinic reef of the south shore of Oahu. In the enclosed harbor of 

 Kaneohe there are numerous examples of hummocks, on the summits 

 of which the corals have died on reaching the surface, while the sides 

 are still covered with magnificent clusters of Pocillopores and Porites. 

 Other hummocks in the same locality, not yet above the surface of the 

 water, remain covered with this luxuriant growth, giving shelter also, 

 wherever sand has accumidated between the single masses, to the simpler 

 Fungire so characteristic of the Pacific reefs. 



Dana has called attention to the manner in which parts of the surface 

 of the inner reef of Tongatabu has become solidified by the cementing 

 material, sand and small fragments, into a huge pavement exceeding in 

 compactness that of the corals themselves, so that coral rock formed 

 from the filling of the interstices of masses of branching corals may 

 become solid enough to be used for building purposes, as is the case at 

 Honolulu. 



The entrance to the harbor of Honolulu (Plates IV., VI.) is nothing 

 but a channel kept open by the flow of the river, which empties to the 

 west of Honolulu from the Nuuanu valley, and has killed the corals in 

 its path, scouring at the same time in freshets the whole harbor and 

 the adjacent limestone walls forming the channel (Plate VII.). This 

 and another channel farther to the westward separate the Pearl River 

 Reef from the Honolulu Reef proper. The river forming the Honolulu 

 harbor brings down a large amount of volcanic mud in its short course, 

 and has deposited this in the harbor and channel, so that there appeal's 

 to be nothing but dark volcanic mud for a considerable distance out 

 towards the entrance of the channel, where the coral limestone reap- 

 pears. 



A similar channel, but not so well defined, exists opposite the creek 

 forming the drainage of Mauoa valley, which empties on to the reef at 

 "VVaikiki (Plates IV., IX.) ; but this river does not bring down the 

 amount of volcanic silt and detritus carried by the Nuuanu drainage, as 

 it deposits a great part of its burden along the plain through which it 

 flows before reaching the shore, whereas the river emptying from the 

 Nuuanu has a very steep course until it reaches the harbor (Plate X.). 



The Pearl River Lagoon outlet, in its turn, divides the reef again by a 

 deep channel (Plates IV., XI.). The amount of fresh water pouring into 

 the lagoon is much larger than that emptying into the harbor, and some 

 of the deep ravines which drain into it extend nearly half the length of 

 the island toward Waialua. A good part of the western slope of the 



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