MUSEUM OF COMPARATIVE ZOOLOGY. 155 



fathoms; between Molokai and Maui, 137 fathoms; and between East 

 Maui and Kahoolawe, only 40 to 50 fathoms ; while between Maui and 

 Hawaii there is a depth of 1107 fathoms, and over 1890 fathoms close to 

 Kaui between Kaui and Oahu. These soundings were kindly given me 

 by Hon. H. A. Wiedemann, and were taken by a vessel sounding for a 

 submarine cable to communicate between the islands. 



It is interesting to note the structure of the reef as we pass over it 

 at high tide from the shore to the sea face. The slope of the channel 

 forming the harbor entrance is made by a steep bank of muddy whitish 

 ooze. The reef-flat itself, varying from half a mile in width to less, is 

 also covered nearer shore with coral ooze, and interrupted by small 

 rounded knobs of decomposed alga?, Nullipores, and stalks of dead Sar- 

 gassum. These cover irregular patches of greater or less size, separated 

 by bare spaces of ooze. A little farther out, in depths varying from five 

 to six or even ten feet of water, we come across numerous rounded 

 patches, covered by clusters of Millepora, with here and there a group of 

 Pocillopora, and in the intervening bare patches the coral limestone is fre- 

 quently pitted by numerous Echinometradse and Diadematidte. Some 

 of the rounded knolls rise close to the surface, and sometimes even are 

 bare, leaving deep pools between them, in which the characteristic reef 

 fauna nourishes. Such knolls, when farther out to sea, and arranged, as 

 they often are, in regular lines of considerable length parallel in a gen- 

 eral way to the trend of the shore, form successive concentric lines of 

 breakers, diminishing towards the shore. Upon these the sea beats, 

 breaking up, pounding to pieces, and triturating the corals growing 

 upon the sides of the knolls, until they are changed into the ooze which 

 gradually cements the shore portions of the reef into a solid limestone 

 mass (see Plate VIII. ), and freely supplies the fine material for the coral 

 sand beaches close to the land. On Plate VI. the lines of breakers on the 

 sea face of the reef are faintly indicated. On smooth days I could fol- 

 low beyond the outer line of the breakers the occasional patches of large 

 Millepores, or of Pocillopora, or Porites, or Astraea, together with the 

 few Gorgonise which run out on the somewhat steeper outer slope of the 

 reef. These gradually diminish, and as far as could be seen with the sea 

 glass disappeared completely in about ten fathoms. It was very easy to 

 examine the Honolulu portion of the reef by accompanying the fishermen, 

 who are in the habit of going out daily in their canoes just outside of the 

 breakers, and whose skill in crossing the swell in their outriggered canoes 

 it is very interesting to watch. The small amount of animal life on the 

 Honolulu reef (on the lee side of the island of Oahu) is surprising, as 



