MUSEUM OF COMPARATIVE ZOOLOGY. 151 



washed material. On the other hand, we may have the coral reef 

 forming merely a shell of very moderate thickness, covering the underly- 

 ing lava rocks. Such is probably the case with the inner reef of the 

 harbor of Kaneohe (Plate V.), where it is easy in the inner harbor to trace 

 all the transitions from lava islets rising high above high-water mark 

 (Mokolii, Plate V.), and surrounded at the base with a thin layer of coral, 

 or to similar islands scarcely reaching above the water level (Ahuo Laka 

 Mokuo Loe, Plate V.), where the lava rock can be seen in the centre 

 of the Pocilloporse surrounding it, and again from these to numerous 

 similar islands (Plate V.), which, judging from analogy, have a nucleus of 

 lava, but, not reaching to the water level, have become entirely coated 

 with coral. Finally, there are larger islets which are covered by dead 

 corals in the centre, and fringed only by a circle of living corals, while 

 outside of the harbor we have a reef of greater thickness, probably form- 

 ing a regular fringing reef on the outside of the entrance to Kaneohe 

 Harbor (Plate V.). The flat plain underlying the northern edge of the 

 harbor, having been built up to reach the water level for nearly its whole 

 width, is covei'ed only with occasional patches of living coral in the 

 deeper parts, and with a flourishing growth of corals on the edges adjoin- 

 ing the inner harbor. Near Kahuku Point there are several most inter- 

 esting cases, showing the thin veneer of coral which must in some 

 instances cover the underlying lava. It is not uncommon to find at a 

 few rods from the shore what may be called coral tables. They are parts 

 of the elevated coral reef, left as pinnacles on the top of a projecting 

 mass of lava, the coral table being at the same level as the adjoining dis- 

 connected elevated coral reefs. These coral tables can hardly have been 

 left cemented where they were unless the intervening coral reef has been 

 all washed away, and they should not be confounded with similar un- 

 attached blocks upthrown and not necessarily cemented in their natural 

 attitude, such as have been described by Dana. A very fine specimen 

 of such a large unattached coral rock block is seen lying on the reef 

 across the entrance of Kaneohe Harbor. 



In estimating the thickness of a fringing coral reef, the following indi- 

 cations, taken from sections of artesian wells bored in the vicinity of 

 Honolulu, will be of interest. 



. "With the exception of Mr. James Campbell's well and the well near 

 Pearl Eiver Lagoon, the artesian wells are at Honolulu or to the east- 

 ward and near Diamond Head. To Messrs. Lewes and Cooke I am in- 

 debted for data regarding the character of many of the wells. Water 

 was reached at depths ranging from three hundred to six hundred and 



