158 BULLETIN OF THE 



One cannot fail to be struck with the hardiness of the large masses of 

 Porites still found living, half exposed to the air at low tide, in the im- 

 purer water of the reef near to the shore, which seem to die more from 

 the effect of sediment than from the effect of the exposure to the sun, 

 or from the impurity of the water. In fact, Porites both at the Sand- 

 wich Islands and at the Tortugas are among the hardiest of reef corals. 

 As Jukes, Guppy, and others have noticed, in many species of corals 

 exposure to air is not always fatal, although in Florida the Madre- 

 pores, which hold to the Atlantic reefs the same relation the Pocilloporse 

 hold to the Pacific, are frequently killed over extensive tracts when 

 exposed to air by low tides or winds. As far as I could judge from an 

 examination of the sea face of the Sandwich Island reefs, the Pocillo- 

 porse do not extend to a depth of more than fifteen fathoms, and then 

 gradually disappear, though the sea face of the reef was swept by a con- 

 stant current running westerly, due to the trade winds, and during the 

 season of trade winds but little sediment found its way there to prevent 

 their active growth. 



Dana has called attention to the great extent of the elevated reef of 

 Oahu, which occurs at the foot of the mountain slopes along the whole 

 southern face, at heights ranging from five to twenty feet above the level 

 of the sea, forming the large fiats of the Pearl River Lagoon. It is 

 nearly continuous from Makapuu to Kahuku Point, extending from 

 there to a small river emptying at Waimea,~where it abruptly ceases, 

 but flourishes again on both sides of Waialua, and along the greater 

 part of the northwestern coast near Waianae. The elevated reef attains 

 its greatest width near Kahuku Point, where it is nearly a mile wide, 

 and we can trace this elevated reef as a fringing reef before the elevation 

 of Oahu just as plainly as we now trace the present fringing reef of the 

 south shore of Oahu, and that in Kaneohe Bay. 



Near Kahuku the drift sand-hills are of great size and height, and 

 resemble an elevated beach. The elevated reef near Kahuku and that 

 along the northwest end of Oahu are quite distinct from the solidified 

 sand-dune deposits. 



At Laie^ the drift sand has formed hills of sandstone hard enough 

 for building purposes. These hills are thirty to forty feet high, much 

 broken and worn by the action of rain and wind into grotesque honey- 

 combed masses and ragged pinnacles, which, as Brigham says, have often 

 been mistaken for elevated coral reef rock. 



The mouth of the stream at Waimea is often completely closed by a 



1 Brigham, Mem. Bost Soc. ISfat. Hist., Vol. I. p. 368. 



