12 Physico-Geo^ostic Sketch of' the Island qfOahti, 



water-mark and the first cliffs in'and, forms a flat space of 

 greater or less breadth, along which the coast-road lifes. This is 

 most generally covered deep with coral sand, which in some 

 places, as between Kahuka and Laie, forms elevated downs 

 along the coast, which conceal the sea from the view of the tra- 

 veller on the road. The specimens of this series are Nos. 31, 

 32, 52, 53. One of the best places for seeing a section of these 

 cliffs is just at the north point of the island, above Kahuku ; it 

 there forms a precipice elevated at its summit about fifty feet 

 above the level of the sea. The limestone forming these cliffs 

 is of two kinds. One is loose and cellular, of a straw-yellow 

 colour, is easily decomposed by atmospheric agency ; when exa- 

 mined with a glass, it appears to be an aggregate of white bo- 

 tryoidal-shaped fragments, and is covered with an ochry looking 

 layer of colouring matter. The other is harder and more com- 

 pact, affords more resistance to the weather, and projects from 

 the cliff' beyond the former ; it is of a yellowish-grey colour, 

 with a small granular foliated, partly, and splintery fracture. 

 It is singular that the latter, which appears the older rock 

 of the two, in mineralogical characters, should be superposed 

 to the former ; it forms a tabular mass, running along the 

 whole of the upper edge of the cliff, giving to it that promi- 

 nence and steepness which renders it a conspicuous object for 

 several miles on the approach from Laie, on the south-east. 

 These coral cliffs, for such I would call them on account of the 

 close similarity between the looser variety and the coral reefs, 

 now forming at the water's edge, form extensive tabular cliffs 

 for some distance round the north point of Oahu at a nearly uni- 

 form elevation. 



The sand forming the extensive plains and downs at the base 

 of these cliffs, is of a dazzling whiteness. After being kept in 

 paper for some time, it has nearly a smoke-grey colour, and 

 consists of variously coloured particles, varying in size from fine 

 dust to that of a millet-seed, made up of fragments of shells, 

 microscopic shells, comminuted limestone, and portions of a 

 dark coloured rock, probiibly lava. 



The soil of Oahu is of two kinds, either sand or a deep black 

 earth, arising from tlic decomposition of lava. Both are so very 

 porous that where there arc not abundant facilities of irrigation, 

 the barrcnnctfs is extreme. The taro fields are almost all in 



