8 Physico-Geognostic Sketch of the Island qfOahuj 



These isolated crateritbrna hills only represent, on a small 

 scale, and from their being more detached, with all their cha- 

 racters better defined, the larger crateriform peaks of the two 

 chains, which being aggregated together in a linear form, lose at 

 least the outline of two of their sides. Such is the idea I have 

 formed from an attentive consideration of the paris at the head 

 of the ravines ; they are only the inner walls of the crater, which 

 has poured forth the two ridges, or lava streams bounding the 

 ravine. 



The total want of any dome-shaped summits, is a remarkable 

 feature in the mountains of Oahu, and one by which they differ 

 materially from Hawaii, where this form is very common, and 

 it is even reported that you can ride to the very summit of 

 Mouna Roa. 



In consequence of the peculiar form of the principal mountain 

 valleys of Oahu, there are hardly any rivers, but only mountain 

 streams. The only one which deserves the name, is that which 

 discharges itself into the sea at Waialua, on the north-west side 

 of the island. It docs not derive its chief supply of water from 

 either of the mountain chains, but from the plain of Eva, and 

 the hilly tract Koolauloa (plain .?) between which it forms a sort 

 of natural boundary. The length of its course is about ten 

 miles. 



General Sketch of Formations. 



These may be viewed as consisting of two great classes, tjje 

 volcanic and the coralline. The first far exceeds the second iu 

 quantity, and forms the whole of the interior of the island, as 

 far as it was open to my inspection. The latter is confined to 

 the reefs skirting the sea-shore, or to the cliffs immediately bor- 

 dering upon it. The former is now on the decrease, from the 

 disintegrating effects of the weather not being counterbalanced 

 by a counteracting formative force. The latter is upon the in- 

 crease, from the incessant labours of its numerous live inhabitants. 

 The coralline is a recent formation, superimposed upon the pre- 

 viously formed volcanic l.ills, unless we adopt the hypothesis of 

 part of this limestone mass having been upraised from the bed 

 of the ocean, by the heaving up of the volcanic mass, which is 

 strengthened by the compact and ancient appearance of some of 

 the coral cliffs above Kahuku, at the north point of the island. 



