18 ('. If. HITCHCOCK — GEOLOGY OF OAHU 



have remained a submerged conical peak. It is obvious that there may 

 be every variety of development from the needles that do not reach the 

 surface, to low-lying shoals, reefs, and to Hawaii, 14,000 feet above the 

 sea. Inasmuch as the living volcano is found at the extreme southeast 

 end of the group and the islands toward the northwest consist of basalt, 

 capped by craters or show evidence of long-continued erosion, it is be- 

 lieved these last are older. Thus Ocean and Midway islands had their 

 bases established long before the high islands of Oahu and Maui began 

 to be formed, and in a general way the growth of the islands has been 

 from the northwest to the southeast. If the Darwinian view of the long- 

 continued subsidence of coral islands is accepted, it may be that the 

 remote series of reefs and shoals represent the tops of high islands 6 or 8 

 miles above the submarine plateau. For our present purpose it is only 

 necessary to say that the origin and development of Oahu has been in- 

 termediate between the earlier and the later islands.* 



Topography 



Oahu has an area of about 600 square miles, one-eleventh of that of 

 the whole archipelago, and in form is an irregular four-sided figure, with 

 a diameter of 46 miles in a northwesterly direction from Makapuu to 

 Kaena point. The distance from Barbers to Kahuku point, east of 

 north, is 30 miles. At Honolulu a northeast line is only 9 miles long 

 from tide to tide. The extreme easterly point lias the longitude of 

 157° 38' east; the extreme Avesterly point has the longitude of 158° 17'. 

 The extreme latitudes are 21° 15' and 21° 43' north. The land rises to 

 two mountain ranges nearly parallel to each other and to the northeast 

 and southwest shores of the island. The larger eastern one, which is 37 

 miles long, is called Koolau. The smaller, 21 miles long and opposite 

 the western shore, is called Kaala. Great subaerial erosion has produced 

 ragged precipitous faces on the seaward sides of these ranges, but the 

 interior slopes are gentle, the height of Kokoloea, the saddle between, 

 being 888 feet. The highest point in the Koolau range is 3,105 feet; 

 that in the Kaala is 4,030 feet. The interior gentle slopes have been cut 

 by canyons perhaps 400 feet deep at the outer edge of the plateau. 



Several years since the author constructed a rude relief of Oahu based 

 on approximate contours furnished by Professor Alexander. This relief 



* Botanical evidence furnishes additional proof of the greater antiquity of the more northwestern 

 islands, for the flora of Hawaii is the poorest and most uniform, while that of Kauai is the richest 

 and most individualized in species, and in general the plants on the intervening islands follow the 

 same ratio, allowing for the greater diversity of climate afforded by elevation. W. F. Eillebrand : 

 Flora of the Hawaiian Islands, 1888, p. xxii. Other proofs leading to the same conclusions may be 

 derived from the study of the Adiatinellidie, as- commenced by John T. Gulick and Alpheus Hyatt. 



