48 C II. HITCHCOCK — GEOLOGY OF OAHU 



On the east side, toward Waialae, the How has been equally extensive. 



The division line between Kaimuki and Mauumae is not well marked, 

 but for practical purposes may he placed at the lowest line between the 

 two not far from the road over the hill. Excavations show all sorts of 

 lava with clinker. Passing to the summit one sees quite a number of 

 lava bombs of small size strewn over the surface. The rock is mainly 

 compact basalt with more or less clinker. It is higher than Kaimuki. 

 Standing on the summit the west side is seen to be very abrupt, and the 

 break-down is toward Waialae. With the bombs are rough fragments 

 that were plastic at the time of eruption, and many stones, up to two 

 feet in diameter, that must have been ejected at the same time. Some 

 of the seams are lined with lime, suggesting the contiguity of the coral 

 rock underneath — the same that underlies the Kaimuki flow on the 

 " white road " — and which has been pierced by the drill in the borings 

 for artesian wells between the continuation of Beretania avenue and 

 Waikiki. 



A'OA'O HEADS 



The eastern and highest Koko head is almost the first bit of land seen 

 by the traveler from the east en route for Honolulu. It is a ver}' well 

 defined volcanic cone 1,200 feet high, 6,000 feet long, or 7,000 in a north- 

 west-southeast direction, and broken down on the east. The inside of 

 the crater is 1,500 feet in diameter from north to south, and 100 feet less 

 in the east-west direction. The ascent is gradual from the sea to the 

 floor of the crater, commencing with some flat lands that may have been 

 of marine origin. It looks as if one could drive a team with ease from 

 the seashore to the inside of the crater. The Hawaiian name for this 

 eastern head is Kokelipelipe. 



An examination of the north side shows it to be composed at the sur- 

 face of ashy beds, very friable, dipping 25 degrees, corrugated by narrow 

 ravines down which large blocks have fallen. There are no fragments 

 of basalt among them. The underlying beds are of palagonite of yel- 

 lowish color. Near the border the dip is much smaller, approaching 

 horizontality. The tuff can be seen to overlie the Koolau basalt for a 

 distance of 300 feet. Some small portions of this tuff may be compared 

 with a cobbly conglomerate; the most of it is not coarse. The facts of 

 superposition are revealed by erosion against a ridge connecting Koko 

 with the Koolau range. 



From the west the structure is clearly seen, the slopes being steep, 

 too much so for comfortable climbing, and the upper layers at the 

 angle have been denuded, showing a fine anticlinal, with the dip varying 

 from 45 to GO degrees. The outer layer is of ashes, the inner yellow 



