t 
596 VAUGHAN MACCAUGHEY 
one another by steep-walled, knife-edged ridges. The ravines open 
upon the precipices, with vertical walls of 200 to 300 feet directly 
below their mouths, so they are true hanging valleys. They lie 
chiefly between the i, 400-2, 000-ft. contours, although some reach up 
the slopes of Kona-hua-nui to 3,000 feet. The hanging valleys, 
like the summit ridges and peaks, are mantled with the somber 
greenery of the rain-forest. 
The sides of these ravines are steep, and very difficult to climb. 
They are 45°-65°; the steeper declivities are constantly marked by 
landslides. These wounds cut through the soil to the underlying rock 
and remain bare for a long time. 
21. SUMMIT RIDGES AND PEAKS 
That portion of the main summit ridge of the Koolau Mountains 
which lies directly above the head of Manoa Valley, i. e., between 
Kona-hua-nui and Olympus, is 1.7 miles long, measured along the 
crest. The ridge, viewed from above, is strongly curved, with its 
concave side facing northeast (windward), into the Ohu-ohi amphi- 
theater. The windward wall is a great precipice, about 1,000 feet 
sheer, covered for the most part with scrubby vegetation, but im- 
passable. The summit ridge forms an arc of 90°. The eastern half 
of this arc definitely bounds Manoa; the western half is part of the 
Kona-hua-nui mass. Erosion is rapidly bevelling the summit ridge, 
which has a strongly serrate silhuette. In the process of time a gap 
will be formed through the mountains, similar to the gaps at the 
heads of Nuuanu and Kahili Valleys. The summit ridge and peaks 
are covered with the dense drapery of the rain-forest. 
The climate of the Manoa rain-forest is similar to that of all 
tropical montane forests. The temperatures are very constant and 
low as compared with those of the lowlands. Frost is unknown, and 
in the absence of accurate records, 45°-50° may be taken as a mini- 
mum. The rain-forest is far enough removed from the warm low- 
lands to be little influenced by them. The Oahu altitudes are not 
sufficient for alpine influences to be felt; this contrasts with the 
great mountains of the island of Hawaii, which rise to nearly 14,000 
feet. 
22. MOUNT KONA-HUA-NUI 
Mount Kona-hua-nui is the highest peak — 3,105 feet — in the 
Koolau Range. It lies as a mighty rampart directly northeast of 
