The lowland between rises gradually to a watershed 888 feet above the sea. Each range represents an elongated dome composed of basaltic layers gently inclined outwards in every direction (quaquaversal). The Kaala dome originated first in igneous ejections outpouring at the bottom of the ocean; they were constantly renewed, and finally emerged above the waters. It was then exposed to the erosive influences of the rains brought by the trade-winds. The streams excavated canons in the basalt upon both sides of the island, eating away more of the rock in certain portions than in others. After a
long period a similar but longer island developed upon the eastern side, becoming the Koolau range, with more marked erosion upon the windward side, and very little upon the northern half of the leeward side. The Koolau lava poured itself out profusely, and covered up some of the earlier formed cañons upon the Kaala range.
The character of the erosion is shown in Figure 2 upon the Waianae side of the Kaala range. The canon has been enlarged to an alcove and the precipitous side—called a Pali by the Hawaiians—presents a curious escalloped surface, or what might almost be called the ribs of the mountain side. Precisely similar waves appear upon the pali at the eastern side of the Koolau range. The most interesting point is at a wind-gap, 1,205 feet above the sea, the only place in the whole range where a road has been cut through from Honolulu by way of Nuuanu Valley to Kaneohe Bay. Tip this valley for about eight miles about a hundred years ago King Kamehameha drove an army of his enemies,
