94 J. D. Dana — Geological History of Oahu. 



that the East Oahu mountain was a dome, like Mt. Loa, rather 

 than a cone like Haleakala. The existence of one or more 

 craters west of the " pali " has been urged, and is possible. 

 I know of no special facts sustaining it. The amphitheater at 

 the head of Manoa valley is referred to by Mr. Brigham as 

 probably the site of a crater ; but I was more inclined from 

 my examination to make it an amphitheater of erosion. 



3. Origin of the long precipice on Oahu. — The long preci- 

 pice of East Oahu has been attributed to erosion. But I have 

 found no evidence that such ' transverse walls are legitimate 

 effects of erosion, either fluvial or marine. As illustrated on 

 Maui (p. 91), the sea works with extreme slowness in batter- 

 ing lava-cliffs, and cannot work at all below the limit of force- 

 ful wave-action — a level not twenty feet beneath the surface. 

 Eluvial action makes long valleys in the long descending 

 mountains and capes which the sea is incapable of obliterating. 

 Land waters have done grand work in alcoving the long preci- 

 pice, and carving battlements and temples out of the rocky 

 piles that were left, as is well exhibited in the Kualoa bluffs, 

 while the sea has not even scraped away the small tufa cones 

 on its borders. It might be said that the cones of Kaneohe 

 and the "pali" have been made since the era of erosion ; but 

 this disconnects their origin by a very long era from the 

 period of activity in the crater. 



Another view with regard to the origin of the precipice is 

 that of my Expedition Beport, namely that it was made by a 

 profound fracturing of the mountain-dome across from south- 

 east to northwest, and a drop-down of part of the outer or 

 eastern section. The line of fracture was irregular — the course 

 rather of a series of fractures ; and subsidences of varying 

 extent may have taken place along the line, becoming smaller 

 to the northwest, where high ridges are left between the preci- 

 pice and the coast. The amount of displacement was not less 

 than the height of Konahuanui, 3105 feet, and probably much 

 exceeded this. 



Great catastrophic subsidences are not uncommon in volcanic 

 regions. In the account of Maui and its crater the fact of a 

 subsidence not less than 2500 feet, accompanying and follow- 

 ing some one of its eruptions, appears to be placed beyond 

 doubt. Hawaii has plain evidences about its crater of subsi- 

 dences hundreds of feet in amount of displacement if not 

 thousands ; and there are high precipices, like that at Kealake- 

 kua Bay, for which there appears to be no other probable source 

 of origin. 



The small western island of the Hawaiian group, Mihau, has 

 a bold precipice as its eastern face, 1500 to 1800 feet in 

 height above the sea, and the lava-streams of the island pitch 



