J. D. Dana — Geological History of Oahu. 95 



from the precipice to the westward, showing that the streams 

 flowed from a point to the eastward, and that a large piece, 

 perhaps the larger part, of an old volcano has disappeared. 

 Kauai, north of ISTiihau, has its Kapali cliff, a dozen miles long, 

 along its southwest side, in a line with the JSTiihau cliff. Molo- 

 kai, to the east of Oahu, was once, as its lava-streams prove, a 

 doublet of volcanoes, like Maui ; but it has been shaved down 

 to a strip of land 35 miles long, and not a fifth of this in mean 

 width. The eastern part has an alcoved precipice facing the 

 north, which rises to a height of 2500 feet above the sea. It 

 encloses a strip of land along the sea shore, and on this spot, 

 thus walled in, it has been found convenient to locate the 

 Leper quarantine-ground of the islands. Lanai, a narrow island 

 south of Molokai about 20 miles long, has a bold front to the 

 south and gradual slopes from it in other directions. Thus 

 such precipices are rather the rule in the Hawaiian group ; and 

 if seashore erosion is not the origin — as an island like Tahiti, 

 with its profound radiating gorges as a result of fluvial action 

 and its non-gorged coast, appears to show* — fractures and 

 subsidence must be. 



A great volcano is a disgorger of lava in vast floods and so it 

 makes its mountain ; and it may make also empty cavities at the 

 same time and as a consequence. As long as the ascensive 

 force keeps the liquid lava-column of the active volcano fully 

 up to the summit crater, the mountain may have only local 

 cavities. But whenever a great discharge takes place, a coequal 

 cavity may result ; and if the discharge is from fissures at the 

 base of the cone, 15,000 to 18,000 feet below the sea level (not 

 a greater depth than exists in the neighboring seas) an enormous 

 cavity may be left, which only the renewed action of the ascen- 

 sive force would fill. If the mountain then became extinct 

 with no return of the liquid, it would be a hollow mountain ; 

 and the greatest of subsidences which the Hawaiian facts seem 

 to indicate, are small compared with the possible consequences 

 of such a condition. 



4. The Tufa and other Lateral cones of East Oahu. — Several 

 of these cones, as already stated,' are represented on Plate 4. 



Punchbowl, fig. 2, stands on the northern border of Hono- 

 lulu (at P on the map).f Its highest point is 498 feet above 

 tide-level. The tufa of the beds constituting it, though rather 

 feebly consolidated, is quarried on the west side of the cone, 

 and specimens may there be conveniently obtained. It is a 

 yellow to brown, in part resin-] ustered, palagonite-like rock, 

 bearing evidence in its constitution and in the dip of the beds, 



* This Journal, xxxii, 247, 1886. 



fThe sketch was taken in 1840 from the deck of the ship Peacock as she lay 

 in the harhor. The native huts at its foot are omitted. 



