478 C. H. HITCHCOCK GEOLOGY OF DIAMOND HEAD, OAHU 



drainage is collected into Pearl river on the south, and reaches the sea at 

 Waialua in several gulches on the north. It would seem that this inter- 

 montane plain must represent about the original surface of the lava 

 flows, in which the gorges are few but very deep. As the surface seems 

 to consist of soft clayey material, one would expect it to consist of sedi- 

 mentary or at least ashy volcanic beds of the Tertiary. On examining 

 the walls of the canyons the rock is made up everywhere of the spherical 

 and elliptical nodules so characteristic of the Hawaiian basalts. They 

 have been exposed so long to the elements that decomposition has 

 reached the lowest depths accessible. 



That part of the western slope of Koolau that is best known shows 

 numerous secondary volcanic cones, scoriaceous, basaltic, and tuffaceous. 

 Some are parasites on Koolau and others lie in the lowland. Scori- 

 aceous ejections have been noted at the Pali, west of it, and near Tantalus ; 

 and perhaps the so-called ashes from Tantalus, the pond east of Kakea, 

 and Punchbowl should be ranked in this category. Secondary basaltic 

 ejections are recognized in Aliamamu, Aliapakai (Salt lake), near 

 Moanalua; nephelite dikes on Punchbowl, Palolo, and Kupikipikio, the 

 craters Mauumae and Kaimuki. For topographical reasons the interest- 

 ing nepheline basalt of the Moiliili quarry seems connected with small 

 craters lying east of Eocky hill. 



All these secondary ejections named were contiguous to one another, 

 and there is no attempt to specify the many others lying east of the 

 region of Diamond head and west of Salt lake. 



There remain the tuff cones, which mostly occupy a zone makai (that 

 is, toward the sea) of the basaltic ejections. These are Makalapa, the 

 two salt craters, Punchbowl, Diamond head, and the two Koko heads. 

 From statements already made, these are clearly allied to the palagonite 

 of Italy, a tuff brownish yellow in color, with a resinous luster, com- 

 posed of the fragments of the earlier basalts, marine limestones, with 

 corals and shells, hydrous and discharged at a temperature less than that 

 of the basalts. These characteristics would seem to point to a sub- 

 marine origin, while the basaltic cones, possibly coeval with them, accu- 

 mulated around terrestrial vents. Diamond head is therefore a typical 

 tuff cone, made of very hot mud, originating beneath the sealevel. 



The Tertiary Limestones 



All the igneous ejections, both the original Koolau basalt, the second- 

 ary scorias and basalts, and the tuff cones, have come up through a Ter- 

 tiary, probably Pliocene, platform- This conclusion appeared first in 



