South from the Waipio cut on the peninsula a calcareous sand stone is found at the south edge of Eo pond. Near Hanaloa pond is a large quantity of marl, and possibly kaolin, G and perhaps F of the section. At the southwest corner of Hanaloa pond is an abundance of limestone with fossil shells and corals. East of this pond the rock appears more like the ordinary reef.
Near Ewa church, northeast from Waipio, the section is more of a volcanic character. At the base is an unaltered basalt of the agglomerate kind, consisting of large stones or spherules, cemented by a reddish material, which is apparently the result of decomposition of the original rock, for there is every grade of transition, from the compact unaltered rock to that containing spherules and that which is entirely a soft earth. There are bunches or areas of the hard basalt in the midst of the softer varieties, and this difference in what seems to be one layer is analagous to variations in the character of the rock at the living volcano. The gases inducing decay are abundant in certain spots and absent from others. The boulders weather concentrically, and are of the same kind with what are often strewed over fields. like the ice-carried stones of glaciated regions. Above this are a few layers of what is very near hematite, a known decomposi tion product of lava. This is covered by earth, and that by a mixture of sand, earth and rubble. The hill or plateau is capped by red and yellow earths, each a fathom or more in thickness. The total thickness must be sixty or seventy feet.
From the Laeloa craters across the eastern part of the Hono lulu sugar plantation or to Halawa station on the railroad the surface is largely composed of the upper earths of the section, constituting the substratum of the soils found to be very suitable for the growth of the sugar cane. At a deep railway cut one fourth of a mile west from Aiea station is a thick mass of earth, capped by eight or ten feet of coarse pebbles and cobbles, cemented together so as to constitute a conglomerate, all of whose con stituents are rounded. These stones increase in size in passing across a stream near the business center of the Honolulu planta tion. Starting at the sea level, at Aiea station, the following is an approximate section up to the top of the pleateau, about sixty feet. At the base, four feet of greenish clay and pebbly earth ; one foot of fine volcanic ash, consolidated ; four feet of tuff ; one foot of clayey ash ; pebbles and clay, four feet ; tuff and ash, eight feet. Back of this cliff is an indefinite amount of drab and gray earths, with layers of silica. On the summit of the plateau I found marine shells and corals, some of which are like those used for food by the natives, so that this is not a clear case of a sub marine deposit, though it probably is, as some of the organisms are not edible. On the branch railroad leading from Halawa up to the sugar plantation is an interesting cut through earth capped by a fine grained volcanic ash, three feet thick, well filled with leaves of dicotyledonous plants. The ash was apparently blown from Makalapa and consolidated. Along the seashore the lower pebbly ash of the Aiea section has been folded and slightly faulted. It is covered by an earth or old soil, which can be traced east wardly directly beneath the tuff of Makalapa, which comes as far west as Halawa stream.
The Pliocene area of Oahu coincides very nearly with the low land tracts utilized for the cultivation of sugar cane and sisal, from Barber's Point to Koko Head ; perhaps to the altitude of 300 feet entirely around the island. Small patches of the rock ap
pear at Waianae, Waialua, the Kahuku plantation, Laie and other places on the northeast coast. The rock also is extensively dis tributed below the surface, as developed in the borings for ar tesian wells. Northeast from Diamond Head Dr. W. H. Dali found fossils in it, referable to the Pliocene, species of Coons, Purpura, Chama and Ostrea, seemingly extinct. This original an nouncement of this conclusion was stated as follows : 9 "To sum up, it is concluded that the reef rock of Pearl Harbor and Dia mond Head limestones are of late Tertiary age, which may corre spond to the Pliocene of West American shores, or even be some what earlier, and in the localities studied there was no evidence of any Pleistocene elevated reefs whatever. It is probable that Oahu was land, inhabited by animals, as early as the Eocene." It would seem that this Pearl Harbor series is a combination of marine deposits, reefs, decayed rock, secondary volcanic pro ducts, ashes and solid basalt. The natural conclusion is that volcanic ejections were intercalated with beds of marine origin illustrated further by the finding of a fine black ash intercalated in the limestone of Ford's Island, several miles away from the nearest volcanic vent. At present it is not possible to separate them. Passing southerly toward the mouth of the river, the lime stones grow thicker and merge into the calcareous beds proved to extend into the earth by the artesian bore-holes. Hence there is ground for the belief that the foundation of the whole archi pelago is a Tertiary limestone traversed by eruptives.
A recent visit to Wahiawa has added to our knowledge of the facts and to modified conclusions. There have been lavas from both Kaala and Koolau as heretofore explained, meeting in the Kaukonahou gulch, and they are to be distinguished from each other by the slopes of the beds. Connected with the more com pact basalt are agglomerate and residual days, still beneath strata of aqueous origin. At the bridge across the stream are fine ex posures of the decayed basalt showing excellently the original composition. The cliffs exposed are crowded with the spherules of concentric structure usually soft throughout but occasionally having the solid core present, which remains simply because the work of decay has not been complete. In one place there is an immense concretionary crust of limonite. Passing to the hill south may be seen beds of pebbles, sandy and clayey layers capped by a considerable thickness of residuary clay. There is evidently a considerable aqueous deposit here overlying the decayed basalt. Another fine exposure of the series may be seen as you stand upon the dam and look at the cliff on the northwest side. The dis covery of fossil marine shells near the dam at as much as eight hun dred feet elevation in the upper sediments will lead to improved conclusions. The basalts from Koolau flowed toward the Kaala sheets, meeting them along the gulch and at the lowest points. Then decay set in, having commenced back in the Tertiary. The later wash from both the mountains has filled all the holes and irregularities and produced the plains sloping downwards to the lowest line, and at the same time extensive sedimentary beds were laid down. It is evident that the ocean covered the plains, mak ing islands of Kaala and Koolau. The gulches leading to Waia lua and Pearl Harbor were excavated later after the renewal of the erosion by elevation of the land.