PEARL HARBOR SERIES.
The coral reefs and limestones are intimately associated with sedimentary deposits and volcanic flows, partly ashes, often dis integrated. The whole assemblage is really a terrane about i,000 feet in thickness. It is best developed about the Pearl River locks, and hence for convenience it may be termed the Pearl Harbor series. Probably this series of deposits began in the Pliocene, and the older layers may be a base on which the volcanic ejections commenced to accumulate. Some authors think that extensive Tertiary deposits are necessary for the starting of volcanic ac tivity in every country. If so, parts of the Pearl Harbor beds will be found beneath Koolau and Kaala. This series is evidently to be compared with the thick limestone deposits in the Fiji Islands, supposed by Dr. Alexander Agassiz to underlie the living coral reefs of the archipelago and to have been elevated as much as eight hundred feet.
Owing to thorough disintegration, it is not easy always to discriminate between a decayed lava and a earthy sediment, especially as lavas or ashes are constantly intercalated with strata. I will speak of these deposits at several localities where they may be easily examined. One of the most important may be seen in a railway cutting a short distance east of the Waipio station, west 3o of Pearl City on the line of the Oahu Railway and Land Company. The deposits seem to be arranged as follows from above down ward : I. Ten feet of a reddish-yellowish earth, constituting the s H. Six feet of gray slaty colored earth.
G. Two to eight feet of limestone and marl.
F. One to two feet of pure kaolin, best seen in the fields east. E. Thrce to four feet of bluish and other clays.
D. Bed of oyster shells, one to two feet thick. Ostrea retusa, Shy.
C. Two and a half feet of ferruginous clay containing large nodular masses of black hard clay, apparently car bonaceous.
B. Six inches of greenish clay, with blue stains of what may be iron phosphate or manganese oxide.
A. Four or five feet thickness of clays, extending downward to the track of the railroad and to an unknown depth.
The uppermost of the layers may be followed along a sort of terrace northerly to the Oahu mill, and the gray layer shows itself wherever a cut has been made deep enough to reach it. West of Oahu mill the kaolin is recognized along the road leading west for one -fourth of a mile, and also along the branch railroad half a mile out from Waipahu station. It comes in contact with basalt, probably unconformably, along the railroad and overlies a rubble whose constituents are so decayed that they will crumble under the pressure of the hand, and is over an agglomerate that may be connected with the basalt. The Waipio cut is repeated on a larger scale in a railroad cut easterly from the Ewa upper pump (October 14, 1898). The basal greensand is thicker, as is the kaolin and the greater part of the upper material is a red earth, the exposure here being about forty feet thick. It is likely there is a direct connection between the kaolin of the Waipio cut, the neighborhood of Oahu mill, and the railroad cut near the Ewa upper pump. At this locality the lava is in part vesicular, in sheets, very much decayed. Following the railroad to the middle pump, this lava is covered by a thick layer of cobbles and pebbles mixed, which continues almost to the lower pump along the ravine, underlaid by what seems to be very soft lava. This is on the edge of the Ewa plantation plateau, which may be sixty feet above the sea, and said to rise to one hundred and sixty feet where crossed by the Government road.
Crossing over the fish pond from Waipio to John Ii's tomb, the rock is calcareous with fossil shells, either D or G of the section.
East of the Waipio cut along the railroad we see first the upper red earth, and then beneath the same pebbly layer observed in the Ewa ravine. Going west from Waipio, at Hoaeae station is a cut in the red earth, cut by two vertical dikes of sand. About a mile west of Hoaeae there are excavations showing a thick earth cov ered by the pebbly deposit unconformably, and both by loam. A dike of sand extends downward from the pebbles into the earth.