ORDER OF EVENTS IN THE GEOLOGICAL HISTORY OF OAHU.
From the descriptions now presented it is possible to make out the order of the principal events in the geological history of this volcanic island. We are satisfied with the existence of Tertiary deposits antedating the rise of the earliest basaltic land, but will not consider whether there may have been any rising of the ocean floor in connection with the eruptions.
T. At the base of Kaala igneous eruptions commenced under water to accumulate sheets of basalt until finally the island of Kaala, a smooth dome rose above the waters, which slowly became covered by vegetation derived from distant regions.
2. This dome became extensively channeled by streams pro duced as now by the condensation of the moisture brought by the northeast trade winds and Kona storms. Both sides suffered erosion.
3. The island of Koolau came up quite near to Kaala in a similar manner, and lava flowed down so as to conceal several hundred feet altitude of the northeast flank of Kaala. Koolau extended out to sea several miles farther to the northeast than at present.
4. Coralline and molluscan limestones commenced to grow as soon as the reef-building animals could migrate hither. Doubt less the work commenced in the first period, and has continued ever since, coeval with the other phases of growth., If we were to judge of age from the amount of work accomplished we should say the earlier stages of growth correspond to the work done else where in the later Tertiary. The slow upbuilding of the volcanic domes and their subsequent erosion required an immensely long period for their accomplishment. The island was also a thousand feet higher than at present, if the Darwinian theory of the origin of coral reefs is true.
5. Eruption of the amygdaloidal basalt at the Pali.
6. The olivinitic basalt formed laccolites at the Pali. Some of the dikes, both in the Kaala and Koolau areas, may have filled fissures at this time.
7. Eruption of an igneous agglomerate containing pebbles of olivine ; may have produced craters in both areas ; developed typically at the Pali.
8. Quite widely extended ejection of red ash, clinker, and lava at the Pali, and the formation of Makakilo and Kupuai of the Laeloa craters ; some of the Tantalus series of craters.
9. Ejection of some of the basalts penetrated in sinking arte sian wells ; including also most of the Laeloa craters, Kuua, Palailai, Kapuai ; also Kaimuki, Mauumae, Rocky Hill.
so. Tuff craters, probably not all active at the same time— the Salt Lake group, Punchbowl, Diamond•Head, the Koko Heads, Kaneohe group, etc. The tuffs came up through coral reefs, the land probably being lower than at present ; vegetation as flourish ing as at present. Five substages indicated along Oahu Railway and Land Company near Moanalua station.
s. Decay of the surface of the tuff and, of course, of all the other rocks, so as to produce soils.
12. Discharge of ashes from Tantalus, Punchbowl, Diamond Head, Koko Head, and elsewhere, followed by showers of stones.
13. Dikes cutting Punchbowl, Diamond Head and coral reef, Kaena point, Kupikipikio, and Koko Head.
14. Time of the accumulation of calcareous talus-breccia with Achatinellidae at Diamond Head.
15. Depression to the extent of two hundred and fifty feet.
16. Elevation to the present level. Accumulation of dunes.