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



A study of the fields at the Waialua plantation gives related results. 

 The cultivated tracts seem like aqueous and residuary deposits, utilized 

 to the height of about 300 feet. I found shells and opercula of the 

 marine gastropods in numerous localities and Melanias up to 250 feet 

 altitude. I had no opportunity to see these remains in any excavations ; 

 they all lie on the surface of the ground. 



I think a little search will prove the existence of seacliffs toward 

 Kaena point, to the west of Waialua. Looking from the railroad train, 

 there seems to be three wave-cut terraces in the basalt, the highest one at 

 about the level of the shells picked up from the sugar fields. The excava- 

 tions may not be strongly marked, as it is presumed that the time of the 

 submergence was brief; but it seems evident that there must have been a 

 very recent depression of the island to the depth of 250 feet, very likely 

 in the Pliocene. If so, the age of the smaller land shells in the talus- 

 breccia will be established. As has been remarked, it would seem neces- 

 sary for as long a period as that to have elapsed to account for the devel- 

 opment of the Achatinellidse. 



Kelation of the basaltic Ejections to Diamond Head 



• The question has arisen, What is the relation of Kaimuku to Diamond 

 head? In my geology of Oahu (page 75) I have referred to the meeting 

 place of the two rocks, the basalt apparently overlying the tuff. The 

 road now passes near the line of junction of the two rocks. It looks as 

 if the basalt had affected the tuff, the former pressing against the latter 

 and the two interlocking. 



If Kaimuki is related to the dike at Kipikipikio, it is later in origin 

 than the tuff; or if the similar rock at Punchbowl is considered, the 

 basalt is the newer, as it lies in the throat of the vent, adjacent to the 

 black ash, which is confessedly the newest volcanic product. The basalts 

 would seem to have been erupted later than the tuff, after the land had 

 risen, because the material is neither fragmental nor hydrous. They are 

 later than the limestones which they have cut through. 



Some of the artesian wells show the presence of a thin basalt inter- 

 calated in limestone or earth, thus indicating an earlier eruption. 



Conclusions 



1. Diamond head is a tuff cone thrown up explosively from beneath 

 the level of the sea, and is to be compared with the Monte Nuovo, near 

 Naples. 



2. It was ejected through fossiliferous limestones of Tertiary age, 

 probably Pliocene. 



