PUNCHBOWL AND DIAMOND HEAD COMPARED.
The structure of Punchbowl is like that of Diamond Head. It is mostly composed of tuff, much of which on the side toward the city has its seams filled with calcite. In the quarry below the reservoir both calcite and zeolites are found, and an occasional piece of basalt. The phenomena prove that the black ash over lies the tuff, and that a long interval must have elapsed between the ejection of the two materials, because the inferior one has been weathered. It is probable that the first material came from beneath the sea, while the later ash, though issuing from the same vent, did not come in contact with water, and with it came another basalt, that on the summit of Punchbowl and in the dikes radiating from it. The extent of the tuff to the southwest is shown in the well boring at the Queen's Hospital, where forty seven feet of it is reported underlying thirteen feet of lime sand and ten of black ash. The Tertiary is well shown in a cutting near by on Vineyard street, fifteen feet of sand with shells being exposed beneath the black ash.
Similar relations of the tuff, soil, and ash have been observed near Moanalua, where the tuff has been covered by an ash in which may be seen upright trunks of trees." Rather than as sume the ashes to have been erupted simultaneously in the Hono lulu district, it may be better to say that similar eolian materials have been discharged at intervals through an unknown part of Tertiary time.
Doctor Dall has noted the greater abundance of limestone in Diamond Head, where the tuff is fairly saturated with it, than in Punchbowl. A walk up the southwest slope of Punchbowl will satisfy any one that the seams are as fully filled with this mineral as in the northern part of Diamond Head, and in the quarry it is not wanting, accompanied with zeolites. It was stated above that
over five hundred feet of limestone underlies the south end of Diamond Head, and only thirty feet in the well at the Queen's Hospital adjacent to Punchbowl. As the volcanic ejection brought up the underlying rock, Diamond Head should show very much more of it than Punchbowl. It is also on the sea shore adjacent to the reef from which come quantities of eolian calcareous sand. Punchbowl is half a mile distant from the seashore, and therefore would not be expected to be supplied so abundantly with blown sand.
An examination of the inwardly dipping layers near the high est point of Diamond Head reveals a very liberal supply of lime stone. It was here that I found coral and shells in 1883. The photograph in Plate 9B shows the abundant supply in the layers of tuff in the foreground on the right-hand side. The stand point is quite near the summit, and the view was taken to show the rim of the cone, the interior, and the black promontory of Kupikipikio in the distance.
In this connection it is proper to advert to the abundance of limestone in the inside of the crater at Salt Lake. Not merely are the fragments abundant, but the original reef itself must be The western Koko Head is equally prolific with lime stone blocks, though from a hasty examination I am not pre pared to say that the original ledge can be detected. The lime stone has not been seen in the lowest part of the inside of Dia mond Head.