DIAMOND HEAD.
Circumstances have led to an extended study of Diamond Head. There are seven tuff cones near the sea shore on the southwest side of Koolaupoko, of which Diamond Head or Leahi is one. The others are the two at the salt lakes Aliapakai and Aliamanu, Makalapa, a short distance to the northwest, Punchbowl or Puo waina at the base of Tantalus and within the city limits of Hono lulu, and the two Koko Heads near the southeast corner of Oahu. They are all composed of palagonite, yellow to brown in color, with resinous luster ; they constitute broad shallow saucer-shaped craters with double quaquaversal stratification, the inner dipping towards the center and the other parallel with the outer slope. The brown color is evidence that warm waters were concerned in the making of the cones, not necessarily exceeding the tem perature of boiling water.
Diamond Head is the most perfect as well as the best known of all the secondary craters about Honolulu. Visitors recall it as the prominence seen just before reaching port from the east, and again upon resuming their voyage. Artists have vied with one another in efforts to display this beautiful hill on paper or can vas, and every one is interested in viewing the channeled water courses upon the outside and the barren rocks as contrasted with the rice fields, coconut groves, and the green plain of Waikiki, a health resort, close to the city at its base. It is a truncated hol low cone, 4,00o feet in the greater diameter of the rim, and in the shorter diameter. The elongation is in the direction of the trade wind, and consequently the southwest side is higher and thicker than its opposite. This fact, first stated by W. L. Green and reiterated by all later authors, applies to many others of the secondary craters as well and to the direction of the spread of the eolian beds. The southern highest part is seven hundred and sixty-one feet above the sea at its base, the opposite end being somewhat lower, and there is not much variation in the rim else where. Inside, in the wet season, there is a pond at the lowest point, two hundred feet above the sea, as near as may be to the eastern wall. From the outside Diamond Head looks like a solid hill, and with its reddish tint and apparent strata is very sug gestive of buttes in the Chalcedony park of Arizona.
The diameters of the base of this crater are 5,00o and 6,000 feet respectively, making the seashore the extreme southwest limit. The tuff has been recognized in the very deep well sunk by James Campbell near the seashore at Waikiki. Two hundred and seventy feet of tuff were penetrated by the drill beneath fifty feet of beach sand and gravel. Beneath the tuff is a mass of limestone five hundred and eight feet thick ; and the section upon Plate 9A shows the relations to each other of the tuff, limestone and basalt as deduced from our various observations. The lowest part of the interior is on one side of the center. A good road follows around the outside of the cone, rising from near the sea level by the artesian well to one hundred and seventy feet where a road turns off to the north. There is very much coral or eolian calcareous sand on the south side of the cone near the lighthouse.
Farther east a marine limestone occupies most of the territory.
Sir Archibald Geikie calls attention to the similarity of Dia mond Head to Monte Nuovo near Naples. This is a scoriaceous tuff cone IN which was thrown up in a few hours in 1538, while there was other activity for a week. Most travelers visit it, so that it is an object well known. It is four hundred and eighty nine feet high and about one and a half miles in circumference. The larger part of the famous Lucerne lake here was filled with the stones, scoria and ashes that were ejected at the time of its origin. Among the fragments thrown out were pieces of Roman pottery and marine shells, which happened to be situated in the path of the ascending outburst. I have been in the habit of using the known history of Monte Nuovo in my lectures for the past forty years to illustrate the formation of tuff cones, emphasizing the brevity of the process, the stratification of the material (double quaquaversal), and the lack of any disturbances in the adjacent territory. The temple of Pluto was partly covered by the debris, but its level has not been affected, as it would have been if the cone had been formed in the manner suggested by L. von Buch and Elie de Beaumont. They believed that the conical shape proceeded from an upheaval or swelling of the ground around the vent from which the materials issued.
Dr. S. E. Bishop has very forcibly stated the brevity of tuff cone eruptions in the American using Diamond Head for the illustration of the subject. Such a cone, he says, "could have been created only by an extremely rapid projection aloft of its material, completed in a few hours at the most, and ceasing suddenly and finally." The first proof of this proposition is the extreme regularity of the elevated circular rim of the cone. Two-thirds of the ele vated perimeter represents nearly a complete circle about 5,000 feet in diameter, and most of it is about four hundred and fifty feet above sea level. The tuff has uniform quaquaversal layers dipping outwardly about thirty-five degrees, but less upon the inside, pointing toward the center. The southwest angle reaches the height of seven hundred and sixty-two feet, because the strong trade wind deflected the lofty jet of tuff to leeward and piled it up disproportionately.
The second evidence of the brevity of the eruption is. derived from an arithmetical computation of the time required to deposit the actual mass of the cone by a fountain of adequate height to deliver its ejecta upon the existing rim of the bowl. The total mass is thirteen billion cubic feet of tuff. This could have been discharged by a fountain with eight hundred and seventy-five feet of velocity per second, raised to a height of 11,925 feet in two hours' time. This is given as an approximate estimate only, and he is disposed to increase the velocity and reduce the time, with a section area of 5,00o feet.
These statements of the symmetry of the cane and of the time required for the deposition of the mass are thought to forbid any other conception of formation.