VIEWS OF VARIOUS GEOLOGISTS 473 



ities studied there was no evidence of any Pleistocene elevated reefs whatever. 

 It is probable that Oahu was land, inhabited by animals, as early as the 

 Eocene." 



The determination of the geological age of Oahu was the main object 

 of Doctor DalPs paper, and no one has since dissented from his conclu- 

 sion. His judgment of the age of the fossil shells can not be called in 

 question. Objections have been made to his view of the structure and 

 origin of Diamond head. Should it be proved that some of the objec- 

 tions have been well taken, the correctness of his main contention re- 

 mains unaffected. 



The first reference to Doctor Dall's views came from Dr S. E. Bishop, 

 a resident of Honolulu, a gentleman conversant with meteorological and 

 volcanic phenomena, at one time assistant on the government trigonomet- 

 rical survey of the islands. His observations on the atmospheric appear- 

 ances produced by the eruption from Krakatoa in 1883 led to the ac- 

 cepted use of the term "Bishop's ring" (cercle de Bishop). His paper 

 was published in the American Geologist.* 



"Brevity oe Tuee Cone Eruptions/' by S. E. Bishop 



The foregoing is the title of Doctor Bishop's paper. The main con- 

 tention therein presented is that a volcanic cone like Diamond head 

 "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 elevated perimeter 

 represents nearly a complete circle about 5,000 feet in diameter, and 

 most of it is about 450 feet above sealevel. The tuff has uniform qua- 

 quaversal layers dipping outwardly about 35 degrees, but less upon the 

 inside, pointing toward the center. The southwest angle reaches the 

 height of 762 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 875 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 in- 



*Vol, xxvii, 1901, p. 1. 



