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



papers previously published in the Bulletin. The third topic will be 

 treated elsewhere. 



Diamond Head 



This is a well formed, secondary crater, adjacent to Honolulu and so 

 conspicuously situated that it is familiar to all travelers. Since the pub- 

 lication of my paper on the geology of Oahu several geologists have visited 

 it and published their observations. As these represent divergent views, 

 I took the pains to reexamine the locality in my last visit, in 1905, and 

 present herewith both the abstracts of the statements of others and the 

 results of the latest investigation. 



As to the cone itself, I stated that 



"The structure of the cone is typical of its class — a broad, shallow, saucer- 

 shaped crater, with layers dipping toward the center inside, and outside out- 

 wardly in every direction at angles of 30 to 35 degrees. It would seem that 

 the mud was forced directly upward from the center, the surplus flowing over 

 the outside of the cone in every direction, and after the supply had ceased to 

 come the inner portions fell back toward the vent. The fragments consist of 

 every variety of the older basalts, with much limestone, corals, and shells that 

 were torn off by the ascencive force of the eruption from the coral reef be- 

 neath. The tuff is a palagonite like that of Punchbowl."* 



Concerning the succession the following is condensed from page 54. f 

 The order of genesis is : 1. The deposition of the coral reef on an ancient 

 lava. 2. The ejection of the tuff in shallow water, bringing up frag- 

 ments of the older rocks. 3. The Head was covered by vegetation, much 

 as it is now; fragments of the tuff rolled down the steep sides, became 

 cemented by lime, whether derived from the pieces thrown up from the 

 underlying coral reef or from the coral beach sand blown up by the wind. 

 Land shells flourished whose remains are abundant in the talus. 4. Sub- 

 mergence from 40 to 200 feet. 5. Emergence to the present level. 



Of the seventeen different periods recognized on the island the follow- 

 ing relate to the Head : Number 4, coralline and shell limestones formed 

 in later Tertiary age. These were penetrated by several basaltic erup- 

 tions. Numbers 5 to 9 and number 10, tuff craters like Diamond head 

 were ejected through the calcareous beds. Number 11, decay of the tuff, 

 producing soil. Numbers 12 and 14, basaltic ejections. Number 15, 

 the accumulation of the calcareous talus-breccia, containing the remains 

 of land shells. Numbers 16 and 17, depression and reelevation. 



* Bull. Geol. Soc. Am., vol. 11, 1900, p. 44. 

 tBull. GeaL Soc. Am., vol. 11, 1900. 



