l»i C. H. HITCHCOCK — GEOLOGY OF OAHU 



Professor Maxwell says the limestone here has been altered to gypsum. 

 At Kaena point I found ledges where a basalt had penetrated the coral 

 limestone and indurated the calcareous rock with included cyprssa. 

 Hence we have the evidence of a very late volcanic eruption at localities 

 very widely separated, upon Oahu. 



Plate 8 represents Diamond head as seen from the summit of Punch- 

 bowl. Maxwell says the slopes of Diamond head and Punchbowl are 

 white with deposits of silica and carbonate of lime, etcetera (page 39). 



ROCKY HILL, KAIMUKI, AM) MAUVMAE 



Three basaltic craters, quite near each other and within easy reach of 

 Honolulu, remain to be mentioned, and the facts should be placed upon 

 record before the extension of the city shall have obscured their present 

 topography. 



Rocky hill lies just east of Oahu college, in Punahou, blocking up 

 Manoa valley. Its height is 297 feet above the sea. The rock is a 

 clinker, weathering roughly. The crater has been broken down on the 

 side toward the college, and the eastern wall must be more than 100 

 feet high. The slope toward Manoa is mostly smooth, the rough ledges 

 having been covered by thick deposits of the black cinders blown down 

 from the Tantalus craters. At the highest point in the road between 

 Rocky hill and Round top is a very large dike of basalt that has been 

 quarried for building stone and road metal. The central portion is com- 

 pact, with few jointed seams. On both sides the material seems to possess 

 the same character, but is traversed by many columnar jointed seams 

 dipping westerly and quite contrasting with the central mass. Still out- 

 side there are multitudes of the spherical columnar stones imbedded in 

 reddish clayey cement, and they seem to be a part of the dike, making 

 a width of 70 or 80 feet. The point of contact with the adjacent Koolau 

 basalt is not seen. The fact of the existence of a v ridge having the direc- 

 tion of the dike from Rocky hill to the base of Round top, and the dike 

 being on the divide itself, suggests its derivation from the crater. The 

 rock all the way to Wilder avenue from the summit, consisting of drab 

 and dark brown compact or vesicular, often chrysolitic basalts, is prob- 

 ably a part of the Koolau series. Along the road there are bunches of 

 hard rock, encircled by red friable cement, that represent probabl} 7 the 

 ordinary decay of the older rocks. 



There is a quarry in the basalt at the end of a tram road to the west 

 of the Moiliili church where very much rock has been excavated. The 

 material is now used for road metal. The limestone occupies the low r 

 ground in front, and in the seams of the rock are many films of calcium 

 carbonate and silica, indicating the presence beneath of the reef. It is 



