AP.STRACTS OF PAPERS 133 



by overtbrust faulting giving displacement of 1,500 feet, and normal faulting 

 isbowing horizontal displacement of 1,200 feet. 



Presented from notes and illustrated by maps and seciiuns. 



Discussion 



In reply to question by Professor Lawson, autbor stated tbat tbe so-called 

 pivotal faults were in form as if produced by rotation of block about a pivot, 

 but really not so formed. Answering question by Louderback, he explained 

 tbat all of tbe faults described were thrust faults, except the two major 

 normal faults; also that faults were more abundant on the steeper limbs of 

 the anticlines. 



TERTIARY ROCKS OF OAHU 

 BY C. H. HITCHCOCK 



i Abstract) 



Basalt constitutes the foundations of the mountains of the Waianae and 

 Koolau ranges, reaching the altitudes of 4.000 and .3,.300 feet. The first named 

 occupy the southwest bordei- and the second named extend parallel to the 

 eastern coast. The sedimentary- members rest on the Koolau range, dipping 

 gently to the southwest. The sides of both ranges near the ocean are precipi- 

 tous, the one having been eroded by storms from the southwest and the other 

 by the trade-wind rains from the northeast. The rainfall may exceed 175 

 inches on the summits and diminish to 2 or .3 feet adjacent to the ocean. 

 There are sediments attaining a thickness of 1,000 feet resting on the basalt, 

 as made known by well borings. The water flows from the base of the sedi- 

 ments, rising 30 to 40 feet above the sealevel. 



The uppermost rock is limestone carrying many oyster-shells of Ostrcd 

 rctusa Sby., now extinct, and therefore esteemed to be of Pliocene age. No 

 other .shell has yet been -proved to be extinct. Below the limestone is a coarse 

 conglomerate more or less continuous from Diamond Head to near Barbers 

 Point. Beneath the conglomerate are masses of clay and volcanic ashes ex- 

 tending to the base of the scries. The succession of strata is not uniform in 

 contiguous wells. As a rule, limestones abound near the top and the clays near 

 the bottom. 



The government is endeavoring to establish a dry dock on the eastern of 

 the Pearl River locks. Borings indicate that the materials i)enetrated consist 

 of volcanic ashes, loose limestones, clays, silts, and other fluviatile deposits. 

 The ashes came from the extinct craters Makalapa and Salt Lake to the 

 northeast. 



After the dry dock had been completed the water was pumped out and the 

 cement floor aijd sides were not strong enough to prevent rupture by the 

 pressure from below. As firm rock can not be reached within 500 feet from 

 the snrfac<>. a niucb stronger ccnicnt liaso must 1)0 built into tbe floor and 

 walls to resist the pressure from below. 



Dikes of basalt penetrate tiie lavas alotig tin- sumnul of lin' Kool.iu range 



