NORMAL FAULTING 511 



covered the country between Hilea and Pun Enuhe, the latest of these 

 flows being dated as 1868. Puu Kaumaikeohu. and Puu Iki are probably 

 cones, as they rise above the level of the surrounding normal mountain 

 slope, but the flat-topped Puu Enuhe, Kaiholena, Pakua, and Makanao 

 resemble horsts left by the inbreak of the amphitheater in a manner sim- 

 ilar to the formation of the curved fault at Kealakakua Bay. 



A fault-line scarp is traced by Professor Hitchcock along the southern 

 boundary of Mohokea from the vicinity of Kapapala toward Waiohinu, 

 but if this line of gentle escarpments represents a displacement of the 

 lava flows, it must be a very old feature of Mauna Loa, long ago con- 

 cealed by lava flows like those at Kilauea which have poured over the 

 Keauhou palis in comparatively recent history. 



Kohala is bounded from Pololu Gulch to Kukuihaele by a fault-line 

 scarp^^ (plate 30, figure 2), and into the center of the old volcano the 

 U-shaped valleys Waipio and Waimanu have been carved, while all the 

 other valleys mounting at this fault-line are small. Even the largest of 

 the smaller valleys — Pololu and Honokane — in no way compare in size 

 with Waipio or Waimanu, although the amount of rainfall is approxi- 

 mately the same at the heads of all these streams. A quadrangular 

 fault-block is suggested as the origin of the high plateau between the 

 Waipio and Waimanu valleys and the fault-lines probably determined the 

 course of these valleys. The lines of evidence supporting this conclusion 

 are : the peculiar direction taken by the head of Waipio Valley transverse 

 to the mountain slope and across the head of Waimanu Valley ; the great 

 depth of these valleys (both appear to be slightly drowned) ; and the fact 

 that a cross-section from the summit of the Kohala Mountains through 

 the block between Waipio and Waimanu compared with a similar section 

 through the continuous mountain slope northwest of Waimanu seems to 

 show an uplift of the block near its head.^^ 



East Maui is well known because of the famous rent on the summit of 

 Haleakala, the origin of which has been discussed by a number of geol- 

 ogists. The rent has a shape which defies description. The central por- 

 tion, 5 miles in length, extends from the summit of the mountain east- 

 ward. The Koolau Gap (plate 31, figure 1), enshrouded in a tropical 

 jungle below the 7,000-foot contour, extends from the center of the 

 mountain northward, narrowing to the north. The Kaupo Gap extends 



25 First recognized by J. C. Branner : Notes on the geology of tlie Hawaiian Islands. 

 Am. Jour. Sci., vol. 16, 1903, pp. 301-306. The submarine contours of 20, 50, 100, 200, 

 300, and 400 fathoms, as mapped by the U. S. Coast and Geodetic Survey, follow in 

 notable fashion the recession of the shoreline along the scarp. 



28 Field observations were made from a triangulation station above Kaauhuhu and 

 from the Hamakua ditch line above the head of Waipio Valley. Cross-sections were 

 drawn from the new U. S. Geological Survey topographic sheets of the area. 



