8. Powers — Notes on Hawaiian Petrology. 263 



an elevation of 660 feet and other exposures are found 

 north of Mr. W. EL Field's house, Kapaniwai. At the 

 bridge near the Needle, elevation 900 feet, the stream is 

 cutting into gravels and in the center of the valley there 

 is a hill of decomposed rock consisting of angular and sub- 

 angular fragments y 2 inch to 3 inches in diameter. 



The existence of similar deposits in three valleys at 

 elevations ranging from 550 to 2,150 feet call for similar 

 explanations. The partly stratified material might rep- 

 resent a volcanic breccia/mud-flow, or landslide material 

 partly reassorted by the stream; or a true conglomerate 

 deposited from a rapid, yet overloaded stream. It is 

 difficult to account for the deposition of all the material 

 in normal stream erosion as there appears to have been 

 no agency which would cause a very rapidly flowing 

 stream to drop gravels which would build so thick a 

 deposit in a very steep- sided valley when the stream de- 

 bouched from the valley over a steep talus cone. The 

 gravels in the Launiopoko valley are found well toward 

 its head where the stream must have been actively cut- 

 ting. Also, there is no indication of a submergence of 

 the island below present sea-level. In view of the evi- 

 dence against normal stream-gravel origin, it is suggested 

 that volcanic explosions took place long after the main 

 volcano became extinct and that the conglomerate repre- 

 sents a breccia* thus blown out and in part reassorted 

 by the stream during the process of accumulation. The 

 amphitheatral head of the lao valley might be pointed to 

 as excavated in part at least by such explosions, both 

 because of its size, its geographically central position, 

 and because of the large deposits of breccia near the 

 narrow mouth. But normal stream erosion, given suffi- 

 cient time under the existing climatic conditions with 

 enormous precipitation on the high mountains and ex- 

 tremely little precipitation at sea-level, could excavate the 

 lao valley. The exact source of the explosions therefore 

 remains uncertain, but it was probably near the head of 

 the present lao valley. 



Haleakala, the volcano which built East Maui, is as yet 

 only slightly dissected. The younger flows of this vol- 

 cano and those of Mauna Kea, Hawaii, closely resemble 

 each other in appearance — dense, aphanitic, bluish rocks 

 — and in composition, olivine basalt to trachyandesite. 



Haleakala has always been classed as an extinct vol- 

 cano because no traditions concerning activity were re- 



