270 S: Powers — Notes on Hawaiian Petrology. 



No trachyte was noted in the field in the Kohala Moun- 

 tains. The flows forming the sides of Waipio and Pololu 

 gulches are in part composed of basalt, bluish grey in 

 color with abundant feldspars and very little olivine seen 

 in the hand-specimen. Similar feldspar basalts are 

 characteristic of Wailau volcano, East Molokai. 



On Maui the trachyte occurs as flows, cones, and, in 

 one instance, probably as a volcanic neck. In every case 

 observed the trachyte is younger than the main moun- 

 tain mass and probably appeared when the dissection of 

 the latter was well under way. The major portion of 

 the erosian of the volcano followed the trachyte erup- 

 tions. West of Puu Launiopoko an olivine basalt flow 

 may be younger than the trachyte, but the two rocks were 

 not observed in contact. 



Puu Paupau, above Lahaina, is a double conical hill, 

 surmounting a spur between two gulches and composed 

 of light-grey, schistose trachyte. The next exposure of 

 trachyte to the southeast is Puu Launiopoko (there is an 

 excellent exposure on the Lahaina- Wailuku highway). 

 Above Puu Launiopoko on a facet at an elevation of 1,400 

 feet there is a flow of trachyte, evidently derived from 

 a fissure eruption. Puu Kilea, back of Olowalu, and two 

 nameless cones between Puu Kilea and Puu Launiopoko 

 are composed of similar rock. A light-colored rock, ap- 

 parently trachyte, is seen on the triangular erosional 

 facets between Launiopoko and Ukumehame gulches and 

 trachyte flows occur on the gently sloping plain west of 

 the mouth of Olowalu Gulch. On the west side of 

 Ukumehame Gulch, at the entrance, there is an inacces- 

 sible mass of white rock, apparently a volcanic neck of 

 trachyte. 20 This rock may be seen from the Interisland 

 steamers passing Maui. 



Trachyte flows cover an area about 3y 2 miles in width 

 and extend to an elevation of over 1,000 feet between 

 Waihe'e and Hakahue gulches northwest of Wailuku. 

 The trachyte has a maximum thickness of over 30 feet on 

 the sides of Waiolai and other gulches. Besides the 

 thin flows which cover the region the rock comprises 

 cones, such as Puu Olai. Trachyte flows of an aggre- 

 gate thickness of over 30 feet cover the facets between 

 Honokahau and Honokahua gulches on the north side of 

 West Maui, a distance of 2~/ 2 miles as traversed by the 

 trail around the island. 



20 S. Powers, Intrusive bodies at Kilauea, Zeitschr. Vulk., 3, p. 32, 1916. 



