86 J. D. Dana — Geological History of Maui. 



and had poured out from time to time small streams like 

 those of a full lava-lake in Kilauea. But they more probably 

 came from fissures cut through to the summit at the time of 

 the last or some one of the later eruptions. 



The fact that lavas of the summit are so very chrysolitic, 

 even at a height of nearly 10,000 feet, has an important bearing 

 on the question as to the effect of high specific gravity in 

 determining the distribution of materials in liquid lavas. 



Crystals of augite and large grains of chrysolite are common 

 in the loose material at the base of the cinder cones at the sum- 

 mit, near the place of descent, and colored glassy crystals of 

 labradorite occur with them — facts first learned from Rev. T. L. 

 Gulick after our return. These summit cones have the recent 

 appearance and other features of those over the crater's bottom, 

 and appear to be of the same series and time of origin ; and the 

 cinder-slope of that side of the crater was probably made in 

 part from the ejections of these summit cones. 



5. The probable nature of the last eruption. — The great dis- 

 charge-ways of Haleakala, one to one and a half miles wide, 

 with the walled valleys confining them, look as if the results 

 of enormous rents of the mountain, made when the moun- 

 tain emptied itself by the wide channels. But they may have 

 been in existence before, and have been simply used for the last 

 of the outflows. They are, nevertheless, evidence of rents at 

 some time, and of a vast amount of removal of material some 

 way — by subsidence, or otherwise. The height of the walls 

 at the gaps, 2000 feet and over at the Koolau gap, and ] 000 

 and over at the Kaupo, are a minimum measure of the amount 

 of material removed. In my Exploring Expedition report I 

 suggest that the mountain was fissured across along the lines 

 of the two discharge-ways, and the eastern block shoved 

 off a mile or two. But a subsidence of the masses that occu- 

 pied them into caverns below, leaving the walls as fault 

 planes, may be more probable. The abyss which received 

 them in this case had been prepared during a long period of 

 undermining through ejections. Still there is some reason to 

 believe in the grander view of a subsidence of the whole east- 

 ern block, after the cross- fracturing. The island, as is seen on 

 the map, is abruptly narrowed (instead of widened) at the 

 spots where the Koolau and Kaupo streams reach the sea ; and 

 the part to the eastward is small, as if narrowed by such a 

 subsidence. Moreover, the mean height of the eastern crater- 

 wall is lower than that of the opposite or western by 500 to 

 1000 feet. A subsidence of 1000 feet increasing in amount to 

 the eastward would account for the narrowing and for the very 

 short eastern radius of the eccentric volcano. The question 

 merits consideration. 



