440 W. T. BRIGHAM ON THE VOLCANIC PHENOMENA 



mountain may be best examined, as the denudation has exposed it in all the deep valleys so 

 common on these high islands. 



In these valleys I have been able to examine the solid nucleus of Mauna Kea on Hawaii, 

 Eeka and Haleakala on Maui, Olokui on Molokai, Konahuanui on 06hu, and Waialeale on 

 Kauai, and I find the general appearance of all these cones to be the same, compact and 

 unstratified ; but the kind of rock at the summit varies slightly. On Waialeale it contains 

 less feldspar, and is more uniform, as if no opportunity had been allowed for it to settle : 

 Konahuanui has more feldspar, and portions of its rock much resemble syenite : Olokui and 

 Eeka almost the same ; while Haleakala and Kea are quite feldspathic, and the former has 

 streams on its flanks of highly feldspathic lava. Olokui contains much iron on its summit 

 overflows (not in its core), as does also Konahuanui, while on Waialeale there are said to 

 be large deposits of ferruginous lava. The base of the cones in all cases is basaltic, so far as 

 exposed. It may be added that the summits of Maunas Loa, Hualalai, and Haleakala are all 

 largely composed of trachyte or a phonolite closely approaching it. 



In Waialeale, Eeka, Konahuanui and Olokui then, the composition of the cone is tolerably 

 uniform, while on the other mountains various gradations between trachyte and basalt may 

 be traced. The mass of these mountains is not sufficiently different from each other to lead 

 us to suppose that a different period of cooling after the action ceased has caused the 

 different distribution of elements which seem to be the same in all ; and we cannot believe 

 that the different lavas have been produced at different times, for it is impossible to draw 

 any line of demarcation, so closely do the intermediate greystones connect the trachytes 

 with the basalts. I infer from this that the mountains which produce the most uniform dis- 

 charges, are the- most active ones, and that when a volcano enjoys a long period of rest, its 

 lavas will present greater variety. Kilauea and Mauna Loa are at present in a constant 

 state of activity, and their lavas have comparatively no rest, and the eruptions are nearly 

 uniform. Vesuvius is exceedingly irregular, sometimes bursting forth after a repose of nearly 

 two centuries, and its lavas are more composite than those of any other known volcano. 



Angle at which Lava flows. 



M. Dufresnoy declares that lavas, to be compact and crystalline, must have cooled on a 

 slope of less than 3 . 1 This statement has been proved incorrect by Sir Charles Lyell in 

 his valuable " Memoir on the Lavas of Etna," 2 and on the Hawaiian Islands slopes of every 

 degree of inclination occur. I have measured streams that have consolidated on angles of 

 from 10° - 90°, and in all cases they were continuous. Rev. Mr. Coan has done even more, 

 and I quote his own words : " On the mountain and in Kilauea I took the angles of several 

 lava-streams, one of 49°, another of 60°, and two of 80° each, several streams on the moun- 

 tain flowed down banks of scoria3 twenty-five and thirty feet high. The fusion was complete 

 — the streams cooled in a perfect state. 



" I saw thin strata, say one inch thick or less, which had flowed down the face of perpen- 

 dicular rocks, adhering to the rocks like paste, and thus cooling. Will you say that I spoil 

 my demonstration hj proving too much, when I assert that I saw more than one place where 

 the lava flowed at an angle of 95° — like the Indian's tree which grew so bolt ujiright 



1 " Les coulees, qui se presentent sous un angle de 4° ne 2 Philosophical Transactions of (he Royal Society, part ii. 

 sont plus que des agglomerations de fragments incoherents." vol. cxlviii. for 1858. 

 Terrains volcaniques des environs de Naples, iv. 342. 



