X. Notes on the Volcanic Phenomena of the Hawaiian Islands, with a description of the modern 



Eruptions. By William T. Brigham, A. M. 



Read June 20th, 1866. 



A.S the study of the volcanic phenomena of the Hawaiian Islands requires a survey of 

 the whole group, a physiographic sketch of all the Islands, even of those on which volcanoes 

 have been long extinct, forms a part of the plan of this essay. 



The Hawaiians reckon twelve islands : four large and four small ones inhabited, and four 

 which are little more than barren rocks. They are named as follows : — 



elevation of highest point 1800 feet. 



<< « « « gooo " 



» « " " 4000 " 



" " " " 3000 " 



" » " " 2000 " 



" " « « 10,200 " 



« « " " 600 " 



u u. « .. 200 " 



" " " « 13,950 " 



The smallest, Kahoolawe, has an area of about fifty square miles, and the largest, Hawaii, 

 of about three thousand eight hundred. The group extends in a north-north-west direction 

 from this last island, and has nearly the average trend of the Pacific groups. 2 The Islands are 

 all high, increasing in height and size, towards the south-east, where they culminate in the 

 lofty domes of Hawaii. The rock of the whole group is volcanic, with the exception of the 

 ancient elevated coral-reef and the resulting sandstone. No true fossiliferous rocks are 

 found ; although the tufa cones often contain fossilized shells, and corals of recent species. 

 It has been the general impression that the lavas were wholly basaltic, but on the tops and 

 in the interior of the mountains a variety of trachyte is found, and the bulk of the moun- 

 tains seems to be composed of phonolites and graystones, forming a complete series from 

 basalt to trachyte. These lavas contain few mineral species, but assume forms of great 

 variety, and while tolerably uniform in composition, present structural differences in great 

 number. 



Occupying a central position in the Pacific these Islands have been visited, since their 

 discovery by the Spaniards, by many government exploring expeditions, whose published 

 accounts have intimated the interesting nature of the volcanic developments constantly 

 taking place ; but, except by the United States Exploring Expedition, no attempt has been 

 made to examine carefully the geology. The Rev. Titus Coan, who has been for thirty 

 years a missionary at Hilo on Hawaii, has constantly observed every outburst of the 

 volcanic fires during this period, and to his accounts we are principally indebted for what 

 is known of their history on these Islands. Professor James D. Dana, also in his " Geology 



1 For the pronunciation and signification of the native names 

 see Appendix. 



2 The principal groups in the Eastern Pacific have the fol- 

 lowing trends : — 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. Pt. 3. 87 



Hawaiian Range, 

 Marquesas Islands, 

 Hervey Group, 

 Samoan Islands, . 



N. 64° W. 



N. 60° W. 



N. 65° W. 



N. 64° W. 



