^ 50 W. T. BRIGHAM ON THE VOLCANIC PHENOMENA 



Volcanoes. Volcanic Line. Major axis of the Crater. 



Teneriffe .... 

 f Chahorra 



t Teyde .... 



Cone of 1798 



Fuente agria 

 Pal ma .... 

 Lanzarote (Montana de Fuego) 



St. Vincent 

 t Montagne Pelee 

 t Guadaloupe (La Soufriere) 



Mauritius 

 t Isle of Bourbon 



South-east African line N. W. — S. E. 



N. E. — S. W. 

 N. E. — S. W. 



The superficial cracks are very much as represented on the Map of the Group (PI. XII). 

 The circles or ovals enclose the centre vents while the radiating lines indicate the supposed 

 fissures which have given rise to the minor lateral vents and tufa cones. It will be seen 

 that all the smaller cones are referred to some centre, and the interesting parallelism of the 

 connecting lines will be evident. I connect Kaula with the centre of Puuokapele, while 

 Lehiia is undoubtedly an offshoot of Niihau. On Oahu, Laeloa and the Waianae craters 

 belong to Kaala; Aliapaakai, Puawaina. Leahi, and Koko, to Konahuanui. On Maui, 

 Molokini is secondary to Haleakala, and the craters near Haliimaila and Maliko all fall on 

 two lines, one to the north-east and the other to the north. Hawaii presents a very regular 

 system of subordinate cones, all that have been observed ranging approximately on north 

 and south and north-east and south-west lines. The cones behind Hilo belong to Mauna 

 L5a, and the Kapoho series in Puna, to Kilauea. 



Theories of Volcanic Action. 



I cannot feel satisfied with the various theories which have been proposed to account for 

 volcanic and telluric phenomena. I am not ready to admit that either electric currents or 

 the waters of the ocean are the source of the heat which presents us with melted rock on 

 the surface of the globe. For in the first case we should have more electricity sensible at the 

 outlets of melted matter, while the lightnings which often accompany eruptions are no doubt 

 due to the expansion and condensation of vapor in the atmosphere ; the magnetic variations 

 are such as may easily be accounted for by the motion of imperfectly fluid basalt which 

 contains much iron ; and both are totally inadequate to the production of such vast results 

 as we witness constantly in various volcanic foci. On the theory that water gaining access 

 to the interior through fissures, causes the liquefaction of rocks through the oxidation of 

 metallic bases, little need be said, as the originator of this theory (Davy) himself abandoned 

 it as untenable. Water may, if it once obtains access to a mass of melted matter, cause 

 explosions and sudden eruptions ; but such action must be exceptional, for the instant water 

 approaches an intensely heated mass it assumes the spheroidal state, and no contact takes 

 place. If it be argued, however, that the water would be under great pressure, that under 



1 Von Buch, Isles Canaries. 



