368 PACIFIC OCEAN. 
day, or a few weeks, and generally cease action soon after the erup- 
tion becomes quiet, though occasionally of prolonged activity. 
VI. That in consequence of the mode of formation pointed out, the 
volcanic mountain is quite uniformly stratified in its internal struc- 
ture; yet its layers are often of small lateral extent, patches innume- 
rable having been added here and there about the mountains at 
different times, till the whole was accumulated. 
VII. That the central portion of a cooled volcanic mountain is 
usually solid unstratified rock, while the circumferential portion is 
distinctly in successive layers. ‘There is evidence that the central 
conduit of fluid lava may not be in all instances a narrow channel of 
a few score of yards, but in former times at least was as large in 
diameter as the terminal vent, and of divergent size below in case 
the heat increased downward instead of decreasing; it may, there- 
fore, have had a breadth of several miles; the cooling of such a mass 
of lava would take place with extreme slowness, and the material 
would necessarily be unstratified.* 
VIII. That the lavas of different adjoining vents act in all ordinary 
eruptions independently, as exemplified in Mount Loa (p. 218): that 
we may with much probability view the volcanoes of the Hawaiian 
Islands as originally communicating by fissures through a common 
opening to internal fires within the globe; that the closing of the 
fissures, except at certain points, reduced each fissure to one or two 
channels, branching from a common trunk below, one corresponding 
to each separate mountain centre of the different islands. The open- 
ing of subordinate fissures around these vents, (we refer here to 
ordinary fissure eruptions,) which became filled again except at 
certain points, produced temporardly other minor ramifications to this 
system of fire-channels in this part of the earth. It may be that the 
channels in various instances became closed below by cooling, and 
even those of the principal craters might consequently descend only 
to isolated reservoirs of lava (p. 220). 
IX. That the ordinary eruptions and usual action of a volcano 
proceed principally from water gaining access to the branch or branch- 
lets belonging to a particular vent, and not to a common channel 
below: the fresh waters of the island are the principal source of 
* If these fluid lavas of the interior were to be drawn off by any wide submarine 
fissure, it might happen that the summit of a volcanic dome or cone should be made to 
fall in ruins and disappear within the emptied cavity. 
