398 w - T. BRIGHAM ON THE VOLCANIC PHENOMENA 



greatest activity. These cones appear as if split through their larger diameter, the inner 

 sides being perpendicular or overhanging, jagged and hung with stalactites, draped with 

 filamentous vitrifications, and encrusted with sulphur, sulphate of lime, and other salts. 



" The outside of these cones are inclined planes, on an angle of forty to sixty degrees, 

 and composed of pumice, cinder, volcanic sand, tufa, etc. You will not, however, under- 

 stand that these semi-cones were once entire, and that they have been rent. They are 

 simply masses of ridges of cinder and dross deposited on each side of the fractures where 

 the action is greatest. It is all a new deposit. After you leave the region of open fissures, near 

 the summit of the mountain all below appears to be a flow on the surface. 



" 1st. We can see no chasms or fractures except those always found in the surface flows. 

 There is no visible evidence that the old substrata had been fractured, except on the higher 

 regions of the mountain. 1 



" 2d. Where there is a throat extending down to the fiery abyss below, there will, we 

 think, always be a column of smoke and gaseous vapor ascending to mark the spot, so long 

 as action continues. This is true of Kilauea, and it is also true of all the eruptions I have 

 noticed. Now if you were at Hilo, you would see a continuous volume of smoke ascending 

 from the terminal point, and another from the terminus of the stream — separated in a 

 direct line forty miles, and by route of the flow seventy miles — while between these 

 extreme points you see no smoke and have no evidence of fire beneath, 2 except the radia- 

 tion of heat as you pass up. The smoke at the fountain is mineral, that at the end of the 

 stream is from vegetation, and only here the fusion now makes its appearance, having come, 

 as I believe, all the way from the mountain under cover, without showing itself at a single 

 point. I do not mean that it has tunnelled the mountain, or melted a lateral duct through 

 its mural sides. The process is this : lavas flowing on the surface and exposed to the 

 atmosphere, unless moving with great velocity, as down steep hills, soon refrigerate on the 

 surface. This hardened surface thickens, until it extends downward from one to two 

 hundred feet, as the case may be. Under this superstratum the lava remains liquid ; 

 consequently at the termini and sometimes along the margins of the hardened streams, you 

 see the fusion gushing out in red lines and points, and in irregular masses. When lavas 

 refrigerate through the whole stratum, and thus rest upon an ancient or previous formation, 

 they form dams which divert the stream of lava from above, unless this obstruction is 

 broken up, tilted, or overflowed by fresh lava. Down the steep sides of the mountain such 

 obstructions occur more rarely ; consequently the lava ceases to reach the surface either at 

 the fountain or down the sides of the mountain, but is confined to channels, mostly covered 

 with fresh, solidified lavas, where it finds a free and rapid passage to the plains below. 

 Here the movement is slow, the obstructions more numerous, and the force to overcome 

 them less patent. This accounts for the spreading laterally, the upliftings, and the ten 

 thousand irregularities which diversify the ever-changing surface of lava-streams. I have 

 seen a dome, some three hundred feet in diameter at base, raised one hundred feet high, 

 and split from the summit in numerous radii, through which the red and viscid fusion 

 was seen ; and I have mounted to the top of such a dome in this state, thrust my pole 



1 A careful examination of the line of eruption resulted in a This has been the case for some eight months. At first 



the conviction that the fissure was originally very small, not the whole ridge of the mountain was lighted with fusion on 



exceeding three or four feet, and did not extend below the the surface ; afterwards no fire was seen except at the end of 



point where the lava first reached the surface. the stream near Hilo. — Note by Mr. Coan. 



