﻿630 DR. TEMPEST ANDERSON ON THE [jSToV. ICJIOy 



Dana * to be even less, sometimes not even more than 1°, an obser- 

 vation which I can personally confirm, in the case of the lavas of 

 Kilauea, It is to be remarked that at Matavann the lava-stream 

 is highest in the centre over the line of the tunnel, and tends to- 

 become more so owing to frequent small flows of lava which, 

 whenever the flow beneath is obstructed from any cause, rise to 

 the surface and then spread out and solidify there. This class of 

 flow is more common as the sea is approached, so that the surface 

 nearer the sea is often higher than that inland, and the direction of 

 the flows in the lower part is thus often away from the sea, and in 

 the reverse direction to that of the flow underneath by which they 

 are supplied. That the surface of the lava over the tunnels is 

 higher than elsewhere is a matter of observation, and that the 

 difference tends to increase is vouched for by careful observers like 

 Mr. Williams and Capt. Allen. They think that this increase of 

 height is also largely due to lava intruding from the tunnel into 

 the surrounding lava and forming sills and dykes ; and, although 

 this is mainly a matter of inference, I see no reason to question 

 its accuracy. On my first attempt to cross the lava and visit the 

 outflow into the sea, our way was stopped by a fairly large flow of 

 lava only a day or two old. It had originated in an opening of 

 the lava-crust near the sea, and spread out inland as mentioned 

 above. My men tried to cross it, and pronounced it impracticable ; a 

 dog tried it, and retreated howling. I found a hummock of cool lava 

 near it, on which I established myself and took photographs of the 

 steam-explosions and the intervening lava (PI. L, fig. 2). This led 

 me to notice particularly a crack in the hummock where the surface 

 had risen apparently by the lateral compression of the surface-crust. 

 When I made another attempt two days later, I succeeded in getting 

 to the same spot, but a new lava-flow had covered a great part 

 of the previous one and advanced even nearer the hummock. 

 I noticed that the surface on which the new flow rested was pressed 

 down and lowered for a distance of some feet in front of its edge ; 

 while the hummock itself was pressed up, and the crack materially 

 widened. This shows that the lava below the surface was still 

 plastic and capable of being squeezed into new positions, and the 

 acuteness of the deformation or bending of the crust showed its 

 small thickness. It is clear that a considerable amount of intru- 

 sive action might take place in such a mass, without leaving much 

 subsequently recognizable alteration. On the lower part of the 

 lava-fields there are also several considerable mounds (or perhaps 

 they might even be called plateaux) formed of large angular blocks 

 of broken compact lava. The mounds were flat-topped, and the 

 blocks presented no trace of igneous action since they had been 

 broken. I could not at the time think of any satisfactory ex- 

 planation of their formation, but now believe that they have been 

 probably formed by intrusion of lava under the previously con- 

 solidated crust, which was broken into pieces as it was pushed up 

 (PI. XLVIII, fig. 2). 



1 J. D. Dana, ' Characteristics of Volcanoes ' 1890, p. 148. 





