204 HAWAIIAN ISLANDS. 
this it diminished to the surface, where it was 185° F. Other trials 
corresponded in their results, though varying in the bottom tempera- 
ture somewhat, according to the activity of the crater, the temperature 
of ebullition at that depth, about 280° F., being seldom attained. 
Now as the lavas consist of different kinds of mineral material, 
having different temperatures of fusion, these currents, with the 
variations in the temperature, must influence somewhat the distri- 
bution of the ingredients, or the constitution of the lavas in the dif- 
ferent parts of the crater. Whatever be the temperature at which 
any of the ingredients tend to solidify, at that temperature such 
ingredients will begin to thicken, and the more fusible portion, still 
fluid, will be carried up by the ascending vapours. In this way the 
superficial material of the great pools must necessarily be the most 
fusible part of the lava, or that which solidifies at the lowest tempe-- 
rature. ‘The analyses of the scoria of the crater show that this is pre- 
eminently true in fact as well as theory. 
Omitting for the present other considerations, we merely direct 
attention here to the fact that the lavas from fissures at the eruption 
of 1540, coming from a depth where the heat was great, abound in 
chrysolite in coarse grains, while in the crater, the lavas of the same 
period contain little chrysolite in small grains. We learn from 
this fact that the formation of chrysolite, a very refractory mineral, 
probably requires a higher temperature than exists at the surface in 
the crater. Consequently any chrysolite existing in the crater lavas 
was probably formed at some depth below, and ascended as grains in 
the liquid lava to the surface; and hence the rarity and minuteness 
of the particles of this mineral. 
We likewise learn from these facts that generally in lavas issuing 
from a crater, a portion of the ingredients has already become partly 
solidified, and the lhquidity is owing to a more fusible part, which 
remains still liquid at the surface temperature, and retains the whole 
in a mobile state. Lava, as is well known, cools with remarkable 
rapidity: we have mentioned its barely scorching the bark of a branch 
clasped by it while liquid. Such rapidity is a necessary consequence 
of the condition here described. As the temperature is nearly that 
which solidifies the more fusible part, and much of the lava has 
already lost its free liquidity, a small change will give solidity to the 
whole; and this change takes place with an abruptness that, in view 
of these explanations, cannot surprise. 
The temperature of the lavas of Kilauea we were unable to ascer- 
