KILAUEA, HAWAITIL 201 
The escape of gases, and the vesicular inflation of the crust, may con- 
tinue in progress while the lava is flowing. But the process is so far 
impeded by the incipient cooling, that the surface cellules, instead 
of being enlarged and inflated are very much drawn out, becoming 
slender or capillary by the onward movement of the stream. 
The formation of pumice is of the same general character, as it is 
the frothy surface from lavas which have a feldspathic constitution. 
No true pumice occurs about Kilauea, since feldspar is not the predo- 
minant ingredient in the lava. The material most resembling it has 
still the composition nearly of the ordinary scoria. 
Ferruginous stalactites —These stalactites are tubular and vermi- 
form, and two to four inches long. They are black, with a slightly 
glistening lustre. Hardness 5 to 5-25. Specific gravity of the tubes, 
(which are cellular,) 1-656. ‘They were collected by the writer from 
the roof of a cavern in the bottom of the crater, where they occurred 
in great numbers. The examination of Prof. Silliman, Jr., shows 
that they are essentially an anhydrous silicate of the protoxyd of iron. 
They were formed, as the mode of occurrence as well as composition 
shows, by the action of steam upon the roof of the cavern, decompos- 
ing the rocks and dissolving some of the silica and iron, which were 
afterwards deposited on evaporation. 
Volcanic salts —The sulphur banks are situated away from the 
main theatre of action, where the vapours rise slowly, and there is 
not too much heat for the sulphur to be deposited and crystallized. 
In the bottom of the pit the sulphur gives a yellow colour to some 
cracks or seams, which is usually mingled with reddish tints from 
the developed iron. The various minerals found about the sulphur 
banks are a result of the decomposition of the lavas by the ascend- 
ing vapours. ‘The sulphar vapour or sulphurous acid, changing to 
sulphuric acid, forms sulphate of lime or gypsum with the lime of 
the lava, one of the constituents of angite. It also forms alum, or 
sulphate of alumina, with the alumina of the feldspar. It forms sul- 
phate of ammonia with ammonia, which is produced by the union 
of the nascent hydrogen (frorm water decomposed) and nitrogen; and 
sulphate of copper, the blue mineral, with oxyd of copper, or more 
probably by a change in some sulphuret of copper. At the same time 
that these changes are going on, iron is set free as an oxyd, and 
usually appears of a deep red colour. Silica is also liberated, and 
forms the siliceous incrustations met with about the banks. The 
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