Real and supposed effects of igneous action. 349 
form, to those that are blown up into innumerable cavities, 
scarcely connected by the thinnest partitions, like the mem- 
branes between the air cells and blood vessels of the lungs, 
and having vastly more pore and space than solid matter.— 
In many pieces, the cavities are so large, that the thumb is 
easily introduced, and we perfectly understand how to .con- 
ceive of those voleanic caverns described by Mr. Goodrich 
and the other Missionaries, and which are occasionally large 
enough to be used as ceméteries, or as refuges from hostile 
pursuit, or as habitations, Similar caverns in lava are nu- 
merous, as is well known, in the Azores, and in Iceland, and 
other distinguished voleanic regions. 
Among the cavities in the vesicular lava of Kirauea, there 
is the most beautiful exhibition of colors that can be imagin- 
ed. The surface is glossy, as if covered with the most per- 
fect enamel or varnish, and the iris and columbine hues are 
richly displayed by every change of position. This splendid 
effect is undoubtedly due, chiefly, to the large dose of iron, 
and the very perfect manner in which the intense heat has 
blended its oxides with the other materials, 
9. Fine spun volcanic glass.—This exists sometimes in 
masses which are scarcely coherent, and seem like what they 
evidently were originally, congealed froth and foam, the float- 
ing scum of igneous fluidity. Their color is like that of 
olivin. <9 
cases, concerned. it 1s this filar giasst c 
Mr. Goodrich in his letter, (Vol. XI. pa. 2.) as being 
blown away by the winds and carried to the distance of 
many miles from the volcanos. 
