Iron . 
/ 
211 
or eight Inches : these are generally hollow in the centre, 
and are easily demolished, owing to their excessive brittle- 
j ness. The colour of this lava is very various ; for the 
most part it is pale yellow mixed with green. Its tenaci- 
ty is so great, that if, while fluid, a small iron hook is in- 
serted into it at a certain degree of heat, and then drawn 
from it with a quick but steady motion, 20 to 50 yards of 
fine glass thread may be formed with ease. If the colours 
are vivid and variegated, the thread will possess, upon a 
minute scale, all the various tints of colouring which is 
found in the columnar mass. When by accident a quan- 
tity of this lava runs back upon the discharging-pipe, it 
is upon the return of the blast impelled with such velocity 
as to be blown into minute delicate fibres, smaller than 
the most ductile wire ; at first they float upon the air like 
wool, and when at rest very much resemble that sub- 
stance. 
The presence of oxygenated crude iron (No. 4,) on the 
furnace-liearth, is indicated by the lava resolving itself 
into long streams, sometimes branched, sometimes co- 
lumnar, extending from the notch to the lowest part of the 
declivity ; here it commonly forms large, flat, hollow 
cakes, or inclines to form conical figures : these are, how- 
ever, seldom perfect ; for the quantity of fluid lava, con- 
veyed through the centre of the column, accumulates fast- 
er than the external sides of the cone are consolidated ; 
and thus, when the structure is only half finished, the 
small crater vomits forth its superabundant lava, and is 
demolished. The current of such lava falls heavily from 
the dam as if surcharged with metal, and emits dark red 
sparks resembling the agitation of straw embers. Its 
colour is still more varied than the former descriptions of 
scoriae, and is found changing its hues through a great 
variety of greens shaded with browns. Another variety 
of scoria, which indicates the same quality of iron, as- 
