Iron , 
n 
The Rottenburn iron-stone of Lancashire, consists of a 
band and an accompanying balh The former abounds 
with fine specimens of the ramification of trees, shrubs, 
&c. In the process of decay, and the substitution of mi- 
neral in place of vegetable substance, the more ligneous 
parts and the bark are distinctly preserved from the heart 
of the shoots 
This iron-stone contains 37ibe in 100 extremely sus- 
ceptible of receiving the carbonaceous principle. 
Another variety of iron-stone, which we have in this 
country, and which will be deemed no less curious by 
the mineralogist, affords maltha, bitumen, mineral pitch, 
&c* This combustible is found in the heart of large fiat 
rounded balls of iron-stone, occupying a number of inter- 
stices, and resembling a cement for the frittered pieces of 
stone. The distillation of 437 grains afforded me a rough 
light charcoal, which weighed only 49 grains ; this, when 
exposed to fire in contact with air, burnt without a resi- 
due ; hence I conclude it to be pure carborm This iron- 
stone in the assay-furnace yields 36 pounds of iron in 100* 
All these strata of iron-stone bear the most evident 
marks of the agency of water* 
Working of Iron-stone * 
When iron-stone is found near the surface, it is only 
necessary to unbare the soil and the super-incumbent 
earths : the stone then presents itself like a pavement more 
or less inclined, and is easily raised by the application of 
wedges, bars, &cc, &c* But as all secondary strata de- 
scend, according to the declivity imposed upon them by 
nature in their formation, it is obvious that, in proportion 
as the excavation extends at right angles to the line of 
level, the stone becomes gradually buried under an accu- 
mulating depth of earth, till such time as the expence of 
throwing this off exceeds either the value of the stone, or 
