Iron * 
29 
with him a similar portion of iron-stone from each side of 
the gallery. The quantity of iron-stone by weight obtain- 
ed from such a working , depends entirely upon its extent 
and the thickness of the band. A square yard of iron- 
stone containing 9 cubical feet, as it lays stratified, will 
weigh from 1850 to 1900 pounds weight. The other 
side of the pit is next perforated, and the same operation 
completed. When the iron-stone is thus exhausted, ano- 
ther pit, sunk at a similar distance from the termination 
of the second gallery in the first, opens up a new field of 
supply. In this manner iron-stone is continued to be 
raised, till such time as the field is totally exhausted. 
These extensive excavations commonly collect a con- 
siderable quantity of water, which would soon impede the 
progress of the workmen : various means have been con- 
trived to remove this consequent obstruction. These have 
chiefly consisted in running a counter gallery as far to the 
declivity of the metals as possible, and of passing the wa- 
ter into it by means of filtration, or communications be- 
twixt gallery and gallery. Where a sufficient quantity 
of running water presents itself, water-wheels have been 
applied, to extract the water from one general reservoir 
by means of pumps. 
Strata of iron-stone are from 1-2 an inch to 12 inches in 
thickness. Those of 3, 4, 5 and 6 inches are most com- 
monly met with ; they are also reckoned to contain a 
quantity and quality of iron superior to larger bands. 
Ball and lunker iron-stone, however large, contain always 
a superior quantity of iron, and are easier reduced in the 
blast-furnace, f Mushet.J 
On Iron Ores particularly , 
1st. As to the state of the iron as it is contained in the 
Ore. 
2dly* As to the quantity of the iron contained in the ore. ' 
