MINING. 125 
Pi. 24, fig. 48, exhibits a general view of the subterranean operations as 
conducted in steps, which is called stoping; by this process the sole of an 
existing level is cut down by steps, or the work may be commenced directly 
from the foot of a shaft; after the work has proceeded for some time, the 
excavation presents the appearance of a series of steps, as seen in fig. 43. 
The height of a step is generally to its length as one to three or four; a 
similar method is adopted in the gold mines of Morro Velho in Brazil 
(pl. 25, jig. 4). The thin coal-seams near Mons are worked in a similar 
manner, a main shaft for the working of the vein and another for the pump 
being first sunk (pl. 26, jig. 3); these shafts are then united by a cross- 
gallery and two principal levels are then driven, the one upon a level with 
the bottom of the pump shaft, and which serves to carry the water to the 
sink, called the swmp, c, the other serving as a working level for the seams 
above. In pl. 24, jig. 32, the levels are run parallel with the vein. Upon 
the left is seen the water shaft, and above it the working shaft, from which 
leads out the working gallery; 6 is the ground level, which leads the water 
to the sump. 
Pl. 26, figs. 4 and 5, shows a’ mode of operation practised in lieu of stop- 
ing, in horizontal or slightly inclined veins. vp is the working shaft, and p’ 
serves for the pumps and also for ventilation; aB is the principal working 
level, either horizontal or slightly inclined towards a. 
A variety of methods are adopted in the working of those mines which 
do not furnish the material with which to support the roofs of the excava- 
tions. Pillars are left which are just sufficient to support the strata above, 
or massive columns are left, a large portion of which is removed when the 
regular working is finished. In other cases levels are driven forward and 
the pillars are cut away by working backwards, allowing the whole super- 
incumbent strata to fall down and follow the miners in their retreat. In 
highly inclined veins covered levels or galleries are oftentimes necessary 
for ventilation (pl. 26, jig. 26 6), in which a is the gallery, m a pillar, and 
the passage for the draught. 
Pl. 25, jig. 5, represents two coal seams, one immediately above the 
other. In such cases the upper seam is first worked and the pillars removed, 
and two years afterwards the lower seam is worked by long pillars and 
galleries running in the direction of the dip; the pillars are then removed, 
and the whole is allowed to fall in after the miners. 
Pi. 24, fig. 31, is the plan of a Sunderland mine in an immense field of 
a million square fathoms. The whole is set upon pillars, and the work is 
driven as far as ventilation and the power of removing the coal to the main 
shaft will permit. a are the large safety pillars ; B is the ventilating shaft ; 
c, a shaft or inclined level. 
Pl. 25, jig. 3, shows the method adopted in the silver mines in the 
vicinity of Freiberg, and in the iron mines of Missen in Rhenish Prussia. 
ICONOGRAPHIC ENCYCLOPXDIA.—VOL, IV. 45 705 
