122 TECHNOLOGY. 
to support the sides for a limited period; this method is not expensive, 
and is not resorted to in excavations of an enduring character. 
In permanent shafts timbering of a more substantial character must be 
made use of. The shafts intended to be stayed with timber are usually 
square or rectangular, as this form renders the timbering easier. Where 
the pressure of the earth is not excessive, the timbers are placed three or 
four feet asunder; where the earth is moist, it becomes necessary to place 
them closer. Pl. 25, figs. 23 @ and 24, show the arrangement of the wood- 
work in elevation, and jig. 236 the same in plan; fig. 25 a, vertical section 
of the timbered shaft. As seen in jig. 23, the shaft is divided into three 
divisions, one for tae service of each of the tubs, and another gor the 
ascent and descent of the miners. 
Pl. 24, fig. 7, shows the first steps to be taken in sinking a shaft. The 
lower and stronger beams of the frame for supporting the windlass are 
parallel with the short sides of the excavation. 6 or 8 feet below the sur- 
face the first rectangular frame of the timbering is placed, which serves as 
a guide for the balance of the shaft, the sides of which, as the work pro- 
gresses, are supported by similar frames at suitable distances from each 
other, and have joists driven down behind them, the spaces between which 
and the walls of the shaft are filled with blocks and wedges of wood, to give 
them a firm bearing, and the longer sides of the framework are strutted 
with stout cross-timbers, the ends of which are seen in pl. 25, jig. 26; these 
timbers are more clearly seen in fig. 236. Pl. 24, jigs. 8 and 9, represent 
different methods of shaft-timbering. 
In very wet mines it becomes necessary to dam out the water, which is 
done either with oaken frames, with cast-iron cylinders, or with masonry 
laid with hydraulic cement. /. 24, fig. 18, is a section of a shaft of a coal 
mine in Belgium thus walled up. 
_ It often occurs that shatts pass through strata of coarse sand filled with 
springs; in this case the excavation is opened much larger than it is ulti- 
mately to remain (pl. 24, jig. 21), and lined with a double timbering, the 
intermediate space being puddled with tenacious clay; this, however, can 
only be accomplished when on penetrating the sand a firm impermeable 
stratum is reached. 
As an example of damming out with cast-iron, we will give an instance 
which occurred in a coal mine near Newcastle, England. At a depth of 
42 feet from the surface, a spring was encountered which poured in 200 
gallons of water per minute; the workmen having succeeded in penetrating 
to a firm impermeable stratum below, a carefully prepared ring of oak was 
laid at the bottom, upon which segments of cast-iron were placed, the joints 
between the segments being chinked with strips of wood, and the space 
behind well puddled, by which the water was completely shut out, and a 
foundation was furnished for the masonry above, which was placed directly 
upon the iron segments. 
Further down a copious spring was encountered, which required a similar 
dam of nearly 40 feet in height, the segments being rather thicker than those 
above. 
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