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yielded in prosecuting the workings to gravitate to fixed 
points, it renders its extraction much less costly. 
FAULTS EN COAL-BEDS. 
It has already been stated, there can be no doubt 
the original position of our coal-beds was horizontal, 
and that extensive denudation has subsequently taken 
place. This is proved by circumstances connected with 
faults ; these faults or slips are very common, scarcely a 
square mile of any coal-field being free from them. They 
have completely severed the strata, and caused the same beds 
of coal to be placed at very different levels. The same bed 
of coal being found on opposite sides of some of these faults 
at from 500 to 3,000 feet separate. 
During the deposition of the whole of the Carboniferous 
rocks, it is believed that none of these faults were formed, 
as hitherto no single fault has been found in the coal- 
measures, which did not reach the upper portion of the coal- 
measures. Immediately after the deposition of the Car- 
boniferous system, the whole of its area seems to have been 
affected by some violent and almost universal agency, 
shivering and displacing the rocks 3 3 000 feet in thickness, 
dividing the coal-area into isolated tracts, situated at various 
relative levels and presenting every possible inclination, and 
locally augmenting the difficulty and expense of extracting 
the coal. Fortunately, this is to a great extent compensated 
for by certain advantages. 
The coal-measures consist of alternations of shale, coal, 
and sandstone, and are frequently in the deeper portions 
overlaid by limestone, the two latter very yullety and porous, 
and, consequently, they pass water very freely and to great 
distances. 
Had the entire extent of any given coal-field been simply 
inclined, without these fractures, slips, or faults, these porous 
