ussian province of Saxony and the
north of England, would be exhausted in 100 to 200 years, the other
British coalfields, the Waldenburg-Schatzlar and that of the north of
France in 250 years, those of Saarbrucken, Belgium, Aachen and
Westphalia in 600 to 800 years, and those of Upper Silesia in more than
1000 years. (O. J. R. H.; H. M. R.)

_Coal-Mining._

Preliminary trial of coalworkings.

The opening and laying out, or, as it is generally called, "winning," of
new collieries is rarely undertaken without a preliminary examination of
the character of the strata by means of borings, either for the purpose
of determining the number and nature of the coal seams in new ground,
or the position of the particular seam or seams which it is proposed to
work in extensions of known coalfields.

[Illustration: FIG. 1.--Proving by Boreholes.]

The principle of proving a mineral field by boring is illustrated by
fig. 1, which represents a line direct from the dip to the rise of the
field, the inclination of the strata being one in eight. No. 1 bore is
commenced at the dip, and reaches a seam of coal A, at 40 fathoms; at
this depth it is considered proper to remove nearer to the outcrop so
that lower strata may be bored into at a less depth, and a second bore
is commenced. To find the position of No. 2, so as to form a continuous
section, it is necessary to reckon the inclination of the strata, which
is 1 in 8; and as bore No. 1 was 40 fathoms in depth, we multiply the
depth by the rate of inclination, 40 X 8 = 320 fathoms, which gives the
point at which the coal seam A should reach the surface. But there is
generally a certain depth of alluvial cover which requires to be
deducted, and which we call 3 fathoms, then (40 - 3 = 37) X 8 = 296
fathoms; or say 286 fathoms is the distance that the second bore should
be placed to the rise of the first, so as to have, for certain, the seam
of coal A in clear connexion with the seam of coal B. In bore No. 3,
where the seam B, according to the same system of arrangement, should
have been found at or near the surface, another seam C is proved at a
considerable depth, differing in character and thickness from either of
the preceding. This derangement being carefully noted, another bore to
the outcrop on the same principle is put down for the purpose of proving
the seam C; the nature of the strata at first is found to agree with the
latter part of that bored through in No. 3, but imm