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they are filled; but ufually called dikes, hitches, and 
troubles. 
Dikes are the'larged: fiffures. They feem to be nothing 
but a crack or breach of the folid ftrata, occafioned by 
one part of them being broken away and fallen from the 
other. They generally run in a llraight line for a con- 
fiderable length, and penetrate from the furface to the 
greateft depth ever yet tried, in a direftion fometimes 
perpendicular to the horizon, and fometimes obliquely: 
the fame kind of Itrata are found lying upon each other 
in the fame order," but the whole of them greatly elevated 
or deprefi'ed on the one fide of the dike as on the other. 
Thefe fiffures are fometimes two or three feet wide, and 
fometimes many fathoms. If the fififure be of any con¬ 
fiderable width, it is generally filled with heterogeneous 
matter, different from that of the folid ftrata on each fide 
of it. It is fometimes found filled with clay, gravel, or 
fand ; fometimes with a confuted mafs of different kinds 
of Itone lying edgeways :; and at other times with a folid 
body of free-done, or even whin-ftone. When the fififure 
is of no greater width than two or three feet only, it 
is then ufually found filled, with a confufed mixture 
of the different matters which cornpofe the adjoining 
■ftrata, confolidated into one mafs. If the dike ftretches 
north and fouth, and the fame kind of ftrata are found 
•on the eaft fide of the dike, in a fitfuation with refpefit to 
the horizon ten or twenty fathoms lower than on the 
.other fide, it is then faid to be a dip-dike, or donsjncnj}- 
-dike, to the eaftward; or, counting from the eaft fide, it 
is then faid to be a rife-dike, or upcaft, of fo many fathoms 
-weftward, if the ftrata on one fide are not much higher 
•or lower with refpect to the horizontal line, than thole on 
the other, but only broken off and removed to a certain 
•diftance, it is then /aid to be a dike of fo many fathoms 
.thick; and from the matter contained betwen the two 
fides of thefiflure, or dike, it is denominated a clay-dike, 
Jlone-dike,.&:c. 
A hitch is. a fiffure of a fmaller degree, by which the 
ftrata on one fide are not elevated or feparated from thole 
on the other fide above one fathom. Thefe hitches are 
•denominated in the fame manner as dikes, according to 
the number of feet they elevate or deprefs the ftrata. 
Some of thefe are met with whofe cavities are filled with 
■fiparr, the ores of iron, lead, vitriol, or other metallic 01- 
mineral matters; all of which, in the coal-countries, are 
called dikes. The ftrata are generally found lying upon 
each other in the fame order on one fide of the hitch as 
on the other, as mentioned above, and nearly of the fame 
thicknefies, appearing to have been originally a continu¬ 
ation of the lame regular ftrata, and the hitch only a 
breach by fome later accident, perpendicularly or obli¬ 
quely down through them, by which one part is removed 
to a fmall diftance, and deprefi'ed to a lower fituation than 
the other. But this is not the only alteration made in the 
ftrata by dikes and hitches; for generally to a confider¬ 
able diftance on each lide of the dike, all the ftrata are in 
a kind of (battered condition, very tender, eafily pervious 
to water, and debafed greatly in their quality, and their 
inclination to the horizon often altered. 
Troubles may be denominated dikes of the fmalleft de¬ 
gree ; for they are not a real breach, but only an approach 
towards it, which has not taken a full effeft. The ftrata 
are generally altered by a trouble from their regular (ite 
-to a different pofition. When the regular courfe of the 
•ftrata is nearly level, a trouble will caufe a fudden and 
confiderable afcent or defcent; where they have, in their 
regular fituation, a certain degree of alcent or defcent, a 
trouble either increafeth it, or alters it to a.contrary po¬ 
fition : and a trouble has thefe effects upon the ftrata in 
common with dikes, that it greatly debates them front 
their original quality; the partings are feparated; the 
backs and cutters disjoined, and their regularity difor- 
dered 5 the original cubic and prifmatic figures, of which 
the Itrata were compofed, are broken, and the diflocation 
A L. 
filled with heterogeneous matter; and the whole ftrata are 
reduced to a fofter. and more friable ftatei 
In working coal-mines, .that kind of combuftible va¬ 
pour, or inflammable air, which will catch fire at a can¬ 
dle, is too often met with. It proceeds from the dikes 
or fiffures of the fioiid ftrata, exhaling from feme in an in- 
fenfibie manner, whillt from others it blows with as great 
impetuofity as a.pair of bellows; When tiiis mephitic air 
is permitted to accumulate, it becomes' dangerous by 
taking firepand burning or deftroying. the workmen, and 
fometimes by its explosion will blow the works out of the 
pit, and do confiderable damage. If a fupply of frefh air 
is forced down the pit by air-boxes and a ventilator, or 
by dividing the pit into two by a dole partition of deals 
from top to bottom, it will be driven out, or fo weakened, 
that it will be. of no dangerous confequence; or, when 
the mephitic air is very Itroag, it may be fafely carried 
off’by making .a clofe Iheathing or lining of thin deals 
quite round the circumference of the pit, or by one or 
two fmall leaden .pipes carried frpm the Iheathing to the 
iurface. If a candle be applied to the orifice of the pipe 
at the furface, the mephitic air will inftantly-take fire, 
and continue burning with a lambent flame until it be 
extinguifhed by fome. external caufe. 
After the pit is funk to the coal, the next confideration 
is the mode of working it. The moll: general pradice is 
to excavate and take away a part only of the ftratum of 
coal in the ftift working, leaving the other part as pillars 
for iupporting the roof; and, after the coal is wrought 
in this manner to fuch a. diftance from the pit as intend¬ 
ed, then tbele pillars, or io many of them as may be 
deemed fafe, are taken out by a fecond working, and the 
roof and other folid ftrata above permitted to fall down 
andftll up the excavation. The quantity of Coal wrought 
away, and the fize of the pillars left in the firft working, 
is proportioned to the hardnefs and ftrength of the coal 
and other ftrata adjacent, compared with the incumbent 
weight of the fuperior ftrata. If there be two or three 
ftrata or feams of coal in the fame pit, having only a Itra- 
tum of a few feet thick betwixt them, it is then materia] 
to oblerve, that every pillar in the fecond learn be placed 
immediately below one in the firft, and every pillar in the 
third feam below one in the fecond ; and in luch a fitua¬ 
tion the upper ltratum of coal ought to be firft wrought, 
or elie all the three together; for it would be unfafe to 
work the lower one firft, "left the roof (hould break, and 
bury the works and the men in one promifeuous ruin. 
When the coals are wrought, they are put in balkets, 
booked to a.chain, and drawn up the pit by a rope to the 
the furface, which is belt effefted by a machine called a gin, 
worked at prefent by liorfes. There are other machines tor 
drawing coals, fome wrought by water, others by the vi¬ 
brating lever of a fire-engine; but thofe wrought by horfes 
are in rnoft general ufe. A very ingenious and much im¬ 
proved method of raifing coals, has-however been lately in¬ 
vented by Mr. Humphrey Jeffreys, engineer,at Newcaltk- 
upon-Tyne. His method has thelandlion of the king’s let¬ 
ters patent, dated Feb. 12,1799; the delcription of which , 
elucidated by an engraving, we Ihall give in his own words, 
viz. “ I the faid Humphrey Jeffreys do hereby declare, 
that my faid invention is fet forth in the following de¬ 
lcription ; that is to lay : My addition to, and improve¬ 
ment of, machinery applicable to the bringing or con¬ 
veying coals, ores, or other minerals, from the interior or 
innerinoft parts of coal-mines, commonly called putting, 
is (hewn in the annexed plate; where fig. 1. is a ground- 
plan of this method of putting, reprefented as placed in 
the interior part of a coal-mine, where (and alio in all 
the other figures the fame letters correfpond to the fame 
parts) X X is the pit or Ihaft. B, B, are full and empty 
corves or balkets, for conveying the coal. C C, is an 
endlels chain, or rope, palling round, and fupported by, 
the wheels D. E, are crols bar*, fupporting the endlefs 
chain C C, at certain diftances, between the wheels D,D, 
1 and 
