704 C O r 
tracts of the furface, fuch as are common in all unculti¬ 
vated countries. And this probability will be reduced to 
more certainty, when we advert to the natural biftory of 
pit-coal, which is met with in all the various dates of 
transformation. Whple trees are converted into pit-coal, 
in fuch quantities together as to exhibit entire forefts ; 
in which- tjhe roots, trunks, branches, bark, and even 
fpecies, are difcemible. Both coal-pits and (late quar¬ 
ries exhibit innumerable marks of impreffions of leaves, 
and other indications of their vegetable origin; and the 
annlyfis of this combultible fubftance tends dill further 
to confirm this truth. On the other hand, if we attend 
to fuch inferences as chemical theory might point out 
from the fa£ts around us, we (ball fee how linall the pro¬ 
bability i% that the mineral kingdom (hould, after a cer¬ 
tain limited time, contain inflammable bodies, if they 
were not occafionally thrown into it, in confequence of 
the operations carried on within organized fubftances. 
For all inflammable lubftances, tending to decompofe the 
oxygen or vital air of the atmofphere, would, in procefs 
of time, revert to the clafs of uninflammable bodies, if 
the operation of organized fubftances, particularly of the 
vegetable kind, did not tend to difengage the vital air 
again, and render bodies combuflible, which were not fo 
when they became parts of thofe fubftances. For the 
chemical analyiis of coal, or carbon, fee the article Che¬ 
mistry, d. 199 , of this volume. 
In proof of the fafts ftated above, we might here ad¬ 
duce th? ingenious obfervations lately made by Mr. Kir- 
wan, in appreciating the immenfe advantages that would 
accrue to Ireland, by eftablifhing a fufficient fupply of 
pit-coal from their own mines. To render the difcovery 
of thofe more intelligible, he gives a general view of the 
internal conftrudtion of hills and plains, which he divides 
into three claffes. 1. Some are formed of rude fhapelefs 
maffes, without any regular fiffures, but which, on atten¬ 
tive infpeStion, are found to conlift of fmall grains of dif¬ 
ferent forts of ftone concreted together, and hence called 
granites : the exafit adaption of thefe grains to each other, 
and the regular cryftallized fliape of l'ome of them, (hew 
that they muft have been once in a foft, or even fluid, 
ftate; their continuity, or want of regular fiffures, indi¬ 
cate their fimultaneous concretion; the fuperior difficulty 
of their folution at prefent, and the immenfe fpace they 
occupy in the globe, of which they conftitute, as it were, 
the kernel, and the total abfence of all organic remains, 
induce us to think that of all others they are the moft 
ancient. 2. Other hills confift of ftony maffes, apparently 
homogeneous, at lead for the greater part, but feparated 
from each other by parallel fiffures: thefe are moftly of 
an argillaceous or calcareous nature, and appear to have 
been formed by a gradual fubfidence from water. As no 
organic remains are found in them, they alfo feem to date 
their origin from the formation of the globe. 3. From 
the decompofition of thefe primaeval maffes, their attrition 
againft each other, the erofion of water, and various other 
accidents, clays, lands, marles, and the component parti¬ 
cles, of freeftone, fandftone, limeftone, flate, and various 
other fpecies of ffone, have arifen. Thefe are-placed over 
each other, in alternate and regular beds, parallel to each 
other, ar.d being commonly mixed with marine exuviae, 
or other animal or vegetable remains, the hills formed of 
them are evidently of a date pofterior to thofe already 
mentioned. In thefe, and in thefe only, (or in plains 
formed of the fame materials,) coal is found, and there 
are fcarcely any of them that do not contain it. It is to 
hills of this fort, therefore, that we muft dire£l our re- 
fearches after coal. The thicker beds of it lie pretty 
deep, generally from twenty-five to forty fathoms, or 
more; and the fureft means of difcovering them is to pe¬ 
netrate into thefe hills with an earth-borer, examining 
the ftrata every two or three feet; if alternate ftrata of 
indurated clay, find, (late, or fandftone, occur, with iron 
ere or mica, we may be certain that coal will be found 
:*£ a greater depth. The beds neareft to the furface are 
A L. 
generally either earthy, flaty, or fulphureous, and com-, 
monly thin and fcanty ; but under thefe, different beds 
of greater thicknefs and of .a better fort are found. Coals 
have alfo been ibmetimes difeovered by collecting the red- 
difh or ytllowifti muddy water that runs down the (ides 
of hills after heavy rains ; this water is collected in a pan 
fuffered to l'ubfide, and gently evaporated ; if the fedi- 
inent appears covered with a black lcum, the hills may 
be prefumed to contain coal. 
Veins of coal are often mentioned by different writers ; 
yet in reality coal is fcarcely ever found in 'veins, but ra¬ 
ther in beds or in heaps ; though thefe beds, from a de¬ 
rangement caufed by the occurrence of (lone or matter of 
a different kind from that which forms the Itrata, are fome- 
times thrown into the form or a horfe-fhoe, with the cur¬ 
vature downwards, and thus aflame the appearance of a 
vein. When a coal-mine is difeovered, its direflion, that 
is, its extent in the lame horizontal line, and its dip and 
rife, or inclination, that is, its fall beneath that line,-are 
next to be traced ; as it fhouid always be worked at right 
angles with its direction, and the draft to drain off the 
■water (hould be funk in the lowed part. To find the in¬ 
clination, three holes, each reaching to tire bed of coal, 
are bored at the dilfance of fix hundred feet from each 
other, forming an equilateral triangle, an the level and 
depth of each are taken. The higheft is the itandard to 
which the diftance downwards of the bed of coal under 
each hole is referred, that which is moft diftant in depth 
from the ftandard being the lowelt. It is alrnoft needlefs 
to add, that the boring fhouid be (kilfully conduced, in 
order that the holes be per(e'dlly perpendicular. The 
tools-or inltruments ufed in boring are very'fimple. The 
boring rods are made of iron from three to four feet 
long, and about one inch and a half fquare, with a lerew 
at each end, by which they are ferewed together, and 
other rods added as the whole increafes in depth. The 
chiffel is about eighteen inches iong, and two and a half 
broad at the end, which being ferewed on at the lower 
end of the rods, and a piece of timber put through an eye 
at the upper end, they are prepared for work. The ope¬ 
ration is performed by lifting them up a little, and letting 
them fall again, at the fame time turning them round ; by 
a continuance of which motions, a round hole is worn 
through the hardeft ftrata. When the chiffel is blunt, it 
is taken out, and a fcooped initrument called a 'wimble 
put on in its Head ; by which the dull or pulverized mat¬ 
ter which was worn off the ftratum in the laft operation 
is brought up. By this fubftance, the borers know ex¬ 
actly the nature of the ftratum they are boring in; and, 
by any alteration in the working of the rods, they per¬ 
ceive the leaft variation of the ftrata. The principal part 
of the art depends upon keeping the hole dean, and ob- 
ferving every variation of the itrata with care and at¬ 
tention. 
In England beds of coal of lefs than two feet and an 
half in thicknefs are judged not woith working; but in 
Germany none exceeding fix inches are neglected. To 
convey a fuller idea of the ftrata of earth or ftone that 
generally accompany coal-mines, we (hall here add Mr. 
Kirwan’s account of thofe that are found in the princi¬ 
pal coal-mines of Europe. 
The moft confiderable coal-mines in England are found 
in the counties of Northumberland and Durham en the 
ealt, and thofe of Lancafhire and Cumberland on the weft; 
they feem to extend acrofs the kingdom, or at leaft to the 
mountains of Cumberland and Weftmoreland. On the 
eaftern coaft, towards Newcaftle, the land gently defeends 
towards the fea, but is here and there interfered with 
deep vallies, in the declivities of which the coaly ftrata 
appear to have been firit difeovered. The ftrata in the 
coal-mines belonging to Nevvcaftle-upon-Tyne, lie in the 
following order: 
Fathoms. Feet. 
s. Mould or clay - -- -- - - -4 0 
3. Brown ferruginous clay and mica - - 3 0 
3. Whitifh 
