322 



M I N E. 



Coal. 



Mines of coal, that they cannot be taken out without destroying 

 and breaking to small pieces a great proportion of the 

 coal to which they are attached j on which account 

 such stoney coals have frequently to be sent to market 

 with the stone in them, which is greatly against their 

 sale. Coals having regular bands of stone in them, 

 and which are easily separated, do not come under the 

 denomination of stoney coals. 



8. Black Coal. This is a trouble which rather af- 

 fects the appearance than the absolute quality of the 

 coal ; it generally occurs suddenly, that is, while in 

 one part of a coal-field the coals have the common 

 bright fracture, a slip or hitch of very trifling magni- 

 tude will produce on the other side coals termed black 

 coal. The appearance is dull, without the least lustre. 

 It is equally compact in texture as the other coals of 

 the field, and burns well. This trouble, however, 

 greatly reduces the value of the coal at market, its ap- 

 pearance being so very much against it. 



9. Sooty Coal. This trouble renders the coal of 

 a dead, sooty, friable appearance, and of no use, 

 is never of great extent, nor does it appear to have 

 arisen from any convulsion of the immediately ad- 

 joining strata, as the roof and pavement where it 

 occurs keep their parallelism with each other. This 

 trouble is, however, generally found when approach- 

 ing some considerable dislocation of the strata, such as 

 a slip or dike. 



10. Dike Coal, named also Burnt Coal, Dander Coal, 

 or Humphed Coal, are all names applied to the same 

 kind of trouble in the bed of coal. The particular 

 names above mentioned are applied by the com- 

 mon workmen and miners, the name dander signify- 

 ing scoria. The appellation humphed is a provincial 

 term, and only used amongst miners, signifying the 

 same thing as burnt or dander coal. This kind of 

 trouble is in general found to exist on both sides of 

 dikes composed of greenstone, basalt, or porphyretic 

 clay; the trouble beginning at a distance from the 

 dike on both sides, the coal at first by degrees losing 

 its bright fracture and becoming black coal, then burnt 

 or dander coal, which next the dike appears run into 

 a tortuous mass, with irregular cellular cavities, and is 

 more of the nature of a dull, black, stoney matter, than 

 .any thing connected with coal. Coal found in this 

 kind of trouble has none of the qualities of glance coal, 

 the blind coal of Scotland, or the stone coal of Wales; 

 for although placed in a heap they will not kindle 

 .though fire is applied, they will grow red hot, but in- 

 stantly cool as stones would do when .heated and the 

 fire withdrawn. Some pieces are found occasionally 

 .of the purest kind of glance coal, with a very bright 

 metallic lustre, and so hard as to be with difficulty 

 scratched with a knife ; such coal is divided by nu- 

 .merous small veins of a white sparry substance. This 

 kind of trouble, besides being found adjoining dikes of 

 the above description, is found occupying considerable 

 districts of a coal-field ; and though no change is ob- 

 served in either the roof or pavement, the coal is com- 

 pletely useless, and will not burn though fire is applied 

 to it. It is, however, in general different in appear- 

 ance from the coal found adjoining dikes as before 

 mentioned, in as much as more of the stratified tex- 

 ture remains, and is not run into a tortuous mass with 



irregular cavities. It has been asserted by some miners, 

 that this change is occasioned by greenstone or basalt 

 being near the coal, either above or below it. This we 

 presume remains to be proved. 



The term burnt coal is not known amongst miner- Mines 01 

 alogists, or rather is not admitted ; the name is applied Coal- 

 by the unlettered miner, from the simple ideas rising S ~ P "Y- 

 in his own mind, being altogether a stranger to those 

 theories which so warmly interest and so much divide 

 the philosophic world. It must be particularly re- 

 marked here, that when a coal-field is working of the 

 common coal, it is sometimes gradually changed into 

 a species of glance-coal, which burns of itself when 

 ignited, and is used for economical purposes, has no 

 smoke, and only a blue flame, with intense heat. 

 This is not reckoned one of the species, of the burnt 

 coal of the miner, but is simply one of those changes 

 in quality incident to coal. 



11. Glazed Backs, Lips, or Leips. This is a trouble 

 in the coal more generally found in an oblique direc- 

 tion as to roof and pavement, seldom perpendicular ; 

 they are also more frequently found lying in the line 

 of bearing, than in a crop and dip direction, and are 

 distinctly different from the natural divisions found in 

 coal. Although there can scarcely be perceived any 

 slip in the roof, it is evidently a slip of the very least 

 degree which occasions this trouble. Both sides of 

 the fissure are smooth and glossy, and the coals thus 

 divided have no tenacity, which renders this trouble 

 dangerous to the miner by the coal falling suddenly 

 forward without warning. A single fissure of this kind 

 can scarcely be called a trouble, but when many of 

 these are near to one another, the coal is injured, and 

 the roof rendered very dangerous. 



12. Troubles in the roof and pavement of the Coal. Troubles i 

 These troubles are more generally found when ap- thereof an 

 preaching a dislocation of the strata, though they are pavement, 

 occasionally found in other parts of the coal-field. 



They affect the roof with narrow pendent ridges or' 

 stone, or protuberances, at times very close together, 

 in other instances like long inverted waves. The 

 troubles in the pavement are generally sudden wave- 

 like swellings. These troubles frequently affect the 

 coal very much, rendering it sometimes not only firmer 

 in the texture, but uncommonly hard ; at other times 

 the coal adjoining them is soft, and so deteriorated as 

 to be altogether useless. 



Besides these troubles, there is frequently another 

 kind found in the roof, of a very singular form, known 

 by the name of a pot bottom, or cauldron bottom; they 

 are from the size of a few inches to five feet in diame- 

 ter. One of these is represented in Plate CCCLXXXIX. 

 Fig. 5. In working the coal, the miner generally 

 knows that he is approaching one of these by the Fi S- 

 coal becoming harder and more twisted in its texture, 

 and this continues till the trouble in the roof is passed. 

 The general form is similar to that represented in Fig. 

 5. a is the bed of coal, b the pot bottom, having an ir- 

 regular and rough inverted mouth of stone, d is coal 

 generally from half an inch to an inch thick, altoge- 

 ther different in texture and appearance from the bed 

 of coal with which it is connected, being of a bright 

 pitchy lustre, and breaks into very small pieces ; 

 sometimes it is of the nature of glance-coal. The 

 stone b v.-hich fills the inverted pot is frequently of the 

 same kind of stone which composes the roof, but more 

 frequently is an argillaceous stone, of the nature of 

 good fire-clay. The sides of the pot-bottom at d are ge- 

 nerally as smooth as glass, and furrowed in the verti- 

 cal direction, so that there is no tenacity where the 

 sides of the pot-bottom join the roof; this circum- 

 stance renders these troubles very dangerous, particu- 



