during the Deposit of the Transition and Coal series, 27 



In working the bed of coal, the miner generally knows that 

 he is approaching one of these by the coal becoming twisted 

 and more difficult to work, and this continues till this trouble 

 in the roof is passed. The general form is similar to that re- 

 presented in the figure, when of course the mouth of the pot 

 is always inverted, the sides of it are generally lined with coal 

 from one-eighth of an inch to an inch in thickness, and the 

 pot or cavity is filled up with stone of the argillaceous kind, 

 or fire-clay, having generally less mixture of sand in it than 

 is in the I'oof-stone around. The under surface of the stone 

 which fills the pot is irregular and waving, not smooth like 

 the roof adjoining. 



Although the coal which lines the pot is connected with the 

 main bed of coal, it is of a texture altogether different, having 

 a bright appearance like jet, and it breaks into very minute cu- 

 bical pieces ; sometimes it has no bitumen in it, and is of the 

 nature of glance coal. The sides of the pot are generally as 

 smooth as glass, with small furrows or grooves in a vertical 

 direction, so that there is very little tenacity between the sides 

 of the pot and the stone which fills it up: this circumstance 

 renders these troubles very dangerous, particularly when they 

 are of a large size, as they fall without giving any warning. 

 The peculiar singularity attending this trouble, is the twisted 

 texture and alteration which are found in the bed of coal im- 

 mediately under and adjoining it, without any mixture of the 

 stone in it which fills up the pot. 



There is sometimes no lining of coal, and it generally hap- 

 pens that a piece of the stone, which fills up the pot, adheres 

 to the upper part of the cavity, so that the trouble may go 

 further up into the strata than is imagined. This trouble 

 requires to be minutely investigated, and the pavement upon 

 which the coal rests should be examined under the trouble, 

 to ascertain if it is in any way altered in its structure, as is 

 the case with the coal. 



I am indebted to my much respected friend Mr. Bald, civil- 

 engineer, for this latter information ; and I am happy to say 

 that it is his intention, at an early period, to devote his atten- 

 tion to these singularly curious objects. 



Were further proof of the vegetable origin of coal wanting, 

 the fact of finding impressions of the SagCnaria; in the solid 

 coal, the thin layers of incoherent carbonaceous matter, having 

 much of the silky aspect of charcoal, alternating with layers 

 of good bituminous coal, and bearing the form of the Calumiles 

 most perfect, should go far to establish the vegetable origin 

 of these combustible beds. 



E 2 Having 



