NATURAL HISTORY. 



331 



surface, then the seam of coal is 

 said to be thrown downwards, and 

 is found below the break. The real 

 fact is, that in some former time 

 there has been some great convul- 

 sion of the earth, in which all the 

 superincumbent covering matter, 

 consisting of seams or beds of stone, 

 coals, or other materials, have been 

 moved upwards in all such uLasms 

 or breaks, leaving the seam or bed 

 of coal below, in one part, where 

 it was at the time the dreadful con- 

 vulsive motion happened. Hang- 

 ing over, and sloping upwards, or 

 downwards, are only relative terms, 

 depending upon which side of the 

 interposed matter you arrive at. 

 Where any seam or field-coal seems 

 thus to end, the interposing matter 

 hangs or slopes one way on one 

 side of the matter, and the contrary 

 on the other side, so that the super, 

 incumbent matter, with the seam of 

 coals, has been invariably thrown 

 upwards by the convulsion, whilst 

 the remaining part of the bed has 

 been left as it was before the mor 

 tion. 



Whitehaven collieries abound 

 with what they there call Dykes, 

 that is, beds of stone of a consi- 

 derable thickness, which separate 

 one field of coal from another. 

 •The principal ones run in a direc- 

 tion nearly east and west. Tliey 

 divide the seams of coal into fields, 

 as they are called, that is, separate 

 tracts of coal almost like the fields 

 or inclosures of a farm. These 

 dykes or separations arc very use- 

 ful, by restraining the water or in- 

 flammable air from flowing out of 

 any adjoining field of coal, where 

 no works are going on, into an- 

 other where men are working, un- 

 til it is found convenient to cut 

 through or work a new field. 



Without these dykes, it would fre- 

 quently be very difficult to keep the 

 works from being overcharged with 

 water, but it is sometimes very 

 troublesome and expensive to cut 

 through them, being ofaconsiderable 

 thickness. Where the covering of 

 superincumbent matter is not ct so 

 great a thickness, which is towards 

 the rise of the seam or field, tliere 

 pillars of coal are left from five to 

 ten yards square, and the workings 

 are from three to four yards wide, 

 so that about one-half of the coal 

 is taken away, and the other half 

 left to support the earth above. 

 Where the coals lie from one hun- 

 dred and fifty to threehundred yards 

 deep, and especially where the coal 

 is drawn from under the sea, the 

 pillars are left from sixteen to twen- 

 ty yards square, so that about one- 

 third part of the coal is taken, and 

 two-third parts are left to support 

 the roof. 



Whitehaven colliery is not so 

 much loaden with water as the col- 

 lieries about Newcastle and other 

 flat countries are, where tney are 

 not able, by what is called day 

 levels, to take away the top water, 

 called surface-seeds, as is practised 

 at Whitehaven. 



The coal-works at Whitehaven 

 have produced, and still do produce, 

 greaterquan titles of inflammable air, 

 commonly called damp, than any 

 other coal-work knov/n. This seems 

 to arise from the coal lying at a 

 greater depth below the level of the 

 sea than any other known colliery. 

 Tills observation holds invariably- 

 true both here and about Newcastle, 

 that in all coal-works lying above 

 the level of the sea little or no in- 

 flammable air is perceived, except 

 in the guts of the dyk<'s, that is, in 

 the cavities or hollows betwixt the 



field* 



