78 Extracts relating to Coal, Sfc. 



mine or quarry, when exposed to the fresh air it falls into very 

 small pieces The most usual colour of this stone is black ; 

 but there are several other liglner colours, down to a light 

 brown or gray. It is easily distinguished from freestone by its 

 texture and colour, as weli as by its other characteristics. It 

 lies in strata of various thicknesses, though seldom so thick as 

 the two last-mentioned kinds of stone. 



5. Shiver. — This stratum is more frequently met with in 

 coaleries than any other. There are many varieties of it, both 

 in hardness and colour; but thev all agree in one general cha- 

 racteristic. The black colour is most common; it is called by 

 the miners black shiver, black metal, or ble.as. It is softer 

 than metal-stone, and in the mine is rather a tough than a hard 

 substance, is not of a solid or compact matter, being easily 

 separable by the multitude of its partings, &c. into very small 

 parts, and readily absorbing water. The substance of this 

 stratum is an indurated bole, commonly divided into thin 

 laminae of unequal thicknesses, which break into long small 

 pieces when struck with force; and, on examination, they 

 appear to be small irregular rhomboids: each of these small 

 pieces has a polished glassy surface; and, when broken cross 

 the grain, appears of a dry, leafy, or laminated texture, like 

 exceeding fine clay: it is very friable; feels to the touch like 

 an unctuous substance ; and dissolves in air or water to a fine 

 pinguid black clay. There are almost constantly found in its 

 inclosed strata lumps or modules of iron ore, often real beds of 

 the same. 



There are other colours of this stratum besides black. The 

 brown or dun shiver is very frequently met with ; it agrees with 

 the above description in every thing but colour. Gray shiver 

 is also very common : it seems to be only a mixture of the 

 black and dun ; and by the different degrees of mixture of these 

 colours others are produced. It lies in strata sometimes of 

 considerable thickness, at other times not exceeding a few 

 feet : they are commonly parted from each other by laminae of 

 spar, coal, or soft matter. 



6. Coal. 



To illustrate how the various strata lie in some places, and 

 how often the same stratum may occur betwixt the surface and 

 the Coal, we shall give the following example. The numbers 

 in the left-hand column refer to the classes of strata before 

 described, to which each belongs. The second column con- 

 tains the names of the strata; and the four numeral columns, 

 to the right hand, express the thickness of each stratum, in 

 fathoms, prds, feet, and inches. 



