106 



TAULTS AND DYKES. 



above or below it, by which its identity with any known stratum may 

 generally be ascertained. The manner in which the strata are in- 

 clined towards the fault, will also determine whether they are thrown 

 up or down, provided they are not shattered where they come in 

 contact with h, which is frequently the case.^ Each bed of coal in 

 a coal-field has certain characters by which it may generally be 

 known to be the same. Its thickness, and the quality of the roof 

 and floor, with that of the upper and under strata, generally serve to 

 identify it, though it may be much deeper in one; place than another. 



The dykes which intersect coal strata are generally impervious to 

 water ; and it not unfrequently happens, that where the strata decline 

 to them, they hold up the water, and occasion springs at the surface, 

 or keep the coal works on that side of the fault under water, when 

 the coal works on the other side are dry. This will be better un- 

 derstood by referring to Plate IV. fig. 2. and 3., where the coal strata 

 on the right hand decline or dip to the fault or dyke ; and the water 

 which passes through or between the strata will be stopped at the 

 faults and dammed up ; in which case the coal beds to the right of 

 the dyke will be under water, and diose on the other side dry. NoWj 

 should a perforation be incautiously made through the dyke, all the 

 water will be thrown upon the works on the left, that were before 

 dry. Where the coal on each side of a fault belongs to different 

 proprietors, a few strokes with a pickaxe may thus do incalculable 

 mischief to those on the one side, and render great service to the 

 other, by laying their pits dry. 



The deepest coal mines in England are those in Northumberland 

 and in the county of Durham, some of which are worked nearly 

 three hundred yards below the surface. The thickest bed of En- 

 glish coal of any considerable extent is the main coal in Stafford- 

 shire, which is thirty feet. The upper, lower, and middle parts of 

 the bed differ in quality. Mr. Keir, who has written an interesting 

 account of the mineralogy of the south of Staffordshire, says that 

 thirteen different kinds of coal occur over each other in this bed ; 

 the uppermost, which is compact, serves as a roof in getting the un- 

 der coal. At the Wood Mill-hill colliery in this county, the coal is 

 said to be forty-five feet thick ; and three beds of coal, from three to 

 four feet in thickness, have been found under it, since Mr. Kier's ac- 

 count was published. The first is only two yards under the thick 

 coal. The main bed of coal in the Ashby-de-la-Zouch coal-field is 

 thirteen feet thick ; the upper and lower seams of this bed also vary 

 in quality ; and the top serves as the roof, being more compact than 

 the stratum over the coal. Few beds of coal in other parts of Eng- 



* 11 the dyke make an acute angle with the upper surface of the strata, they 

 are thrown up on that side ; but if it make an obtuse angle, they are thrown down 

 See Plate IV, fig. 2, d; and fig. 3. c/. 



