324 



M I N E. 



Mlnetof with the corresponding Figures, Plate CCCLXXXIX. 

 W '" elucidate. Fig. 6'. represents a horizontal section 

 or P' an ot a coal-field, as found immediately under the al- 

 cccixxxix l uv ' a ' cover. Only twobeds of coal are represented in this 

 Fig. 6. example, that the subject may he rendered as little com- 

 plex as possible, and, therefore, whatever changes in 

 position, and whatever dislocations take place in the 

 coals, take place also in all the accompanying strata, at 

 least this may be admitted in a general point of view. 

 The area in the figure is supposed to contain a space of 

 64 square miles, viz. a square of 8 miles on the side. 

 The coal district is bounded by transition rocks on the 

 North, more elevated than the coal district. A, is an 

 elliptical bason-shaped coal-field, where the coals a, b, 

 dip inwardly as represented by the points of the ar- 

 rows, but they dip much quicker next the transition 

 rocks, as they then conform with the dip of these; and 

 though the coals are the same distance from each other 

 in every part of the bason, when measured at right 

 angles to the pavement, they appear in the horizontal 

 section much closer upon the north than on the south 

 side of the bason. This apparent difference depends en- 

 tirely upon the angle of inclination which the coals 

 make in particular positions with the horizon, as will 

 be shewn distinctly in the vertical section. Upon the 

 south of the coal-field A, the slip B is found dislocat- 

 ing the strata, throwing the coals down from the sur- 

 face 140 yards to the south, and forming the coal-field 

 C, where the same coals of the coal-field A are found 

 again, having the same parallelism of dip. The slip D 

 is found upon the south of the coal-field C, dislocating 

 the strata, and throwing the coals down from the sur- 

 face 100 yards to the south, and forming the coal-field 

 E, where the coals of the coal-field C are also found. 

 The slip F is found dislocating the strata, and throws 

 the coals down 210 yards, and forms the coal-field G in 

 the same manner as the former coal-fields, as repre- 

 sented by the coals a, b. The coal-field G, in place of a 

 slip to the south of it, takes, as it is termed, a counter 

 dip, occasioned by a ridge in the strata of a saddle 

 shape, beyond which ridge the same coals form with a 

 contrary dip, as represented by the arrows, and form 

 the coal-field H. In this manner coal-fields are found 

 stretching over a district of country in a crop and dip 

 direction, somewhat similar to what is represented in 

 the Figure, but with many varieties arising from the 

 obliquity of the slips to each other. This spreading out 

 of the coal-fields in the crop and dip direction is pro- 

 duced by slips generally lying, not parallel, but some- 

 what in the direction of the line of bearing, and by 

 ridges and counter dips lying in the same direction. 

 Besides the coals a, b, inserted in the Figure, as an ex- 

 ample, all the coals, above and below these, with their 

 accompanying strata, suffer the same alteration as be- 

 fore mentioned. 



While these slips and dislocations lying nearly in the 

 line of the bearing of the coal have the effect of throw- 

 ing the coals over a district of country in the line of dip 

 and rise, the dikes, slips, and dislocations which lie in 

 an oblique direction to the former, such as the slips 

 marked K in the Figure, have the effect of stretching 

 or extending the coal-field over the country in the line 

 of bearing. The lines marked L, are dikes which only 

 separate the strata the thickness of the dike, without 

 throwing the coals and the accompanying strata either 

 p or down. It will be seen from the Figure that the 

 oblique dislocations, when they throw the strata down, 

 and the same parallelism of dip remains unaltered, that 

 the crops extend to a greater distance before they meet 

 the alluvial cover ; and, on the contrary, when the slip 



is an up-throw, the crops of the coals and accompanying Mines of 

 strata are diminished in breadth by coining sooner in Coal, 

 contact with the alluvial cover. K c, is ;i slip down to '"""V"' 

 the east, forming the coal-field M. K d is a slip down ' 

 to the west, forming the coal-field N. K e is a slip up i?,g"g X ' X ' 

 to the west, which cuts off the coal-field N in that direc- 

 tion. K f is an upthrow slip to the east, which has 

 the effect of throwing back the crops of the strata. 

 K g is a down-throw slip to the west, which has the ef- 

 fect of throwing forward the crops of the coals and stra- 

 ta. K It and K i being down-throw slips to the west, 

 have the same effect as in the last instance. K k being 

 an up-throw slip to the west, has the effect of throwing 

 back the coals and accompanying strata. In tin's man- 

 ner coal fields are extended over a district of country 

 in the line of bearing, in every variety of change, ac- 

 cording to the line of obliquity in which the slips oc- 

 cur with regard to the line of bearing, and the extent 

 of'the dislocation, as to the magnitude of the slip. These 

 of course frequently change the direction of the line of 

 level at times to the extent of 90, as must be obvious 

 from inspecting the Figures; because, generally, the 

 line of level is a line parallel to the crop, that is parallel 

 to the line of the coals where they intersect the plane 

 of the alluvial cover, which will be more particularly 

 exemplified when the working of coal is treated of. 



The next point for consideration is the vertical sec- 

 tion of the coal-fields before exemplified. Such sections 

 are generally made in the line of dip and rise, on which 

 account the section, Fig. 7. is in the direction of the dot- K; g . 7. 

 ted line OP, Fig. 6. and the coal-fields, beds of coal, 

 slips, counter dips, and crops, are marked with the 

 same letters as in the horizontal section, which exem- 

 plifies the positions noticed in the horizontal section. 

 These sections are to be considered only as diagrams, 

 shewing within a very limited space the phenomena 

 connected with coal-fields, it being impossible to shew 

 the several parts in equal proportions to one another, 

 as the sections represent miles in extent, whereas coals 

 are only a few f<-et in thickness, and the distance be- 

 tween them a few fathoms. In order, however, to shew 

 the effect of a great slip upon a scale of proportion, 

 Fig 8. represents three coals a, l>, c, rising southward 1 Fig. 8. 

 in 5 ; the coal b is 1 5 fathoms distant from the coal c, 

 and the coal a is 10 fathoms distant from the coal b; 

 the coals a and li crop out at the line of junction with 

 the alluvial cover, but the coal c is cut off by the slip 

 AB down to the south, forming the south coal-field, 

 where the coals a, b, c, are found dislocated and slipped 

 down. The magnitude of this dislocation is measured 

 by taking the distance betwixt the pavements of any of 

 the coals in the north and south fields, measured along, 

 the face of the slip, which in this instance is 50 fathoms. 

 It will also be observed, from this figure, that though 

 the distance betwixt the coals a and b is only ten fa- 

 thorns perpendicular, yet their distance, when they 

 crop out, is 50. fathoms in a horizontal line ; and the 

 distance betwixt the coals b and c being 1 5 fathoms, 

 their distance, when they crop out, is 75 fathoms. It 

 follows, of course, that those coals which have a great 

 dip, or make a great angle with the horizon, have the 

 less difference betwixt their perpendicular distance from 

 each other, and their distance from the one crop to the 

 other where they meet the alluvial cover, whereas 

 those coals which lie comparatively very flat, or at a 

 small angle with the horizon, have a very great diffe- 

 rence betwixt their perpendicular distance from each 

 other, and their distance where they crop out or meet 

 the alluvial cover, as may be seen by inspecting the fi- 

 gure. The proportion betwixt these is found by muhi. 



