MINE. 



329 



Mines of will reach the upper stratum of the former bore at a 

 CotL depth less, by 20 yards, than the depth calculated 

 from a horizontal line from the top of No. 1. bore. 

 Ravines frequently cut the strata in various directions, 

 as at A, so as to* lay the strata open to view ; and if 

 these are very deep, an advantage may be gained by 

 boring there, and proving the strata to a considerable 

 extent by a bore of moderate depth. In all instances 

 where a series of bores are carried on, a correct and 

 distinct profile of the surface ought to be made in the 

 line of the bore*. In No 2. a coal is found near the 

 surface, and another at the bottom of the bore, which 

 last rests upon the first stratum d, found in the bore 

 No. 1. The bore No. 2. is continued a few feet farther, 

 until it is decidedly ascertained that it has reached the 

 stratum d. These two bores have thus proved the 

 strata to the depth of 120 yards. No. 3. bore having 

 been placed according to the rule before given, it 

 passes through two coals near the surface, and after 

 being pat down nearly to its proposed depth, it strikes 

 the stratum A, which is the upper stratum found in 

 No. 2. bore; but as a coal was found in No. 5. under 

 the stratum A, the proof i* rendered more complete bv 

 continuing the bore through that coal. This bore, with 

 the two former, proves the strata to the depth of 180 

 yards. No. 4. bore having been placed in the same 

 manner as the former, a coal is found after passing 

 through a few yards of the strata, and the bore i* con- 

 tinued downwards until the two coals found near the 

 nrfncc in No. 3. havtbeen passed through. This, with 

 the throe former bores, ascertains the strata under exa- 

 mination TO the depth of S40 yards, so that to reach 

 the lower stratum a of No. 1. the bore No. 4. would re- 

 quire to be put down to the said depth of 240 yards. 

 The bore No. 5. being placed in the same manner as 

 the former, a coal is found within a few yards of the 

 surface; but after reaching the depth at which the 

 coal at the top of No. 4. b*re should hare been found, 

 strata altogether different occur. In this case it in 

 usual to go on with the bore ten or twenty yards far- 

 ther than the intended depth of the bore, to ascertain 

 the alternations of the strata. In some case* no coals 

 of any value will be found, as in the present example, 

 the cause of which is, that a slip or dislocation B of the 

 strata has occurred, throwing up nil the coals patted 

 through in the former bores, and that of such a mag- 

 nitude that the strata b, a, of the bore No. 1. are found 

 immediately after perforating the slip ; and within a 

 few yards of the surface, in place of being found at 

 the depth of 300 yards, as would have been the case 

 had the strata continued at the regular dip of 1 in 10, 

 and no dislocation had taken place. Since dikes, slip*, 

 hitches, and troubles of every kind and degree, n- 

 merly mentioned, occur in coal-fields, example* of 

 which are given in the preceding part - itise, 



it will easily be seen, by an inspection of thee figures, 

 what difficulties may occur in boring a coal-field which 

 i* much dislocated and troubled. Some coal-field* are 

 so intersected with these as to bewilder the ideas even 

 of the oldest and most experienced miners ; for in- 

 stance, since slips are of every magnitude, as regarding 

 the rxtent or distance the particular strata are separat- 

 ed in a vertical direction, it not unfrcqucntly happens 

 that n lower coal is thrown upon one side of a slip, di- 

 rectly opposite to an upper coal situated upon the 

 other side of it ; so that if the two coals are of the same 

 thickness, erroneous conclusions are most inadvertently 

 .ormed, and mistake* with the most cautions will take 

 place. Very many instances might be given of the*e 



VOL. XIV. PART I. 



anomalies found in the practice of mining, but it would Mines of 

 be endless to elucidate them by figures. In the exam- Coat 

 pie given of a progressive set of bores, it is evident _~ ""T 

 that the first coal likely to be found to the southward f ^" B 

 of No. 5. bore, and in the new coal-field formed by the 

 upthrow slip, will be that found in the bottom of No. 

 2. bore; and if so, there is reason to conclude that all 

 the other superincumbent coals will be found in suc- 

 cession southward, excepting some great dislocation or 

 off cut of the strata takes place to interrupt their regu- 

 larity. Caution must also be observed, in approaching 

 primitive or secondary rocks, it being found, as before 

 mentioned, that coals and their accompanying strata 

 flatten in the line of dip towards these rorks, form a 

 trough or bason, from which they rise suddenly, and 

 form edge or half-edge strata upon the face of those 

 rocks. 



If a line of bores is to be conducted from the dip 

 of the strata towards the rise or direction of the crop, 

 the same rules hold as to the placing the bores at the 

 proper distances from each other, according to the dip 

 or the angle of inclination made by the strata with the 

 horizon ; with this correction, that the bores are placed 

 some yards nearer each other than the distance result- 

 ing by multiplying the dip by the depth of the bore, 

 in order not to overstep the last strata passed through 

 in the preceding bore ; for if any of the strata are 

 overstepped, several of them will not appear in the 

 journal, and a valuable coal may be in these strata 

 which have escaped being bored through. The general 

 rule in this case is, to place each successive bore so 

 that the first of the strata passed through shall be the 

 last which were passed in the bore immediately pre- 

 ceding. The bore* No. 4, 3, and 2, elucidate this prin- 

 ciple in boring from the dip to the crop; but suppose 

 that the bore No. 2. had only gone to the depth of the 

 stratum/, and that the bore No. 1. was put down in 

 the position as marked in the Figure, in this case the 

 stratum c. with the coal immediately below it, would 

 be overstepped, none of the bores would pass through 

 them ; of course they would not appear in the journal, 

 and the existence of that coal would be unknown. 



Having described the mode presently practised in 

 boring in the crop and dip-line of direction, where the 

 dip is known before the boring is commenced, the 

 next operation to be described is the proof bores in the 

 line of bearing, which are necessary in proving a coal- 

 field in a district where coals were not known to exist 

 before. The line of bearing being at right angles to 

 the line of dip and crop, let it be supposed that these 

 bore* are to be put down at right angles to the bore 

 No. 4. at the distance of four to six hundred yards ; I'm* 

 the one on the west, the other on the east fide. After ccc * c - 

 making the requisite allowance for the difference of F * *' 

 level betwixt the top of these bores and No. 4. bore, 

 the two coals found in . the bottom of No. 4. ought to 

 be found at the same depth in each of the bores put 

 down in the line of bearing if the strata are lying re- 

 gular and free from dislocations ; having however this 

 correction in view, that as all coal-fields are bason- 

 shaped, and of very various magnitude*, the absolute 

 line of level along any bed of strata deflects either in- 

 wards or outwards from the line of bearing, which is 

 at right angles to the line of dip and crop ; and, there- 

 fore, referring to the shape of coal-fields formerly dis- 

 cussed, it will be seen that bores put down in a proper 

 bason-formed field, in the line of bearing, will strike 

 the coals sought after sooner than calculated upon ; 

 and, in the cue of the form being an inverted bason, 



*T 



