MINE. 



331 



Boring for 



M'in of the ground. But highly satisfactory as this is, the plan 

 Col- has not succeeded, and is not yet known in common 

 "" " > practice. Several eminent coal proprietors patronized 

 ^ Ryan, and Rave his process a fair trial ; the bores 

 were not deep, but, so far as executed, thev were sa- 

 tisfactory. The impression which the public has at 

 present regarding this mode of boring is. that it is 

 very expensive, and not practicable in deep bores. 

 It U, howevi-r, but too well known, how much man- 

 kind areattached to old plans, strongly prejudiced against 

 new ones, and that it is no easy matter to change par- 

 ticular hahit<: this may have operated apiin>t Mr. 

 i's invention, and have prevented success attend- 

 t. The lxre-holes formed by the Ixjring bits are 

 larger than those in c< : , in order that the 



core may be about 3 or + inch' r, and Mr. 



Ryan proposed by this plan to Ix-re holes of more than 

 one foot in diameter, to ventilate coal-mines, but it is 

 supposed this did not succeed, or th.it the cxpence 

 rendered it no saving. It is understood, however, 

 that by this process, with boring-bit* ;md wimble* of 

 large size, alluvial cover mixed with gravel and boiil- 

 der-stones has been passed through, where the old 

 plans did eed ; and c,.ver is tlie 



most difficult to bore through of any. 



As boring for coal i* always carried on in a line per- 

 pendicular to the plane of the horizon, and as coals and 

 thrir accompanying strata, lie at every various angle of 

 inclination to that plane. from nearly horizontal to the 

 perpendicular line, it results that the thickness of tin- 

 strata, or of any coal bored through, if lying at a 

 great angle with the horizon, will measure consid- 

 erably more than what they absolutely are, because 

 the true thickness of any stratum or coal is only ob- 

 tained by taking the measurement at right angle* to 

 the plane upon which each stratum or coal reals ; for 

 example, in boring through the flat-lying cool. Fig. 

 *. the difference betwixt the line pawing through it, 

 perpendicular to thehoriron, and that which is at right 

 angles to the plane on which it rests, is so trifling as 

 need not be noticed ; but thin difference betwixt the 

 two perpendiculars, increases with the enlar 

 the angle formed with the huri/on. so th.-t in Fig. 5. 

 the thickne-s of the coal, as ascert.-iiix il by boring, is 

 the distance a, b, whereas the absolute tUotMsj of tlie 

 coal iiire It. r. that is, a line perpendicular to 



the plane on which the coal rests. In uiis example, the 

 measurement of the coal by boring. i< |fi feet, where- 

 as its absolute thickness, b, c, is exactly six feet, pro- 

 "liicing an error of 10 feet. From these circumstances, 

 it ;- :,..; the practice to ascertain a coal-field, composed 

 of dge coals, by boring, because being nearly vertical, 

 very few of the strata would IK- pssl through, even 

 with a deep bore ; therefore, when edge coals are not 

 laid open to view in a ravine where the alluvia) cover 

 moved, it is the practice, if the rover i-. not thick, 

 t a trench through it p.l right angles to the line of 

 bearing of the strata, and as edge coals lie generally at 

 short distance from each other, a trench of two hun- 

 dred yards in length will discover nearly that thick- 

 ness of the strata ; but if the cover is too thick for ctit- 

 thc rock head, the plan is to sink a pit 

 a few fathoms into the rock, from the bottom of which 

 wo mine- are earned in :i li-vcl direction. ;it ri^ht analr- 

 to the line of bearing, the one to the rise, tl 

 the dip of the strata. By this plan, the thickness and 

 ls w ill be accurately ascertained. Fig. 

 5. shews the plan of proceeding with edge coals, a, a, 



*,,. 4. 



f't- *- 



rig. e. 



are the edge coals, b the pit, c, c, the mines which in- Mines of 

 tersect the strata. CoaL 



With regard to searching for coal in what is termed 

 by Werner the second coal formation, composed of the 

 newest flcctz trap rocks, it is attended with more diffi- the second 

 culties than are found in any other of the coal-fields, coal forma 

 In this formation the coals are fctmd of uncommon tion. 

 thickness, in some instances 100 feet, the prevailing 

 strata above the coals, are various alternating beds of 

 soft slate clay having very little tenacity, with some, 

 times a few beds of sandstone; and over these, next 

 the surface, thick beds of greenstone ; which, where 

 dislocations of the strata have taken place, form high 

 precipitous cliff-', such as greenstone precipices always 

 assume. The coals found in these fields do not ex- 

 tend over a great district of country ; in some instances 

 they do not extend to a mile in length, the coals lie 

 irregularly, and in a short distance very from lying 

 : rntcly flat to very steep. 



Coal-fields, of this singular kind have been found 



more by accident than from regular surveys and mi- 

 nute searching, for this reason, that the masses of 

 greenstone present such an unfavourable appearance, 

 and MI forbidding, that trials by boring would scarcely 

 be recommended by a mineral surveyor, particularly 

 a* limestone is more frequently found under very thick 

 beds of greenstone than coal, with this difference, how. 

 ever, that the strata accompanying limestone in such 

 cases, are stronger and more compact. If, in such 

 instances, no vestiges of coal can be found, where the 

 alluvial cover can be cut through near the crop of the 

 coal, the next step is to bore beyond the edge of the 

 greenstone, and also to search for the softer strata ly- 

 ing under any of the greenstone cliffs, which, when 

 found, a bore may be put down to any requisite depth 

 to ascertain the strata ; and if coals are found there, it 

 is probable they will be found under the greenstone in 

 the flat part of the country, which also must be ascertain- 

 ed by taring. If coal is found in one place, its dip, line 

 of bearing, and extent, require to be found according to 

 the process before described. These uncommon beds 

 of coal are of various quality, some parts of them being 

 hard, others soft, of a rich caking quality ; but by far 

 the greatest part is of an inferior kind, having sul- 

 phur combined with it, and yields, when burnt, a*hes 

 of a dark reddish brown colour, which i* one of the pe- 

 culiar characters of all sulphurous coals. Such coals 

 are very liable to spontaneous ignition, after being 

 opened up and wrought for some time. 



Glance coal, which is the blind coal of Scotland, and Starching 

 the stone coal of Wales, is sometimes found alternating for glance 

 with the other kinds of coal; at other times, the com- coa1 ' 

 mon coals pass into this kind ; it is, however, more 

 commonly found in Scotland, where greenstone 

 abounds in the strata, and is very abundant in Ire- 

 land. 



No rules can be lai.l down for searching district 

 for this coal, beds of it have generally been found by 

 accident. 



For particular information regarding the different 

 kinds of coal. (See the Article COAL.) 



Bovey coal, being wood, or great collections of trees Searching 

 found in the alluvial cover, semi-mineralized, and Iv- for botey 

 ing nearly horizontal, it cannot, in strict mmeralogi- 

 cal language, be named coal, though some of it is so 

 like coal, as to b* termed brown coaJ. The only con- 

 siderable extent of this kind of coal which has been 

 found, and continues to be wrought in Great Britain 



