1815,] An Essay on Uents. 85 



cannot have been so numerous, nor so perfect in their nature, as 

 to describe with sufficient accuracy the general laws, much less the 

 peculiarities of the laws, respecting the figures of the larger rents, 

 and other necessary particulars; but many mines, probably, are 

 sufficiently large to enable skilful miners to determine the particu- 

 lars necessary to describe all phenomena peculiar to the smaller 

 rents, and to show that the larger cmrespond with the smaller in 

 every particular known of the latter rents. This is particularly the 

 case with the Earl of Lonsdale's coal-mines at V/hhehaven,* m 

 which I made the many new observations respecting the shapes and 

 positions of this rent, and the peculiar arrangement of the strata 

 contii^uous to them, which will appear in these es-.ays. 



4^'riie Positions of Bemkd-TatuUir Re7its.—TheiY\ost of these 

 rents liave angular positions ; but some have a position which is 

 angular in one part and perpendicular in another ; others, one that 

 is angular in one part and horizontal in another; and others, one 

 which is angular in one part, perpendicular in another, and hori- 

 zontal in a third. The positions of these rents depend on those of 

 the strata which form their sides ; if, as Williams says, " the strata 

 lie in a horizontal position, the fissure of the slip," or the position 

 of a rent, " will lie nearly perpendicular; but if the strata harig 

 with any considerable degree of declivity, the fissure of the slip will 

 be found in a slanting direction, as all these sections cut trans- 

 versely, or right across the strata, or nearly so." This law arises 

 from tiiat which follows : The surfaces of separation of the strata 

 contiguous to the sides of this rent are at right angles, or nearly so, 

 to the upper and under surfaces of these strata. Therefore when 

 the stratum A, fig. 3, Plate XXX., is horizontal, as when it is 

 represented by the letters ig c d h k, its small surface, or surface 

 of separation, of which cd is the perpendicular direction, and 

 which is at right angles to the stratum's upper and under surfaces, 

 will give a perpendicular position to the rent, n o, of which it 

 forms a part of one side. On the same principle, when the stratum 

 A, is bent upwards till it acquire the position represented by the 

 letters i, g, a, b, h, k, it will give an angular position to that part of 

 a rent, (the part / m,) where it forms a i)art of one of its sides. If 

 this stratum be bent downwards till it be represented by the letters 

 i, g, e,f, h, ^y tlie side of tlie rent, p fj, of which it forms a part, 

 win be angular also ; but in this instance the angular direction 



• In (he WhitchavcB coal-mines three strata of coaJ are work.-d : "•« first, tlic 

 thirknesi ..f *l.ich varies fron. four to six feet, is called (he Rani.ock lia.ul, aiid 

 aupeaiB at ti.e earlh'k surface at tlie bigl.e:,t part of ihe ii.ii.o, hut is more ll.an 90 

 fathoms below it at tI.e lowest part: li.e second stratum, wl.ose thickness varies 

 from six to twelve feet. Is called the Main Hand, and is sitnuted at a dis a.ice 

 below Ihe liithest l>and, that, if taken in ditlVrent places, «ill vary troni H to 

 more than VO faihoms: the third, the Six Quarteis Hand, is trom lour to s.x feet 

 in thickness; and is nitualed in some places . 'JO, in others 4(1, fathoms l.elow the 

 Main Hand; and in others any distances between lhe,c extremes, Ihe s.rtac« 

 area, under which the first twl. named bands are excavated, is not less than trom 

 ten to twelve square miles. This is aa area of mine, not to be equalled, 1 believe, 

 ky Ihat of any other proprietor. 



