1815.] -A'l Essay on Rents. 88 



parts of Enj^land and vScotland they are called troubles and faults. 

 Bended-tabu'ar rents, containing eartliy and metallic tabular masses 

 and crystals, are generally called metallic veins ; and in Cornwall, 

 metallic lodes. 



2. Tlie Shape of this Rent descriled.^^The shape of tin's rent 

 is as follows: — Let fi;^. I, Plate XXIX., repreiant a perpendicular 

 view of its angular direction in a situation which is in the middle of 

 its horizontal direction; let the empty spaces between the strata 

 £, D, C, B, &c. be supposed to be filled with strata also, but 

 which are not represented, to avoid confusion in the figure; and let 

 the strata be continued uninterruptedly from the rent, ?i w v, to 

 the pit, K. Then if a miner be excavating the stratum E, he 

 may proceed a considerable distance in it, say beyond the point o, 

 without meeting with a rent ; but in excavating the stratum D, he 

 may meet with one at /; and if su, he will meet it in the strata 

 C, B, A, F, G, H, at i, g, a, q, s, u, and in the stratum I, at z; ; 

 there it terminates, probal)ly near the upper surface of this stratum. 

 Let a straight line, ?if, be drawn from the lii^hest to the lowest extre- 

 mity of ilie rent. This line passes thvougli the rent at its centre, 7v, 

 only, for the rent's upper lialf is a slightly curved line, n m k b tc, 

 which lies before the straight line ; and the lower half is a similarly 

 curved line, lo pit v, that lies above it. Again, let fig. 1, 

 Plate XXX., represent this rent as a person sees it in approaching 

 its upper side; and let the parts of fig. 1, Plate XXIX., be referred 

 to by the same letters : then the parts of the strata shaded dark in 

 the latter figure arc on the under side, n, h, p, v, of the rent ; and 

 the parts represented i^y the pricked lines only, are on its upper 

 side, 7/, g, q, v. The horizontal direction of the rent is greatest 

 opposite its centre, or opposite the stratum A ; there let it termi- 

 nate at A and a 1 : then if this distance be bisected, and a line, n v, 

 drawn at right asgles to the points A, a 1, it will bisect the angular 

 direction of the rent. The horizontal direction of the rent de- 

 creases in length upwards and downwards from this stratum, with 

 such a ratio, that if four straight lines be drawn, two ui)wards till 

 they meet in the line, n v, at w, each meeting it at an angle of 

 ^S"^, and two downwards, till they meet the same line at ti under 

 angles of 45° also, these lines will enclose a square figure; whose 

 position is such, that two of its opposite angles, A and a 1, are 

 situated both on the same horizontal line, and the other two, ?i and 

 V, both on the same perpendicular line. There is a general in- 

 crease in the width of this rent in every direction, from the lines 

 that join together its sides to its centre. This, thcrclbrc, is a square 

 bounded bended-tabular rent ; whose width is greatest at its centre, 

 and decreases to the lines that join togetlier its sides. 



Such is the general shape of every bcndcd-tabulitr rent ; but 

 particular parts of the angular directions of these rents deviate n ore 

 or less from the curved line just dcscril)cd, and their hori/ontal 

 directions deviate aho from ktruight linos, while the widths of thes* 



V J 



