INCLINATION or RooKs.] becomes parallel with its former course. Both of the parallel lines of strike run in a11 east-and-west direction, but in the one the dip is to the south, and in the other to the 11orth. The strike may be conceived as always a level line on the plane of the horizon, so that no matter how much the ground may undulate, or the outcrop may vary, or the dip may change, the strike will remain level. Hence in mining operations it is commonly spoken of as the level- GEOLOGY 299 course or level-bearizzg. A level or underground road-way, driven through a coal-seam at right angles to the (lip, will undulate in its course if the dip changes in direction, b11t it may be made perfectly level and kept so throughout a whole coal-field so long as it is not interfered with by any dislocations or other disturbances of the regularity of the rocks. The accompanying figures (figs. l8 and 19) will serve to show some of these terms as expressed on maps and Z I .‘:‘‘}“‘-‘»,..-._ H " -7’ . ,,/:','.'.'.:.§;g~ml»s§§§§§l ..ei.-,‘,{.¢/;,,;;g/4%/;; ‘." 5" I’ I. u, ' ‘.1 . xx, //’/11”“_ 1 H Z! l‘_ ' § ’/I , Q .
‘I
.‘ 7//Z.‘ '71 0 iii»-.‘'‘ /// . //r/M5’; /'lIi‘‘§l§‘~ {'/// 54’; w'‘ §~ './/J "W‘~‘‘‘ “‘ {hi i u/‘.':.'!-,“" - § 5 0 o C‘
. .t . ‘ -‘ - ~ ~‘. |h“”‘‘E |‘'.‘§i‘-‘t‘
. i -s »» (‘I {/ It I K ‘_-x ~ ii-fll. 0 lxiih ‘C3 9 " ' ' .- l I O . 253*’
- wol"cot.
~n' FIG. 1S.—Gcological map of a portion of a rocky coast-line, and the country inland. (J. B. J ukcs.) sections. Fig. 18 represents a geological map in which a series of strata dips iii a south-south-easterly direction (S. 98° The angle of inclination increases from 35° at the northern to 50° at the southern end of the beach. On the flat shore (AA) outcrop and strike coincide, but along the inner margin, where the ground ascends in a line or cliff (BB) to the inland country CC), the outcrop is seen to be deflected a little so as to cross the plateau along a slightly more northerly line than on the beach. A section drawn at a right angle to the strike along the line DD would show the structure represented in fig. 19. Such a section, expressing graphically the result of careful measure- A/art}: 2.9- I I’. SezzD ‘ 300 feet below the ‘level of t.7u°Sc(z Dlcvel FIG. 19.—Scction along the line DD on fig. 18. ment in the field, would give not only the order of succes- sion of beds at the surface, but their actual depth at any point beneath it. Thus a bore or shaft sunk at the point marked d on the map would have to pass through rather more than 425 feet of rock before reaching the stratum b. The total thickness of rock measured at right angles to the dip in fig. 19 is somewhat more than 850 feet. These various strata, if restored to their original position, would lie one over the other to that depth. If they were on end
they would occupy exactly that breadth of ground But