There dots not appear any general law as to the line of direction of these slips, only the ramifications are generally more in a dip and rise direction, than in the line of beating of the coal-fields.
The effects of dikes and of slips upon the coal strata, when viewed in a vertical section, are more evident than in the horizontal section, where they only appear like wails, veins, and lines of simple separation. Fig. 10. Plate CCCLXXXVIII. is a vertical section of a coal field from dip to rise, with three strata or beds of coal, a, b, c. AB is a dike at right angles to the plane of the coal strata. This rectangular dike has only the effect of dividing and separating the coals, and all the accom panying strata, but produces no alteration in the line of rise ; but further to the rise, the oblique dike CD in terrupts the coals a, b, c, and not only divides and separ ates them, but throws them and all their accompanying strata gteatly lower down; but though thrown down, as represented in the figure, the coals and strata still keep the same parallelism and direction of rise. Still fur ther to the rise, the oblique dike EF interrupts the coals a, b, c, and not only divides and separates them, but throws them, and all their accompanying strata, greatly up, and produces a much quicker dip and rise, as represented in the figure. Sometimes the coals in the division H, betwixt the dikes C and E, are found nearly horizontal, and the effect of the dike EF is sometimes such as to throw out the coals altogether, so that no vestige of them can be found in the division K. Such are the most prominent changes in the strata, as to their line ol direction produced by dikes; but of these changes there are various modifications.
The effect of slips on the strata is represented in the vertical section, Fig. 11, where a, b, c, are coals with their accompanying strata. A B is a slip which intersects the strata, and throws all the coals of the first compart ment very much lower, as represented in the compart ment No. 2.; and, from the magnitude of the slip in this instance, it throws in other coals, marked 1, 2. 3, which were nut found in the compartment No. 1. CD repre sents a slip having the same effect, but not to the same extent. El: represents a slip intersecting the strata, but contrary to the former in its position ; the effect of this is. that the coals a, b, c, are thrown up, as repre sented in the compartment No. 4. Sometimes this slip brings into view coals situated under these mat keel a, b, c, such as the coals 4, 5 6 ; and when it happens, as we have freequently seen, that a coal marked 4 is directly op posite a well known coal, as e in the compartment N., 3,
the case is difficult and bewildering to the miner. Be sides these varieties, we find a number ol slips or hitches often very near to one another, as in the compartment No. 5, where the dislocation of each slip is not great, hut the amount of the whole forms a considerable slip as to the coal in the compartment No. 6. These are the treneral effects of dikes and slips in a vertical section of the strata from the dip to the rise ; whether these dislo cations lie in the line of bearing, or with a moderate angle of obliquity to it, that is under 45 degrees. The effects of dikes and slips, in pursuing a dead level course direction, are exemplified in Fig. 12. Plate CCCLXXXVIII. Wlierc the coals and accompany ing strata are of course horizontal, and the dikes and slips, lying at a greater angle thati to the line of bearing, they arc termed dip and rise dikes, or slips, as A B, CD, E.F.
From what has been stated regarding the effects of dikes and slips, as to the dislocation of the strata, inde pendently of any changes produced in the coal and strata adjoining, to be noticed afterwards, those who are employed in conducting the operations of collieries, consider that these dislocations follow a general law, which is this: Let Fig. 1, Plate CCCLXXXIX. repre sent a stratum, or bed of coal, with the accompanying strata; A, the pavement of the coal, and B the roof; if, in prosecuting the mine, as at C, a dike, D, is met with, -which forms with the pavement a right angle, viz. of 90°, it is concluded that the dike only has divided and separated the strata its own thickness, so that when a mine is driven through it, the coal is found directly op posite ; but, in the further prosecuting of the mine, if a dike, F, is met with as at E, which forms an obtuse angle with the pavement, that is, an angle greater than 90°, it is concluded that the dike has not only divided and separated the strata its own thickness, but has thrown up the coal and accompanying strata, which, on running a mine through the dike, is found to be the case as at G. Lastly, if a dike H is met with at I, form ing an acute angle with the pavement, as in the figure, that is, an angle less than 90 degrees, it is concluded that the dike has not only divided and separated the strata its own thickness, but has thrown down the coal and ac companying strata, which, on running a mine through the dike, is found to be the case, as at K.