FAULTS 



331 



Fig. 854 shows a colliery in plan, and the amount of tho movement produced by the 

 dislocations. 



854 



Coal viewers or engineers regard the dislocations now described as being subject in 

 one respect to a general law, -which may be thus explained: ~Letfig. 855 be a portion 

 of a coal-measure ; A. being the pavement and B the roof of the coal-seam. If, in 

 pursuing the stratum at c, a dyke D 

 occurs, standing at right angles with the 

 pavement they conclude that the dyke 

 is merely a partition-wall between the 

 beds by its own thickness, leaving the 

 coal-seam undisturbed on either side; 

 but if a dyke F forms, as at E, an obtuse 

 angle with the pavement, they conclude 

 that the dyke is not a simple partition 

 between the strata, but has thrown up 

 the several seams into the predicament 

 shown at o. Finally, should a dyke H 

 make at i an acute angle with the pavement, they conclude that the dyke has thrown 

 down the coal-measures in the position of K. 



Dykes and faults are denominated upthrow or downthrow, according to the posi ion 

 they are met with in working the mine. Thus, in Jiff. 849, if the miner is advancing 

 to the rise, the dyke A B obviously does not change the direction ; but c D is a down- 

 throw dyke of a certain number of fathoms towards the rise of the basin, and E F is an 

 upthrow dyke likewise towards the rise. On the other hand, when the dykes are met 

 with by the miner in working from the rise to the dip, the names of the above dykes 

 would be reversed ; for what is an upthrow in the first case becomes a downthrow in 

 the second, relative to the mining operations. 



3. Hitches are small and 856 



partial slips, where the dis- 

 location does not exceed the 

 thickness of the coal-seam; 

 and they are often correctly 

 enough called steps by the 

 miner. Fig. 856 represents 

 the operation of the hitches 

 A, B, c, D, E, F, G, H, on the 

 coal-measures. Though ob- 

 served in one or two seams of a field, they may not appear in the rest, as is the case 

 with dykes and faults. 



f-roubles are smaller, but often numerous faults, by which the beds of coal are dis- 



