136 



strata thus thrown in we have as yet failed to discover workable 

 veins of coal. 



Hitherto we have been considering dislocations, which, 

 although of great extent, present nothing that is unusual or 

 abnormal. We will now take an example of another kind, viz., 



THE 8i FATHOM FAULT, 



situated 275 yards to the north of Tyning Pit, Radstock, 

 which exhibits an extraordinary peculiarity, for which it is 

 extremely difficult to account. 



It has commonly been regarded as a fixed principle in 

 practical geology that a fault may exist in the lower part of a 

 formation without the upper strata showing any trace of the 

 disturbance, but that the reverse of this cannot occur. It has 

 been considered certain that a dislocation met with in the upper 

 part of a formation must, as a matter of necessity, affect the 

 strata immediately beneath it, and that it must affect them to 

 the same extent and in precisely the same way. In the 8^ 

 ' fathom fault, however, we have a very extraordinaiy exception 

 to the rule, inasmuch as in the "great" or upper vein of the 

 first series it is an upthrow of 51 feet, while in the lowest 

 veins of the same series it has been proved to be a dowTithrow 

 of 21 feet. How this can have arisen it is difficult to say, but 

 of the fact itself there is no room for doubt. 



It may have originated in the fault having occurred as a 

 downthrow of 72 feet shortly after the lower vein had been 

 formed, and the upper veins having in the meantime been 

 deposited without disturbance by the strata being upheaved 

 in the old line of fractm-e to the extent of 51 feet. Or it 

 might be accounted for were we to suppose some extraor- 

 dinary perpendicular pressure applied to the strata on the 

 south side of the fault while they were in a semi-plastic state, 

 causing the remarkable thinning of the stratification which 

 exists at that point. But it is impossible to imagine a cause 



