166 



MESSRS. KIRKBY AND DUFF ON THE 



away, the throw is only eighteen in 

 ches ; but the strata on each side of 

 it form a fiattish anticline, from which 

 we suppose that in this instance the 

 dislocation was caused by a force 

 acting laterally. 



In regard to the period of origin 

 of the faults of the Coal Measures, it 

 is certain that some of the greater of 

 them date from after the deposition 

 of the Magnesian Limestone ; for the 

 ' ' Ninety Fathom Dyke ' ' of the north- 

 ern part of the coal-field brings in a 

 patch of the latter formation on its 

 depressed side. It is also evident 

 that the fault at Houghton-le-Side 

 (p. 186), from the tilted position of 

 the strata in Toitup Quarry, likewise 

 disturbs the Magnesian Limestone. 

 But we do not know whether this is 

 the case with the Butterknowle or 

 any other large faults. It is cer- 

 tainly well known that many dislo- 

 cations found in the Coal Measures 

 do not affect the Magnesian Lime- 

 stone, where that formation overlies 

 the former in the east of Durham. 

 We have even seen a " hitch" in the 

 George Pit, Etherley, where the roof 

 matter (sandstone) of the Brockwell 

 seam has evidently, at the time when 

 the fault was formed, been soft, to 

 admit of it being run or squeezed 

 into the coal, on the dip side, in thin 

 tongue - like pieces. (Similar in- 

 stances have occurred to one of us in the Fifeshire coal- 

 From these facts we are inclined to look upon the faulting 



field.) 

 of the 



