188 MESSRS. KIEKBY AND DUFF ON THE 



the Yoredale rocks, at a considerable elevation above the Mag- 

 nesian Limestone. It is not easy to determine the amount of 

 throw that here takes place, which is undoubtedly great ; but at 

 the same time it should be remembered that the sharp northerly 

 dip of the strata at Houghton Bank, at the old quarry near to 

 Park House, at Brussleton, and other places in the neighbour- 

 hood, must bring the Yoredale rocks rapidly nearer to the sur- 

 face at this point, and cause the actual displacement to be less 

 than would at first sight appear. 



It will be observed, from the preceding remarks, that the ge- 

 neral dip of the Carboniferous strata, where affected by these 

 faults, and to the south of them, is northerly, varying from 

 N.W. to N.N.E., whereas the normal dip of the same strata to 

 the north of the faults is easterly. Instead, therefore, of having 

 as usual the outcrop of the Measures to the west, the outcrop is 

 to the south, as shown in fig. 17, which represents the manner 

 in which the coal-field appears to terminate in the south-west, 

 according to our observation. The presence of the last described 

 fault at Houghton-le-Side renders it probable that other disloca- 

 tions may exist to the south of the Wigglesworth fault which 

 are not included in the accompanying sketch section ; but there 

 is nothing in the geology of the country to the south that indi- 

 cates the existence of any displacements of strata that would 

 again bring in the workable coals, so that for all practical pur- 

 poses it may be looked upon as correct. 



It ought to be pointed out that attention was drawn to the 

 northerly dip of this portion of the coal-field by Professor Sedg- 

 wick, in his admirable memoir on the Magnesian Limestone, 

 published in the Geol. Trans., sec. Ser., Vol. III. At p. 59, he 

 remarks, "The south-western extremity of the Durham coal- 

 field is deposited in the form of an irregular trough or basin. 

 The beds on one edge of this trough rise to the lead-measures, 

 and dip to the south-east; but on the south-eastern edge they 

 rise towards the terrace of Magnesian Limestone, and dip on the 

 whole to the N.W. Over this south-eastern edge ranges the 

 limestone ; and in its whole course, from Houghton-le-Side to 

 Ferry Hill, dips to the S.E. It is impossible to conceive a more 



