486 Dr. J. E. Marr^The Dufton and Eeisley Groups. 



In the east quarry the Keisley Beds of nodular type are dipping 

 southward from the Dufton Beds, to pass below the Skelgill Beds. 

 Some of the upper beds of the Keisley Limestone may be faulted 

 out here, but the beds which actually exist are not more than forty 

 feet thick, and therefore no thicker than the beds of this age in 

 Swindale, where they appear to present a normal sequence. To the 

 north of the anticline which brings up the Dufton Beds, the Keisley 

 Beds dip nearly due north for a very little way, and still further north 

 there is a continuous southerly dip at angles varying from 60° to 75° 

 for a distance of about 200 yards. Unless a fault exists along the 

 line where the dip in the Keisley Beds changes from north to south, 

 the Dufton Beds should come to the surface at no great distance to 

 the north of the change of dip. There is no sign of any such fault, 

 and the alternative explanation is that the Keisley Limestone is here 

 folded into a series of isoclines, with the Dufton Beds concealed 

 beneath at no great distance below the surface. 



It is well known that the bulk of the Keisley fossils have been 

 obtained from a highly crystalline whitish limestone, though here and 

 there they occur in compact limestone, as in the case of the abundant 

 Illceni in a horny limestone whose position is marked on the plan. 

 One would naturally expect that the crystalline and compact 

 limestone belonged to different beds, and at the outset we attempted 

 to prove that the crystalline limestones were above the nodular and 

 compact limestones. A further examination proved that they were 

 quite irregularly distributed, as shown on the plan, where the 

 principal exposures are indicated, the crystalline limestones being 

 marked ' cryst.' and the compact nodular limestones ' nod.' Further 

 search proved that this irregular distribution was traceable on a very 

 small scale, so that at times a hand-specimen could be obtained with 

 one portion compact and the other crystalline, the two being 

 separated by very irregular junctions, with no traces of bedding- 

 planes. It seems impossible to escape the conclusion that the 

 compact limestone was the original rock, and that crystallisation, as 

 the result of subsequent change, has affected it sporadically in this 

 Keisley tract, where there is clear proof of much thickening by 

 folding, whereas in the Swindale section, where there is no evidence 

 of thickening, the crystalline variety is absent. 



It is interesting to note that little knolls of crystalline limestone 

 occur in profusion in the shale-band of the lower part of the northern 

 face of the west quarry, in a way which recalls similar little knolls 

 which I elsewhere described in the shales associated with the 

 limestone of the Draughton Quarry of the West Riding of Yorkshire.^ 



The question arises, why should the limestone be thickened and 

 crystallised at this point and not in Swindale ? In connection with 

 this I would point out that elsewhere the Dufton Shales show 

 evidence of much repetition, and the limestone may have resisted 

 folding when sandwiched between the soft Dufton Shales below and 

 the Ashgill and Skelgill Shales above. Here the Dufton Shales are 



^ "On Limestone Knolls in the Craven District of Yorkshire and elsewhere": 

 Quart. Journ. Geol. Soc, 1899, vol. Iv, pp. 336-338. 



