Vol. 55.] THE CEAYEN DISTRICT OF YOEKSHIEE. 353 



were formed prior to the fault, and accordingly their continuation 

 ought to be traceable to the north (which is not the case) if the 

 fault were normal ; if the fault be a thrust, the disposition of the 

 rocks is perfectly explicable, as I shall proceed to show in greater 

 detail. 



The east-and-west anticline has its centre immediately north of 

 the Craven system of faults, where the Lower Palaeozoic rocks are 

 exposed at the surface. If the folding were simple, one would 

 expect the minor folds to have axes coinciding with the major folds, 

 which is not the case. The northern edge of the Burnley Coalfield 

 and the southern edge of the Millstone Grit mass of the Pells near 

 Lancaster trend in a general north-easterly and south-westerly 

 direction, and between them is the anticline, broken up into still 

 smaller folds, in which the knolls occur. jSTow the Craven Fault 

 system has its greatest throw on the west, and dies out to the east; 

 accordingly, if the movement be one of thrust from the north, the 

 beds below the thrust should be moved southward to an ever- 

 increasing extent as we pass from east to west, and beds which once 

 had an east-and-west strike would in that way acquire the strike 

 that they now possess, namely, east-north-east and west-south-west 

 near Cracoe, and north-east and south-west to the west of this. 



As corroborative evidence of the nature of the fault, I may 

 remark that, if my interpretation of the structures south of the fault 

 be true, these structures require thrusting to account for them. 

 This remark may appear like arguing in a circle, but the whole of 

 the evidence must be considered together. 



"Whatever be the nature of the folding south of the faults, we are 

 all agreed that the rocks are thrown into a series of anticlines and 

 synclines the axes of which vary from north-east and south-west to 

 east-north-east and west-south-west. In the saddles of these axe?- 

 the Lower Carboniferous rocks and knolls are found, in the troughs 

 the Millstone Grit ; furthermore, the knolls do not occur singly in 

 each anticline, but in clusters, having a general linear arrangement, 

 and also a subsidiary irregular grouping. The reason for this- 

 disposition may now be discussed, and I ofier the following remarks 

 as worthy of consideration. 



Between the comparatively rigid Millstone Grits above, and 

 the Lower Palaeozoic rocks below, lie the yielding Clitheroe Lime- 

 stones and still more yielding group of shales and limestones above 

 these. Tbe formation of the folds with north-easterly and south- 

 westerly axes must have resulted in the accumulation of the rigid 

 Millstone Grits above in great masses into the synclines, and their- 

 dragging away from the tops of the anticlines. Accordingly, we 

 find horizontal slickensiding by no means rare in the Millstone 

 Grits of the Lancaster fells. There may have been actual rupture 

 of the Grits at the top of the arches, but in any case there would 

 be relief of pressure there, causing the limestones to be squeezed out 

 from below the synclines and to accumulate in the anticlines, and 

 I believe that it is in this way the knoll-reefs were formed, while- 

 Q. J. G. S. No. 219. 2 a 



