Yol. 55.] THE CRAVEN DISTRICT OF YORKSHIRE. 329 



It will be observed that the estimated thickness of the Lower 

 Carboniferous rocks on the south side of the fault-system is much 

 greater than that on the north side. 



The irregular masses of limestone which Mr. Tiddeman has called 

 reef-kuolls, to which I shall allude in the following pages as 

 knolls, are found on the south of the fault-system, and he si>eaks 

 thus of their occurrence in the Pendleside and Clitheroe Lime- 

 stones : — ' The form and the system of arrangement of the white 

 limestones [of the knolls] are peculiar. The strati n cation of the 

 deposits is usually somewhat obscure, and the masses rise in the 

 form of conical or ovoid eminences up to a height of 300 or 400 feet. 

 The change of thickness occurs in a very limited horizontal extent. 

 These eminences ordinarily present upon their sides strata which 

 dip away from the mass in all directions ; but when the rocks of 

 the eminences have been quarried, or denuded by atmospheric 

 agents, one sees that the stratification, rough as it is, preserves its 

 horizoutality or agrees with the direction of inclination of the sur- 

 rounding country The knolls are seen at Malham in the 



valley of the Aire, at Winterburn Eeservoir, Swinden, and other 

 localities in the neighbourhood of Grassington, in the valley of the 

 Wharfe, where they are found in profusion. They have never been 

 discovered north of the Craven Faults. In the localities which have 

 been mentioned they are all developments of the Pendleside Lime- 

 stone. In the neighbourhood of Clitheroe, on the other hand, these 

 knolls are all excrescences of the Clitheroe Limestone. In the case 

 of the Pendleside Limestone, they ])enefcrate the Bowland Shales 

 which surmount them ; around Clitheroe they bury themselves in 

 the Shales-with-limestones.' ^ 



Associated with the knolls are breccias,, described as follows : — 

 'At the foot of these mounds, or reef-knolls as I would call them, 

 we have in many places a breccia formed of fragments of the 

 limestone, which, I take it, have been broken off the reef above 

 between wind and water, and have subsequently been covered up 

 by the mud of the Bowland Shales and compacted into a breccia. 

 Fragments of limestone similarly consolidated occur, though more 

 rarely, on the sides of these knolls themselves. I would call these 

 reef-breccias.'^ The shales of the breccias at Winterburn 'were 

 seen curving round to the shape of the boulders, showing their 

 deposition while the shales were still in a soft plastic form.'^ 



It will be seen that the main points of interest are (i) the fault- 

 system ; (ii)the differences in thickness and characters of the rocks 

 north and south of the fault; (iii) the knolls; and (iv) the accom- 

 panying breccias ; and of these our knowledge of the latter two is 

 entirely due to Mr. Tiddeman. I now proceed to give a brief outline 

 of his explanation of the phenomena. 



^ The passage above quoted is translated from the Report of the Internat, 

 GpoI. Congress, 4th Sess. 1888 [18911 p. 321, with a few verbal alterations, 

 which do not aifect its meaning. 



- Tiddeman, Rep. Brit. Assoc. 1889 (N'castle-on-Tyne) p. 602. 



3 Trans. Leeds Geol. Assoc, pt. vi (1891) p. 112. 



