328 MR. J. E. MARK ON LIMESTONE-KNOLLS IN [Aug. 1 899, 



It is with regret that I have been driven to adopt another ex- 

 planation for these phenomena, but my regret is mitigated by the 

 fact that the explanation is a matter of opinion, which will staud or 

 fall, as the result of future work, while the actual structure of the 

 area which has been unravelled by Mr. Tiddeman single-handed is of 

 prime importance, and he has described phenomena which, whatever 

 be the explanation offered to account for them, are undoubtedly 

 of extreme interest. 



II. General Structure of the District. 



Under this heading I propose to give a brief account of 

 Mr. Tiddeman's work, extracted from the papers to which I have 

 already alluded, in order to render my own communication more 

 intelligible to the reader. In doing so it will be unnecessary to 

 specify the work done previous to Mr. Tiddeman's elucidation of the 

 phenomena which it is the main purpose of this paper to describe, 

 for everyone interested in the geology of the North of England is 

 aware of the existence and general natur<^ of the Craven Eaults, 

 and is acquainted with the principal geological features of the country 

 north and south of those faults. 



There are three main branches of the Craven Pault, the northern- 

 most of which runs from Ingleton at least as far as Pateley Bridge ; 

 the middle branch runs through Ingleton, a short distance south 

 of the first, to Gordale ; while the southernmost leaves the middle 

 branch near Settle, and runs to Skipton.^ The Carboniferous rocks 

 on the north of the fault-system differ as a whole from those lying 

 on the south in their present characters and thickness, and in the 

 amount of disturbance that they have undergone. The rocks on the 

 north side of the faults exhibit little evidence of disturbance, while 

 those on the south side are thrown into a series of anticlinal and 

 synclinal folds, of which the axes run in a general east-north-easterly 

 and west-south-westerly direction.^ The difference in the characters 

 of the rocks of the two areas is very marked. The following 

 classification is tabulated by Mr. Tiddeman ^ : — 



Thickness in Thickness in 



Southern Type. feet. Northern Type. feet. 



Coal Measures (Ingleton). 1500 Coal Measures ... 1 Incomplete near 



Millstone Grits 3900 Millstone Grits ... J the faults. 



Bowland Shales SOOtolOOO] 



Pendleside Grits (incon- I Yoredale Series ... 400 to 900 



stant) Oto 250 | 



Pendleside Limestone ... to 400 \ 

 Shales-with-limestoues ... 2500 I Carboniferous 



Clitheroe Limestone -f 3250 (no [ Limestone 400 to 800 



base). J 



^ Tiddeman, Rep. Brit. Assoc. 1889 (N'castle-on-Tyne) p. 600. 



2 Tiddeman, Congres Geol. Internat. Compte-rendu, 4feme Sess. 1888 [1891] 

 p. 319. 



'^ Eep. Brit. Assoc. 1889 (N'castle-on-Tyne) p. 601 & Congres Geol. Internat. 

 Compte-rendu, 4feme Sess. 1888 [1891] p. 814. 



