r4 



ranging E.S.E. between the Rivers Lune and IVharfe. 17 



coincident. And it is so often found in the slate of the middle division in the 

 Lake district, as in Langdale and Coniston Fells, that the planes of cleava"-e 

 cross alternate layers of finer and coarser matter, that most persons conclude 

 the cleavage of such slates to be nearly at right angles to the strata. 



After taking much pains in measuring the angles at which the smooth planes 

 of slate meet each other in different quarries, in order to ascertain what rc^'-u- 

 larity might be ascribed to them, I was obliged to conclude that their symmetry 

 is confined to particular places^ and by no means to be stated in «>eneral terms. 

 Indeed I found that next to the cleavage planes, the most constant of all the 

 great joints were those which crossed the cleavage nearly at right angles in a 

 vertical direction. 



The "bate" or false cleavage, w hich some observers have taken to represent 

 the laminge of deposition, is indeed generally constant in the same place ; but 

 even this has exceptions ; — and notwithstanding the seductive nature of the 

 appearances, it will probably be found on full investigation that the only really 

 constant planes in slate are those of the cleavage ; and that they are not always 

 parallel over even a moderate tract is evident, by inspecting the quarries near 

 Horton, where, within the compass of half a mile, they dip in opposite direc- 

 tions under the level top of limestone. 



Dislocation south of the range of Slate. 



Besides the great dislocation which accompanies the southern border of 

 these aberrant slate rocks^ and depresses the limestone strata on that side 

 another very important fault of the same kind running in the same direction, 

 and also depressing the beds on the south side, is clearly traceable across the 

 valley of Ribblesdale, and over Malham Moors toward Wharfdale. 



The general history of this great fault must be in some degree known to all 

 geologists who have visited the rocks of Gordale and Malham, or travelled up 

 the steep ascent of Giggleswick Scar. It may be without hesitation affirmed, 

 that no dislocation of strata in the island is more distinctly marked on the sur- 

 face, by the equal opposition along a certain line of rocks, which in their un- 

 disturbed places are separated by five hundred feet of other strata. 



In order to understand the nature of the appearances presented in the 

 neighbourhood of Settle, it will be convenient to examine the stratification of 

 Ingleborough and Penygent. 



Commencing with the top of Penygent, the series stated in general term.s 

 with estimated thicknesses appears in the following order : 



VOL. III. — SECOND SERIES. D 



