Tin: CARBONIFEROUS s\ 



259 



attain a great thickness and their base is nowhere exposed ; north 

 of it the base is exposed in several places, resting on a floor of 

 upturned Ordovician and Silurian rocks, but the series is much 

 thinner (see Fig. 90). 



For the following comparative view of the succession in the 

 two areas I am indebted to Dr. Vaughan. 



Clitheroe District. 

 /Millstone grit 

 M G I (4th grit). 



' | Bowland shales . 



[.Fondle grit . 

 D y . Pendleside limestone 

 D 2 . Pendleside shales 



S & Dj. Clitheroe knoll-limestones 



Feet. 



100 

 400 



800 



The Clitheroe and Cracoe limestones have not yet been com- 

 pletely zonalised, but Dr. Vaughan informs me that the main 

 Clitheroe knolls include representatives of D l and of S (Seminula 

 zone), and that the beds at the base of the main knolls belong to 

 C 2 (Syringothyris zone), but there is a considerable thickness of 

 limestone below that horizon. 



Near Ingleborough the lowest beds are not older than the top of 

 the Syringothyris zone, and the total thickness of Visdan limestones 

 is only 600 feet. 5 Northward, however, they thicken again con- 

 siderably till near Kirkby Stephen there is 3700 feet of them. 

 Then they again diminish by the rapid thinning out of the lower 

 beds till in the Cross Fell district they are once more reduced 

 to 600 or 700 feet, and much of this is sandstone. Fig. 91 

 illustrates the position and composition of the Visean Group at 

 Ash Fell and Roman Fell, east of Appleby, and the map (Fig. 89) 

 sho\v.s the course of the buried ridge of Ordovician rocks which 

 causes this thinning-out a ridge which forms a natural northern 

 limit to the region we are describing. 



Returning now to the north-east of Lancashire the higher 

 stage, comprising the Pendleside and Yoredale Beds, remains to be 

 dealt with. The succession of beds forming the Pendleside Group 

 was fully described by Dr. W. Hind, 6 and is given above ; 

 the black Pendleside shales are characterised by Posidonomya 

 Becheri and Pterinopecten papyraceus, and the Pendle limestone 

 by the same with Glyphioceras spirale and G. reticulatum. In the 

 (Mi tlit-roe and Pendleside districts the total thickness of this group 

 is at least 2500 feet, but it thins northward, and when the Settle 

 faults are crossed its place is taken by such a different set of beds 

 ihat the identity of the two groups has been for a long time in 



