60 Prof. Sedgwick on the general Structure 



Continuing the range towards the north, the elevatory forces seem to have 

 operated more feebly, as the limestone is not brought up to the surface. But 

 their line of action is, in some places, marked by an irregular saddle of mill- 

 stone grit, forming the water-shed between our eastern and western coasts. 

 The great saddle of millstone grit at Blackstone Edge, flanked by the Lanca- 

 shire and Yorkshire coal-fields, is a good example of this arrangement*. 



A few miles further towards the north the mountain limestone is again pro- 

 truded: the chain gradually arises to a commanding elevation, and is continued 

 as far as Stainmoor, preserving throughout a great similarity in its external 

 forms, and an almost perfect identity in its internal structure. 



Near that part of this range where the carboniferous mountains begin to 

 present a decided escarpment towards the west, commences a great longi- 

 tudinal fault (or perhaps a system of faults), which has been traced by Mr. 

 Phillips from the heart of Craven to the hills near Kirkby Lonsdale, and ex- 

 cellently described in a paper published in a former volume of our Trans- 

 actions f. I must refer to this paper for the proof that the great Craven fault 

 has rent asunder a part of the carboniferous chain, and produced such a down- 

 cast on the west side, that mountain masses of limestone are tumbled into the 

 neighbouring regions with an inverted dip ; and that a coal-field which ought 

 to appear above the top of Ingleborough, has sunk below the level of its 

 base];. 



From beneath this coal-field the limestone beds again rise up, and after 

 passing in the form of a great arch over Farlton Knot, recover their hori- 

 zontal position, and are prolonged into those tabular hills mentioned above, 

 which form the south-western skirt of the Cumbrian mountains. From which 

 it appears, that the southern calcareous zone of the Cumbrian system, is cut 

 off from the central chain by the intervention of the great Craven yawZi. 



I once imagined that this greai fault ranged through the neighbourhood 

 of Kirkby Lonsdale and Farlton Knot, and there terminated. It is unques- 

 tionable that lines of dislocation do range in the direction here indicated (as 

 is proved by the position of the limestone of Kirkby Lonsdale bridge, and the 

 still more remarkable position of the limestone between Casterton and Bar- 

 bon) ; but after several subsequent visits to the neighbourhood, I found that 

 the leading branch of the Craven fault ranged along the line of junction of 

 the central chain with the skirts of the Cumbrian system, passing along the 

 south flank of Casterton Low Fell, up Barbondale, thence across the valley of 

 Dent, through the upper part of the valley of Sedbergh, and along the flanks 



* See PI. V. fig. 2. f See Geol. Trans., Second Series, vol. iii. p. 5 — 15. 



X See PI. V. fig. 3. 



