Man : The Rigidity of North-west Yorkshire. 67 



pre-Permian is shewn by the overstep of the Permian rocks 

 from Lower Carboniferous rocks on to Millstone Grit in the 

 middle of the depression. This has an economic bearing, 

 indicating the possibility of the occurrence of coal at workable 

 depth, beneath the Red Sandstones of Edenside. 



It was probably during this period of movement that the 

 extensive sheet of once-molten rock known as the Whin 

 Sill, was forced along the nearly horizontal strata of Carbon- 

 iferous rocks of the rigid block, and this rigid block is account- 

 able for the existence of this Sill, which, like the block itself, is 

 unique in our county as regards the extent of its areal develop- 

 ment. 



Next, the red rocks of Permo-Triassic date were laid 

 down, and as shewn by Professor Kendall, movements similar 

 to those which occurred previously, went on during the actual 

 accumulation of these rocks, giving rise to the Pennine Fault, 

 along which motion continued (probably with pauses) until 

 after the accumulation of these red rocks had ceased. This 

 movement, like the others, gave a trough-like arrangement of 

 the red deposits, for the oldest (the Penrith Sandstone) occurs 

 on the west of the trough, and also on the east, being here 

 brought up in several places parallel to the fault fracture, 

 while the newest rocks, the St. Bees Sandstone, are found in 

 the space between. 



There was yet later movem.ent of a similar kind, indicated 

 by the occurrence of the little patch of Liassic rocks in the 

 neighbourhood of Carlisle, and as argued elsewhere, this latest 

 movement may even be of Tertiary age. It would appear, 

 therefore, that again and again the earth-wave broke S-gainst 

 the western side of the rigid block along its northern extension . 



Let us now return to Yorkshire, and consider the nature 

 of the movements at the southern margin of the block, along 

 the line of the Craven system of earth-fractures. As to the 

 exact nature of these fractures, as regards the inclination of 

 the fissures, I need say nothing. It does not affect the rigidity 

 of the block, whether it has been pushed over the rocks to 

 the south, or whether the latter are thrown down almg a 

 nearly vertical plane. The general arrangement of the rocks 

 is very hke that to the east of Edenside. At Ingleton, the 

 Coniston Limestone is "Sent down from the older rocks to the 

 north. It is true that as we pass eastward a considerable 

 belt of slate rocks, newer than the Coniston Limestone, lies 

 north of the Craven Faults, but this is in accordance with 

 the view that the rigidity of the block extended outwards 

 from its core, owing to the stiffening of the crust formed of newer 

 rocks, when these were compressed by intense folding. South 

 of the fault system the sunken tract must be underlain by 

 rocks newer than the Coniston Limestone, for some distance, 



1921 Feb. 1 



