323 



FAULTS AS A PREDISPOSING CAUSE FOR THE 

 EXISTENCE OF POT=HOLES ON INGLEBOROUGH.* 



HAROLD BRODRICK, MA. 



Ingleborough Hill consists of a large plateau of Carboniferous 

 limestone about 500 feet in thickness and capped by a cone of 

 Yoredale rocks with a summit of Millstone Grit. On this 

 plateau there are a large number of pot-holes or vertical shafts 

 in the limestone : there are upwards of thirty of these at present 

 known to exist, and it is probable that there are many more 

 still covered with the deposit of glacial drift. Within the last 

 few years many facts have come to light which prove that 

 many, if not all, of the deeper pot-holes owe their existence to 

 faults. Rift Pot, a pot-hole on the south-east side of the hill, 

 was recently explored and found to extend to a depth of over 

 300 feet : the first portion consists of a vertical shaft 114 feet 

 deep, the lower portion of which consists of a chamber 130 feet 

 long- and 25 feet broad ; from the south end of this the pot 

 descends for a distance of about 200 feet with a series of 

 platforms of jambed stones wedged between the walls of a 

 vertical fissure, finally ending in a short passage which, at the 

 end, is waterlogged. The pot-hole at the surface takes the 

 form of a fissure 60 feet long and from one to seven feet wide. 

 At the northern end of this fissure, within a few feet of the moor 

 level, the east wall is slickensided, and in the main chamber at 

 the foot of the first shaft, the east wall is also slickensided over 

 an area 50 feet in length and at least 20 feet in height. At the 

 surface the slickensides occur along successive master joints, 

 while those in the main chamber occur along another master 

 joint at a horizontal distance of about 15 feet. These slicken- 

 sides are horizontal, showing that the fault was one of 

 horizontal displacement, and as a careful examination shows 

 that the beds of limestone on either side of the upper part 

 of the pot correspond, it is clear that no vertical movement 

 accompanied the faulting. The slickensides near the surface 

 are coated with clear crystals of calcite which, when removed, 

 leave the slickensides clearly marked. 



Only one fault is marked on the maps of the Geological 

 Survey : this is a fault which runs from near Horton to God's 



* A paper read to Section C of the Meeting- of the British Association, 

 York. 



igo5 September i. 



