Notices of Memoirs — H. Brodrick — Cause of Pot-holes. 517 



I. — On Faults as a Prkdisposing Cause for the Existence 

 OF PoT-HOLKS ON Inglebokough. By Harold Brodrick. 



INGLEBOROUGH Hill consists of a large plateau of Carboniferous 

 Limestone ab lut 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 probal)le that there are many more still covei'ed 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 : tiie 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 jarabed 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 ia 

 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 

 slickensides 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 corre- 

 spond, 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 slickensidesvery 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 Bridge, in 

 Chapel-le-Dale. Along the line of this fault are several pot-holes, 

 all of which have their longer axes in the direction of the fault. 

 Sulber Pot, which is about 59 feet deep, and Nick Pot, which receives 

 an inflowing stream, and has recently been explored to a depth of 

 about 80 feet, exhibit no direct evidences of faulting; but Mere 

 Gill, on the other hand, does. Mere Gill consists of a fissure, about 

 80 yards long, which is bridged in three places by rock. As a rule 

 this fissure is filled with water to within 30 feet of the surface ; in 

 times of normal rainfall the water escapes through a tunnel below 

 the water-level, which leads in a southerly direction (away from the 

 valley) ; it then makes two vertical descents of 80 feet each and 

 turns northwards to emerge in the valley near God's Bridge in the 

 direct line of the fault. On the limestone, which is usually covered 



1 Abstracts of six papers read before the British Association, Section C (Geology), 

 York, 1906. 



