OF THE CLIFTON FAULT. 



149 



In Messrs. Buckland and Conybeare's paper on the S.W. Coal- 

 district (Trans. Geol. Soc. 2nd series, vol. i. p. 242), attention is 

 drawn to the fact, " that the fault may be traced up the gully 

 which bounds the northernmost of the two Roman camps in Leigh 

 "V\'ood." Beyond this suggestive observation I am not aware of any 

 published account of attempts to trace the further south-western 

 extension of the fault. But since the Upper Limestone Shales 

 faulted down are softer than the solid limestone, we might very 

 probably, so it seemed to me, find a line of depression marking the 

 line of fault and running south-westward from this gully. Such a 

 line of depression actually exists ; and I have ventured to mark it 

 in the accompanying map as Upper Limestone Shales. It runs from 

 the neighbourhood of Hill Farm across Beggars' Bush. Lane, through 

 the northern corner of the Ashton Park estate, across the Abbots 

 Leigh road, in which the depression is well marked, and so to the 

 head of Mghtingale YaUey, along which this natural line of drainage 

 then passes, deserting the line of fault, which crosses i*^ightingale 

 Yalley about halfway up, and so passes to the gully mentioned by 

 Messrs. Buckland and Conybeare. It is interesting to notice that 

 the point where the fault crosses the i^^ightingale Yalley is indicated 

 by a weU-marked change in the physical features. Up to that point 

 the ascent is steep ; beyond that point it is much more gradual. 

 Up to that point the southern (left hand) side is precipitous, beyond 

 that point it has a more gentle slope. Up to that point the valley 

 is a deep notch, beyond that point it widens out. These changes 

 result from the bringing in of the softer rock by the downthrow of 

 the fault. 



Another point is of interest. West of the point T have just 

 alluded to, a triangular wedge of limestone is cut off by the line of 

 fault and the line of the valley, which intersect at this point. (See 

 map.) This triangular wedge of limestone formed too marked a 

 natural feature to be missed by the Britons, who accordingly 

 strengthened it by building a vallum along its faulted side ; so that 

 the line of this Stoke Leigh Camp (marked " camp " on the map), 

 as suggested by Buckland and Conybeare, shows roughly the line 

 of the fault. 



I have before mentioned that beds of grit belonging to the Upper 

 Limestone Shales are found on the Somersetshire bank at the point 

 marked b on the map. Where the Upper Limestone Shales come 

 in on the north side of Nightingale YaUey, I have, however, not 

 succeeded in finding any definite bands of grit, though fragments ot* 

 siliceous rock are abundant. jSTear the head of IN'ightingale Yalley, 

 at c, beds of clayey shale are exposed. And in the Ashton Park 

 grounds, across the north corner of which I have been able, through 

 the kindness and courtesy of Sir Greville Smyth, to follow the line 

 of depression, there are some quarry-pits, at d (see map), in which 

 white clayey bands are interstratified with bands of limestone. 

 And, yet further to the south-west, in the fields that lie between 

 Beggars' Bush Lane and Hill Farm House, there are many sandstone 

 fragments mingled with stones of Mountain Limestone. 



