146 C. L. iLOK&AN 0]Sr THE S.W. EXTEXSIOX 



18. On the S.W. ExTEiJfsio:N of the CLZFTOif Eatjlt. By Peoe. C. Lloyd 

 MoEGAif, F.G.S., Assoc. E.S.M. (Eead December 17, 1884.) 



On the right bank of the Avon, somewhat below the Suspension 

 Bridge and a little beyond the Clifton station of the Bristol Port 

 railway, the Clifton fault cuts across the strata somewhat obliquely. 

 On the southern side of the fault is massive Mountain Limestone, 

 forming the bold bluff of the Observatory Hill. On the northern 

 side are much contorted red grit and limestone shales (see Map, 

 p. 147). 



Yiewed from the opposite side of the river, the right bank, from 

 the Suspension Bridge for half a mile northwards, shows the following 

 features. The eastern tower of the Suspension Bridge is built on a 

 solid mass of limestone, the western face of which fronts the river 

 as an almost perpendicular wall of rock. At right angles to this, 

 and parallel with the bridge-road, there is a second face due probably 

 to a joint plane, or a minor dislocation of the strata parallel with that 

 caused by the Clifton fault. This vertical face forms the southern 

 boundary of a little recess in the rocks, in which lies the Clifton 

 station. On the northern side of the station rises the somewhat 

 dislocated mass of limestone which forms Observatory Hill, and 

 which, on its southern side, abuts against Millstone Grit and Upper 

 Limestone Shales brought down by the Chfton fault. The whole 

 appearance of the side of the ravine now changes, and in place of 

 vertical limestone cliffs there is a wooded slope. Close to the river, 

 however, the rocks are weU seen in section, and show bands of hard 

 grit characteristic of the Upper Limestone Shales. These bands, 

 passing under the Avon at the point marked a on the map, have 

 hitherto caused a shallowing of the river at this point. Blasting 

 operations are at present in progress by which this obstruction will 

 be removed. Some 370 paces from the fault, solid limestone rises 

 from the river-side (at c), but is, a little further north, cut into by a 

 wooded notch (6) in which runs the path, known as the jS'ew Zigzag, 

 which joins the road near Proctor's Fountain. This notch starts 

 from the point of junction, at the surface of the downs, of the solid 

 Mountain Limestone and the Upper Limestone Shales, which are, 

 however, here unconformably overlain by the dolomitic conglomerate 

 of the Trias. 



The throw of the fault on this Gloucestershire bank I estimate at 

 about 1150 feet vertically, which is some 350 feet greater than that 

 given by Buckland and Conybeare (Trans. Geol. Soc. 2nd series, vol, 

 i. p. 241), and by W. Stoddart (Proceedings of the Bristol 

 Naturalists' Society, new series, vol. i. p. 328). On the Somersetshire 

 bank I make the throw 50 feet less. This difference may be due, 

 in part at least, to the dying-out of the fault in that direction. 

 Taking as a datum-point the intersection of the line of fault and 

 that of high water on the Gloucestershire side, the rocks which have 

 been relatively shifted downwards are Mountain Limestone, about 

 710 feet, and Upper Limestone Shales about 440 feet. If we take 



