South-western Coal District of England. 239 



dipping- southward, in the same direction as the limestone, and apparently 

 beneath it. Rocks of this coal-grit skirt the northern mouth of the ravine on 

 both sides, where it opens into a marshy plain, extending between the prin- 

 cipal and divergent ridges of limestone. [Plate XXXII. fig. 3. C] On the 

 western side of the ravine the mass of coal-grit rises up towards the limestone 

 of Walton Down, upon the flank of which it evidently reposes in the manner 

 shown in the sectional profile, Plate and figure last quoted. On neither side of 

 the ravine is the fault marked by any irregularity of surface, the line of its 

 occurrence being concealed by grassy slopes. To the east of the ravine the 

 coal-grit occupies the escarpment of Leigh Down for the space of 4 miles, as 

 far as the coal-mines of Clapton, beyond which it is concealed beneath the 

 marshy plain. In this interval the stratification of the coal-measures is very 

 much disturbed, but their general dip is southerly, towards the fault. 



The point in the escarpment where the fault is arrested in its progress 

 towards the east, and begins to run northwards, is about 1 mile east of the 

 village of Clapton, about halfway between two conspicuous villas, Naish-house 

 and Charlton-house, situated on the brow of the ridge. A line of moist 

 springy ground, and a deep swallet-hole near the summit of the escarpment, 

 indicate the exact position of the fault, which crosses the road from Naish- 

 house to Portbury at the distance of about half a mile from the point where the 

 road branches off" to Portishead. The coal-grit here abuts against the old red 

 sandstone, which appears in its regular place beneath the mountain limestone 

 on the eastern side of the fault. From this point the fault is probably con- 

 tinued in a northerly direction, beneath the marshy plain, to Portishead-bay 

 on the Bristol Channel. 



Walton Down, formed by the subsided mass of limestone, is divided along 

 its summit, by a longitudinal valley, into two parallel crests, the southern con- 

 sisting of mountain limestone, the northern of old red sandstone; an interme- 

 diate valley marking the shale that divides the two formations. This valley is 

 occasionally flanked by precipitous rocks, particularly above the village of 

 Walton, where a transverse valley intersects the ridge. The strata uniformly 

 dip to the south-east, or towards the Clapton coal-field, at an angle of about 40°. 

 The continuation of the limestone ridge is concealed, a little to the north of 

 Weston-in-Gordano, by overlying masses of dolomitic conglomerate ; but the 

 ridge of sandstone extends about a mile further, until it reaches the southern 

 extremity of Portishead-bay, where it terminates against the fault. The fault 

 is indicated by contortions in the strata on the eastern side of the bay. The 

 whole coast, from the bay of Clevedon to that of Portishead, is skirted by low 

 cliffs of dolomitic conglomerate, which here forms a talus at the base of the 



VOL. VI. 2 I 



