246 Messrs. Buckland's and Conybeare's Observations on the 



defile of the Avon to Westbury it is known by the name of Durdham Down ; 

 its strata dip to the south-east at an angle of 30°. The northern part of the 

 zone is called Brinterry Hill : the strata here dip northwards, and are nearly 

 vertical; and the ridge in consequence becomes much narrower than before. 

 The southern extremity of Brinterry Hill, called Gorham's Chair, is separated 

 by a deep and precipitous ravine from the prolongation of the calcareous zone, 

 which receives the name of King's- Weston Down. The hill on which Blaze 

 Castle stands, borders this ravine on the south-west, and being cut off by 

 another defile from King's-Weston Down, presents a remarkable insulated 

 summit. The position is strengthened by ancient entrenchments. The Trim, 

 which rises without the calcareous chain, avails itself of the breach of Blaze 

 Castle to flow through the chain, and thence to pass through the internal area 

 into the Avon. Were a dam of inconsiderable height to be constructed across 

 the ravine, the brook would find its way through the mouth of the broad val- 

 ley, in which it rises, into the marshes of the Severn. 



King's-Weston Down ranges W.S.W, through Lord de Clifford's park, 

 until it terminates at Penpole-point, being bounded by the marshes. The 

 strata are highly elevated, and dip W.N.W. To the west of the road, at the 

 western foot of the down, are some limestone quarries, in which the dip appears 

 to be almost inverted. The whole of this ridge is skirted along its outer flank 

 by the overlying deposits, which we before traced over Durdham Down to the 

 west of the village of Westbury. From Penpole-point the limestone ridge 

 points exactly to Portishead-point, on the south of the confluence of the Avon 

 with the Severn ; and on examination the strata at that point are found to consist 

 of mountain limestone mantling round the central nucleus of old red sandstone. 

 The limestone may be traced from the northern extremity of Portishead-point, 

 ranging in a southerly direction along the summit of a woody hill, to the old 

 Battery commanding Portishead-bay. In the north-eastern angle of the bay 

 the lower strata of the limestone, here approaching to the fault of the Clapton 

 coal-field, are bent into zig-zag curves. On the south-east the old red sand- 

 stone emerges from beneath the limestone, and forms an almost insulated hill 

 between the village of Portishead and the limestone. On the north-west along 

 the coast, particularly near to Portishead-point, a covering of dolomitic con- 

 glomerate greatly conceals the inclined strata, which are displayed, at intervals 

 only, in low cliffs. At low-water, however, we discover the Pennant coal-grit 

 reposing against the calcareous chain, and may trace it nearly all the way from 

 Portishead-point to the fort ; ancj in the cliffs of a small cove, half way between 

 the northern cape and the fort, the crop of a bed of coal is seen, having a roof 

 of the Pennant abounding in vegetable remains. These strata are highly 



