South-western Coal District of England. 24/7 



elevated^andoccasionally verticaloreven reversed in their dip. [See PI. XXXII. 

 fig-. 3.] These coal-measures seem to indicate the existence of a yet unexplored 

 coal-basin in the valley of the Severn between the calcareous chain now treated 

 of, and that of Monmouthshire. The limestone rock, called the Denny, in the 

 mid-channel opposite the mouth of the Avon, is situated exactly in the line 

 which would connect the two calcareous chains. The strata, however, are 

 nearly parallel to those at Portishead, dipping- N. W. at an angle of 60 . 



We now proceed to describe the third calcareous ridge of the western fron- 

 tier. It will be seen in the Map that the lias, skirting round Brinterry-hill, 

 overlies the northern prolongation of Durdham Down. A continuity of ele- 

 vation is thus maintained through an interval of more than two miles between 

 Henbury and Almondsbury, over thedepressed beds of limestone,which are seen 

 on either side dipping towards one another along- the line of submersion be- 

 neath the superstrata. The limestone re-emerges from beneath the red marl 

 and lias in the hillock upon which stands Over House, and thence it stretches 

 in a north-north-easterly direction. The lias, however, continues to overtop 

 the limestone as far as the brow which gives name to the ancient mansion of 

 Knoll. This is crowned by a cap of lias, cliffs of mountain limestone sweeping 

 round its base. From this point the limestone passes through Almondsbury^ 

 where it dips to the S.E., and is nearly vertical, and thence forms a distinct range 

 along- which the road from Bristol to Gloucester proceeds. Near the inn 

 called Alveston Ship, this range inosculates with Alveston Down, a part of the 

 calcareous zone which protrudes westwards, and appears to mantle round a 

 nucleus of old red sandstone. A gritty sandstone, apparently of that formation, 

 may be observed on the north of the common marked by the windmill above 

 Olveston, and the old red sandstone undoubtedly appears at the northern foot 

 of this range close to the hamlet of Kingston ; and though difficult to trace, 

 owing to inclosures and the inaccuracy of the Maps of the district, it is probably 

 continuous with the sandstone that occurs at the point first mentioned. On the 

 west the limestone dips from this central axis of sandstone towards the villages 

 of Olveston and Elberton, and on the south-east towards Tockington. The 

 brow of the hill towards Kingston has a hanging mass of lias and red marl 

 abutting against mountain limestone ; and two or three detached summits be- 

 tween Littleton and Elberton, on the principal of which is an extensive Roman 

 camp, consisting of these overlying formations. 



The chain of Olveston Down is separated from the Severn by an interval of 

 more than 2 miles, in which the overlying deposits prevail. The mountain 

 limestone, however, may be seen in the bed of the Severn at the base of Aust 

 Cliff during low water, bearing across the river in a westerly direction for a 



VOL. VI. 2 K. 



