South-western Coal District of England. 297 



as reposing" on the mountain limestone on the ascent of the new road from 

 St. Vincents rock to Durdham down. Its appearance between this point and 

 Redland, to the south-east of Durdham down^ and in the vale of Westbury, 

 has been fully described by Dr. Bright. Further to the north it is seen at 

 Henbury and Almonsbury, and thence along the exterior base of the calca- 

 reous boundary of the coal-basin, by Thornbury and Tortworth to Wickwar. 

 Within the coal-basin it appears on the western side, emerging from beneath 

 beds of lias from Bristol to Titherington, and on the eastern side, reposing 

 on the inclined strata at Wick rocks. 



The conglomerate is found pretty extensively along the channel and on the 

 left bank of the Severn, to the distance of 2 or 3 miles on either side of the 

 mouth of the Wye. At the New Passage beds of conglomerate and dolo- 

 mitic sandstone occupy the low shores on both sides of the river, and also 

 compose those extensive flats called the Welsh and English shores. The 

 largest of these, which becomes uncovered at half-ebb, is nearly 3 miles long 

 and 1 broad. At low-water it forms, together with two similar flats, one to 

 the north, the other to the south of it, a bar almost entirely across the Severn. 

 These shoals are intersected by channels of dangerous navigation, through 

 which the tides rush with enormous velocity. Their northern portion is 

 composed of conglomerate, their southern of a yellow dolomitic sandstone, 

 forming a link between common yellow dolomite and the newer red sand- 

 stone. 



At Chapel rock, the promontory close to the Old Passage-house at the mouth 

 of the Wye, an interesting section is displayed of the junction of the conglo- 

 merate with mountain limestone. In the low cliff, which extends half a mile 

 to the north of the Passage-house, the conglomerate passes into a homoge- 

 neous rock of dolomite, which, at the lofty precipice of Annards cliff, is 

 covered by superstrata of red marl and lias. At Tidenham the conglomerate 

 reposes on the basset edges of mountain limestone ; at Wollaston upon old 

 red sandstone. Small flats and shoals, composed of the conglomerate and 

 dolomitic sandstone, occur in the bed of the river for 4 or 5 miles above the 

 Passage-house ; these rocks have of late been taken in great quantities from 

 the river near Tidenham, for building the foundation of the new bridge at 

 Chepstow. 



§ 2. That member of the newer red sandstone formation, which imme- 

 diately reposes on the conglomerate, consists of a friable red, white, or yel- 

 lowish sandstone, which sometimes, where it passes into the conglomerate, is 

 abundantly charged with dolomite. This sandstone is seldom hard, tough, 

 and fissile enough for tile- or flag-stone. It is usually characterized by the 



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