South-western Coal District of England. 251 



and Mells. Its greatest breadth is about 2^ miles, in the meridian of Holcombe. 

 On the south the coal measures occasionally cross the Nettlebridge stream, to 

 rest against the calcareous chain of the Mendips : on the north the inferior 

 oolite comes in contact with them, along a somewhat elevated table-land from 

 Holcombe to Mells. At either extremit}^ the dolomitic conglomerate closes 

 over them, on the east forming cliffs overhanging the river from Vobster to 

 Mells-park, on the west crowning with precipitous scars the ravine through 

 which the same river issues between Stratton-on-the-fosse and Ashwick. 



The Eastern Coal-tract is laid open in the Golden Valley, or Vale of the 

 Buoyd, at Wick and Upton, and in the course of the brook falling into the 

 Buoyd from Tracey-park ; and at Newton St. Leo, on the left bank of the Avon 

 below Bath, the coal-measures are again displayed, dipping towards the inte- 

 rior of the basin. 



The denudations of Wick and Tracey-park show the millstone grit incum- 

 bent on the mountain limestone ; and several coal-seams are laid open and 

 worked at Upton and Newton. The eastern tract is encircled by dolomitic 

 conglomerate, newer red sandstone and lias. 



The Western Coal-tract lies at the south-eastern foot of Leigh Down near 

 Bristol. The strata bordering on the millstone-grit are the only coal-measures 

 that are exposed on the surface ; and we have already traced their longitudinal 

 extent from Kencot-cross to Rownham-ferry and the upper part of Bristol in 

 treating of Leigh Down and the defile of the Avon. These coal-measures are 

 bounded on the east by overlying beds of red marl, which form the upper 

 strata in the shafts of all the coal-pits between Long-Ashton and Bedminster. 



The coal-field of Nailsea may be regarded as a continuation of this western 

 tract. The fragments of strata of newer red sandstone that hang on the slopes 

 of Leigh and Broadfield Downs to the north-west and south-east of this basin, 

 show that the exposure of the coal-measures is here the result of denudation. 

 The subsided coal-tract of Clapton has already been noticed. 



In order to obtain a connected view of the distribution of the coal-measures 

 throughout the basin, it is necessary to observe that, by a great undulation in 

 the strata*, the lowest of the coal-measures are thrown up at very high incli- 

 nations into a saddle-shaped ridge, extending through Kingswood across the 

 basin from east to west, and subdividing it into two partial troughs ; — one on 

 the north of the ridge, having its centre in Coal-pit Heath, to the east of the 

 Engine-pit at Bittervvell, and extending to the limestone at Cromehall ; the 



* The elevation of this ridge and the faults of St. Vincent's Rock and of the Clapton coal-field 

 are very possibly the result of the same convulsion ; since the disturbances appear on the conti. 

 nuation of nearly the same line. 



