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



the valleys eastwards to the neighbourhood of Llantrissant. These deposits are 

 protruded within the g-reat Glamorganshire coal-basin, reposing partly on the 

 inner side of its southern calcareous frontier, and partly on the basset-edges of 

 the coal-measures within the basin. Near Bridgend the lias prevails ; further 

 east the dolomitic conglomerate, beneath which, in the parish of Llanharran, 

 coal is worked. To the west also of Bridgend we find the conglomerate ; 

 near Pyle, resting on the coal-measures ; and near the sea-shore, at Kenfig, on 

 the east side of the bay of Swansea, on mountain limestone. 



Before we close this general account of the south-western coal-district of 

 England, we are desirous of noticing its resemblance in geological structure 

 and picturesque features to the country extending along the Meuse between 

 Namur and Liege. There also we are presented with coal-basins encircled 

 by mountain limestone, and based upon old red sandstone, which latter is dis- 

 played at Huy. These rocks are all highly inclined, and are covered by over- 

 lying formations. The defiles of the Sambre and the Meuse present an exact 

 counterpart of those of the Avon and the Wye. For a most able and accurate 

 description of this district, we beg to refer to a paper by Mons. Omalius 

 D'Halloy, published in the 24th volume of the Journal des Mines. 



We shall now proceed to describe in detail the two coal-basins : 1st, that of 

 Bristol ; 2dly, that of the Forest of Dean, as far as relates to the inclined 

 strata of which the basins are composed. We shall afterwards treat, in a 

 separate chapter, of the horizontal strata of the entire district. 



Chapter II.— ON THE COAL-BASIN OF BRISTOL. 



We shall first give the character of the inclined formations that compose 

 the frontier of this coal-field ; we shall next trace these formations in their 

 joint progress round the frontier, and finally treat of the coal-measures occur- 

 ring within the basin. No further mention will here be made of the overlying 

 horizontal strata, than is necessary to explain the local phenomena connected 

 with the appearance of the older rocks. 



On the Rocks composing the Frontier of the Basin. 



1. Grey-wacke. 



This rock does not occur on the frontier of the Bristol coal-basin. It is 

 found at some distance to the south of the area at the Quantock hills in So- 

 mersetshire. 



2. Transition limestone. 



We can scarcely regard the transition limestone as properly belonging to 



