88 Mr. F. FoiiSTun's Observations on the South Welsh Coal Basin. 



about 935 square miles. This extensive field is distributed among the 

 five counties through which it ranges, as follows, viz. : 



Miles. 



Pembrokeshire, 80 



Carmarthenshire, 133 



Brecknockshire, 68 



Glamorganshire, 569 



Monmouthshire, 85 



Total 935 Sq. Mites. 



THE GENERAL DIP OR INCLINATION OF THE STRATA 



In this district will be best understood by an examination of the 

 section (PI. XL). It may, however, be remarked here, that the 

 strata, cropping out on the north or inland side, dip, with occasional 

 undulations, to the southward, across about three-fifths of its width, 

 when the direction of their dip is reversed, and they rise to the southward, 

 through the remaining two-fifths of the width of the Basin ; hence the 

 greater inclination of the beds on the south, than on the north side of 

 the trough.* The angle of inclination varies from 5° to 46°, or 

 from 6 inches to 6 feet per fathom, being through its whole extent 

 greatest near the edges, and least near the centre of the Coal-field ; and, 

 as regards its different parts, the strata are much flatter in the wider or 

 eastern portion of the Basin, than in the western, or more contracted 

 part. Near its eastern extremity, indeed, the dip is altered, the 

 strata rising gently in that direction, and but for the occurrence of 

 a number of Dykes, traversing the district from north to south, and 

 generally throwing the strata down to the eastward, it is probable that 

 their extent would have been much less considerable. It is, in all 

 likelihood, from the same cause that the bottom of the Basin in Pem- 

 brokeshire, on the west or upcast side of these Dykes, approaches so 

 near the surface. Here, according to Mr. Martin, the thickness of 



• The whole of the Coal strata in Pembrokeshire, as well as the underlying mass of 

 Limestone, are so much contorted (apparently by their contiguity to the Trap and Transi- 

 tion rocks) as to form, in some degree, an exception to the general inclination here given. 



