. Mr, F. Forster's Observations on the South Welsh Coal Basin. 89 



the strata above the Limestone, does not exceed 100 fathoms, while 

 he calculates their depth, in Carmarthenshire, to be 600 or 700. My 

 observations have led me to conclude, that their depth, at this latter 

 point, will considerably exceed that amount, and will in fact approach 

 very nearly to 1000 fathoms. 



The basis of Old Red Sandstone, on which this Coal-field reposes, rises 

 in one part to the great elevation of 2862 feet, forming the bold moun- 

 tains called the Beacons of Brecon. The Coal Measures themselves, 

 along their northern or inland range, also attain a considerable eleva- 

 tion ; Mynydd Mawr in Carmarthenshire, as will be seen by a reference 

 to the section, is about 1000 feet in height, and Craig-ar-Avon, near 

 Merthyr Tydville in Glamorganshire, is 1859 feet in height. The 

 southern edge of the Basin is generally much less elevated, but Mar- 

 gam Downs, on the East side of Swansea Bay, are 1100 feet high. The 

 whole of the district is intersected by deep vallies, extending across it 

 from north to south, which, together with the elevation of the strata, 

 afford unusual facilities for draining and working by level immense 

 tracts of Coal and Iron Stone ; advantages, from which the great Iron 

 smelters of Wales are enabled to obtain their materials, at a rate un- 

 equalled for cheapness in other parts of the kingdom. The great north 

 and south vallies intersecting this district are ten in number, viz. : 



1st. and 2d. The Valleys formed by the Cliddy and St. Lawrence 

 Rivers, which extending inland from Milford Haven, completely in- 

 tersect the Pembrokeshire part of the district about its centre. 



3d. The opening or breach formed by Carmarthen Bay. 



4th. The Vale of the Llwchor River extending with its branches 

 across the Basin, from Pembrey nearly to Llandibie on its northern edge, 

 rising 150 feet in that distance, 100 feet of which takes place in the last 

 three miles. 



5th. The Vale of the River Tawe, extending inland from Swansea to 

 the North Limestone Hills, at Hennoyadd, and accompanied by a canal 

 nearly to that point 



6th. The Vale of Neath, through which flows the river of that name, 

 extending from Neath to Dynas Rock, and accompanied by a canal to 



VOL. I. N 



