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XVII. Description of the Mineral Bason in the Counties of 
Monmouth , Glamorgan , Brecon , Carmarthen, and Pembroke . 
By Mr. Edward Martin. Communicated by the Right Hon. 
C. F. Greville, F. R. 5 . 
Read May 22, 1806. 
1. The irregular oval line, delineated on the annexed map 
(Plate XIV.) shows nearly the inner edge of a limestone 
bason, in which all the strata of coal and iron ore ( commonly 
called Iron Stone) in South Wales are deposited ; the length 
of this bason is upwards of 100 miles, and the average breadth 
in the counties of Monmouth, Glamorgan, Carmarthen, and 
part of Brecon, is from 18 to 20 miles, and in Pembrokeshire 
only from 3 to 5 miles. 
2. On the north side of a line, that may be drawn in an 
east and west direction, ranging nearly through the middle 
of this bason, all the strata rise gradually northward ; and on 
the south side of this line they rise southward, till they come 
to the surface, except at the east end, which is in the vicinity 
of Pontipool, where they rise eastward. 
3. The depths from the surface to the various strata of 
coal and iron ore depend upon their respective local situations. 
4. The deepest part of the bason is between Neath, in Gla- 
morganshire, and Llanelly, in Carmarthenshire ; the upper- 
most stratum of coal here does not extend a mile in a north 
