THE GEOLOGIST 



DECEMBEE, 1858. 



ON THE MARINE SHELLS OE THE SOUTH WALES COAL- 

 BASIN. 

 By G. P. Bevan, M.D. F.G.S. 



{Read before the British Association, at Leeds, September, 1858.) 



Until of late years, the South Wales coal-field was considered to be very 

 barren in fossils, and those few which were known were all thought to 

 be of land or fresh-water origin. During my endeavours to work out 

 the geology of this district for the last four years, I have, however, 

 discovered sufficient to redeem it from such a reproach, and to prove 

 that not only are there fossils, but that these are even in great numbers 

 and variety. 



The basin, which occupies portions of Monmouthshire, Glamorgan- 

 shire, Breconshire, and Carmarthenshire, may be separated into two great 

 divisions, both geologically and chemically. The first is the division 

 into upper and lower coal-measures, separated by a thick mass of 

 Pennant sandstone, or grit, while the chemical is the division into 

 bituminous and anthracitic coals. The upper measures are principally 

 found in Glamorgan and Carmarthenshires, the only coal-seam of that 

 series in Monmouthshire, being known as the Mynyddswlyn vein. 

 Westward of the Taff, however, which is the boundary between the 

 two countries, the upper measures appear more frequently, and in 

 more regular sequence; while, in Carmarthenshire, we obtain a 

 complete section of these beds down to the Pennant rock, in the neigh- 



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