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, Glamorganshire, 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 neighbourhoods of Llanelly, Penllergare, and Lloughor. The middle, or Pennant rock series attains its greatest development at Swansea, where it is 3,000 feet in thickness, and presents several important beds of coal; but in the eastern portion of this field they are very much thinner, and contain little or no workable coal. The summits of the hills which bound the parallel valleys on the north crop, are nearly all capped with this grit, which adds much to the peculiar configuration of the country, and gives a certain identity of outline to its general features.