288 
SILURIA. 
[Chap. XII. 
the map annexed to this work, the Carboniferous rocks are most fully developed 
in the great South- Welsh basin of Carmarthen, Glamorgan, and Monmouth, 
where an ascending order from the summit of the Old Red Sandstone, through 
shale, limestone, sandstone, and grits, upwards into an enormously thick coal- 
field, is clearly exhibited in lofty escarpments, particularly around the northern, 
eastern, and western edges of that grand basin. The same succession, though on 
a minor scale, is seen around the smaller basin of the Forest of Dean, and again, 
with certain mineral variations and an expansion of the lower shale, in the 
county of Pembroke. 
Towards the north, the calcareous and lower members of the series are more 
developed, as observed in the Oswestry coal-field, and in Shropshire and Flint- 
shire, than in most parts of South Wales. This expansion of the inferior zone 
of these rocks towards the north becomes still more striking in the range of the 
strata from Derbyshire into Yorkshire and Northumberland, and particularly in 
the great central Carboniferous trough of Scotland. 
In some of the coal-tracts within or adjacent to the Silurian region, as at 
Dudley and Wolverhampton, the whole base and central mass of the group, or 
the Carboniferous Limestone and the Millstone-grit, are wanting, the upper 
productive measures there reposing at once on Silurian rocks (see woodcut, Sil. 
Syst. p. 79). In those districts, however, and along the banks of the Severn, 
good evidences are obtained of the relations of the coal-strata to the overlying 
red deposits now termed Permian, of which hereafter. 
When viewed, therefore, as a whole, particularly in the region of the coloured 
map, the Carboniferous group (b to g) may be stated to lie between the sub- 
jacent Old Red, a, and the red overlying Permian, h, thus : — 
GrENERAL KELATIONS OP THE CARBONIFEROUS ROCKS IN THE CENTRAL AND SOUTHERN 
Parts op England. (See Sil. Syst. p. 79.) 
a. Upper beds of the Old Red Sandstone (Devonian), b. Sandstone and Lower 
limestone-shale, c. Carboniferous Limestone, d. Millstone-grit. e. Coal a nd iron- 
stone. /. Mam Coal-measures, g. Upper coal with a peculiar limestone, h. Red 
sandstone (base of the Permian rocks, here represented as conformable to the Coal, 
but usually transgressive.) 
As it is impracticable to treat in detail of the various component parts of the 
strictly Carboniferous deposits in different British districts, a slight sketch only 
of some of their peculiarities is attempted in the following pages. 
Separated from the upper band of the Old Red Sandstone by beds of dark and 
party-coloured shale (6 of the section), the Carboniferous or Mountain Lime- 
stone, c, is the dominant rock of the lower division in the South of England. 
The massive nature of these calcareous strata and their vast development in 
Derbyshire, Yorkshire, and Northumberland have long been well known to 
geologists. Of late years attention has been directed to the still greater expan- 
sion of the middle and lower strata in Scotland, where so many beds of excellent 
coal and much valuable iron-ore are interstratified with various bands of the 
Carboniferous Limestone, of which hereafter. 
Within the region, however, of the annexed map, this Carboniferous Lime- 
stone (2000 feet thick) is of simple and uniform structure, and contains no 
