i] 
uy 
} 
Parr II. Seor. iv. §2.] CARBONIFEROUS. 737 
‘subdivisions which can be recognized, with modifications, in all parts of 
the country : 
(Red and grey sandstones, clays, and sometimes breccias, with 
occasional seams and streaks of coal and Spirorbis limestone 
(Cythere inflata, Spirorbis carbonarius). 
Middle or chief coal-bearing series of yellow sandstones, clays, 
Coal-measures{ and shales, with numerous workable coals (Anthracosia, Anthra- 
comya, Beyrichia, Estheria, Sptrorbis, &c.). 
Gannister beds, flagstones, shales, and thin coals, with hard ‘sili- 
ceous (gannister) pavements (Orthoceras, Goniatites, Posidonia, 
Aviculopecten, Lingula, &e.). 
MillstoneGrit Grits, flagstones, and shales, with thin seams of coal. 
(Yoredale group of shales and grits passing down into dark 
| shales and limestones (Goniatites, Aviculopecten, Posidonomya, 
Lingula, Discina, &c.). 
Thick (Scaur or Main) limestone in south and centre of Eng- 
land and Ireland, passing northwards into sandstones, shales, 
Carbonifarcusl and coals (abundant corals, polyzoans, brachiopods, lamelli- 
Limestone? branchs, &c.). 
series Lower Limestone Shale of south and centre of England (marine 
fossils like those of overlying limestone). The Calciferous 
Sandstone group of Scotland (marine, estuarine, and terrestrial 
organisms), represents the Lower Limestone Shale and lower 
part of the English Mountain Limestone, and graduates down- 
\ ward insensibly into the Upper Old Red Sandstone. 
Carboniferous Limestone series and local equivalents —In the south-west 
of England, and in South Wales, the Carboniferous system passes down 
conformably into the Old Red Sandstone. The passage beds consist of 
yellow, green, and reddish sandstones, green, grey, red, blue, and 
variegated marls and shales, sometimes full of terrestrial plants. They 
are well exposed on the Pembrokeshire coasts, marine fossils being there 
found even among the argillaceous beds at the top of the Red Sandstone 
series. They occur with a thickness of about 500 feet in the gorge of 
the Avon near Bristol, but show less than half that depth about the 
Forest of Dean. At their base there les a bone-bed containing 
abundant palatal teeth. Not far above this horizon plant-bearing strata 
are found. Hence these rocks bring before us a mingling of terrestrial 
and marine conditions. In Yorkshire, near Lowther Castle, Brough, and 
in Ravenstonedale, alternations of red sandstones, shales, and clays, 
containing Stigmaria and other plants, occur in the lower part of the 
Carboniferous Limestone. Along the eastern edge of the Silurian hills of 
the Lake district, what is commonly regarded as the Old Red Sandstone 
_ appears here and there, and passes up through a succession of red and 
grey sandstones, and green and red shales and marls with plants, into the 
base of the Carboniferous Limestone. It is highly probable, however, that 
these red strata occur on many successive horizons; so that they should 
be regarded not as marking any particular period, so much as indicating 
the recurrence of certain peculiar littoral conditions of deposit (p. 717). 
In the south and south-west of England, and in South Wales, the base 
of the Carboniferous system consists of certain dark shales known as 
Lower Limestone Shale, in which a few characteristic fossils of the 
Carboniferous Limestone occur. These basement beds vary up to rather 
more than 400 feet in thickness. They are overlaid conformably by the 
thick mass of limestone, which in Britain and Belgium forms a most 
characteristic member of the. Carboniferous system. 
On referring to a geological map of England it will be seen that from 
o.B 
