interstratified with thin limestones, and from underneath these comes out an assemblage of beds of pure limestone several hundred feet in thickness, forming all the beautiful hill country that spreads from Dovedale to Matlock and thence to Castleton and Buxton. This group of limestone is called the Mountain or Carboniferous Limestone, and the black shale between it and the Millstone grit is known as the Upper Limestone Shale.
The Carboniferous Limestone, either simple as a group of beds of pure limestone or complicated by being more or Jess interstratified with shales and sandstones, extends from Derbyshire to the borders of Scotland with a mean thickness of probably 2,000 feet at least; it re-appears as a simple limestone in North Wales, in Flintshire, and Denbighshire, and in the same form in South Wales and the adjacent parts of England, varying in thickness from 500 to 1,000 feet. The Coal-measures of the South Welsh coal-field are certainly 7,000 feet, even if they are not in some places 12,000 feet, in aggregate thickness, and have a thick group of sandstone beds at the base, which may be called the Millstone Grit, as well as another higher up, known as Pennant Grit. But from underneath the Carboniferous Limestone, which forms the thick enamelled lining, as it were, of the basins of the South Welsh and Forest of Dean coal-fields, there rises on all sides a great group of red and brown sandstones and red marls, known as the Old Red Sandstone. This Old Red Sandstone forms whole mountains of 2,700 feet in altitude (as the Vans of Brecon), and cannot in some places have a less aggregate thickness than about 10,000 feet.
Now these vast formations of Old Red Sandstone and Carboniferous limestone (to say nothing of the lower part of the Coal-measure series or Millstone grit) are altogether absent in South Staffordshire, neither is there the slightest reason for supposing that any part of them ever existed in that district. For not only are they absent in South Staffordshire, but there is a band of country running E. and W. across England from Leicestershire, through Warwickshire, South Staffordshire, North Shropshire, into Montgomeryshire, along which they are equally deficient.
In Leicestershire, the Carboniferous limestone, thinning out
