A HISTORY OF WARWICKSHIRE 



bournes, south-west of Atherstone, this rests on the edges of the 

 Stockingford Shales, including two sheets of diorite. As these latter 

 have not affected the Coal Measures they must have been intruded in 

 pre-Coalmeasure times ; and Professor Watts seems disposed by general 

 considerations to think that the intrusions are of immediately post- 

 Cambrian age. 



CARBONIFEROUS 



Between the period of the Cambrian rocks of Nuneaton and that of 

 the Coal Measures which overlie them there is a great gap, unfilled in 

 our district by any known formation. We know that during this 

 enormous interval thousands of feet of muds and volcanic ashes the 

 Ordovician rocks were deposited over what is now Wales and the west 

 and north of England ; but none of these is known to occur eastwards 

 of the Malvern district, and it therefore seems probable that what is 

 now central England was occupied by an extensive island formed of 

 the upraised Cambrian sediments which stood up above the waters of 

 the Ordovician Sea. This land tract however slowly sank and contracted 

 in area, for the Silurian deposits, which immediately followed the 

 Ordovician, extend farther eastwards over the subsiding area ; but the 

 higher parts of the district seem still to have kept their heads above 

 water during this and the succeeding Devonian period, for these vast 

 accumulations of mudstones, limestones and red sandstones are unrepre- 

 sented in our county ; and it is practically certain that parts of the old 

 island were still in existence as such while the Carboniferous or Moun- 

 tain Limestone and Millstone Grit of Derbyshire and Yorkshire, Wales 

 and Ireland were accumulating. This Lower Carboniferous sea lay to 

 the north, east, and south of our area ; we even obtain a glimpse of its 

 coast-line at Grace Dieu in Charnwood Forest, but nearer than that it 

 appears not to have approached. By the time that the higher ridges 

 of Cambrian rocks at the north of the county had sunk to the water 

 level the physical aspect of the midlands had changed. The sea had 

 become shallowed, land-locked areas developed, and ultimately com- 

 munication with the open ocean was cut off. The district became 

 converted into ' an immense delta or fenland, including many large 

 lagoons and wide channels, surrounded by swamps which were never 

 much above the level of the sea.' * These delta deposits are our Coal 

 Measures. 



Thus the Millstone Grit and Carboniferous Limestone are alike 

 unrepresented, and the only Carboniferous rocks present on the surface 

 in the county are the Coal Measures of the Warwickshire coalfield. 



The Coal Measures form a narrow belt of country extending for 

 about fifteen miles from Bedworth on the south-east, past Nuneaton and 

 Atherstone, to Tamworth on the north-west, where the outcrop attains 

 its greatest breadth of about four miles. They rest unconformably on 

 the Cambrian, and are succeeded with every appearance of perfect 



1 A. J. Jukes-Browne, The Building of the British Isles, ed. 2 (1892), p. 133. 



10 



