274 Palao-Geological and Geographical Maps of the British Islands. 
without the intervention of the Lower Carboniferous beds ; at the same time, over 
the region lying along the borders of France and Belgium, the waters of the Lower 
Carboniferous sea prevailed, and the limestone formation is grandly represented. 
Puatre XXVIII. 
Upper Carboniferous Period. 
The Upper Carboniferous strata are the chief depositories of coal in the British 
Isles and the adjoining continental districts. They are separated from the Lower 
Carboniferous strata represented in Plate XXVII., by the middle division of the 
system, including the following in descending order :—* 
Middle f 1. The Gannister Beds, or Lower Coal-measures. 
Carboniferous J 2. The Millstone Grit, or Flagstone Series of Ireland. 
Series. 3. The Yoredale Beds, or Upper Shale Series of Ireland. 
All the above are essentially of marine origin ; those of the Upper Carboniferous 
series are of estuarine or lacustrine origin, with occasional marine bands at distant 
intervals. 
Nature of the Upper Carboniferous Beds—The strata included under this head 
consist of two divisions; the Lower, or Middle Coal-measures, consisting of yellow 
and gray sandstones, blue and black clays and shales, bands of coal and ironstone. 
They contain plants, bivalves (Anthracosia), and fish remains. The occasional 
marine bands are to be recognised by the fossils. The Upper Coal-measures consist 
of reddish and purple sandstones, red and gray clays and shales, thin bands of coal, 
ironstone and limestone, with Spirorbis carbonarius, and fish. These two divisions 
combined attain, in Lancashire, a thickness of 5,000 to 6,000 feet, but thin away 
rapidly in the direction of Leicestershire and Warwickshire. In Belgium these 
beds are also of great thickness, though the uppermost have generally been denuded 
away. 
Distribution of Strata.—The Coal-measures of England and Scotland were origi- 
nally distributed in two, or possibly three, large sheets, lymg to the north and 
south of a central ridge, ranging from North Wales through Shropshire eastwards.+ 
This I have called the central barrier (Fig. 2). It is uncertain whether it was 
not connected with the ridge of the Wicklow Mountains across the Irish Channel. 
This old ridge may be a prolongation of a land area stretching southwards from 
Scandinavia, and it existed in wider dimensions during the Lower Carboniferous 
period.{ It is also uncertain whether the coal-measures of Scotland stretched 
* This is a classification proposed in my paper ‘On the Upper Limits of the essentially marine beds of 
the Carboniferous group, &e.” Quart. Journ., Geol. Soc., Vol. XX XII., pp. 613-651. It has not been 
considered necessary to prepare a plate of this division, which would be intermediate in its arrangements 
between Plates XX VII. and XXVIII. 
{ The evidences of this ridge cannot here be discussed, but the reader is referred to the Geological 
Survey Memoir, “ On the Triassic and Permian Rocks of the Central Counties of England ;” also to the 
“ Ooalfields of Great Britain.” 4th edition, p. 520. 
+ Compare Fig. 2, in Plate XX VIIL., with that in Plate XX VII. 
