22 Original Articles. [Jan., 



in a regularly curved line, but as it were in a series of promontories 

 jutting northward from the mainland, which we may call " The Barrier." 

 (See map.) The northern margin appears to have been irregular in 

 outline, frequently indented with bays, in which tracts of coal-measures 

 were formed, such as the coal-fields of the Forest of Wyre and of War- 

 wickshire. In some places only the very uppermost beds were formed, 

 the land not having been submerged till towards the close of the 

 period. This barrier of land is shown on the accompanying map, 

 crossing the centre of England in a narrow and indented band. 



The southern margin of the barrier can only be very roughly 

 determined. The northern limits of the great coal-tract of South 

 Wales must have extended far beyond its present bounds, and the 

 same may be said in a lesser degree of the coal-fields of the Forest of 

 Dean and Somersetshire. It is therefore probable that the greater 

 part of the slaty region of South Wales was once covered by beds of 

 coal, and that along the valley of the Severn the barrier was extremely 

 narrow at the close of the Carboniferous period. Mr. Godwin- Austen 

 has shown the probability that a band of coal-measures originally 

 stretched across the south of England from Somersetshire into France 

 and Belgium. That this band did not stretch far to the north of the 

 estuary of the Thames there is reason for concluding, from the results 

 of the boring experiments at Harwich. Here cleaved slaty rock of 

 Silurian or Cambrian age was reached beneath the Cretaceous beds, 

 without a trace of the intervening formations. We may well believe 

 that this slaty rock forms but a part of the tract of ancient land 

 which stretches under the Eastern Counties, and of which the 

 rocks of Charnwood Forest formed the margin towards the north- 

 west. 



From the above observations it will be seen that the coal-measures 

 of England formed originally two separate areas, one lying to the 

 north, the other to the south, of The Barrier, as indicated in the map. 

 These have subsequently been broken up and formed into separate 

 " coal-fields," which may be thus arranged : — 



Coal-fields North of The Barrier. — North Wales, Forest of Wyre, 

 North Staffordshire, South Staffordshire, Warwickshire, Leicestershire, 

 Derbyshire, and Yorkshire, Northumberland, Durham, and Cumber- 

 land. 



Coal-fields South of The Barrier. — South Wales, Somersetshire, 

 Forest of Dean, and supposed band along the Thames valley. 



The coal-fields of the central valley of Scotland were probably 

 connected with those of the north of England, round the eastern coast, 

 but space does not admit of further reference to them on this 

 occasion. 



2. The Distribution of the Carboniferous Strata themselves. 



There are three main causes tending to increase or lessen the 

 thickness of any group of strata at special points of its area during 

 deposition. First, the sediment may be deposited over a deep-sea bed, 

 or a shelving shore ; secondly, the sediment deposited may be near or 



