The Severn. 503 



the larger river valleys, there is a great deal that is 

 difficult to account for. One thing is certain, that 

 before the Glacial epoch the greater contours of the 

 country were much the same as they are now. The 

 mountains of Scotland, Wales, and of Cumberland, 

 and the great Pennine chain, existed then, somewhat 

 different in outline, and yet the same essentially ; the 

 central plains of England were plains then, and the 

 escarpments of the Chalk and Oolites existed before the 

 Glacial period. All that the ice did was to modify the 

 surface by degradation, to smooth its asperities by round- 

 ing and polishing them, to deepen valleys where glaciers 

 flowed, and to scatter quantities of moraine-detritus, 

 partly in the shape of boulder-clay and of marine boulder 

 beds, and sands and gravels, over the plains that form 

 the east of England, and the Lias and New Ked Sand- 

 stone in the middle. 



If we examine the valley of the Severn from Bristol 

 northwards through Coalbrook Dale, we find that for 

 a large part of its course the river runs down a broad 

 valley, between the old Palaeozoic hills and the escarp- 

 ment formed by the tableland of the Cotswold Hills 

 which are highest in the neighbourhood of Cheltenham. 

 That valley certainly existed before the Glacial epoch, 

 because we find boulders and boulder-drift far down 

 towards Tewkesbury ; and therefore, I believe that 

 before the Glacial epoch this part of the Severn ran 

 very much in the same course that it does at present. 

 During part of the Glacial epoch the country sank 

 beneath the sea, and Plinlimmon itself, where the 

 river rises, was perhaps buried in part beneath the 

 waters. When the country again emerged, the old sys- 

 tem of river-drainage in that area was resumed ; and 

 the Severn, following in the main its old course, cut a 



