138 ORIGIN OF SCENERY OF BRITAIN 



In the former, the greater prominence of the high 

 grounds arises primarily from the existence of masses 

 of volcanic rocks, which from their superior durability 

 have been better able to withstand the progress ot 

 degradation. In the latter the heights are merely 

 the remaining fragments of a once continuous table- 

 land of Old Red Sandstone. 



The Lake District presents a remarkable radiation 

 of valleys from a central mass ot high ground. It 

 might be supposed that these valleys have been deter- 

 mined by some radiating system of fractures in the 

 rocks ; but an examination of the area shows them 

 to be singularly independent of geological structure. 

 So much do they disregard the strike, alternations, 

 and dislocations of the rocks among which they lie 

 that the conclusion is forced upon us that they have 

 been determined by some cause independent of that 

 structure, and before the rocks now visible were 

 exposed at or could affect the surface. This could 

 only have happened by the spread of a deep cover of 

 later rocks over the site of the Lake mountains. The 

 former presence of such a cover, which is demanded 

 for the explanation of the valleys, can be inferred 

 from other evidence. The Carboniferous Limestone 

 on the flanks of the Lake District is so thick that it 

 must have spread nearly or entirely over the site of 

 the mountains. But it was overlain by the Millstone 

 Grit and Coal-measures, so that the whole area was 

 probably buried under several thousand feet of Car- 

 boniferous strata which stretched continuously across 

 what is now the north of England. At the time of 

 the formation of the anticlinal fold of the Pennine 



