562 T. Mellard Reade — British Geology. 



juxtaposition to tlie less disturbed Carboniferous, tlie latter being 

 let down by an enormous fault of unascertained throw. Again, in 

 Herefordshire and South Wales we see a considerable extent of 

 horizontal Old Red, which, as it approaches the Silurian mountain 

 folds, becomes itself conformably inclined. 



Not less interesting and instructive are the dome-like structures, 

 such as the celebrated dissected Silurian dome of Woolhope, which 

 rises in successive rings through the Old Red, which it carries on 

 its flanks. May Hill is another similar structure, not so perfectly 

 formed and also bisected by faulting against the Trias. 



The physical constitution of Herefordshire and Brecknockshire is 

 largely a horizontal plane of Old Red Sandstone, which, where it 

 approaches the folded Silurian areas at the margins or round the 

 enclosed domes, takes on the folds of the older rocks on which 

 it lies. 



Silurian and Old Bed of the South-east of Scotland. 



It will be instructive now to turn our attention to the rocks of 

 a similar age to be seen dissected in the splendid line of cliffs from 

 Berwick-on-Tweed to the far north of St. Abbs Head and Siccar 

 Point. Here the Silurian (Lower Silurian) are intensely folded, 

 and instead of the conformable succession from the Silurian, through 

 the Old Red and Carboniferous which we have just seen obtains in 

 Herefordshire and South Wales we see the Upper Old Red Sand- 

 stone conglomerate resting upon the edges of the Lower Silurian in 

 the strongest unconformity. Well may the justly celebrated Button 

 have exhibited this phenomenon, as seen at Siccar Point, as one of 

 the best illustrations of the views he developed in the " Theory of 

 the Earth." 



So perfectly are the two formations cemented together that it is 

 possible to get hand specimens of the unconformity. It would 

 appear that while the sediments of South Wales were being laid 

 down in quiet waters from the beginning of the Upper Silurian to 

 the close of the Carboniferous, the succession of events was several 

 times broken in Scotland, as shown, not only by the strong uncon- 

 formity already spoken of between the Upper Old Red and the 

 Lower Silurian, which I have myself seen, but by the unconformity 

 Sir Archibald Geikie shows exists between the Lower Old Red 

 and the Lower Silurian, ^ and even between the Upper and Lower 

 Old Red^; and he further states "that the great earth moA'ements 

 which plicated the Highlands and Southern tjplands were probably 

 simultaneous, and took place chiefly during the long series of ages 

 represented by Upper Silurian deposits."'* As the Upper Silurian in 

 Lanarkshire passes gradually into the overlying Old Red Sandstone,* 

 it is probable that the break between the Upper and Lower Silurian 

 we have seen exists in England and Wales also extends to Scotland. 

 The succession of events in the latter country are indeed more 



1 "The Geology of Eastern Berwickshire" : Memoirs of Geological Siu'vey, p. 20. 

 " Scenery and Geology of Scotlaud," second edition, p. 122, also p. 138. 



2 Ibid. p. 329. 3 Ibid. p. 299. * Ibid. p. 327. 



