52 



THE BRITISH ISLES. 



surface leutures of the interior of the principality. A large portion of South Wales, 

 anciently covered by the sea, has, since its emergence, been sculptured by the sur- 

 face water into the succession of ravines, glens, and valleys which now intersect 

 the basins of the Usk, AVye, and other rivers, for the most part designated by 

 the same name slightly modified, as Taf, Tawey, Towey, Taivi, or Daffy. The 

 hill-tops and isolated table-lands of Cardiganshire rise to an ideal line which 

 ascends gently as we proceed to the eastward, and it is thus clear that the inequali- 



Fig. 25.~The Suspension Biudge, Menai Stkait. 



ties of the surface must be of comparatively recent origin, whilst the hills are tbe 

 remains of an ancient plateau which had a gentle slope to the westward. 



A few rocky islands have been severed b}' the waves of the ocean from the coast 

 of South Wales, but Anglesey is the only large island of the principality. It 

 formed originally a portion of North Wales. Of its ancient connection with the 

 neighbouring mainland there can be no doubt, for the geological formations on 

 both sides of the Menai Strait correspond. The dividing strait passes through 

 carboniferous rocks, bedded between Silurian strata and rocks of porphyry. Pro- 

 fessor Ramsay is of opinion that the valley now occupied by the strait is of 

 glacial origin, and was scooped out, not by the glaciers of Snowdon, whicb never 

 reached so far, but by those of Cumberland.* If it is true that horsemen were 

 formerly able to cross the strait at low water, great changes must have taken 



« Quarterly Journal of the Geological Society, ilay, 1SG6. 



