62. 



View near Llanwrtyd Wells, from a drawing ly Mrs. Traherne. 



CHAPTER XXVII. 



SILURIAN ROCKS OF BRECKNOCKSHIRE. 



Silurian Rocks in Brecknockshire, including the anticlinal Ridge of Brecon. — Trap 

 and altered Rocks and Mineral Waters of Llanwrtyd. (PI. 31. figs. 1, 6, 

 7, 8 and 9.) 



ON consulting the Map it will be seen that Upper Silurian Rocks undulate along both 

 banks of the Wye between Builth and Erwood. They are usually in discordant positions 

 on the opposite banks of this river, which thus runs in a fissure transverse to the line 

 of elevation, and similar to those fractures before alluded to, in which the rivers Severn, 

 Onny, Teme, and Lugg, have their course 1 ; for like them, this fissure of the Wye pro- 

 ceeds from north-west to south-east and at right angles to the strike of the strata. 

 Among the numerous dislocations by which the form of the valley was predetermined, 

 none are more instructive than those near the boundary between the Old Red Sand- 

 stone and the Silurian System. Ludlow Rocks with their distinguishing fossils mount 

 up into the hills of Upper Llangoed and dip to the south-east under the Old Red 

 Sandstone, whilst at Llanstephan, on the Radnorshire bank, similar beds are thrown 



» pp. 230 to 240. 



