DESCRIPTION OF THE SECTIONS. 



717 



into a double flexure and dip beneath the Old Red Sandstone of Mynidd Epynt and Brecon. 

 A complete section of the Upper Silurian Rocks is exposed in descending the escarpment of 

 that tract to the vale of the Irthon (Cwm-craig-dhu). 



The Brecon anticlinal is the continuation of that of Ludlow explained in f. 5. See Map and. 

 pp. 336 et seq. 



Fig. 7- Traverse of the same "Brecon anticlinal/' as in f. 6., where it has diminished to a single 

 ridge, having a powerful fault on its north-western face. See pp. 338 et seq. 



Fig. 8. Traverse of the same anticlinal where still more diminished, one mile from its termination. 

 The fault here is on the south-eastern face. See p. 338. 



Fig. 9. Traverse of the same anticlinal at Corn-y-fan, where it terminates in a single rock flanked 

 by Old Red Sandstone, which is violently dislocated on the south-eastern face. See p. 337. 



PLATE 32. 



Fig. 1. From the Caradoc, on the E.S.E., to the valley of the Severn in the W.N.W., across the 

 Cambrian Rocks of the Longmynd or great mineral axis of west Salop into the adjoining parts 

 of Montgomeryshire. The Silurian System lies to the south-east, as expressed in PI. 31. figs. 3 

 and 4. On the north-western flank of the Longmynd and Linley Hills appears the striking 

 ridge of quartz rock called the "Stiper Stones/' succeeded by the dislocated and mineralized 

 region of Shelve and Cornden, where the Lower Silurian rocks (Caradoc and Llandeilo) undulate 

 conformably with bedded trap rocks, and are also pierced by intrusive masses of trap. A 

 trough of Upper Silurian Rocks is exposed towards the vale of the Severn, with a cone of 

 intrusive trap and altered rocks at Nant-cribba. The most productive lead veins lie between 

 the Stiper Stones and the Cornden, and occur exclusively in the stratified deposits near the. 

 intrusive trap rocks. See pp. 223, 256 et seq., 268 et seq., 300 et seq. 



Fig. 2. A second traverse across the same mining district in another parallel, showing still more 

 clearly the distinction between the bedded trap, formed contemporaneously with the Lower 

 Silurian strata and the intrusive trap which has pierced and altered them. The great trough 

 of unaltered Upper Silurian Rocks on the W.N.W. is well exhibited in the Long Mountain. 

 At the western extremity of the section, the trap dyke of Welch Pool penetrates beds of Cara- 

 doc sandstone and impure limestone. See pp. 223, 268 et seq. 



Fig. 3. A third traverse of the same mineral tract further to the S.S.W. ; to show that the anti- 

 clinal and synclinal lines of Nos. 1 and 2 are not continuous to any great distance, but change 

 with each short outburst of intrusive trap rock. See pp. 268 et seq. 



Fig. 4. Unconformable relations of the Upper Limestone of the Caradoc formation to the Cambrian 

 rocks of Linley ; also showing veins of copper ore running through the strata of both systems. 

 See p. 258. 



Fig. 5. Transverse section of the Breidden Hills, marking their eruptive character, the Silurian 

 schist and sandstone on their flanks being much dislocated and altered. See pp. 587 et seq. 



Fig. 6. On the south-eastern flank of the Breidden Hills, near Middleton, proving that the strati- 

 fied masses contiguous to points of eruptive trap are penetrated by mineral veins : a repetition 

 of evidence similar to that which is offered in figs. 1, 2 and 3. See pp. 587 et seq. 



Fig. 7- General relations of the Breidden Hills to the country on their flanks at their north-eastern 

 extremity. Stratified trap alternates with Lower Silurian schist and sandstone (Bauseley Hill) 

 in vertical beds, while intrusive trap appears in Brimford Wood. The coal-field of Bragginton 



4 Y 



