DESCRIPTION OF THE SECTIONS. 



719 



Fig. 5. Traverse across the trappean or volcanized district of Llandrindod and Gelli, to the Cam- 

 brian rocks on the west ; showing thin-bedded and contemporaneous beds of trap, repeatedly 

 alternating with Lower Silurian rocks (Caradoc and Llandeilo), and rugged knolls of intrusive 

 trap bursting through all the stratified masses and throwing them into anticlinal and synclinal 

 forms. The mineral waters of Llandrindod issue from pyritous and altered shale in contact 

 with the trap. See pp. 324 et seq. 



Fig. 6. Across the Llandegley rocks (same district as No. 5.) indicating repeated alternation of 

 bedded trap and Caradoc sandstone. Bosses of unstratified greenstone appear near Llandegley 

 village, and the mineral waters of that place issue from the pyritous and altered strata. See 

 pp. 324 et seq. 



Fig. 7. Great transverse section exposed on the banks of the Wye between the hills of Old Red 

 Sandstone on the south-east to the slaty Cambrian rocks of Rhaydr on the north-west. Strong 

 ridges of Upper Silurian rocks are exposed, together with a small dislocated tongue of Old 

 Red Sandstone, the north-eastern extremity of the great expanse of that system in Mynidd 

 epynt. Lower Silurian rocks are thrown up on the sides of the eruptive trap of Carneddau 

 near Builth (the southern termination of the chain traversed in figs. 5 and 6.) ; while Upper 

 Silurian Rocks, chiefly their lower members, are repeated in a trough between the Carneddau 

 and the Cambrian rocks of Dol-fan. The Cambrian rocks appear in great undulating masses, 

 chiefly dipping to the north-west, and are in most parts affected by slaty cleavage. The mine- 

 ral waters of the Park Wells, near Builth, like those of Llandrindod and Llandegley, issue 

 from dislocated and altered strata in contact with trap. See pp. 317, 224 et seq. 



PLATE 34. 

 (Caermarthenshire.) See pp. 347 to 369. 



Fig. 1. From the Cwm dwr near Trecastle, to Llandovery, showing a passage from the tilestones 

 of the Old Red Sandstone into the Upper Silurian Rocks, and great undulations between the 

 Upper and Lower Silurian Rocks. The subdivisions of the Silurian System are better seen in 

 figs. 3 and 5. See pp. 347 e t se( J' 



Fig. 2. From the left bank of the Towy, south of Llandovery, to the vale of Dole-cothi, being a 

 traverse across part of the Cambrian rocks exposed by the new road to Llampeter, showing 

 large concretions of quartzose grit, which mark the bedding and undulation of imperfect slates 

 which are affected at intervals by oblique cleavage lines. The position of the veins of quartz 

 and pyrites excavated by the Romans at Gogofau is indicated. (N.B. This section should 

 have been placed to the left hand of f. 1. to complete the descending series.) See pp. 347, 360. 



Fig. 3. From the junction of the Old Red Sandstone and Upper Silurian Rocks in the escarpment 

 of Mynydd bwlch-y-groes (a continuation of Mynydd epynt) to the hills of Cerrig-gwynion, 

 where the Lower Silurian Rocks pass into the slaty schists of the Cambrian System. In this 

 section the Caradoc Sandstone is well exposed in bold flexures and occupies the hills of Noeth- 

 griig, the Llandeilo flags occupying the space between Cefn-y-garreg and Cerrig-gwynion. 

 The strata are affected by an oblique slaty cleavage. See pp. 352 et seq. 



Fig. 4. Cambrian rocks of Cerrig-mwyn and Nant-y-moen, containing productive veins of lead ore. 

 See p. 366. 



Fig. 5. From the Millstone Grit and Carboniferous Limestone of the South Welch coal basin to 

 the Towy at Llangadock, showing conformable passages from the Carboniferous System into 



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