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INTRUSIVE TRAP. — BAXTER'S BANK, CARNEDDAU, ETC, 



Baxter's Bank. 



Another small ridge of trap rock, in the neighbourhood of Llandrindod, called Baxter's Bank, 

 remains to be noticed K It is situated about five miles north-west of Llandrindod, about three 

 quarters of a mile south-east of Camllo Hill, and two miles and a half from the sequestered valley of 

 Abbey Cwm-hir. The adjacent country consists of round and featureless hills composed of black 

 decomposing shale, with concretionary masses and ribs of quartzose conglomerate ; the latter, 

 however, occur only to the west and north-west, and are part of the upper division of the Cambrian 

 System before described at Gwastaden and Rhayader. The hill called Baxter's Bank is a narrow 

 wall of trap, 500 feet high and rather more than half a mile in length. Its course is from north-east 

 to south-west, and therefore parallel to the ridges of Llandrindod. The rock is partly a coarse- 

 grained hornblendic greenstone, passing into a fine-grained and more felspathic variety, partly 

 grey- coloured granular felspar with dark freckles, probably hornblende. The flanks of this wall of 

 trap present precisely similar altered and dislocated strata to those mentioned in other places. Near 

 the Carmel chapel, the beds thrown off are thick and hard white veined blue flags, quarried as 

 building- stones, some of them perhaps deserving the name of volcanic grit. On the north-west 

 flank near Rhiw-goch, the black shale unfortunately appearing carbonaceous, has again induced 

 individuals to drive horizontal galleries in search of coal through the highly inclined strata until 

 stopped by the highly indurated and silicified schist which here, as in other districts, is connected 

 with igneous rocks. In this case the mistake of the speculators is, if any thing, still more inexcusable 

 than in the instances previously cited, for this little ridge is traversed by a road at its north-eastern 

 termination, where the unaltered and the indurated shale near the trap have been long clearly exposed, 

 and an inspection of the section on the side of the road might have saved the miners the trouble and 

 expense of underground drifts. About one mile south-south-west of Baxter's Bank, another little 

 boss of trap is quarried on the north side of the high road from Radnor to Rhayader, near a spot 

 called Caer-fagii. Here the intrusive rock tilts the black schist to the north-west, which in con- 

 tact is hardened and silicified. The trap of Caer-fagii is a spotted, granular felspar rock with a 

 tendency to amygdaloidal structure, and is much discoloured on the exterior by ferruginous stains : 

 it is traversed by veins of quartz, the whole being in a state of decomposition. It is covered by an 

 accumulation of sandy detritus, including pebbles derived from the rocks of the adjoining district. 



Carneddau and Builth. 



In the southern and south-western extremity of this district are the loftiest and most 

 important masses of intrusive trap rocks. It will now be shown that as many of the 

 stratified trap rocks of the Llandegley district were evolved from volcanic apertures 

 during the submarine accumulation of the Lower Silurian Rocks, unbedded volcanic 

 masses have been intruded subsequently, dismembering and altering all the strata with 

 which they came in contact. This hilly district, rising to 1600 feet above the sea, is called 



1 I was directed to this ridge by my friend the Right Honourable Frankland Lewis, who, in despite of a life 

 of labour in the public service, has cultivated with spirit the pursuits of natural history, and is well acquainted 

 with the structure of this county. 



