364 



TRAP AND QUARTZ ROCK. — MINERAL VEINS. 



trap, dips towards the hill or to the south-east. In other spots upon the sides of this little hill, I 

 collected some very slightly altered sandstone, charged with fossils which characterize the beds of 

 the same age in Shropshire. By continuing a transverse section from the centre of the hill to the 

 north-west, a small valley is passed, beyond which the sandstone and grit resume their ordinary 

 characters, the beds dipping to the north-west, or from the eruptive trap 1 . I could discover no 

 traces of the prolongation of this trappean axis in its strike to north-east, for the beds of shale 

 and flag fold round it, and in the beds of the Sowdde at Rhydd-y-sant are little disturbed. But to 

 the south-west the line of altered rocks is most strikingly marked for several miles. Gnarled and 

 broken bosses of quartzose sandstone, passing into quartz rock, occupy the wooded hills of Pentre- 

 bach, whence they rise by Carreg-alt to the hill of Cairn-goch, 700 feet above the sea. This hill, 

 so very remarkable from the natural strength of its position, stands out between the rectilinear and 

 mural ridge of the Truchriig before described, and the valley of the Towy. Hence, doubtless, it 

 was selected by the Romans as an encampment 2 . 



We thus observe, that the phenomenon of altered rocks is just as strikingly displayed in this 

 corner of Caermarthenshire, where trap protrudes, as in the north-east of Shropshire, distant nearly 

 one hundred miles, and therefore we are completely borne out in referring these effects to igneous 

 action ; the same causes and the same effects being invariably associated. 



It may be asked, whether the analogy is further proved in Caermarthenshire by the exhibition of 

 metallic veins. Now it has been shown, that wherever trap rocks protrude, in the counties 

 of Salop, Montgomery, Radnor, or Brecknock, the strata in contact are more or less veined, 

 and although these veins do not always contain valuable ore, the point (as respects theory) appears 

 to be quite as conclusively established by the existence of poor veins, containing merely crystallized 

 pyrites, lime, barytes, &c, as if such veins were loaded with the richest metals. The truth of this 

 assertion has been very clearly proved in the Corndon and Shelve district in Shropshire. It is 

 doubtless dangerous to assert, that all mineral veins are connected with igneous operations, but as 

 wherever trap rocks intrude, the hardened and indurated strata are more or less intersected by veins, 

 we are led to conclude that such veins are as much the result of the intrusion of the volcanic 



1 From specimens collected by the Rev. Henry Lloyd, of Tan-yr-allt, two other thin bands of porphyritic 

 and slaty trap have pierced through the strata, the one ranging from Gorrllum by Carreg-folgam, the other by 

 Hendre-felin, between Pont-meredith and Tal-y-garn ; the protuberances of quartz grit along their lines favour 

 the supposition. I am also indebted to Mr. Henry Lloyd for pointing out to me the position of an ancient 

 Crom-llech, called Llech-filart, which stood in the low grounds to the north of Blaen-dyfFrin-garn, but which 

 was barbarously destroyed a few years ago by an ignorant tenant. According to the tradition of the country, 

 this was the last place in Britain where human sacrifices were offered, and in more recent times, feuds were 

 reconciled and good fellowship re-established by shaking hands over this stone. In an excavation, Mr. H. Lloyd 

 found bones beneath this Crom-llech, which proved to be human. This is one of the many spots in South 

 Wales and the adjoining English counties which have great antiquarian interest attached to them. 



2 The form of the encampment is a parallelogram, the larger diameter of which corresponds with the axis of 

 the ridge, and is therefore in line with the main direction of all the deposits in this region. Four entrances 

 are still discernible : a slight depression in the centre must have added much to the security of the camp. The 

 north-western, or one of the largest faces, is a natural defence of quartz rock in situ, the beds of which dipping 

 to the north-west, present a bold precipitous face to the valley of the Towy. The other walls, which in places 

 are still twenty to thirty feet high, have been formed by piling large and shattered blocks, which, from their 

 angularity, give a cyclopean character to these venerable and desolate ruins. 



