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the continuatioa of beds, which form the summit of the Vans is only a few feet 

 below the Carboniferous Limestone at Merthjrr, which Sir H. De la Beche supposes 

 may have covered the Vans, just as it does the opposite height of Pen-ceryg-calch. 

 One can well imagine the denudation of the soft marls, leaving the harder Con- 

 glomerate imtouched, for even at the present day the rivers of the district, When 

 swollen after a storm, bring down enormous quantities of red marl, presenting 

 a nearly bloody appearance. Our way then lay under the hiUs of Mountain 

 Limestone for about four miles, until we arrived at Gilwern, where we abruptly 

 turned from the vaUey of the Usk, and entered the South Wales Coal field, through 

 the picturesque gorge of the Clydach. The road soon becomes deeply interesting, 

 both artistically and geologically — winding through the narrow valley, with the 

 Clydach foaming below — the escarpments of the Limestone are seen towering 

 above us — while on the left the light of innumerable fires, and the roar and clank 

 of engines, tell us that we have left the agricultural for manufacturing districts. 

 The LlaneUy works Jire placed in a deep dingle, bounded on both sides by the 

 limestone, which is extensively worked to assist in the reduction of the iron ore ; 

 while on the hill towards the south, numerous chimneys are scattered, marking 

 the shafts of the pits. In the Geological Survey, vol. I., page 149, is seen an 

 interesting account of a visit made by Llwyd in 1697, to Llanelly, in which he 

 describes the mode of working the pits and levels, and also the discovery of the 

 stigmaria, which seemed to perplex him much. 



After descending to visit the Pwl-y-cwm waterfall, we mounted the hills 

 directly above us, and commenced an examination of the limestone quarries. 

 VVe are now standing on the thin belt which immediately surrounds the South 

 Wales Coal field. Running up from Pontypool to Abergavermy, it forms the 

 range of the Blorenge mountain, at which point it turns and runs due west to 

 Carmarthen Bay. From Pontypool to this latter place there is a gradual diminu- 

 tion of the thickness of the mass, preparing us for the final disappearance of the 

 same range of beds in Pembrokeshire. There is also a change in the character 

 of the beds — the lower shales, which are so conspicuous in the south border of the 

 Coal field, have disappeared, except now and then in the gullies and ravines. 

 The limestone is much worked on the whole of the Pengwern mountain — the 

 thickness at Llangattock being about 520 feet. The lowest beds consist of a 

 hard grey crystaUine-looking stone, containing but few fossils. In the upper 

 beds I have found large quantities of corals, and in small thin partings of blue 

 shale, great numbers of producti in tolerable preservation — euomphalus, phanero- 

 tinus nudus, different varieties of Uthodendron and fungites, and a few leptaenae. 

 In the lower beds at Llangattock the prevailing form is spirifer. Continuing 

 our course westward from Llanelly or Llangattock, we do not get any more 

 sections of limestone until we arrive at the Trefil quarries, near Tredegar. They 

 are of enormous extent, and worked as it were in terraces, so that an easy descent 

 can be made from the top to the bottom beds. The junction of the Millstone 

 Grit is here extremely well marked. Boulders of quartzose grit overhang the 

 edges of the upper beds, frequently rolling over and being mixed with the lime- 

 stone. These quarries are not so rich in fossUs as those at Llsmelly. I have found 

 productus giganticus very perfect — some good specimens of Uthodendron — 

 rhynconeUa, and a number of casts of euomphalus filled with spar* 



