THE GEOLOGIST. 



51 



smoke from tlie vallies, telling of the enormous population on the 

 surface, and the inexhaustible wealth below. 



As a good introduction to the coal-field, the pedestrian geologist can 

 scarcely do better than start from Abergavenny, a tolerably- sized town 

 on the IS'ewport and Hereford Eailway. He there finds himself in a 

 valley of old red sandstone, looking up the Yale of Usk. To the north 

 of the valley is a line of mountains capped with old red conglomerates, 

 as the Sugar Loaf and Skyrrid, from under which creep out here and 

 there an abundant development of cornstones and brownstones; and, 

 although but few of the fishes of that period have been discovered there, 

 there is little doubt that they are as abundant as in the neighbouring 

 county of Herefordshire. This Vale, like the parallel vallies in the 

 coal-field, shows the enormous powers of the denuding force, which 

 has scooped out the softer marls, leaving the harder conglomerates 

 untouched. 



To the south the eye glances along the line of escarpment of the 

 carboniferous limestone, which, rising up from Pen ty pool, makes a 

 rather sudden turn, of which the Blorenge Mountain forms the corner- 

 stone, and runs tolerably due west. JS'ear to Carmarthen the 

 observer will see, during his walk along this range, several utilitarian 

 signs, such as an inclined plane or the shaft of a pit, indicating the 

 approach to a manufacturing district. About four miles from Aber- 

 gavenny, the road suddenly leaves the Yale of Usk to enter the north 

 limestone gorge of the Clydach. In this valley are situated the 

 Llanelly ironworks, flanked on each side by steep hills, along the 

 north side of which the road gradually ascends for another four miles. 



The thickness of limestone at Llanelly and Llangattock, on the 

 Mynydd Pengwern, is about 520 feet, and is of good quality, being 

 much worked to supply the farmers. The lowest beds are the purest, 

 and best for agricultural and smelting purposes. There are frequent 

 sections to be met with along the whole line of country; the nearest to 

 the Llanelly quarries are those of the Trefil, of enormous size, and worked 

 in terraces, from whence the stone is brought to supply the Ebbw Yale 

 works. The junction of the millstone grit with the limestone is well 

 seen here, as boulders of grit frequently roll over the summit and 

 mingle with the dehris below ; indeed, in a small cavern to the east of 

 the quarry the walls are of limestone, while the roof is of grit. This 

 cavern was turned to good account by some blacksmiths at the time of 



