THE GEOLOGIST. 
51 
smoke from the 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 Newport and Hereford Ilailway. He there finds himself in a 
valley of old red sandstone, looking up the Vale 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 Pontypool, makes a 
rather sudden turn, of which the Blorenge Mountain forms the corner- 
stone, and runs tolerably due west. Near 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 Vale 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 Vale 
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 dehi is below ; indeed, in a small cavern to the east of 
the quarry the walls are qf limestone, while the roof is of grit. This 
cavern was turned to good account by some blacksmiths at the time of 
