Bevan— Coal-basin of South Wales. 159 
the limestone-escarpment is a tolerably uniform moorland plateau 
(fig. 1), varying from one to three miles in breadth, and consisting 
s N 
A 
2 ( A <a 
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Fig. 1.—Diagram showing the Hills of Pennant Sandstone, with Terraces on the Sides and the 
Lower Coal-measures cropping out at the foot: the plateau of Millstone-grit is on the right. 
A, Coal—measures. B. Pennant Sandstone. c. Coal-measures, D. Millstone-grit. 
E. Mountain-limestone. 
of Millstone-grit overlying the limestone. At the line where the 
Coal-measures impinge upon the grit, forming what is called ‘the 
North crop,’ a marked depression is observed, immediately to the 
south of which rise, pretty abruptly, lofty ranges of Pennant Sand- 
stone, forming the divisions between the deep parallel valleys 
through which the rivers that rise in the Millstone table-land run 
due south to the Bristol Channel. This depression, which therefore 
cuts at right angles the heads of all these valleys, has been taken 
advantage of by railway companies to accommodate the population 
and mineral traffic of the large ironwork towns on ‘ the North crop.’ 
The peculiarity of the Pennant Hills consists in their extraordi- 
nary similarity in outline and height, as also in the fact that they 
are all distinguished by a series of terraces, the remains of ancient 
beaches (fig. 1). 
Commencing at the east, we have, parallel with the limestone belt, 
1. The Valley of the Afon, commencing at Blaenafon and leaving 
the basin at Pontypool. 
2. The Ebbw Valleys, running from Beaufort and Brynmawr 
respectively, converging at Aberbeeg, and emerging at the Risca 
‘South crop.’ (See figs. 2 and 3). 
Fig. 2.—View of the Pennant Rocks, from the Millstone-grit Plateau ; showing the Terraces and 
Parallel Valleys. The shading of escarpments below the Terraces indicate where the ‘ Patch- 
workings ’ of the seams on the ‘ North Crop’ have been carried on. The buildings at the 
heads of the valleys are the Ironworks of Ebbw-Vale and Tredegar. 
3. The Sirhowy Valley, from ‘Tredegar, which also joins that of 
the Ebbw at Risca. 
