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ments. On the north and east sides the Limestone is continuous and persistent, 

 but on the south, beyond Caerphilly, it is considerably intercepted by inter- 

 vening patches of Permian and Lias deposits. Further west, at Swansea Bay, 

 the Limestone is wanting altogether, the coal beds of the Swansea district being 

 exposed on the shore and running under the bay ; but from ]Mumble3 to Pem- 

 brokeshire the Limestone reappears in great force, forming the magnificent 

 coast-line for which Gower and Tenby are so celebrated. Nearly all the noith 

 crop, which at the east end near Llangattoc is about 250 feet in thickness, is 

 extensively quarried for the various furnacr s and iron works in the neighbour- 

 hood ; one reason indeed of their original establishment being the vicinity of this 

 Limestone, wliich is recessary as a flux in the smelting of iron ore. 



Lying conformably on the Carboniferous Limestone, is a thin belt of 

 Millstone Grit, wliich, like the limestone, is thickest on the North and East 

 crops, and gradually diminishes Westward. On the South crop it is only a few 

 yards in breadth. Here (on the North crop) it is of some scenic importance, as 

 it forms an extensive plateau from which the various rivers of the Coalfield take 

 their rise. The junction of the Millstone Grit with the Limestone is well seen 

 at the Trefil Quarries, where, indeed, great boulders of conglomerate (plum- 

 pudding stone) roll over tlie edges of the quarries and mix with the debris of 

 the Limestone. Commercially speaking, the Millstone Grit, which is of an 

 exceedingly hard quartzose character, is unimportant, it being only used for 

 hearth-stones and for sand employed by the moulders in the furnaces. To the 

 geologist it is interesting simply as an horizon, the fossO remains in it being 

 limited to a few indistinct Calamites and some annelid tracks. 



We now arrive at the veritable Ooalbeds, which in this case we see repose 

 conformably on the Millstone Grit in regular geologic succession. They do not 

 always do so- as for instance in South Staffordshire, where the Grit, Limestone, 

 and Old Red are absent, and the Coalbeds repose directly on the Silui-ian 

 Rocks, and in Cumberland, where they lie ui)on the Limestone, without the 

 interposition of the Grit. On the other hand, the Grit, which in South Wales 

 is regular, though only to a small extent, becomes in the North of England a 

 very important feature, and constitutes large Moorland districts. And now, 

 before we pass to the consideration of the Coalbeds themselves, I would briefly 

 direct your attentin to the physical conformation of the Coalfield, which to a 

 geologist is full of the most significant and interesting facts. At the point, 

 or I should rather say the line, where the Lower Coal Measures crop out on 

 the MiUstone Grit there is a singular and imiform depression, or nick, which has 

 been taken advantage of on the North crop by the London and North Western 

 Railway to carry their line through Brynmawr and Beaufort to Tredegar, 

 eventually to be extended to Merthyr. Immediately to the South of this line 

 is seen a very singular series of terraced hUls, rising suddenly to the height of 

 1,800 feet, or thereabouts, each hill being very nearly of the same height, and 

 presenting to the North the same kind of face, viz., a series of terraces or 



