166 DISLOCATIONS ON THE WESTERN EDGE OF THE SOUTH WELSH COAL BASIN. 



extruded from their regular line of bearing, and forced into the area of the Old Red 

 Sandstone by movements which miners would call "lateral shifts"; an explanation 

 which would naturally suggest itself by inspection of the relative position of the masses 

 on the map. These appearances can, however, be more simply explained by the up- 

 ward and downward movement of the faults in question, and by the different angles at 

 which the separate masses are inclined 1 . 



The limestone emerging from this morass at Pant-y-gwasted, where the strike is true 

 south-westerly, is well exhibited in low parallel ridges crowned by high ridges of mill- 

 stone grit. The strata dip S.E. and S.S.E. at angles of about 30°. These calcareous 

 terraces diminish successively in height, and terminate near the cavern from which the 

 river Lwchwr bursts forth. Between this point and the house of Cwrt-a-barddh the 

 limestone is wanting, and the distance is occupied by the Old Red Sandstone or its 

 detritus. 



The surface of the ground near the source of the Lwchwr is singularly marked by seve- 

 ral funnel-shaped cavities, which are not peculiar to the limestone of this spot, but are 

 also observable along the lines of greatest dislocation around the promontory of Carreg- 

 ogof, and beneath the northern face of Carreg-las. They seldom exceed 60 to 70 feet in 

 their diameter at the surface, tapering downwards to depths of 30 to 40 feet, and appa- 

 rently terminating in vertical tubes. As they occur at or near points of the greatest dis- 

 locations of the strata, may we not be allowed to speculate upon their having formerly 

 been the spiracles by which certain gases were evolved, during those periods when 

 earthquakes produced the adjoining elevations and depressions of the strata ? 



I invite special attention to the locality of Cwrt-a-barddh, because this portion of the 

 margin of the coal basin is directly opposite to the remarkable outlier of carboniferous 

 limestone called Castell Cerrig Cennen, with the position of which I shall now attempt 

 to prove that the break in the escarpment is directly connected. (See Map.) 



3. Castell Cerrig Cennen. (PL 34. fig. 6.) 



The picturesque ruin called "Castell Cerrig Cennen," is built upon an insulated 

 rock of carboniferous limestone, which projects in bold relief on the right bank of the 

 little stream called the Cennen, and nearly in the centre of a valley in the Old Red 

 Sandstone, as represented in the wood-cut at the head of this Chapter 2 . (See also PI. 34. 



1 This solution of the modus operandi was first, I believe, suggested by Mr. Lonsdale, from the examination 

 of a series of beautiful models. He is in possession of much valuable knowledge respecting mineral faults and 

 their complications, which I trust he will soon lay before the public. 



2 I am indebted to Mrs. Stackhouse Acton for a beautiful sketch of Gastell Cerrig Cennen, from which the 

 wood-cut is engraved. The castle is the property of the Earl of Cawdor, and being one of the most striking 

 ruins in South Wales, is well worthy of the attention of the antiquary. The well of the fortress (supposed to 

 have been reached by cutting to a great depth through the solid rock) is, I believe, a natural fissure. 



