182 TILESTONES IN CAERMARTHENSHIRE, BRECKNOCKSHIRE AND RADNORSHIRE, 



In this district, however, these lower red and yellowish beds, or "bur stones," are 

 seldom so fissile as the "tile stones" described in South Wales. They occasionally 

 contain a few organic remains, such as Avicula, and a small Lingula, both of new 

 species, which will presently be described. In the Shropshire beds the remains of fishes 

 prevail more than those of mollusca, including the Dipterus macrolepidotus (Sedgwick 

 and Murchison), ichthyodorulites of the genus Onchus, and small bufonites the remains 

 of palates of fishes. (See PI. 1. fig. 2, 2 a. PI. 3. and subsequent description of the shells 

 and fishes of the Old Red System.) 



In the southern parts of Caermarthenshire and in Pembrokeshire, the tilestones can- 

 not be traced as a persistent zone, and the triple subdivision of the system can no 

 longer be observed. Thus, in following the escarpment of the carboniferous limestones 

 of Caermarthenshire to the low hills near the coast, we gradually lose the distinct traces 

 of the red conglomerate below it. Beds of cornstone are very rarely to be detected 

 in the central masses, and the tilestone of Middleton Park (between Llandeilo and Caer- 

 marthen) are the last well-defined examples of that variety of stone. At Black Pool and 

 Castel Goylan near the mouth of the Towey the lower beds do not afford tilestones, but, 

 on the contrary, are thick-bedded, slightly conglomerated, mottled, quartzose sandstones. 



The previous sketch, however, of the lower member of the Old Red has been de- 

 rived from numberless transverse sections, made between Pont-ar-lleche on the south- 

 west and the environs of Ludlow on the north-east, being a distance of near ninety miles. 



Reverting to the section at Pont-ar-lleche (PI. 34. fig. 5.), the shale and cornstone are thereunder- 

 laid by alternations of red and green sandstone, some of the lowest of which are the "Tilestones " 

 which give the name to the bridge. Below these are other bands of a quartzose, deep red sandstone, 

 indurated shale, and slightly conglomerate purplish brown sandstone, containing small pebbles of 

 quartz, which gradually disappearing, the beds pass into the underlying grey Silurian rocks of the 

 district. These conglomerate beds, though not seen at the base of the Old Red System in any other 

 parts of its course between Caermarthenshire and Ludlow, are found in the same position in Pem- 

 brokeshire and at Thornbury, Gloucestershire. (See the chapters on Pembrokeshire and Tortworth.) 

 Casts of Orthoceratites and other fossils occur in the finely laminated beds associated with the tile- 

 stones at Pont-ar-lleche, similar to those of other localities. 



The transverse section of these beds afforded by the valley of the Cwm Dwr, be- 

 tween Trecastle and Llandovery, is of high interest. (PI. 34. figs. 1 and 3.) Tilestones 

 are here quarried rising at an angle of sixty degrees from beneath the marly and sandy 

 beds of the cornstone group, the lower tilestones graduating downwards into the 

 equivalent of the Ludlow rock. The uppermost beds are of a dark purple colour, their 

 surface being covered by large plates of a grey mica, and here and there indented with 

 certain impressions resembling those in the Old Red Sandstone of Scotland called 

 ' ■ Kelpie's feet 1 ." The lower beds, as worked on the steep acclivity west of the meeting- 



1 It is highly probable that the Arbroath pavement beds of the Old Red Sandstone of Scotland, will be found 

 to correspond with the tilestone formation of South Wales. 



