384 



OLD RED SANDSTONE — RANGE AND SUCCESSION OF. 



coast eastwards, the beds of the same age are again exposed in Skrinkle Bay, where, though very 

 highly inclined, they repose on the Old Red Sandstone at an angle of 80°, and consequently decline 

 beneath the great mass of limestone, ranging in the cliffs to Tenby. A similar order is observable 

 in the interior of the south-eastern division of the county, along the escarpment of the limestone in 

 the parishes of Mynwer and Marros, where yellowish sandstone with casts of shells and crinoidal 

 impressions, immediately overlies and passes conformably into the Old Red Sandstone at angles of 

 30° to 35°. 



In certain spots the limestone of the Stackpole coast is rich in fossils. It contains corals and 

 two or three species of very beautiful unpublished small trilobites, all differing specifically from 

 any which occur in the Silurian System. 



In a collection presented to the Geological Society by the Earl of Cawdor, Professor Phillips and 

 Mr. J. de C Sowerby have recognised many species well known in the mountain limestone of 

 other tracts. The species have been already enumerated, p. 161. It is worthy of remark that a 

 portion of a Cidaris is among them, the Echinidce being of very rare occurrence in this forma- 

 tion 1 . 



The lower limestone shale also contains fossils, and where they occur, the round impressions of 

 encrinite stems, on the surface of the thin beds of yellow sandstone, give to the rock very much the 

 rough external aspect of some strata of the Lower Silurian Rocks. I can, however, confidently 

 assert, from specimens collected by myself in Angle Bay and also near Stackpole, that none of the 

 organic remains found in these strata, which rest upon the Old Red Sandstone, agree in species with 

 those of the Silurian Rocks beneath it. 



In concluding these remarks upon the carboniferous limestone of this coast, I cannot 

 avoid expressing my belief, that this rock constitutes the margin of a great coal-field, 

 which has either been destroyed, or may, iudeed, still exist in the area now occupied by 

 the Bristol Channel ; for however much the calcareous strata are contorted and broken, 

 their prevailing inclination is southwards ; i. e. they dip away from the Old Red Sand- 

 stone, and thus when viewed upon the great scale, they seem to form part of a vast 

 trough, other portions of which occur in the Worms Head and southern headlands of 

 the promontory of Gower, and also in the limestone cliffs on the eastern side of Swansea 

 Bay 2 . 



Old Red System. 



The Old Red Sandstone of Pembrokeshire, as included between the carboniferous 

 limestone and the Upper Silurian Rocks, differs in some details of lithological structure 

 from the great mass of the system described in other counties. 1st. The attempt to 

 subdivide it into precise formations (conglomerate and sandstone, cornstone, and tile- 



1 A Cidaris has, however, been observed in the limestone of this age in Scotland. (See Ure's Ruther Glen, 

 PL 16. f. 7, 8. p. 318. 



2 A singular patch of pipe-clay and gravel on the surface of the Stackpole promontory, pointed out to me 

 by Lord Cawdor, will be described in the concluding chapters on drift and alluvia, in which the blown sands and 

 submarine forests of this tract will be also considered, and Giraldus Cambrensis referred to. 



