Mr. De la Beche on the Geologi/ of Southern Pembrokeshire. 9 



line passes from west to east^ beginning in the cliffs of St, Bride's Bay^ a little 

 to the north of Broad Haven, and leaving our district at Lethergloyn, near 

 Narberth, So much of this greywacke-tract as falls within our present scope, 

 may be divided into two portions, that of St. David's, and that of Haverford- 

 west ; the former lying to the north and west, the latter to the south and east 

 of the Cuffern range of trap. 



St. David's Grej/wacke District. 



Greywacke, mixed with trap, occurs abundantly from Aberciddy Bay to 

 Penberry Rock, which it nearly surrounds. It is worked for roofing-slate at 

 some rocks which project into the sea near Penberry Crags. From the cliffs 

 under Penberry Rock to Cesselvawr Head it is much intermingled with trap. 

 Perpendicular beds of slaty greywacke, bearing from north-east to south-west, 

 occupy the space between the two trap-ridges of Llacithty and Cesselvawr. 

 To the south of Llacithty Rock, greywacke extends from the Slate-quarry 

 on the northern side of Whitesand Bay to the re-commencement of the trap 

 opposite the Horse Rock, forming in its way the cliffs in the neighbourhood 

 of Pencarnon. At the Slate-quarry the strata are perpendicular, bearing east 

 and west, conformably to the range of Llacithty; from Pencarnon southwards 

 they dip to the west, ranging north and south, conformably to the trap-range 

 which stretches from Crosswoodig. In the immediate neighbourhood of St. 

 David's, from the quantity of trap-blocks on the surface, and the want of natural 

 sections, the greywacke can hardly be traced as distinct from the trap. From 

 St. David's to Newgate Bridge the two rocks are much intermixed ; but except- 

 ing near Solfach, the cliffs on the northern side of St. Bride's Bay, from about 

 a mile to the west of Porthclaise as far as Newgate Bridge, consist entirely of 

 greywacke, disposed for the most part in thick beds, interstratified with a rock 

 resembling old red sandstone. It is from the latter that the stone for the new 

 work at St. David's cathedral has been quarried. The small bays between 

 Porthclaise and Carbudie Mill, and thence to Trellerwer, afford good sections 

 of this rock ; which is also found between Roche Bridge and New Mill. A 

 quartzose conglomerate, resembling one of old red sandstone, occurs between 

 Clegir Bridge and the sea. The general bearing of the greywacke, between 

 St. David's and the Cuffern range of trap, is from east to west, the dip being 

 to the south. 



Haverfordwest Greywacke District. 

 This is bounded on the north by the Cuffern range of trap ; on the north- 

 west, from Roche to Druson Haven, by coal-measures : on the south-west, 



VOL. II. SECOND SERIES. C 



