332 Reports and Proceedings — 



To the north of tlie ridge of rock running eastward from Eock 

 Castle, claimed as Archcean by Dr, Hicks, they have discovered 

 Lingula Flags, with Olenus spimdosus, Wahl, and Agnostus pisi- 

 formis, Linn. These beds are seen underlain by conglomerate, 

 resting upon older rocks, near Trefgarn Bridge. 



South of Dr. Hicks's Archasan ridge, a great fault brings beds of 

 Bala age in juxtaposition with the rocks of the ridge ; heuce, in the 

 tract described, no rocks of Tremadoc and true Arenig age have been 

 met with. In the area south of the ridge the rocks are thrown into 

 a complex synclinal, with a complex anticlinal to the south-east, 

 near the town of Narberth. 



The succession which the authors attempted to establish in this 

 area is as follows (in ascending sequence) : — 



i. Didymograptus shales, with MurcMsoni-iorm Graptolites. 



ii. Llandeilo limestone, with Asaphus tyrannus, Murch., etc. 



iii. Dicranograptus shales, with Dicranograptus, Climacograptus 

 hicornis, Diplograptus foliaceiis, etc., having a zone at the summit 

 marked by the abundance of OrtJiis argentea, His. 



iv, Robeston Wathen Limestone, with many Corals and Brachio- 

 pods, and few Trilobites. 



V. Trinucleus-seticornis beds, characterized by abundance of Tri- 

 nucleus seticornis, His., and its variety T. Bucldandi. These are 

 subdivided into three stages, viz. : — (a) Sholeshook limestone, with 

 Cystideans and an abundant Trilobite fauna, including Agnostus 

 trinodus, Salt., Trimicleus seticornis, His., Stygina latifrons, Portl., 

 Phillipsia parabola, Barr., Cheirurus parvus, Salt., Encrinurus sex- 

 costatus, Salt., Phacops Brongniarti, Portl., etc. 



(b) Eedhill beds, blue-grey shales, generally poor in fossils, but 

 containing here and there a fair abundance, especially of Phacops 

 Brongniarti, Portl., and Trimicleus Bucldandi, Barr., and many 

 Lamellibranchs and Gasteropods. 



(c) Slade beds, consisting of gritty green shales with calcareous 

 bands crowded with fossils. Glauconome disticlia, PhyUopora His- 

 ingeri, M'Coy, Phacops Brongniarti, Portl., Trinucleus seticornis, His., 

 Calyrnene trinucleina, Linns., Orthis testudinaria, Dalm., are abundant. 

 Climacograptus, sp., also occurs. 



vi. Conglomerate, containing many quartz pebbles, succeeds the 

 beds of the Slade stage in many localities, and does not seem to 

 mark a great discordance, as the authors have nowhere found it 

 resting on lower beds. 



vii. Lower Llandovery beds. Green gritty shales, with grit and 

 very fossiliferous calcareous bands, characterized especially by Nidu- 

 lites favus, Petraia suhduplicata, var. crenidata, Stricklandinia lirata, 

 etc., and containing Phacops elegans, Boeck and Sars, Phacops mucro- 

 natus, Aug., and Deiphon Forbesi, Barr. 



The authors attempted a correlation of the Haverfordwest rocks 

 with those of other areas : — ■ 



Conglomerate and grit of Trefgarn = Harlech ? 



Lingula Flags of Trefgarn, etc. =Dolgelly beds. 



Didymograptus shales =:Llanvirn. 



