Fearnsides, Elles, Smith — Falceozoic Rocks of Pomeroy. 103 



The next division, however, was better seen, especially in an up- 

 standing cliff partly undercut by the Little River, just south of the Slate 

 Quarry, and, together with various varieties of Trinucleus co7ice?itn'c2is, 

 yielded abundant examples of Ampyx rostratus. These beds when 

 weathered take on a bright ochreous yellow or brown colour, and 

 break up characteristically into little lenticular flakes or chips of 

 shivery shale before they pass into the final dark brown marly clay of 

 the soil above. In many respects this division is exceedingly like the 

 Dindymene shale of Austwick, Yorkshire, and certain beds among 

 the Slade series of Wales. 



Upward, these ochreous mudstones, with their swarms of Trinucleus 

 and Ampyx, pass into the sombre leaden grey micaceous mudstones, 

 which on the north side of the Little River, east of the Slate Quarry, 

 have yielded a few examples of Remopleurides, with fragments of 

 other Trilobites and a few Lamellibranchs. "Whether Remopleurides 

 invariably occurs at a higher horizon than Trinucleus we could not 

 decide, for our only exposure with Remopleurides in situ occun'ed 

 in the immediate neighbourhood of a large structural fault ; and hence 

 Phacops beds and Trinucleus beds, with leaden shales and a probably 

 higher flaggy bed containing Diplograpti, are here grouped together as 

 Killey Bridge beds. In the higher part of the leaden shales the 

 bedding planes become quite prominent; and gradually the mud- 

 stones pass up into flags. Here the flaggy beds, as seen at the 

 bottom of the old Slate Quarry mill-sluice, are distinguished from 

 the basal Killey Bridge beds only by the absence of mica. With the 

 incoming flaggy conditions, Lamellibranchs, Gastropods, Cystids, and 

 Crinoids seem completely to oust the Trinuclei, while Harpes and 

 a Lichas again become conspicuous, and with them a few fragments 

 of Biployrcq^tus truncatus can usually be found. 



With the exception of a single Graptolite-bearing exposure at 

 Lime Hill, the top of the Killey Bridge beds seems to represent the 

 highest fossil-bearing horizon which was known to Portlock ; and 

 hence, considering the date, his estimate that the rocks belong to 

 Caradoc Sandstone must be regarded as a very wonderfully close 

 approximation to the truth. 



The Lower Tirnaskea Beds. 



The Tirnaskea beds form the highest member of the Ordovician 

 System, and are exceedingly interesting in that they contain both 

 Graptolites and Trilobites. They have been observed only in two 



