Yol. 65.] ORDOVICIAN AND SILURIAN ROCKS OR CONWAY. 189 



at Conway being represented by unfossiliferous Pale Shales. For 

 the rest, the beds can be correlated almost zone by zone, although in 

 some cases, owing to poverty of exposures, it has not been possible 

 to subdivide the beds, with the same degree of accuracy as in the 

 Central Wales district. 



Lake District. — The correlation with the Lake-District beds is 

 also fairly clear for the upper beds, and it seems possible that the 

 Conway Mountain Volcanic Series may be comparable with the 

 Borrowdale Volcanic Croup. The Cadnant Shales of the Conway 

 area are, however, represented in the Lake District by rocks of a 

 different lithological type, and no close comparison can therefore be 

 made. It would, nevertheless, seem likely that the Bodeidda 

 Mudstones correspond with the 3tauroce2>7iahis-liimestone, since the 

 Deganwy Mudstones are undoubtedly, in the main at any rate, the 

 equivalents of the Ashgill Shales. 



The Gyffln Shales may also be regarded as comparable with the 

 Stockdale Shales (Skelgill + Browgill Beds), and the Benarth Flags 

 and Grits are certainly very much like the Brathay Flags, although 

 the Grits are as a rule less conspicuous in the Lake District ; the 

 faunas are, however, practically identical. 



South Scotland. — The whole succession has also certain points 

 of resemblance with the South of Scotland, though the Caradocian 

 beds of the two areas are represented by different lithological types. 

 Nevertheless, the faunas of the remaining beds appear to correspond 

 so closely that the horizon of these is not left in doubt. 



The Cadnant Shales of Conway are clearly represented by the 

 upper part of the Glenkiln Shales of the South of Scotland and 

 the lower zones of the Hartfell Shales. The Deganwy Mudstones, 

 containing Orthograptus truncatus var. abbreviates, must correspond 

 generally with the Zone of Dicellogi-aptiis anceps ■ and it therefore 

 follows that the Bodeidda Mudstones must be represented by the 

 Zone of Pleurograptus linearis and the Barren Mudstones. The 

 correspondence of the higher beds in both areas is also close 

 (see table, facing p. 190). 



North Ireland. — In the Pomeroy District (County Tyrone) 

 the succession, so far as it goes, also agrees well with that of the 

 Conway area, .though neither the highest nor the lowest beds 

 are represented. The Killey Bridge Beds of Pomeroy have a fauna 

 almost identical with that of the Bodeidda Mudstones, and the 

 Tirnaskea Beds agree closely both in fauna and in lithological 

 characters with the Deganwy Mudstones ; there are no grits com- 

 parable with the Conway Castle Grits, but the shales and mudstones 

 which overlie the Tirnaskea Beds can be paralleled almost bed for 

 bed in the Conway country. 



The resemblances and differences in these various areas are 

 summarized in the accompanying table (facing p. 190). 



