Vol. 65.] ORDOVICIAN AND SILTJEIAN EOCKS OF CONWAY. 



183 



These Phacops-Mudstones are also seen at various other localities 

 beneath the grit ; especially in the big quarry north of Bryn Seriol, 

 close to Conway, where the grits have been quarried away close to 

 the mudstones : these are left as a long wall on the north-eastern 

 face, various specimens of Phacops (Dalmannites) mucronatus being 

 visible on the weathered surface. The mudstones are seen again 

 on the Gyffin road immediately below Conway Castle, where, in 

 the associated shales, several specimens of Orthogr aphis truncatus 

 var. abhreviatus, E. & W., were found : this is a characteristic fossil 

 of the Zone of Bicellograptus anceps. Best of all, however, are these 

 beds displayed in the large quarry on the southern slope of the 

 Deganwy Hills, whence they derive their name, and where, imme- 

 diately beneath the grits, a series of shales and mudstones is exposed. 

 In a band in the lowest shales Orthograptus truncatus var. abhreviatus 

 was again found, beautifully preserved and in fair abundance ; 7 feet 

 above this band is a bed of brownish calcareous mudstone which 

 yields abundant remains of huge specimens of Ph«cops {Dalman- 

 nites) mucronatus, Brongn., and, in addition, such forms as 



Orihoeeras vagans, Salt. 



Orthoceras sp. 



Orthis (Dalmanella) elegantula, Dalm. 



Orthis sp. 



Chonetes lavigata, Sow. 



Holopella. 



Clddophorus planulatus (?) Com - . 



Ctenodonta varicosa, Salt. 



Theca (?). 



Tentaculites anglicus, Salt. 



In the 5 feet of mudstone intervening between the calcareous 

 bed and the grits, numerous specimens of the Phacops, but of 

 smaller size, may be found. 



(5) Conway Castle Grit. 



The Conway Castle Grit is the highly calcareous grit upon which 

 Conway Castle is built, and which Jukes at one time correctly 

 considered to be the equivalent of the Hirnant Limestone. It 

 always makes a feature wherever it occurs, and its outcrop brings 

 out the structure of the country very clearly. In the western part 

 of the district it is folded into two synclines with an anticline in 

 between, although the actual outcrop appears to be concealed by 

 overthrusting ; it is then faulted three times in quick succession in 

 the immediate neighbourhood of Conway, and again along the line 

 of the estuary. The grit is by no means uniform in character ; it is 

 thickest and coarsest on the Deganwy side of the river, where the 

 massive grit-beds are separated by flags with thin grits among them 

 (see fig. 5, p. 184). In the big quarries at Deganwy and Bryniau 

 the following fossils have been obtained from the higher beds : — 



Deganwy. 



Orthis hirnantensis, M'Coy. 

 Christiania tenuicincta (M'Coy). 

 Petraia subduplicata, M'Coy. 

 Fragments of corals and criooids. 



Bryniau. 

 Orthis hirnantensis, M'Coy. 

 Orthis calligramma, Sow., var. 

 Orthis (Dalmanella) elegantula, Dalm. 

 Streptelasma sp. 

 Petraia subduplicata, M'Coy. 

 Favosites cf. gothlandica, Fougt. 

 Crinoid-stems and fragments of corals. 



