﻿Vol. 64.] BALA AND LLANDOVEKT EOCKS OF GLTN CEIEIOG. 



559 



List of Fossils from the Teirw Beds. 





In this and the following hsts those species that 



i 



il 



are common or fairly 



common are indicated by 



II 



^■^ 



the letter (c). These 



) may be either locally 



1^ 



1^ 



abundant, or widely 



distributed in smaller 



XI \ numbers. 



fe i 







X Montimdijpora fibrosa, Goldf. (c). 



Ctenod.onta cf. regularis, Portl. 







Ctenodonta varicosa, Salt, (c) 



X 



? 1 Ortonia sp. (c). 



CuculUlla CO sp. 

 1 Modiolopsis cf. platyphyllus, Salt. 





X 1 Lingula ovata, M'Coy. 



Modiolopsis M' Coiji, Salt. ( = M. 





\Ungula temdgranulafa, M'Coy. 



modiolaris, Coiir. of M'Coy.) 





X i OrtMs calligramma, Balm. (c). 



Pterincea (1) sp. 





X ; Orthis elegantula, Dalm. 



i 



i Orthis veRperiilio, Sow. (c). 



Orthoceras politum, M' Coy 1 X 



X ; Orthis retrorsistria, M'Coy (c). 







! FhoUdops cf. implicata, Sow. 



Asaphus Powisi, Murch. (c). 





X Tlectamboiiites sericea, Sow. (c). 



Cah/me7ie CaradaciCO Salt ! X 



X Eafinesquina deltoidea, Conrad. 



Caiymene senaria ' (Conrad) 



X 1 Bafinesquina expansa, Sow. (c), 



1 



Salter (c) X 



Homalonotus sp. 



X 1 Bellerophon hilohatus, Sow. 



Illcs)ius JBowmanni, Salt ; X 



'■ Belleropho7i nodosus, Salt. 



Trinudeus concentrimis, Eaton (c). X 



1 Cyclonema crehristria, M'Coy. 





Eitomphalus corndensis (1) Sow. 



Tetradella complicata, Salt, (c) . . . X 



X ' Murchisonia gyrogonia, M'Coy (c). 





Fleicrotomaria (?) sp. 





and reappears below in the banks and bed of the river. For some 

 500 yards above Pont Hafod-y-gareg it occurs on both sides of 

 the stream, and is greatly sheared in the neighbourhood of a fault 

 that runs nearly along the line of the stream. The fault is 

 visible a little east of the bridge, in a small tunnel that has been 

 driven into the side of the hill. 



At the bridge the band of ash crosses the river, and thence forms 

 the rocky crest of the northern bank of the valley as far as 

 Craig-y-Pandy. Along* this rugged crest the thickness of the band 

 appears to vary considerably ; but, as the strike of the beds above 

 is sometimes oblique to the outcrop of the ash, it seems probable 

 that, in places at least, a fault may run along the upper margin of 

 the ash, and to this maj' possibly be due the apparent variation in 

 thickness. The relations of the ash to the beds below are also 

 extremely complex. Sometimes extensive masses of slate occur in 

 the lower part of the ash, and sometimes great masses of ash occur 

 in the upper part of the slates. These masses are not lenticular in 

 shape, but often present square and abrupt terminations ; and 

 they have evidently not been deposited contemporaneously with the 

 beds among which they lie. 



One of the most remarkable cases of this kind is to be seen just 



