Vol. 56.] 



SHALES OP THE WELSH BORDERLAND. 



385 



The lowest beds of the Ludlow Group are seen in a quarry west 

 of Pen-y-cloddiau, and in the stream that runs past that farm. 

 Between these beds, or perhaps representing them in part, occurs 

 a discontinuous bed of limestone, which I believe to be the repre- 

 sentative of the Wenlock Limestone in this district. This limestone 

 is exposed in an old quarry north-east of Pen-y-cloddiau, and again 

 on the Aberedw road near Llanfaredd. 



Fig. 4. 



Map illustrating 

 the ZONES in the 



WENLOCK SHALES. 



Builth District. 



The beds yield an abundant fauna of trilobites and brachiopods. 

 The following have been recognized : — Phacops Musheni, Salt., 

 Leptama rhomboidalis, Wilck., Wilsonia Wilsoni, Sow., Atrypa 

 marginalis, Dalm., Pentamerus sp., Orthis rustica, Sow., 0. hybrida, 

 Sow., corals, and crinoid-s terns. 



The Irfon section and that on Aberedw Hill are extremely 

 useful, as confirming the succession of the upper series, which might 

 have remained doubtful had no other exposures than those in the 



